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Chemistry and technology of agrochemical formulations Knowles

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Chemistry and Technology of
Agrochemical Formulations
Edited by
D. A. Knowles
FORM-AK Formulation Consultancy Services,
Tonbridge, Kent, UK
Kluwer Academic Publishers
Dordrecht / Boston / London
A C.I.P catalogue record for this book is available from the Library of Congress
ISBN 0-7514-0443-8
Published by Kluwer Academic Publishers,
P.O. Box 17, 3300 AA Dordrecht, The Netherlands.
Sold and distributed in North, Central and South America
by Kluwer Academic Publishers,
101 Philip Drive, Norwell, MA 02061, U.S.A.
In all other countries, sold and distributed
by Kluwer Academic Publishers,
P.O. Box 322, 3300 AH Dordrecht, The Netherlands.
Printed on acid-free paper
All Rights Reserved
© 1998 Kluwer Academic Publishers
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical,
including photocopying, recording or by any information storage and
retrieval system, without written permission from the copyright owner.
Printed in Great Britain
Preface
Agrochemical products and adjuvants are of vital importance in agriculture
to protect food and fibre crops from weeds, insect pests and diseases in
order to feed and clothe the ever-growing population of the world, which is
expected to double over the next 50 years. The total world market for
agrochemical products has been estimated at more than US$30 billion in
1997 and the industry plays an important part in the economies of most
countries.
Enormous changes have taken place in the chemistry and technology of
agrochemicals over the last 20 years or so, and therefore it is timely that a
new book should be published to review the most important areas of
technology and legislation in the research and development of new products, and to describe the current and likely future trends which will carry the
industry forward into the next millennium.
In recent years there have been increasing pressures from governments
and regulatory authorities to produce new agrochemical products which are
safer to the user and have a reduced impact on the environment in general.
Consequently, agrochemical companies and other organizations have been
reviewing their product/pack strategies to provide products which are effective at low doses and have low toxicity to mammals and other non-target life
forms. There is an increasing trend towards the use of water-based formulations, water-dispersible granules and controlled-release formulations.
Improvements are taking place in safer and more convenient packaging of
products. Spray application techniques are also being developed to improve
targeting on the crop and reduce waste in the field. Effluent treatment and
waste minimization technologies are also well advanced in the factory and
on the farm. New standards are being set to control and regulate the use of
agrochemical products.
The use of surfactants and other additives to give special effects and to
impart long-term product stability is another rapidly developing area of
technology. Surfactant and oil-based adjuvants are also being used to enhance the biological activity of active ingredients, either as part of the
formulation or as spray tank additives. These important aspects of
bioenhancement are reviewed and future trends are highlighted.
This book brings together well-known experts from a number of
agrochemical companies, formulation additives and adjuvants suppliers,
consultancies, academic and other organizations with many years of
practical experience of the most important aspects of the chemistry and
technology of agrochemical formulations. One of the aims of the book is to
show how the various technologies are linked together in the development
of new-generation user and environmentally friendly agrochemical products. Future trends in all of these areas are discussed fully and should
provide the basis for safe technology into the next millennium.
This book would not have been possible without the cooperation of a
wide range of authors involved in the agrochemical business, and I am
indebted to them for their timely contributions, the comprehensive reviews
of their special subject areas and for their insight into likely future trends.
Finally, I would like to dedicate this book to the memory of my wife
Mary who, despite her own serious illness, gave me a great deal of support
and encouragement during the long hours of preparation of the manuscript,
and inspired me to complete it. Sadly, she did not live to see the book
published.
D. A. Knowles
Tonbridge, 1997
Contributors
G. A. Bell
Zeneca Agrochemicals,
Jealott's Hill Research Station,
Bracknell,
Berkshire RG42 6ET, UK
L. G. Copping
LGC Consultants,
34 Saxon Way,
Saffron Walden,
Essex CBIl 4EG, UK
P. D. Curie
Dow AgroSciences,
Crossbank Road,
King's Lynn,
Norfolk PE30 2JD, UK
W. K. de Raat
OpdenKamp Consultancy Group,
Koninginnegracht 23,
2514 AB The Hague,
The Netherlands
C. D. Emmerson
AgrEvo Ltd,
Cambridge Road,
Hauxton,
Cambridge CB2 5HU, UK
A. H. Gregory
Pac-Tech,
Treetops, Scotland Close,
Haslemere,
Surrey GU27 3AE, UK
B. C. Hakkert
TNO Nutrition and Food Research Institute,
Department of Occupational Toxicology,
PO Box 360,
3700 AJ Zeist,
The Netherlands
J. Hartmann
Bayer AG,
Alfred Nobel Strasse 50,
D-40789 Monheim,
Germany
P. J. Holloway
lACR-Long Ashton Research Station,
Department of Agricultural Sciences,
University of Bristol,
Long Ashton,
Bristol BS41 9AF, UK
G. F. Houben
TNO Nutrition and Food Research Institute,
Department of Occupational Toxicology,
PO Box 360,
3700 AJ Zeist,
The Netherlands
S. T. Humphrey
Borregaard UK Ltd,
Unit 16, Ponthenri Industrial Estate,
Ponthenri,
Llanelli,
Carmarthenshire SA15 ITY, UK
K. S. Johnson
EPEC,
78 Pound Road,
East Peckham,
Tonbridge,
Kent TN12 5BJ, UK
D. A. Knowles
FORM-AK
10 The Forstal,
Hadlow,
Tonbridge,
Kent TNIl ORT, UK
G. A. Matthews
International Pesticide Application Research Centre,
Imperial College of Science, Technology and Medicine,
Silwood Park,
Buckhurst Road,
Ascot,
Berkshire SL5 7PY, UK
P. J. Mulqueen
Dow AgroSciences,
Letcombe Laboratory,
Letcombe Regis,
Wantage,
Oxfordshire OX12 9JT, UK
P. Nixon
Novartis AG,
CH-4002 Basle,
Switzerland
S. Reekmans
ICI Surfactants,
Everslaan 45,
Everberg B-3078,
Belgium
I. A. van de Gevel
TNO Nutrition and Food Research Institute,
Department of Occupational Toxicology,
PO Box 360,
3700 AJ Zeist,
The Netherlands
J. M. Wagner
Zeneca Ag Products,
1800 Concord Pike,
PO Box 15458,
Wilmington,
DE 19850-5458, USA
Contents
Preface ................................................................................. xiii
List of Contributors ...............................................................
xv
1. Introduction ..................................................................
1
References ...............................................................................
7
2. Review of Major Agrochemical Classes and
Uses ..............................................................................
8
2.1
Introduction ....................................................................
8
2.2
Future Needs .................................................................
9
2.3
World Markets, 1996 ......................................................
9
2.4
Sales by Category, 1995 ...............................................
10
2.5
Sales by Crop, 1995 ......................................................
12
2.6
Sales by Region, 1995 ...................................................
13
2.7
Herbicides ......................................................................
13
2.7.1
Photosynthesis .............................................
15
2.7.2
Amino Acid Biosynthesis ..............................
17
2.7.3
Lipid Biosynthesis ........................................
17
2.7.4
Interference with Plant Hormones .................
18
2.7.5
Cell Division .................................................
19
2.7.6
Cellulose Biosynthesis .................................
19
2.7.7
Respiratory Uncouplers ................................
19
Insecticides ....................................................................
20
2.8.1
21
2.8
Organophosphorus Insecticides (OPs) .........
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v
vi
Contents
2.8.2
Carbamate Insecticides ................................
22
2.8.3
Insecticides that Interact with
Neurotransmitter Ligand Recognition
Sites ............................................................
22
Insecticides that Interfere with Ion
Channels .....................................................
23
2.8.5
Inhibition of Oxidative Phosphorylation .........
24
2.8.6
Insect Growth and Regulation ......................
25
2.8.7
Compounds with Uncertain Modes of
Action ..........................................................
26
Fungicides .....................................................................
27
2.9.1
Protectant Fungicides ...................................
27
2.9.2
Protein Biosynthesis .....................................
28
2.9.3
Nucleic Acid Metabolism ..............................
28
2.9.4
Cell Division .................................................
28
2.9.5
Sterol Biosynthesis .......................................
28
2.9.6
Triglyceride Biosynthesis ..............................
29
2.9.7
Chitin Biosynthesis .......................................
29
2.9.8
Respiration ...................................................
29
2.9.9
Indirectly Acting Fungicides ..........................
30
2.10
Plant Growth Regulators ................................................
30
2.11
Biological Screening: Discovery and Development
of a New Agrochemical ..................................................
30
2.11.1 Chemical Synthesis ......................................
31
2.11.2 Biological Evaluation ....................................
35
References ...............................................................................
38
2.8.4
2.9
3. Formulation of Agrochemicals ................................... 41
3.1
Introduction ....................................................................
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41
3.2
3.3
3.4
Contents
vii
Conventional Formulations ............................................
43
3.2.1
Granules (GR) ..............................................
43
3.2.2
Solution Concentrates (SL) ..........................
44
3.2.3
Emulsifiable Concentrates (EC) ....................
45
3.2.4
Wettable Powders (WP) ...............................
46
3.2.5
Suspension Concentrates (SC) ....................
47
3.2.6
Seed Treatments (DS, WS, LS, FS) .............
49
New-Generation Formulations .......................................
50
3.3.1
General Trends ............................................
50
3.3.2
Oil-in-Water Emulsions (EW) ........................
51
3.3.3
Suspoemulsions (SE) ...................................
52
3.3.4
Microemulsions (ME) ....................................
53
3.3.5
Controlled-Release Formulations .................
53
3.3.6
Water-Dispersible Granules (WG) ................
55
3.3.7
Formulations Using a Built-In Wetter ............
56
Surfactants for Agrochemicals .......................................
57
3.4.1
General Characteristics ................................
57
3.4.2
Adsorption and Surface Tension ...................
59
3.4.3
Micellization .................................................
61
3.4.4
Kraft Temperature and Cloud Point ..............
61
3.4.5
Wetting and Contact Angle ...........................
61
3.4.6
Particle and Droplet Stabilization ..................
62
3.4.7
Wetting Agents .............................................
63
3.4.8
Dispersion ....................................................
64
3.4.9
Emulsification ...............................................
65
3.4.10 Solubilization ................................................
66
3.4.11 Bioenhancement ..........................................
67
3.4.12 Conventional Surfactants .............................
67
3.4.13 Recent Surfactant Developments .................
70
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Contents
3.5
Other Formulation Additives ..........................................
71
3.5.1
Carriers and Diluents ...................................
71
3.5.2
Solvents .......................................................
71
3.5.3
Anti-Settling Agents ......................................
73
3.5.4
Water-Soluble Polymers ...............................
74
3.5.5
Preservatives ...............................................
75
3.5.6
Anti-Freeze Agents ......................................
78
3.5.7
Anti-Foam Agents ........................................
78
3.5.8
Anti-Caking Agents ......................................
78
References ...............................................................................
79
4. Water-Dispersible Granules ........................................ 80
4.1
Introduction ....................................................................
80
4.2
Manufacturing Methods .................................................
83
4.3
Physical Properties ........................................................
87
4.3.1
Granule Size and Shape ..............................
88
4.3.2
Particle Assemblies and Structures ..............
91
4.3.3
Quantity and Type of Binders .......................
98
4.4
Design: Modern Methods ............................................... 112
References ............................................................................... 114
5. Recent Developments on Safer Formulations of
Agrochemicals ............................................................. 121
5.1
Introduction .................................................................... 122
5.2
Liquid Formulations ....................................................... 125
5.2.1
Emulsifiable Concentrates (EC) .................... 125
5.2.2
Concentrated Emulsions (CE) ...................... 126
5.2.3
Suspension Emulsions (or
Suspoemulsions) .......................................... 130
5.2.4
Microemulsions ............................................ 131
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5.3
ix
5.2.5
Multiple Emulsions ....................................... 131
5.2.6
Suspension Concentrates ............................ 132
Controlled-Release Formulations .................................. 132
5.3.1
Methods of Encapsulation ............................ 134
5.3.2
Advantages of Microencapsulation ............... 142
5.3.3
Microencapsulated Products ........................ 146
5.3.4
Future Trends in Microencapsulation ............ 147
5.4
Water-Soluble Packaging .............................................. 147
5.5
Dry Products (Water-Dispersible Granules) ................... 148
5.6
Adjuvants ....................................................................... 148
5.7
Other Formulation Types ............................................... 149
5.8
5.7.1
Seed Treatment Formulations ...................... 149
5.7.2
Biotechnological Improvements .................... 149
Summary and Future Possibilities ................................. 152
References ............................................................................... 154
6. Agrochemical Formulations Using Natural
Lignin Products ............................................................ 158
6.1
6.2
6.3
6.4
Introduction .................................................................... 158
6.1.1
Lignosulphonates: Some Basic
Information ................................................... 158
6.1.2
Lignin Modification ....................................... 159
Wettable Powders (WP) ................................................ 160
6.2.1
Formulation .................................................. 160
6.2.2
Production Methods ..................................... 162
Water-Dispersible Granules (WG) ................................. 163
6.3.1
Formulation .................................................. 164
6.3.2
Production Methods ..................................... 166
Suspension Concentrates (SC) ..................................... 167
6.4.1
Formulation .................................................. 167
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Contents
6.4.2
6.5
Production Methods ..................................... 170
Oil-in-Water Emulsions (EW) ......................................... 172
6.6
6.5.1
Formulation .................................................. 172
6.5.2
Production Methods ..................................... 172
Controlled Release ........................................................ 172
6.6.1
Granules ...................................................... 173
6.6.2
Tablets ......................................................... 173
6.6.3
Gels ............................................................. 173
6.6.4
Microencapsulation ...................................... 174
6.7
Ultraviolet Protection ...................................................... 175
6.8
Compatibility Agents ...................................................... 176
6.9
Adjuvants ....................................................................... 176
6.10
Complexing Agents ........................................................ 177
6.11
Environmental and Regulatory Information ................... 177
6.11.1 Personnel .................................................... 177
6.11.2 Environmental .............................................. 177
References ............................................................................... 178
7. Novel Surfactants and Adjuvants for
Agrochemicals ............................................................. 179
7.1
Polymeric Surfactants and Stability ............................... 179
7.1.1
Introduction .................................................. 179
7.1.2
(De)Stabilization of Colloidal Systems .......... 179
7.1.3
Colloidal Stabilization ................................... 180
7.1.4
Structure of Polymeric Surfactants for
Steric Stabilization ....................................... 183
7.1.5
Polymeric Surfactants in Agricultural
Formulations ................................................ 187
7.1.6
Conclusion ................................................... 195
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Contents
7.2
7.3
xi
Trends towards Environmentally Safer
Surfactants ..................................................................... 196
7.2.1
Surfactants and the Environment .................. 196
7.2.2
Toxicity and Biodegradation ......................... 197
7.2.3
Hazard Labelling of Surfactants .................... 204
7.2.4
Effect of Chemical Structure ......................... 204
7.2.5
New-Generation Surfactants ........................ 209
7.2.6
Conclusion ................................................... 211
Enhancing Biological Activity Using Adjuvants .............. 212
7.3.1
Introduction .................................................. 212
7.3.2
Relevance of a Surfactant's Properties ......... 213
7.3.3
Built-In Activators and Spray-Tank
Mixtures ....................................................... 220
7.3.4
Future Trends in Surfactants and
Adjuvants ..................................................... 221
7.3.5
Conclusion ................................................... 226
Acknowledgements .................................................................. 226
References ............................................................................... 226
8. Improving Agrochemical Performance: Possible
Mechanisms for Adjuvancy ......................................... 232
8.1
Introduction .................................................................... 232
8.2
Chemical Composition of Adjuvants .............................. 233
8.2.1
Surfactants ................................................... 233
8.2.2
Emulsifiable Oils .......................................... 237
8.2.3
Polymers ...................................................... 239
8.2.4
Polymer-Forming Compounds ...................... 240
8.2.5
Phospholipids .............................................. 240
8.2.6
Inorganic Salts ............................................. 241
8.2.7
Other Ingredients ......................................... 241
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xii
Contents
8.3
8.4
Mechanistic Approaches for Investigating
Adjuvancy ...................................................................... 241
8.3.1
Atomization .................................................. 241
8.3.2
Retention ..................................................... 244
8.3.3
Predicting Retention Performance ................ 246
8.3.4
Spreading and Coverage .............................. 250
8.3.5
Uptake and Translocation ............................. 252
8.3.6
Predicting Uptake Enhancement
Performance ................................................ 253
Future Prospects ........................................................... 257
Acknowledgements .................................................................. 259
References ............................................................................... 260
9. Packaging of Agrochemicals ...................................... 264
9.1
9.2
Selection of Packaging Types ....................................... 264
9.1.1
Selection of Packaging Materials for
Solid Formulations ....................................... 264
9.1.2
Selection of Packaging Materials for
Liquid Formulations ...................................... 267
9.1.3
Plastics ........................................................ 267
9.1.4
Metal ............................................................ 269
9.1.5
Glass ........................................................... 269
9.1.6
Recommended Tests to Be Carried Out
on the Main Types of Containers .................. 269
9.1.7
Specifications ............................................... 271
9.1.8
Packaging Instructions ................................. 271
Closures ......................................................................... 272
9.2.1
Prevention of Leakage ................................. 272
9.2.2
Tamper Evidence ......................................... 273
9.2.3
Closure Diameter – Liquid Products ............. 274
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9.2.4
xiii
Dispensing Liquid Products from Packs
Designed for Pouring ................................... 275
9.3
Labelling ........................................................................ 277
9.4
Shelf Life ........................................................................ 278
9.5
Pack Design with Regard to Easy Rinsing and
Disposal ......................................................................... 279
9.6
Types of Secondary Packaging ..................................... 279
9.6.1
Unit Cartons ................................................. 281
9.6.2
Combination with Primary Pack .................... 281
9.6.3
Methods for Protection of Unit Loads ............ 281
9.7
United Nations Performance Tests ................................ 281
9.8
Rinsing Methods ............................................................ 283
9.9
Closed Transfer Systems .............................................. 285
9.10
Collection of Containers after Use ................................. 287
9.11
Summary of Key Design Criteria ................................... 289
9.12
Returnable Packaging Systems ..................................... 289
9.12.1 Small-Volume Returnable Containers ........... 289
9.12.2 SVR Design Criteria ..................................... 290
9.12.3 Stewardship ................................................. 290
9.12.4 Closures ...................................................... 291
9.12.5 Labelling and Marking .................................. 291
9.12.6 Handling ...................................................... 291
9.12.7 Disposal ....................................................... 291
9.13
ECPA Standard SVR Interface ...................................... 291
9.13.1 Container Interface/Extractor Valve .............. 291
9.13.2 Coupler ........................................................ 292
9.13.3 Extractor Valve and Coupler Combined ........ 293
9.14
Future Direction ............................................................. 295
Glossary of Terms and Definitions ............................................ 295
Bibliography .............................................................................. 299
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Contents
10. Application Techniques for Agrochemicals .............. 302
10.1
Hydraulic Nozzles .......................................................... 302
10.1.1 Types of Hydraulic Nozzle ............................ 308
10.2
Portable Sprayers .......................................................... 312
10.3
Tractor Sprayers ............................................................ 315
10.3.1 Portable Lines .............................................. 320
10.3.2 Orchard Sprayers ......................................... 320
10.4
Aerial Application ........................................................... 321
10.5
ULV and CDA Ground Application ................................. 324
10.6
Fogs, Mists and Aerosols .............................................. 327
10.6.1 Mists ............................................................ 328
10.7
Electrostatically Charged Applications ........................... 329
10.8
Chemigation ................................................................... 330
10.9
Granule, Dust and Seed Treatments ............................. 331
10.9.1 Seed Treatment ........................................... 332
10.10 Miscellaneous ................................................................ 332
10.10.1 Weed Wiper ................................................. 332
10.10.2 Lure and Kill ................................................. 332
10.10.3 Tree Injection ............................................... 332
10.11 Standards ...................................................................... 333
References ............................................................................... 333
11. Regulatory Requirements in the European
Union ............................................................................. 337
11.1
Introduction .................................................................... 337
11.2
Some Basic Features of 91/414/EEC ............................ 339
11.2.1 Which Plant Protection Products? ................ 339
11.2.2 Authorization of Active Substances and
Plant Protection Products ............................. 339
11.2.3 Existing and New Active Substances ............ 340
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xv
11.2.4 Harmonization of Methods and
Procedures .................................................. 341
11.2.5 Quality Standard .......................................... 341
11.2.6 Mutual Recognition ...................................... 342
11.2.7 Data Protection ............................................ 342
11.2.8 Exemptions from the 'Standard'
Authorization Procedures ............................. 343
11.3
Overview of Authorizations ............................................ 344
11.4
Data Requirements ........................................................ 345
11.5
Dossier Preparation ....................................................... 348
11.6
Inclusion of Active Substances in Annex I of
91/414/EEC ................................................................... 353
11.6.1 Introduction .................................................. 353
11.6.2 Initial Evaluation ........................................... 355
11.6.3 Detailed Evaluation and the Preparation
of the Monograph ......................................... 356
11.6.4 Procedure .................................................... 361
11.7
Authorization of Plant Protection Products .................... 361
11.7.1 General Requirements ................................. 361
11.7.2 The Uniform Principles ................................. 362
11.7.3 Evaluation .................................................... 363
11.7.4 Authorization Criteria .................................... 366
11.8
Transitional Measures and the Review
Programme .................................................................... 370
11.8.1 Transitional Authorizations ........................... 370
11.8.2 Review Programme ...................................... 371
11.9
Adjuvants ....................................................................... 374
Acknowledgements .................................................................. 374
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Contents
Appendix 11.A An Overview of European Community
General Legislation Associated with Plant
Protection Products ....................................................... 375
12. Regulatory Requirements in the USA ........................ 377
12.1
Introduction .................................................................... 377
12.2
Federal Pesticide Laws .................................................. 377
12.2.1 Federal Insecticide, Fungicide, and
Rodenticide Act ............................................ 378
12.2.2 Federal Food, Drug, and Cosmetic Act ......... 379
12.2.3 Food Quality Protection Act, 1996 ................ 379
12.3
EPA Office of Pesticide Programs ................................. 383
12.3.1 Organization ................................................ 384
12.3.2 Operating Objectives .................................... 385
12.4
Product Registration: Obtaining a License to Sell .......... 386
12.4.1 Experimental Use Permit .............................. 386
12.4.2 Registration .................................................. 387
12.4.3 Tolerances and Exemptions from
Tolerances ................................................... 393
12.5
Registration and Tolerance Data Requirements ............ 397
12.6
Data Evaluation ............................................................. 397
12.6.1 EPA Risk Assessment Process .................... 402
12.6.2 Industry Interaction with EPA: Practical
Advice .......................................................... 403
12.7
Data Protection and Compensation ............................... 404
12.8
Reregistration and Product Defense .............................. 405
12.8.1 Data Call-in and Industry Task Force
Groups ......................................................... 406
12.8.2 Special Review Process and
Cancellation of Registrations ........................ 406
12.9
Product Labeling ............................................................ 407
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xvii
12.10 State Registration Requirements ................................... 409
12.11 Conclusions ................................................................... 411
Acknowledgements .................................................................. 412
Appendix 12.A Index of EPA Study Guidelines ........................ 412
Appendix 12.B Sources of Registration Information ................. 412
Appendix 12.C Office of Pesticide Programs: Senior EPA
Contacts ......................................................................... 415
References ............................................................................... 416
13. Waste Management and Disposal of
Agrochemicals ............................................................. 418
13.1
Introduction .................................................................... 418
13.2
Site Management Responsibilities ................................. 418
13.3
Waste Minimization ........................................................ 419
13.3.1 General Principles and Definitions ................ 419
13.3.2 Examples of Source Reduction Options ........ 420
13.3.3 Example of Recycling, Use and Reuse
of Waste and Reclamation ........................... 421
13.4
Waste Types .................................................................. 422
13.5
Waste Handling ............................................................. 422
13.5.1 Operator Safety ............................................ 422
13.5.2 Workplace Designated Waste Collection
Areas ........................................................... 423
13.5.3 Site Waste Collection ................................... 423
13.5.4 Secure Waste Storage ................................. 423
13.5.5 Waste Preparation Prior to Disposal ............. 423
13.5.6 Detoxification of Containers .......................... 427
13.5.7 Toxic Wastes ............................................... 428
13.6
Documentation and Records ......................................... 428
13.6.1 Waste Producer (Originator) ......................... 428
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xviii
Contents
13.6.2 Identification ................................................. 428
13.6.3 Consignment ................................................ 428
13.7
Waste Disposal .............................................................. 428
13.7.1 Waste Disposal Options ............................... 429
13.7.2 Waste Disposal Contractors ......................... 429
13.7.3 Waste Transfer Stations ............................... 429
13.7.4 Transport ..................................................... 429
13.8
Treatment and Disposal of Aqueous Effluents
Arising from Formulation and Packaging of
Agrochemical Products .................................................. 430
13.8.1 Introduction .................................................. 430
13.8.2 Treatment Process ....................................... 430
13.8.3 Plant Details and Layout .............................. 431
13.8.4 Final Effluent Quality .................................... 431
13.8.5 Effluent Disposal .......................................... 434
13.8.6 Sludge Disposal ........................................... 434
References ............................................................................... 434
Index .................................................................................... 435
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1 Introduction
D. A. KNOWLES
Enormous changes have taken place in the chemistry and technology of
agrochemicals over the last 20 years or so, particularly in the discovery of
new active ingredients, their formulation, packaging, use, regulation and
general management. Similarly, the formulation additives and adjuvants
supply industry has developed new products to meet the needs of the
agrochemical industry for products having greater safety to the user, much
lower environmental impact and improved biological efficacy to the specific
target pest. Great strides have been made in understanding the modes of
action of both pesticides and adjuvants, so that molecules can now be
designed for activity at the target site only, and which are effective at low
doses and have low toxicity to mammals and other non-target life forms. A
book on Pesticide Formulations was published in 1973, which reviewed the
state-of-the-art of the technology at that time [I]. Since then many books
have been published covering the proceedings of conferences on pesticide
technology developments, and a few books have been published on the
basic principles of colloid science and surfactants applied to agrochemicals
[2, 3], and specialized technology such as controlled release formulations
[4,5]. It is appropriate, therefore, that a new book is published to review the
most recent developments in the chemistry and technology of agrochemical
active ingredients and formulations which will carry the industry forward
into the next millennium. This book brings together well-known experts
from a number of major agrochemical and formulation additives supplier
companies, consultancies, academic and other organizations with many
years of practical experience of the most important aspects of the discovery
and development of new and more environmentally friendly agrochemical
products.
The book includes reviews of the synthesis, modes of action and biology
of active ingredients, their formulation, packaging and application in the
field, product regulation by governments and general waste management
control. Reviews are also included by manufacturers of dispersing and
emulsifying agents and surfactant and oil-based adjuvants who are developing tailor-made products to improve the long-term stability of formulations
as well as to enhance the biological activity of the active ingredients. The
additives and adjuvants themselves must have low toxicity and environmental impact, and the end result can often be a reduction in the dose rate of
active ingredient per hectare of crop. Much greater understanding is now
available on the colloid and surface chemistry of formulation stability, and
the modes of action of surfactants and other adjuvants on sprays and crop
leaf surfaces. Another area of development, which is sometimes overlooked, is the improvement in process technology and equipment for the
safe formulation, packaging and application of agrochemical products. New
equipment and techniques enable high standards of HSE (health, safety
and the environment) to be met. Plant and equipment are available for all
kinds of water-based or dust-free water-dispersible granular formulations
to be made. Recent developments in spray application technology (including Global Positioning Systems, GPS, using satellites) are enabling chemical sprays to be better targeted with consequent reduced waste and
pesticide load per hectare. Waste mangement techniques are available to
produce clean effluent in the factory and the field and to minimize waste by
recycling wherever possible.
Inevitably, most of these areas of science and technology overlap to a
certain extent and, indeed, one of the aims of the book is to show how the
various areas work together to produce the most effective, safe, convenient
and environmentally friendly agrochemical products. Likely future trends
in all areas of technology and regulation are discussed with a view to
producing low-risk products for the sustainable development of crop protection and public health throughout the world. Moves towards international product quality, safety standards and regulatory harmonization are
also covered.
Agrochemical products have been used widely for many years to increase
the yield and improve the quality of food and fibre crops and to improve
public health all over the world. The agrochemical industry has become a
major business producing products with a total world sales value estimated
in 1997 at over US$30 billion, and it plays an important part in the economies of most countries. The agrochemical business represents a significant
opportunity for surfactants and other essential formulation additives as well
as adjuvants for spray applications. Although the agrochemical industry
markets have reached maturity in North America, Western Europe and
Japan, there is still considerable scope for new, more environmentally
friendly active ingredients and formulations. Developing areas, especially
the Asia-Pacific region and South America, have a rapidly increasing need
for safe agrochemical products to increase crop yields. Indeed, the market
for agrochemical products in the Asia-Pacific area (including Japan) is now
almost as big as that of the Western European market and in the future
could rival that of North America.
Changes in the population of the world and increasing urbanization and
industrialization of communities are placing a great demand on the efficient
use of available land for agriculture. For example, the United Nations has
forecast that if present trends continue, the population of the world will
increase from about 5 billion now to about 10 billion by the year 2040, and
the fastest rate of growth will be in the less developed areas, particularly the
Asia-Pacific region [6]. There will, therefore, be an increasing need for
agrochemical products as an important input to the management of food
and fibre crops to improve their yield and quality.
The ability to protect growing crops from weeds, pests and diseases has
been known since ancient times in the Old World of the Middle East, Asia
and China. However, the greatest improvements in crop protection efficiency and productivity in terms of crop yield and quality have occurred
mainly in the West and within the last century. Simple emulsifiable oils and
soaps have been used as agricultural sprays to control insect pests for many
years. The modern era of weed control can be said to have started in the
1940s with the development of the phenoxy acid herbicides such as 2,4-D
acid. Since then, and particularly since the 1960s, many new synthetic
pesticides have been introduced to combat a very wide range of weeds,
pests and fungal diseases. A great deal of research and development
has been carried out by all the major agrochemical companies and other
organizations to produce new active ingredients and formulations which
can be applied easily to crops and which will optimize the activity of the
pesticide [7].
Although in the last few decades there have been remarkable developments in new agrochemical active ingredients and formulations, most companies are now reviewing their product-pack strategies and government
regulatory authorities are introducing controls and legislation which are
leading to the introduction of reduced-risk active ingredients, and safer and
more environmentally friendly formulations in more convenient packaging.
There is also a need to reduce the total amount of active ingredients applied
per hectare. The cost of the development of new products is becoming
increasingly high and it is estimated that it can cost US$150-200 million to
develop one new active ingredient with a development timescale of 7-10
years from initial discovery to first registered commercialization of the
product. This is causing the industry to consolidate by mergers of companies or research joint ventures between companies. Generic manufacturers are also able to introduce off-patent products without the initial high
cost and risk of research and development. Research and development is,
therefore, concentrated on the major world crop and pest problems, and
patenting of new active ingredients and formulations is very important to
protect intellectual property rights in all the important markets of the
world.
Because of the variety of active ingredients which are available, many
different types of formulations have been developed depending mainly on
the physico-chemical properties of the active ingredients [8]. In the past
most formulations were simple solutions in water, emulsifiable concentrates
in a solvent, or dusts and dispersible powders. The current trends are to
eliminate petroleum-based solvents as much as possible and to replace
them with water in water-based suspensions and emulsion formulations. At
the same time, there is a move away from dusty powders towards essentially
dust-free water-dispersible granules. Controlled release formulations and
seed treatment formulations (also usually water based) may enable better
control and placement of the active ingredient. In particular, flowable seed
treatment formulations can be supplied in bulk containers, are safe to the
operator and, because they are applied directly to the seed, they reduce
wastage of pesticide and environmental impact in the field.
The wide variety of agrochemical formulations which is available requires a range of different formulation additives to produce safe and usable
products. Probably the most important of the formulation additives are
surface-active agents. Surfactants have been obtained from natural products by extraction or modification for thousands of years. Examples of
surfactants which are well known are soaps for cleaning, greases and tallows
for waterproofing, and glue, egg white and natural gums as dispersing and
emulsifying agents.
Synthetic surfactants, which have been specially synthesized in order to
obtain surface-active effects, represent a relatively modern development
which may be said to have evolved from the 'sulphonated oils' of the 19th
century. The early period of the 20th century was a very active phase in the
development of sulphated and sulphonated anionic surfactants with long
hydrocarbon chains. In the second half of the 20th century, the development of surfactants entered a more specialized phase with the introduction
of amphipathic molecules for specific applications. Non-ionic surfactants
became available in which the hydrophilic part of the molecule was based
on condensed chains of ethylene oxide. A wide range of surfactant properties can be achieved by varying the ethylene oxide chain length. This development has led to a better understanding of the colloid and surface
chemistry principles involved in the fundamental functional properties of
wetting, dispersion, emulsification and solubilization in the formulation of
pesticides. As a result of all this work, it is now possible for surfactant
suppliers to prepare 'tailor-made' surfactants to suit particular functions [912]. For nearly all formulations the most important formulation additive is
the surfactant in terms of preparation and production. The surfactant often
determines the maximum concentration of the formulation that can be
achieved, the particle or droplet size, long-term stability and sometimes
even the biological activity of the formulation. Surfactants, either alone or
mixed with oils, are essential components of adjuvants which can enhance
the biological activity of the spray mixture by affecting spray droplet size,
retention and spreading on leaf surfaces or by assisting uptake and
translocation of the active ingredient into the crop.
Many other additives are used for specific purposes, such as anti-settling,
anti-freeze and anti-foam agents for water-based formulations, and fillers
and disintegrants for powders and water-dispersible granules. Preservatives
are also important additives to formulations to prevent biodegradation
during preparation and storage, particularly where the formulations
are aqueous based and contain carbohydrates, or where the products are
exposed to the atmosphere after application, as in the case of baits and
pellets [13].
Agrochemical companies are now paying increasing attention to the
packaging of pesticides as part of the total 'delivery system' for convenient
use and user safety. Rinsing and safe disposal of plastic bottles is becoming
very important. In some cases this can be overcome by using bulk or minibulk containers, or small-volume returnable containers, all of which are
returned to the manufacturers for cleaning and refilling. The move from
liquids to granules allows the use of simple bags or cartons for ease of
disposal. Powders and granules can also be supplied in water-soluble bags
to eliminate operator contact entirely.
Despite the extensive research and development which goes into the
introduction of a new product, when the product is diluted and sprayed
onto crops in the field it is likely that only 10-20% of the active material will
reach the target site. This can be caused by many factors, such as poor
spraying conditions, spray droplets missing the crop and hitting the soil,
droplets bouncing or running off the crop leaves and general adverse
weather conditions [14]. There is, therefore, a great deal of scope for
improving the efficiency of the whole spray application process, and also
understanding the effect that formulations and adjuvants can have on it.
This is an area where all the technologies of formulation, packaging and
spray applications can work together to produce safer and more efficient
'total delivery systems'.
The disposal of factory and farm effluents and waste of all kinds is
becoming a sensitive and costly issue. Waste minimization by recycling is
being introduced wherever possible, and clean water effluent from treatment plants can sometimes be returned to the start of the formulation
process.
This book is arranged so that it takes the reader through the development
process of agrochemical products in a logical way from discovery and
modes of action of the active ingredients, through to all types of formulations from conventional to novel, use of surfactants in formulations and
adjuvants and understanding of how adjuvants affect biological performance, to packaging issues and spray application techniques, regulatory
protocols in Europe and the USA, and finally effluent treatment and waste
management legislation for pesticides.
Chapter 2 is a review of the major agrochemical classes and uses. It
provides an up-to-date assessment of the world markets for agrochemicals
and then describes the groups and modes of action of the main types of
pesticides. Chemical synthesis and screening, including combinatorial techniques, are discussed up to the stage of field evaluation.
Chapters 3, 4 and 5 provide a complete review of the most important
agrochemical formulation types from the well-known conventional formulations through to detailed technical accounts of recent developments in
water-dispersible granules, oil-in-water emulsions, controlled release formulations and other novel safer formulation types. The use of surfactants
and other formulation additives is described along with examples of typical
formulations. Likely future trends in formulation technology and processing are outlined.
Chapters 6 and 7 are accounts given by two supplier companies of the use
of natural and synthetic dispersing agents in formulations, and surfactants
and adjuvants for enhanced activity. Some novel applications are described
and typical examples are given to show how the surfactants and dispersing
agents can be tailor made to suit particular formulation situations, especially for the new-generation safer formulations. The environmental safety
and biodegradability of surfactants are highlighted, with special mention of
alternatives to alkylphenol ethoxylates.
Chapter 8 is a fundamental review of the mechanisms of how adjuvants
can improve the performance of agrochemical formulations. It includes the
most recent knowledge of how adjuvants can affect spray atomization,
wetting, speading and deposition on the leaf surface, and finally uptake and
translocation of systemic pesticides.
Chapter 9 covers all aspects of the packaging of agrochemical formulations and the recent legislative pressures which are driving changes in areas
such as pack rinsing and disposal, mini-bulk and small-volume returnable
containers for liquid products, and water-soluble bags for powders and
granules. Closed transfer systems for spray tanks are also discussed.
Chapter 10 reviews the spray application techniques for agrochemical
products from portable sprayers to large-scale tractor-mounted sprayers
and aerial application. It also covers the use of controlled droplet and
electrically charged droplet techniques for more accurate targeting of
pesticides. The need for spray application training, especially in developing
countries, is emphasized. The new technique of Global Positioning
System (GPS) to program a computer on a tractor for patch spraying is
introduced.
Chapters 11 and 12 deal with the data requirements for the registration of
agrochemical products in Europe and the USA. They also give details of
the latest changes to legislation in these regions. All requirements for the
registration and reregistration of active ingredients, formulations, adjuvants
and inerts are described. It is realized that the registration procedures in the
EU and USA are still being developed, but the lists of data requirements
given here are likely to form the basis of all registration submissions.
Chapter 13 completes the technology of agrochemical formulations, production and use by describing the legislation applying to the safe disposal
and management of all pesticide and contaminated wastes. A procedure for
the treatment of factory and farm effluents is given in detail. The need for
waste minimization and recycling is highlighted.
All the chapters describe the current situation and indicate likely future
trends. The chapters also contain detailed tables, figures and photographs
which illuminate the text. At the end of each chapter is a list of references
for further study. The book is, therefore, a comprehensive review of the
current state-of-the-art of the chemistry and technology of all the important
aspects of agrochemical research and development, and is intended for use
by experienced workers in the field as well as by new people looking for an
introduction to the current technology and regulation. It also indicates the
likely trends towards safer and more environmentally friendly technology
which will sustain the use of agrochemical products for crop protection into
the new millennium.
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Valkenburg, W. van (ed.) (1973) Pesticide Formulations, Marcel Dekker, New York.
Tadros, T.F. (ed.) (1987) Solid/Liquid Dispersions, Academic Press, London.
Tadros, T.F. (1995) Surfactants in Agrochemicals, Marcel Dekker, New York.
Kydonieus, A.F. (1980) Controlled Release Technologies: Methods, Theory and Applications, Vol. 2, CRC Press, Boca Raton, FL.
Wilkins, R.M. (ed.) (1990) Controlled Delivery of Crop Protection Agents, Taylor and
Francis, Bristol, PA.
Sugavanam, B. (1990) UNIDO's activities on pesticides. In Recent Developments in the
Field of Pesticides and their Application to Pest Control (eds K. Holly, L.G. Copping and
G.T. Brooks), UNIDO, Vienna, pp. 262-71.
Green, M.B., Hartley, G.S. and West, T.F. (1987) Chemicals for Crop Improvement and
Pest Management, Pergamon Press, Oxford.
Tomlin, C.D.S. (1997) Pesticide Manual, llth edn, BCPC, UK.
Karsa, D.R. (ed.) (1987) Industrial Application of Surfactants I, Royal Society of
Chemistry, Cambridge, UK.
Karsa, D.R. (ed.) (1990) Industrial Application of Surfactants II, Royal Society of
Chemistry, Cambridge, UK.
Karsa, D.R. (ed.) (1992) Industrial Application of Surfactants III, Royal Society of
Chemistry, Cambridge, UK.
Porter, M.R. (1994) Handbook of Surfactants, 2nd edn, Blackie, Glasgow, UK.
Knowles, D.A. (1995) Preservation of agrochemicals. In Preservation of Surfactant
Formulations (ed. F.F. Morpeth), Chapman & Hall, London, pp. 140-46.
Matthews, G.A. (1992) Pesticide Application Methods, 2nd edn. Longman, Harlow, UK.
2 Review of major agrochemical classes and uses
L. G. COPPING
2.1 Introduction
Agrochemicals are represented by today's press as being noxious chemicals
that do no good to the environment or to the people who eat treated food.
The situation is becoming so bad that it is uncommon to see those involved
in the business use the word pesticide, and many of the leading producers of
pesticides are beginning to talk about crop protection and plant health
rather than agrochemicals. However, it is not all bad news. As Steve Jones,
Professor of Genetics at University College, London, pointed out on the
Food Programme on BBC Radio 4, the population of the world is increasing at an alarming rate and has been doing so for some 20-30 years.
Nevertheless, the amount of food for each individual on earth, not just the
total amount of food, has increased over that same time period. So each
person living today has more to eat than their parents had 30 or even 20
years ago. Clearly we are getting something right.
The main problem is that it is bad news that people report. The fact that
DDT saved millions of lives at the end of the World War II and into the
1950s and 1960s is not news, but the fact that it is persistent and accumulates
in the food chain causing the death of birds is. I am sure that I am not alone
when I say that I would rather have a small residue of DDT in my body than
suffer from malaria. Today we have choices in the insecticides that we can
use. In 1945 we did not.
How many reports are there that, in the UK, yields of wheat per hectare
have risen significantly over the last 20 years? It is not unusual for yields of
around 10 tonnes of grain per hectare to be harvested from winter wheat
crops. The direct effects of agrochemicals to the farmer range from between
three and five times the value invested (LeBaron, 1990; Pimentel, 1991).
WHO reports indicate that the use of pesticides has made a significant
contribution to farming practice by reducing labour requirements, conserving fossil fuels, increasing crop yields, lowering food costs and improving
food quality (National Research Council Board on Agriculture, 1989;
Borlaug, 1990; World Health Organisation, 1990; Smith et al, 1990; Sweet
et a/, 1990; LeBaron, 1990).
Recent studies in the USA have indicated that if crop protection chemicals were banned, yields of fruit, vegetables and cereal crops would decline
by 32-78% (Smith et a/., 1990; Pimentel, 1991). What effect would this have
on the price of food?
2.2 Future needs
It is estimated that there will be an additional 3 billion people to feed in the
world by 2025 and, by 2050, the population is expected to exceed 11 billion,
more than twice the present population (Urban and Dommen, 1989). This
means that within the next 50 years it will be necessary to produce more
than twice as much food as is currently being produced (Borlaug, 1990). It
must always be remembered that if the population increases, the land
available for agricultural production will fall as these new people will have
to live somewhere. Today, the amount of arable land available for the
production of food per person is down from about 0.5 ha in the 1960s to
about 0.33 ha (Urban, 1989). Each available hectare must support more and
more people as world population continues to increase at a rate of 1.7% per
year (90 million more people to feed and clothe each year), whilst the rate
of expansion of world cropland is less than one-tenth of this rate (0.15% per
year or 50-60 million new hectares of cropland by 2010; Urban, 1989). In
less than 20 years each person will have to be supported by only 0.2 ha.
With more people and less land per person, the only way that the population of the world can be fed is to increase productivity per hectare. The
only way to do this is with improved crop protection. We will not be able to
survive without the strengths of science and technology and the judicious
application of crop protection agents.
2.3 World markets, 1996
Global agrochemical sales rose by 5.5% to US$30560 million at end-user
level in 1996. When this figure is discounted for the effects of inflation and
currency fluctuations, growth in real terms is estimated to be 2.2% over
1995. This is the third year where real increases in sales value have been
recorded (1994 sales were 5.1% higher than 1993 figures and 1995 sales
were 4.3% higher than 1994 figures; Woodburn, 1997).
The majority of these agrochemical sales are controlled by the 25 largest
companies whose annual income from agrochemicals represents over 90%
of the pesticide market. This indicates that to be a successful player in the
pesticide industry it is necessary to be a large organization with the ability
to invest a great deal of support into the discovery (in most cases), development, manufacture and marketing of products. There are some organizations that have built their successful position on their ability to manufacture
and formulate commodity products, those products that were discovered
some years ago and whose patents have lapsed, thereby allowing organizations, other than the inventor, to make, formulate and sell the product
internationally.
Most of the 25 largest companies are involved in discovery research
targeted at the synthesis of new chemicals with new chemical structures,
new modes of action and low rates of application that can be protected by
international patents and that will give the inventing company an advantage
over its competitors. Other generic manufacturers also invest in research,
but this is more applied in terms of manufacturing opportunities and formulation advances.
The money that is invested in research and development is thought to be
a reflection on the chances of successful discovery. Without a doubt, the
more money that is invested, the more research that can be done, but it is
important to ensure that the return on the money invested in research is
recouped through an increase in the profitability of the company. If returns
on research investment fall below the current rates of interest, then it would
be more profitable in the short term to put the money in a bank deposit than
to spend it in the hope of 'jam tomorrow'.
The number of agrochemical companies is reducing as many merge to
form larger, more securely financed companies or are acquired by their
larger competitors. Such acquisitions include the takeover of Shell Development (USA) by Du Pont and the subsequent acquisition of Shell Research by American Cyanamid (and its later acquisition by American
Home Products), Ciba-Geigy's purchase of Maag, Sumitomo's acquisition
of Chevron to form the US-based operation Valent, and Rhone-Poulenc's
acquisition of Union Carbide. Mergers are also well established with the
most important being that between CIBA and Geigy to form Ciba-Geigy
and the subsequent merger with Sandoz to form Novartis (now the largest
agrochemical business with predicted annual sales of around $4 billion),
Dow and Blanco to form DowElanco, and Hoechst and Schering (who had
already purchased the UK-based merged company FBC formed by the
collaboration of Boots and Fisons) to form AgrEvo.
2.4 Sales by category, 1995
In the developed world, in markets such as small-grain cereals, soybean,
maize and rice, the value of the herbicide market is much larger than either
insecticides or fungicides (Figure 2.1). This is because the economies of
developed countries have led to a move of the population from rural environments, where they worked the land, to the urban environment, which
are common in Europe and North America. Weeds can be guaranteed to
occur within any intensively farmed area and will always have a deleterious
effect on the crop. This effect may be a direct yield loss through competition
Herbicides $14 billion
Fungicides $5.5 billion
Others $1.3 billion
Insecticides $8.2 billion
Figure 2.1 World agrochemical market sales by category, 1995.
for light, water or nutrients. It may also be an indirect effect on the value of
the crop through increased difficulty in harvesting. It may be through the
introduction into the crop of poisonous weed by-products with a deleterious
effect on the health of the consumer, or it may contain weed seeds that will
reduce the crop's value. The movement of people from the land removes
the labour that was available for hand-weeding and so chemical weed
control becomes essential.
The fungicide market worldwide has always been smaller than those for
either herbicides or insecticides. It is often said that this is because farmers
cannot see the causal agents of the diseases that damage their crops and so
they do not treat for them. Whilst this may be true of developing nations,
where the education of farmers may be lower than that of the developed
world, this cannot be true of North America, where fungicide use is very
low indeed. In these extensive agricultural systems, it is usually factors such
as lack of water rather than attack by disease that reduce yield. It is also true
that it was not until the last 30 years that compounds became available to
demonstrate the catastrophic losses that can be associated with disease. If a
crop cannot be grown in the absence of disease how can one show the
benefits of disease control? Couple this with the use of conventional disease
resistance breeding, and it becomes clear that fungicides are the 'new boys'
in crop protection; as we learn more about the impact of poor disease
management on crop productivity we understand the value of disease
control.
The global insecticide market is a key market in the developing world,
and in high-value crops such as fruit and vegetables, and cotton, where
damage to the flower or developing boll, the square, can lead to a complete
loss of yield. Certain crops can be expected to suffer from insect attack on
a routine basis. Maize planted in the mid-western USA will succumb to corn
rootworm (Diabrotica spp.) unless the soil is treated and Colorado potato
beetle (Leptinotarsa decimlineatd) will attack potatoes in North America
and continental Europe.
Other products represent only a small share of the crop protection
market, with plant growth regulators being the largest of this sector.
Other biological effects include rodenticides, molluscicides, avicides and
nematicides.
2.5 Sales by crop, 1995
The main crop protection markets include those high-acreage crops that
represent the bulk of the processed or fresh produce consumed by the
world's population or its livestock, including oil crops. An exception to this
is the cotton market that is important for the production of fibre for clothing, oil for food processing and protein for animal feed, and is susceptible to
insect attack. Figure 2.2 shows how the agrochemical sales are divided
between crops. The grain crops maize, rice, wheat and barley represent
almost one-third of all chemical inputs, totalling more than the whole of the
vegetable market. This is a representation of the size of the cultivated area
of these crops and the high quality control standard that is applied to
vegetable crops in today's world. When was the last time you found a
caterpillar in a cabbage at the supermarket?
One consequence of this split of agrochemical usage by crop is that
agrochemical companies will always target established markets where they
can expect a return from their investment. If $100 million has been invested
on a new chemical and its effective life in the market place is expected to be
10 years, and it is desired to make enough profit from that new product to
ensure the security of the operation and its employees, it will be necessary
to make a profit of over $10 million each year. This will mean sales of over
$25 million each year. If a new compound achieves 10% of the sales in a
particular field it is doing very well, so any market that is less than $250-500
million is too small for investment. Hence, the large markets remain as large
Vegetables $7.1 billion
Cereals $4.3 billion
Rice $3.9 billion
OSR $0.5 billion
Cotton $2.9 billion
Others $4.8 billion
Maize $3.2 billion
Soybean $3.4 billion
Figure 2.2 World agrochemical market: sales by crop, 1995.
markets with intense competition and increasingly high standards of biological effect and low environmental impact.
2.6 Sales by region, 1995
The North American share of the agrochemical market continues to grow
and Western Europe shows an increased market share in dollar terms, but
much of this increase is due to exchange rate factors (Figure 2.3). The
Eastern European market remains depressed by economic considerations
and represents less than 3% of the total global agrochemical sales. Although the Eastern bloc has significant potential in the crop protection
industry, it is no longer recorded as a separate region, rather contributing to
the rest-of-the-world figure. The Far East's share of the market has also
increased in dollar terms but again much of this was due to currency
fluctuations. The Japanese market continues to contract, due in part to
currency fluctuations and to reduced rice plantings. Increased herbicide
usage in Australasia and Latin America contributed to an increase in these
regions' share of the agrochemical market.
As with the review of agrochemical usage on crops, it is the developed
world that consumes the majority of the pesticides produced. As these
countries are the richest nations, it is unlikely that this will change within
the foreseeable future. This again means that agrochemical companies will
target established markets in wealthy countries, but with an eye on the
situation in large potential markets such as China (population 1200 million)
and India (population 900 million).
2.7 Herbicides
The development of weed resistance to applied herbicides has led to the
formation of the Herbicide Resistance Action Committee (HRAC), and it
W.Europe $7.6 billion
Far East $7.5 billion
NAFTA $8.4 billion
RoW $5.5 billion
Figure 2.3 Agrochemical sales by region, 1995.
Table 2.1 Summary of Herbicide Modes of Action
Group
Mode of action
A
Inhibition of acetyl CoA
carboxylase (ACCase)
B
Inhibition of acetolactate
synthase (ALS)
(acetohydroxyacid
synthase (AHAS))
Inhibition of photosynthesis
at photosystem II
Cl
C2
C3
D
E
Inhibition of photosynthesis
at photosystem II
Inhibition of photosynthesis
at photosystem II
Photosystem I electron
diversion
Inhibition of protoporphyrinogen
oxidase (PPO)
Kl
Bleaching: inhibition of
carotenoid biosynthesis
at the phytoene desaturase
step (PDS)
Bleaching: inhibition of
4-hydroxyphenyl pyruvate
dioxygenase (4-HPPD)
Bleaching: inhibition of
carotenoid biosynthesis
(unknown target)
Inhibition of EPSP synthase
Inhibition of glutamine synthetase
Inhibition of dihydropterate
synthase (DHP)
Microtubule assembly inhibition
K2
Inhibition of mitosis
K3
Inhibition of cell division
L
Inhibition of cell wall (cellulose)
biosynthesis
Uncoupling (membrane disruption)
Fl
F2
F3
G
H
I
M
Chemical family
Aryloxyphenoxypropionates
Cyclohexanediones
Sulfonylureas
Imidazolinones
Triazolopyrimidines
Pyrimidinylthiobenzoates
1,3,5-Triazines
Triazinones
Uracils
Pyridazinone
Phenyl carbamates
Phenylureas
Amide
Nitriles
Benzothiadiazole
Phenyl pyridazine
Bipyridyliums
WSSA3
group
1
2
5
7
6
22
Diphenyl ethers
Af-Phenylphthalimides
Thiadiazoles
Oxadiazoles
Triazolinones
Pyridazinones
Nicotinanilides
Others
14
Triketones
Isoxazole
Pyrazole
Triazoles
Isoxazolidinone
Phenylurea
Glycines
Phosphinic acids
Carbamates
28
Dinitroanilines
Phosphoroamidates
Pyridazines
Benzoic acid
Carbamates
Benzylethers
Chloroacetanilides
Carbamates
Acetamides
Benzamides
Oxyacetamides
Nitriles
Benzamides
Dinitrophenols
12
11
13
9
10
18
3
23
27
15
20
21
24
Table 2.1 Continued
Group
Mode of action
N
Inhibition of lipid biosynthesis
- not ACCase inhibition
O
Synthetic auxins
P
Inhibition of indoleacetic acid
action
Unknown
Z
Chemical family
WSSAa
Group
Thiocarbamates
Phosphorodithioates
Benzofurans
Chloro-carbonic acids
Phenoxy alkanoic acids
Benzoic acids
Pyridine carboxylic acids
Quinoline carboxylic acids
Phthalamates
8
Arylaminopropionic acids
Organoarsenicals
Others
4
19
25
17
27
8
a
WSSA - Weed Science Society of America classification.
From Herbicide Resistance Action Committee Classification of Herbicides by Mode of
Action.
has put together a classification of herbicide modes of action in an attempt
to persuade farmers to use compounds with different modes of action as a
strategy to combat the onset of resistance. This classification is also useful as
a list of different biochemical modes of action and can be used to summarize the target sites of commercial herbicides (Table 2.1).
2.7.1 Photosynthesis
Photosynthesis involves the conversion of light energy into chemical energy, the light reaction, and the incorporation of carbon dioxide into sugars,
the dark reaction. The light reaction captures light energy and converts this
into chemical energy through the electron transport chain. The products of
the light reaction are chemical energy in the form of ATP, reducing power
in the form of NAPDH and oxygen as a by-product. The light reaction is
divided into two cycles: photosystem I or cyclic photophosphorylation and
photosystem II or non-cyclic photophosphorylation. Both involve the capture of light energy by chlorophyll, a photoreceptor, and the acceptance of
electrons from the splitting of water. The capture of these electrons increases the energy level of the chlorophyll to the so-called singlet state and
this then returns to the ground state as the electrons flow through an
electron transfer chain to produce ATP and NADPH. If the electron transport chain is interrupted and light continues to fall on the chloroplast, the
energy level of the chlorophyll is raised from the singlet state to the triplet
state. Triplet chlorophyll can interact with membrane lipids in a damaging
way but, more importantly, it can excite oxygen, there in abundance because of active photosynthesis, to a singlet state. This singlet oxygen is very
reactive and it interacts with cellular lipids, proteins, nucleic acids and many
other plant cell components, thereby inducing cellular disorganization and
plant death. A large number of herbicides interfere with photosystem II
(non-cyclic photophosphorylation), diverting the electron flow on the
chloroplast membranes and causing the chlorophyll molecules to become
highly reactive. The classifications Cl, C2 and C3 include compounds that
interfere with photosystem II, with the three categories representing different binding sites of the inhibitors.
The bipyridyliums paraquat and diquat (classification D) also interfere
with photosynthesis, but at photosystem I (cyclic photophosphorylation).
Cyclic photophosphorylation is also a highly energetic reaction. Paraquat
and diquat capture electrons from the chloroplast and this reduces the
herbicide, and the reduced herbicide reacts with oxygen to form
superoxide. Superoxide produces hydrogen peroxide within the chloroplast
and these two compounds interact to form hydroxyl radicals in the presence
of an iron catalyst. Hydroxyl radicals are very damaging and lead to the
destruction of the cellular components, leading to rapid plant death.
There are a number of other herbicides that affect photosynthesis indirectly. Pyrazole herbicides, such as benzofenap, pyrazolynate and
pyrazoxyfen, and the relatively new classes of herbicides, the triketones
(sulcotrione) and isoxaflutole, interfere with the enzyme p-hydroxyphenylpyruvate dioxygenase that is involved in the conversion of /?-hydroxyphenyl pyruvate to homogentisate, a key step in plastoquinone biosynthesis.
Inhibition of this enzyme has an indirect effect on carotenoid biosynthesis as
plastoquinone is a cofactor of the enzyme phytoene desaturase. This inhibition leads to the onset of bleaching in susceptible weeds and ultimately plant
death (Luscombe and Pallett, 1996; classification F2).
In addition to the green chlorophyll pigments in the leafs chloroplasts,
there are other pigments that can also capture light energy but which also
protect the leaf from damaging radicals by quenching them. Carotenoids
are examples of this type of pigment. The inhibition of carotenoid
biosynthesis removes these protective pigments from the chloroplasts and
leads to damaging effects within them. Herbicides that have been shown
to interfere with carotenoid biosynthesis include norfluazon, fluridone
and diflufenican (classification Fl). These compounds interfere with the
desaturase enzymes that convert phytoene to lycopene, whereas amitrole
and herbicides that contain 3-trifluoromethylphenyl substituents (e.g.
fluometuron) have also been shown to affect carotenoid biosynthesis
(classification F3) by preventing the cyclization of lycopene to form the
carotenes.
There are several products that exert their effect through the accumula-
tion of abnormally high levels of chlorophyll precursors (Dayan and Duke,
1996). A structurally diverse range of herbicides has been shown to inhibit
the enzyme protoporphyrinogen oxidase, a pivotal enzyme at the branching
point of the porphyrin pathway leading to both haeme and chlorophyll
biosynthesis. The inhibitors of this process can be classified into three major
chemical groups: the nitrodiphenyl ethers (acifluorfen and lactofen), the
phenyl heterocycles (oxadiazon and sulfentrazone) and the heterocyclic
phenylimides (flumiclorac) (classification E).
These compounds exert their effect through inhibition of membranebound chloroplastic protoporphyrinogen oxidase, leading to a transient
accumulation of protoporphyrinogen IX. The protoporphyrinogen IX leaks
out into the cytoplasm where it is converted into protoporphyrin IX by the
herbicide-insensitive plasma membrane protoporphyrinogen oxidase. This
protoporphyrin IX reaches very high levels in or near the plasma membrane and, being a photodynamic pigment, generates highly reactive oxygen radicals in the cytosol. The plasma membrane is therefore rapidly
destroyed, leading to cell death.
This mode of action has been shown to be very effective at controlling
weeds with rates as low as Ig/ha, leading to plant death for two good
reasons. First, there is little substrate competition with the herbicide because the substrate is lost to the cytoplasm when inhibition occurs, and
second, because protoporphyrin IX will accumulate even when only a small
proportion of the chloroplast protoporphyrinogen oxidase is inhibited.
2.7.2 Amino acid biosynthesis
Plants synthesize all the components necessary for effective growth including the building blocks of proteins, amino acids. A number of herbicides
interfere with the biosynthesis of these amino acids. Branched-chain amino
acid biosynthesis is inhibited by various groups of herbicides including
sulfonylureas, imidazolinones, triazolopyrimidines and pyrimidinylthiobenzoates (classification B). The enzyme acetolactate synthase (ALS),
also known as acetohydroxyacid synthase (AHAS), is the target for these
compounds.
Aromatic amino biosynthesis is the target for glyphosate, the world's
largest-selling pesticide. The enzyme 5-enolpyruvyl shikimate-3-phosphate
synthase (EPSP synthase) is inhibited by this herbicide (classification G).
Glufosinate-ammonium inhibits the enzyme glutamine synthetase (classification H).
2.7.3 Lipid biosynthesis
Lipids are essential plant components as they are constituents of membranes and cuticular waxes, as well as being major seed storage products.
The fatty acid constituents of lipids are synthesized from acetyl coenzyme
A under the influence of the enzyme acetyl coenzyme A carboxylase
(ACCase). Two groups of herbicide inhibit the action of ACCase, the
aryloxyphenoxypropionates and the cyclohexanedione oximes (classification A). The failure to synthesize fatty acids and the subsequent membrane
lipids leads to a cessation of growth, necrosis in the actively dividing
meristematic tissue and plant death. It is interesting that these groups of
compounds are very effective post-emergence treatments for the control of
grass weeds in broadleaved crops, although selectivity for some compounds
in cereal crops has been introduced. They have no activity against
dicotyledonous or cyperaceous species.
The conversion of fatty acids into very long-chain fatty acids is specifically inhibited by the thiocarbamate herbicides such as EPTC and triallate
(classification N). These compounds are used, pre-plant incorporated, for
the control of grass and some small-seeded broadleaved weeds in crops
such as maize and small-grain cereals.
2.7.4 Interference with plant hormones
Compounds that control the growth and differentiation of plants are well
known and compounds that interfere with the function or that mimic the
effects of such plant growth regulators would be expected to be effective as
herbicides. Indole-acetic acid is a plant growth regulator whose concentration in the plant is carefully regulated by synthesis, conjugation and degradation. It is believed that the auxin or hormone herbicides act by imitating
the natural auxin, but with no means of controlling the level of the synthetic
auxin within the treated plant. Such compounds have been available to the
farmer for over 40 years, the first compounds being 2,4-D and MCPA, both
discovered during World War II. They brought a revolution in weed control, being originally developed to control charlock (Sinapis arvensis) in
cereals; they showed good broad-spectrum broadleaved weed control following post-emergence application, and they were truly selective (unlike
copper sulphate and sulphuric acid). A wide range of compounds with
modes of action that are thought to be the same as those of aryloxyalkanoic
acids have been introduced since 1945 (classification O). Notable amongst
these are the benzoic acids (dicamba) and the pyridinecarboxylic acids
(clopyralid). Although the symptoms of all these compounds are similar,
stem enlargement, callus growth, epinasty, leaf deformities and the formation of secondary roots, the absolute mode of action has yet to be confirmed. It is thought that the compounds act as auxins, binding to the auxin
receptor in the sensitive weed, and that they continue to exert their effects
because the plant is unable to reduce their concentration.
Recently, two new herbicides that are quinoline carboxylic acid derivatives have been introduced. Quinmerac and quinclorac are effective
through the formation of ethylene that is stimulated through the induction
of 1-aminocyclopropane-l-carboxylic acid (ACC) synthesis which leads
to massive accumulation of abscissic acid. This results in reductions in
stomatal aperture, water consumption, carbon dioxide uptake and plant
growth (Grossmann and Scheltrup, 1995; Scheltrup and Grossmann, 1996).
Interestingly, quinclorac is effective at controlling barnyardgrass
(Echinochloa crus-galli) in rice culture while quinmerac controls weeds
such as cleavers (Galium aparine) in a variety of different crops. Compounds that inhibit the action of IAA are also useful herbicides (classification P).
2.7.5 Cell division
Cell division is a fundamental prerequisite for plant growth. The
meristematic regions of the plant are the targets of two major groups of
herbicide that interfere with the organization of the microtubules that are
essential for the formation of the mitotic spindle along which the chromosomes separate during mitotic cell division. The microtubules are composed
of both a-tubulin and |3-tubulin that are brought together at the microtubule organization centre to produce the microtubules themselves. The
2,6-dinitroanilines (classification Kl) interfere with the formation of the
tubulins themselves whilst the carbamates (classification K2) prevent
the organization of the microtubule organization centre itself. The result
of this disruption is a failure of the cell division process and plant death.
Both of these groups of compounds are only effective on germinating weed
seeds and the majority are used pre-plant incorporated.
The 2-chloroacetanilides (classification F3) are also suggested to inhibit
cell division in susceptible weeds. These compounds have found a major
commercial market for the pre-emergence control of grass and some smallseeded broadleaved weeds in crops such as maize and soybean. It is likely
that 2-chloroacetanilides also alkylate the sulfhydryl groups of certain essential plant enzymes.
2.7.6 Cellulose biosynthesis
Several compounds exert their herbicidal effects through the inhibition of
cellulose biosynthesis (classification L), the major component of plant cell
walls.
2.7.7 Respiratory uncouplers
One of the earliest herbicides was dinitro-orthocresol (DNOC), a compound that is effective through the uncoupling of oxidative phosphorylation
(classification M). This mode of action is not considered to be a useful
target for modern herbicides since uncouplers have severe effects on nontarget organisms.
2.8 Insecticides
The control of insects has traditionally been associated with interference
with nerve function. This makes many insecticides relatively toxic to nontarget organisms and in particular beneficial insects and mammals, including humans.
The target sites within the nervous system of insects known at present are
very restricted. They consist of the sodium channel, the components of the
nicotinic cholinergic synapse and the GABA and octopamine receptors.
Benson (1991) lists potential target sites within the insect neuronal and
muscular system. These are shown in Table 2.2.
Nerve function is a transfer of electrical pulses through nerve cells and
across the gaps between nerve cells, the synapse, so that a message is
Table 2.2 Potential neuronal and muscular insecticide target sites
Target
In vivo activator
Neurotransmitter receptor ligand recognition sites
Cholinergic
Acetylcholine
Nicotinic
Muscarinic
Glutaminergic
Octopaminergic
GABAergic
Ion channels
Na + channel
Cl" channel
GABA regulated
Acetylcholine
Glutamate
Octopamine
y-Aminobutyric acid
Depolarization
y-Aminobutyric acid
Secondary messenger systems
Cyclic AMP
Octopamine, 5HT
Transmitter re-uptake and breakdown systems
Acetylcholine
Cholinesterase
Mitochondrial respiration
Oxidative
phosphorylation
Muscle
Contraction
Commercial insecticide class
Nicotine
Cartap
Nitromethylenes
None
None
Amitraz
None
Pyrethroids
DDT
Cyclodienes
Avermectins
Fipronil
None
Organophosphates
Carbamates
Rotenone
Dinitrophenols
Diafenthiuron
Depolarization
Ryania extract
transmitted from the brain to a muscle or other responsive tissue or from
sensory tissue to the brain. It is possible to interfere with nerve function in
a number of ways. Nerve impulses pass down the axons of nerve cells (long
processes of each nerve cell) as a result of changes in the permeability of the
axon membrane to sodium and potassium ions. When at rest, the electrical
potential within the membrane is negative in comparison to the outside.
The concentration of sodium inside the cell is low and the concentration of
potassium is high. Potassium and sodium ions enter the cell using two
mechanisms: sodium and potassium channels (or gates) allow a rapid passive movement when opened, whilst a slower, active movement occurs
through ion pumps. A nerve impulse passing down an axon is a wave of
changing polarity that is caused by the sodium gate opening so that sodium
passes in, and then the potassium gate opening so that potassium can move
out, thereby restoring the electrical polarity. The resting condition is restored by the operation of the ion pump taking up potassium at the expense
of ejected sodium.
At the end of an axon, where it meets another nerve cell or an effector
cell (a cell such as a muscle or a gland cell), there is a gap or junction that
is usually about 10-20 nm wide and this is known as a synapse. The passage
of the nerve impulse across this synapse is chemical rather than electrical.
When the nerve impulse reaches a synapse it causes the release of a chemical transmitter that is usually acetylcholine. Other transmitters have been
identified and these include L-glutamate and y-aminobutyric acid (GABA).
The released acetylcholine interacts with a receptor on the adjoining cell,
and the binding of the acetylcholine with this receptor causes this postsynaptic cell to pass on the impulse (if it is another axon) or to do work (if
it is a muscle or gland cell). If this chemical signal were not controlled then
the message would continue to be transmitted without the electrical stimulation from the axon. The control is achieved by the presence of
acetylcholinesterase, an enzyme that hydrolyses the acetylcholine and
thereby prevents the continual surge of signals and frees the receptor to
receive another signal. The site of action of all organophosphorus and
carbamate insecticides is this enzyme, acetylcholinesterase, which hydrolyses the synaptic transmitter, acetylcholine.
2.8.1 Organophosphorus insecticides (OPs)
The inhibition of acetylcholinesterase by OPs is through an attack on the
relatively positive phosphorus atom by the hydroxyl group of a serine
residue at the enzyme's site of action. Electron-withdrawing substitutions
within the OP tend to make the phosphorus more positive and therefore
more reactive. Unfortunately, this type of substitution also makes the compound less stable hydrolytically. The discovery and development of OP
insecticides has always been a balance between activity against the enzyme
of the insect, selectivity in comparison to mammalian systems and stability within the insect. The binding of OPs to acetylcholinesterase is often
irreversible.
The importance of this group of compounds is reflected by the fact that
chlorpyrifos has been the world's largest-selling insecticide (in tonnage
terms) for the last 10 years.
2.8.2 Carbamate insecticides
Carbamate insecticides interact with acetylcholinesterase in exactly the
same way as OPs, with the hydroxyl group in the serine at the enzyme's
active site attacking the carbamate residue in the insecticide. However, the
binding to the active site is reversible.
Both OPs and carbamates inhibit the active site of the target enzyme.
This results in the uncontrollable firing of neurons leading to loss of coordination and a massive release of hormones resulting in water loss and death.
2.8.3 Insecticides that interact with neurotransmitter ligand
recognition sites
OPs and carbamates interfere with the enzyme that hydrolyses the chemical
messenger, acetylcholine, thereby preventing a new electrical pulse being
detected by a new surge of acetylcholine. Clearly, if the ligand to which the
chemical messenger binds is filled with an inhibitor that mimics the normal
acetylcholine transmitter, then the binding of these inhibitors to the
receptor will lead to uncontrollable firing of neurons. Several compounds
exert their insecticidal effects in this fashion. There are two cholinergic
acetylcholine receptors, termed nicotinic and muscarinic. The names are
derived from inhibitors that were originally found to block the receptor:
nicotinic from nicotine, an alkaloid from tobacco, Nicotiana tabacum, and
muscarinic from muscarine, an alkaloid from the fly agaric, Amanita
muscaria.
Nicotine has been known to be insecticidal for over 300 years (Schmeltz,
1971) and was used as a foliar spray and as a vapour to control insects,
particularly in glasshouses and other covered crops. The toxin derived from
the marine worm Lumbriconereis heteropoda, nereistoxin, has been modified to produce an analogue, cartap, which is converted into nereistoxin in
the insect, leading to its death. An analogue of cartap, bensultap, was
developed later with reduced mammalian toxicity. All of these compounds
exert their toxicity by binding to the acetylcholine receptor and mimicking
the effect of acetylcholine.
A recently introduced insecticide from the nitromethylene group,
imidacloprid, has been shown to work in exactly the same way as nicotine
and cartap, but is of more interest commercially because it has much
reduced mammalian toxicity and because it has systemic properties. This
means that the compound can be applied to the soil around infested plants
and it will be taken up by the plants and control the insects that are infesting
it. This is a valuable property for the control of insects such as aphids that
feed on the phloem. It should be emphasized, however, that imidacloprid
controls both sucking and chewing insects and is effective through the
stomach and by contact action (Elbert et al, 1990).
Although their are some natural inhibitors of the muscarinic receptor, no
insectidal product has yet been commercialized with this mode of action.
In addition to acetylcholine there are three other neurotransmitters in
animal nervous systems: glutamate, octopamine and GABA. Surprisingly,
only inhibition of the octopaminergic receptors has led to the introduction
of a product. This is amitraz, a compound that is unusual in that it is a very
effective acaricide, with additional effects on cattle ticks, but it also shows
activity against lepidopteran insect eggs and against selected homopteran
insect species, particularly pear sucker, Psylla pyricola, and cotton whitefly,
Bemisia tabaci. Related formamidine insecticides have now been withdrawn from the market.
2.8.4 Insecticides that interfere with ion channels
DDT was introduced as an insecticide in the 1940s, and following its introduction a large number of chlorinated hydrocarbon insecticides were developed and marketed. These compounds were responsible for a revolution in
insect control methods, but have lost their importance because of their
unacceptably long persistence in the environment, their fat solubility, which
meant that they accumulated in fatty tissue of non-target organisms, and
because of the onset of insect resistance. DDT binds to the sodium channel
of the insect's nervous system, causing leakage and thereby preventing the
electrical pulse from moving through the axon. One of the most successful
insecticide groups ever introduced comprises the synthetic pyrethroids, and
these compounds have been shown to bind to the sodium channels in
insects, prolonging their opening and thereby causing knockdown and
death. (For an outstanding account of the history and development of
synthetic pyrethroids, see Elliott, 1996.) The synthetic pyrethroids have the
same mode of action as the natural pyrethrins. Recent developments in the
chemical structures of these synthetic analogues have produced a wide
range of related but novel chemical classes. All are characterized by good,
broad-spectrum insecticidal activity with some showing effects against
mites. Use rates are usually low and this increases the safety of the compounds to non-target organisms. In addition, the compounds are bound in
the soil, rendering them unavailable to soil insects, are generally nonvolatile, reducing their drift, and possess insect-repellent activity thereby
reducing their impact upon beneficial insects. More recent substitutions
have led to the synthesis of non-ester pyrethroids (e.g. etofenprox), compounds containing silicon (silafluofen) and compounds with good volatility
characteristics allowing their use to control soil-inhabiting insects
(tefluthrin).
The target for two major discoveries within microbial products for insect
and mite control (avermectins and milbemycins) is the yaminobutyric acid
(GABA) receptor in the peripheral nervous system. Both classes of compound stimulate the release of GABA from nerve endings and enhance the
binding of GABA to receptor sites on the post-synaptic membrane of
inhibitory motor neurons of nematodes and on the post-junction membrane
of muscle cells of insects and other arthropods. This enhanced GABA
binding results in an increased flow of chloride ions into the cell, with
consequent hyperpolarization and elimination of signal transduction resulting in an inhibition of neurotransmission.
More recently, the new insecticide fipronil has been shown to act as
a potent blocker of the GABA-regulated chloride channel. It is being used
to control both foliar and soil insects (Colliot et al., 1992) whilst the
avermectins and milbemycins can only be used against foliar pests.
2.8.5 Inhibition of oxidative phosphorylation
Many of the earliest insecticides exerted their effects through an inhibition
of oxidative phosphorylation; they were uncouplers. This meant that they
uncoupled the electron transport chain from the production of ATP (the
formation of chemical energy). 2,4-Dinitrophenols, such as dinitro-o-cresol,
were effective as winter washes and later were developed as herbicides
because compounds of this type were general toxicants, causing death to
most living organisms that they encountered. The natural insecticide
rotenone, found in the plant genera Derris, Lonchocarpus and Tephrosia,
interferes with respiration at site I, a fact that might explain its original use
by the people of Asia and South America as a fish poison.
Recently introduced insecticide/acaricides, pyrimidifen and fenazaquin,
also inhibit the mitochondrial electron transport chain by binding
with complex I at coenzyme site Q. A recently introduced insecticide/
acaricide, chlorfenapyr, has been shown to disrupt the electrochemical
gradient in mitochondria and thereby uncouple oxidative phosphorylation.
There is also evidence that the compound is a pro-insecticide, being converted into the active form by mixed-function oxidases within the insect or
mite.
More recently, a new class of insecticides derived from naphthoquinones
found in the South American alpine plant Calceolaria andina has entered
development. Compounds are being developed jointly through BTG (following the discovery at Rothamsted Experimental Station) and by Bayer.
The mode of action of these compounds is believed to be an inhibition of
respiration at site III. Consequently, some of the compounds show significant phytotoxicity to crops.
It is interesting that a new group of fungicides based on the natural
products from the fungus Strobilurus tenacellus also inhibit mitochondrial
respiration at the site of complex III (bcl-complex) of the respiratory chain
(section 2.9.8). Recently synthesized compounds from within this class are
showing interesting insecticidal effects.
2.8.6 Insect growth and regulation
Insects pass through a number of developmental stages from egg to adult.
As a general rule it is the larval stages that grow rapidly through feeding
whilst the adult stages are involved in reproduction. For this reason it is
usually the larval stages that are the crop-destructive segments of the insect's life cycle and it is these that are targeted by insecticides. This is clearly
not the case with vectors of human or animal endoparasites such as malaria,
sleeping sickness and Dengue fever, where it is the adult that transmits the
parasites, and it is these that are attacked in protection strategies. Other
insects, such as aphids, give birth to live young and, although these young
shed their cutinous skin as they expand and grow, they do not have the
classical life-cycle stages that are typical of many phytophagous pests, including lepidopterous, coleopterous, hemipterous and acarinal species.
There are a number of complex developmental processes that can be
interrupted within the growth cycle of most insect pests, and a number of
compounds has been developed to exploit these. The benzoylurea insecticides, sometimes known as insect growth regulators (IGRs), are compounds that interfere with chitin biosynthesis in the insect. Hence, as a larva
prepares to moult and replace its shed outer skin with a newly synthesized
replacement, there is insufficient chitin available to complete the construction of the outer layers and the larva dies either during or immediately after
moulting. The name 'insect growth regulator' is probably derived from
the often distorted shapes of dead and dying insects treated with these
compounds.
Some of these compounds are active against a wide range of insect and
mite species but the most sensitive are those that grow rapidly and moult
frequently, such as Lepidoptera. Because the insects have to take up the
compound, and inhibition is not effected until moulting, the compounds are
relatively slow acting in comparison to neural toxins. However, because
they have poor contact activity and have to be consumed to be effective,
they are relatively safe to non-target and beneficial insect species. Consequently, these compounds are widely recommended as components of integrated crop management systems. The insecticide/acaricide buprofezine
has the same mode of action but is unusual in its spectrum of activity, being
particularly effective against whitefly, Bemisia sp. and Trialeurodes sp. In
addition, the acaricide clofentezine is thought to have the same mode of
action as the benzoylureas as it shows cross-resistance to benzoylurearesistant mites. This has yet to be demonstrated directly.
Insect growth hormones have been studied as possible targets for new
insecticides but have generally been found to be ineffective. Some hormones have found small markets as insecticides but this has not proved to
be a useful source of commercially viable products. Methoprene is an insect
juvenile hormone mimic and interrupts the normal development of adults
when applied to larval stages. Such a compound would tend to prolong the
crop-destructive larval stages of many phytophagous insects, and hence
shows little promise as a crop insecticide. It is used to control fleas and
several stored-product pests as well as ants and mosquitoes.
Many insects communicate using the release and detection of volatile
compounds known under the general title of pheromones. These compounds are used to find a suitable food source, to alert other members of the
species of potential danger and to find a mate. Mating pheromones were
identified as very useful compounds to disrupt mating and thereby reduce
insect populations through the failure of females to lay fertile eggs. It is
usual for the fecund unfertilized female to release a sex pheromone that will
attract males who fertilize the female. Subsequently, the female lays her
eggs. These pheromones are volatile compounds that can be detected by the
adults at low concentrations over relatively long distances. They are also
species specific. Attempts to release pheromones such that mating is
disrupted through an amplification of the pheromone concentration, leading to confusion of the adult males, has been partially successful in that the
pink bollworm, Pectinophora gossypiella, pheromone has been commercialized and is used successfully to disrupt the mating of this important
cotton pest.
Sex pheromones have found a place in monitoring for the presence of
insects as a guide to when spraying of conventional chemicals might be
needed. However, the use of pheromones to attract insects and then trap
them is not an effective control strategy because males only are attracted
and the trapping has to be close to 100% effective to reduce mating in the
field and this, to date, has been unachievable. The use of 'lure-and-kill'
pheromone traps is moderately effective in some situations. Here the males
are attracted by a sex pheromone and are immediately treated with an
insecticide or an entomopathogen that will kill them. In practice, this is an
improved trapping device.
2.8.7 Compounds with uncertain modes of action
Tin-containing compounds have been used in agriculture for many years
as both fungicides (section 2.9.1) and as acaricides. Tricyclohexyltin
hydroxide and several related compounds are very active against adult
spider mites and are believed to act through an inhibition of oxidative
phosphorylation.
2.9 Fungicides
Fungicides are applied to crops for the control of plant pathogens that cause
disease. Traditional remedies involved the application of compounds that
act upon the surface of the crop, presenting a barrier to fungal invasion;
these are protectant fungicides. More recently, compounds have been
developed that exert their effect on established diseases - eradicant
fungicides. It is usual for the protectant fungicides to be compounds that are
general toxicants, and their activity and selectivity to the crop is determined
by the failure of the compound to enter the plant and disrupt its metabolism. Eradicant compounds, however, generally have a single biochemical
mode of action and are taken up by plants and often move systemically
within them.
2.9.1 Protectant fungicides
Compounds such as copper, tin and mercury salts have been used for many
years as protectant compounds. Indeed, Bordeaux mixture was discovered
over 100 years ago when it was applied to grapes to deter passers-by from
picking the crop and was subsequently shown to prevent the establishment
of grape downy mildew (Plasmopara viticold). Mercury salts were a major
contributor to the elimination of ergot (Claviceps purpurea) and bunt
(Tilletia caries) from cereal crops, but the toxicity of these compounds has
led to their subsequent withdrawal and replacement by newer, more specific compounds. It is interesting that as farmers move towards organically
grown cereals, the incidence of both diseases has increased. All metal-based
fungicides are effective through their general toxicant activity, interfering
with enzyme function and binding to sulfur within living cells. Sulfur itself
is a very effective fungicide, particularly against diseases such as powdery
mildew, although it is applied at very high rates and can cause some leaf
scorching, particularly under high-temperature conditions.
Other broad-spectrum protectant fungicides include alkylenebis(dithiocarbamates) such as maneb and mancozeb and the dimethyldithiocarbamates such as thiram. These compounds are still widely used to
control a wide range of fungal pathogens. Aromatic hydrocarbons such as
quintozene and Af-trihalomethylthio analogues such as captan and
folpet also find markets as broad-spectrum protectant sprays or seed
treatments.
2.9.2 Protein biosynthesis
The acylalanine fungicides metalaxyl, benalaxyl and furalaxyl are very effective against a wide range of downy mildew-causing plant pathogens. The
compounds are systemic and move freely around the treated crop, thereby
eradicating the disease. They are also relatively volatile and this increases
the opportunities for the compound to move within the treated crop canopy
and give overall protection to the crop. All compounds interfere with
protein biosynthesis by inhibiting the synthesis of ribosomal RNA through
interaction with the RNA polymerase-I-template complex. Unfortunately,
treated pathogens develop resistance to these compounds very rapidly and
as a consequence commercial formulations are sold in admixture with
broad-spectrum protectant fungicides.
Blasticidin S inhibits protein biosynthesis by preventing the incorporation of amino acids into protein, kasugamycin interferes with the binding of
aminoacyl-tRNA to the mRNA-30S ribosomal subunit complex and
mildiomycin has been shown to inhibit the incorporation of phenylalanine
into polypeptides.
2.9.3 Nucleic acid metabolism
The hydroxypyrimidine fungicides ethirimol and bupirimate inhibit
adenosine deaminase, an enzyme in the purine salvage pathway. This leads
to inhibition of germ tube elongation and appressorium formation. Activity
of these compounds is limited to powdery mildews and resistance to them
developed very soon after their commercialization.
2.9.4 Cell division
The benzimidazole fungicides such as benomyl and carbendazim and the
benzimidazole precursors such as thiophanate-methyl were the first compounds discovered that were truly systemic and eradicant in action. They
also had a wide spectrum of activity and could be used as seed treatments
or as foliar sprays. They are active through an inhibition of (3-tubulin
biosynthesis, leading to a failure of the formation of the mitotic spindle
thereby preventing cell division. The later compound diethofencarb has the
same mode of action but is only effective on pathogens that show resistance
to benzimidazole fungicides.
2.9.5 Sterol biosynthesis
Compounds that inhibit sterol biosynthesis in plant pathogenic fungi
have revolutionized agricultural disease control (and also in the pharmaceutical industry). A number of compounds are effective through this mode
of action, either at the site of 14-demethylation of the substrate 24methylene dihydrolanosterol through inhibition of the cytochrome P45014DM - the azoles, pyrimidines, triforine and pyrifenox - or through an
inhibition of A8,7-isomerization and A14-reduction - the morpholines and
fenpropidin. More compounds inhibit ergosterol biosynthesis through the
inhibition of 14-demethylation than any other mode of action, and compounds have found use as protectant and eradicant sprays and seed treatments in cereals, tree fruit, ornamental plants and vegetables. Some
compounds also inhibit gibberellin biosynthesis in plants and this can lead
to a temporary reduction in plant height, particularly when used as seed
treatments.
2.9.6 Triglyceride biosynthesis
The dicarboxamide fungicides are characterized by activity against
sclerotia-forming fungi such as Botrytis cinerea, Sderotinia and Monilia.
These compounds are believed to inhibit triglyceride biosynthesis in plant
pathogens. Resistance has developed to all members of this chemical class
and their use alone has been severely restricted.
2.9.7 Chitin biosynthesis
The organophosphorus esters, edifenfos and iprobenfos, used for the control of rice blast (Pyricularia oryzae) are effective through the inhibition of
chitin biosynthesis, both directly as a non-competive inhibitor and indirectly through an inhibition of phosphatidylcholine biosynthesis. Other
fungicidal organophosphorus esters may have similar modes of action.
Polyoxins also inhibit chitin biosynthesis by competitive binding to Nacetylglucosamine.
2.9.8 Respiration
Two new classes of fungicide have shown effects either directly or indirectly
on respiration. The strobilurins, a new group of fungicides based on the
natural products from the fungus Strobilurus tenacellus, inhibit
mitochondrial respiration at the site of complex III (bcl-complex) of the
respiratory chain. These compounds show relatively broad-spectrum fungicidal activity. Recently synthesized compounds from within this class are
showing interesting insecticidal effects.
The cyanopyrrole fungicides, also based on a natural product,
pyrrolnitrin, have a primary mode of action that is based on the inhibition
of transport-associated phosphorylation of glucose that may cause a cascade of metabolic effects which eventually lead to inhibition of fungal
growth and death.
2.9.9 Indirectly acting fungicides
A number of compounds are not in themselves fungicidal but when applied
to crops protect them from invasion. Those most widely used at present are
compounds that inhibit melanin biosynthesis in fungi such as Pyricularia
oryzae. Melanin is an important component of the cell wall of these pathogens, and it strengthens the appressorium allowing the pathogen to penetrate the cell wall of the host and colonize the crop. Tricyclazole and
phthalide are typical examples of compounds with this mode of action.
Probenazole, used to control rice diseases, is also without fungicidal
effects in vitro but elicits a rice immune response following application
rendering the crop tolerant of attack by rice fungal and bacterial pathogens.
The new compound from Novartis, acibenzolar, to be commercialized
under the trade name Bion, is a benzothiadiazole that acts as a plant
activator turning on the natural immune system. It is effective in a wide
range of crops and affords protection for several weeks following an initial
lag period against a wide range of pathogens. It is particularly effective in
combination with conventional fungicides.
Another relatively new class of fungicides is the anilinopyrimidines.
These compounds are effective against a range of fungal pathogens but are
particularly effective against Botrytis cinerea. These compounds have been
shown to reduce the secretion of a range of cell wall-degrading enzymes at
very low dose rates and this reduces significantly the lytic function of the
pathogen, preventing host penetration.
2.10 Plant growth regulators
Plant growth regulators have assumed a much lower level of importance
within the product portfolios of the major agrochemical companies. This is
because the huge markets predicted for these compounds in the 1970s and
1980s have never materialized. Products that are commercially successful
are limited primarily to growth retardants to prevent lodging in cereals, to
stop excessive vegetative growth in fruit tree crops and to inhibit the growth
of ornamental plants. For more information on the mode of action of crop
protection agents see Copping et al. (1989) and Copping and Hewitt (1998).
The chemistry of all compounds used in crop protection can be found in the
Pesticide Manual (Tomlin, 1997).
2.11 Biological screening: discovery and development of a new
agrochemical
It has been established that there is a very large market for crop protection
agents globally and that these markets are dominated by crops such as
wheat, barley, maize, soybeans, rice, cotton, grapes and top fruit, and also
by total weed control, in regions such as the USA, Western Europe and
Japan. The opportunities in South and Central America are beginning to be
realized and, as the economies of Eastern Europe and the former Soviet
Bloc improve, there is considerable potential in these areas as well. Countries such as India and China will also present significant opportunities for
the development of agrochemicals, but the restraints on trade that include
non-conformity with international patent law (although the introduction of
GATT legislation - General Agreement on Tariffs and Trade - and acceptance into the league of friendly trading nations is changing this) have
restricted penetration into these markets. For more details of the approaches to screening and early field testing, see Copping et al. (1990) and
Copping (1990).
So how do companies search for new agrochemicals? In simple terms,
each company has a list of key crop areas and a list of insects, pathogens and
weeds that infest those crops. The targeted crops are usually those that
command significant agrochemical input, and the target pests, diseases and
weeds are those for which there is an established market. For example,
insects attack cotton (bollworms, boll weevils, aphids, thrips, jassids and
whitefly), maize (cutworms, earworms, corn borers and corn rootworm),
rice (leafhoppers), top fruit (mites, aphids, codling moth) and vegetables
(caterpillars, aphids and whitefly), fungal pathogens infest small grain cereals (powdery mildew, rusts, Septoria and eyespot), rice (blast and blight),
grapes (Botrytis, powdery and downy mildew) and top fruit (powdery
mildew and scab). Weeds, of course, invade all fields laid down to
the monoculture of a single crop, as such single-crop culturing is unstable in
environmental terms and will invariably require inputs of energy to
maintain. This energy input can be in the form of mechanical energy
(from cultivation), manual energy (hand-weeding) or chemical energy
(herbicides).
2.11.1 Chemical synthesis
There are several ways of finding new compounds to test in an agrochemical
screen. These can be summarized as 'blue sky' chemistry, 'me-too' chemistry, natural product chemistry and biorational chemistry. Traditionally,
agrochemical companies used random synthesis to provide compounds for
evaluation within biological screens. These compounds could be made by
the chemists within the organization or brought in by the random selection
of compounds from sources outside the company (usually bought from
universities, specialist chemical companies or from chemical companies not
involved in agrochemical research). This empirical approach was eventually
considered to be expensive and insufficiently focused on the commercial
targets of the company to be a technique that a major player in discovery
research should adopt, and so the emphasis was changed from random
synthesis to targeted research or natural compound evaluation. However,
the pharmaceutical industry led the move towards combinatorial chemistry
and this approach to the synthesis of compounds is now under development
within many agrochemical organizations. The benefit that the pharmaceutical industry has is that it is targeting specific biochemical reactions that have
been identified as being effective and have been accepted by the regulatory
authorities as being of value in the treatment of a particular disease or
illness. The introduction of a new compound that is more effective against
a proven enzyme and/or less damaging to the patient will be completed
easily and will bring the company an immediate return for the investment.
This means that new compounds can be screened against in vitro enzyme
targets quickly and evidence of a useful biochemical effect can be generated
very rapidly. The problem is to provide the several hundred thousand
compounds a year that can be accommodated by these screens. This has
been solved through the application of combinatorial chemistry.
The successful application of combinatorial chemistry is based on the
screening technique of taking the screen to the compound(s) rather than
testing each compound separately in the screen. To be an effective and
selective inhibitor of a target enzyme, the chemical must bind specifically to
the target enzyme. It may bind to a cofactor in the biochemical reaction,
and such compounds are generally less desirable as pharmaceuticals because cofactors are rarely enzyme specific and the inactivation of a cofactor
will lead to unwanted side effects. This may not be so undesirable as a mode
of action of a new agrochemical.
Chemists make combinatorial collections, or libraries, in a rather simple
way. Standard chemical reactions are used to assemble selected sets of
building blocks into a huge variety of larger structures. To simplify the
principles, imagine that there are four molecules, Al, A2, Bl and B2. Al
and A2 are related chemically, as are Bl and B2, and these two different
classes of compound can react to form new molecules. Combinatorial
chemistry allows the rapid synthesis of all possible analogues, Al-Bl, AlB2, A2-B1 and A2-B2. The early work was undertaken with the construction of polypeptides and involved much larger numbers of compounds. If 30
compounds containing an amino group are selected and these are to be
reacted with 30 compounds containing a carboxylic acid residue, then there
are 30 X 30, or 900 possible combinations. The addition of a third set of 30
building blocks would lead to 30 X 30 X 30, or 27000, different possible
combinations.
Two different techniques can be used to make these combinations. Parallel synthesis was invented in the 1980s by Mario Geysen, now at GlaxoWellcome. Reactions are usually carried out in 96-well microtitre plates. If
the idea is to react eight amines with 12 carboxylic acids, the first amine
would be placed in the first row of wells, the second in the second, and so on.
The first carboxylic acid would then be added to the wells sequentially,
allowing the synthesis of 96 compounds from only 20 different starting
materials. It is common for the reagents to be attached to a solid support,
such as a polystyrene bead, as this allows any unreacted material to be
removed by washing, leaving the desired products attached to the bead.
Such a procedure requires techniques to attach the starting material to the
bead and then remove the product at the end of the reaction sequence, but
the advantages of purification outweigh these problems. Much of this work
can be done by robots and some companies have developed methods for
the preparation of over 1000 compounds a day. When making this number
of compounds it has to be rembered that doubling the number of products
requires nearly twice as much time. This restraint limits the number of
compounds that can be produced by parallel synthesis to tens of thousands
of compounds rather than many more.
The other technique for combinatorial chemistry was developed by
Arpad Furka at Advanced ChemTech and is known as split-and-mix. This
technique can be addressed simply in the following way. If chemists react
three related compounds, Al, A2 and A3, to polystyrene beads separately
and mix them together thoroughly and separate them into three vessels
once again, then each of the new vessels will contain an equal amount of
Al, A2 and A3. If the second reagents, Bl, B2 and B3, are added to these
vessels then each will contain Al-Bl, A2-B1, A3-B1 or A1-B2, A2-B2,
A3-B2 or A1-B3, A2-B3, A3-B3. A further mixing, separating and
reacting with Cl, C2 or C3 will produce the 27 products Al-Bl-Cl,
A1-B1-C2, A1-B1-C3, A2-B1-C1, A2-B1-C2, A2-B1-C3, A3-B1-C1,
A3-B1-C2, A3-B1-C3, A1-B2-C1, A1-B2-C2, A1-B2-C3, A2-B2-C1,
A2-B2-C2, A2-B2-C3, A3-B2-C1, A3-B2-C2, A3-B2-C3, A1-B3-C1,
A1-B3-C2, A1-B3-C3, A2-B3-C1, A2-B3-C2, A2-B3-C3, A3-B3-C1,
A3-B3-C2 and A3-B3-C3. These molecules can be tested in enzyme assays
for biological activity and the problem is then identifying which of the
products is the most active. This can cause problems, but these may be
overcome by putting an identifiable label on the bead that holds the molecule and checking this after the assay has been run, or by the direct
identification of the molecule using the advanced analytical techniques now
available to the research chemist. The application of robots to this technique has allowed the synthesis of millions of molecules in a few weeks. The
robots deliver the chemicals, perform the mixing and pardoning of the solid
support. (For more detailed descriptions of the approaches to combinatorial chemistry, read Thompson and Ellman, 1996; Czarnik and Ellman,
1996; Broach and Thorner, 1996; and the special report in Chemical and
Engineering News: Anon., 1996).
These techniques allow the synthesis of large numbers of related compounds and these can be screened with relative ease against specific biochemical targets. Whole-organism assays are less amenable to this type of
screening, but it should be remembered that if a family of related compounds is under evaluation then it is likely that the biochemical mode
of action of the compounds will be known and the most active against
the target enzyme can be reprepared in a quantity sufficient for a wholeorganism test and, in addition, data on a large number of compounds will
have been generated, allowing a broadly based patent claim to be filed with
supporting data.
Natural product chemistry has been shown to be a great source of biologically active compounds. It has been stated that 25% of all prescription drugs
in the USA include natural products as the active ingredient. The value
of plant products to the developed world's medicine may be well over
$6 billion each year. Microorganisms have provided a wealth of
pharmaceutically active compounds from penicillin to immunosuppressants
and cholesterol-lowering medicines, and a wide range of biologically active
compounds have been identified in algae and in animals. Traditionally, it
has been the Japanese companies who looked to natural products for new
agrochemicals, and a large number have been isolated as herbicides
(bilanafos), fungicides (polyoxins, kasugamycin and validamycin), plant
growth regulators (gibberellins) and insecticides (polynactins).
The opportunities that exist in the natural world are now being exploited
by many agrochemical companies, and several exciting compounds have
been developed directly as commercial products or as analogues of natural
products. The avermectins, milbemycins and, more recently, the spinosyns
have been developed as insecticides more or less as the microorganism that
produces them. The pyrethroid insecticides are a good example of how
well-thought-out synthesis can lead from a compound with insecticidal
activity but poor environmental stability to one that has outstanding biological effects with good stability. Recent advances in fungicide design have
led to the synthesis of the strobilurins from secondary metabolites of
the fungus Strobilurus tenacellus, and modification to the structure of
pyrrolnitrin, produced by rhizosphere bacteria, has led to the commercialization of two cyanopyrrole fungicides. There is plenty of evidence that
there are a number of useful compounds available in nature that can be
used directly as agrochemicals, which can be modified synthetically to produce new commercial products or that will provide a unique mode of action
for targeted synthetic efforts.
The problems are very different in the evaluation of plant, animal or
microorganism extracts for useful biological effects. In most cases the sample under test is a complex mixture of many different compounds at very
different concentrations. It is likely that the biologically active compound is
not new or that it is a general biocide. If it is the case that a biological effect
is achieved with a new compound that is specific against the biological
target, it has to be extracted and characterized and then a method of
production has to be established for the compound that is cost effective. It
may also be the case that the active compound is a protein. This used to be
addressed by eliminating the compound from the assay by boiling or
treating with organic solvents. Today, however, if a new protein is discovered that has good insecticidal or fungicidal activity, it may be that the
gene coding for the protein is a candidate for the transformation of crops.
This then involves much molecular biological activity and considerable
expense.
Biorational design is often defined as identifying a biological process
within the target organism and then designing a compound that will inhibit
this process. This may be the identification of key biochemical processes or
it may be behavioural responses. Insect pheromones and insect regulators
may be described as rational designed compounds, but it is a fact that within
the agrochemical industry no product yet exists that has been designed. It is
true that techniques can be used to confirm the importance of particular
processes to a target weed, pathogen or insect, and this will provide a new
in vitro biochemical assay to be included in the armoury of tests but it will
not lead to the discovery of a new compound. It just gives more places to
look.
2.11.2 Biological evaluation
Biological screening can be divided into three different levels, and each
compound will be tested at one of these levels depending upon what is
known about them. If the compound has no known relationship with any
previously tested compound that has shown activity in earlier tests, it will
enter at phase 1. Phase 1 testing is designed to reject as quickly as possible
all inactive compounds, so that little effort is spent on the test. Such tests are
high dose and high volume against selected 'indicator species'. Indicator
species are those that have been selected either because they represent a
significant market in their own right or because they represent a group of
pests, diseases or weeds that make up a potentially significant agrochemical
market. Typical phase 1 test organisms might be:
• for herbicides:
• barnyard grass (Echinochloa crus-galli - a non-temperate grass);
• wild oats (Avena fatua - a temperate grass);
• chickweed (Stellaria media - a temperate small seeded broad-leaf);
• mayweed (Tripleurospermum maritimum - a temperate large-seeded
broadleaf);
• purslane (Portulaca oleracea - a non-temperate small-seeded
broadleaf);
• morningglory (Ipomoea purpurea - a non-temperate large-seeded
broadleaf);
• nutsedge (Cyperus esculentus - a non-temperate sedge);
• for fungicides:
• vine downy mildew (Plasmopara viticold)\
• potato late blight (Phytophthora infestans)\
• wheat (or barley) powdery mildew (Erysiphe graminis)',
• grey mould (Botrytis cinered)\
• wheat blotch (Septoria triticfy
• rice blast (Pyricularia oryzae)\
• striped rust (Puccinia striiformis)\
• rice sheath blight (Rhizoctonia solani)\
• for insecticides:
• vetch aphid (Megoura viciae)\
• boll worm (Helicoverpa zed)\
• army worm (Spodoptera littoralis)\
• diamondback moth (Plutella xylostelld);
• mustard beetle (Phaedon cochleariae)\
• corn rootworm (Diabrotica undecimpunctata)',
• whitefly (Bemisia tabaci)\
• red spider mite (Tetranychus urticae).
The selection of the species used in a primary screening programme
will depend upon the facilities available to the organization, the local or
regional restrictions on the cultivation or breeding of pathogenic species
or phytophagous insects and mites, and on the interests of the company.
For example, if a company has a significant presence commercially in a
particular crop area with existing products, it is likely that this crop and
its pests and diseases will feature more strongly than they would if the
company were poorly represented in that crop. The reason for this is
that because the company already has a major presence in that crop, the
introduction of a new product will be easier than entering a completely new
crop where it has no representation. It is always good to reinforce the
commercial products available where a significant market share is already
held.
If a compound is not found to be inactive in the primary screening (or if
it comes from an area of chemistry that has been found to show consistent
biological activity) then it will enter a secondary screen. Here the questions
being asked are different to those of the primary screen. Instead of 'is this
compound inactive?' the question is 'how active is this compound against
the target organisms in the screen and how does it compare with standard
compounds?'. The standard compounds may be typical commercial products that have a proven level of effect or selected best compounds from
the chemical group(s) under evaluation, an 'internal standard', or both. The
argument for the commercial standard is that it confirms the validity of the
test and allows comparisons to be made from month to month between
compounds screened at different times of the year. The argument for the
best internal standard is that the commercial potential for the best compound tested to date is known, and it is hoped that further synthesis and
testing will improve biological activity, crop selectivity, environmental
impact or all of these.
Secondary screening will look at reduced rates in lower-volume sprays
and with greater replication. LC50 figures can be determined against some
organisms. If the biochemical mode of action is known, then the biological
effect can be compared to the activity against the target enzyme. All these
data will be compared to physico-chemical characteristics such as volatility,
partition coefficient, solubility (in water and organic solvents), photostability and soil half-life. Many of these parameters will not be determined
for each potentially active compound but they can be calculated within the
accuracy of an order of magnitude, thereby giving an idea of the probable
behaviour in the field. These tests enable compounds with preferred biological activities or cost advantages or reduced environmental risk to be
selected for further study.
The further study is whatever is required, bearing in mind that the
tertiary screening is designed to allow sound decisions to be made on the
selection of compounds for transition into field development programmes.
These development programmes are costly and the correct choices have to
be made. Hence tests consist of looking at formulations in comparison to
earlier compounds, looking at crop selectivity, timing of application,
systemicity, spectrum of effect, lowest dose that has an effect, soil persistence, effects on non-target crops and beneficial organisms, and so on. They
must be designed to ensure that only compounds with an advantage are
taken further although there are arguments for testing a compound that
falls below the expected level of activity if it is the first within a chemical
class.
It will be remembered from earlier that there is a potential for testing in
vitro against identified biochemical targets. This is a major policy of the
pharmaceutical industry where testing of experimental compounds on the
potential customer of the commercial drug is not a possibility. Traditionally
the agrochemical industry has argued that its key advantage is that compounds can be tested against the potential target. A problem exists, however, in increasing the throughput of compounds such that the large
numbers produced through improved synthesis strategies can all be tested.
One agrochemical company has addressed this problem by miniaturizing
the screens and has thereby increased the whole organism screening capacity to over 200000 compounds per year. Others have adopted the policy of
combining in vivo and in vitro screens. This policy demands that several
enzymes have been identified that would be good targets for new
agrochemicals. All compounds are then screened against these targets while
many are also tested against whole organisms. The data generated are
valuable as they will identify compounds that are biologically effective
against the target organism and those that are good inhibitors of a recognized biochemical target. Often good inhibitors are inactive against the
whole organism as the compound does not reach the biochemical target
within the organism. Correlation of these data allows the experimenter to
build up a picture of the shape of compounds that inhibit the enzyme and,
because the inhibitor must bind to the active site of the enzyme to be
effective, a picture of the size and shape of the binding site can be determined. In addition, the physico-chemical characteristics that will allow the
compound to enter the organism and move to its biochemical target will
also be identified. Putting these data together will allow rapid progress in
the design of inhibitors with characteristics that will permit their delivery to
the biochemical target.
One important point that is rarely mentioned in treatises on discovery
research is the formulations used in screening tests. These are clearly very
important as the primary screening is the only time a compound will be
tested if it is inactive. If it is presented to the target in a way that prevents
the biological effect occurring, then a potentially active compound is lost.
Most companies today use a simple acetone-wetter-based suspension of the
compound in the first screen and many continue to use this formulation
throughout the laboratory and glasshouse testing. Despite the knowledge of
the importance of formulation on the activity of commercial products, there
is often surprise when compounds are taken into the field as a 'standard'
formulation type and are either inactive or phytotoxic. Increasingly, companies are considering the appropriate formulation of compounds before they
enter field evaluation trials such that an appropriate response can be expected from these tests.
The synthesis, screening and field evaluation of compounds is a complex,
expensive, time-consuming but exciting activity. There are many conference volumes written on this subject and the reader is directed to Caseley
et al. (1983), Makepiece et al. (1983), Copping et al. (1989) and Hewitt et al.
(1994).
References
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Benson, J.A. (1991) Toxins and receptors: leads and target sites, in Neurotox '91: Molecular
Basis of Drug and Pesticide Action (ed. LA. Duce), Elsevier Applied Science, London, pp.
57-70.
Broach, LR. and Thorner, L (1996) High-throughput screening for drug discovery. Nature,
384, Supplement 6604, 14-16.
Bourlag, N.E. (1990) The challenge of feeding 8 billion people. Farm Chemicals International,
Summer Issue, 10-12.
Caseley, LC., Copping, L.G. and Makepiece, RJ. (eds) (1983) Influence of Environmental
Factors on Herbicide Performance and Crop and Weed Biology. Aspects of Applied Biology,
4, Association of Applied Biologists, Wellesbourne, UK.
Colliot, F., Kukorowski, K.A., Hawkins, D. and Roberts, D.A. (1992) Fipronil: a new soil and
foliar broad spectrum insecticide, in Brighton Crop Protection Conference - Pests and
Diseases, 1992,1, pp. 29-34.
Copping, L.G. (1990) Aspects of pesticide discovery, in Recent Developments in the Field of
Pesticides and their Application to Pest Control (eds K. Holly, L.G. Copping, and G.T.
Brooks), United Nations Industrial Development Organisation, Vienna, 1990, pp. 16-26.
Copping, L.G. and Hewitt, H.G. (1998) The Chemistry and Mode of Action of Crop Protection
Agents. Royal Society of Chemistry, Cambridge.
Copping, L.G., Hewitt, H.G. and Rowe, R.R. (1990) Evaluation of a new herbicide, in Weed
Control Handbook: Principles, 8th edn (eds RJ. Hance and K. Holly), British Crop Protection Council, Farnham, UK, pp. 261-300.
Copping, L.G., Merritt, C.R., Grayson, B.T. et al. (eds) (1989) Comparing Laboratory and
Field Pesticide Performance. Aspects of Applied Biology, 21, Association of Applied Biologists, Wellesbourne, UK.
Corbett, J.R., Wright, K. and Baillie, A.C. (1984) The Biochemical Mode of Action of Pesticides, Academic Press, London.
Czarnik, A.W. and Ellman, J.A. (eds) (1996) Combinatorial chemistry. Accounts of Chemical
Research, 29(3), March 1996, (Special Issue).
Dayan, F.E. and Duke, S.O. (1996) Porphyrin-generating herbicides. Pesticide Outlook, 7(5),
22-7.
Elbert, A., Overbeck, H., Iwaya, K. and Tsuboi, S. (1990) Imidacloprid, a novel systemic
nitromethylene analogue insecticide for crop protection, in Brighton Crop Protection Conference - Pests and Diseases, 1990,1, pp. 21-8.
Elliott, M. (1996) Synthetic insecticides related to natural pyrethrins, in Crop
Protection Agents from Nature: Natural Products and Analogues (ed. L.G. Copping), Royal
Society of Chemistry, London, pp. 254-300.
Grossmann, K. and Scheltrup, F. (1995) On the mode of action of the new, selective herbicide,
quinmerac. Brighton Crop Protection Conference - Weeds, pp. 393-8.
Hewitt, H.G., Caseley, J.C., Copping, L.G. etal. (eds) (1994) Comparing Laboratory and Field
Pesticide Performance IL British Crop Protection Council Monograph, 59, BCPC, Farnham,
UK.
LeBaron, H.M. (1990) Weed science in the 1990s: will it be forward or in reverse? Weed
Technology, 4, 671-89.
Luscombe, B.M. and Pallett, K.E. (1996) Isoxaflutole for weed control in maize. Pesticide
Outlook, 7(6), 29-32.
Makepiece, RJ., Caseley, J.C. and Copping, L.G. (eds) (1983) Influence of Environmental
Factors on Herbicide Performance and Crop and Weed Biology. Aspects of Applied Biology,
4, Association of Applied Biologists, Wellesbourne, UK.
National Research Council Board on Agriculture (1989) Alternative Agriculture, Committee
on the Role of Alternative Farming Methods in Modern Production Agriculture, Washington, DC, National Academic Press.
Pimentel, D. (1991) Diversification of biological control strategies on agriculture. Crop Protection, 10, 243-53.
Pimentel, D. (ed.) (1997) Techniques for Reducing Pesticide Use: Economic and Environmental Benefits, John Wiley & Sons, Chichester, UK.
Scheltrup, F. and Grossmann, K. (1996) Abscissic acid is a causative factor in the mode of
action of the auxinic herbicide, quinmerac, in cleaver (Galium aparine L.). Journal of Plant
Physiolology, 147, 118-26.
Schmeltz, I. (1971) Naturally Occurring Insecticides (eds M. Jacobson and D.G. Crosby),
Marcel Dekker, New York.
Smith, E.G., Knutson, R.D., Taylor, C.R. and Penson, J.B. (1990) Impacts of Chemical Use
Reduction on Crop Yields and Costs. College Station, Texas, Agricultural and Food Policy
Center, Department of Agricultural Economics, Texas A & M University System.
Sweet, R.D., Dewey, I.E., Lisk, DJ. et al. (1990) Pesticides and Safety of Fruits and Vegetables. Comments from CAST (1990-1991) Ames, Iowa, Council for Agricultural Science and
Technology.
Thompson, L. A. and Ellman, J.A. (1996) Synthesis and applications of small molecule libraries.
Chemical Reviews, 96(1), 555-600.
Tomlin, C. (ed.) (1997) The Pesticide Manual. British Crop Protection Council, Farnham, UK.
Urban, F. (1989) Agricultural resources availability, in World Agricultural Situation and
Outlook Report, Washington, DC, US Department of Agriculture, Report WAS-55, pp. 816.
Urban, F. and Dommen, AJ. (1989) The world food situation in perspective, in World
Agriculture Situation and Outlook Report, Washington, DC, National Agrichemicals
Association.
World Health Organisation (1990) Public Health Impact of Pesticides Used in Agriculture,
Geneva.
Woodburn, A. (1997) Agrochemicals - Executive Review, Allan Woodburn Associates, Edinburgh, UK.
3 Formulation of agrochemicals
D. A. KNOWLES
3.1 Introduction
Farmers and growers in all the main agricultural areas of the world rely very
substantially upon crop protection chemicals to help them meet the everincreasing demand for food and other materials such as natural fibres. The
consumer continues to seek higher quality and greater variety of produce.
Simple dusting powders and spray oil formulations have been used for
many years to protect growing crops from weeds, pests and diseases.
However, since the 1940s the chemical industry has endeavoured to satisfy
the demands of farmers and growers for increased crop yield and quality by
the continuous development and introduction of crop protection chemicals
into the international market place. Today, there is an effective herbicide,
insecticide or fungicide to combat almost every significant problem faced by
the modern farmer and grower.
This development has led to a need for a wide range of product formulations, additives and process technology to accommodate the variety of
physical and chemical properties of the pesticide active ingredients. For
example, water-soluble active ingredients may be prepared as aqueous
solutions or powder formulations, whereas oily liquid active ingredients are
usually formulated as hydrocarbon solvent-based emulsifiable concentrates. Active ingredients which have very low solubility in either water or
hydrocarbon oils may be formulated as suspensions, powders or waterdispersible granules [I].
In the 1980s and 1990s, pressure from government authorities and the
consumer highlighted a need for products and formulations which are safer
and more convenient to use, more effective at much lower application rates,
less toxic to non-target species and more environmentally friendly.
By far the most important method of application of agrochemicals is by
spraying, usually with water but occasionally with oils as the principal
carrier. Formulations are also made for direct application to the soil or for
treating seeds before planting, and for protecting stored crops from various
pests and diseases (fungi, insects or rodents), which in some countries could
destroy as much as 30-40% of the harvest.
Pesticidal active ingredients encompass a broad range of chemicals, each
with its unique chemical and physical properties and mode of action. The
main categories of pesticides are herbicides, insecticides, fungicides, plant
growth regulators, molluscicides and rodenticides. A great deal of research
work has been carried out into understanding the modes of action and
physiological effects of active ingredients and the influence of formulation
type on the biological performance of the pesticide [2].
The successful use of any active ingredient depends on its correct formulation into a preparation which can be applied for crop protection safely and
with low risk to those applying the material, to non-target species and to the
environment in general. The earliest pesticide formulations were based on
simple dusts, powders, granules, aqueous solutions and mineral oil-in-water
emulsions. In recent times, particularly during the period from 1970 onwards, there has been a rapid development of more sophisticated formulations based on the availability of more powerful surfactants and other
additives, and a much better understanding of the principles of colloid and
surface chemistry to improve formulation stability and biological activity.
Processing technology has also developed over this period to give much
smaller particle size for better stability and activity for water- and solventinsoluble active ingredients.
The main objectives of formulation can be summarized as follows: to
provide the user with a convenient, safe product which will not deteriorate
over a period of time, and to obtain the maximum activity inherent in the
active ingredient.
The formulation chemist needs to take into account a number of interacting factors in the choice of the specific formulation type for each active
ingredient. The main factors which need to be taken into account are
•
•
•
•
•
•
physico-chemical properties;
biological activity and mode of action;
method of application;
safety in use;
formulation costs;
market preference.
Once these parameters have been determined, proper selection can be
made of the final formulation type and the use of inert ingredients, including surfactants and other additives, to produce a stable formulation with at
least a 2-year shelf life during storage under varying climatic conditions.
The most common formulations are still soluble concentrates for watersoluble chemicals, emulsifiable concentrates for oil-soluble chemicals, and
wettable powders and suspension concentrates for insoluble solids. Granules and seed treatments for direct application have also been produced for
many years. In recent years the number of formulation types has increased
enormously to meet the needs of operator and environmental safety or to
improve the activity and persistence of the active ingredient. An international coding system was therefore devised by GIFAP in 1984 (in 1996
GIFAP was renamed GCPF - Global Crop Protection Federation, based in
Table 3.1 Major types of pesticide formulations
Formulation type
Granules
Solution concentrates
Emulsifiable concentrates
Wettable powders
Suspension concentrates
O/W emulsions
Suspoemulsions
Microemulsions
Water-dispersible granules
Microcapsules
Seed treatments
Code
GR
SL
EC
WP
SC
EW
SE
ME
WG
CS
DS, WS, LS, FS
Brussels, Belgium). The major types of formulations and international
codes are shown in Table 3.1.
The most common formulations are those which are made for dilution
into water in a spray tank. In these cases the choice of formulation additives
is very important to ensure that the product mixes and dilutes easily. Sometimes products may be mixed together in the spray tank or may be mixed
with spray adjuvants to enhance biological activity. Products such as granules or seed treatments are usually applied undiluted to the soil or to the
seed respectively. A few products are formulated to be diluted and sprayed
in oils, and there are many minor formulations such as baits, pellets, smokes
and aerosols for special purposes.
3.2 Conventional formulations
3.2.7 Granules (GR)
Granular formulations are used for direct broadcasting to the field, often as
pre-emergence herbicides or as soil insecticides. The active ingredient concentration is usually between 1 and 40% and the granule mesh size is
generally between 250 and 1000 ^m. The granules should be non-caking,
non-dusty, free flowing and should disintegrate in the soil to release the
active ingredient.
Granules are usually made either by coating a fine powder onto a
substrate, e.g. sand, using a sticker such as PVP solution, or by solvent
impregnation onto an absorbent carrier. Resins or polymers may be
sprayed onto the granules to control release rates. Absorbent carriers may
be mineral or vegetable, as shown in Table 3.2.
The absorptive capacity of the carrier is an important parameter and is a
function of the crystalline structure and the available surface area of the
carrier particles. Some typical absorptive capacities are shown in Table 3.3.
Table 3.2 Classification of carriers
Class
Examples
Silicate clays
Carbonates
Synthetics
Botanicals
Others
Attapulgite, montmorillonite, kaolin, talc, mica, vermiculite
Calcite, dolomite
Calcium silicate, precipitated silica, fumed silica
Corn cob grits, ground grains, rice hulls, soybean, walnut shell, coconut shell
Pumice
Table 3.3 Absorptive capacities of granule carriers
Carrier
Oil absorption (g/lOOg)
Silica
Attapulgite
Montmorillonite
Kaolin
Talc
Calcium carbonate
Corn cob grits
Walnut shell
200
100
23-70
20-54
20-40
5-18
60-80
20-40
3.2.2 Solution concentrates (SL)
The simplest of all formulations to make is the solution concentrate, an
aqueous solution of the active ingredient which merely requires dilution in
the spray tank. The number of pesticides which can be formulated in this
way is limited by solubility and hydrolytic stability. Some solution concentrate formulations contain a surfactant, usually a non-ionic ethylene oxide
condensate, to assist wetting onto the leaf surface. Solution concentrate
formulations are usually very stable and therefore present few storage
problems. Some problems do occur occasionally, such as precipitation during dilution and corrosion of metal containers or spray applicators. A
typical solution concentrate formulation (per cent by weight) is shown
below:
Active ingredient
Wetting agent
Antifreeze
Water
1
Water-miscible solvent J
TT T
A
«1
1
1
*
\
20-50%
3-10%
5-10%
t o i n 0 o/
IO
IUU
/O
Nonylphenol or tallow amine ethoxylates are often used as tank mix wetters
for solution concentrate formulations. Alternatively, the wetting agent may
be built into the formulation to ensure that the correct rate of wetting agent
is applied to optimize biological activity. This is often the case, for example,
with paraquat and glyphosate formulations. A considerable amount of
work is being carried out on new surfactant wetting agents for glyphosate
formulations [3]. In some cases preservatives may be nessessary to prevent
mould growth or bacterial spoilage during long-term storage.
3.2.3 Emulsifiable concentrates (EC)
Emulsifiable concentrate formulations have been very popular for many
years and represent the largest volume of all pesticide formulations in terms
of consumption. Emulsifiable concentrates are made from oily active ingredients or from low-melting, waxy, solid active ingredients which are soluble
in non-polar hydrocarbon solvents, such as xylene, C9-C10 solvents, solvent
naphtha, odourless kerosene or other proprietory hydrocarbon solvents.
Surfactant emulsifiers are added to these formulations to ensure spontaneous emulsification with good emulsion stability properties in the spray tank.
Careful selection of a 'balanced pair' emulsifier blend is frequently necessary to ensure that emulsion dilution stability is maintained over widely
differing climatic conditions and degrees of water hardness. Emulsion
droplets of 0.1-5 ^m are produced when the formulation is mixed with
water.
The formulation of emulsifiable concentrates has been greatly facilitated
by the commercial development over the last 20 years of non-ionic emulsifying agents in which the hydrophilic portion of the molecule consists of a
polyethylene oxide chain. The non-ionic surfactant which is commonly used
is a nonylphenol hydrophobic chain condensed with 12 or more moles of
ethylene oxide. The other component of the balanced pair is generally an
anionic surfactant such as the oil-soluble calcium salt of dodecylbenzene
sulphonic acid. Recently, however, nonylphenol ethoxylates have been suspected of having endocrine modulating properties from metabolites in effluents or by leaching into ground drinking water. Because of this potential
toxic effect, alternative ethylene oxide condensates based on aliphatic
hydrophobes are being investigated.
The total concentration of the emulsifier blend is usually 5-10% of the
formulation. There are no definite rules to determine the ratio of anionic to
non-ionic surfactant in the mixed emulsifiers, but guidance can be obtained
from the HLB (hydrophile-lipophile balance) system: the higher the HLB,
the more hydrophilic (water-soluble) is the surfactant. The HLB range 8-18
will normally provide good oil-in-water emulsions. The optimum ratio of
anionic to non-ionic surfactants is determined experimentally to give spontaneous emulsification in water, and to give a stable emulsion with very
little creaming and no oil droplet coalescence.
Emulsifiable concentrates are limited in the number of active ingredients
for which they are suitable. Many pesticides are not soluble enough to be
supplied economically in this form. However, it may be possible to boost
the solubility of the active ingredient by the addition of a more polar solvent
without increasing the risk of crystallization in the spray tank. A typical
emulsifiable concentrate formulation (per cent by weight) is shown
below:
Active ingredient
Emulsifier blend
20-70%
5-10%
fP1™' 1
Cosolvent J
to 100%
The presence of solvents and emulsifiers in emulsion concentrate formulations can sometimes give enhanced biological efficacy compared with
other formulations. Many insecticides, e.g. organophosphorous compounds
and pyrethroids, are oil-soluble active ingredients and are readily formulated as emulsifiable concentrates, and a few active ingredients need to be
formulated with solvents for optimum biological activity.
Health, safety and environmental pressures on the use of petroleumbased solvents generally are influencing a move away from these solventbased formulations. However, it seems unlikely that solvents can be
replaced entirely for some products, and safer high-flash-point solvents are
being introduced along with new ideas for packaging to reduce physical
contact between the product and the operator.
3.2.4 Wettable powders (WP)
Wettable powder formulations of pesticides have been known for many
years and are usually made from solid active ingredients with high melting
points which are suitable for dry grinding through a mechanical grinder,
such as a hammer- or pin-type mill, or by air milling with a fluid energy
micronizer. Air milling gives much finer particles than mechanical milling
and can also be more suitable for active ingredients with lower melting
points. However, care must be taken to prevent, suppress or contain dust
explosions which may occur if a source of ignition, such as static energy, is
present in either type of mill.
Wettable powders usually contain dry surfactants as powder wetting and
dispersing agents and inert carriers or fillers. They frequently contain more
than 50% active ingredient and the upper limit is usually determined by the
amount of inert material, such as silica, required to prevent the active
ingredient particles fusing together during processing in the dry grinding
mills. An inert filler such as kaolin or talc is also needed to prevent the
formulated product from caking or aggregating during storage.
Wettable powders have a high proportion of particles less than 5 ^m and
all the particles should pass through a 44 ^m screen. Ideally, the amount of
surfactants should be sufficient to allow the spray droplets to wet and
spread over the target surface, but the particles should not be easily washed
off by rain. Powder formulations contain a wetting agent to lower the
interf acial tension between the solid particles and water and ensure that the
powder wets and mixes with water in the spray tank easily. A dispersing
agent is also necessary to prevent the particles in the spray tank from
flocculating or aggregating together, and to ensure that the particles remain
suspended during the spraying operation. The types of wetting agents commonly used are
•
•
•
•
•
sodium dodecylbenzene sulphonate;
sodium lauryl sulphate;
sodium dioctyl sulphosuccinate;
aliphatic alcohol ethoxylates;
nonylphenol ethoxylates.
The comments on nonylphenol ethoxylates mentioned previously for
emulsifiable concentrates also apply to wettable powders.
The following dispersing agents are often used in wettable powder
formulations:
• sodium lignosulphonates;
• sodium naphthalene sulphonate formaldehyde condensates.
A typical wettable powder formulation (per cent by weight) is shown below:
Active ingredient
Wetting agent
Dispersing agent
Inert filler/carrier
25-80%
1-3%
2-5%
to 100%
Wettable powders can also be made from liquid pesticides by using absorbent fillers such as diatomaceous earth or high-surface-area synthetic silica.
However, in this case the active ingredient concentration is usually limited
to 40%. Many pesticides, especially herbicides and fungicides are formulated as wettable powders. However, due to their low-technology image
arising from their dustiness, which creates toxic hazards on handling, they
are now being superseded by suspension concentrates or water-dispersible
granules.
3.2.5 Suspension concentrates (SC)
Suspension concentrate technology has been increasingly applied to the
formulation of many solid crystalline pesticides since the early 1970s. Pesticide particles may be suspended in an oil phase, but it is much more usual
for suspension concentrates to be dispersions in water. Considerable attention has been given in recent years to the production of aqueous suspension
concentrates by wet grinding processes such as bead milling. The use of
surfactants as wetting and dispersing agents has also led to a great deal of
research on the colloidal and surface chemistry aspects of dispersion and
stabilization of solid-liquid dispersions [4].
Water-based suspension concentrate formulations offer many advantages, such as high concentration of insoluble active ingredients, ease of
handling and application, safety to the operator and environment, and
relatively low cost. They also enable water-soluble adjuvants to be built into
the formulation to give enhanced biological activity. Farmers generally
prefer suspension concentrates to wettable powders because they are nondusty and easy to measure and pour into the spray tank. However, there are
some disadvantages, notably the need to produce formulations which do
not separate badly on storage, and also to protect the product from freezing,
which may cause aggregation of the particles.
In most cases, suspension concentrates are made by dispersing the active
ingredient powder in an aqueous solution of a wetting and/or dispersing
agent using a high-shear mixer to give a concentrated premix, followed by
a wet grinding process in a bead mill to give a particle size distribution in the
range 0.1-5 (im. The wetting/dispersing agent aids the wetting of the powder
into water and the breaking of aggregates, agglomerates and single crystals
into smaller particles. In addition, the surfactant which becomes adsorbed
onto the freshly formed particle surface during the grinding process should
prevent reaggregation of the small particles and should ensure colloidal
stability of the dispersion. Typical wetting/dispersing agents used in suspension concentrate formulations are:
•
•
•
•
•
sodium lignosulphonates;
sodium naphthalene sulphonate formaldehyde condensates;
aliphatic alcohol ethoxylates;
tristyrylphenol ethoxylates and esters;
ethylene oxide-propylene oxide block copolymers.
Also available are polymeric surfactants which adsorb strongly on particle
surfaces and may give considerably improved stabilization of suspension
concentrates for long-term storage [5]. A typical suspension concentrate
formulation (per cent by weight) is shown below:
Active ingredient
Wetting/dispersing agent
Propylene glycol antifreeze
Anti-settling agent
Water
20-50%
2-5%
5-10%
0.2%-2%
to 100%
The anti-settling agent is added to increase viscosity and build up a threedimensional network structure to prevent separation of particles during
long-term storage. The anti-settling agent is usually a swelling clay such as
bentonite (sodium montmorillonite) and may be mixed with water-soluble
polymers to give synergistic rheological effects. The water-soluble polymers
are often cellulose derivatives, natural gums or other types of polysaccharides, such as xanthan gum, and they are generally susceptible to
microbial attack. For this reason, preservatives are usually added to suspension concentrate formulations to prevent degradation of the anti-settling
agent so that long-term stability of the product is not impaired. A great deal
of research has been carried out using rheological techniques to measure
the forces acting between particles and polymers to enable storage stability
to be predicted. However, it is still necessary to carry out long-term storage
tests over a range of temperatures to ensure that the particles do not
aggregate or separate irreversibly under normal storage conditions in the
sales pack [6].
Many crystalline solid active ingredients are now available as suspension
concentrates. However, there is increasing pressure, especially in Western
Europe and the USA, to enforce stringent pack rinsing and disposal regulations, which may have a serious impact on the future of suspension concentrates and their packaging.
3.2.6 Seed treatments (DS, WS, LS, FS)
Although most pesticide formulations are applied by spraying onto crops or
weeds, significant quantities of fungicide and insecticide products are applied directly onto seeds prior to planting into the soil. It is estimated that
the market value of seed treatment formulations currently represents about
3-3.5% of the total market for agrochemical products, and approximately
50% of seed treatment formulations are applied to seeds in Europe.
Fungicides dominate the seed treatment market with about a 70% share.
The most important seed treatment applications are on small-grain cereal
seeds, which comprise over 50% of the world market and over 60% of the
European market.
Products for seed treatment fall into four categories:
• powder for dry seed treatment (DS);
• water-slurry able powder for seed treatment (WS);
• non-aqueous solution for seed treatment (LS);
• flowable suspension for seed treatment (FS).
The choice of formulation type is usually governed by the physico-chemical
properties of the active ingredients, the type of application equipment
available or market preference. Powder formulations (DS) are dusty and
have poor retention on seed. Water-slurryable formulations (WS) are still
used to a certain extent, particularly in France. Solvent-based formulations
(LS) are gradually being phased out because of operator handling safety
problems. Water-based flowable suspensions (FS) are more environmentally friendly than powders or solutions, have good retention on seed and
are now becoming more popular.
The technology for producing flowable suspensions is similar to that for
producing suspension concentrates, and the surfactants used are also
similar to those used for suspension concentrate formulations. Extra thickeners and anti-settling agents are usually added to prevent separation of the
dispersed phase because these products are generally applied directly to the
seed without dilution. Seed treatment formulations can be applied to seeds
in simple rotating mixing bowls, auger mixers such as the Plantector, or
sprayed into rotating bowls such as the Rotostat or the Centaur [7]. Highvalue seeds such as vegetable and horticultural seeds are sometimes coated
with polymers to prevent loss of the seed treatment chemical. They may
also be pelleted with clays and polymers to produce a spherical seed pellet
which is easy to handle and plant.
Because seed treatments are applied directly to the seed, there is very
little wastage of active ingredient. Seed treatments are, therefore, seen as a
very efficient means of targeting pesticides to crops and are regarded as an
environmentally safe way of applying pesticides. They may become more
important in the future with the introduction of transgenic crops and an
increasing need to protect such high-value seeds with fungicides and
insecticides.
3.3 New-generation formulations
3.3.1 General trends
Over the last few years there has been increasing pressure from government
and regulatory authorities to develop formulations which have less impact
on the environment generally [8]. The main issues which are being
addressed are
•
•
•
•
•
safety in manufacture and use;
convenience for the user;
ease of pack disposal or reuse;
reduction of the amount of pesticide applied;
reduction of waste and effluent of all kinds.
The current trends in the development of pesticide formulations are
• to use safer solvents or to eliminate solvents wherever possible and use
aqueous emulsions;
• to replace wettable powders by aqueous suspension concentrates or
water-dispersible granules;
• to develop multiple active ingredient formulations;
• to build in bioenhancing surfactant wetters;
• to control release rate and targeting of pesticides by encapsulation
techniques and seed treatment;
• to develop novel formulations such as tablets or gels;
• to develop more effective spray adjuvants to enhance biological activity
and reduce pesticide dosage.
These complex requirements are being met by technical advances in
surfactants and other formulation additives, particularly blends of
surfactants, more powerful dispersing agents and a better understanding of
the principles of colloid and surface chemistry and rheology [9]. The ideal
product would seem to be one which is free from volatile solvents, gives
no operator exposure hazard, has the maximum biological activity at the
lowest dose level, and produces the minimum of pack disposal problems.
Water-dispersible granules or wettable powders in water-soluble sachets,
which can be added directly to a spray tank, go a long way towards meeting
these requirements, and development work is being carried out on these
options by all the major agrochemical companies. However, it will never be
possible to formulate all active ingredients this way, and so other options
are being evaluated extensively, along with ideas for packaging and closedtransfer spray application systems. Aqueous-based formulations will be a
necessary and safe alternative to water-dispersible granule formulations,
and these options include (in addition to suspension concentrates which
have been already discussed):
•
•
•
•
suspoemulsions;
OAV emulsions or concentrated emulsions;
Microemulsions;
microencapsulation.
Other possibilities involving specialized packaging are gels and effervescent tablets. The new-generation formulations are discussed in more
detail in separate chapters in this book. Only brief summaries are given
here [1O].
5.3.2 Oil-in-water emulsions (EW)
Oil-in-water emulsions are now receiving considerable attention because of
the need to reduce or eliminate volatile organic solvents for safer handling.
Because they are water based, oil-in-water emulsions can have significant
advantages over emulsifiable concentrates in terms of cost and safety
in manufacture, transportation and use. However, they require careful
selection of surfactant emulsifiers to prevent flocculation, creaming and
coalescence of the oil droplets, as shown diagrammatically in Figure 3.1.
Non-ionic surfactants and polymeric surfactants are now being used to
produce stable emulsions. In the case of non-ionic surfactants it is sometimes useful to combine a low and a high HLB surfactant to give an average
HLB of 11-16 for optimum emulsion stability [6].
Droplet size is also a good indicator of stability and should be below 2 ^irn.
The emulsions are usually thickened with polysaccharides such as xanthan
creafninq
phase
inversion
sedimentation
coalescence
Ostwald
ripening
Figure 3.1 OAV emulsion stability problems. (From Morpeth, F.F., Preservation of Surfactant
Formulations, Blackie Academic and Professional, London, 1995.)
gum to prevent separation of the oil droplets. Sometimes polymers such as
polyvinyl alcohol are used as both emulsifier and thickener/stabilizer.
3.3.3 Suspoemulsions (SE)
Mixed formulations are becoming more popular because of their convenience, to ensure that the farmer applies the correct amount of each component pesticide and to overcome problems of tank mix incompatibility. If one
active ingredient is a solid and the other is a liquid, it is necessary to produce
a suspoemulsion formulation which consists of three phases:
• liquid oil droplets;
• solid dispersed particles;
• continuous phase, usually water.
Suspoemulsions can, therefore, be considered to be mixtures of suspension concentrates and oil-in-water emulsions with added surfactants to
prevent flocculation and thickeners to prevent separation of the dispersed
phases. Surfactants used as dispersing agents for the solid phase are similar
to those already mentioned for suspension concentrates. Emulsifiers for the
oily liquid phase are similar to those used for oil-in-water emulsions. As
these formulations are aqueous based and generally thickened with
polysaccharides, it is necessary to add a preservative to prevent degradation
of the thickener. Some problems of heteroflocculation between the solid
particles and oil droplets can occur, and extensive storage testing of these
formulations is necessary [U].
3.3.4 Microemulsions (ME)
Microemulsions are thermodynamically stable, transparent emulsions and
are stable over a wide temperature range. They have a very fine droplet size
of less than 0.1 pirn and consist of three components:
• oily liquid or solid dissolved in organic solvent;
• water;
• surfactant/cosurfactant.
These components form a single phase containing relatively large 'swollen
micelles' in which the non-aqueous phase of the active ingredient and
solvent are dissolved or solubilized.
In the preparation of microemulsions, two different types of surfactants
are needed: one water soluble and one oil soluble. The water-soluble
surfactant is usually anionic or non-ionic with a very high HLB value, and
the hydrophobic part of the molecule should match the oil. The
cosurfactant should be oil soluble and should have a very low HLB value,
such as hexanol. The total concentration of surfactants for a microemulsion
can be as high as 10-30%, compared with about 5% for an O/W emulsion
[6]. Microemulsions have relatively low active ingredient concentrations,
but may have enhanced biological activity.
3.3.5 Controlled-release formulations
The application of controlled release technology has been slow to reach
commercialization despite interesting research and development work by
the major agrochemical companies over the last 10-20 years. Controlledrelease formulations can have a number of advantages over conventional
formulations: they
•
•
•
•
•
•
•
•
•
have longer residual biological activity;
may reduce mammalian toxicity;
control or reduce evaporation of pesticide;
may reduce phytotoxicity to the crop;
improve compatibility in the spray tank;
reduce fish toxicity;
reduce groundwater leaching;
reduce solvent usage in the formulation;
may reduce the pesticide application rate.
Controlled-release pesticide formulations can be divided into four main
types:
•
•
•
•
coated pesticide granules;
matrix systems containing physically trapped pesticides;
polymer systems containing covalently bound pesticides;
polymer membrane-pesticide reservoir systems, e.g. microencapsulation.
The polymer membrane, or microencapsulation, technique has become
popular in recent years. A well-known method of microencapsulation
uses the principle of interfacial polymerization. In this process the active
ingredient, usually a liquid or low-melting waxy solid, is dissolved in an
aromatic solvent, such as the C9 and C10 solvents used for emulsifiable
concentrates. An oil-soluble monomer such as toluene diisocyanate (TDI)
is dissolved in the solvent mixture. A fine emulsion of the oil phase in water
is made by high-shear mixing with an aqueous solution of an emulsifier and
a reactive amine, such as ethylene diamine. An emulsion with droplets of
10-30 |im is formed, and polymerization between the isocyanate and the
amine occurs at the oil-water interface, giving a polyurea membrane
around each droplet. Alternatively, the interfacial polymerization process
may be carried out by allowing the isocyanate to react with water at the
interface to form an amine in situ, which then reacts with more isocyanate
to form a polyurea membrane [12]. The rate of release of the active ingredient can be controlled by adjusting the droplet size, the thickness of the
polymer membrane and the degree of crosslinking or porosity of the polymer. The rate of release of the pesticide is, therefore, a diffusion-controlled
process.
A typical microencapsulated suspension (CS) formulation (per cent by
weight) is shown below:
Active ingredient
Emulsifier
Polymer
Solvent
Anti-settling agents
Water
10-30%
1-5%
10-15%
5-15%
1-3%
to 100%
Microcapsule suspensions need to be stabilized with surfactants and thickeners in the same way as suspension concentrates and emulsions, and
similar additives are used. A few microencapsulated products are now on
the market, including selective herbicides to reduce volatility and solvent
usage, insecticides to reduce toxicity and to increase residual activity, and
pheromones to maintain the required vapour concentration over a period
of 10-14 days. The benefits of microencapsulated products over conventional formulations in terms of bioavailability may be demonstrated graphically as shown in Figure 3.2, where the optimum level of pesticide
availability can be maintained over a much longer period than with conventional formulations.
Chemical Dosage
Conventional
Formulation
Microencapsulated
Formulation
Optimum Range
for Effectiveness
Time (days)
A f t e r Application.
Figure 3.2 Bioavailability of microencapsulated formulation compared with conventional
formulation. (From Morpeth, F.F., Preservation of Surfactant Formulations, Blackie
Academic and Professional, London, 1995.)
3.3.6 Water-dispersible granules (WG)
Water-dispersible granules, or dry flowables, as they are sometimes known,
are a relatively new type of formulation and are being developed as safer
and more commercially attractive alternatives to wettable powders and
suspension concentrates. They are becoming more popular because of their
convenience in packaging and use, being non-dusty, free-flowing granules
which should disperse quickly when added to water in the spray tank. They
therefore represent a technological improvement over wettable powders
and imitate liquids in their handling characteristics, with the minimum of
pack disposal problems.
The technology for water-dispersible granules is rather complex because
they can be formulated using various processing techniques, but in each
case the resultant product must redisperse in the spray tank to give the same
particle size distribution as the original powder or suspension from which it
is made. This requires careful choice of the surfactants and other additives,
and the process of granulation [13]:
• pan granulation;
• mixing agglomeration;
• extrusion granulation;
• fluid bed granulation;
• spray drying.
Several factors, such as the physico-chemical properties of the active
ingredient and additives, need to be considered when deciding upon which
process to use. These factors and the various processing techniques used to
make water-dispersible granules determine the main properties of the final
product in terms of granule shape and size, degree of dustiness, and ease of
dispersion into water. The dispersion time in water is a very important
property, and to ensure that no problems occur in the spray tank it is usually
necessary for all the granules to disperse completely within 2min in varying
degrees of water temperature and hardness [14].
Water-dispersible granules usually contain a wetting agent and a dispersing agent in the same way as a wettable powder or a suspension concentrate. They may also contain a water-soluble salt to act as a disintegrant in
the spray tank. The remainder of the formulation is usually a water-soluble
or a water-dispersible filler. A typical water-dispersible granule formulation
(per cent by weight) is shown below:
Active ingredient
Wetting agent
Dispersing agent
Disintegrating agent
Soluble or insoluble
filler
50-90%
1-5%
5-20%
0-15%
to 100%
The wetting and dispersing agents commonly used in water-dispersible
granules are often similar to those used in wettable powder and suspension
concentrate formulations.
3.3.7 Formulations using a built-in wetter
There is increasing pressure from regulatory authorities and for marketing
reasons to include surfactant adjuvants in the formulation in order to
optimize biological activity and to reduce the rate of active ingredient
usage. In some cases the regulatory authorities require specific data on the
formulation, which includes the biological enhancing wetter.
The potential effects of built-in wetters to formulations are
•
•
•
•
•
better foliar wetting and spreading;
better adhesion of the droplets;
reduced droplet size of the spray;
increased drying time and water retention;
increased uptake and translocation in plant.
Non-ionic surfactants are often used as built-in wetters to give the above
benefits. They can increase the solubility of the pesticide in the droplet by
micellization, making it easier for the active ingredient to enter the target.
Built-in wetters are useful for hydrophilic active ingredients, such as
paraquat and glyphosate, to enhance their uptake through the leaf surface.
They may also improve the physical compatibility of different pesticide
formulations in the spray tank mixture.
No universal surfactant wetter exists for all pesticides, and it is necessary
to carry out stability tests and biological activity tests with a range of
different surfactant wetters to find the optimum system. However, surfactants such as aliphatic alcohol ethoxylates and aliphatic amine ethoxylates are often used. The mechanism of action of surfactant adjuvants in
contact with the target organism is not fully understood, but it seems that
lowering the interfacial tension, reducing the contact angle and increasing
the movement of pesticide through the leaf surface are all important processes [15]. The mode of action of adjuvants is discussed in more detail in
Chapters 7 and 8.
3.4 Surfactants for agrochemicals
3.4.1 General characteristics
Surfactants are essential components for the formulation of most
agrochemical products. They have several functions the most important of
which are:
•
•
•
•
•
wetting;
dispersing;
emulsifying;
solubilizing;
bioenhancement.
Surfactants are able to wet powders into water by lowering the surface and
interfacial tensions so that concentrated premixes can be made. They also
help in the particle dispersion process by adsorbing onto the freshly formed
surface and preventing reaggregation. Surfactants can emulsify oils into
water and in some cases can increase the concentration of active ingredients
by solubilization of the material in the surfactant micelles. Surfactants play
a major role in the stabilization of pesticide formulations, to impart good
shelf-life stability. During the spray application process they enable solid
products to wet out and disperse into the spray tank dilution and liquid
products to emulsify and disperse. Surfactants are also used by themselves
or as components of adjuvants for tank mixing with pesticide products. A
knowledge of the physico-chemical properties of surfactants is essential for
the successful design of agrochemical formulations and adjuvants [16].
Agrochemical,formulations usually contain 1-10% of surfactant or a mixture of surfactants. For spray applications, surfactants are sometimes added
to the spray tank at levels of 0.01-0.1% to improve droplet wetting, spreading and adhesion on the foliage. In recent years higher concentrations of
surfactants up to 1-2% have been used to enhance the biological performance of the pesticide, by increasing uptake into the plant and
translocation within the plant. It has been estimated that the world consumption of surfactants for agrochemical use is about 230000 tonnes, representing about 3.3% of the total consumption of surfactants for all end
uses [17].
The nature of surfactant molecules is that they have an affinity for interfaces. Even in solution they have a preference to associate together rather
than survive as individual molecules. Surfactants derive these properties
from their molecular structure. They are amphipathic molecules which
consist of one part or parts which prefer to be in or on one type of phase or
surface, and another chemically different part which prefers to be in or on
a quite different phase or surface. As water is the earth's most common
liquid, the usual example is of a surfactant molecule which has a
hydrophilic, water-preferring part, and a hydrophobic (or lipophilic) waterrejecting part. The simplest surfactant molecule comprises a lipophilic part
which prefers an oil phase, attached to a hydrophilic head group which
prefers water. A common and simple example is sodium dodecyl sulphate:
C12H25SO4-Na+.
Surfactants are classified into the following types:
•
•
•
•
anionic: negatively charged hydrophilic head group;
cationic: positively charged hydrophilic head group;
nonionic: uncharged hydrophilic head group;
amphoteric: negatively and positively charged hydrophilic head group.
Some common examples of the different types of surfactants used in
agrochemical formulations are shown schematically in Figure 3.3. A wide
range of surfactants is available to enable the formulator to make the best
choice for a particular formulation. Surfactants are used primarily as wetting agents, emulsifiers and dispersing agents, but also have uses as antifoaming agents and anticaking agents and an increasingly important use as
agents to enhance the biological activity of active ingredients by improving
capture by and penetration of the biological target.
Anionic and non-ionic surfactants are much more commonly used with
agrochemical formulations than cationic and amphoteric surfactants in
order to prevent flocculation problems with other anionic formulation
additives. However, where they are used, cationic surfactants may also
exhibit bactericidal properties. Amphoteric surfactants ae rarely used in
agrochemical formulations, but in some cases they can have interesting
effects at different pH values. For agrochemical formulations anionic
surfactants comprise about 50% of the total surfactant usage, whereas for
spray application adjuvants, non-ionic surfactants comprise about 75% of
the total surfactant usage.
Hydrophobic/Lipophilic Chain
Hydrophil ic
Head Group
Anionic
Cationic
Nonionic
Amphoter ic
Hydrophobic (Lipophilic)
Part
Mydrophilie
Part
Figure 3.3 Surfactant classifications and examples. (From Morpeth, F.F., Preservation of
Surfactant Formulations, Blackie Academic and Professional, London, 1995.)
3.4.2 Adsorption and surface tension
Because of their preference for surfaces rather than bulk solution,
surfactants adsorb at interfaces. At quite low concentrations monolayers of
surfactant molecules form, which means that the interface is completely
filled with surfactant as a single molecular layer. The surfaces can be the
air-water, water-oil, water-solid or solid-oil interfaces. Adsorption reduces interfacial tensions significantly. Most conventional surfactants will
lower the surface tension at the air-water interface from 72 to 30-35 mN/m.
The oil-water interface can be reduced from around 30 mN/m to very low
tensions of around 1-5 mN/m. A diagram showing the effect of surfactant
concentration on the surface tension of aqueous solutions is shown in
Figure 3.4. Beyond the concentration where a close-packed monolayer is
reached, the surfactant molecules begin to aggregate into micelles. This
point is known as the critical micelle concentration or CMC. Table 3.4 gives
some examples of surface tensions for a few surfactants. It can be seen that
fluorinated and silicone-based surfactants give the lowest surface tensions,
but these tend to be more expensive than conventional hydrocarbon-based
surfactants.
Surface
tension
surfactant 1
surfactant 2
surfactant
concentration
monolayer
of
surfactant
Figure 3.4 Surface tension versus concentration for surfactants.
Table 3.4 Surface tensions for the water-air interface (mN/m)
Surfactant concentration (%)
DDES3
CTABb
NP8EOc'd
NP15EO
NP30EO
Silicone
Fluoro
a
b
c
d
0.001
0.01
0.1
48
_
33
40
52
22
25
32
34
29
33
47
22
18
27
DDBS = dodecylbenzene sulphonate.
CTAB = cetyltrimethylammonium bromide.
NP = nonylphenol.
EO = no. of ethylene oxide units.
29
33
43
21
18
Table 3.5 Critical micelle concentrations
Surfactant
CMC (mol/dm3)
Sodium dodecylbenzene sulphonate
Sodium dodecyl sulphate
Hexadecyltrimethylammonium bromide
Dodecanol 6EO
Octylphenol 6EO
1.2
8.3
9.2
8.7
2.1
X 10~3
X 10~3
X ICT4
X 10~5
X 10"4
3.4.3 Micellization
In order for the lipophilic parts of the molecule to avoid, as far as possible,
being in contact with water molecules, the surfactant molecules aggregate
to form micelles, with the lipophilic parts in the interior and the hydrophilic
parts on the outside. There are different shapes of micelles but the most
common is the spherical micelle, which can contain many tens or hundreds
of molecules and is capable of solubilizing organic molecules. Micelles form
at the critical micelle concentration. Examples of CMCs for some common
surfactants are given in Table 3.5.
3.4.4 Krafft temperature and cloud point
Below certain temperatures, anionic and cationic surfactants can lose their
surface activity and solubility in water, and separate out. This is known as
the Krafft temperature. On the other hand, non-ionic surfactant solutions
can become cloudy at higher temperatures due to the ethylene oxide chains
rejecting the solvating water molecules. It is important to be aware of these
properties to ensure that a product is held within a temperature range away
from these effects. The presence of electrolytes can raise Krafft points and
lower cloud points. Examples of cloud points are given in Table 3.6.
3.4.5 Wetting and contact angle
Water in contact with a solid surface normally forms a contact angle. For
poorly wetted surfaces the contact angle is greater than 90°. The contact
angle is determined by the balance between the three surface tensions:
Table 3.6 Cloud points of non-ionic surfactants
Surfactant
NP-8EO
NP-15EO
C13/C15-7EO
Cloud point (0C)
29-35
64-69
45-50
AIR
Water
Contact angle
Solid
Figure 3.5 Contact angle of liquid on solid.
• air-solid tension;
• air-water tension;
• water-solid tension.
The force vectors for an aqueous surfactant solution droplet on a solid
surface are shown in Figure 3.5.
The relationship between interfacial tensions is known as Young's equation. Spontaneous wetting and spreading can occur in the presence of
surfactants if they reduce the liquid-solid tension and the liquid-air tension
until they are less than the solid-air tension.
3.4.6 Particle and droplet stabilization
Small particles in water or other media will normally cluster together to
form floccules, unless stabilized. Droplets will go one step further by coalescing to form a separate continuous phase. Surfactants can prevent this
behaviour by adsorbing onto the particle or droplet surface. The hydrophobic part anchors to the particle or droplet surface, and the hydrophilic part
provides a charge stabilization in the case of anionic and cationic
surfactants, and steric stabilization in the case of the non-ionic surfactants.
Deryagin, Landau, Verwey and Overbeek developed the DLVO theory
to calculate the interaction energies between charged particles required to
give repulsion and hence stabilization. Steric stabilization is caused by a loss
of entropy and an increase in osmotic pressure due to the overlap of the
hydrophilic chains on adjacent particles. Energy curves for charge and
steric stabilization are shown in Figure 3.6. In the case of particles stabilized
with charged surfactants, there is a shallow attraction into a secondary
minimum, but the charge provides an energy barrier to prevent the particles
flocculating into the deep primary minimum. This energy barrier can be
reduced significantly in the presence of electrolytes, sufficiently in order to
Primary min
Figure 3.6 Schematic representation of energy-distance curves for three cases of stabilization:
(a) electrostatic, (b) steric and (c) electrostatic plus steric.
cause flocculation at high concentrations of monovalent electrolytes or by
lower concentrations of multivalent counterions.
For the particles stabilized by uncharged non-ionic surfactants, there is
also a weak attraction between particles but, provided that the surfactant is
strongly adsorbed, the steric barrier is very large and will prevent
flocculation, given that the temperature is below the cloud point.
3.4.7 Wetting agent
A wetting agent can be defined as a substance which when added to a liquid
increases the spreading or penetration power of the liquid by reducing the
interfacial tension between the liquid and the surface on which it is spreading. The contact angle between the liquid droplet and the surface is reduced
until, if the contact angle reaches zero, complete wetting will take place.
Wetting agents are therefore used for two main functions in agrochemical
formulations:
• during processing and manufacture to increase the rate of wetting of
powders in water to make concentrates for soluble liquids or suspension
concentrates;
• during mixing of the product with water in a spray tank to reduce the
wetting time of wettable powders and to improve the penetration of
water into water-dispersible granules.
Because of their amphipathic nature, surfactants are very active at interfaces and are able to lower the interfacial tension. The more the interfacial
tension is lowered, the greater is the wetting property. Diffusion of the
surfactant to the surface is also important, and therefore low molecular
weight surfactants are usually better wetting agents than high molecular
weight surfactants.
The general relationships between the chemical structure of the
surfactant and wetting properties are as follows:
• the shorter the hydrophobic chain the better the wetting action: optimum
wetting occurs at around a C12 carbon chain length;
• ortho-substituted alkyl benzene sulphonates are better wetting agents
than straight-chain or p^ra-substituted aromatics;
• additional polar groups in the molecule (e.g. ester, amide or ethylene
oxide (EO)) usually result in loss of wetting power;
• ethoxylated aliphatic alcohols are better wetting agents than similar
ethoxylated aliphatic acids;
• addition of long-chain alcohols and non-ionic cosurfactants improves the
wetting properties of anionic surfactants;
• pH can be important when weak basic or acidic groups are present.
The most important wetting agents used in wettable powder, suspension
concentrate and water-dispersible granule formulations are
• sodium lauryl sulphate;
• sodium dioctyl sulphosuccinate;
• alkyl phenol ethoxylates (7-14EO);
• aliphatic alcohol ethoxylates (C12-C17,10-18 EO).
They are generally used at 2-10% of the total formulation.
3.4.8 Dispersion
A dispersing agent can be defined as a substance which adsorbs onto the
surface of the particles and helps to preserve the state of dispersion of the
particles and prevents them from reaggregating. Dispersing agents are
added to agrochemical formulations to facilitate dispersion and suspension
during manufacture, and to ensure the particles redisperse into water in a
spray tank. They are widely used at about 1-6% of the total formulation in
wettable powders, suspension concentrates and water-dispersible granules.
Surfactants which are used as dispersing agents have the ability to adsorb
strongly onto a particle surface and provide a charged or steric barrier to
reaggregation of particles. They are therefore an essential part of the
stabilization mechanism for suspension concentrates. In practice it is found
that dispersing agents are very different to wetting agents. Instead of being
small molecules, which are necessary for rapid diffusion in the wetting
process, dispersing agents tend to be much bigger molecules which provide
as many anchoring points as possible onto the particle surface. The type of
surfactant which will give the most efficient dispersing properties will also
depend upon the nature (polarity) of the solid to be dispersed.
As the majority of solid particles have a residual negative charge in water,
the most commonly used surfactants are anionic or non-ionic, or mixtures
of the two types. For wettable powder formulations, the most common
dispersing agents are sodium lignosulphonates. For suspension concentrates, very good adsorption and stabilization are obtained using polyelectrolytes, such as sodium naphthalene sulphonate formaldehyde
condensates. Tristyrylphenol ethoxylate phosphate esters are also used.
Non-ionics such as alkylarylethylene oxide condensates and EO-PO block
copolymers are sometimes combined with anionics as dispersing agents for
suspension concentrates. In recent years, new types of very high molecular
weight polymeric surfactants have been developed as dispersing agents.
These have very long hydrophobic 'backbones' and a large number of
ethylene oxide chains forming the 'teeth' of a 'comb' surfactant. These high
molecular weight polymers can give very good long-term stability to suspension concentrates because the hydrophobic backbones have many anchoring points onto the particle surfaces [18].
Dispersing agents for water-dispersible granules are usually chosen according to the technology used for making the granule. In general, a solid,
non-sticky dispersing agent is preferred which will give a granule with good
porosity and rapid dispersion and solution in the spray tank.
The most important dispersing agents used in agrochemical formulations
are
•
•
•
•
•
•
•
sodium lignosulphonates;
sodium naphthalene sulphonate formaldehyde condensates;
tristyrylphenol ethoxylate phosphate esters;
aliphatic alcohol ethoxylates;
alkylphenol ethoxylates;
EO-PO block copolymers;
'comb' graft copolymers.
3.4.9 Emulsification
An emulsifying agent can be defined as a substance which stabilizes a
suspension of droplets of one liquid phase in another liquid phase. Without
the emulsifying agent the two liquids would separate into two immiscible
liquid phases. It is therefore an essential ingredient in the formulation of
liquid oily active ingredients and solvents which need to be emulsified into
water in the spray tank.
The use of emulsifying agents in emulsifiable concentrate formulations is
the most important application of surfactant emulsifiers because these formulations are generally based on water-immiscible solvents. However, in
recent years the trend has been to reduce the use of solvents on toxicity
grounds, and to use surfactant emulsifiers to emulsify the active ingredients
directly into water as the bulk medium of the formulation.
The design of the emulsifier system depends upon the polar properties of
the active ingredient, the solvent employed and any additional additives
required. Emulsifiable concentrates generally contain an average of 50%
active ingredient, up to 10% emulsifier and the remainder is a solvent or
solvent mixture. Careful selection of a 'balanced pair' emulsifier blend is
necessary to ensure spontaneous emulsification when mixed with water in
the spray tank, and also to ensure the emulsion formed is stable over a wide
range of water temperature and hardness.
The most commonly used emulsifer blends contain alkylphenol or
aliphatic alcohol with 12 or more ethylene oxide units and the oil-soluble
calcium salt of dodecylbenzene sulphonic acid. A range of HLB values from
8 to 18 will normally provide good stable emulsions. Emulsion stability can
sometimes be improved by the addition of a small amount of an EO-PO
block copolymer surfactant. Nonylphenol ethoxylates are now being
avoided as described earlier for emulsifiable concentrates.
The requirements for surfactants which will produce stable oil-in-water
emulsions (EW) are different to those for emulsifiable concentrates. In the
case of O/W emulsions, the surfactant should be very strongly adsorbed
onto the surface of the oil droplet to impart long-term stability to the
emulsion. Higher molecular weight and polymeric surfactants are sometimes used for this purpose.
3.4.10 Solubilization
A solubilizing agent is a surfactant which will form micelles in water
at concentrations above the critical micelle concentration. The micelles
are then able to dissolve or solubilize water-insoluble materials inside the
hydrophobic part of the micelle.
The appearance of the solution is the same as before the oil was added,
and the systems are stable and do not separate on standing. The amount of
water-insoluble material which can be stabilized increases as the size of the
micelle increases. Non-ionic surfactants will usually give higher degrees of
solubilization than anionic surfactants.
The difference between solubilization and the formation of microemulsions is not very clear, and there is a current view that microemulsions
are really swollen micelles as the surfactant concentration reaches 30% or
more of the total formulation. The addition of a cosurfactant, such as
octanol, may increase the size of the micelle and allow further solubilization
to take place. The problem of crystallization of the active ingredient from
micellar solutions needs to be monitored during long-term storage stability
tests.
The type of surfactants usually used for solubilization are non-ionics:
• sorbitan monooleates;
• sorbitan monooleate ethoxylates;
• methyl oleate esters.
3.4.11 Bioenhancement
Surfactants are sometimes used, either alone or with other additives such as
mineral or vegetable oils, as adjuvants to spray-tank mixes to improve the
biological performance of the active ingredient on the target. There is an
increasing trend, however, to incorporate a surfactant into the formulation
to enhance the biological activity of the active ingredient. These formulations are often known as 'built-in-wetter' formulations. Thus it is possible to
give the farmer a single formulation in one pack and at the same time
provide all the relevant toxicity, efficacy, safety and environmental data to
the regulatory authorities.
The types of surfactants used for bioenhancement depend on the nature
and mode of action of the active ingredient. However, they are often nonionics such as:
• alkylphenol ethoxylates;
• linear aliphatic alcohol ethoxylates;
• aliphatic amine ethoxylates.
3.4.72 Conventional surfactants
Wettable powder formulations usually contain a wetting agent such as
sodium lauryl sulphate or a sodium sulphosuccinate derivative shown
below:
C12H25SO4' Na+
CH2COOCnH2n+1
-SO3-CHCOOCnH2n+1 Na+
n = 6-8
The most commonly used dispersing agent for wettable powders is sodium lignosulphonate. Another popular dispersing agent is naphthalene
sulphonic acid formaldehyde condensate sodium salt. The structures of
these two complex polyelectrolyte anionic dispersing agents are shown in
Figures 3.7 and 3.8. Both of these polyelectrolyte anionic dispersing agents
are also useful for the preparation of suspension concentrates. They are
sometimes combined with non-ionic surfactants such as alkylphenol
ethoxylates or long-chain alcohol methoxylates with typical structures
shown below:
CnH2n+1O-O(CH2CH2O)n, H
n = 8-9
m = 6-20
CnH2n+1O(CH2CH2O)n, H
n = 12-17 m = 6-20
Increasing the number of ethylene oxide units in the molecule increases the
hydrophilicity of the surfactant and reduces its lipophilic tendencies, e.g.
solubility in oils.
Figure 3.7 Structure of a typical section of polymeric lignosulphonate salt. Lignosulphonates
are anionic polyelectrolytes whose molecular weight varies between 1000 and 20000. Their
organic structure has not been completely determined, but it is known that the basic lignin
monomer unit is a substituted phenylpropane. (From Morpeth, F.F., Preservation of Surfactant
Formulations, Blackie Academic and Professional, London, 1995.)
By changing the mass of the lipophile or hydrophile, the hydrophiliclipophilic balance can be changed, thereby modifying the surface activity
and solubility of the molecule. For example, increasing the ethylene oxide
chain length increases the cloud point of the surfactant and can prevent
flocculation problems during storage at high temperatures.
Another common group of surfactants used in suspension concentrate
formulations is based on polypropylene oxide as the hydrophobe and
polyethylene oxide as the hydrophile. These are formed as ABA blocks
where A is the polyethylene oxide unit and B is the polypropylene oxide
unit. A large number of surfactants having a wide range of properties can be
obtained by changing the A/B ratio and the molecular weights of A and B.
The number of ethylene oxide units can range from two to a few hundred.
Figure 3.8 Structure of naphthalene sulphonic acid formaldehyde condensate sodium salt.
Naphthalene sulphonate formaldehyde condensates are a mixture of low polyelectrolytes in
the approximate molecular weight range 500-2200 (corresponding to a naphthalene nucleus
content of 2-9 per molecule). Major components of the mixture are believed to have the
structure shown. (From Morpeth, F.F., Preservation of Surfactant Formulations, Blackie
Academic and Professional, London, 1995.)
Polypropylene oxide chains with less than about 12 units are not really
hydrophobia and can range from this minimum to a few hundred units.
One of the advantages of non-ionic surfactants is the way that their
properties can be modified by changing the level of ethoxylation, i.e. the
hydrophile-lipophile balance (HLB). Products in the HLB range 1-4 are
likely to be immiscible in water at room temperature, those in the HLB
range 4-7 form unstable dispersions, those in the HLB range 7-9 give
opaque stable dispersions, those in the HLB range 10-13 give hazy solutions and in the HLB range 13-20 clear solutions. Non-ionic surfactants in
the HLB range 2-7 are preferred for water-in-oil emulsions, whilst the
HLB range 7-18 forms good oil-in-water emulsions. Wetting, foaming and
defoaming properties are also HLB dependent. A wide range of degrees of
ethoxylation is available, normally in the range 4-50 EO units. Some properties are summarized in Table 3.7 for nony!phenol (NP) ethylene oxide
condensates with 8-20 moles of ethylene oxide.
The properties of long-chain alcohol ethoxylates vary in a manner similar
to the alkylphenol derivatives, as determined by the degree of ethoxylation.
Data on physical properties are shown in Table 3.8 for some linear alcohol
ethoxylates based on C13-C15 synthetic aliphatic alcohols. As mentioned
earlier, the alcohol ethoxylates are now being preferred to the nonylphenol
ethoxylates because of safety to the environment generally and continuity
of supply.
Table 3.7 Properties of nonylphenol ethoxylates
Product
NP8
NP12
NP15
NP20
HLB
12.3
13.9
15.0
16.0
Cloud point (0C)
Water
10% NaCl
31
82
97
-
54
67
73
Pour point (0C)
Surface tension
(0.1%) (mN/m)
<0
14
21
30
29
33
35
42
Table 3.8 Properties of linear alcohol ethoxylates
Degree of ethoxylation (moles EO)
Physical form
0
Pour point ( C)
Cloud point (0C)
HLB
Surface tension (0.1 %) (mN/m)
7
11
20
Viscous liquid
Soft paste
Hard wax
21
45-49
12.2
28.6
27
84-89
13.9
32.8
37
100
16.2
41.3
3.4.75 Recent surfactant developments
In recent years there has been considerable interest in the preparation of
'tailor-made' surfactants with improved properties to suit specific functions
in formulations and spray adjuvants. For instance, the trend towards
aqueous suspension and emulsion formulations has provided a need for
surfactants with better adsorption characteristics and long-term stabilization properties. Conventional surfactants have molecular weights of about
1000-2000 and generally give incomplete coverage of particle surface area.
They may also desorb from the surface, leading to flocculation and problems of increased viscosity on storage. The need for improved long-term
stability has led to the development of polymeric surfactants with molecular
weights of 20000-30000 for the hydrophobic 'backbone', which has multiple anchoring points for adsorption onto surfaces. These polymeric
surfactants can have more than ten times the adsorption affinity of conventional surfactants, and are much less likely to desorb from the surface.
Polymeric surfactants, therefore, impart better stability and allow higher
volume concentrations of particles to be suspended in water without increasing viscosity [18]. A good example of a polymeric surfactant of this
type is a graft 'comb' copolymer which has a hydrophobic backbone of
polymethyl methacrylate-methacrylic acid onto which are grafted 'teeth' of
polyethylene oxide.
Examples of other surfactant developments are the silicone-based and
the fluorinated surfactants which give very low surface tensions, as low as
15-20 mN/m compared with 30-40 mN/m for conventional surfactants.
There is also considerable interest in using surfactants which are as environmentally friendly as possible. The trend in the future will be towards
surfactants which are fully biodegradable and have low toxicity to mammals
and fish. Surfactants based on sugars, the alkyl polysaccharides, are now
available as alternatives to the conventional alkylphenol ethoxylates and
other synthetic surfactants. They are non-ionic surfactants and are environmentally safer alternatives to petroleum-based surfactants.
3.5 Other formulation additives
3.5.1 Carriers and diluents
A carrier or diluent in an agricultural formulation is an inert material added
to the active ingredient to give a product of the required active ingredient
strength which can be safely and conveniently diluted to spray strength for
application. Carriers are usually inert materials with high absorptive capacities, while diluents are usually inert materials with low absorptive capacities. Carriers and diluents are used in the formulation of dusts, wettable
powders, granules and water-dispersible granules. The properties of these
materials are important because they can affect the stability and biological
performance of the final product. Carriers and diluents must
•
•
•
•
•
be compatible with the active ingredient;
have good absorptive capacity;
be free-flowing powders;
have suitable bulk density;
be dispersible in water, except for dusts and granules.
The most important characteristic is the absorptive capacity because the
prime purpose of the carrier is to spread the active ingredient over a large
number of particles that can be applied uniformly in the field. Fine particle
size with a narrow particle size distribution is also needed. In addition, bulk
density will determine the coverage of the active ingredient, wind drift,
foliage penetration, the degree of sinking in water and general ease of
handling of the formulation. Another important factor when choosing a
carrier or diluent powder is the compatibility of the active ingredient
with the material. Many active ingredients are chemically unstable during
long-term storage at elevated temperatures, and this has been found to be
due to the presence of active acidic, basic or catalytic sites on the carrier
and diluent particles. Deactivators such as glycols, glycol ethers, cyclohexanol or long-chain alcohols have been found to be useful to stabilize the
formulation.
The classification of carriers and diluents has been shown earlier in Table
3.2, and information on the absorptive capacities of some common fillers is
shown in Table 3.3.
3.5.2 Solvents
Organic solvents are used mainly in the formulation of emulsifiable concentrates, ULV formulations and to a lesser extent granular formulations. EC
and ULV formulations can contain more than 50% solvent, and granular
formulations up to 10%. EC formulations still represent the largest volume
of all the types of agricultural formulations, although the trend is now
to move away from solvent usage because of toxicity and environmental
factors, as described earlier.
Organic solvents are used most conveniently when the active ingredient is very soluble in the solvents. The properties for an ideal solvent
are
•
•
•
•
•
•
•
•
good solvent power for the active ingredient;
low phytotoxicity to crop;
does not react with the active ingredient or emulsifier;
good thermal stability;
low toxicity and skin irritation;
low flammability;
compatible with materials used in packaging and application equipment;
ready availability and low cost.
No one solvent will meet all these requirements and compromises must be
made. Sometimes mixtures of solvents are used. The first main groups of
solvents are aliphatic paraffinic oils such as kerosene or refined paraffins,
which are characterized by very low solubility in water, poor solvent power,
low toxicity and low phytotoxicity. The second main group and the most
common comprises the aromatic solvents such as xylene. However, due to
its low flash point, xylene is being replaced by higher molecular weight
fractions of C9 and C10 aromatic solvents. These solvents usually have very
good solvent power for most active ingredients and form more stable emulsions than do aliphatic solvents, but they may be more phytotoxic and they
may increase the acute toxicity of the active ingredient. The chlorinated
hydrocarbons are useful because of their low flammability. They possess
good solvent power but are difficult to emulsify. However, they may be
useful as cosolvents to prevent crystallization of active ingredients when the
formulation is emulsified into water. Certain ketones are useful for EC
formulations because they are powerful solvents. However, they are fairly
polar and may be reactive, and also have some water solubility. The most
popular members of this group are
•
•
•
•
•
cyclohexanone;
methyl cyclohexanone;
isophorone;
acetophenone;
TV-methyl pyrollidone.
Alcohols are polar compounds which are sometimes used as cosolvents to
increase solvent power and to improve emulsion stability. The lower members have low flash points and the higher members such as octanol and
nonanol can be very phytotoxic. The most commonly used alcohols in EC
formulations are
Table 3.9 Some properties of commonly used solvents
Class
Solvent
Water solubility
(gfeg)
Flash point
(0C)
Boiling
0 point
(Q
Hydrocarbons
Xylene
Kerosene
Isopar L (Exxon)
Solvesso 100 (Exxon)
Solvesso 150 (Exxon)
Solvesso 200 (Exxon)
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
25
72
70
49
69
102
140
222
194
168
196
249
Chlorinated
hydrocarbons
1 ,1 ,1-Trichloroethane
Insoluble
None
73
Ketones
Cylcohexanone
Methylcyclohexanone
Isophorone
Acetophenone
N-methylpyrollidone
50
25
12
5
Miscible
43
53
96
82
95
156
170
215
202
202
Alcohols
Butanol
Benzyl alcohol
78
38
29
90
117
205
Ethers
Anisole
Diethoxol
Insoluble
Miscible
51
96
154
200
•
•
•
•
butanol;
nonanol;
benzyl alcohol;
tetra hydrofurfuryl alcohol.
The ethers are a useful group of polar solvents with low phytotoxicity,
and are sometimes used as cosolvents. Examples of these are
• diethylene glycol;
• dipropylene glycol;
• diethoxol.
Some data on water solubility, flash points and boiling points for all the
solvents and cosolvents commonly used in EC formulations are shown in
Table 3.9.
EC formulations are convenient and easy to use and in many cases the
biological activity is improved by the presence of a solvent, which may
enhance uptake and translocation. However, in some cases the presence of
a solvent may damage the crop, leading to phytotoxicity problems. Table
3.10 shows some data on phytotoxicity as an average effect on six crops.
3.5.3 Anti-settling agents
Thickeners or gelling agents are used mainly in the formulation of suspension concentrates, emulsions and suspoemulsions to modify the rheology or
Table 3.10 Phytotoxicity ratings for some solvents
Solvent
Benzyl alcohol
Butanol
Cyclohexanone
Diethoxol
Isophorone
Kerosene
Mineral oil
1,1,1-Trichloroethane
Xylene
Phytotoxicity ratinga
5% emulsion
0.5% emulsion
3.0
O
O
1.0
1.1
1.8
2.1
1.7
2.6
0.2
O
O
0.4
O
0.2
O
O
0.5
a
Ratings: O = no crop damage; 1 = slight damage; 2 = moderate damage; 3 = heavy damage; 4 = crop dead.
flow properties of the liquid and to prevent separation and settling of the
dispersed particles or droplets. They are therefore essential additives to
these water-based formulations to impart good long-term shelf life to the
product, while at the same time allowing the product to flow and dilute
easily in the spray tank. Thickening, gelling and anti-settling agents fall into
two categories, namely water-insoluble particulates and water-soluble
polymers.
It is possible to build three-dimensional networks of fine particles in
suspension concentrate formulations using clays and silicas. The types of
material which are commonly used are as follows.
• Swelling clays:
• montmorillonite, e.g. bentonite (many suppliers);
• magnesium aluminium silicate, e.g. Vangell (R. T. Vanderbilt).
• Non-swelling clays:
• attapulgite, e.g. Attagel (Engelhard Industries).
All of these are used at up to 3% of the formulation.
• Silica:
• fumed silica, e.g. Aerosil 200, surface area 200m2/g (Degussa).
Silica is used generally at up to 1% of the formulation.
3.5.4 Water-soluble polymers
Water-soluble polysaccharides have been used as thickening-gelling agents
for many years. The types of polysaccharides most commonly used are
natural extracts of seeds and seaweeds or are synthetic derivatives of
cellulose:
•
•
•
•
•
•
•
guargum;
locust bean gum;
carrageenam;
alginates;
methyl cellulose;
sodium carboxymethyl cellulose (SCMC);
hydroxyethyl cellulose (HEC).
Other types of anti-settling agents are based on modified starches,
polyacrylates, polyvinyl alcohol and polyethylene oxide. Most thickeners
have problems of incompatibility with electrolytes and can be affected by
pH, temperature and other formulation components, such as surfactants.
In the early 1970s a novel polysaccharide was developed based on a semisynthetic microbial fermentation process. The product is a very long,
branched-chain polysaccharide called xanthan gum, with a molecular
weight of about 2 million. Xanthan gum is highly pseudoplastic in water at
low concentrations compared with the conventional polysaccharides, and is
therefore ideal for stabilizing aqueous suspension and emulsion formulations. Xanthan gum solutions have reasonably stable viscosity over a wide
range of pH, temperature and electrolyte concentrations. It is now widely
used as the most important anti-settling component for suspension and
emulsion concentrate formulations.
It can be used alone at levels of up to 0.5% of the formulation, or it can
produce synergistic crosslinking with clays or silica at levels of up to 0.2%
of the formulation. By crosslinking with insoluble clays or silica or with
other soluble materials, xanthan gum is able to build up a structure or gel
network in the bulk phase to give high low-shear viscosity to overcome
gravitational separation of particles or droplets. This three-dimensional
network also has sufficient elastic modulus or yield value to overcome
compression of the total network and reduce clear layer separation or
creaming.
The advantages of using synergistic mixtures of dispersed phases and
water soluble polymers are:
•
•
•
•
greater shear thinning properties for pouring;
better dilution properties in water;
less temperature dependence;
better long-term physical stability, especially at high temperatures.
3.5.5 Preservatives
Microorganisms which cause spoilage of formulated products can enter
formulations in a number of ways, such as by using unclean plant and
equipment, contaminated raw materials and water, or by exposure to the
atmosphere. In order to grow and develop, microorganisms need a nutrient
source. Most agrochemical pesticide types do not provide a nutrient source
for microorganisms and are not susceptible to microbial degradation. Indeed, some fungicides act as preservatives themselves to prevent the growth
of fungal spores in formulated products. However, because of the need to
formulate agrochemicals to give products which have good biological activity and long-term storage stability, it is necessary to add preservatives to
protect the formulation additives from microbial attack and prevent spoilage of the final product. Surfactants and carbohydrate-based thickeners
may sometimes act as nutrient sources for microorganisms and generally
require preservatives to protect them.
Dry products such as dusts, wettable powders and granules, and solventbased formulations such as emulsifiable concentrates, do not contain
enough water to support the growth of microorganisms. These formulations, therefore, are not susceptible to biodegredation and do not require
the use of preservatives. Aqueous-based formulations such as solution concentrates, suspension concentrates and OAV emulsions are particularly vulnerable to attack by microorganisms, and this is the area where the bulk of
preservatives are used. It is likely that the use of preservatives will increase
in the future because of the trend towards safer aqueous-based formulations and also the use of formulation additives which are more biodegradable. The problems that can occur if preservatives are not added to
aqueous-based formulations are summarized:
•
•
•
•
•
•
•
production of gas;
production of bad odours;
discoloration;
pH change;
viscosity change;
phase separation;
sedimentation.
All the above problems need to be avoided to give products which perform
satisfactorily and have a long shelf life.
Once present in a formulation, a viable population of microorganisms
may grow very rapidly. A few organisms will normally become dominant,
and this is determined by the nature of the formulation components, and
other parameters such as pH, temperature, and oxygen and water concentration. Microorganisms tend to grow best at around neutral pH and between 15 and 4O0C, although significant growth can occur between pH 4 and
9 and temperatures of 7-6O0C.
The presence of a suitable carbon source, such as a polysaccharide thickener, is necessary to support the growth of microorganisms. Many microorganisms secrete enzymes which break down polymeric molecules into
smaller fragments to act as a source of carbon. These enzymes may persist
after the organism has been killed, making it important that microorgan-
isms are controlled throughout the manufacturing process. Good plant
hygiene is essential to minimize the likelihood of microbial contamination
of agrochemical products. However, in order to avoid problems occurring
during long-term storage, it is necessary to add a suitable preservative.
Preservatives are usually required for aqueous-based formulations, and
baits or pellets which are used as molluscicides and rodenticides. The general requirement for preservatives is that they should have the widest
possible spectrum of anti-microbial activity and should be effective at very
low concentrations. For many years formaldehyde, used as formalin (a 40%
solution in water and ethanol), has been added to formulations as a general
bactericide. However, in recent years its use has been very much reduced
due to the potential mammalian carcinogenicity of formaldehyde. Cationic
surfactants, especially quaternary salts such as cetyl trimethyl ammonium
bromide or cetyl pyridinium chloride, are also well known as anti-microbial
agents.
However, many agrochemical formulations contain anionic surfactants
or anionic polysaccharide thickeners which would be destabilized by
cationic surfactants. Other preservatives which are sometimes used for
aqueous-based formulations are
•
•
•
•
•
propionic acid and its sodium salt;
sorbic acid and its sodium or potassium salts;
benzoic acid and its sodium salt;
p-hydroxy benzoic acid sodium salt;
methyl p-hydroxy benzoate.
These preservatives are regarded as quite safe to use and some are used as
food product preservatives [19]. However, problems have sometimes occurred due to deactivation of the bactericide during storage of the formulated product. This effect is thought to be due to the presence of non-ionic
surfactants which can solubilize the preservative inside the surfactant
micelle, thus reducing the availability of the bactericide [2O].
In recent years some new preservatives have been developed which are
active against a wide range of microorganisms, effective over a wide range
of pH values and not deactivated by surfactants in the formulations. One of
the most popular of these newer bactericides is l,2-benzisothiazalin-3-one
(BIT), which is compatible with most anionic and non-ionic surfactants and
also with polymeric and clay-type anti-settling thickeners used in aqueous
suspension and emulsion formulations. It is usually available as a solution in
propylene glycol, and is normally added to formulations at about 0.030.06%. BIT has very good long-term stability. With increasing knowledge
of biocides and how they are stabilized and deactivated, combinations of
isothiazolone preservatives have been introduced [21].
In the formulation of aqueous suspension concentrates and emulsions, it
is sometimes necessary to make a stock solution of the polysaccharide
thickener, and this is often done in the case of xanthan gum. These thickeners are stable in the dry state, but when made up as dilute stock solutions
the use of a preservative is necessary to prevent the growth of microorganisms, which eventually leads to spoilage and a reduction in viscosity. This
applies to stock solutions which may be held for longer than 24 h before use.
Solid agrochemical formulations such as molluscicide baits and rodenticide pellets are a special case, where the product may be attacked by
soilborne or airborne microorganisms during prolonged exposure after application. In these cases preservatives are sometimes used to inhibit mould
growth due to weathering. However, the presence of a preservative can
sometimes lead to 'bait shyness' which may prevent the target pest from
eating the bait.
3.5.6 Anti-freeze agents
Anti-freeze agents are added to aqueous-based formulations, especially
suspension concentrates, to reduce the freezing point below zero, usually to
-5 or -1O0C. Ethylene glycol or propylene glycol, at 5-10% of the total
formulation, are widely used. In a few formulations, where the active ingredient is partially soluble in a glycol, urea may be used as an anti-freeze. In
some countries, propylene glycol is preferred to ethylene glycol, because
the latter may break down to oxalic acid, which is potentially carcinogenic.
3.5.7 Anti-foam agents
The presence of surfactants, which lower interfacial tension, often causes
water-based formulations to foam during mixing operations in production
and in application through a spray tank. In order to reduce the tendency to
foam, anti-foam agents are often added either during the production stage
or before filling into bottles.
There are two types of anti-foam agents, namely silicones and nonsilicones. Silicones are usually aqueous emulsions of dimethyl polysiloxane,
while the non-silicone anti-foam agents are water-insoluble oils, such as
octanol and nonanol, or silica. In both cases, the function of the anti-foam
agent is to displace the surfactant from the air-water interface. This property can sometimes lead to flocculation problems with suspension concentrates, and care must be taken to use the minimum level of anti-foam agent
in the formulation, usually up to 0.2%.
3.5.8 Anti-coking agents
Anti-caking agents are used at up to 2% in powder formulations and some
granular formulations to prevent caking during storage. They may also be
added during production to improve the flow properties of powders. The
most usual anti-caking agents are finely divided precipitated silicas.
References
1. van Valkenburg, W. (ed.) (1973) Pesticide Formulations, Marcel Dekker, New York.
2. Chow, P.N.P., Hinshalwood, A.M. and Simundsson, E. (eds) (1989) Adjuvants and
Agrochemicals VoIs 1 and 2, CRC Press, Boca Raton, FL.
3. Foy, C.L. (ed.) (1992) Adjuvants for Agrichemicals, CRC Press, Boca Raton, FL.
4. Tadros, T.F. (ed.) (1987) Solid/Liquid Dispersions, Academic Press, London.
5. Heath, D., Knott, R.D., Knowles, D.A. and Tadros, T.F. (1984) Stabilisation of aqueous
pesticidal suspensions by graft copolymers, in Advances in Pesticide Formulation Technology (ed. H.B. Scher), ACS Series, 254, American Chemical Society, Washington, DC, pp.
11-28.
6. Tadros, T.F. (1995) Surfactants in Agrochemicals, Surfactant Science Series, 54, Marcel
Dekker, New York.
7. Jeffs, K.A. (ed.) (1986) Seed Treatment, 2nd edn, BCPC Publications, Bracknell, UK.
8. Holden, W.T.C. (1992) Future formulation trends - the likely impact of regulatory and
legislative pressures, Brighton Crop Protection Conference, Vol. 1, BCPC, Brighton, pp.
313-20.
9. Seaman, D. (1990) Trends in the formulation of pesticides - an overview. Journal of
Pesticide Science, 29, 437^9.
10. Foy, C.L. and Pritchard, D.W. (eds) (1996) Pesticide Formulation and Adjuvant Technology, CRC Press, Boca Raton, FL.
11. Tadros, T.F. (1988) The development of suspoemulsion formulations for agrochemicals, in
Proceedings of the 2nd World Surfactants Congress, Section D, ASPA, Paris, pp. 271-83.
12. Scher, H.B. (1983) Human welfare and the environment, in IUPAC Pesticide Chemistry
(eds J. Miyamote and P.C. Kearney), Pergamon Press, Oxford, pp. 295-300.
13. Capes, C.E. (1980) Particle Size Enlargement, Vol. 1, Elsevier, Amsterdam.
14. Bell, G. (1990) The structure/physical property relationships of a model water dispersible
granule. Journal of Pesticide Science, 29, 467-73.
15. Holloway, PJ. and Stock, D. (1990) Factors affecting the activation of foliar uptake of
agrochemicals by surfactants, in Industrial Applications of Surfactants II (ed. D.R. Karsa),
Royal Society of Chemistry, Cambridge, pp. 303-37.
16. Porter, M.R. (1994) Handbook of Surfactants, 2nd edn, Blackie, Glasgow.
17. Hewin International (1994) Reports on Agricultural Surfactants and Related Materials,
VoIs I and II, Hewin International, Amsterdam.
18. Knowles, D.A. (1995) Trends in the use of surfactants for pesticide formulations. Pesticide
Outlook, Royal Society of Chemistry, 6(3), 31-4.
19. Smith, J. (ed.) (1991) Food Preservatives, Blackie, Glasgow.
20. Lehmann, R.H. (1988) Synergisms in disinfectant formulations, in Industrial Biocides (ed.
K.R. Payne), published for SCI by John Wiley, London, pp. 82-7.
21. Knowles, D.A. (1995) Preservation of agrochemicals, in Preservation of Surfactant Formulations (ed. F.F. Morpeth), Blackie, Glasgow, pp. 140-5.
4 Water-dispersible granules
G. A. BELL
4.1 Introduction
Agrochemical water-dispersible or soluble granules (WG) have been on
sale since the 1960s ([1] [2]; 'Weedol' was an established product when the
first edition of [3] was published). 'WeedoP and Tathclear' formulations,
for example, are household names in the UK, having been available to the
general public for over 30 years. It is a common occurrence however, at
conferences and symposia, to find water-dispersible granule formulations
being classified as novel. This may be a consequence of the relatively low
percentage of the market historically taken by the WG formulations. Despite this there are in fact hundreds of WG formulations currently commercially available, covering a very diverse range of chemistries and physical
forms of active ingredient (survey carried out by S. M. Critchley for Zeneca
Agrochemicals pic, 1994).
In recent years WG formulations have taken an increasing share of the
agrochemical marketplace (paper on Trends in pesticide formulation presented by B. Frei at Formulation Forum #94, Washington, 1994). Estimates
vary as to the actual size, which seems to be about 10%. This represents a
very sharp rise compared to a few years ago, and it is clear that the current
climate of safety and environmental concern has been the driving force.
The rise of importance of the WG as a physical form can be seen by
examining the published patent literature in the area (Figure 4.1; unpublished patent database results collected over several years to 1996 by G. A.
Bell for Zeneca Agrochemicals pic). Clearly there was a step change in the
rate of production of patent applications in about 1990, which implies there
was a decision to work in this area at some time in the middle of the 1980s.
Further evidence to back this up comes from the number of new products
launched between 1990 and 1994. Arguments over package disposal, operator safety and waste limitation have been going on for many years. However
it may have been at that time that the economics of green formulations
really became apparent.
Prior to that time the number of WG formulations commercially available was quite low. The added cost of manufacture may have been part of
the reason for this, however, and another major factor, one which is common to all formulation types, would have been the suitability of the available active ingredients.
Number
Year
Figure 4.1 The number of WG related patent applications by year.
Many of the early water-dispersible granules contained actives which had
high melting points and low water solubilities, for example atrazine, as
these were relatively easy to formulate. The absence of a solvent such as
water was a key aspect of the formulation type and led to the inclusion of
some other types of active ingredient (AI). Highly water-soluble materials
were usually sold as simple solutions (SL), whereas those materials which
did not dissolve in water became emulsion concentrates (EC) or perhaps
suspension concentrates (SC). The obvious niche for WG formulations was
to deal with those AIs which had low solubility in both water and organic
solvents. Pirimicarb is a good example, having a water solubility of 3 g/1, and
would therefore have been uneconomical as an SL. Its solubility in organic
solvents was also rather low, so an EC was of limited use. As an SC its
solubility tended to give rise to crystal growth, so the obvious answer was
granulation (Aphox 50 WG is manufactured and sold by Zeneca Agrochemicals; the first reference to this product is believed to be [4].)
Arguments such as these are still valid. However, nowadays there is a
greater willingness to tackle difficult problems, and the result has been that
the variety of active ingredient types which are formulated has grown.
Materials which would previously have been sold as liquid formulations are
now available as solids and the result is that the marketplace can be broken
up into different types of WG, depending on the active ingredient physical
form (Table 4.1).
The expansion of the basic formulation to be able to cope with more
difficult active ingredients has created other opportunities which are likely
to be exploited in the near future. The increase in patenting activity in the
Table 4.1 Examples of different types of water-dispersible granule
Formulation
SL
EC
EW
SC
CS
SE
Active ingredient
Commercial WG
Glyphosate
Deltamethrin
Fluazifop P butyl
Hexaconazole
Alachlor
Isoproturon/fluoroglycofen ethyl
'Roundup dry'
'Decis 6.25'
'Fusilade 25'
'Anvil 5'
'Partner'
'Competitor'
industry has created a significant amount of information on these areas, and
has highlighted those which are being actively researched. This is usually a
good indicator of the direction in which an industry is travelling.
The formulation of new mixtures of active ingredients has always been an
area of expertise. Interactions between active ingredients and their
formulants can create difficulties which take time and effort to resolve.
Granule mixtures are one way to avoid these problems [5-8]. Similarly,
waxes and oils were previously avoided because of the effects they have on
granule dispersion and dry strength. Many adjuvants fall into this category,
which is why there are few examples of built-in-wetter granules on the
market. However, there is evidence that this will change [9-16]. Other
ingredients such as non-ionic polymers are being exploited as melt granulation binders and dispersants. These ingredients can be awkward to handle
under normal circumstances, whereas the use of heat to turn them into
liquids alters the process conditions and can lead to some very interesting
results ([17-37]; paper on the new basis for new generations of pesticide
formulations, presented by G. Beestman at Formulation Forum 94,
Washington, 1994). Similarly, the use of bentonite clays and silica would
have been avoided previously, other than as hardening agents for GR
formulations, but they are now mentioned regularly in the literature, and at
conferences [38-48].
The basic WG formulation was originally a very simple means to avoid
selling a liquid. It had simple and cheap packaging, which was considered
environmentally friendly, and there was no need for solvents or expensive
ingredients. It was considered safe because spillage could easily be cleaned
up, with few concerns about contamination, and the formulation was low in
dust and easy to pour. Volumetric measurement was possible and, unlike
SC or EC formulations, the product did not suffer from solvent evaporation, which could be a problem with partly used liquid packs. On the down
side they were sometimes difficult to formulate, and were more expensive
to manufacture.
Modern WG formulations, however, tend to be considerably more sophisticated. The basic advantages are the same but the standards which are
applied in terms of packaging and performance are now higher than ever.
Table 4.2 Survey of granulation methods cited in patent
applications
% of patents
27.5
26.5
14.5
10.5
8.5
5
4.5
3
Manufacturing method
Extrusion
Not specific
Spray drying
Agglomeration
Melt granulation
Fluid bed
Various other
Pan
Part of this drive towards quality has been a significant change in the
technology which is used to manufacture the products. Examination of the
patent literature shows that extrusion has become the predominant method
of manufacture (Table 4.2). This is also apparent from the number of new
extrusion production plants which have been built in Europe and the USA
over the past 5 years. At one time extrusion was recognized as the most
economical method of granulation, a consequence of the small size of the
plant and the low throughput of air required. Now, however, the cost of
manufacture has risen, because of SHE (safety, health and environmental)
concerns and the added complexity of the formulations being made. The
economic benefit from extrusion compared to other methods has therefore
diminished, yet it has become the major manufacturing process. It is
thought that the reason for this change has arisen from the need to control
the size and shape of the product, as these are critical to physical performance and handling characteristics. It is another indicator that current
requirements have changed compared to, say, 10 years ago.
A great deal is known about extrusion technology, although much of it is
related to the engineering aspects of manufacture [49]. Published data on
the formulation side tends to be specific to the pharmaceutical and detergent industries. In terms of agrochemical information, the patent literature
can be useful and contains a large number of interesting observations, but
it can be difficult to assimilate data presented in that format. The purpose
of this short review is to present some of the known information about the
formulation and colloid chemistry of agrochemical granulation. It is hoped
that this will add something to this fast-growing area.
4.2 Manufacturing methods
Many types of granulation have been used to form agrochemical products
[5O]. The historical perspective is that industries have used those techniques
with which they were familiar, and for which they had production equip-
ment readily available. (Reviews of the equipment used by various industries provide the background to their use in agrochemicals. References
[51-56] cover the major methods of manufacture from the perspectives of
the industries in which they have been most prominent.) In Europe spray
drying was very common as a means of forming dyestuffs, whereas in the
USA pan granulation was used to agglomerate steel and coal. When
agrochemical products started to appear in the market, these techniques
were used in the respective continents. Examples are available of multinational companies selling the same product, but made by different granulation techniques depending on the country of sale [5O]. Clearly economics
was the most important factor.
The different technologies, however, produce materials which are quite
distinct in terms of the size and shape of the granule formed. Commercial
samples of spray-dried granules typically demonstrate wide size distributions (Figure 4.2). Essentially all of the material is below 0.3mm, compared
with extruded products where none of the material would be that small. The
extremes of size which are possible are most noticeable when granule
volumes are compared (Table 4.3).
lsoproturon
Captan
Figure 4.2 Examples of sieve fractions collected from commercial spray-dried WG samples.
Table 4.3 Comparison of size for single granules prepared by different manufacturing routes
Method
Spray dry
Extrusion
Pan
Relative volume
Average dimension (mm)
Range (mm)
Shape
1
1000
300
0.15
1.0 X 5.0
1.0
0-0.3
0.6-1.2
0.25-2.0
Sphere
Cylinder
Oval
The size of the granule is very important in determining the physical
properties of the product. For example, the time taken for granules to
disperse in water is related to how large they are (Figure 4.3). It has been
found that for the same formulation the key parameter in determining the
dispersion time is the diameter of the granule.
When it comes to dustiness and the dry properties of the formulation, size
is also important. In this case, separation of the dust formed during manufacture, the strength of the granules, and the difference in size between the
granule and what is perceived as dust are key factors.
The five types of granulator which are known to have been used to
produce agrochemical formulations are outlined in Table 4.4. The use of
high-shear mixers, however, is not thought to be very common at the
present time.
The two most popular forms of granulation are currently extrusion and
spray drying, the former being most prominent. These granulation methods
form quite different products in that one is large and cylindrical whereas the
other is small and spherical. There are other obvious differences, however,
Dispersion (sec)
Matrix mixer
Extrusion
Shugi
Linear (Extrusion)
Linear (Matrix mixer)
Linear (Shugi)
Diameter (mm)
Figure 4.3 The relationship between granule size and dispersion time for a single formulation
maufactured by three different methods.
Table 4.4 Some comments on the different manufacturing options for water-dispersible
granules
Product
Plant
Extrusion
Hard compact
granules
Optional size,
easy to scale up,
small recycle
Suitable for
heat-sensitive
materials
Versatile
Pan
Spherical,
usually soft
Optional size,
small recycle
Suitable for
heat-sensitive
materials
High operator
skill needed
Spray drying
Small spheres
like coarse
powder
Large scale
only, small
recycle
Not for heatsensitive
materials
Large air
throughput
Fluid bed
Uniform
spheres,
optional size
Optional size,
easy to scale up,
small recycle
Suitable for
materials of m.p.
>80°C
Large air
throughput
High shear
Irregularly
shaped granules
Large recycle
Suitable for
heat-sensitive
materials
Method
Restrictions
Comments
which arise from the mechanism of manufacture, for example the internal
structure formed within the granules.
Within any specific granulation area it is possible to tune a formulation so
as to form an acceptable product. Care must be taken when comparisons
are made between granulation methods because the nature of the formulation is also very important in determining the physical properties of the
product. In addition there are other factors, such as the particle size distribution of the starting powder which has been used. Examples of this are
shown in Table 4.5. Each sample is a commercial spray-dried formulation,
but the size distributions, and the formulation additives and active ingredients, vary. Sample 4 shows a higher level of respirable dust than the others,
but this is deceptive because the usage rate for this product is only 120g/ha,
whereas sample 3, for example, is used at 5000g/ha. Sample 1 is less dusty
than sample 5, but it is ten times as toxic, which perhaps explains the
extremely low dustiness of this product.
Table 4.5 Measurements made on five commercial samples of spray-dried water-dispersible
granules
Sample
1
2
3
4
5
Dustiness
(Heubach)
Dustiness
(Lorenz)
Dispersion (s)
d(4,3) (um)
sd (|im)
0.1
0.5
0.5
4.6
0.7
56.2
60.4
39.2
21.8
20.1
30
60
25
90
30
15.7
13.7
Soluble
8.6
4.7
40.2
18.3
Soluble
13.3
6.2
Two types of dust measurement have been used here, one concerned with
respirable dust and the other with the appearance of the product. Sample 4
has a large respirable dust content, but it does not appear to be as dusty as
the other samples.
It is clear that within each area of granulation it is possible to control the
physical properties of the product, either by engineering changes, careful
process control or by clever formulation. Comparison of different samples
is, however, made difficult by the wide difference in granule sizes. A major
benefit of the move towards extrusion is that it will allow standardization of
test methods. At the present time progress is being made in this important
area [57].
4.3 Physical properties
One of the primary purposes of formulation is to allow suitable physical
properties to be attained. Active ingredients have a variety of physical
properties of their own and this has led to a range of formulations which can
cope with this. Some of the properties of interest are specific to a particular
manufacturing route and reflect the size and shape of the granules which
form. A good example of this is spray drying, which tends to form highly
spherical, but small, granules. A consequence of the small size is that the
granules do not in themselves carry much momentum. Penetration of the
surface of a spray tank is therefore often difficult for this type and relies to
a large extent on the tap density of the bulk material. Tap density is of less
importance for other, larger granules although it is important that it is
constant during manufacture. This not only ensures room in the packaging
for each dose but also allows volumetric measurement at the site of application. Other properties such as granule size distribution can be of importance, depending on the particular manufacturing method.
The following properties are thought to be universally important:
• dry properties:
• strength;
• friability;
• dustiness;
• wet properties:
• dispersion time;
• dispersion quality (particle size/sieve residue);
• dispersion mechanism.
These physical properties are dependent on several factors. Three main
headings can be used to categorize the areas which are most important:
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Two types of dust measurement have been used here, one concerned with
respirable dust and the other with the appearance of the product. Sample 4
has a large respirable dust content, but it does not appear to be as dusty as
the other samples.
It is clear that within each area of granulation it is possible to control the
physical properties of the product, either by engineering changes, careful
process control or by clever formulation. Comparison of different samples
is, however, made difficult by the wide difference in granule sizes. A major
benefit of the move towards extrusion is that it will allow standardization of
test methods. At the present time progress is being made in this important
area [57].
4.3 Physical properties
One of the primary purposes of formulation is to allow suitable physical
properties to be attained. Active ingredients have a variety of physical
properties of their own and this has led to a range of formulations which can
cope with this. Some of the properties of interest are specific to a particular
manufacturing route and reflect the size and shape of the granules which
form. A good example of this is spray drying, which tends to form highly
spherical, but small, granules. A consequence of the small size is that the
granules do not in themselves carry much momentum. Penetration of the
surface of a spray tank is therefore often difficult for this type and relies to
a large extent on the tap density of the bulk material. Tap density is of less
importance for other, larger granules although it is important that it is
constant during manufacture. This not only ensures room in the packaging
for each dose but also allows volumetric measurement at the site of application. Other properties such as granule size distribution can be of importance, depending on the particular manufacturing method.
The following properties are thought to be universally important:
• dry properties:
• strength;
• friability;
• dustiness;
• wet properties:
• dispersion time;
• dispersion quality (particle size/sieve residue);
• dispersion mechanism.
These physical properties are dependent on several factors. Three main
headings can be used to categorize the areas which are most important:
1. granule size and shape;
2. pore size distribution;
3. quantity and type of binders.
4.3.1 Granule size and shape
The first of these areas, granule size and shape, has been mentioned
already, and is commonly used as a means of controlling properties such as
dispersion time. For example, during the life of the commercial product
'Cymbush', its diameter was changed from 1.2 to 0.6mm, in order to speed
up its dispersion in cold water (results taken from statistical analysis of
production figures over the period 1985-1989 at Zeneca's production plant
at Yalding, Kent, UK; Table 4.6). Figure 4.3 displayed the dependence of
dispersion time on granule diameter for samples made by different processes. This included spherical as well as cylindrical granules [58].
Granule size and shape also affect other properties such as dustiness and
strength. In terms of crush strength, the quoted figures for typical pangranulated material are often surprisingly low (say 10-2Og) [59, 6O]. Despite this, samples of commercially available product do not often appear to
have suffered excessive crush damage. The reason for these apparently
contradictory facts is of course the shape factor. Examination of a single
spherical granule in a crushing device demonstrates the problem. A sphere
cannot distribute the applied load in any way other than straight through
the middle of the granule. Compare this to an extruded shape, where the
granule lies flat, and it will be apparent that the extrudate has an advantage,
i.e. the volume which takes the load is significantly larger (Figure 4.4).
Nevertheless, a collection of spheres held within a volume can pack
efficiently, and in that case the load would be distributed in three dimensions. The result of this is that examination of a single sphere displays an
apparent weakness which is not seen when a gross sample is studied. Comparisons between the crush strength of different granule types is therefore
a pointless exercise. However, it is possible within any one granulation type
to measure crush strength and to use this as a criterion for design. In
practice though, the range of granule sizes present in samples, other than
Table 4.6 Average results made on successive production
campaigns on a commercial WG prepared at two different
diameters
1.2mm
0
Dispersion (s) (temperature, C)
Friability (%)
Dustiness (mg/g)
Dispersed particle size (^m)
0
152 (2O C)
2.0
2.2
25.0
0.6mm
135 (1O0C)
0.5
0.2
3.0
extrudates, makes examination of single granules very difficult. Examination of bulk attrition is considerably easier than examination of bulk
strength, and this has been the more common approach.
Properties such as dustiness are related to the surface of the granules and
reflect the ease with which particles can be scrubbed off the outer layers
[61]. In considering shape, the details of surface texture need to be taken
into account as these can influence this property. One study of a formulation showed that narrow-diameter granules can sometimes form with a
smoother surface than would larger-diameter samples. This can be effective
in reducing the dustiness of a product (Figure 4.5). In this example, granule
size apparently influenced a property, but it was in fact a change to the
surface texture that was responsible. Clearly care is required when analysing results. Spray-dried products, which tend to have smooth surfaces, often
display low surface abrasion dustiness, although the small size of the granules can lead to other dust-like properties [61].
Where granules are very small, they start to display the properties of dust.
An exact definition of the term dust is open to debate [62]. However, it is
clear that the greater the gravitational pull on the granule, the less likely it
is that dust-like behaviour will be observed. An example of this is shown in
Figure 4.6, which displays light obscuration from different size fractions
taken out of a spray-dried WG sample. The apparent dustiness measured
from the observation of a dust cloud settling under gravity is dependent on
granule size. This can easily be detected for granules up to about 0.3mm in
diameter.
Suitable dry properties tend to be favoured by large granules, whereas a
small granule would be preferred for fast dispersion. The balance between
the two demands, in the case of extrusion, seems to lie most favourably with
Figure 4.4 Uniaxial crushing force applied to a spherical granule and to a cylinder.
Dustiness mg/g
Binder %
Figure 4.5 Dustiness readings taken for WG samples at three diameters, plotted against
binder concentration.
Obscuration
seconds
seconds
seconds
seconds
Sl eve fraction
Figure 4.6 Light obscuration for different sieve fractions. Readings taken over various time
scales after pouring.
a diameter of about 0.6mm, although the ease of manufacture of the product may also be a factor which has to be taken into account.
The fact that granule diameter is so closely linked to both the wet and dry
properties has prompted work in the area of diameter control. In order to
produce very narrow diameters it has been found necessary to experiment
with new process technology, and this is at the present time an area of active
research [63]. A product which contains both a small and a large dimension
would appear to go some way towards satisfying both needs, and for this
reason extrusion, as a method of manufacture, is growing in popularity.
4.3.2 Particle assemblies and structures
The second factor mentioned, the pore size distribution within the granule
structure, has also been examined [58]. Where the particle size distribution
is kept constant but the porosity (density) of the granule is varied, it has
been shown that faster dispersion is possible where a more open structure
is present (Table 4.7). Unfortunately this also leads to weaker granules, and
the trade-off was found to be quite poor.
The use of open-granule structures would be complicated by the need to
control the degree of openness, and this, combined with the inherent weakness of such structures, argues strongly against this option for product design.
Extrusion is very good at forming dense granule structures. Where this
method is used, the pore size distribution formed and the internal surface
area present are principally governed by the particle size distribution of the
starting powder mixture (e.g. [64]). Powder samples have previously been
milled to different particle sizes and on these occasions it has been shown
that the finer samples were slower to disperse (Table 4.8; G. A. Bell,
Table 4.7 Physical properties of WG samples with differing
porosities and bonding strengths
Porosity (%)
41.7
95.5
52.2
80.7
Bonding
Dispersion (s)
Friability (%)
Strong
Strong
Weak
Weak
105
110
50
35
0.9
0.8
2.0
11.0
Table 4.8 Influence of particle size on the time taken for granule dispersion
Particle diameter (\im)
25.3
11.2
3.3
Granule dispersion (s)
15
25
50
unpublished results, 1988). The reasons for this are debatable, but possible
explanations are thought to be that with smaller particles, and therefore
smaller pores, the rate of intrusion of water, and the total surface area
which has to be wetted out, combine to slow down the dispersion process.
A water-dispersible granule can be regarded as a cluster of particles. The
cluster will have an external shape which may be quite complicated, and it
will have an internal structure with associated surface area, pore volume
and pore size distribution. Control of these factors should lead to control of
the physical properties of the granule, which is of interest with respect to
product design.
The importance of the pore size distribution has been examined with
reference to the liquid content required for granulation. Apart from the
quantity of liquid required, it also affects the basic rheological parameters
of the wet granule, and this in turn affects the degree of dispersion of the
powder [64] in the wet mass, during manufacture. It has been shown that
starting powders with wide size distributions lead to dense granules, with
small internal pore volumes and narrow pores. Close size distributions lead
to open structures with larger mean pore sizes, assuming the same mean
particle size for the starting powder.
We might expect, then, that a WG prepared with a broad range of
particle size would be different to one made with a narrow range. This
should influence several of the physico-chemical properties of the
formulation.
(a) Particle assemblies: wet agglomerates. Paste rheology is a complicated
area, and the relationships between individual particle interactions and the
bulk observation of flow are not well understood. Laboratory observations
have shown that the mean particle size is very important in determining the
quantity of water required, and also the ease of extrusion of a paste. Samples with fine particles often need large water additions and can display
dilatency, whereas samples with large particles need smaller amounts of
water, but the range over which they extrude can be small. The green body
strength of granules containing fine particles is usually higher as would be
expected from a consideration of Rumpff s equation [65, 66]. Note that //,
the bond strength holding the two particles together, usually has a particle
diameter term (d) depending on the type of bonding present:
=
•• -^(l - B]H
<4i>
where ot is the tensile strength of the agglomerate, e is the porosity of the
granule, d is the diameter of the particles which make up the granule and H
is the bond strength between each pair of particles in the granule.
The work of Newitt and Conway Jones [67] is often cited to explain the
behaviour of wet agglomerates. This compares changes in behaviour of the
Table 4.9 Quantity of water required to form a paste depends
on the particle size of the powder used
Particle size (|im)
2.6
9.4
24.2
Water requirement (%)
20.1
12.4
8.4
particle assembly as the pore volume within the granule becomes filled with
the granulating liquor. Much of the work carried out subsequently has
examined the behaviour of pastes at varying water contents [68-75]. Varying the amount of water used is one of the easiest ways to control a
granulation process. This is dependent upon the pore spaces between the
particles, and for this reason the particle size distribution of the starting
powder can be an important process parameter.
Studies on pharmaceutical samples of wet pastes have been carried out
with mixer torque rheometers and have shown the value of instrumentation
in assessing paste quality [76-89]. Particle size and the effects of the ingredients are both key aspects in determining paste behaviour, especially
where specialized materials such as microcrystaline cellulose are used. Such
specialized materials are usually avoided in the agrochemical industry because of the cost. However, recently there have been references to similarly
priced materials in the patent literature. This may indicate that these materials are becoming commercially viable, especially where agrochemical
tablets are concerned [90-94].
Typical figures for the amount of water required for extrusion are shown
in Table 4.9. In this instance the particle size spread was similar for each
sample. The volume of water required may depend upon the colloidal
forces operating within the wet agglomerate, as well as the degree of mixing, or shear, applied. In addition the soluble components will have an
effect. Consequently, prediction of the required water cut for manufacture
is difficult.
Broad size distributions should permit better packing which in turn
would reduce the internal void volume. We would expect to use lower water
additions under these circumstances.
(b) Particle assemblies: dry structure. When a load is applied through an
extrudate, there will be a distribution of force, and in the case where it is
greater than the strength of the granule, fracture will occur. All fracture is
tensile in nature, in the sense that crack propagation requires the surfaces to
move apart. We would expect granule strength to depend upon
• the nature and amount of the binding material holding the granule
together;
• the size and distribution of particles in the matrix;
• the strength of the particles.
Clearly, the variables outlined above are important and can be altered to
allow a change in the granule strength to be made. Table 4.10 shows some
typical data for extruded samples; the figures relate to the strength of
individual granules, and the quoted materials represent the bulk of the
particles which made up the formulations. As mentioned earlier, it is impossible to quote universally acceptable figures because of the limitations of
granule shape. Note, however, the remarkable strength of single granules
made from inorganic materials.
As the strength of a package of granules will be considerably larger than
the individual strength, there appears to be little to worry about from this
property. The exception would be where large amounts of liquid are
present within the granule formulation, since in that case there would be
more of a challenge. A commercial sample containing 25% of a liquid active
ingredient, however, was examined and found to have a crush strength of
235 g. This appears to be more than adequate for the conditions of use.
A wide particle or pore size range should lead to a granule which is
denser, and therefore stronger, than one formed from a narrow size range.
Consideration of tensile strength [65, 66] or resistance to bending moments
[95] also suggest that a smaller mean particle size will lead to a stronger
granule.
(4.2)
a? = f
where otis the tensile strength of the agglomerate, E is the elasticity of the
material, y is the surface energy of the material and d is the particle size.
The situation becomes more complicated, however, when other factors
are taken into consideration. For example, where a finer particle size is used
the surface area of the powder will be larger. Based on a unit mass of
material, there is a reciprocal-law relationship between particle size and
surface area, so that halving the mean diameter will increase the area by a
factor of two. For a similar binder loading there will be less material per unit
Table 4.10 A selection of granule crush strength values;
in each case a binding agent comprises about 10% of the
formulation
Material
Bentonite clay
Wetter/salt
Oil/silica
Pirimicarb
Crush strength of WG (g)
5217
3007
994
671
area. This may or may not influence the individual bond strengths within
the granule, depending on whether there is an excess present. At low binder
levels an increase in surface area may lead to a weakening of the structure.
Practical measurements made on model granules to determine the size of
these effects show that they are relatively small, covering a factor of about
two. Table 4.11 shows the results for a range of particles which vary by
about an order of magnitude and are within the practical limitations available for typical products.
As a complicating factor, particle size distribution can be included. This
makes analysis more complicated, but if we examine a range of mean size
and size distribution, then some idea of the range of crush strength values
can be gained (Table 4.12). This is considerably less than would be expected
from theory and may indicate that the strengths which have been realized
are in fact rather lower than is possible. Note that the particles used for this
series of experiments were very hard (calcium carbonate) and probably do
not take into account fracture of the particles themselves. Individual granule strengths of about 3kg are, needless to say, quite high.
The dustiness of a granule is known to be influenced by its surface
smoothness, i.e. to the ease of removal of particles from that surface. In the
case of an extrudate this will be strongly influenced by the rheology of
the paste used. Any dust which forms will be related to the particle size of
the starting powder. Finer starting materials may lead to finer dusts [96].
Table 4.11 Crush strength values for calcium carbonatedispersible granules are dependent on the particle size of the
starting powder
Sample
1
2
3
Crush strength (g)
3747
2887
2690
Mean particle size (^m)
2.6
9.4
24.2
Table 4.12 Particle size and size distribution (coefficient of variance) are influencing factors
on crush strength; a range of crush strength values displays the complicated nature of the
relationship
Crush strength (g)
4280
4008
3747
3376
3328
2887
2690
Particle size (^m)
Coefficient of variation (%)
17.4
13.7
2.6
16.8
6.7
9.4
24.2
135
160
123
158
112
93
105
Table 4.13 Dry properties of a WG are independent of one another
Dustiness
(mg/g)
2.9
2.2
2.1
1.8
2.3
2.0
1.6
Friability
(%)
Crush strength
(g)
Particle size
dim)
Size distribution
(%)
0.7
0.7
0.8
0.8
1.0
1.4
1.4
2887
4008
3747
3328
3376
4280
2690
9.4
13.7
2.6
6.7
16.8
17.4
24.2
93
160
123
112
158
135
105
Coarse powders, on the other hand, may lead to weak granules which
produce a coarse dust, whereas fine powders may form stronger granules
which, if they do break down, would be considerably more dusty in
appearance. A compromise in terms of particle size may therefore be better
in terms of product design.
Similarly, a broad size distribution may include a fine component which
has the potential to form dust, whereas the breadth of the distribution might
be expected to make the granules stronger (Table 4.13). The ideal distribution may have to be found experimentally.
(c) Particle assemblies: disintegration in water. In order that a granule can
disperse in water, it is important that the surfaces are initially wetted out.
Simple powder wetting considerations show that this will be related to a
y cosG term, and to the total surface area present [97]. The important
parameter when comparing different distributions of the same material will
therefore be the surface area. Smaller mean sizes or wide distributions
would be expected to take longer to wet out. Similarly the ease of penetration of water into a granule would be expected to be related to the pore
size, which in turn will depend upon the starting particle sizes.
The Washburn-Rideal equation [98, 99] suggests that large pores will
lead to faster penetration, and this points towards a narrow distribution and
a large mean size (e.g. [10O]):
d/
dt
=
rycosO
41H/
^
where dl/dt is the rate of penetration of the fluid, T] is the fluid viscosity, / is
the length of the capillary, r is the radius of the capillary, y is the air-liquid
interfacial tension and O is the contact angle between the fluid and the solid.
Dissolution of the binding material is a further complication which is
harder to quantify. For a set loading of binder, it could be argued that
spreading the material as a thinner layer will help to permit faster dissolution. Halving the mean diameter of the powder particles should in a simple
case allow the binder to be dissolved in half the time. However, this ignores
the fact that water penetration through the pores will be sequential, so there
is the potential for a rate-limiting step. Should the limiting step be dissolution, then fine particle size will lead to fast granule dispersion, but the
opposite would be true where pore penetration is critical. A real situation
may be a complicated version of both of these scenarios.
Where work has been carried out to determine the importance of size and
distribution on, say, dispersion time, the results have in general followed the
theory, although the scale of the effect was considerably less than expected.
Table 4.14 shows that the dispersion times vary by a factor of just over two.
Unfortunately, in this case, the dispersion times were all quite fast, so the
spread of results was rather narrow compared to the error in the measurement. Other examples of this type of work are not known and, therefore,
the conclusion at the present time must be that particle size does affect
dispersion time, but its effect is relatively small.
In addition to the wetting-out and dissolution steps, there will be the
process of particle separation. This is an area which is not well understood
at the present time, although some work has been done to understand the
contributions of the various viscous, electrical and steric effects. A starting
granule represents a very high concentration of particles, and as these wet
out and disperse, the nature of the paste or slurry that forms will change.
Clearly the interparticle spaces will be important in determining the behaviour of the concentrated dispersion that forms (discussed later). After complete dispersion, a consideration of the sedimentation rate of the individual
particles should provide some idea of the ease with which they can be swept
away by any agitation that is supplied. This, however, represents the final
step of the dispersion process, and the area between this and the binder
dissolution should not be ignored:
(]?-& Ap
sedimentation rate a —2—*-
(4.4)
T)
Table 4.14 Dispersion time in water is related to particle size,
but size distribution also has an effect
Dispersion time (s)
25
30
35
35
40
50
60
Particle
diameter
(l*m)
24.2
9.4
17.4
6.7
16.8
13.7
2.6
Standard deviation (%)
104
93
135
111
158
160
122
where d is the diameter of the settling particles, g is the gravitational
constant, Ap is the density difference between the particle and the fluid
and T) is the viscosity of the fluid.
4.3.3 Quantity and type of binders
The quantities and types of binders present in granule formulations are also
major contributors to the measured physical properties (e.g. [101-114]). It
is known, for example, that increasing the level of a dispersant increases the
dispersion time in a roughly linear fashion. A minimum quantity of binder/
dispersant, however, is required to prevent ageing, and to allow for complete dispersion, and there is therefore a balance between this and the need
to reduce the level in order to obtain fast dispersion.
Similarly, the other granule properties, particularly the wet ones, are also
influenced by the dispersant level. The dry properties are less obviously
linked. However, the dispersant influences the rheology of the paste used in
extrusion, and this in turn affects the surface smoothness of the granules.
Surface texture has been shown to influence properties such as dustiness.
Where a combination of dispersants and binders are used, it is clear there
is synergy between the components (see later). Balancing the dry and wet
properties is therefore possible by using the right combination of ingredients, for example with a binder, dispersant and wetter.
In practice, the formulation is normally altered until the best compromise
has been reached, at which point the diameter of the granule will be examined to fine tune the product further. This sequence tends to arise because
the formulation will become fixed quite early during the development process, whereas the diameter can be selected at a later date.
If we consider the dry properties of a granule, then it is clear that there
are three areas of interest, namely the crush strength, friability and
dustiness.
(a) Dry properties: granule strength. Figure 4.7 shows the crush strength
results for WG samples prepared using both 6 and 10% loadings of different
surfactants and combinations. Obviously the granules become stronger as
greater amounts of binding materials are added. The different binders show
different efficiencies in their ability to impart strength to the WG samples,
each of which has been prepared with the same active ingredient powder
sample. Synergy has often been observed in WG research, so one important
question relates to these possible interactions. In this case the situation is
very simple in that the effects seem to be additive. This is demonstrated
in Figure 4.8 where practical binder mixture results are compared to the
expected results from the pro rata addition of the individual component
effects. Each individual binder result was divided by the concentration used
and this was added to the account for the mixture sample, along with values
Comparison of Granule Hardness For WGs Containing 6 & 10 %
Surfactant
Granule Hardness (g)
10% Surfactant
6 % Surfactant
Binder
Disp.
Wetter
Disp./
Wetter
Disp./
Binder
Wetter
Binder
ALLS
Sample Content
Figure 4.7 Granule crush strength values from a range of binding agents.
Calculated and Actual Granule Hardness Results for WGs Containing
Various Surfactants
Hardness (g)
Calculated
Actual
EFW and D425
D425 and PVP
EFW and PVP
Granule Components
D425/EFW/PVP
Figure 4.8 The crush strengths of granules prepared by using mixtures of components can be
calculated by summing the individual contribution from each binder. Generally the mixture is
found to be stronger than expected by 15-20%.
for the other ingredients in the formulation. As can be seen, the fit is very
good, being accurate to within 20% of the real figure. The actual figures are
consistently higher than the calculated ones, and this may be evidence of a
small amount of synergy.
(b) Dry properties: friability. It was thought at one time that granule
hardness, friability and dustiness were all related factors. The surprising
results indicating that they were independent led to confusion until it was
realized that crush strength or hardness was a bulk property, whereas the
other two were related to surface damage. As friability and dustiness tend
to measure different particle size fractions, the fact that these properties are
different is also explainable. The term friability, however, needs to be
defined.
Where large granules are made and sold, there is a concern that they will
break up in transport, and this will lead to small fragments in the packaging.
These fragments may be as small as dust, and have the problems associated
with dust, or they may simply detract from the visual appearance of the
product. A simple sieve test applied after some form of attrition is therefore
common, and typically the size range studied would be below 0.25 or
perhaps 0.15mm (G. A. Bell, 1987, results of a survey carried out in the UK
showing that sieving with a 150 pirn sieve was the most common approach
used, British Agrochemicals Association WG sub-group, unpublished
results). The use of a friability machine is also known, although this has not
been standardized across the industry (several methods are available commercially; for references to nine see [115]).
Examination of the material below 250 pirn in commercial samples shows
that it contains a variety of fragments and primary particles. Whereas the
crush strength of a WG responds directly to the addition of larger amounts
of binder, this is not the case with friability [96]. Figure 4.9 shows some
typical results, in this instance based on granules which have been shaken
gently for 20min. The minimum in a plot of friability against binder level
has been observed for some samples after the application of this test, but
only in cases where very high friabilities were found. It is thought that in this
case the data points were essentially random.
(c) Dry properties: dustiness. Dust can be created during the production
process, in which case it will be present all the way through the life of the
product, up to the point where it is dropped into the spray tank. Alternatively it can form during handling. The term dust is not specific enough on
its own because there are several aspects, or problems, associated with
broken granules or fine material. The dust which is visible is likely to be
very small in size, especially where it has the ability to hang in the air. This
is the worst sort of dust because it represents an inhalation hazard to the
user [62]. Apart from the risks due to toxic ingestion, there is also a consid-
Friability (%)
Binder (%)
Figure 4.9 Variation during sample preparation often outweighs the friability benefits gained
from higher binder loadings.
erable nuisance factor associated with fine dust, for example because it is
visually unattractive. Wetting agents are a common ingredient in the formulation of water dispersible granules and these have a noticeably irritating
effect on the mucous membranes of the inner nostrils. Where dusts form,
these materials often cause problems.
The question as to how fine a dust is can be misleading, because this
concentrates on the size rather than the quantity present. Both factors have
to be taken into consideration, as does the source of the dust. The reason
the source is important is that much of the dust which causes a problem is
formed during pouring and handling, and may not be present until the
package is opened.
The term dustiness is difficult to define per se, other than to define it as a
quantity measured by the use of a particular dust tester. There are three
types of dust tester which are commonly used in the agrochemical industry
[116], and these examine two different size ranges of dust. Heubach and
Cassella dustmeters (Heubach Eng. GmbH, D-3394, Langelsheim,
Germany; the Cassella dust-measuring method has been adopted as CIPAC
method MT 171, apparatus available from Hoechst AG, Abt. IngForschung, PO Box 80 03 20, D-6230, Frankfurt, Germany) examine the
dust which can be picked up from the surface of a granule in a stream of air
and as such they are commonly thought to represent the inhalation process
and to produce a measure of the risk posed by respiration. The Lorenz dust
tester covers a wider size range of dust and correlates well with the visual
appearance of samples (Lorenz Messgeratebau, Max Planck Strasse 1,3411
Katlenburg-Lindau, Germany). Visual examination of samples is able to
take account of a wide range of particle sizes and, as it is an optical assessment, also measures light scattering efficiency. The use of a laser beam to
measure the visual effect the dust has on the appearance of a WG is
therefore sensible. Note that the Cassella can also be used with an optical
sensor.
Figure 4.10 shows two particle size analyses, one taken from the dust
drawn off from a WG in a Heubach test, and the other by dispersing the
gross sample in water. Clearly the dust is considerably finer than the average from the starting granule, and this represents some form of particle size
segregation.
Figure 4.11 shows the results of dust collected against time from two
different samples of WG. The two samples were selected from a range, and
were the most, and least, dusty samples available. The two lines on the
graph are straight, which indicates that the dust has formed from the motion
of the granules in the tester. Presumably this represents fine particles being
scraped off the surface as the granules slide past one another.
In order to formulate a granule which is low in dust, we might expect that
higher loadings of binder would be effective because they would allow
greater quantities of glue to be attached to each surface particle. The
problem is, of course, that the amount of glue on the surface is less critical
percentage
Granule 0(4,3)36.1 |^m
Dust mean size D(4.3) 5.9 u,m
Particle size (^m)
Figure 4.10 A comparison between the dispersed particle size from a water-dispersible
granule, and the dust particle size extracted by an air stream apparatus during a dustiness
measurement.
than the texture of the surface, hence we find the results shown in Figure
4.12. Here the quantity of binder is relatively unimportant over a range of
3-8% w/w.
The quantity of dust which is being measured in this type of experiment
is usually very small, say 0.1% w/w of the overall formulation. Adding large
quantities of binder in order to tie down this small fraction of particles
Signal from low dust sample X10
Dustiness (mg/g)
High dust
Low dust
Time (min)
Dustiness (mg/g)
Figure 4.11 Dust collected from two WG samples in a Heubach dust meter. The quantity of
dust given off varied by about two orders of magnitude.
Binder (%)
Figure 4.12 Dustiness, which is a surface property, shows little dependence on binder
concentration.
seems excessive but it is, of course, very important for safety reasons. The
use of oil as a de-dusting agent is known to be effective. However, great
care must be taken so that the benefit is present over the lifetime of the
product, because oil is known to be absorbed into granule structures
with time.
The visual appearance of dust is, perhaps, better analysed using a Lorenz
tester [116]. Small amounts of fine dust will clearly detract from the visual
appearance of a granule and it is clear that effective sieving of the product
is essential. Formulation can alter the surface smoothness of the granules
and this would appear to be the best way to prevent the formation of dust
during handling.
Particle size (urn)
(d) Wet properties: degree of dispersion. Adsorption isotherms carried
out to ascertain the quantity of dispersant required to form a monolayer on
typical WG samples showed that it was about 0.5 to 1 % w/w for a sample
with a particle size of lOjim. Surface coverage by lignosulphonates
and naphthalene sulphonates typically displays strong Langmuir-type
isotherms, and the adsorbed dispersants do not desorb on dilution. Based
on these data, it might be thought that a suitable fine dispersion could be
formed from a WG formulated with this amount of dispersant. This has not
been found to be the case and it is well known that ten times this amount
would be more typical (Figure 4.13).
Examination of a dried granule by sectioning often shows a significant
concentration profile of the dispersant, the centre being leaner than the
exterior. This is a consequence of a chromatographic effect brought about
Dispersant (%)
Figure 4.13 Below a critical threshold of dispersant, aggregation can easily be detected.
Dispersion (sec)
by the high solubility of most dispersants, and the drying mechanism which
siphons the dispersant solution out through the pores between the particles
[117]. Clearly then, a lot of the dispersant is not available for surface
coverage, although this does not explain the basic aggregation phenomenon. Where strong isotherms have been observed, it is possible to dry and
redisperse particles without loss of the dispersant to the solution phase.
Further evidence which relates to the problem comes from spray drying,
where it is known that a residual water level is essential for good dispersion,
depending on the particle size of the slurry used. It would seem then that
particle coating by the dispersant is the least of the problem, but that
dispersed particles which come into intimate contact have a habit of aggregating. There are many explanations which could be given to explain this.
However, as it is a common enough phenomenon from other areas of
particle technology, there is no need to do so. A large excess of dispersant
is essential, and part of the reason for this appears to be in order to provide
multiple layers between the particles during drying.
Gross failure of the dispersant system occurs over quite a narrow range of
concentration (Figure 4.13). For this reason, an excess of dispersant is
highly recommended, but there are other aspects to this that should also be
stated. For example, ageing is a very common occurrence and has been
observed with most types of WG product. The ageing of solid formulations
is well known and is often associated with the movement of water soluble
components with time. This is well illustrated by examining salt granules at
different temperatures (Figure 4.14). Most formulations will be required to
have a long shelf life, and this should be used as a criterion for selecting
the optimum dispersant concentration. If it is accepted that a certain degree
of mobility will occur, then the control measure to prevent ageing would be
Age(days)
Figure 4.14 WG ageing is known to be temperature dependent.
Table 4.15 Effect of dispersant concentration on dispersed particle size
Particle size
Fine
Medium
Coarse
Dispersant 1
10%
Dispersant 1
20%
Dispersant 2
10%
Dispersant 2
20%
7.4
8.3
9.0
3.8
4.7
9.3
7.3
14.4
9.3
4.6
5.2
9.3
the concentration used. A less mobile ingredient may suffice at a lower
concentration.
The particle size of the powder used to form the granule is clearly one of
the most important factors in determining the degree of dispersion
achieved. As the size is reduced, the surface area will be increased, and this
will influence the quantity of dispersant required. Table 4.15 should give
some idea of the importance of this effect.
In the case of the coarse powder, 10% of either dispersant was enough,
and little evidence of aggregation could be observed by microscopic examination. Where excess was added it was not beneficial. A small amount of
aggregation was seen for the medium-sized samples, in this case 20% dispersant would be chosen as it reduced this to an acceptable amount. The
sample with a fine particle size was highly aggregated in all cases; this
sample contained submicron primary particles and the problem was related
to poor deaggregation prior to granulation. Although an increase in the
dispersant quantity clearly helped, the problem was in fact related to grinding of the starting sample.
(e) Wet properties: speed of dispersion. Sodium lauryl sulphate has been
reported as an additive for pharmaceutical solid dosage forms, its purpose
being to enhance wetting and improve dissolution rates [118]. Similarly in
the agrochemical industry, wetting agents such as silicone copolymers or
fluoroaliphatic surfactants [119] have been quoted as useful ingredients for
enhancing the rate of dissolution of pesticide water-soluble or dispersible
granules.
The exact effect of a given surfactant on a particle surface will be determined by the degree and mode (orientation) of its adsorption on the various interfaces, and the reversibility of that adsorption [12O]. Some evidence
to support this is available from experiments carried out on pharmaceutical
tablets.
The Washburn equation relates to the rate of penetration (dl/dt) of a
liquid of viscosity TI in a capillary of radius r and length /:
where y is the interfacial surface tension. Thus to facilitate penetration of
the liquid we would want to
• maximize YLV cos 9;
• minimize the viscosity (TJ);
• maximize pore size.
If we consider the granule structure to be a simplified assembly of pores,
then the Washburn equation is potentially a mathematical model by which
to identify the important physical characteristics of the dispersants and
binders which are incorporated into the granule formulation.
The dispersion process covers a range of concentrations, starting with a
solvent-free system and finishing with a very dilute one. The viscosity of the
binders and dispersants present must therefore be examined over a similar
range of concentrations. Some kinematic viscosity data for typical dispersants are shown in Figure 4.15.
The types of materials which are commonly selected are obviously those
which dissolve readily, and are usually free from liquid crystal formation,
such as polyelectrolytes. Where polymers that can gel are used, care is taken
to control the amount present such that this does not lead to dispersion
problems. Note, for example, that the grade of PVP shown in Figure 4.15 is
rarely used at levels higher than about 2% w/w, which is the point where its
viscous behaviour becomes important.
It was at one time thought that wetting of the pores of the granule would
be a critical factor in determining the dispersion time. The data in Table
4.16, however, show that this is inconsistent with theoretical models of
wetting which depend on a y cos 6 term (G. A. Bell, presentation made to
the Royal Society of Chemistry, London, 6 April 1997). Instead, the key
viscosity cSt
Morwet D425
Morwet EFW
PVP
D425/EFW(1:1)
D425/EFW/PVP (1:1-1)
solution concentration (%w/w)
Figure 4.15 The variation of dispersant viscosity with concentration is an important basic
property of the material.
Table 4.16 The term y cos 9 is commonly used in descriptions of capillary penetration; typical
binders, wetters and dispersants used in the agrochemical industry show similar values, and are
not very different to that for water
Ingredient
Surface tension (yLv)
Contact angle (9)
yLV cos 9
48.3
31.2
35.2
-79
61
O
33
68
23.4
31.2
29.5
26.2
MorwetD425
MorwetEFW
PVP
Water (deionized)
dissolution time (s)
Geropon T36
Tamol PP
Morwet D42S
Morwet EFW
Disp-SS-Dry
PVP
disc thickness (I)
Figure 4.16 Pressed tablets of typical dispersants dissolve linearly with time.
parameter seems to be the rate at which the binders dissolve. Evidence for
this comes from an examination of pressed discs of the binder materials.
Figure 4.16 shows that the dissolution behaviour is essentially quite simple,
with linear plots of thickness against dissolution time.
If we correlate the dispersion times of larger granules with the relative
dissolution rates of the binders which were used to hold them together, then
a linear relationship is apparent. (One of the problems associated with the
dispersion times is that they are closely related to the size of the granules
used. To improve the accuracy of the test method, it can be convenient to
use larger granules where the size can be more accurately controlled. The
size used in these tests was 3mm.) The effect is shown for three different
starting powders (Figure 4.17). Note that as the powders had different
starting particle sizes, they display different gradients.
Dispersion time (sj
China day (GTY)
Carbendazim
Talc ATExtra
Rate of Dispersant Dissolution (mm/min)
Figure 4.17 WG samples disperse according to the dissolution rate of the binder used to hold
them together. Three different powder samples were used to display the effect of particle size
and surface hydrophilicity.
It is well known within the agrochemical industry that the addition of
wetting agents can produce faster-dispersing granules. It was once thought
that this was a consequence of faster penetration of the pores. However, as
mentioned earlier, this is now thought to be incorrect. Examination of the
effects produced by wetting agents leads to the conclusion that very small
quantities are required. Figure 4.18 shows the effect of adding varying levels
of alkyl sulphosuccinate to a granule which contains a typical polyelectrolyte (Morwet D425) as the principal dispersant.
Here the effect is apparent with a one-hundredth part addition. Where
10% of Morwet D425 is used, this would equate to a 0.1% formulation
addition of the wetter, clearly a highly effective way of reducing the dispersion time. The rise in dispersion time evident at higher loadings of alkyl
sulphosuccinate is associated with an increase in viscosity. Good wetting
agents, which act at the air-water interface, of necessity show poor, and
slow, water solubility. A solubilizing surfactant is required to enhance their
rate of dissolution and to prevent gelling. It is believed that the product
Morwet EFW acts in a similar fashion, although this has not been confirmed
by the manufacturer (Figure 4.19). In this instance the rate of dispersion has
been doubled by adding a one-tenth part of the wetter to the dispersant,
and it is clear that the gelling problem does not arise at higher loadings.
Morwet EFW is a common ingredient in many WG formulations, and
dissolution rate (s)
[Aerosol OTB] %w/w
Dissolution rate (s)
Figure 4.18 Dissolution rates of tablets prepared from a typical binder/dispersant benefit
greatly from the addition of a small amount of wetter, in this case 1 % w/w. Higher loadings
lead to viscosity problems.
Morwet EFW cone (%w/w)
Figure 4.19 Dissolution rates of tablets prepared with a wetter which displays low viscosity at
high concentrations.
Dispersion time (s)
appears in many patent applications. The exact composition, however,
has not been disclosed, and as a result there has been little published
work which examines the behaviour of this interesting blend of ingredients
[121-126].
Elucidation of the effect brought about by wetting agents was made by
examining the dissolution of dispersant discs in solutions of different
wetting agents (G. A. Bell, presentation made to the Royal Society of
Chemistry, London, 6 April 1997). This showed that the dispersants dissolved more rapidly when dynamic surface tension reducing agents were
employed. Figure 4.20 shows a plot of dynamic surface tension against
dispersion time for large water-dispersible granules. A similar plot, with a
better correlation coefficient (0.97), has been measured for the dissolution
of dispersant discs in solutions of the dynamic wetters.
It would appear then that the wetting agent is able to increase the rate at
which the binding agent dissolves. The final piece of evidence which is
available to add to the current state of knowledge about granule dispersion
comes from an examination of the concentration behaviour of non-ionic
wetting agents which display good dynamic activity. Figure 4.21 shows that
the ability of the wetter to dissolve a block of dispersant begins at concentrations of about 0.5% w/w. Clearly this is well above the CMC (critical
micelle concentration) of the surfactant and it may be concluded that the
effect is genuinely a dynamic one.
DST (m N/m)
Figure 4.20 The most efficient wetting agents for a reduction of dispersion time for waterdispersible granules are those which display low dynamic surface tensions.
Dissolution rate mnVhr
Surfactant concentration %
Figure 4.21 The concentration of wetting agent required to reduce the dispersion time of a
water-dispersible granule is well above the CMC. This occurs because it is a dynamic effect.
4.4 Design: modern methods
The design of a water-dispersible granule, as with the design of most formulations, is a balancing act to achieve the best properties of each ingredient,
without upsetting those of the other ones (Figure 4.22). The balance insofar
as granule size and particle size are concerned can be shown diagrammatically with respect to four of the key physical properties (although note
should be made that the theoretically ideal position for dustiness has not
been verified practically). Similar conflicting requirements can be specified
for the ingredients used to formulate a WG (this problem was outlined by
H. T. Delli Colli of Westvaco Products, where a three-pointed star was
used to convey the conflict between dry strength, dispersion time and
suspensibility). The properties which are of concern tend to drive the formulation chemist in opposite directions, and there appears to be little that
can be done about this, other than to reach a compromise.
The task of formulating a water-dispersible granule is much the same as
for any other type of product; it requires sample preparation and testing
followed by a good deal of iteration. Methods which have been employed to
try to simplify this problem include the use of techniques such as statistical
experimental design [127-131]. These techniques can be useful, especially
for process examination, but there are problems associated with this approach when applied to formulations.
High crush strength
Low (lustiness
Granule size
Fine suspension
Fast dispersion
Particle size
Figure 4.22 Optimizing a formulation is complicated as different physical properties require
different combinations of granule and particle size.
One problem is that the ingredients in a formulation are not independent
of one another. This leads to the use of triangular diagrams rather than
square ones, which complicates the analysis of any response surfaces which
are found. In addition to this, the number of variables, even for a relatively
simple formulation, is large, which leads to an excessive number of surfaces
which need to be examined. Recently there have been attempts to shorten
this process, and although the results have not yet supplanted the standard
formulation method, they hold out a good deal of hope for the future. One
area in particular, the use of neural networks, is worth mentioning.
Expert systems have been available for many years and have been used
to dramatic effect in many industrial applications (e.g. [132]). One obvious
limitation, though, is that in order to set one up in the first place there is the
need for an expert to supply the rules of thumb and theoretical backing
material. In the area of agrochemicals there are many undoubted experts.
However, the diverse nature of the WG product and the range of ingredients available are serious limitations which those individuals have to
contend with. In addition to this, the cost and effort required to set up good
expert systems have so far prevented their common adoption.
Neural networks, on the other hand, are inexpensive and easy to set up,
being commercially available as Windows-driven software packages (e.g.
[133]). Mention was made earlier of the common occurrence of synergy.
Although it is often claimed that predictive packages can cope with this, it
is nevertheless an added complication which increases the difficulty of the
task.
Table 4.17 Examples of the ability of a commercial neural network system to predict the
physical properties of a WG formulation
Property
Constraint
Constraint met
Predicted value
Actual value
Dispersion time
Wet sieve residue
Dispersed particle size
Dustiness
Hardness
Tank residue
<75 s
<0.1%
<35um
<2.0mg/g
>450g
<5%
No
No
Yes
Yes
Yes
Yes
23 s
-0.1%
21.9 um
1.9mg/g
466 g
2.0%
94 s
1.6%
20.3 um
1.8mg/g
795 g
3.6%
There does not appear to have been much work reported in the literature
on WG formulation using neural networks, although some work has been
done to test the system (G. A. Bell and S. E. Skelton, unpublished results,
Zeneca Agrochemicals, 1996). Data relating to the formulation of ten
samples of a WG containing an AI and three further ingredients (wetter,
dispersant and binder) were added to a commercial neural network package. The package was then asked to optimize the formulation, at which
point the optimized formulation was prepared. Table 4.17 shows the constraints which were made prior to computation, the predicted results and
the actual results which were measured practically.
The task which was set in terms of the criteria for success was not
impossible. In fact, one of the formulations fed into the database met all
of the requirements (except for dustiness, which was 2.2mg/g instead
of 2.0mg/g). The neural network formulation was placed roughly in the
middle of the list of formulations in terms of its overall performance. The
fact that the formulation did not meet all of the requirements, however, was
not seen as a total failure. It met six out of nine constraints and it was
remarkably accurate in predicting dispersed particle size and dustiness, two
key properties of the formulation. If network systems such as these can be
used to predict some of the physical properties, then they will undoubtedly
find a use in most laboratories across the world. At the present time,
however, this remains to be proven.
References
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5 Recent developments on safer formulations of
agrochemicals
P. J. MULQUEEN
There is an increasing need for the crop protection industry to continue
to develop new products and delivery systems which are optimized with
regard to safety, environmental behaviour, biological performance and
cost. Agrochemical products are often perceived to be hazardous. Products
may often have a high acute toxicity profile and problems are encountered
with handling, application and use of products. Whilst considerable efforts
have been focused on improvements to the handling of pesticides in the
transfer between pack and spray tank, with closed transfer systems being
introduced and better application knowledge permitting improved application techniques, there has also been much greater attention paid by formulation scientists to maximizing the activity of a particular pesticide. This is
being achieved by a more complete understanding of the mode of action of
a pesticide, of how that pesticide interacts with adjuvant chemicals and
thereby often the preparation of specific mixtures to optimize the biological
performance. These studies often lead to an increase in the inherent toxicity
of a product. Superimposed on this knowledge base, the formulation
chemist still has to work with the key drivers which affect the final choice of
formulation. These include
•
•
•
•
•
•
•
•
physical and chemical properties of the pesticide;
biology (activity and crop selectivity);
application;
safety;
registration requirements;
cost;
suitability for large-scale manufacture;
shelf life.
With an overall stagnating market and increasing regulatory requirements concerning user safety and environmental compatibility of their
products, innovative solutions to emerging customer needs become allimportant. Under 'responsible care' activities it is necessary to inform the
public of the benefits and risks of products and to aim for continuous
improvements in product handling systems with regard to safety for the
user. The main targets concerning the protection of the environment
include saving resources with better products and manufacturing processes,
introducing environmentally compatible products, and minimizing waste by
optimizing production processes and packaging designs.
Over the past 10 years, much progress has been made in the design and
development of new formulations and packaging options. In particular, by
reduction of organic solvents in liquid formulations, the environmental
impact and toxicity of products may be reduced. A reduction in dermal
toxicity may be obtained by encapsulation of the active ingredient. Improved worker and environmental safety is also achieved by replacing
powders with water-dispersible granules which can minimize dusting during
handling, or by packaging them in water-soluble film, which offers a variety
of advantages. Seed treatment provides an elegant way to minimize the
amount of chemical needed, by placing it directly where it is needed at the
right time.
In terms of packaging strategy, waste reduction and improved handling
safety are prime considerations. Refillable container programmes aimed
at larger growers and custom applicators will contribute to the reduction
of one-way packaging and associated secondary packaging. For smaller
growers and also for the use of highly active compounds, the introduction of
solid formulations and gels, which can be packaged in water-soluble film, is
a means by which a reduction in packaging waste can be achieved.
This chapter will review progress in the development of safer formulations of agrochemicals, which lead to an overall improved and safer performance of a pesticide.
5.1 Introduction
Formulations should be easy to reconstitute, measure or meter and transfer
to the application equipment. Mobile liquids and free-flowing granules are
the easiest types to handle. They should present no problems of filter or
nozzle blockage or leave residues in the application equipment which are
difficult to remove. Compatibility with other products is important.
Dermal penetration of the active ingredient through the skin is the major
route by which pesticides enter the body. Formulation type can influence
the penetration of both protective clothing and skin itself. Pack decontamination is also critical. Formulations and pack design must allow rinsing to
the accepted standards to be achieved.
Formulation safety is usually concerned with mammalian toxicity, but it
can also be related to environmental toxicity, crop selectivity and manufacturing safety. Four ways in which formulations can be made safer therefore
are as follows.
• High-quality liquid formulations (EC, SC, EW, SE, SL and ME) for
conventional or returnable containers:
• low dermal toxicity;
• mobile, easily metered and rinsed;
• preferably of low or zero solvent content;
• good spray tank compatibility.
• Controlled release formulations. A significant step towards increased
safety for the user may be obtained by encapsulation of the active ingredient. As has been shown for some insecticides, capsule suspensions often
show a remarkable reduction in oral and dermal mammalian toxicity as
compared to emulsifiable concentrate (EC) formulations. Moreover,
encapsulation may also offer an advantage with pesticides which are
volatile.
• Products in water-soluble packs. The problems with all wettable powder,
granule and liquid formulations relate to dispersibility and compatibility
of the water-soluble film. It is necessary to select a film compatible with
a given product or to modify the composition of a product to make it
compatible with an existing film.
• Non-dusty formulations. The use of non-rigid packaging minimizes the
bulk of contaminated packaging for disposal. Water-dispersible granule
(WG) formulations have been available for many years and are now
widespread. The use of tablets is of particular interest with compounds of
low application rates. Gel blocks or tubes also provide a means of formulating materials in a dust-free, non-spill form with reduced pack disposal
problems.
Improved packaging design and the formulation types WG and SC are
topics discussed at length in other chapters and will therefore not be discussed further.
The major routes to making a formulation safer are to reduce or eliminate the solvent or to prevent the active ingredient from coming into
contact with unintended targets. Clearly, dry products are important in this
aspect, but also the removal of solvent and, crucially, replacement of that
solvent by water so that the continuous phase is water, has a considerable
impact on the toxicity of a formulation.
A variety of formulation types are presented in Table 5.1 with the advantages and disadvantages listed for each. Granules (dry applied) currently
have major markets in soil insect control and pre-emergent weed control, as
well as speciality markets. In all likelihood this will continue to be a niche
market in the future with the advent of genetically encoded seed (Bacillus
thuringiensis expression in corn) changing certain markets (European corn
borer control). Tablets have been reintroduced recently which contain
glyphosate for retail home use. It is unlikely that tablets will ever have the
impact of water-dispersible granules, and again will fill niche needs. Gels
have received recent scrutiny based on the large number of patents generated by Rhone-Poulenc, where they claim gels in polyvinyl alcohol (PVA)
Table 5.1 Common formulation types and their characteristics
Main ingredients
Advantages
Disadvantages
Wettable
powders
Active ingredient
Absorbant/carrier
Wetting agent
Dispersant
Cheap to produce and
pack; easy to handle;
tolerant to low
temps; no solvent
Produces dust; difficult
to measure and mix;
poor efficacy and
rainfastness; may
block lines and
nozzles; some active
ingredients degraded
by certain filters
Emulsifiable
concentrates
Active ingredient
Solvent
Emulsifier
Activator
Easy to produce;
easy to handle and
mix; useful for
water-insoluble, low
melting point active
ingredients; high
efficacy
Expensive to pack and
transport; sensitive to
freezing; risk of
thickening; can cause
phytotoxicity; may be
corrosive to metal
and plastic; often
toxic and volatile;
may be sensitive to
water hardness
Granules
Active ingredient
Binder
Carrier
Easy to handle and
pack; no solvent; low
drift; long residual
activity; low
phytotoxicity
May be consumed by
non-target organisms
(especially birds);
may be expensive;
need specialist
application
equipment
Soluble
concentrates
Active ingredient
Wetter
Surfactant
Water (or watermiscible solvent)
Cheap and easy to
produce; no solvent;
low volatility; low
phytotoxicity; easy
to mix
Expensive to pack
and transport; frost
sensitive; may
corrode metal;
cannot contain high
active ingredient
concentrations; poor
rainfastness; poor
wetting and spreading
Suspension
concentrates
Active ingredient
Absorbant/diluent
Wetting agent
Dispersant
Thickener
Anti-freezing agent
Anti-foaming agent
Preservative
Water
No solvent; can
contain high
concentrations of
active ingredients;
easy to mix and
store; compatible
with aqueous
concentrates
Difficult to produce
successfully; can
settle out in storage;
sensitive to
freezing; can cause
phytotoxicity;
sensitive to active
ingredient purity and
form
Concentrated
emulsions
Active ingredient
Emulsifier
Solvent
Thickener
Anti-freezing agent
Anti-foaming agent
Preservative
Water
Minimal skin and eye Time-consuming
irritation; less, or no,
development effort;
solvent; minimal
container disposal;
phytotoxicity; low,
little, or no,
or no, flammability;
manufacturing
ease of incorporating flexibility
adjuvants
Table 5.1 Continued
Main ingredients
Advantages
Disadvantages
Capsule
suspensions
Active ingredient
Solvent
Emulsifier
Dispersant
Thickener
Anti-foaming agent
Preservative
Wall-forming agent(s)
Low dusting; easy to
handle; low solvent;
low toxicity; less
prone to leaching;
long residual activity
Need expensive
production
equipment; sensitive
to freezing; may
thicken at high
temperatures;
expensive to package
Tablets
Active ingredient
Lubricant
Binder
Disintegrant
Easy to use; less risk
of incorrect dosage;
minimal packaging
Only suitable for
highly active
ingredients
Water-dispersible
granules
Active ingredient
Absorbant/carrier
Wetting agent
Dispersant
Low dusting; cheap
to pack; easy to
handle and measure;
tolerant to freezing;
no solvent
Needs expensive
production
equipment; dispersion
is affected by low
temperatures
as a delivery form [I]. This is an excellent way to improve the safety of an
otherwise restricted-use pesticide (Buctril) when other formulation and
packaging options do not exist, but the cost is high. Microcapsules have
been proven to extend residuality of control for certain actives over conventional delivery forms, but also have been shown to reduce the teachability
of certain actives into groundwater due to a more controlled delivery
rate [2, 3].
5.2 Liquid formulations
Liquid formulations are preferred by the farmer for preparing spray solutions for several reasons. They can be measured volumetrically, are easy
to handle, spontaneously form stable emulsions or dispersions and, given
appropriate container design, are usually easy to rinse out of the package.
They are also easy to handle in today's bulk handling systems and generally
do not cause application problems.
5.2.1 Emulsifiable concentrates (ECs)
Although, apart from salt solutions (SLs), they are the most widely applied
liquid formulations, ECs have some disadvantages. Most of the solvents
used in ECs are aromatic hydrocarbons with boiling ranges in the XyleneAromatic 200™ range. These are increasingly regarded with concern due
to their toxicity, volatility and the flammability of the lower boiling range
fractions. However, they are excellent solvents for a wide range of
pesticides, and in conjunction with a polar cosolvent such as Nmethylpyrrolidone (NMP) or dimethylformamide (DMF), can be used to
formulate most EC formulations in a cost-effective manner.
Efforts to replace aromatic solvents continue with the introduction of
the alkylated vegetable oils (such as methyl oleate, alkyl canolate and
refined rapeseed oil), TV-alkyl pyrrolidones and complex blends of aliphatic
oils with glycol ethers, designed to match the solubility parameters of
the original EC solvent system. Whilst there are selected successful examples, it has to be said that, to date, none of these new solvent blends has
matched the aromatic solvents in general performance, and especially cost
impact on the formulation. The nearest has been the glycol ether-aliphatic
oil blends which have given good performance in the concentrate, but on
dilution into water for application, the water-soluble glycol ether has migrated into the aqueous phase, causing the active ingredient remaining in
the aliphatic oil to be supersaturated and thereafter to crystallize in the
spray tank.
5.2.2 Concentrated emulsions (CEs)
To overcome some of the disadvantages of ECs - such as skin irritation and
flammability - formulators are switching to concentrated emulsions, which
are concentrated emulsions of a liquid or low melting point lipophilic active
ingredient. These formulations may contain 30-50% active ingredient and
40% of water or external phase. These are also referred to as EW (oilin-water) and WO (water-in-oil) emulsions depending on whether the continuous phase is either water or oil respectively. For the formulation of
hydrolytically stable compounds, EWs are an attractive alternative to
emulsifiable concentrates. Notably they contain fewer VOCs (volatile
organic compounds) and the advantage of an EW over an EC increases as
the concentration of the active ingredient decreases because the solvent is
replaced by water. To ensure a good emulsion stability for this new aqueous
system over an extended period of time at both elevated and freezing
temperatures, demands a long development period. However, concentrated
emulsions are inherently less flammable than emulsifiable concentrates and
exhibit - in the same way as do aqueous suspension concentrates - much
lower eye and skin irritation, and phytotoxicity.
EWs, unlike ECs in the undiluted state, are only stable in the kinetic
sense. This is because the system is inherently thermodynamically unstable
and can only be formed non-spontaneously. These systems change with
time usually degrading. There are four main degradation processes: sedimentation (creaming), flocculation, coalescence and Ostwald ripening. In
practical systems, all four processes may appear to occur simultaneously or
sequentially in any order, and this will depend upon the relative rate constants for the four basic processes under the conditions of storage of the
emulsion.
Approaches to stabilization of emulsions generally take the form of
attempting to induce a repulsion between droplets by electrostatic or steric
means, and this usually means the use of surfactants.
The best surfactants (emulsifiers) tend to be those of the block or graft
type, consisting of two main groups: the anchoring group B, which must be
chosen to have minimum solubility in the continuous medium and high
affinity for the oil surface, and A, which must be chosen with maximum
solvation by the continuous medium and minimum affinity for the oil surface. The ratio of groups A and B must be adequately chosen such that
maximum adsorption occurs. It is clear that one should minimize
micellization of the block or graft polymer in order to allow adsorption to
become more favourable. The length of the A chains must be optimized to
give adsorbed layers with sufficient length such that the energy minimum
seen in a typical energy interaction-distance curve for a sterically stabilized
particle becomes small. Various combinations of A and B groups may be
produced of which A-B, A-B-A block copolymers and BAn graft copolymers are the most common.
It is also essential to choose materials that enhance the Gibbs elasticity.
For this reason, surfactant mixtures, polymer-surfactant combinations or
liquid crystalline phases are most effective in producing stable emulsions.
To prevent sedimentation and/or creaming of emulsions it is essential to
build up a 'structure' (gel network) in the system that has (1) a high lowshear viscosity to overcome gravity and (2) sufficient elasticity (modulus or
yield stress) to overcome compression of the whole network. Both can be
achieved by the addition of a second phase that forms an 'elastic' threedimensional network in the medium. Several systems are available, of
which xanthan gum ( a microbial polysaccharide), sodium montmorillonite,
microcrystalline cellulose and finely divided (fumed) silica are perhaps the
most commonly used. Xanthan gum forms a highly elastic system as a result
of polymer chain overlap. Sodium montmorillonite and microcrystalline
cellulose form a gel structure as a result of interaction of extended double
layers around the thin clay platelet and/or edge-to-face flocculation. Fumed
silicas form an elastic network as a result of the formation of chain aggregates. It is common to use mixtures of xanthan gum with sodium montmorillonite, microcrystalline cellulose or silica.
Various other methods may be used to build up a gel structure in emulsions. An example is controlled flocculation of electrostatically or sterically
stabilized dispersions. With electrostatically stabilized dispersions, controlled flocculation is produced by addition of electrolyte, which results in the
formation of a sufficiently deep secondary minimum (of the order of 15/cT). This method must be applied with extreme care since coagulation
may occur if the electrolyte concentration reaches a certain limit. With
sterically stabilized dispersions, controlled flocculation may be achieved by
reducing the thickness of the adsorbed layer. Another method of controlled
flocculation is that induced by the addition of a free non-adsorbing polymer
to a sterically stabilized suspension. Above a critical volume fraction of the
free polymer (such as polyethylene oxide), weak flocculation occurs. This is
usually referred to as depletion flocculation.
Clearly, to form an oil-in-water emulsion (EW) an oil phase is needed.
This may be obtained by the use of liquid active ingredients, but where the
active ingredient has a melting point above say, -1O0C, a suitable solvent
should be employed to produce the active material in a liquid form. That
solvent should be immiscible (or of low solubility, say <0.1%) in water. The
oil solution thus obtained should be stable (no crystallization) at all temperatures likely to be encountered during production and storage of the
product. If an oil solution with a crystallization point above a likely storage
temperature is employed, then crystallization during storage is a likely
outcome with resultant poor dilution and spray properties of the product.
The basic components of an EW are therefore
• a stable oil phase;
• surfactants to form and stabilize the oil-water interface;
• optionally, a colloid stabilizer (to prevent creaming, sedimentation, coalescence); this may just be a rheological additive;
• an anti-freeze agent (appropriate to the storage needs of the product)
such as a glycol or a salt;
• an anti-microbial agent;
• optional adjuvants to improve the biological performance of the product.
Approaches to the production of 'stable' emulsions include the following.
• Matching the densities of the oil phase to the aqueous phase (to minimize
creaming or sedimentation), but this is difficult to achieve in practice due
to variation of density with temperature, as well as such a limitation
resulting in low levels of active ingredient in a formulation.
• Preparation of emulsions with a narrow particle size distribution. This is
because a monodisperse emulsion will not Ostwald ripen, and clearly the
narrower a distribution that can be achieved during processing, the less
will be the drive to Ostwald ripen in the system.
• Selection of the 'best' surfactants to achieve charge stabilization and
steric stabilization.
• Use of colloid stabilizers, such as polyvinyl alcohol.
• Stabilization by adsorbed solid particles at the liquid-liquid interface, the
so-called Pickering emulsion.
It has been found that several of these approaches have to be employed in
a single formulation to achieve a storage-stable product. Even then, the
products will only be kinetically stable (i.e. have a limited shelf life, which
may be 2-3 years) and given time will degrade. These approaches are
exemplified by the following examples.
1. American Cyanamid [4] works to produce a suspension emulsion. In this
three-step process, an SC of a solid imidazolinone was first prepared by
a bead-milling process. The oil phase was then prepared by adding
solvent to molten acetanilide followed by addition of surfactants. This
oil phase was then slowly added to the stirred SC. Typical levels of
surfactants were not adequate to produce a suitably stable product.
Further work identified that high levels of non-ionic surfactant could
stabilize the product against flocculation.
2. Wigger and Giickel found [5] that the use of xanthan gum in combination with oil-soluble emulsifiers improved the stability of a suspension
emulsion.
3. Researchers at Rhone-Poulenc [6] have utilized titanium dioxide to
stabilize oil-in-water emulsions as Pickering emulsions.
4. Polyvinyl alcohol (PVA) has been used as both a colloid stabilizer and a
polymeric surfactant to produce very stable emulsions [7, 8]. The use of
such products seems to be effective because PVA does not appear to
increase the water solubility of the emulsified oils.
5. Use of complex solvents [9] (such as diethylhexyl phthalate in combination with aromatic solvents) has been found to be effective by some
workers both for emulsions and for suspension emulsions.
6. Latices have been used to produce emulsions with very high stability
[10, U].
7. Wessling et al [12] have disclosed novel graft copolymers comprised of a
reactive surfactant base polymer and a non-ionic, hydrophobic grafted
composition that also give enhanced stability of various emulsified
phases compared to earlier systems that tended to coalesce. Further
work has resulted in the filing of other patents on stable emulsions by use
of such polymers [13, 14].
8. Recently ICI has introduced a new range of polymeric surfactants [15]
for the preparation of concentrated emulsions. These surfactants have
been designed to make optimal use of the steric stabilization phenomenon. Three different types of chemistry have been employed to produce
these surfactants, as illustrated in Table 5.2.
The polymeric surfactants are dissolved in the oil phase prior to emulsification into the aqueous phase. To achieve optimal performance, both phases
need to be heated to 50-550C prior to and during the emulsification. At
these temperatures the polymeric surfactants extend fully in solution and
give the best performance. Many of the polymeric surfactants have an HLB
(hydrophile-lipophile balance) <9 and will preferentially form water-in-oil
emulsions. To combat this tendency, and to ensure the formation of oil-in-
Table 5.2 Polymeric surfactants and their chemical nature
Polymeric series
A-series
B-series
E-series
a
b
Chemical nature
Polymeric surfactants
PEG-alkydsa
PHSA-PEG-PHSAb
Oligomerics
Hypermer™ A 109, A394, A409, Atlox™ 4914
Hypermer™ B261, Atlox 4912
Hypermer™ E475, E476, E488
PEG: polyethyleneglycol
PHSA: poly(12-isohydroxystearic acid)
water emulsions, these products are mixed with a high-HLB surfactant such
as Atlox™ G-5000. This is an alkoxylated short-chain alcohol (HLB value
c. 16.9). These surfactants have proven extremely versatile, producing
stable emulsions across a range of oil types from aromatics to oxo-alkyl
acetates to isoparaffins. Small changes in particle size were noted after
storage, but clearly these surfactants have potential to make a significant
improvement to the ability of a chemist to produce 'stable' emulsions.
Clearly there are many methods of stabilizing an emulsion, some specific
to one product and others offering a more versatile approach (such as the
new surfactants described above (8)).
A new method of emulsion stabilization has recently been described [16].
This employs the addition of small amounts of a stabilizer which effectively
prevents Ostwald ripening and thereby stabilizes the emulsion. Moreover,
this technology has been employed to produce 'template' emulsions of
stabilizer which are rapidly swollen with added pesticidal oil to produce
stable emulsions. A similar patent from Ciba-Geigy [17] describes the
preparation of stable pesticidal oil-in-water emulsions by the use of an oil
phase containing a substantially hydrophobic pesticide dissolved in a hydrophobic solvent and an aqueous phase containing surfactants and/or dispersants. This composition also contains a stabilizer, which is a polymer or
polymer mixture which is more soluble in the organic phase than in the
aqueous phase.
5.2.3 Suspension emulsions (or suspoemulsions)
Polymer latices have been used for the preparation of suspension emulsions
(or suspoemulsions). A detailed review is available [1O]. These formulations are popular for combining several types of compound into a single
formulation. The greatest challenge in the preparation of suspoemulsions
is the physical stabilization of the system. This stability can be imparted
through the careful choice of inert components and process control parameters. Much of the technology employed to produce kinetically stable
EWs can be effectively transferred to the preparation of suspoemulsions.
Alkylglucoside surfactants have been successfully employed in both phases
of a suspoemulsion [18].
5.2.4 Microemulsions
Microemulsions are thermodynamically stable, isotropic dispersions of hydrocarbons and water stabilized by anionic and/or hydrophilic non-ionic
surfactant and a cosurfactant, usually an alcohol. Microemulsions are
already frequently applied in cutting oils, dry cleaning fluids and drug
formulations, and are rapidly gaining importance as pesticide formulation
types. Microemulsions can be of the oil-in-water or water-in-oil type, and
about 30-50% of the oil phase is required as surfactant. A pesticide microemulsion is usually of an oil-in-water type. Water-in-oil microemulsions are
easier to produce but economically not very attractive. Owing to the high
surfactant concentration, these formulations are expensive and not competitive when compared with the traditional emulsifiable concentrates. A
recent review describes the structure and properties of microemulsions [19].
Agricultural uses of microemulsions are in specialized applications such as
stored grains [20], but are being developed for crop protection agents with
improvements such as increased active ingredient concentration [21], lower
viscosity [22], broader temperature stability [23] and as a means of preparing stable mixtures of oil phases with water-soluble pesticides [24].
5.2.5 Multiple emulsions
A multiple emulsion is one in which an oil droplet may contain water
droplets and in turn be emulsified in an aqueous phase. The final system is
then a water-in-oil-in-water emulsion (W/O/W). The reverse type, an oil-inwater-in-oil (O/W/O) can also be formulated.
Commonly used in the formulation of drugs, cosmetics and foods [25,26],
multiple emulsions are gaining use for the formulation of pesticides [27].
The oil phase of this W/O/W multiple emulsion prevented a pesticide within
the inner aqueous core from freely diffusing into the external continuous
aqueous phase. The multiple emulsion provided significantly reduced toxicity of the pesticide. Stabilized multiple emulsions can provide controlled
osmotic diffusion of compounds to tailor delivery, or may provide multiple
compartments for incompatible compounds within a single formulation.
Pesticide multiple emulsions are usually of the W/O/W type and one or
more active ingredients - soluble in the water and/or oil phase - may be
incorporated. In recent years, increasing attention has been given to multiple emulsions as possible vehicles for the controlled release of water- or
oil-soluble pesticides.
The development of multiple emulsions is very costly and time consuming, and their utilization has been impeded by the lack of physical stability
often attributable to the addition of active ingredients. Future developments will include emulsions that are sufficiently robust to tolerate the
storage and handling forces common in agricultural practice.
5.2.6 Suspension concentrates
Over the past 20 years many pesticide formulators have become involved in
the development of suspension concentrates or flowables. Suspension concentrates are concentrated dispersions, with around 50-80% w/v of pesticide with a particle size in the typical range 0.5-5 |im. These formulation
types will be discussed extensively in another chapter. The main challenge
has been to develop formulations which have shelf lives of at least 2 years.
They should be able to withstand any slight variation in the quality of the
components of the formulation, such as technical pesticide and the wetting,
dispersing and rheological additives. In addition, the flexibility of suspension concentrates, when there is a need to incorporate adjuvants or nonionic surfactants - which act as foliar wetting, spreading and sticking agents
or enhancers of the biological efficacy - has led to a rapid increase in their
popularity. This is particularly important as these adjuvants may be present
at concentrations similar to those of the pesticide.
5.3 Controlled-release formulations
Controlled-release technology has been receiving increasing attention in
pesticide formulation because it has a large number of possible advantages
over conventional pesticide formulations. Controlled release is a technique
or method whereby active ingredients are made available to a specified
target at a certain concentration and duration to produce an intended
effect. The initial application level of a conventional formulation is quite
often at the maximum tolerated level at the action point, and greatly exceeds the minimum pest inhibitory concentration. In a controlled release
formulation, the levels of the initial application are chosen in order to
maintain the pesticidal concentration above the minimum inhibitory
concentration (MIC) for the pest, until the end of the desired period of
effectiveness.
Controlled-release formulations can be designed to
• extend the activity of the active ingredient. The rate of release of the
active ingredient depends primarily on the rate of diffusion out of the
capsule matrix and is a function of the formulation ingredients, the degree of capsule thickness and strength achieved during manufacture;
• reduce evaporative losses caused by the action of wind and weather;
• reduce pesticide levels in the environment. Most pesticide sprayed or
incorporated in the soil is wasted. Controlled-release formulations use
a much lower concentration of active ingredients and might reduce the
damage to the environment and to non-targeted plants and animals;
• reduce phytotoxicity with application of lower amounts of herbicide;
• protect pesticides from environmental degradation caused by the action
of sunlight, bacteria, wind and water;
• reduce leaching in the soil;
• reduce mammalian toxicity to those handling the product;
• reduce solvent levels in a formulation;
• reduce formulation odour;
• improve formulation rainfastness.
The four main techniques applied to controlled-release formulations are
• coated pesticide granules;
• polymer systems containing covalently bound pesticides;
• matrix systems containing physically trapped pesticides;
• microencapsulation.
The major route to controlling the release of pesticides appears to be
microencapsulation, the process whereby small particles are created consisting of a core containing one or more materials surrounded by a barrier
layer, which has become the basis of the carbonless copy paper industry and
is important in other areas such as pharmaceuticals and flavourings. Despite
a number of successful applications of this technology to pesticide formulations, it has not been widely developed as a formulation method for agricultural chemicals.
Microencapsulation can be distinguished from both 'matrixing' and
'macroencapsulation'. Whilst both can be used to address some of the
objectives as microencapsulation, they differ greatly in the technologies
they employ and the products they produce. Matrixing is the dispersing of
the compound to be formulated in a second (usually solid) inert material
having some degree of barrier properties. It differs from microencapsulation in that the active material is in the form of many small particles
dispersed more or less evenly throughout a continuous phase which is the
barrier material, and in that the active material may be exposed at the
surface of the particle. USDA's starch encapsulation technology is a good
example of a matrix [28-3O]. Taking this to the limit, we can have thermoplastic granules which contain an active ingredient dispersed throughout
the matrix, either eroding with time under an environmental challenge or
solely releasing via diffusion. Examples of these have been the early
DURSBAN™ !OCR, a thermoplastic granule containing chlorpyrifos
based on a polyvinyl polymer and the more recent Suscon Blue™ granule
(again containing chlorpyrifos), both of which were successfully targeted at
the control of white grubs attacking the roots of sugar cane [31]. Patents
have very recently been published on the use of safer resin compositions for
controlling soilborne pests which are focused on reducing the toxicity of
pesticides (especially terbufos) to non-target organisms (including mammals) [32-34]. These are essentially extruded matrix systems containing
physically trapped pesticides.
A more recent application of matrix technology has been the preparation
of water-dispersible formulations (WG) by spray encapsulation. Previously
carried out by Hoechst [35], this was refined by Misselbrook [36] and later
by Bergman [37], wherein trifluralin was emulsified into water and the
resultant emulsion was spray dried in the presence of a water-soluble filmforming polymer to produce a dry, water-dispersible product. It was also
claimed that that the process produced a crystalline pesticidal active ingredient preserved in a preferred polymorphic form which enhanced the biological efficacy of the product. Whilst not a strict microencapsulation, this
product, at least in the dry form, met the description of a matrix granule
above, but on dilution into water for application, released the pesticide for
immediate activity.
Macroencapsulation differs from microencapsulation primarily in the
size of the capsules generated. A process that generates capsules of hundreds or thousands of micrometres can be considered macroencapsulation.
Wurster coating [38] and orifice drop formation [39] methods are examples
of macroencapsulation processes. Whilst materials in this size range can be
very useful for specific applications, the difficulty of suspending such large
particles in a spray solution makes them difficult to formulate for agricultural sprays.
Microencapsulation can generally produce capsules from 100 nm to about
100 ^m which encompasses the new concept of nanocapsules.
5.3.7 Methods of encapsulation
Many different encapsulation processes have been proposed [40-42]. Both
chemical and physical methods of creating a diffusion-limiting barrier have
been used. Improved methods for specific applications are constantly being
developed. All the processes have in common, however, the placement of
the compound(s) of interest within an inert barrier or shell wall.
Some processes such as coacervation, in situ polymerization and interfacial polymerization have been widely applied in fields other than pesticides.
Many others have been technical but not commercial successes. The major
encapsulation methods applicable to pesticides are summarized below.
(a) Interfacial polymerization. Interfacial polymerization [43] is a widely
used technique for making condensation polymers. It is distinguished from
other methods of polymer synthesis by the fact that the reaction takes place
at the interface between two non-miscible phases rather than in the bulk of
a single phase [44].
The basic procedure for encapsulating a material using the most common
form of this process is quite simple. The first monomer is dissolved in the
core material. The resulting solution is then dispersed in the continuous
phase (usually water), which normally contains one or more dispersing
and/or emulsifying agents. The second monomer is added to the aqueous
phase of the resultant emulsion. The shell wall-forming reaction occurs at
the oil-water interface of the emulsion droplets. The resultant suspension
of microcapsules can then be further formulated to produce the final
product.
There are, however, limitations on both the materials that can be encapsulated and the monomers that can be used. The greatest limitation is that
the material to be encapsulated must exist as a liquid dispersed in the
continuous phase, which is usually water. It must be either a liquid that is
essentially insoluble in the continuous phase, or a suspension or a solution
in a suitable solvent under the encapsulation conditions. In addition, there
must be no significant reaction between the monomers and the materials to
be encapsulated. The most important limitation on the shell wall materials
is that one monomer must be soluble in each phase. In addition, the reaction of the monomers with each other must be significantly faster than any
side reactions with the solvents or other ingredients. For pesticides, an oilin-water emulsion (EW) is the most usual form for the two-phase system,
with the reaction taking place at the surface of the oil drops. This produces
a suspension of pesticide particles in water which can be further processed
to a finished formulation.
The most commonly used oil-soluble monomers are polyfunctional
isocyanates and acid chlorides. Polyfunctional amines are preferred as the
water-soluble monomers because they dissolve readily in water and yet
react with the oil-soluble monomers more rapidly than water. These
monomer combinations produce a polyurea if an isocyanate is used, or a
polyamide if an acid chloride is used. By selecting suitable other monomers,
it is possible to form shell walls of other classes of polymers, such as
poly(sulphonamide), polyurethane and even polyepoxide. Monomers can
even be mixed to generate mixed polymers. Polymer shell walls can be
produced which will give a variety of release characteristics for a given core
material [45]. The result of this process is a suspension of microcapsules in
water.
Interfacial polymerization is the most important encapsulation technology for pesticides. It is also, however, an area in which continual improvements are being made. Great possibilities for rapid improvements have
been opened by the EPA's policy of rapidly granting exemptions from
tolerance to wide classes of polymers. This has the potential to greatly
increase the range of shell walls that are commonly used.
Another major potential area for improvement in this technology is the
physical properties of the formulations. Beestman and Deming showed that
microencapsulation could become a viable technology when directly
usable, stable suspensions of microcapsules were produced which contained
a high concentration of active compound [46]. The key feature is the use of
lignosulphonates to produce stable emulsions of a molten organic com-
pound in water. Reaction of monomers to form the shell wall around the
emulsion droplets produced suspensions that contain a larger volume of
organic compound inside the microcapsules than the volume of water suspending the capsules. Subsequent patents identify other sulphonated
polymers which are useful as emulsifiers for high concentration microencapsulation. These sulphonated polymers produce highly polydisperse
suspensions; consequently, irreversible settling of microcapsules can be a
result once the suspensions are diluted to spray. Beestman further found
that the use of co- or terpolymers of vinylpyrrolidone as dispersants in
interfacial polymerization gives formulations with improved properties
[47]. It is claimed that the resulting formulations do not form hard-packed
sediments when the diluted formulations are allowed to settle out in the
spray tank.
Whilst the observation had been made originally by Pennwalt that their
capsules of Penncap-M were longer lived than EC formulations, and partly
attributed to the protection of the contents against ultraviolet radiation
degradation, there have been a number of patents focusing on the improvement in performance obtained by use of a UV stabilizer, either in the
capsule suspension, or in the wall or the core of the capsule. Some of these
are applicable to coacervate systems [48-5O].
Mixtures of encapsulated and non-encapsulated pesticide offer advantages and a few patent applications have been made in this area. An example of this is the Sumitomo patent containing a mixture of an encapsulated
organophosphate pesticide and a dispersion of a pyrethroid insecticide [51].
A further development is the preparation of microcapsules containing suspensions of an active material dispersed in a water-immiscible oil which will
give very slow release of the solid active ingredient [52].
Recently, American Cyanamid has disclosed the preparation of microcapsule compositions, especially of dinitroaniline herbicides, which show
reduced tendency to crystallize on storage. This is achieved by formulating
the product in salt solutions, choosing the surfactants from earlier published
data [53].
The key for all encapsulation processes is the preparation of the emulsion. Much research effort has been expended in the identification of appropriate surfactants to produce and stabilize the emulsion prior to adding the
second reactant to produce the capsule by the interfacial polycondensation
reaction. The surfactants identified above, whilst not interfering with the
interfacial reaction, do not allow preparation of small emulsions (e.g.
<2jim). There remains a need to identify effective surfactants that allow
the preparation of small emulsions which can be stable over a wide temperature range whilst not significantly interfering with the interfacial reaction. An alternative approach to this has been taken by Fuji Photo Film Co.,
which uses a carefully machined linear bearing arrangement to produce
small emulsions with a very narrow span in the size distribution [54]. This
results in capsules of small size with also a narrow particle size distribution.
This is important in producing small-sized particles in that capsules at the
small end of the particle size distribution will have extremely thin walls,
often so much so that they are effectively free pesticide which can upset the
physical stability of a product. Control of the width of the particle size
distribution is therefore an important aspect in optimizing a capsule composition. As a compromise, the best method of obtaining reproducible emulsions in the presence of reactive monomers, especially those such as
isocyanates which react with water, is to employ an emulsification method
which produces the emulsion very quickly.
Interfacial polymerization has been the most commercially successful
method of encapsulation of pesticides. This is primarily because it has a
number of advantages over the other traditional encapsulation methods. It
is relatively inexpensive, the reactions are rapid and it is possible to produce
material on a large scale. It is also possible to produce more concentrated
pesticide formulations than with other encapsulation methods, and the wide
range of starting materials available makes it possible to optimize the shell
wall properties for a particular active ingredient. Its primary disadvantages,
which it shares with most other methods of encapsulation, are higher
manufacturing costs, when compared to non-encapsulated formulation
types, and in some cases a reduction of post-emergent or knockdown activity [55-58].
(b) Complex coacervation. In complex coacervation a shell wall is formed
around a water-immiscible active ingredient when an anionic, water-soluble
polymer is reacted with a cationic material (which may or may not be a
second polymer) [59, 6O]. The resulting so-called coacervate is insoluble in
water and separates from the solution as a second phase. If a dispersed
phase is present in the solution, the coacervate will tend to coat the suspended particles creating a protective shell.
The best-known example of coacervation is the reaction of gelatin with
gum arabic. The basic method for producing a formulation using this system
is similar to the procedure for interfacial polymerization. A suspension or
emulsion of the core material is prepared in warm, dilute gelatin solution.
To this is added a dilute gum arabic solution and the pH lowered to less
than 4.5, causing a coacervate to form around the dispersed core material,
which acts as a locus for deposition. The system is then cooled, causing the
coacervate, which is a 1:1 mixture of gelatin and gum arabic, to gel. For the
shell walls to form properly, this material must completely coat the particles
of core material. The final step is the hardening (crosslinking) of the soft
shell walls by adding an aldehyde, typically formaldehyde or glutaraldehyde, raising the pH to about 9 and warming the mixture. Following
preparation, capsules made by this process may be isolated and dried by an
appropriate method if required.
This process has received much attention in the microencapsulation literature and has been tested in a wide range of applications, including
agricultural chemicals. Capsules made by complex coacervation have been
commercial successes in several other industries but, due to the complexity
and cost of the process, coacervation has not been found to be of significant
value for agricultural formulations. The primary advantage of coacervation,
which is the source of interest, is that any core material which can be
dispersed in a liquid phase can potentially be coated. This is a significant
advantage over interfacial polymerization, which is limited to liquid or
liquefiable materials.
Recently there has been further work on coacervate systems. Allied
Colloids [61] has disclosed improved pH control which gives improved
coacervate deposition on the locus for deposition of the coacervate, and
Monsanto has disclosed the use of polyaspartic acid as a coacervation
component [62].
(c) In situ polymerization. In situ encapsulation is a term that is used to
describe two very different encapsulation processes. Although in both processes a water-insoluble pesticide is dispersed in an aqueous phase, the
processes differ in both the type of shell wall produced and the phase in
which the shell-wall polymerization occurs. In one method, the shell wall
forms from the polymerization of a polyamine and an aldehyde in the
aqueous phase. This is commonly known as the melamine-formaldehyde or
urea-formaldehyde encapsulation, after the ingredients commonly used. In
the other class of in situ encapsulation, the shell wall polymer forms from
within the dispersed pesticide-containing oil phase, usually by the hydrolysis of an isocyanate.
Polyamine formaldehyde shell walls. In this process, low molecular
weight melamine-formaldehyde or urea-formaldehyde prepolymer is first
dissolved in water. The water-insoluble material to be encapsulated is then
emulsified (or dispersed) into this solution. The pH is then lowered to
around 3.5 and the mixture heated to 5O0C for several hours, causing the
prepolymers to polymerize further into an insoluble shell around the active
material. The use of prepolymers avoids the need to add free aldehyde to
the reaction. The main disadvantages of this method are the long reaction
time for the shell wall formation and the limited number of polymers that
can be made by this process. The material must be stable at low pH and
must not contain any functional groups that can react with the amine or the
aldehyde [63-65].
Isocyanate hydrolysis. In the other process commonly referred to as in
situ polymerization, an oil-soluble monomer or prepolymer is converted to
a polymer shell by reaction with the water from the aqueous phase. In the
commonest version of this process, as in interf acial polymerization, the shell
wall is predominantly a polyurea. Instead of reacting the isocyanate with an
aqueous amine, some of the polyisocyanate starting material in the oil
phase is hydrolysed by the surrounding water to an amine. This amine then
reacts with the remaining isocyanate groups, to produce a polyurea somewhat similar to those produced by the reaction of polyisocyanate and
polyamines by interfacial polymerization.
The major advantage of this process of in situ polymerization is that the
amine does not have to be introduced into the aqueous phase. This avoids
potential problems with variable amine concentrations during the reaction.
There are, however, a number of problems that can be encountered with
this method. They include the generation of carbon dioxide from the amine
hydrolysis reaction. This can lead to processing problems and may also
cause the shell walls to be porous and have poor integrity. Since the hydrolysis reaction is slower than the reaction between amine and isocyanate,
the time required to create the shell may be longer than that for a similar
interfacial polymerization.
There have been a number of interesting advances in this area. For
example, Scher and Rodson have disclosed a novel twist on the standard
urea-formaldehyde in situ polymerization method of encapsulation [6668]. In this case, the urea-formaldehyde prepolymer is 50-98% etherified
with a C4-C10 alcohol, making it soluble in the oil phase. Because of this, the
polymerization takes place inside the dispersed oil droplet rather than in
the continuous aqueous phase. This has several advantages, including the
ability to produce a higher concentration of capsules in the formulation.
A use of this in situ polymerization technology is exemplified by Sandoz
[69], which uses the technology to produce capsules of herbicides with
reduced leaching characteristics. The product has to be stable at greater
than 10O0C to allow processing and curing of the product.
(d) Solvent evaporation. This process is one that is often proposed for
Pharmaceuticals, but which has not yet had significant applications in agriculture. Unlike the preceding processes, except complex coacervation, in
which the shell wall polymer is formed by reaction of low molecular weight
monomers, in this process the shell wall is made from a pre-existing polymer which is deposited around the active ingredient. To make the encapsulated product, the active ingredient to be encapsulated and the polymer
from which the shell wall is to be formed are dissolved in a volatile waterinsoluble solvent. The polymer and the active ingredient must both be
soluble in the solvent, but not in each other. The solution of active ingredient and polymer is emulsified in water containing a suitable surfactant. The
solvent is then removed by an appropriate means, such as heat or reduced
pressure or both. As the solvent evaporates, the polymer separates from the
solution, forming a continuous layer at the surface of the emulsion droplets.
The primary advantage of this process is that a wide range of pre-existing
polymers with well-defined physical properties can be used to form the shell
wall. The appropriate solubilities of the polymer in the volatile solvent, core
material and continuous phase are the only limitations on which polymers
can be used. The cost and hazard involved in evaporating and recycling the
highly volatile solvents that must be used in this process are its primary
drawback. The requirement that the polymer must be soluble in the volatile
solvent also limits this approach to polymers with little or no crosslinking. It
is, however, possible to perform a hardening reaction, similar to that used
for coacervation systems, after stripping the solvent. Because of the solvent
volumes and costs involved, the process has been more appropriate to the
lower volumes and higher values of pharmaceutical products.
(e) Spray encapsulation. This is one of the oldest encapsulation techniques and has many variations. Several related methods that produce
capsules using air rather than a liquid as the continuous phase are combined
in this class. These methods are particularly useful if the desired product is
a dry formulation rather than an aqueous suspension, since it is unnecessary
to remove the aqueous phase. In its simplest form, this technique consists of
spray drying an emulsion (or suspension) of a core material dispersed in an
aqueous solution of the shell wall material. When the water is removed, the
dissolved polymer remains behind, coating the core material. With the
simpler versions of this process, the particles that are produced are usually
matrices which contain several core particles rather than true microcapsules. The capsules produced by these methods also tend to be larger
than those made by other methods discussed earlier, since it is difficult to
produce very fine drops with ordinary spray equipment. The average size of
the resulting powder is usually in the range 10-150 ^m and more often at the
upper end of the range. It can be difficult, therefore, to produce sprayable
products having handling properties comparable to conventional formulations by these methods.
'Drop formation' techniques have been developed based on nozzle engineering improvements to produce truly encapsulated products containing
single cores. These, however, tend to be rather large particles (up to
3000^m). The methods have the advantage that solids as well as liquids can
be encapsulated in high loadings of active ingredient.
These spray encapsulation methods are potentially useful, but have so
far been only of limited application to agricultural products. They have
the advantage of producing dry capsules that can be incorporated into
non-aqueous systems and that a wide range of active ingredients and coating materials are compatible with the technology. The primary shortcomings from the point of view of applications to agriculture are the large
particle size and the relatively low manufacturing capacity of most
equipment.
The most important issues for this technology have always been the cost
and availability of equipment and ability to make sufficiently small particles. Some original work was carried out by Surgant and Deming, who
produced microcapsules of pesticides with selected surfactants and then
dried those capsules (by an appropriate technique) to produce waterdispersible granules [7O]. These capsules were large (c. 8^m) with a thick
wall but dispersed readily in water, providing an effective method of mixing
encapsulated and non-encapsulated pesticides. More recently DowElanco
has discovered that dry, stable encapsulated products can be obtained by
using polyvinyl alcohols (PVA) as the surfactants, as well as the spray
drying of water-soluble polymer [71]. Moreover, they achieve extremely
small particle sizes (down to 0.5 |im). Zeneca have also carried out similar
work, spray drying capsule suspensions in PVA solutions to produce waterdispersible compositions [72].
(f) Other technologies for encapsulation. The technologies of complex
coacervation and solvent evaporation discussed above appear less likely to
be immediately useful for typical pesticides. Compounds with low rates of
use may, however, cause increased interest in these methods. In addition
to the methods that have been investigated over many years, new types of
encapsulation technology are constantly being proposed for pesticides.
New types of pesticides, such as biological products or living biological
systems, will require new approaches.
The encapsulation of living organisms is an area of great current interest.
Controlled-release formulations of microbial pesticides have been reviewed
by Connick [73]. A related area is the encapsulation of pesticides (usually
biologically derived agents) in cells. Mycogen Corporation has described
a technology for producing biotoxins such as Bacillus thuringiensis (Bf)
encapsulated in killed cells [74]. Yeast has also been used as an encapsulation medium, but to date no commercial agricultural product has been
launched. The original work carried out by Shank [75], Dunlop [76,77] and
AD2 [78] was taken further by The Wellcome Foundation Ltd to produce
formulations of photosensitive pesticides which gave improved performance [79].
Landec has promoted a technology for encapsulating pesticides in polymers that undergo a change in crystallinity at a particular temperature [8O].
This technology has considerable potential against pests (such as some soil
pests) whose activity is temperature dependent. The potential exists to
develop formulations that release their active ingredient only when the
target organisms are active. The primary difficulty that must be overcome is
the development of formulations that have satisfactory storage stability at
temperatures above the release temperature.
The production of very small capsules (<l|im) is an area of potential
interest. Various technologies exist for making very fine emulsions that
could be adapted to the existing emulsion-based encapsulation technologies
such as interfacial polymerization. The major question about very small
capsules is whether a sufficiently strong shell can be formed without using
a large amount of wall material. Even for 10 ^m particles, the shell walls are
typically very thin. Reducing the particle size by a factor of ten or more is
likely to produce capsules with shell walls with a thickness of less than
10 nm. Release characteristics may be ill defined because of the very thin
shell walls at the small end of the particle size distribution.
5.5.2 Advantages of microencapsulation
Microencapsulation can produce formulations with many desirable attributes. These include reduced acute toxicity, reduced degradation of unstable active ingredients, reduced volatility, reduced leaching, modified
biological activity, improved rainfastness and protection of the active ingredients from other incompatible components. These attributes of safer formulations are illustrated below.
(a) Controlled release of active ingredient. There is a tremendous amount
of data which demonstrates the longevity of efficacy of encapsulated pesticide compared to non-encapsulated pesticide. Originally demonstrated
with encapsulated parathion methyl, many other pesticides have shown this
effect. There is often an increase in the inherent toxicity of the pesticide to
target pests. \
(b) Improved targeting. By proper definition of the target for a pesticide,
better efficiency of use of a pesticide can be achieved. Microencapsulated
chlorpyrifos (as EMPIRE 20™) is targeted against cockroaches and as such
has been formulated to a specific particle size distribution for optimum
pick-up by the cockroach. The product has been designed to be a no-release
product until ingested by the cockroach as it preens itself of the debris
picked up by its foraging, when it then releases the toxic contents. The
photomicrographs shown in Figures 5.1 and 5.2 demonstrate the significant
number of capsules attached to the cockroach following exposure to a
treated surface. Moreover, the capsule composition and size ensure that the
product is not deactivated by different substrate compositions.
(c) Reduced acute toxicity. Microencapsulation can have a substantial
impact on the mammalian toxicity of a pesticide being formulated. This can
be of great importance when the pesticide has a relatively high inherent
toxicity. For example, Penncap-M (encapsulated methyl parathion) was
found to be 12 times less toxic by dermal absorption than the emulsifiable
concentrate, and at least six times less toxic orally, depending on the test
species [81, 82]. Similarly, encapsulated fonofos, used as a seed treatment,
Figure 5.1 Microencapsulated pesticide on a synthetic substrate.
had acute toxicities (LD50) of 2370mg/kg for oral rat and 1500mg/kg for
dermal rabbit, which were 100 times (oral) or ten times (dermal) less than
the values for technical-grade fonofos [83].
(d) Slower degradation of active ingredient. An active ingredient inside a
shell wall is not as exposed to the chemical, photochemical and microbial
factors known to degrade pesticides. Again, Penncap-M was found to be
more resistant to photodegradation than the emulsifiable concentrate. In
tests on glass plates, the half-life of the encapsulated product was increased
by about three or four times and control of Heliothis zea was similarly
extended [82].
(e) Reduction of solvent. Many of the active ingredients used in agricultural formulations have low melting points, which makes it difficult to
formulate them as suspension concentrates or water-dispersible granules
(two newer formulation types which are seen as more environmentally
friendly than emulsifiable concentrates) and thus are often sold as
emulsifiable concentrates. These products may contain large amounts of
organic solvent to prevent the formulations from crystallizing during storage. Microencapsulation could then provide formulations with improved
characteristics in the areas of flammability, air and water pollution, and
odour, as well as reduced raw material costs.
Figure 5.2 Microencapsulated pesticide adhering to a cockroach.
(f) Improved conservation tillage efficacy. Encapsulation can also be used
to modify the biological activity of a pesticide. For example, it has been
reported that Micro-Tech (encapsulated alachlor) is more effective under
no-till and conservation tillage systems than Lasso EC, the comparable
emulsifiable concentrate [84,85]. It has been proposed that this is due to the
greater ability of the encapsulated product to penetrate the topsoil thatch
layer without being adsorbed or lost to volatility.
(g) Reduction of volatile loss. Encapsulation can also reduce the rate of
evaporation of a volatile pesticide. This can lead to activity modifications,
such as reduced off-site injury caused by volatility, and in some instances
extended residual control because less pesticide is lost to the atmosphere.
This is well illustrated by the patent application from FMC [86] with encapsulated clomazone which demonstrates reduced vapour loss (and damage
to surrounding sensitive crops) by encapsulation. An almost identical patent application was also recently issued from Monsanto [87].
(h) Reduction of leaching. The use of various types of entrapment to
reduce the leaching of pesticides is well established in the literature. This
can both increase the activity of the pesticide by maintaining the concentration in the area where it is useful, and improve the environmental characteristics of the product. Encapsulated alachlor was found to leach less than the
emulsifiable concentrate, and therefore presumably maintains a greater
amount of the active material in the area where its biological effect is
required [88].
(i) Reduction of formulation odour. In some cases, encapsulation can
reduce formulation odour. If the odour in question is that of the active
ingredient, entrapping it within a shell wall may reduce it. If the odour is
due to the organic solvents used in the formulation, replacing them with
water by microencapsulation will eliminate the problem.
(j) Improved stability. Encapsulation has the potential to protect an unstable active ingredient from the other components of a formulation. This
may allow the preparation of formulations containing ingredients which
would otherwise be incompatible. In the case of biological pesticides such
as pathogenic microorganisms, encapsulation and matrixing have proved
successful in maintaining the viability of such organisms prior to use [73,
89].
(k) Reduced phytotoxicity. Some pesticides can have their phytotoxicity
to desirable species reduced by encapsulation. Penncap-M is less phytotoxic
to plants on which it was used than the emulsifiable concentrate [90, 91].
Similarly, fenitrothion when encapsulated has been shown to be less
phytotoxic to Chinese cabbage than the comparative emulsifiable concentrate (EC) formulation [92]. The rationalization was that this was due to
wall thickness, but the phytotoxicity was explained as being due to rupture
of capsules and/or release of the active ingredient from the microcapsules
by diffusion. A similar effect was observed with a pyrethroid capsule formulation [93].
(I) Improved rainfastness. Rainfastness of pesticide formulations is a significant mechanism by which pesticide efficacy may be reduced. Two interesting pieces of work have shown that encapsulation can markedly reduce
the loss of pesticide from plants following rainfall, resulting in improved
performance of the product. This was carried out by Sumitomo with both
fenitrothion [92] and pyrethroids (fenvalerate and fenpropathrin) [93]. The
effect was confusing in that with a large wall thickness, the capsules appeared to be easily washed off and also demonstrated poor activity; with
thin walls there was excellent resistance to wash-off whilst maintaining
efficacy.
5.3. 3 Micro encapsulated products
Microencapsulated pesticides have not achieved the importance that the
numerous advantages attributed to them would suggest. Table 5.3 indicates
some of the commercial encapsulated products available.
Table 5.3 Commercial microencapsulated pesticide formulations
Active ingredient
Trade name
Shell wall polymer
Company
Herbicides
Alachlor
Alachlor
Alachlor
EPTC
Micro-Tech
Bullet
Partner
Capsolane
Polyurea
Polyurea
Polyurea
Polyurea
Monsanto
Monsanto
Monsanto
Zeneca
Insecticides
Chlorpyrifos
Chlorpyrifos
Chlorpyrifos
Chlorpyrifos
Diazinon
Diazinon
Fenitrothion
Fonofos
Parathion
Parathion-methyl
Parathion-methyl
Permethrin
Pirimiphos methyl
Tefluthrin
Empire 20
Pyrinex
Kayatack MC
Pennphos
Knox-Out 2FM
No-Roach
Kareit MC
Dyfonate MS
Penncap-E
Penncap-M
Parashoot
Penncapthrin 200
Actellic M20
Tefluthrin CS
Polyurea
Polyurea
Polyurea
Polyurea
Polyamide/Polyurea
Polyurea
Polyurethane
Polyurea
Polyamide/Polyurea
Polyamide/Polyurea
Polyurea
Poly amide/ Polyurea
Polyurea
Polyurea
DowElanco
Mahkteshim
Nippon Kayaku
Elf Atochem
Elf Atochem
Kedem Chems
Sumitomo
Zeneca
Elf Atochem
Elf Atochem
Cheminova
Elf Atochem
Zeneca
Zeneca
Little information is publicly available on the market for most of these
products. Encapsulated alachlor (Micro-Tech™, Bullet™ and Partner™)
has probably been by far the largest-volume encapsulated pesticide. Most
of the other products are intended for special applications and have relatively low sales volumes.
5.3.4 Future trends in microencapsulation
The future of microencapsulation will be driven by two kinds of factors,
changes in the industry and improvements in technology. Both are critical
to the increased use of microencapsulation in agricultural products. The
changes in the industry have the potential to make the existing microencapsulation technologies more attractive in comparison with the more
traditional formulation types.
Concurrently, improvements in the technology present the opportunity
to overcome the shortcomings of existing technologies and increase their
usefulness. The ability of new technology to deliver improved performance
will be desired, but this will compete against greater speed to market and
lower risk of failure of well-established technologies.
The other potential driver for microencapsulation is the introduction of
new technology that would make a step change in its viability as a formulation method. The literature is full of new patents and discoveries in the area
of encapsulation, but from a commercial point of view the number of
products being introduced remains small. Whilst most of the patents are
minor improvements or applications of old technologies to new active
ingredients, some new and interesting improvements are being discovered
as has been indicated above.
5.4 Water-soluble packaging
This will be discussed extensively in another chapter. However, packing oilbased products as gels has become an interesting method of reducing packaging waste on selected formulations. Gel formulations are innovative
products which can be described as thickened ECs packed in water soluble
bags, as reported by Dez et al [94]. The viscosity is increased with thickeners, the final gel viscosity being a compromise between the transport
stability in the water-soluble bag and the dispersibility in water. This formulation approach is to resist leakage from the pinhole imperfections of the
water-soluble bags. This concept offers the crop protection market a new
form of a product-packaging combination. The first fungicide formulated as
a gel is propiconazole as a 625 g/1 EC launched as PRACTIS™ in France in
1991. Gel products offer many benefits that are highly appreciated by
farmers. The premeasured doses in water-soluble bags offer advantages in
Next Page
Previous Page
Little information is publicly available on the market for most of these
products. Encapsulated alachlor (Micro-Tech™, Bullet™ and Partner™)
has probably been by far the largest-volume encapsulated pesticide. Most
of the other products are intended for special applications and have relatively low sales volumes.
5.3.4 Future trends in microencapsulation
The future of microencapsulation will be driven by two kinds of factors,
changes in the industry and improvements in technology. Both are critical
to the increased use of microencapsulation in agricultural products. The
changes in the industry have the potential to make the existing microencapsulation technologies more attractive in comparison with the more
traditional formulation types.
Concurrently, improvements in the technology present the opportunity
to overcome the shortcomings of existing technologies and increase their
usefulness. The ability of new technology to deliver improved performance
will be desired, but this will compete against greater speed to market and
lower risk of failure of well-established technologies.
The other potential driver for microencapsulation is the introduction of
new technology that would make a step change in its viability as a formulation method. The literature is full of new patents and discoveries in the area
of encapsulation, but from a commercial point of view the number of
products being introduced remains small. Whilst most of the patents are
minor improvements or applications of old technologies to new active
ingredients, some new and interesting improvements are being discovered
as has been indicated above.
5.4 Water-soluble packaging
This will be discussed extensively in another chapter. However, packing oilbased products as gels has become an interesting method of reducing packaging waste on selected formulations. Gel formulations are innovative
products which can be described as thickened ECs packed in water soluble
bags, as reported by Dez et al [94]. The viscosity is increased with thickeners, the final gel viscosity being a compromise between the transport
stability in the water-soluble bag and the dispersibility in water. This formulation approach is to resist leakage from the pinhole imperfections of the
water-soluble bags. This concept offers the crop protection market a new
form of a product-packaging combination. The first fungicide formulated as
a gel is propiconazole as a 625 g/1 EC launched as PRACTIS™ in France in
1991. Gel products offer many benefits that are highly appreciated by
farmers. The premeasured doses in water-soluble bags offer advantages in
ease of handling and increased user safety while the outer packaging is
sometimes considered as non-contaminated with product and therefore
more easily disposed of.
Water-based gels that have stable formulations of hydrolytically unstable
sulphonylurea herbicides have been developed by DuPont [95]. Gels containing sulphonylurea and copesticides add a new dimension to delivery of
compounds that will rapidly degrade.
5.5 Dry products (water-dispersible granules)
The development and utilization of water-dispersible granules (WG) has
been significant because they offer many advantages compared with the
older wettable powders from which they have been derived as a means of
producing low-dust products. These formulation types are discussed extensively in Chapter 4.
5.6 Adjuvants
It is becoming a trend to include within a formulation other chemicals - or
a combination of chemicals - mostly surface-active agents, capable of improving the biological activity of a pesticide. This can often be achieved
without affecting the environmental or mammalian toxicity profile of the
pesticide. The effects of these chemicals, referred to as adjuvants, can be
summarized as follows.
• Better foliar wetting and spreading of the deposited droplets of applied
spray. Rapidly absorbing surface-active agents may be expected to wetout the surface microstructure of the target quickly and to inhibit retraction of the spread drop, thus diminishing the splashing of the droplets.
• Better adhesion of the droplets by retaining the spray on the target crop
or weed.
• Decreasing the particle size of the droplets. Large droplets are poorly
retained on the target.
• Increasing the drying time of the droplets and the water retention at
various humidities. The active ingredient may stay wet for a longer period
of time, allowing a higher pick-up by insects and a continuous uptake by
plants.
• Non-ionic surfactants can influence the size and shape of the dried-down
active ingredient crystals. The particle size of the pesticide can, for some
active ingredients, exert a considerable effect on the performance and
persistence.
• Non-ionic surfactants can increase the solubility of the pesticide in the
droplet. During the drying process, the concentration of non-ionic
surfactants increases and results in a higher solubility of the active ingredient, owing to micellization.
• Improving the rainfastness of the spray solutions. Rewetting of the active
ingredient by rain or dew and subsequent dissolution of the active ingredient may decrease the activity dramatically because of the wash-off
effect.
• Improving the physical compatibility of different pesticide formulations
in the spraytank solution. Formulation incompatibilities can impair the
function of the active ingredient, cause plant injury and destabilize
the emulsion or dispersion.
• Non-ionic surfactants can influence the uptake and penetration in the
plant. Good leaf wetting increases the probability of penetration because
non-ionic surfactants may modify and dissolve waxes in the cuticle, cause
swelling of the pathways and disrupt membranes. Surfactants can enhance the uptake of active ingredients, but a surfactant level or an ethylene oxide content that is too high can cause blocking of the translocation
of the active ingredient within the plant.
Adjuvants are (as with SCs and WGs above) discussed extensively in
Chapters 7 and 8.
5.7 Other formulation types
5.7.1 Seed treatment formulations
Tailor-made formulations for the treatment of seeds have become established over the past 15-20 years. The underlying principle is to place the
pesticide as near as possible to where it is required to control seed- or
soilborne pests and for uptake by the plant roots. Due to the specific
placement of the pesticide directly on the seed, benefits include a more
efficient use of product, less environmental contamination and reduced
exposure of non-target organisms. The major drawback with seed treatment is the availability of pesticides which are active by a seed treatment
route. It is recognized that seed treatment does not currently give the
financial returns required by major agrochemical companies, and therefore
such pesticides will not be routinely screened for, resulting in a very small
incidence of active ingredients which are effective by this route.
5.7.2 Biotechnological improvements
Biotechnology covers both the delivery of live organisms in formulations
and genetic incorporation of pesticide genes into plants, as well as the
development of herbicide crop tolerance, specifically to the herbicides
glyphosate and gluphosinate.
We can include in living organisms bacteria, fungi, viruses as well as
organisms such as parasitic nematodes. They can be conveniently combined
under the general title of biopesticides, although erroneously some chemical pesticides derived from biological processes, such as fermentation procedures, are also sometimes referred to as biopesticides.
Two short key reviews of note are those by Bishop [96] and Cibulsky
et al [97]. Bishop's review concerns the general issues of biopesticides and
Cibulsky's is a review of progress in formulation and application technologies and future trends dealing almost exclusively with Bacillus thuringiensis
(Bt). Very little other literature deals with formulations or delivery systems
for these biopesticides, although a small number of patents are appearing
on the stabilization of such products and better methods of targeting against
the pest. This is probably a reflection of the current lack of real options for
producing long-term stable products.
Bt, an aerobic soil dwelling, gram-positive, spore-forming, rod-shaped
bacterium, remains the focus of the majority of research on bacteria and
biopesticides in general. It is distinguished from other members of the large
Bacillus genus by the production in each mature cell of a proteinaceous
crystal. When Bt is commercially produced in large-scale fermentation
tanks, the mature Bt cells break open, or lyse, at the completion of their
growth cycle, releasing delta endotoxin crystals and spores into the liquid
medium. These naked crystals and spores constitute the active ingredient of
conventional Bt products. While Bt delta endotoxins can be quite toxic to
target organisms (LC50 values of 5-20 ^ig/ml delta endotoxin are common
for susceptible beetle, mosquito and caterpillar larvae), results of toxicology tests with Bt varieties kurstaki, aizawai, israelensis, tenebrionis and
son diego have indicated a consistent lack of toxicity against non-target
organisms: mammals, birds, fish, ducks, aquatic invertebrates, beneficial
insects and plants. In addition, the Bt active ingredient - a protein - breaks
down in the environment, usually within 1-4 days after application, which
confers the mixed blessing of biodegradability and lack of residuality
to Bt products. Although Bt delta endotoxins are regarded as the primary active ingredient in #/-based products, it should be noted that Bt
spores appear to play a still as yet uncharacterized role in certain Bt-host
interactions.
The thousands of Bt isolates thus far discovered are currently classified
into over 30 varieties or subspecies in a specific taxonomic system. Bt is
characterized as a stomach poison. When susceptible organisms ingest Bt
protein crystals, the first gross symptom observed is the cessation of feeding, usually within 1 h. This is followed by a slow, apparent poisoning of the
insect, resulting in death 1-7 days after ingestion. There are more Abased
products now than ever before, currently producing sales of about
$130 million per year, a total expected to increase to about $300 million
[98] by the year 2000.
In an attempt to improve the foliar persistence of Bt toxins, Mycogen
Corporation has developed the CellCap encapsulation system [99]. This
system is based on a non-pathogenic bacterium, Pseudomonas fluorescens,
which has been genetically engineered to produce Bt delta endotoxin, and
has been killed prior to release. In this system the dead bacterial cell wall
serves as a biological microcapsule which protects the fragile Bt protein
toxins from environmental degradation. Results from field trials suggest
that such CellCap products have two to three times the residual activity of
conventional Bt products. Environmental degradation does still occur 7-10
days after application. These products are also more stable in the sales pack
than non-encapsulated Bt products.
Finally a number of patents describing stabilization procedures for Bt
endotoxins, both in a sales pack as the concentrated formulation and as a
sprayed product on a leaf surface, are beginning to appear [100-109]. The
latter tends to act by control of pH and addition of ultraviolet light screens.
In the biofungicide area, Bayer have reported control equivalent to
aldicarb with granulated fermenter 'pellets' of a wild-type strain of
Metarhizium anisopliae against black vine weevil when used as a soil insecticide [UO]. This product (common name: BIO 1020/'Metarhizium
anisopliae) consists of dust-free and insoluble mycelial granules of the
fungus which are produced according to a patented procedure [111]. The
granules are stored at a low temperature (40C) until used. Experimental use
rates of 0.2-1.0 g/1 of soil would require 20-100 kg/ha to treat the top 1 cm of
soil, suggesting that the product's main use would be in high-value horticultural crops. To ensure high sporulation rates of the fungus under unfavourable conditions, for example when temperatures are low at potting time, a
premix is prepared by mixing the granules into compost and incubating at
temperatures of 15 or 250C for 7 or 4 days respectively until sporulation on
the granules is completed. The premix can then be used directly for potting
after this incubation period. BIO 1020 develops its biological activity in two
ways. The first step is the formation of infectious spores on the granules
after rehydration, and the second is the infection of the pests after contact.
Both processes are dependent on environmental conditions, mainly temperature. Spores of Metarhizium anisopliae survived for a long time in the
soil after application. In Bayer trials, an activity period of up to 8 months
was achieved.
Ecoscience had developed a novel delivery technology, the Bio-Path
chamber system [112]. Fungal spores are suspended on upside-down petri
dishes and the apparatus is designed so that insects, attracted into the
device by various means, pick up doses of the lethal fungus. The fungus can
then be carried into insect colonies, eliminating the whole population.
It would appear that agricultural biotechnology will slowly transform
itself into a major contributor to the pesticide global business. However,
it is unlikely that a broad-spectrum insecticide will result since such an
approach, even if possible, could well produce products with such wide
spectra of activity that they pose safety risks to non-target organisms. It
seems that research will therefore concentrate on genetically improved
products. This is likely to be achieved by genetic manipulation as well as
genetic engineering. Coupled with the further development of recombinant
bacteria (killed to encapsulate the desired organism), more stable products
are likely by the year 2005. Advances in conventional formulation chemistry technology will also offer improvements in terms of more stable
products and increased residuality on the crop. This is based on a key
assumption that transgenic plants do not gain approval for use in major
markets such as cotton or tomatoes. The specificity of the Bt gene expression means a very limited pesticide spectrum and, coupled with the public
concern over consumption of food containing such organisms, may well
prevent large-scale expansion of this technology. Living organisms provide
the formulation chemist with considerable challenges because of their lack
of stability in the environment. Genetic manipulation of some organisms,
especially Bt, has resulted in improved products as well as encapsulated
products from recombinant bacteria. Formulation efforts can complement
these efforts and may produce better products which could include a range
of stabilizers, such as UV stabilizers, pH adjustment, encapsulation, addition of appropriate nutrients, stickers to improve rainfastness and other
additives.
5.8 Summary and future possibilities
Development of safer formulations is one aspect of the response of the
agricultural industry to meet the many challenges. It is likely that this
initiative will continue and the results will be applied to not only established
pesticides, but also to the emerging pesticides which will have to be environmentally better than existing products. The molecules will come from both
traditional synthetic routes and biological origin with possibly some subsequent synthetic modification. These active ingredients will very probably be
higher in molecular weight, more structurally complex and, as a result, will
have more sites for degradation. Environmental and toxicological screening
will favour the advancement of molecules with a shorter half-life and lower
aqueous solubility. The higher molecular weight, lower solubility in water
and increased instability will, overall, increase the need for developing
more targeted delivery systems.
The increased complexity and instability of new molecules will require
systems to be discovered that will temporarily stabilize them against the
environmental effects of light, heat and moisture. Systems developed for
older, lower molecular weight molecules were designed to decrease environmental loss from volatility, hydrolysis and water solubility. Of these
three, hydrolytic stabilization will still be critical for new molecules; however, prevention of losses due to volatility or solubility will decline in
importance. In addition to hydrolytic stabilization, there will be an increased need for technologies to stabilize against degradation from ultraviolet light.
Formulations in the future will tend to be aqueous solutions, water-based
suspensions of solids and granules either for dispersion in water or for
direct application in response to a market need for safer end-use products
in terms of worker exposure and environmental impact. While there could
be some advantage to looking for solvent replacements for the hydrocarbon
solvents used in today's emulsifiable concentrates, it is likely that they
will lack sufficient solubility to make them economical for most new actives.
If a molecule is very highly active, however, a low-concentration emulsifiable concentrate, using such a 'safe' solvent, would still be viable and
acceptable.
As indicated previously, new molecules are likely to be more unstable to
water, heat and light. At the same time, formulation processes for waterbased liquid and dry formulations will result in greater exposure to these
three factors; this will increase the need for stabilization of the active
ingredient during processing and storage of the formulation. Liquid suspension formulations are two-phase systems that will need to be physically
stabilized to prevent irreversible separation or particle size growth during
storage.
There is a real need for the development of technologies that will release
an active ingredient on the basis of some 'trigger' mechanism. Such a burstrelease would provide the active ingredient at a higher concentration than
can be achieved with diffusion. In addition, if the trigger could be coupled
to an event such as seed germination or egg hatch, it would provide the
active ingredient at exactly the time needed.
Target-specific delivery systems are needed to provide optimum performance of future pesticides. Such systems will be developed only through
consideration of the several steps involved in delivering the molecule to the
ultimate biological active site.
Improving the contact and permeation at a biological membrane surface
is one of the best ways to make active agents more target specific. Additional research on adjuvants needs to focus on the requirements of new
molecules, rather than just studying the materials that are currently used.
Bait research needs to match the biological need with the simplest matrix
that will deliver a response.
New controlled-release technologies, designed to provide release of the
active ingredient in response to some external 'trigger', are needed.
Colloid science research will continue to develop an understanding of the
processes involved in stabilization (and destabilization) of dispersions, and
further effort on the development of dry products will yield dividends in
processing technology and combinations of dry technology with adjuvant
and controlled-release technologies.
The current industrial approaches to producing improved liquid formulations, especially water-based systems, more specific controlled-release technologies and non-dusty dry products seem well aligned to the need to
produce safer formulations in terms of reduced toxicity, increased target
specificity and reduced environmental impact.
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6 Agrochemical formulations using natural
lignin products
S. T. HUMPHREY
6.1 Introduction
Lignosulphonates have a long association with the formulation of
agrochemical products. They are to be found in many traditional formulation types, but are also considered an invaluable resource for formulation
researchers looking at new and novel agrochemical delivery systems.
For the purpose of this article the term lignosulphonates will be taken to
embrace those products derived from both sulphite and kraft pulping
processes.
6JJ Lignosulphonates: some basic information
Commercial development of lignosulphonates and their specialized derivatives has resulted in what was once a waste product becoming an important
part of the speciality chemicals market, and lignin must be regarded as a
valuable natural resource. The raw material for the cellulose industry wood - consists mainly of three types of chemical compounds: cellulose,
hemicellulose and lignin.
A number of models have been proposed to describe the structure of the
lignin, but Freudenberg's 1964 formula (Figure 6.1) gives a good representation of a softwood lignin, while Figure 6.2 proposes a structure for
sulphomethyl kraft lignin.
Lignin in its natural form is insoluble in neutral liquids and organic
solvents. The two most commonly used methods of separating cellulose and
lignin are described briefly below.
(a) Sulphite pulping. One way of separating cellulose from lignin and
other compounds is to treat wood chips with a hot acid solution of calcium
bisulphite. During this digestion process part of the lignin becomes
sulphonated, while simultaneously some linkages become hydrolysed. Hydrolysis causes the lignosulphonate molecules to dissolve, together with
other soluble compounds such as sugars.
(b) Kraft pulping. Another method of separating lignin from cellulose is
to treat the wood chips with a hot alkaline solution of sodium salts; the pH
Figure 6.1 Structural model of softwood lignosulphonate.
of this solution is around 13-14. The resultant liquor contains lignin that is
totally dissolved, and hemicellulose that is only partly dissolved.
6.1.2 Lignin modification
The lignosulphonate molecule can be modified by a variety of chemical
processes. It is possible to enhance selectively certain properties and tailormake lignosulphonates for specific applications. This has allowed the commercial development of a range of speciality high-performance chemicals
that show similar broad characteristics while being distinctly different in
their specific properties.
Figure 6.3 illustrates the different molecular weight distribution characteristics as a function of chemical modification. Compared to the standard
refined product BORRESPERSE NA, it highlights the shift towards a
higher mean molecular weight with the ultrafiltrated product UFOXANE
3A, and the much tighter distribution characteristic of an oxylignin such as
VANISPERSE CB.
Figure 6.2 Structural model of sulphomethyl kraft lignin.
6.2 Wettable powders (WP)
The methodology and technology involved in developing a WP is mature,
and well understood. The dust problems associated with wettable powders
have resulted in them being superseded by suspension concentrates (SC)
and water-dispersible granules (WG). However, WPs still offer a viable
formulation system, and the recent advent of water-soluble packaging has
given a new lease of life to many WP formulations.
6.2.1 Formulation
(a) Active ingredients. Individual active ingredients will have different
milling requirements, but as a general rule the best results are obtained
when all the components (if their physical form allows) are preblended
with the active ingredient before milling. It is important to keep the particle
size distribution as narrow as possible, otherwise powder compacting
can lead to poor wetting and dispersing characteristics. Liquid active
ingredients must be absorbed on a suitable carrier prior to the preblending
stage.
Borresperse NA
Ufoxane 3A
% Fraction
Vanisperse CB
Molecular Weight
Figure 6.3 Molecular weight characteristics as a function of chemical modification, for three
product types.
(b) Fillers. A wide range of fillers is available to the formulator, both
natural and synthetic. The particular physical and chemical properties of a
WP system will dictate the selection, and it is not necessary to go into such
detail here. Suffice to say that all the fillers currently used are compatible
with lignosulphonate dispersants.
(c) Anti-coking agents. If the active ingredient has a low melting point, or
the loading of the active ingredient is high, an anti-caking agent will assist
the grinding process and improve the flow characteristics of the WP, both of
which improve the final suspensibility. Many of the carriers used to absorb
liquid active ingredients also function as anti-caking agents.
(d) Wetting agents. The combination of lignosulphonate dispersants
and sodium alkylnaphthalene sulphonate works well for most active
ingredients, but occasionally a non-ionic ethoxylate may be more effective.
The synergy observed between lignosulphonate dispersants and a
wetting agent can permit the use of reduced amounts of these higher-cost
components.
(e) Dispersants. Lignosulphonate dispersants have a long association
with the formulation of WPs, and these products are used for formulating a
wide range of pesticide active ingredients. High dispersion efficiency coupled with economy of use make them an obvious choice. The extensive
range of commercially available lignosulphonates includes products with
differing degrees of sulphonation and molecular weight distribution. The
significance of these two characteristics lies in the differing hydrophobic
nature of pesticide active ingredients. A certain amount of trial and error
will always be necessary, but generally the more hydrophobic active ingredients require a dispersant with a lower degree of sulphonation, and higher
mean molecular weight.
This effect is well illustrated in Figure 6.4, which shows increased
suspensibility of an 80% sulphur WP as a function of dispersant type and
concentration. As an example, the series Borresperse NA, Ultrazine NA
and Ufoxane 3A is in order of increasing dispersant hydrophobicity
(which is derived from their respective methods of manufacture). The
ultrafiltrated (high molecular weight) and desulphonated Ufoxane 3A has a
greater affinity for the hydrophobic sulphur. This allows a higher level of
interaction and subsequent dispersion efficiency.
(f) Water-soluble packs. Experimental work has shown that lignosulphonate's dispersion performance is not affected by the presence of the
dissolved polymers used in water-soluble films, nor do they affect the disintegration rate of these films in water.
6.2.2 Production methods
(a) Solid active ingredients. Where physical form allows, all powder components should be preblended prior to milling, though it may be necessary
to pregrind the active ingredient. The blended material is then milled in a
pin mill or air-jet mill. Experience has shown that lignosulphonate dispersants assist the milling process by becoming adsorbed onto the crystalline
active ingredient, thus increasing electrostatic repulsion and improving
milling efficiency. This can also be of assistance when milling lower melting
point active ingredients.
(b) Liquid active ingredients. Liquid technical (active) ingredients and
liquid or waxy wetting agents must be incorporated into a carrier, by spraying onto the absorbent in a suitably equipped blender. The wetting and
% Suspensibility
Borresperse NA
Ultrazine NA
Ufoxane 3A
% Dispersant
Figure 6.4 Suspensibility of 80% sulphur wettable powder as a function of dispersant type and
concentration.
suspensibility of the WP may be improved by incorporating the wetting
agent into the absorbent before the liquid technical ingredient. The remaining powder ingredients including the lignosulphonate are then added, and
the blend then milled by standard techniques.
Table 6.1 presents some typical examples of WP formulations.
6.3 Water-dispersible granules (WG)
This type of formulation is becoming increasingly popular, due mainly to
the requirement to improve the safety and efficiency of dosing and handling. A WG can be regarded as the granular form of a wettable powder,
Table 6.1 Typical WP formulation examples (wt%)
Active ingredient
Lignosulphonate
dispersant3
A
Captan
Carbendazim
Diuron
Malathion
Mancozeb
Sulphur
a
b
85
50
80
50
80
8 0
B
C
Wetting
agentb
D
2
A
B
Fillers etc.
Anticaker
3
1
4
4
2
3
6
3
3
1
1
30
4
Kaolin
to 100
to 100
to 100
to 100
to 100
t o1 0 0
Dispersants: A = Borresperse NA; B = Ufoxane 3A; C = Vanisperse CB; D = Polyfon H.
Wetting agents: A = Naphthalene sulphonate; B = Non-ionic ethoxylate.
and lignosulphonate dispersants are an invaluable aid to the formulator
looking to develop WG from existing WP formulations or new novel WG
applications.
6.3.1 Formulation
(a) Active ingredients. When using solid active ingredients it is necessary
to mill the technical component to obtain a particle size of l-10.[im. However, it is important to optimize the particle size distribution. If the distribution is too broad, the particles become closely packed and redispersibility of
the granule is impaired. Also, if the active ingredient is milled too finely, a
disproportionate amount of dispersant will be required to obtain good
suspensibility. Liquid active ingredients can also be formulated if they are
first adsorbed onto a silica carrier, though selection of the optimum granulation method then becomes more important.
Lignosulphonate products have also been found to function as grinding
aids. The dispersant becomes adsorbed onto the crystalline active ingredient, and by increasing the electrostatic repulsion between the crystals
it helps the grinding media function more efficiently. In addition, if the
dispersant is present in the grinding stage, the final suspensibility of the WG
will usually be improved.
(b) Wetting agents. The sodium alkylnaphthalene sulphonates are found
to work well in combination with lignosulphonate dispersants for most
formulations. However, in certain cases an ethoxylated block copolymer
type may be the choice.
(c) Fillers, carriers and disintegrators. Individual formulation recipes and
their mode of manufacture can have a distinct effect on the final properties
of a WG, and precipitated silicas have been found to be effective (as
grinding aids or carriers). The balance of filler, whether it is kaolin or a
disintegrating agent, is left to the formulator's discretion, though experience has shown that these materials function well in combination with
lignosulphonate dispersants. In addition, it is worth mentioning that although lignosulphonates are not true disintegrating agents, selection of the
correct lignosulphonate dispersant will greatly assist redispersibility and
granule spontaneity.
The best formulations are usually those that contain the lignosulphonate
dispersant that gives the best balance between redispersibility and dispersion efficiency.
(d) Binders. Lignosulphonates are very effective hydrophilic binders,
forming an inactive film binding system. They are particularly useful in
developing WG formulations as they combine both binding and dispersing
properties.
(e) Dispersants. The wide range of lignosulphonate dispersants commercially available is suitable for formulating a wide range of pesticide
actives as WGs. The formulator can find products with varying degrees of
sulphonation and varying molecular weight distribution. The significance
of these two characteristics lies in the differing hydrophobic nature
of pesticide actives. A certain amount of trial and error will always be
necessary, but as a general rule the more hydrophobic active ingredients
require a dispersant with a lower degree of sulphonation, and a higher mean
molecular weight.
Occasionally a lignosulphonate dispersant will function best when
used as a codispersant. Among some of the effective combinations
known are their use with polycarboxylates and naphthalene sulphonate
derivatives.
In addition to traditional trial-and-error techniques, quantification of the
relative affinity of a dispersant for the pesticide substrate being dispersed
can give invaluable information [1, 2]. This can also aid future formulation
studies, by characterizing more precisely the performance of a surfactant
system. Figure 6.5 shows adsorption isotherms obtained by the serum replacement method for a herbicide-lignosulphonate system. It clearly shows
the higher level of surface adsorption for a sulphomethylated kraft lignin
with a low degree of sulphonation (e.g. Reax 85A from Westvaco or
Diwatex 40 from Borregaard), compared to a standard refined product such
as Borresperse NA. Although these isotherms were obtained for dilute
systems containing only the dispersant and active ingredient, the higher
level of adsorption can be extrapolated to increased dispersion efficiency in
a finished formulation.
Adsorption (mg/m2)
Purified Sodium Lignosulphonate
Sulphomethylated Sodium Kraft Lignin
Thousands
Concentration (ppm)
Figure 6.5 Surface adsorption on Diuron as a function of product type and concentration.
6.3.2 Production methods
Lignosulphonate dispersants are used to formulate WGs by all the common
granulation processes, and no particular limitations are encountered when
selecting a product for use in a certain process. However, one formulation
recipe will give different granule characteristics depending on the granulation method employed, and minor modifications to the initial recipe can
improve the final properties of the WG.
(a) Pan granulation. Although pan granulation gives a product with good
redispersion properties, they often have poor resistance to handling. If
however, during the final stages of granulation a small quantity of lignosulphonate is sprayed onto the pan, the granule surface will become more
tightly bound and have less tendency to dust. A slight increase in redispersion time may occur but this will not be enough to detract from the
WG's essential properties.
(b) Fluid bed granulation. WGs made by this process share much the
same properties and corresponding drawbacks as those made by pan granulation. The final product has excellent disintegration properties, but this
also means that it is the least resistant to handling, and it is often necessary
to use a lignosulphonate in the granulating fluid to aid agglomeration and
final hardness.
(c) Spray drying. Generally spray drying produces easily redispersible
granules. However, to minimize the effects of surfactant migration
(which can give poor handling resistance and inferior redispersibility), the
insoluble solids content of the atomizer feedstock should be as high as
possible.
Use of a high-performance lignosulphonate dispersant will keep the
feedstock sufficiently fluid, even with a high solid loading.
The wide range of lignosulphonate dispersants commercially available
are particularly effective as dispersants for spray-dried formulations, and
the product Ufoxane 3A from Borregaard is worthy of special attention.
Experience has shown lignosulphonate dispersants of this type to have
excellent heat stability, and spray-dried WG formulations containing them
show higher suspensibilities than those made with other lignin types or
some synthetic dispersants.
(d) Extrusion granulation. Obtaining good WG properties by extrusion
requires a rather different approach compared to the other methods. Granule durability is not a problem, and indeed must be limited if the WG is to
have acceptable redispersibility. It is important to optimize the level of
dispersant required to suspend the active ingredient, so that the total binder
content of the system is kept to a minimum. Normally lignosulphonate
products have a sufficiently high rate of dissolution, but if greater
redispersibility is required a suggested combination is a lignosulphonate
dispersant (high dispersing/low binding grade) with an auxiliary binder of
very high dissolution, or addition of a suitable disintegrating agent. In all
cases the moisture content of the extruder feedstock is vital. Too high a
moisture content will result in granules with an almost closed or impervious
surface. If a relatively dry mix is used, the extruded granules have a rougher
texture, and a much higher surface area available for wetting.
Table 6.2 gives examples of WG formulations.
6.4 Suspension concentrates (SC)
The absence of dust and solvents, combined with the ease of handling that
SCs offer, has made them justly popular. However, recent initiatives on the
disposal of used packaging may limit significant further development of SC
formulations in some agrochemical markets.
6.4.1 Formulation
(a) Active ingredients. One of the drawbacks of the SC system is that it is
not suitable for every type of active ingredient. The main criterion for a
suitable active ingredient is that it must be practically insoluble in the water
phase. Problems of crystal growth (Ostwald ripening) during storage can
Table 6.2 WG formulation examples (wt%)
Active ingredient
Lignosulphonate
dispersant3
A B
Bacillus thuringiensis
Carbendazim
Copper hydroxide
Chlortoluron
Diuron
Mancozeb
Simazine
Thiram
Wetting
agents Codispersantsb
C D A B
80
8
80
6
80
20
80
12
80
12
75 15
90
8
85
9
3
2
C
Production
method0
Fillers etc.
Anticaker
Kaolin
to 100
to100
5
8
3
3
2
3
to 100
to 100
3
to 100
PG
FB
SD
FB
EX
SD
EX
PG
a
Dispersants: A = Borresperse NA; B = Reax 85A; C = Ufoxane 3A; D = Ultrazine NA.
Wetting agents: A = Naphthalene sulphonate; B = Non-ionic ethoxylate; C =
Polycarboxylate dispersant.
0
Production Method: PG = pan granulation; FB = fluid bed granulation SD = spray drying;
EX = radial extrusion.
b
occur even at very low levels of solubility. The latter problem can be
minimized if the dispersants employed are also good crystal growth inhibitors, and there are a number of commercial lignosulphonate dispersants
that function very effectively in this area.
(b) Wetting agents. It will not always prove necessary to use a wetting
agent in combination with lignosulphonate dispersants. However, if
milling problems are encountered, the addition of a small quantity of
an ethoxylated block copolymer wetting agent will often smooth the
process.
(c) Dispersants. In an SC system, stability against irreversible flocculation
can be achieved by use of high-performance dispersants. A polyelectrolyte
material such as lignosulphonate prevents flocculation in two ways:
• electrostatic repulsive forces are generated by the presence of an
electrical double layer at the particle-solution interface [3];
• steric repulsion, arising from the apparent expansion of the particle due
to the adsorbed dispersant [4].
The latter effect is more prevalent with dispersants of higher mean molecular weight and a lower degree of sulphonation. However, other factors
can also have influence and experience has shown that more detailed experimental work into the nature and degree of the pesticide-dispersant
interaction (as mentioned in the WG section) can greatly assist selection of
the optimum surfactant system [5]. Figure 6.6 illustrates the significant
Viscosity (cp)
System Viscosity Profile
Concentration (% Lignin)
Figure 6.6 Effect of dispersant concentration on the viscosity of a 59% kaolin clay slurry.
decrease in slurry viscosity for a typical high-solids suspension when using
a lignosulphonate dispersant.
(d) Thickeners. The purpose of thickening agents is to achieve sufficient
long-term stability by means of gravitational stabilization; this prevents
sedimentation and keeps the active in suspension. SC formulations are
often stabilized by anti-settling agents such as xanthan gum and bentonite
or smectite clays, either alone or in combination. Individual experiments
are required to balance the effect of dispersant viscosity reduction, and the
thickening of the system by gravitational stabilization.
Solutions containing xanthan gum can be prone to bacterial degradation,
and it is important that a suitable biocide is incorporated.
(e) Anti-freezing agents. Monoethylene glycol (MEG) and monopropylene glycol (MPG) are suitable for use with lignosulphonates, but caution
must be exercised to ensure the active ingredient is not soluble in the
antifreeze as this can lead to crystal growth problems.
(f) Anti-foaming agents. The physical and chemical nature of the SC system will dictate the selection of the best anti-foaming agent. Polysiloxanes
have been found to work well in combination with lignosulphonate
dispersants.
6.4.2 Production methods
The surfactant system of a SC performs four major tasks during production.
(a) Particle wetting. Low molecular weight surfactants and lignosulphonates help to bring about the rapid conversion of the coarse technical
component into a form that can be efficiently milled by prewetting the
active.
(b) Efficient milling. After the initial wetting of the active ingredient, the
surfactant then becomes adsorbed onto the particle surface. As the mechanical breakdown of the active ingredient proceeds, the available surface
area also increases, and in order to maintain a sufficiently low viscosity the
lignosulphonate becomes adsorbed onto the newly created particle surfaces, and stops reagglomeration of the active ingredient. At this point care
must be taken, since over-grinding or an insufficient level of dispersant will
give a total surface area in excess of the capacity of the dispersant, and the
viscosity can increase very quickly.
(c) Prevention of flocculation. The adsorbed lignosulphonate generates
forces of repulsion to counter the van der Waals attractive forces of the
dispersed active, which will otherwise lead to agglomeration and
flocculation. Long-term stability is achieved by the use of additional gravitational stabilizers.
(d) Maintaining a manageable viscosity. At certain stages of production,
and especially at the final product packaging the SC must be in a form
where it flows easily and can be pumped without difficulty (Figure 6.6).
(e) Rheological properties. The rheological behaviour of SC systems is
worthy of closer study, as a way of fine tuning a formulation to give the
optimum balance between suspension stability and product viscosity. The
example selected here is a 450 g/1 Carbendazim SC that utilizes a combination of both organic (xanthan gum) and inorganic (smectite clay) thickening
agents. These two materials actually display quite different rheological
properties, the combined effects of which can give beneficial properties to
an SC formulation.
An SC formulation must have a sufficiently high viscosity to protect it
against sedimentation during storage, but the viscosity must not be so high
that the product is difficult to handle or shows insufficient 'bloom'. Figure
6.7 shows viscosity as a function of shear stress for the Carbendazim SC
system using two different lignosulphonate dispersants.
ULTRAZINE NA
Viscosity (mPa s)
Borresperse NA
Shear Stress
Figure 6.7 Effect of shear stress on viscosity for Carbendazim 450 SC.
The system using Ultrazine NA shows sufficient thixotropic behaviour
for the suspension stability to be maintained during storage. However, since
the system also displays pseudoplastic behaviour, the viscosity drops dramatically when slight shear is applied. As a result of this the formulation
containing Ultrazine NA is easier to both handle and store.
Table 6.3 presents formulations for SCs using speciality lignosulphonate
dispersants.
Table 6.3 SCs formulated with speciality lignosulphonate dispersants (g/1)
Active ingredient
Atrazine
Carbendazim
Chlortoluron
Sulphur
Ziram
a
b
c
Lignosulphonate Wetting
dispersant3
agentb Thickeners0
A
B
500
450
500
800 40
500
40
C
25
D
A
A
30
30
2.0
0.5
1.0
4.0
1.0
0.5
0.5
2.0
2.0
B
C
3.0
4.0
4.0
Other additives
M P G Antifoam
50
50
50
50
50
2.0
2.0
2.0
2.0
2.0
Water
to
to
to
to
to
IL
IL
IL
IL
IL
Dispersants: A = Borresperse NA; B = Reax 85A; C = Ufoxane 3A; D = Ultrazine NA.
Wetting agent: A = Non-ionic ethoxylate.
Thickeners: A = Xanthan gum; B = Bentonite; C = Veegum.
6.5 Oil-in-water emulsions (EW)
6.5.7 Formulation
The main difference between EWs and ECs is that in the former some or all
of the solvent is replaced with water, and it is the growing desire to reduce
solvent use in agricultural applications that has resulted in increasing interest in EW formulations in recent years. This type of formulation is particularly useful for liquid active ingredients that are not easy to absorb onto a
carrier, and low melting point solid active ingredients that cannot be finely
milled to produce a suspension concentrate.
The stabilization of emulsions by lignosulphonates is a result of adsorption at the oil-water interface, establishing electrostatic repulsive forces
and a semi-rigid film.
The presence of this semi-rigid film contributes significant mechanical
stability to these emulsions. Lignosulphonate dispersants are very effective
in stabilizing immiscible liquids in water to give oil-in-water emulsions.
These emulsions are resistant to variations in pH, temperature variations,
high electrolyte concentrations and ageing. It is not recommended to use
lignosulphonates in combination with other surfactants and emulsifiers
when producing EWs, as compatibility problems can arise due to competing
stabilization mechanisms.
6.5.2 Production methods
Lignosulphonate dispersants stabilize EW formulations by preventing
the coalescence of the suspended oil-solvent phase containing the active
ingredient. Lignosulphonates do not significantly lower the surface and
interfacial tensions, so the oil phase must be first subdivided in a
homogenizer to obtain a fine-grained emulsion which is then added to
the dispersant solution under further homogenization to produce the oilin-water emulsion.
6.6 Controlled release
The mode of action of a controlled-release formulation is often tailored
very specifically to a particular application, and as such use a wealth of
different techniques and technologies.
The diversity and selectivity of controlled release systems means that
they deliver a wide range of quite specific features to their individual
applications. However, it can be said that they all aim to fill the following
criteria:
• improve efficiency;
• use no toxic solvents and inert components;
•
•
•
•
reduce phytotoxicity;
reduce environmental impact;
limit groundwater contamination;
reduce health risks during production and use.
Lignosulphonates and their many modified forms offer great versatility for
developing tailor-made controlled-release mechanisms. As an example,
lignin can be adapted to give varying degrees of solubility, polarity,
compleximetry and porosity, etc.
6.6.1 Granules
The traditional granule formulation is a crude form of controlled release in
that it can have a longer effective pest control period than spray application.
Lignosulphonates are effective binding and agglomeration aids in granule
production, forming an inactive film binding system. They also combine
dispersion ability with good resistance to caking of the agglomerated
product. The controlled-release capabilities of a granule can be refined by
addition of agents to either speed up or slow down the rate of diffusion into
the soil. Varying the quantity of binder can impart different rates of granule
disintegration.
6.6.2 Tablets
Lignosulphonates offer two important characteristics to the chemist
developing controlled-release tablets:
• as a naturally occurring polymer lignin is environmentally benign, and is
classed as inherently biodegradable, offering possibilities for use as a
controlled-release matrix;
• high dispersion power; high-performance lignosulphonate dispersants
can be used to modify the release rate of the active ingredient from the
tablet.
6.6.3 Gels
The ability to produce crosslinked gel structures by modifying lignin with a
suitable crosslinking agent offers many possibilities. These gels display a
high degree of reswellability in water, of particular use when formulating
water soluble pesticides such as 2,4-D, though water-insoluble active ingredients can also be formulated by pretreatment with a suitable solvent. The
release rate can be tailored to a specific application, from a dump release
mechanism right through to an extended period of continuous uniform
release.
The inclusion of absorbent fillers for volatile active ingredients or void-
creating materials into the gel matrix can have a pronounced effect on the
absorptive characteristics of the gel, allowing a greater range of pesticide
actives to be formulated in this manner.
Which crosslinking agent used is also important in terms of the absorptive capacity of the gel. Typically a formaldehyde crosslinked gel will swell
to around six times its dry weight, whereas epichlorohydrin gels show
roughly half this capacity. Selection of the crosslinking agent will also be
dictated by the desired release rate.
6.6.4 Microencapsulation
At present this is the most important of the controlled release methods, and
has seen the greatest commercialization. The principal methods for producing microcaps with lignosulphonates are by processes of coprecipitation.
There are numerous documented methods for producing microcaps in this
way, but a general method is as follows:
1.
2.
3.
4.
5.
6.
7.
prepare a lignosulphonate/emulsifier solution;
incorporate the active into the aqueous phase;
mix to form an emulsified dispersant-active ingredient system;
precipitate the solution with a mineral acid or polyvalent salt;
harden the microcaps by pH buffering;
separate and concentrate;
process into desired formulation type.
Selection of the most suitable lignosulphonate will depend on many factors,
including the physical and chemical nature of the active ingredient, the
target pest and the controlled-release period required. This can be illustrated by two examples.
• Microencapsulation of a stomach contact insecticide (e.g. Carbosulfan).
The lignin-encapsulating polymer will be insoluble at neutral or acidic
pH, as found in normal soil contact. However, the lignin will be soluble in
the alkaline pH environment of an insect's digestive system, thereby
providing very specific release conditions.
• The soil mobility of the herbicide Atrazine can be controlled when encapsulated with a lignosulphonate of low solubility and high molecular
weight. Certain lignosulphonates have a high adsorptive capacity for
Atrazine, providing a ready mechanism of controlled release, and also
help to limit leaching into groundwater.
As well as providing the encapsulating polymer, the presence of a
lignosulphonate dispersant can greatly improve the microcap's efficiency
and fine tune the ultimate release rate. Systems have been investigated
where one material provides both the encapsulation media and the
dispersant.
The diverse and selective nature of controlled-release mechanisms,
particularly in the area of microencapsulation, means it is difficult to give
an exhaustive list of all the modified forms of lignin available to the
pesticide formulator. However, it should be stated that the versatility of
lignin for such specialized delivery systems has probably not yet been fully
exploited.
6.7 Ultraviolet protection
Absorbance
Many biopesticides, pesticide active ingredients and agrochemical agents
are susceptible to decomposition when exposed to UV radiation from
sunlight. The active ingredient can be rendered biologically inactive by
UV-initiated or catalysed degradation.
An important part of lignosulphonates' versatility as controlled-release
matrices is that, due to their high aromatic content, lignin derivatives
show excellent UV absorption properties. The range and degree of UV
absorbance changes as a function of the chemical bonds and groups present
in the lignin molecule (Figure 6.8).
One procedure is to encapsulate the pesticide active ingredient in a wall
material consisting of lignin or a lignin-gelatin complex. Water-soluble
active ingredients can also be protected in this manner by the emulsification
in water of an active ingredient, lignin and gelatine mixture prior to
encapsulation. As an example, the photolytic degradation of the pyrethoid
Wavelength (nm)
Figure 6.8 Ultraviolet absorbance by lignin as a function of wavelength.
% Degradation
Lignin Encapsulated
Unprotected
Time (4 week period)
Figure 6.9 Ultraviolet protection of Parathion: degradation versus time.
insecticide Permethrin, can be reduced by up to 50% over a 2-week
period. Figure 6.9 gives another example, showing the increase in UV
protection of Parathion when encapsulated with a specifically modified
lignosulphonate.
6.8 Compatibility agents
In order to reduce expensive multiple applications, it is often desirable to
combine the application of liquid fertilizer and pesticide. The stability
and compatibility of the resulting tank mix must be ensured. The use of
high-performance lignosulphonate dispersants gives good compatibility,
and allows efficient uniform application.
6.9 Adjuvants
The true potential for lignosulphonates and their derivatives as adjuvants
has probably not yet been fully recognized. Lignosulphonates show many
of the basic properties required of an adjuvant, and their presence as
formulation additives can assist efficacy. However, there could be further
possibilities, for example the use of high molecular weight derivatives as
spray control additives.
The use of lignin derivatives as tank-mix additives is a potential develop-
ment area, and interest should increase as the inventory of chemicals used
in agriculture comes under even greater scrutiny.
6.10 Complexing agents
Where problems of hard water occur, it is advantageous if the
lignosulphonate dispersant employed also exhibits chelating and sequestering properties. Lignosulphonates can be regarded as complexing agents,
though chemical nature and specific modification mean that certain products are more effective. Products such as Reax 100 M from Westvaco, and
Marasperse AG from Borregaard, have been specifically developed to have
superior complexing abilities.
6.11 Environmental and regulatory information
Environmental issues for lignosulphonate products can be divided into two
areas:
• health and safety of personnel handling the products;
• effect of the products on the natural environment.
6.11.1 Personnel
Toxicological studies carried out on lignosulphonate products (including
chemically modified variants), together with over 50 years of experience
in use, have shown them generally to be non-toxic and non-irritant.
No human health problems are attributable to long-term exposure to
lignosulphonates.
6.11.2 Environmental
Lignosulphonates have been applied to roads, used in animal feeds, and a
host of other applications where the final product comes into contact with
human foodstuffs, for more than 30 years without deleterious effects.
Standard lignin products have the following properties:
• no dioxins present; no other organics are present at dangerous levels;
• toxic trace minerals are below EPA toxicity limits (as set by the US
Environmental Protection Agency);
• a low order of toxicity towards fish;
• non-toxic orally, and non-irritating to the skin and eyes of animals;
• very low toxicity towards plant life: studies have shown that lignins are
not phytotoxic to plant foliage and root systems;
• residuals are resistant to decay;
• they are a renewable and strictly managed resource.
Even when spread on land there is little risk of groundwater contamination. Published data indicate that at less than 10kg/m2, no environmental
damage occurs.
Lignosulphonates do not solubilize toxic heavy metals and transport
them to the groundwater. Lignosulphonates form insoluble salts with heavy
metals.
The US Food and Drug Administration has issued regulations for the
safe use of lignosulphonates in agrochemical formulations:
1. as adjuvants in pesticide chemical formulations exempt from requirements of tolerance when applied pre- or post-harvest: 21 CFR 182.99,
40 CFR 180.1001, section (c);
2. exempt from requirements of tolerance when used as ingredients in
pesticide formulations applied to animals: 40 CFR 180.1001, section (e);
3. as dispersants or stabilizers in pesticides applied pre- or post-harvest to
bananas: 21 CFR 172.715.
The relevant EPA registration numbers are as follows:
Calcium lignosulphonates
Sodium lignosulphonates
Ammonium lignosulphonates
B-058-1511
B-058-1486
B-058-1956
The Chemical Abstracts series numbers are:
Calcium lignosulphonates
Sodium lignosulphonates
Ammonium lignosulphonates
CAS 8061-52-7
CAS 8061-51-6
CAS 8061-53-8
References
1.
2.
3.
4.
5.
Humphrey, S.T. (1994) IUPAC Pesticide Congress, Washington, DC.
Misselbrook, J. (1991) in Proceedings of the Brighton Crop Protection Conference - Weeds.
Heath, D. and Tadros, T. (1983) Colloid and Polymer Science, 261, 49-57.
Le Bell, J. (1983) Unpublished dissertation, Abo Akademi.
Larsson, A. (1994) Surface Characterisation Techniques, YKI, Stockholm.
7 Novel surfactants and adjuvants
for agrochemicals
S. REEKMANS
7.1 Polymeric surfactants and stability
7.1.1 Introduction
Polymeric surface-active agents and colloidal chemicals have been encountered in industry for a long time. Moreover, the number of industrial processes and products in which these materials can be used has been
increasing continuously for the last two decades.
The most commonly used polymeric surfactants include
• ethylene oxide-propylene oxide block copolymers, which are used extensively as low-foaming surfactants and wetting agents, dispersing agents
and dispersion stabilizers, demulsifiers, defoaming and anti-foaming
agents, etc.;
• condensation products of formaldehyde with substrates that contain
active hydrogen, notably naphthalene sulphonates and phenols or alkyl
phenols: the former are superior dispersing agents for solids in media that
have a high polarity;
• chemically modified natural polymers, for example lignosulphonates
(dispersing agents), cellulosic derivatives (thickeners and suspending
agents), proteins (gelling agents, flocculants, and dewetting agents);
• acrylic and vinyl polymers (dispersing and suspending agents, and
thickeners).
The main characteristics of polymeric materials that are important in
these applications are their adsorption properties at the interface between
immiscible substances. The benefits of using such materials are derived
from these adsorption properties, which enable interfacial properties to be
modified in a controlled manner, either to stabilize or to destabilize a
colloidal system (Bohn and Lyklema, 1976; Napper, 1968; Bognolo, 1990).
7.7.2 (De)stabilization of colloidal systems
Before considering the stabilization of colloidal systems, it is first necessary
to understand the causes of destabilization, and then to examine the pos-
sible ways of preventing it from occurring. The principle sources of instability are
• flocculation, coagulation and coalescence of the particles in the dispersed
phase resulting from collisions during, for example, a Brownian
encounter;
• growth of larger particles at the expense of the smaller ones, owing to the
finite solubility of the dispersed phase in the continuous medium (crystal
growth or Ostwald ripening);
• destruction or modification of the particle stabilizing barriers by chemical
or physico-chemical interactions.
Destruction or modification of the particle stabilizing barriers usually
results from the use of a chemically unstable agent; this clearly must
be avoided. Modifications that result from ageing of the adsorbed layer, e.g.
crosslinking, gelling, etc., may also lead to destabilization; this too must be
prevented.
Instability caused by the growth of larger particles can be controlled by
choosing a continuous medium with a lower solubilization power, or a
dispersed phase with lower solubility, if this is possible. Proper surfactant
choice may eliminate or reduce the tendency towards Ostwald ripening.
However, in the vast majority of cases, the instability is the result of
particles colliding. This leads to flocculation as a first stage, which is often
followed by coagulation and/or coalescence. Thus the main mechanisms for
stabilizing colloidal systems are to provide the particles in the dispersed
phase with a sufficiently strong protective layer, which prevents their close
approach where strong attractive London or van der Waals forces would
lead to their irreversible aggregation, or alternatively to make the attraction
between particles when they approach closely so small that the contact can
be reversed with thermal energy (Verway and Overbeek, 1948).
In principle, any material that can be adsorbed onto the surface of
the particles in the dispersed phase, and which extends stabilizing chains
towards the continuous medium, can be used to provide the protective
barrier. A variety of chemical species have been used in laboratory
experiments and industrial applications for this purpose. They include alkyl
aryl hydrocarbons, alkoxylated alcohols or alkyl phenols, polyvinyl alcohol
block copolymers of alkylene oxide, graft copolymers of polystyrene or
polymethyl methacrylate, etc.
In practice, it is generally acknowledged that polymeric species give more
effective steric stabilization than monomeric molecules (Walbridge, 1975).
7.1.3 Colloidal stabilization
The use of ionic, usually anionic, surfactants to stabilize colloidal particles
by electrostatic force is well known. The DLVO theory of electrostatic
stabilization is very familiar and has been used for guidance when preparing
formulations with ionic surfactants (Friberg and Jones, 1993). Coupled with
the fact that ionic surfactants were available earlier than ethoxylated nonionics, and that they are more cost effective when compared to non-ionic
surfactants in less demanding conditions for emulsions or dispersions, the
use of ionic surfactants is still fairly widespread. Nevertheless, their use
does have some serious drawbacks:
• sensitivity of the stabilising moiety to electrolyte concentration;
• their effectiveness is limited to media with a high dielectric constant;
• difficulty in producing tailor-made molecules for maximum interfacial
adsorption and charge density distribution.
In a climate where formulation chemists demand much broader applicability of surfactants and where formulations are becoming even more
complex, it is the steric stabilization phenomena induced by non-ionic
surfactants that are becoming more important. Not only are these steric
stabilization mechanisms used to stabilize emulsions and dispersions in
aqueous media (Clayfield and Jumb, 1968), but in some types of surfactants
these same mechanisms are used to stabilize non-aqueous media (section
7.1.5).
The advantages of steric stabilization are very clear:
• emulsification and dispersion effects in aqueous and non-aqueous media;
• the possibility of designing tailor-made molecules;
• reduced sensitivity to high electrolyte concentration.
All the advantages of non-ionic surfactants are fully employed when polymeric surfactants are used. In practice, it is generally acknowledged that
polymeric surfactants are better at generating the conditions needed for
steric stabilization to be effective; these include
• complete surface coverage, thus preventing contact between unprotected
areas;
• no desorption of anchoring chains during particle collision;
• the maximum number of configurations possible for the stabilizing
moiety when collisions are not occurring;
• good solvation of the stabilizing chains by the continuous phase.
To enable complete surface coverage and no desorption on collision
requires that the adsorption energy of the stabilizing molecule must
be large. This is achieved better with polymers because of the greater
number of points of contact with the surface per molecule; this makes
the total net adsorption energy high even if individual contacts are weak.
Also, statistically, it is more difficult to desorb a molecule that is attached
through multiple anchoring points than one that is adhering via a single
linkage.
The number of possible configurations increases rapidly with molecular
size. Small molecules may be regarded as essentially non-flexible, only
their orientation relative to the surface is counted as different conformation. With polymeric materials the possibility of additional conformations arises owing to the relative size of the loops and, because of their
comparatively large dimensions, from the actual steric arrangement of each
loop.
The structural suitability of the materials described above for steric
stabilization can be inferred from measurements of the hydrodynamic
thickness of the surface layer and of the equilibrium polymer concentration
in the solution and in the surface layer. These have shown the following
features.
• Low molecular weight oligomeric species result in thinner hydrodynamic
barriers than the corresponding more highly polymerized molecules
(Walbridge, 1975).
• Random copolymers form diffuse layers, in which the concentration of
polymer is not significantly greater than in solution. Graft copolymers,
in contrast, give much more concentrated layers, and the difference
in the equilibrium concentration between the solution and the layer
is significantly higher. This effect enables suspension concentrates,
suspoemulsions and oil-water emulsions of higher concentrations to be
made (Knowles, 1995).
Experimental evidence is in line with theoretical predictions and with
stabilities observed in practical conditions. There are also indications that,
for polymeric materials with a broad molecular weight distribution, the
thickness of the sterically stabilized protective layer is higher than the
hydrodynamic one, whereas for oligomeric species the two values are probably similar (Walbridge, 1975).
A key feature of sterically stabilized colloids is that the dispersion is
indefinitely stable as long as complete surface coverage by the protective
molecules is achieved and no desorption or surface displacement occurs
when particles collide (Tadros, 1991; Friberg and Jones, 1993). This is valid
in principle for systems with either monomeric or polymeric stabilizers, but
is better realized with polymeric species. Calculation of the total potential
energy shows that it is always positive, apart from the possible existence of
a small minimum at relatively high separation distances, and increases
sharply as the interparticle distance decreases (Evans and Napper, 1973).
The minimum is small compared with the thermal energy, so flocculated
particles can be redispersed easily when thermal energy is applied.
This particular aspect of steric stabilization has probably been the main
driving force behind both the academic investigations and the industrial
applications, and of the use of polymeric surfactants in a large variety of
systems, quite often with remarkably successful results.
7.1.4 Structure of polymeric surfactants for steric stabilization
Not every polymeric material behaves as an effective steric stabilizer.
Oligomers, homopolymers or random copolymers are usually unsuitable,
particularly if they are soluble in the continuous phase and lack strong
anchoring points for the dispersed particles; in these conditions sufficiently
extended chains or loops cannot be established and strong adhesion to the
surface cannot be achieved. Preferred molecular structures include block
copolymers of the A-B or A-B-A type, or graft copolymers, which contain
groups that anchor to the particles in the dispersed phase, and solvatable
stabilizing chains that extend into the continuous medium. One realization
of this concept is amphipathic molecules, which contain moieties that are
insoluble (anchoring) and soluble (stabilizing) in the continuous phase. The
characteristics required of each of the individual groups for optimum
stabilization are discussed below.
(a) Stabilizing moiety. The main requirement of the stabilizing moiety is
that it must be very soluble in the continuous phase. This can be explained
intuitively as the stabilizing chains must prevent particles approaching too
closely, and this is achieved better if they have a higher affinity for the
continuous medium than for similar chains adsorbed on other particles. In
fact, any interpenetration of the stabilizing layers will cause solvent molecules to diffuse into the overlapping region, hence pulling the particles
apart, while flocculation will inevitably occur if the interchain attraction
prevails (Elias et al, 1966; Napper, 1968; Hesselink et al, 1971).
(b) Anchoring moiety
Solubility. Because of its affinity for the continuous phase, the soluble
moiety cannot be adsorbed strongly enough onto the surface of the particles
in the dispersed phase to ensure that no desorption or displacement occurs
on collision. Therefore anchoring groups must be present in the stabilizing
molecule.
A method which is conveniently employed to achieve this is to block or
graft copolymerize the soluble chains onto a backbone that is insoluble in
the continuous phase. The adhesive force to the dispersed particles then
arises from the insolubility itself, or from weak interactions (van der Waals,
dipolar, low-energy hydrogen bonding) or, depending on the nature of the
anchoring moiety and dispersed particles, from stronger interactions such
as acid-base or covalent links.
When the dispersed phase is a liquid, the anchoring group, as well as
being insoluble in the continuous phase, should also be fully soluble or at
least compatible with the dispersed phase. As well as producing a stronger
adsorption at the interface, there is a substantial gain in energy owing to the
entropy of solution (in some instances spontaneous emulsification between
the two phases may occur); this further contributes to the stabilization of
the system, as an additional energy input (corresponding to the desolvation
of the anchoring moiety) will then have to be provided for coalescence to
occur.
Anchoring points. Apart from being soluble, the stabilizing molecule
must contain a sufficient number of anchoring points and the mechanism of
adhesion must allow for the stress that it is expected on the stabilized
system. Moreover, evidence obtained by studies into stabilization through
acid-base anchoring suggests that the insoluble moiety must have a certain
minimum molecular weight, otherwise the dispersant molecules tend to
behave like random copolymers with little or no stabilizing properties. For
block structures of the .. .A-B-A-B... type anchoring through acid-base
interactions, it has been demonstrated that a minimum molecular weight of
about 500 is needed for effective stabilization.
(c) Types of polymeric surfactants. Three types of polymeric surfactant
structure seem to be most relevant: 'random', 'ordinate' and 'comb'
polymeric structures (Bognolo, 1990).
'Random' polymeric structures. These products are three-dimensional
networks synthesized from polyalkylene glycols, polyols, aliphatic carboxylic acids, aliphatic and/or aromatic polycarboxylic acids or anhydrides.
An example of this type of polymeric surfactant is Atlox 4914 (HLB = 6;
Figure 7.1). The hydrophilic interactions are provided by multiple polar
Figure 7.1 Schematic representation of a random structure polymeric surface, Atlox 4912.
moieties such as ester and ether groups. The hydrophobia interactions are
provided by chains of high molecular weight hydrocarbons that are well
solvated by high- and low-polarity hydrocarbons. Such low-HLB polymeric
surfactants can be used to stabilize water-in-oil emulsions. Oil-in-water
emulsions can be stabilized by combination with high-HLB block copolymers of the A-B or A-B-A type (section 7.1.5(c)).
'Ordinate' polymeric structures. These molecules are A-B-A block
copolymers. Classical non-ionic surfactants of this type are EO-PO-EO
block copolymers. Although these structures are established emulsifiers
and dispersants for agrochemical formulations, their use has some
disadvantages. The most significant disadvantage is that desorption of
the surfactants from the interface often occurs owing to the similarity in
polarity and solubility of the alkylene oxide groups. Additionally, the
solvation of ethylene oxide units is dependent on the ionic strength of
the medium and the temperature. A further disadvantage is that propylene
oxide units have a low solubility in hydrocarbons, especially aliphatic
hydrocarbons.
A-B-A polymeric surfactants that are similar in structure to, but differ
from, ethylene oxide-propylene oxide condensates have been developed;
they have
• a more pronounced difference in polarity and solubility between A and
B;
• a stabilizing moiety (A) that is soluble in a variety of oily phases, such as
aliphatic hydrocarbons;
• the possibility of designing the hydrophilic moiety to achieve the desired
interactions with aqueous phases or different compositions;
• irreversible anchoring in the oil droplet and strong steric repulsion
between particles.
Atlox 4912 is representative of this type of polymeric surfactant (Figure
7.2). It is obtained by esterification of poly(12-hydroxystearic acid), PHSA
(A), with poly alkylene glycols (B) to give an A-B-A-type block copolymer.
Because of their structure, ordinate-type polymeric surfactants are extremely suitable as emulsifiers. Atlox 4912 (HLB = 5.5) is not only a very
effective water-in-oil emulsifier, but it can also be used to stabilize oil-inwater emulsions when combined with high-HLB block copolymers of the
A-B type, for example Atlas G-5000 (HLB - 16.9). In a concentrated oilin-water emulsion the hydrophobic PHSA chains act as the anchoring
groups into the internal oil phase, and the hydrophilic, high molecular
weight polyethylene glycol centre provides the stabilization in the external
aqueous phase. The extension of the hydrophobic side chains into the oil
phase may be several times larger than for a conventional C18-sorbitan
ester.
Figure 7.2 Schematic representation of an ordinate structure polymeric surfactant, Atlox
4912.
'Comb' polymeric structures. Comb or graft copolymers are structured
polymers that comprise a continuous adsorbing polymer backbone into
which water-soluble segments are combined like teeth in a comb. They
are highly effective at stabilizing suspended particles. Adsorption of a
continuous hydrophobic backbone onto a particle surface is stronger
and is affected less by the tendency of water-soluble portions to move off
the particle surface than it is with random polymers (Friberg and Jones,
1993).
The composition of the polymer backbone, which is insoluble in the
continuous phase, ensures strong absorption on the surface (Foy, 1996),
while the water-soluble polyethylene oxide chains extend into the aqueous
environment to ensure proper steric stabilization. Hence adhesion to the
dispersed particles arises from the insolubility itself or, depending on the
nature of the anchoring moiety and dispersed particles, arises from stronger
interactions such as acid-base or covalent links.
Atlox 4913 is a comb-type polymeric surfactant; it consists of a
polymethacrylic acid and acrylate backbone as the anchoring moiety
and polyoxyethylene chains of suitable length as the stabilizing moiety
(Figure 7.3).
Silicone surfactants can be considered to be a special type of graft
copolymer, with the silicone backbone as the hydrophobic part and the
Figure 7.3 Schematic representation of a comb-type structure polymeric surface, Atlox 4913.
polyethylene oxide chain as the hydrophilic part. They produce extremely
low surface tension (<25mN/m), interfacial tension and contact angles
(<20°) and, as such, are extremely good wetting agents. Alkylated (graft)
vinyl pyrrolidone copolymers, such as the 'Agrimer' range, are other examples of surface-active comb copolymers. Their surface activity and oil and
water solubility depend on the alkyl chain length and the concentration of
the alkyl group in the polymer (Narayanan, 1996).
7.1.5 Polymeric surfactants in agricultural formulations
(a) Aqueous suspension concentrates. With suspension concentrates the
formulation chemist always has two objectives:
• to produce highly deflocculated suspensions;
• to prevent formation of dilatant sediments as the suspension tends to
settle under gravity.
The graft copolymer Atlox 4913 is an example of a powerful dispersant that
allows the primary objective of producing highly deflocculated suspensions
to be attained; it is a broad-spectrum dispersant for organic and inorganic
active ingredients in water. Highly concentrated dispersions with a volume
fraction above 0.6% can be obtained, since this comb polymeric surfactant
adsorbs strongly onto the particle surface and provides a permanent
steric barrier that prevents flocculation. As a starting point, a concentration
of 2-3% by weight of the end formulation is recommended.
Atlox 4913 is combined ideally with Atlas G-5000 or Atlox 4894
(0.5-2%), both of which diffuse rapidly and act as a wetting, dispersing and
liquefying agent before and during milling. After milling, Atlox 4913 is
irreversibly adsorbed onto the particle surface and acts as a stabilizer. Nonadsorbing polymers, such as hydroxyethyl cellulose or polyethylene glycols,
can be added after milling to build up a three-dimensional structure (a
viscoelastic gel) in the continuous phase.
Sulphonated naphthalene formaldehyde condensates and lignosulphonates are also commonly used in agrochemical formulations. These
systems exhibit a combined electrostatic and steric repulsion. The
stabilization mechanism of polyelectrolytes is sometimes referred to as
electrosteric (Tadros, 1994). These polyelectrolytes offer some versatility
in suspension concentrate formulations, exhibiting both dispersing and
wetting properties. Since the interaction is long range in nature due to
the double layer effect, the hard-sphere type of behaviour that may result
in the formation of hard sediments is not obtained. Steric stabilization
ensures that the colloid remains stable and prevents aggregation upon
storage.
When using ionic surfactants and polyelectrolytes, it is necessary to make
sure that the electrolyte content in the medium is reduced to a minimum.
This is particularly important with polyvalent ions, such as Ca2+ or Mg2+
(ionic impurities which are present in the water that is used to prepare the
suspension), as these tend to cause flocculation at a lower concentration
than do monovalent ions (Tadros, 1994).
Control of physical stability
Crystal growth. There are several ways in which crystals grow in an
aqueous suspension. One of the most familiar is the crystal growth which
occurs because of the difference in solubility between the small and large
crystals. Another mechanism is related to polymorphic changes in solutions, and again the driving force is the difference in solubility between the
two polymorphs. In both cases the less soluble form grows at the expense of
the more soluble phase. Crystal growth is usually assumed to be governed
by two main processes: diffusion of the solute to the surface of the growing
crystal, which is followed by incorporation of particles into the structure of
the crystal lattice.
The growth of crystals in suspension concentrates may create undesirable
changes. The drastic change in particle size distribution may lead to accelerated settling of the particles, which results in caking and cementing together of some particles in the sediment. Moreover, an increase in particle
size may lead to a reduction in biological efficiency. Consequently, preventing crystal growth, or at least reducing it to an acceptable level, is essential
in most suspension concentrates.
Surfactants affect crystal growth in a number of ways (Tadros, 1973).
• They may affect the rate of dissolution by affecting the rate of transport
away from the boundary layer at the crystal-solution interface.
• If the surfactant forms micelles that can solubilize the solute, the diffusion coefficient of the solute in a micellar solution is reduced. However,
as a result of solubilization the concentration gradient is greatly increased, thus increasing the rate of crystal growth. Only when the diffusion of the dispersing agent molecule is sufficiently rapid does it lower the
flux of the solute (compared to solute in which it is absent), and thus
lower the rate of crystal growth.
• Dispersing agents are expected to influence crystal growth, which is
controlled by surface nucleation, in other ways: adsorption of a dispersing
agent at the surface of the crystal can drastically change the specific
surface energy and effectively make it inaccessible to the solute.
The success of comb or graft copolymers as crystal growth inhibitors
can be explained first because they do not form conventional micelles,
and second because they show a strong affinity for the crystal surface of
many active ingredients. Many surfactants and polymers will act as
crystal growth inhibitors and prevent solute deposition if they adsorb
strongly onto the crystal faces. However, the choice of an inhibitor is still an
art, and there are few rules that can be used when selecting crystal growth
inhibitors.
Claying and caking. Highly deflocculated concentrated suspensions can
be obtained by using block or graft copolymers. Because the material is
completely and irreversibly covered by the dispersant, the stabilized dispersion can be weakly flocculated by adding a free (non-adsorbing) polymer
such as polyethylene oxide above a critical concentration; the critical concentration depends on the molecular weight of the free polymer. This
phenomenon is known as depletion flocculation and can be induced only
when no polymer can adsorb on the particle surface, that is when the
particles are completely and irreversibly covered with surfactants. It is easy
to redisperse the weakly flocculated structure or sediment. Depletion
flocculation may be used as a way of preventing claying of suspension
concentrates (Heath et al, 1984; Tadros, 1994).
(b) Non-aqueous suspension concentrates. In aqueous pesticide formulations the formulator can be confronted with an active ingredient that is too
soluble in the aqueous phase, which may lead to Ostwald ripening, or an
active ingredient that is chemically unstable in water. To overcome these
problems and still produce a formulation with dispersed solids, the formulator has to use non-aqueous suspension concentrates.
The stabilization of non-aqueous suspension concentrates relies on a
careful choice of surfactant. The stabilizing moiety must be optimized to
show excellent steric stabilization in the given external phase. Depending
on the external phase, a different surfactant may be needed.
Non-aqueous dispersants have gained importance in agricultural formulations because of the formulation of paraffin oil-based suspension concentrates, ready-to-use products (RTUs) and ultra-low-volume (ULV) systems
which are often based on aromatic or aliphatic solvents. Polymeric dispersants offer the following benefits:
• improved productivity due to wetting andfluidizationof solid particles the fluidizing effect permits the formulation of dispersions with a high
active ingredient content at low viscosity where, traditionally, formulators were limited by well-defined maximum solid loadings;
• improved quality because of their excellent dispersion properties in the
solvent alone - no thickening agents have to be added to the formulation;
• compatibility with many solvent systems;
• activity only at the solid-liquid interface - they do not act as emulsifying
agents and will not interfere with the emulsification of the emulsifiable
concentrate or the suspoemulsion.
Mechanism of action. A dispersion of particles in a non-aqueous
medium can only be stabilized by forming a steric barrier which prevents
flocculation. The polymeric dispersant molecule is therefore made up of
two parts.
• A polymeric chain, which has a strong affinity for the solvent or is
compatible with the dispersing medium. Polymeric dispersants are
based on a variety of different polymeric chains that are selected for
their compatibility with a wide range of solvents used in pesticide
formulations.
• The anchoring group, which is designed to be strongly adsorbed on
the surface of the active ingredients. As active ingredients vary widely
in surface characteristics, it is necessary to select a polymeric
dispersant appropriate to that surface or to use 'synergistic polymeric
dispersants'.
Synergistic polymeric dispersants. Polymeric dispersants work on the
concept of multiple weak anchoring groups so that adsorption is irreversible. If the pesticide is too lipophilic, the adsorption of the dispersants is not
as effective. It is for this reason that synergistic polymeric surfactants have
been designed. These modify the surface of the active ingredient so that the
dispersant adsorbs onto the synergistic molecule and provides stabilization
for the dispersed particles.
They are particularly useful when active ingredients that have a lipophilic
surface have to be dispersed because they have powerful anchoring groups,
which are adsorbed on the lipophilic surface, and themselves adsorb prime
polymeric dispersants. Their mode of action does not require them to be
soluble in the system in which they are being used.
The application rate is approximately one part of synergist polymeric
dispersant to three parts of prime polymeric dispersant by weight. When
synergistic polymeric dispersants are used it may be advantageous to
premix them for a short time with the prime polymeric dispersant in the
liquid dispersing medium. Examples of such synergistic polymeric dispersants are Atlox LP2 (for low polar solvents) and Atlox PSl (for polar
solvents; Bognolo et al, 1990).
(c) Concentrated emulsions. A concentrated emulsion can contain 3050% of a liquid or low melting point lipophilic active ingredient, and 40%
water as the external phase. To ensure good emulsion stability for this type
of aqueous system over an extended period at both elevated and freezing
temperatures, the demands on the surfactant are very severe. To form
stable concentrated emulsions, irreversible anchoring in the oil droplet and
strong steric repulsion between particles are required.
Irreversible flocculation, or coalescence, of the emulsion can be prevented by creating an energy barrier that is sufficient to prevent the droplets
approaching each other closely. In this respect, steric stabilization produced
using non-ionic surfactants or polymers (block or graft copolymers) is the
most efficient. Using macromolecular surfactants, such as gums, proteins
and synthetic polymers, for example A-B or A-B-A block copolymers and
graft copolymers, produces very stable films and reduces coalescence because the strong adsorption of the B groups (the 'anchor points') of the
molecules leaves the A chains (the 'stabilizing points', strongly solvated by
the medium) dangling in solution to provide the strong steric barrier that is
required to prevent coalescence.
Polymeric surfactants such as Atlox 4912 (HLB = 5.5) and Atlox 4914
(HLB = 6) have been shown to improve the long-term physical stability of
concentrated emulsion formulations. They must be used in combination
with high-HLB block copolymers of the A-B type, such as Atlas G-5000
(HLB = 16.9), to alter the HLB of the surfactant system in favour of an oilin-water emulsion. Typical solvents used to emulsify the formulation are
aromatic and isoparaffinic solvents. In a concentrated oil-in-water emulsion, hydrophobic chains, such as PHSA chains, act as the anchoring groups
to the internal oil phase, while the hydrophilic, high molecular weight
polyethylene glycol centre provides the stabilization in the external aqueous phase. As a starting point for a formulation, a concentration of 1-2.5%
by weight of the end formulation is recommended. Atlox 4912 is an A-BA type block copolymer with a high molecular weight (c. 5000). This
molecular weight ensures fast diffusion to the emulsion interface. The
extension of the hydrophobic side chains into the oil phase may be several
times larger than for a conventional C18-sorbitan ester (Bognolo et al,
1990).
The suitability of ordinate and random polymeric structures to stabilize
oil-in-water concentrated emulsions can be illustrated by the following
example. Concentrated oil-in-water emulsions were prepared using the
direct emulsification method whereby the oil phase was slowly added to the
aqueous phase whilst stirring continuously. The final formulation was homogenized with high-shear mixer. To obtain optimum performance, both
phases were heated to 50-550C before and during emulsification to ensure
full extension of the polymeric surfactants in solution. Depending on their
solubility in the non-aqueous phase, the polymeric surfactants are dissolved
either in that phase or in the aqueous phase. The standard formulation
(shown below) contained no thickening agent, as the formulations were
designed to evaluate the stability of the emulsion droplets that resulted
from using surfactants with different effects. Combinations of Atlox 4912
with Atlas G-5000, and of Atlox 4914 with Atlas G-5000, allowed all of the
following solvents to be emulsified: xylene, Solvesso 150, Solvesso 200,
Exxol DlOO, Exxate 700, Exxate 1000, Isopar L, Isopar M, Isopar V
(Bognolo et al, 1990). The standard formulation was as follows:
Solvent
Polymeric surfactant(s)
Water
50 wt%
5 wt%
45 wt%
Polymeric surfactants also affect the rheology profile positively: the
additional stabilizing effect induced by polymeric surfactants allows
the formulator to minimize the quantity of thickener added, which results
in concentrated emulsions that flow easily and show acceptable
autodispersibility.
Because polymeric surfactants are irreversibly adsorbed at the interface
and have very good properties in high electrolyte media, they are also
ideally suited for use in suspoemulsions and multiple emulsions.
(d) Suspoemulsions. Suspoemulsions combine a suspension concentrate
with a concentrated emulsion and provide the opportunity to develop a
formulation that has multiple active ingredients but combines the advantages of both separate formulations, such as
• low or no flammability problems owing to the use of either low levels of
or no solvent;
• minimal eye and skin irritation;
• ease of incorporating adjuvants.
The challenge to formulation chemists in optimizing suspoemulsions is even
greater. Not only is the formulator confronted with the problems of
destabilization that can occur in the two separate formulations, but by
combining the formulations, additional problems are created, such as
heteroflocculation and enhanced emulsion coalescence.
• Heteroflocculation is the type of flocculation that occurs when a solid
dispersed particle comes into contact with an emulsion droplet because of
insufficient stabilization of the two dispersed phases.
• When a solid particle is wetted by an oil droplet, a depletion of surfactant
can occur at the oil-water interface. If the solid particle is wetted
by several oil droplets, emulsion coalescence may occur. The rate of
coalescence is increased because the solid particle acts as a catalyst.
By careful choice of surfactants it is possible to overcome the problems of
heteroflocculation and enhanced emulsion coalescence. Using an irreversibly adsorbed polymeric surfactant, such as a comb copolymer, on the solid
particle to create a stable dispersion will influence heteroflocculation in the
suspoemulsion (Rogiers, 1993).
Stabilizing the oil-in-water emulsion with ordinate polymer surfactants
creates a suspoemulsion that is stable against heteroflocculation and
emulsion coalescence. The strong anchoring of the surfactant in the oil
droplet, and the strong steric repulsion, mean that wetting of a suitably
protected solid particle is very unlikely, thus emulsion coalescence is not
encouraged.
Ethoxylated comb- and block-type coplymers used in suspensions are
also useful for stabilizing the suspension component of suspoemulsions
(Beestman, 1996).
(e) Multiple emulsions. A multiple emulsion is a system in which one
internal phase is emulsified into a second phase with different polarity, the
resulting primary emulsion being further emulsified in an external
phase that can be identical to or different from the initial phase. The
end system is, depending on the nature of the different phases, either a
water-oil-water (W/O/W) multiple emulsion or an oil-water-oil (O/W/O)
multiple emulsion.
Multiple emulsions used for pesticide formulations are usually of the
water-in-oil-in-water type, where one or more active ingredient that is
soluble in the water and/or oil phase may be incorporated. They have
received increasing attention as possible vehicles for the controlled release
of water- or oil-soluble pesticides. Since most pesticide formulations are
diluted in water, a water-in-oil-in-water multiple emulsion can be expected
to perform as a simple water-in-oil emulsion once the pesticide is diluted in
the spray tank and the droplet has hit the target. The rate of release of the
active ingredient will then depend on the rate at which the oil droplets burst
open (Bognolo et al., 1990).
Achieving adequate stability has, until recently, been a major limitation
in the research into multiple emulsions and also in their industrial applica-
tion. With the use of random structure polymeric surfactants, an important
step has been taken towards achieving the degree of stability that is
required in W/O/W multiple emulsions. A random polymeric species,
such as Atlox 4914, stabilizes the primary water-in-oil emulsion. The
hydrophilic interaction is provided by multiple polar moieties such as
ester and ether groups. The hydrophobic interaction is provided by chains
of high molecular weight hydrocarbons that are well solvated by high- and
low-polarity hydrocarbons. The secondary oil-in-water emulsion has to
be stabilized by a high-HLB polymeric surfactant such as Synperonic
PE/F 127.
The products used for the formulation of multiple emulsions are the same
as those recommended for the production of stable concentrated emulsions,
both oil-in-water (EW) and water-in-oil emulsions. Polymeric surfactants
have been shown to perform extremely well in the production of multiple
emulsions.
Surfactant selection. For oil-in-water emulsions, high-HLB polymeric
surfactants:
• Synperonic PE series (high ethoxylation degree: Synperonic PE/F127);
• Atlas G-5000.
For water-in-oil emulsions, low-HLB polymeric surfactants:
• Atlox 4912, Atlox 4914;
• Non-ionic block copolymers.
For the formulation of a typical multiple emulsion (80wt% primary
water-in-oil emulsion and 20wt% external water phase), the following is
recommended as a guide.
For production of the primary emulsion: W/O:
Oil phase:
Paraffinic oil
Atlox 4914
Water phase: MgSO4-VH2O
Water
24%
4%
0.7%
to 100%
Both phases are heated to approximately 750C. The water phase is added
to the oil phase while stirring intensively. Whilst cooling to ambient
temperature mechanical stirring is continued.
For production of the secondary emulsion: (W/O)/W:
Oil phase: Primary emulsion
80%
Water phase: Synperonic PE/F 127
5%
Water
15%
The primary emulsion is added slowly to the water-surfactant solution
while stirring gently. Stirring is continued until an homogeneous emulsion is
obtained.
(f) Water-dispersible granules. Common dispersants for water-dispersible
granules include lignosulphonates and naphthalene sulphonates. It has
been reported that the combination of anionic dispersants with non-ionic
polymeric surfactants can impart better granule hardness and a greater
level of suspension than classical formulations, which are stabilized solely
by anionic dispersants, particularly in hard water, as non-ionic surfactants
are less sensitive to water hardness than anionic surfactants. Each type of
surfactant has its advantages, and the blend minimizes the disadvantages
(Utz etal.,1995).
One of the biggest concerns about using non-ionic surfactants in dry
formulations is their relatively low melting point and the effect that
this might have on storage stability. It has been shown, however, that
high molecular weight ethylene oxide-propylene oxide block copolymers
(>1800PO molecular weight; Utz et al, 1995) can be used to stabilize
dry formulations in both pan granulation and extrusion processes. The
waxy nature of these polymeric surfactants does not cause agglomeration as granules were shown to maintain constant particle size at elevated
temperatures - and the level of suspension remains constant and
solutions easily dispersed. Both the molecular weight and the ethylene
oxide content of the EO-PO block copolymer are key factors in determining the particle size, level of suspension and settling properties of
the granules. Particularly in the extrusion process, including an anionicnon-ionic surfactant combination allows only a very narrow optimum
range.
Vinyl pyrrolidone homo/copolymers can be used as binders in waterdispersible granules (Narayanan, 1995). Mixed solutions of polybasic acids,
such as citric acid, and vinyl pyrrolidone homo/copolymers can be used
as the preferred binders during granulation either in pan, extrusion,
fluidized-bed or spray-drying processes. The resulting formulations exhibit
an increased rate of dissolution of the active ingredients, high hardness and
low friability.
7.7.6 Conclusion
The introduction and systematic use of the polymeric surfactants has
opened a new era of formulation technology, which has been taken up by
the agrochemical industry, looking to prolong the use of its active ingredients by introducing new formulation types of the active ingredients or
by combining them with other pesticides. Polymeric surfactants provide
formulation stability under extreme conditions due to their irreversible
adsorption at an interface, and are opening the way to facilitate the
production of formulation types such as multiple emulsions and
suspoemulsions.
7.2 Trends towards environmentally safer surfactants
7.2.1 Surfactants and the environment
It is widely recognized that surfactants can have an adverse environmental
impact, not only in terms of the pollution that may be caused by stable rafts
of foam and inhibition of aeration, as was the case during the 1950s, but also
in terms of their impact upon aquatic and marine life as a consequence of
their surface activity and its interference with the respiration of organisms
(Scholz, 1991). One of the best-documented cases of surfactants causing
environmental damage occurred in the late 1950s and early 1960s. At that
time branched-chain alkylbenzene sulphonates (ABS) were extensively
used in various applications. These agents were poorly biodegradable,
and consequently large quantities of foam developed at sewage treatment
works and in rivers that received treated sewage effluent. The problem
was overcome by replacing ABS with the biodegradable linear
alkylbenzene sulphonates (LAS; Swisher, 1981, 1987; Gerike, 1987); their
annual use in the USA, Western Europe and Japan is 1 000 000 tonnes.
More recently, the replacement of alkylphenol alcoxylates in its many
applications has become a major concern and is an objective in various
industries (White and Russell, 1994; Talmage, 1994; for further details see
section 7.2.4).
For pesticide control legislation, the most common targets are efficacy,
and safety to users, crops and the environment. Apart from their active
ingredient, crop protection formulations contain a number of other components that are included to modify the characteristics of the product. Even
though it is acknowledged that adjuvants and coformulants are not pesticides (Stickle, 1995; Levine, 1996), they could pose toxicological or environmental risks since they are sprayed directly onto fields, and biotreatment
before they are discharged into the environment is generally absent. The
possible contamination of drinking water, for example, is one of the most
emotive issues facing producers and formulators. However, surfactants
sprayed onto fields are generally strongly adsorbed by the soil, where
they readily degrade (Routledge and Sumpter, 1996). Hence there is little
concern over leaching into groundwater, and concentrations of surfactants
from spray drift and runoff are normally well below no-observed-effect
levels (NOEL; Brown et al, 1986).
Nevertheless, although any possible impact of a surfactant on the environment strongly depends on its application, the level of perception of
environmental issues surrounding the use of surfactants has considerably
increased amongst politicians and consumers. The demand to use materials
which, regardless of the application, are seen to be 'not dangerous to the
environment' has increased. As a result of the growing environmental
awareness and concerns about agricultural applications, the use of, for
example, 'standalone' adjuvants which contain one or more unlisted inert
components has become regulated (Smith, 1993): it is now necessary to
register such products, which requires that a minimum data package demonstrating toxicology, mutagenicity, environmental fate, etc. (by the US
EPA), is supplied; further data may be required if there is any indication
that there may be an unreasonable risk to human health or the environment
(Stickle, 1995; Levine, 1996).
There is now an irreversible trend towards identifying and using
surfactants that meet both performance and environmental requirements.
Nowadays the first selection of possible types of surfactant for a particular
application will be based often on regulatory, toxicological and ecological
information. Only for those types that meet the criteria will a technical
evaluation and final cost-performance assessment be made. Furthermore,
as surfactants are often selected for use in crop protection formulations that
will be used globally, the most stringent regulatory requirements have to be
considered.
The effect of a surfactant released into the environment depends on its
concentration, tendency to persist in its active form and toxicity. In general,
a substance that is readily biodegradable is unlikely to cause serious harm,
whereas a compound that is poorly degradable may, if toxic, build up to
levels that are hazardous. Since biodegradability and toxicity are the key
properties when assessing the possible environmental impact of a
surfactant, and constitute the prime data requested for any registration,
particular attention is paid in this chapter to these two features.
7.2.2 Toxicity and biodegradation
The effect of a surfactant released into the environment depends on its
concentration, tendency to persist in its active form and toxicity. In general,
a substance that is readily biodegradable is unlikely to cause serious harm,
whereas a compound that is poorly degradable or which degrades into
poorly degradable metabolites may, if toxic, build up to levels that are
hazardous. Hence the two properties of a surfactant that are particularly
important in assessing its possible impact on the environment are its biodegradability and its toxicity.
(a) Biodegradation. Biodegradation is the process by which microorganisms, such as bacteria, fungi and algae, break down (or decompose) organic
substances. It occurs all around us in nature as microorganisms utilize plant
and animal waste as a source of nutrition. Using their enzyme systems,
microorganisms process sugars, carbohydrates, proteins and amino acids
for growth. During this process, complex organic molecules are consumed
as a food source, together with trace nutrients, and are broken down to
biomass, carbon dioxide and water. Biodegradation can occur by oxidation
in the presence of oxygen (aerobic biodegradation) or by reduction in the
absence of oxygen (anaerobic biodegradation; Swisher, 1987).
The first steps in the biodegradation of a surfactant almost invariably lead
to a loss of surface active properties. This stage is often referred to as
primary biodegradation. The intermediates which result are called
metabolites. Primary biodegradation must take place if a surfactant is not to
accumulate in the environment. Subsequent biological reactions may result
in decomposition of the metabolites and lead to the complete breakdown of
the compound. This is known as ultimate ('ready') biodegradation or
mineralization. Another concept that is sometimes used is that of environmentally acceptable biodegradation, which simply means decomposition
into products that do not harm the environment (Table 7.1).
The measurement and testing of the biodegradability of a surfactant is
littered with a plethora of test methods and means of monitoring which
have grown out of the technical complexities associated with finding a
simple, meaningful and universally applicable means of measurement.
A single, definitive technique does not exist. Consequently a variety of
methods are used (Birch, 1984).
Primary biodegradability. The biodegradability of a surfactant can be
measured by subjecting a solution of the surfactant to attack by a microbial
inoculum, normally derived from sewage treatment works sludge, under
controlled conditions. The amount of surfactant that has degraded after a
specified time can be determined by specific or semi-specific analytical
methods (Painter, 1995). The results of such tests are often expressed in
terms of the extent of the biodegradability over a particular period and
Table 7.1 Biodegradation of surfactants and analytical procedures used
Biodegradation of surfactants
Primary
<
>
Ultimate
Environmentally
Acceptable
Loss of surface-active
properties
Partial breakdown to
metabolites considered
to be non-harmful
Complete breakdown to inorganic
materials, etc.
Analytical procedure
Specific analysis
Bioassay
Non-specific analysis
Surface tension
Methylene blue (MBAS)
Wickbold (BiAS)
Fish
Bacteria
Daphnia
Biochemical oxygen demand (BOD)
Dissolved organic carbon (DOC) loss
Carbon dioxide evolution
should be quoted with reference to the test method used (Struijs and
Stoltenkamp, 1994).
Primary biodegradability is defined as the level of microbial alteration of
a molecule that is sufficient to remove a characteristic property, such
as surface activity (foaming), or its response to an analytical test procedure
specific to the starting compound but not to its degradation products
(metabolites; Struijs and Stoltenkamp, 1994). For anionic compounds it is
often the response to the methylene blue active substance (MBAS); for
non-ionic compounds it is often the response to the Wickbold bismuth
active substance (BiAS) or cobalthiocyanate active substance (CTAS;
Wickbold, 1973). Only functional chemical groups can be assayed. Essentially, this analytical approach determines primary degradation by measuring the disappearance or removal of the parent compound, and not
mineralization to carbon dioxide and water.
OECD Screening Test. The simplest test for biodegradability is the
static or shake flask test. This is a 'die-away' test in which a dilute solution
of the surfactant is mixed with a bacterial sample from a sewage treatment
plant and inorganic nutrients. The mixture is then agitated under carefully
controlled conditions for a period of up to 19 days. During this period the
change in concentration of the surfactant is measured using the analytical
methods described above. The results obtained are compared with those
obtained from two control substances, LAS (linear alkylbenzene
sulphonate) and ABS (alkylbenzene sulphonate), tested in an identical way
at the same time. If, in this test, the parent surfactant is reduced by 80% or
more, the substance is accepted as being biodegradable. If the Screening
Test does not give satisfactory results, the OECD Confimatory Test is
carried out.
OECD Confirmatory Test. The OECD Confirmatory Test is designed
to provide a laboratory simulation of an activated-sludge sewage treatment
plant. It allows more opportunity than the Screening Test for microorganisms to adapt to the breakdown of the surfactant being treated.
It may be supposed that a substance showing a high level of primary
biodegradability would also show good ultimate biodegradability. In the
vast majority of cases this is quite true, since surfactants that are initially
readily attacked by enzymes usually continue rapidly to fragment and mineralize. However, it is not true in all cases; with some surfactants the parent
molecule can be altered sufficiently that the assay method becomes insensitive to the remaining fragments or metabolites. In some cases these
metabolites may exhibit almost as much surface activity as the parent
molecule and therefore still have a potential environmental impact.
Whether this happens is determined by the structure and water solubility of
the fragments in question (G. Holliday, ICI Australia Detergency seminar,
1993).
Today, primary biodegradability is still a valuable concept. However,
the total mineralization or 'ultimate biodegradability' is being more widely
considered to gain a more complete view of the process of biodegradation.
Ultimate biodegradability. Ultimate biodegradability or mineralization
is a term employed to describe the biodegradation of surfactant molecules
into inorganic products and cellular materials (or biomass). It is usually
measured by analysing the dissolved organic carbon (DOC) loss, oxygen
consumption (O2 uptake) or carbon dioxide evolution (OECD, 1993; Struijs
and Stoltenkamp, 1994).
The oxygen that is required for the biodegradation of an organic chemical is its biochemical oxygen demand (BOD). Data are often reported as
BOD5 or BOD28 values - the number of grams of oxygen consumed during
the biodegradation of 1 g of material over a period of 5 or 28 days. Biochemical oxygen demand can be measured using for example OECD
Method 301C for assessing ready biodegradability. This involves stirring the
test substance for 28 days in a sealed vessel together with a quantity of
activated sludge obtained from a sewage works. As biodegradation occurs,
oxygen is consumed and carbon dioxide is produced. The carbon dioxide is
absorbed in a pellet of potassium hydroxide suspended in the neck of the
test vessel. The reduction in pressure that results can be measured and, with
suitably calibrated equipment, used to give a direct reading of biochemical
oxygen demand. The extent of removal of parent compound or dissolved
organic carbon may also be determined by analysing the contents of the
vessel at the end of the test period.
It is possible to assess whether a surfactant is readily biodegradable by
comparing its biochemical oxygen demand with its chemical oxygen
demand (COD), which is the amount of oxygen required for the complete
conversion of an organic substance to carbon dioxide and water. If
the chemical composition of the substance is known, the theoretical oxygen
demand (ThOD) can be calculated. Otherwise the substance is heated
with chromic acid, a strong oxidizing agent, and the amount of chromic
acid consumed is determined by titration. When microorganisms
biodegrade an organic substance, they use it both as an energy source
and as food to build up more cellular material. Only the former process
consumes oxygen and releases carbon dioxide, so the BOD value for the
substance is almost invariably much lower than the COD. According to an
expert group of the OECD, a BOD5/COD ratio greater than 50%, or a
BOD28/COD ratio greater than 60%, should be considered to represent
'ready' biodegradability.
Another measure of ultimate biodegradability is the removal of dissolved
organic carbon (DOC) from the test solution over the test period. This can
be estimated by removing solids from the sample by filtration and analysing
the filtrate for organic carbon. A substance for which the DOC removal is
greater than 70% after a 28-day OECD test can be regarded as 'readily'
biodegradable. Indeed for many water-soluble and 'readily' biodegradable
substances, DOC removals approach 100%. DOC results obtained for substances which are poorly soluble in water, or which are strongly adsorbed,
may not represent the true biodegradation of the substance, but they do
indicate its potential for bioelimination.
The OECD 301C method outlined above is one of six OECD prescribed
tests for 'ready biodegradability'. The methods OECD 301C, D and F
measure oxygen uptake, OECD 301B measures carbon dioxide production,
and OECD 301A and E measure DOC loss. There are also OECD
methods for examining the potential of organic substances to biodegrade
under conditions which more closely imitate sewage treatment (the
'simulation' method). The various test methods, and the range of analytical
techniques associated with them, can give rather different numerical
values for biodegradation. It is important to be aware of this and to exercise
caution when comparing biodegradation data obtained by different
methods (OECD, 1993).
Biodegradation mechanisms. The biochemical mechanisms used by
bacteria for biodegradation are those that are used to metabolize their food
and involve the enzyme processes of their normal cell function. This usually
involves initial oxygen insertion and oxidation of terminal alkyls followed
by alkyl chain breakdown by |3-oxidation. It is a relatively rapid process,
provided there is no hindrance from alkyl branching (Patterson et al, 1970;
Swisher, 1987).
The mechanisms for aerobic biodegradation of fatty alcohol ethoxylates
are determined by the hydrophobe linearity and steric hindrance; they can
be central fission, or initial attack at the terminal end of the ethoxylate
chain, or at the terminal end of the alcohol (Schoeberl and Kunkel, 1981;
Kravetz, 1981; Talmage, 1994; Madsen et al., 1996).
The initial degradation of linear alcohol ethoxylates is believed to
proceed via central fission with cleavage of the hydrophobe from the
hydrophile followed by rapid (3-oxidation of the alkyl moiety to carbon
dioxide and water, with slower oxidation of the polyoxyethylene group.
Steric hindrance close to the hydrophobe-hydrophile junction - for
example, significant alkyl branching or aryl functionality adjacent to the
hydrophile - has a negative influence on the rate of biodegradation because
the oxidative metabolic processes which bacteria use to break down molecules are most effective when dealing with simple, linear alkyl chains of
moderate size (Patterson et al, 1970). It is thought that a highly branched
alcohol ethoxylate biodegrades much more slowly than a corresponding
linear alcohol ethoxylate as the biodegradation is initiated at the terminal
methyl group (co-oxidation followed by (3-oxidation) of the fatty alcohol,
and/or oxidation at the terminal end of the polyoxyethylene chain, followed
by stepwise shortening of this chain, rather than by central fission at the
hydrophobe-hydrophile junction (Schoeberl and Kunkel, 1981; Talmage,
1994).
(b) Aquatic toxicity and biodegradability. The most important natural
phenomenon which generally reduces the aquatic toxicity of surfactants
is biodegradation (except for alkylphenol ethoxylates) and it has been
demonstrated that primary degradation is particularly effective in this
respect. This may be illustrated in a test using surfactants which have been
allowed to degrade for varying periods from O to 7 days before a bioassay of
the residual toxicity was carried out by introducing fish (Weber et al, 1988).
For the vast majority of surfactants that exhibit high levels of primary
biodegradability ('soft' surfactants), complete mineralization also occurs
rapidly and the surface activity, and therefore aquatic toxicity, is quickly
destroyed during the initial step of the biodegradation process (Brown,
1987).
Degradation of surfactants leads to structural breakdown via a number of
metabolic routes, but in general serves to reduce the effects of surface
activity and aquatic toxicity of parent molecules and their metabolic fragments. Practical ecotoxicity and exposure levels do normally not increase
from biodegradation of surfactants since the process does not usually yield
metabolic products which are more surface active, and therefore more
ecotoxic, than the parent compounds (Dorn et al, 1990; Kravetz et al.,
1991). However, intensive studies focusing on the oestrogenic effects and
bioaccumulation of alkylphenol, a lipophilic molecular fragment from
alkylphenol ethoxylate, have taken place. They have highlighted the importance of the ultimate biodegradability of surfactants and the possible impact
of trace residues or metabolites resulting from incomplete biodegradation
(Scholz, 1991).
(c) Aquatic toxicity. At sufficiently large levels of exposure, surfactants,
regardless of chemical class, are quite toxic to aquatic organisms, particularly those animals with higher respiratory rates. This phenomenon seems
to be connected with physiological and chemical issues, particularly the
lowering of surface tension and wetting effects, which cause disruption of
gas transport on the surfaces of the gills (Markarian and Hinman, 1990;
Dorn etal, 1990). Gill epithelia can swell and form secretions which further
inhibit oxygen diffusion (Swedmark et al, 1971; Shell Chemical Co., 1983).
Wetting and emulsification of oils and lipids in membranes can also affect
membrane fluidity, altering the distribution of natural enzymes and inhibiting proper cell function. A chain length of 12 carbon atoms appears to
exert the maximum effect on membrane permeability (Florence et al.,
1984).
Some surfactants can be physically adsorbed onto cellular protein,
causing more long-term chronic damage at lower dose levels. Anionic
and cationic surfactants will adsorb more strongly to protein than non-ionic
surfactants. Non-ionic surfactants, while often causing more immediate
acute affects owing to their higher surface activity and lower critical micelle
concentration, do not interact with protein, however, and the toxic dose
effects are rapidly reversed when exposure levels drop below toxic thresholds (Shell Chemical Co., 1983).
All surfactants exhibit, to some degree, ecotoxic effects upon aquatic
organisms if the dose or exposure level is sufficiently large (Markarian and
Hinman, 1990). Response is usually varied and depends on the sensitivity of
the organism and length of exposure. It is usual to view the toxic effects of
any substance from two perspectives:
• acute effects, which relate to the short-term exposure of an organism to
a substance;
• chronic effects, which relate to the long-term exposure of an organism
to a substance; it is possible for organisms to display evidence of
chronic effects at exposure levels that are lower than those which
induce shorter-term acute exposure owing to the phenomenon of
bioaccumulation.
Surfactants are in general biodegradable, so it is usually more important
to assess their acute effects on aquatic organisms rather than long-term
effects.
Acute toxicity testing involves exposing the organism to different
concentrations of the test substance for a specified time and measuring, for
example, death in the case of fish and water fleas, and growth inhibition of
algae.
Acute tests. Acute toxicity testing is generally carried out on freshwater
fish (e.g. small rainbow trout) and other food chain organisms such as the
water flea (Daphnia magnd) may also be used. For marine applications, fish
such as the plaice and turbot, or invertebrates such as the brown shrimp
(Crangon crangon), may be used.
In tests, aquatic organisms are exposed to the test substance at a range of
concentrations for a specific period; with fish this is normally 96 h. For most
surfactants, toxicity does not increase after this period. The percentage of
organisms killed or affected within the test period is observed. Often there
is a very narrow concentration range between which there is a 100% kill
(LC100) and no death (LC0); the ratio LC100/LC0 is usually less than 10.
Standard statistical methods are used to calculate a 96 h LC50 value, that is,
the concentration of substance which is lethal to 50% of the fish exposed to
it over a 96 h period.
For Daphnia magna the test period is 48 h and results are expressed as
48 h EC50 values, the concentration required to have an effect on 50% of the
organisms over 48 h.
For many surfactants the 96 h LC50Or 48 h EC50 is in the range 1-10 mg/1
(or parts per million). These values emphasize the importance of preventing any discharge of surfactants from reaching natural waters without
treatment.
The NOEC (no observable effect concentration) is environmentally the
most relevant concentration, because the concentration of the surfactant
below which all the organisms will not be harmed in the aquatic environment is the most important. LC50 values are, however, the figure most
commonly quoted in the literature (Kravetz et al., 1991).
Toxic effects are generally classified in terms of acute effects according to
LC50 or EC50 exposure levels, and are reflected in the 'R' risk phrases
available on safety data sheets which accompany the products.
7.2.3 Hazard labelling of surfactants
When assessing the hazard to the aquatic environment, both biodegradability and aquatic toxicity are taken into account. The assessment of biodegradability used in this case is not primary biodegradability but ready
biodegradability as measured either by removal of dissolved organic carbon
(DOC) in excess of 70% or by the ratio of biochemical oxygen demand
(BOD) to chemical oxygen demand (COD) in excess of 60%, as measured
by prescribed test procedures.
In addition to the classical hazards associated with chemical substances
(toxicity, flammability, corrosivity, explosivity, etc.), the European Commission has introduced, through the 6th and 7th Amendments to Directive
67/548/EEC (the so-called Dangerous Substances Directive), the hazard
classification 'Dangerous for the Environment'. This has associated with it
a particularly nauseating symbol of a dead tree and a dead fish (Table 7.2).
As indicated in Table 7.2, R50 refers to toxicity, whereas R53 refers to
ready biodegradability and bioaccumulation. R50 carries the classification
and symbol 'dangerous for the environment'.
The provisional assessment for some anionic and non-ionic surfactants
proposed by CESIO is reviewed in Table 7.3.
7.2.4 Effect of chemical structure
(a) Factors influencing biodegradability. All surfactants will undergo biodegradation given enough time and the right conditions. Hence it is the rate
Table 7.2 EU criteria for Environmental Hazard classification (CESIO)
Acute aquatic toxicity (EC50, mg/1)
Readily biodegradable
Risk phrasesa
Label
No
Yes
No
Yes
No
Yes
50,53
50.00
51,53
52,53
-
Yes
Yes
Yes
No
No
No
<1
<1
1-10
1-10
10-100
10-100
3
R50: very toxic to aquatic organisms (EC50 < 1 ppm).
R51: toxic to aquatic organisms (EC50 = 1-10ppm).
R52: harmful to aquatic organisms (EC50 = 10-100ppm).
R53: may cause long-term adverse effects in the aquatic environment.
CESlO: Comite Europeen des Agents de Surface et leurs Intermediares Organiques.
Table 7.3 Provisional assessment of some anionic and non-ionic surfactants proposed by
CESIO
Anionic surfactants
Alkyl benzene sulphonates
Alcohol sulphates
Alcohol ether sulphates
Dialkyl sulphosuccinates
Not classified
Not classified
Not classified
Not classified
Non-ionic surfactants
Linear3 C9-C11 alcohol ethoxylates
Linear3 C12-C15 alcohol ethoxylates: EO 2-10
>10EO
Linear3 C16-C18 alcohol ethoxylates
Alkylphenol ethoxylates
Isotridecanol ethoxylates
Isodecanol ethoxylates
Not classified
R50
Not classified
Not classified
R53
Not classified
Not classified
a
Linear includes alkyl groups with one branch, such as Synperonic and Dobanol products.
at which biodegradation occurs which is important in determining environmental concentrations. 'Environmentally acceptable' biodegradation of a
surface-active agent is achieved when the surfactant is degraded to a nontoxic surface-inactive form within a defined period. Anything which reduces
the rate of the basic biochemical reactions reduces the biodegradability of
the substance (Kravetz, 1981; Birch, 1984; Gerike and Jasiak, 1986; Kravetz
etaL91991).
A summary of how hydrophobe and hydrophile types affect biodegradability is shown in Table 7.4.
(b) Factors influencing toxicity. The relationship between structure and
aquatic toxicity appears to follow the relative hydrophobicity of the
surfactant molecule - so for alcohol ethoxylates the toxicity decreases as
the level of ethoxylation on a specific alcohol increases, but increases
with increasing alcohol chain length for a particular level of ethoxylation.
Table 7.4 Effect of hydrophile and hydrophobe characteristics on biodegradability
Chemical structure
Biodegradability
Hydrophile type
Hydrophile type is not generally as important as hydrophobe type,
unless serious steric hindrance exists (S wisher, 1987)
Hydrophile length
Rate and extent of degradation of ethoxylates falls off steadily
with increasing ethoxylate chain length; above 2OEO units the
rate of degradation is significantly retarded (Sturm, 1973)
Hydrophile branching
Introducing propylene oxide or higher alkyl groups in the
hydrophilic moiety hinders biodegradation, probably by methyl
branching (steric hindrance). Single and double propylene
groups are degradable, but multiple groups, greater than four, do
not appear to be practically biodegradable (Naylor et al, 1988)
Hydrophile shape
Ultimate biodegradability of non-ionic polyethylene oxide is very
similar to that of the naturally derived sugar-based alkyl
polysaccharide, despite the considerable additional complexity
of the glucose moiety (Holliday, 1993)
Anionic hydrophiles usually have little impact on biodegradability
Hydrophobe length
Alkyl chain length influences biodegradability only slightly
(Larson and Games, 1981)
Hydrophobe branching
Single terminal methyl groups in an otherwise linear chain do not
have any significant effect on biodegradation and the effect of
several methyl groups attached to different carbon atoms is
small. The slight branching of linear oxo derivatives (20-50%
alkyl branched) poses little hindrance (S wisher, 1987)
Quaternary branching, especially at or near the end of the chain,
has a significant and inhibitory effect on biodegradation. Highly
branched alcohol ethoxylates (AE) synthesized from oxoalcohols derived from polyolefines, such as tetrapropylene, are
only slowly broken down (Hughes et al., 1989)
AE derived from linear secondary alcohols degrade slightly more
slowly than the corresponding linear primary AE (Kravetz et
aL, 1978)
It is recognized that biodegradation effectively reduces the aquatic
toxicity of these products, but nevertheless care against spillage of these
products directly into natural water is required. A summary is shown in
Table 7.5.
The structure and molecular weight of EO-PO block copolymer appreciably reduce the biodegradation potential in short-term laboratory tests, and
they are of very low toxicity to fish.
Status of alkylphenol ethoxylates in crop protection products. Alkylphenol ethoxylates (APEs) were among the first commercially available
non-ionic surfactants and have enjoyed widespread use in applications such
Table 7.5 Summary of factors influencing aquatic toxicity
Chemical structure
Alkyl chain
Length
Branching
EO chain
Length
Branching
Aquatic toxicity
Increasing the alkyl chain length will enhance the toxicity to aquatic
organisms (Markarian and Hinman, 1990)
Linear primary AE surfactants are more toxic than AE with branched
alkyl structures (Dorn et al, 1990; Kravetz et al, 1991)
Toxicity decreases with increasing EO chain length (Markarian and
Hinman, 1990)
Introduction of propylene oxide to give the required low-foaming
properties makes the molecule more hydrophobic than the
corresponding alcohol ethoxylates. It is expected that this increase in
hydrophobicity will increase the relative toxicity to aquatic
organisms
as cleaning agents, agrochemicals, emulsion polymers and textile auxiliaries. World production is currently around 600000 tonnes annually, of
which about 10% are used in crop protection products. Nonylphenol
ethoxylates (NPEs) are by far the most important APEs, accounting for
about 80% of total APE volume. During the 1980s, environmental studies
identified the presence, in surface waters, of recalcitrant metabolites which
had arisen from biodegradation. Subsequent studies have shown that NPEs
biodegrade in sewage treatment works by the sequential loss of ethylene
oxide (EO) units from the hydrophile chain; this gives rise to increasingly
lipophilic metabolites, which have a greater aquatic toxicity (Stephanou
and Giger, 1982; Jobling and Sumpter, 1992; Ahel et al, 1994). Final treated
streams of sewage effluent have been shown to contain short-chain
ethoxylates as well as derived carboxylic acids and the ultimate degradation
product, nonylphenol (Naylor, 1995; Routledge and Sumpter, 1996). This
degradation product tends to be associated with particulate matter and
sediment, in which it may be found at concentrations that are significantly
higher than those in the aqueous phase. Bioaccumulation of the lipophilic
metabolites of NPEs has been observed in freshwater and marine organisms (Clark and Rosen, 1992).
Alkylphenol ethoxylates are relatively slow to degrade. The first and
most obvious factor that influences the rate of degradation is the molecular
weight of the molecule. It will take longer to break down a larger molecule
than a smaller one. For example, the degradation of a dioctylphenol derivative that has an aromatic ring with two side chains requires two methyl
oxidation and eight (3-oxidation stages, whereas the degradation of a
monooctylphenol or single side-chain aromatic compound, involves one
methyl oxidation and four (3-oxidations; the aromatic oxidation stage is
common to both derivatives. The second influential factor is the structure of
the molecule. All alky !phenol derivatives degrade slower than essentially
linear or monobranched alcohols with the same molecular weight and HLB
value. A common misconception is that this difference is because the aromatic ring is non-biodegradable. This is not so; it is because the hydrolytic
splitting of hydrophobe and hydrophile does not occur with phenol derivatives, but does occur with alcohol derivatives. In the case of alcohol derivatives, the hydrophobic and hydrophilic fragments can be attacked from
both ends once splitting has occurred, but since this does not happen with
alkylphenols, the number of points of attack is automatically halved and the
rate of degradation thereby reduced (Holliday, 1993).
The growing concern regarding the potential endocrine-modulating
properties of environmental chemicals was recognized at the 1995 North
Sea Ministerial Conference, where it was decided to expand the definition
of 'hazardous substances' to include those which have adverse effects on the
endocrine system. Nonylphenol, and nonylphenol ethoxylates and related
substances, were specifically mentioned as substances that should be substituted by less hazardous alternatives. Recognizing that nonylphenol
ethoxylates may be degraded to persistent and toxic metabolites, and that
alternatives which give a satisfactory performance were available for use as
cleaning agents, the Paris Commission (PARCOM) agreed, in its Recommendation 92/8, that all uses of NPEs and similar substances which lead to
their discharge to sewer or surface waters should be examined with a view
to reducing their use. In addition, it was recommended that the use of NPE
in domestic detergents should be phased out by 1995 and that their use in
industrial detergents should be phased out by 2000. The Recommendation
also requires that care should be exercised to ensure that any materials used
to replace NPEs in current applications are less damaging to the aquatic
environment (Consultants in Environmental Sciences, 1993).
In crop protection, APEs are widely used as wetters and emulsifers
because of their low cost and effectiveness in a wide range of products. The
amounts of nonyl- and octylphenol ethoxylates applied to crops is typically
equivalent to 50-200 g/ha, the higher rates being used when they are employed as wetters and the lower rates when they are employed as emulsifiers. There are proposals in Scandinavia to phase out APEs from all
applications, and countries such as Sweden have apparently stopped giving
registration to formulations that contain APEs. The Danish Environmental
Protection Agency (DEPA) has an objective to phase out coformulants that
are believed to be oestrogenic or have the potential to degrade with oestrogenic compounds; it has created two lists, one for pesticide product
coformulants and one for adjuvants, of materials which it considers to be
oestrogenic or which degrade into oestrogenic compounds. The target
is to phase out identified coformulants and adjuvants by the year 2000.
The ECPA (European Crop Protection Agency) and EAA (European
Adjuvant Association) share their understanding on the current global
regulatory position and strongly recommend that industry does not initiate
the development of new formulations containing APE.
7.2.5 New-generation surfactants
The regulatory pressure to reduce the doses of surfactants used and their
loss to non-target sites has forced the agricultural industry to consider
closely the ecotoxicological impact of formulation design (Stock, 1996).
Particular attention has been paid to surface-active coformulants and
adjuvants, as these products are most often incorporated, or tank mixed, to
ensure low foaming and good wetting properties. However, the surfactants
which provide these benefits tend to be relatively hydrophobic, sparingly
soluble and thus relatively toxic to aquatic organisms. In some cases it may
be necessary to compromise performance to achieve a reduced hazard
classification.
For the creative, market-focused surfactant manufacturer, the present
greater environmental awareness has created the opportunity and
challenge to identify or develop surfactants that meet performance,
ecotoxicological and handling requirements without compromises.
Examples of such surfactants are listed below.
(a) Sugar ether-based surfactants. Sugar surfactants with linear hydrophobes rapidly undergo primary biodegradation, that is initial hydrolysis (Madsen et al, 1996). Sorbitan-based fatty acids and sorbitan- (or
sorbitol-) based fatty acid ethoxylates are an established class of sugarbased materials (Swisher, 1987; Knaut, 1993); they are extensively used in
crop protection formulations both as coformulant and adjuvant. Alkyl
polysaccharides (APS) are still considered a new type of non-ionic compound (Madsen et al., 1996; Callens et al., 1996). Strictly speaking, they are
not new surfactants but were described 100 years ago by Fischer (1893).
Although proven to be commercially successful in various applications
(Smith, 1993), few articles address their performance and environmental
properties when used as adjuvant or built-in wetter.
Alkyl polysaccharides show unique properties when compared to other
non-ionic surfactants, for example fatty alcohol ethoxylates. In certain
ways, such as their wetting and foaming behaviour, they behave more like
anionic surfactants; this is largely a consequence of the high level of hydrogen bonding exhibited by the hydroxyl groups in the glucose ring carrying
a hydration sheath of a size similar to an anionic or cationic surfactant. As
is typical with other surfactants, the water solubility and surfactancy change
with APS chain length, hence particular care is necessary when selecting
both the alkyl chain and the degree of polysaccharide polymerization if
APSs are used to enhance efficacy (Balzer, 1997).
The polysaccharide chain confers limited oil solubility to the surfactant,
thereby preventing phase migration and maximizing interfacial packing.
APSs exhibit unique properties as coemulsifiers, particularly for different
polar oils. They have very good stability in the presence of electrolytes and
are stable over a wide pH range and at high normal working temperatures
(0-4O0C). Although APSs are acetals and are thus susceptible to hydrolysis
in an acidic medium, this is expected to occur only below pH = 3 (R.
Bongiorno, ICI Australia, Detergency seminar, 1993).
Recent work clearly demonstrates that considerable variations in biodegradability and toxicity are evident within structurally related glucosebased surfactants (Madsen et al, 1996), and that alkyl chain length and the
degree of polymerization have a major impact on enhancing efficacy (Hoyle
and Holloway, 1997). Hence identifying the proper APS for biological
enhancement implies that various structural variants have to be screened
and that the final selection should be made based on the outcome of
bioassays, and toxicological and ecological studies.
(b) 'Speciality' alcohol alcoxylates. Basic formulators moving away from
nonylphenol ethoxylates are conscious of the impact of the hazard classification, and obviously look to replace them with products that carry no
hazard label and that show an environmental profile which meets current
regulations, and which have the best chance of surviving future regulations.
Essentially linear (including methyl branching) C12-C15 alcohol ethoxylates
have been widely used in various applications, but now carry hazard labels
on account of aquatic toxicity (Table 7.3), and are likely to be the subject
of future regulatory restrictions. For a branched isotridecanol ethoxylate,
although the aquatic toxicity is reduced, its biodegradability is less rapid,
owing to hindrance caused by branching (Table 7.4).
Monobranched alcohol alcoxylates (MBA) are a new class of non-ionic
surfactants that have been shown to be particularly suitable for NPE replacement in both liquid and solid pesticide active ingredient formulations
(Reekmans, 1997a). This range of 'speciality' alcohol (ranging from C11 to
C15) alcoxylates does not carry a hazard classification and, because of a
particular type of branching, is characterized by a lower gelling and foaming
tendency opposite linear (including alkyl groups with one branch) alcohol
ethoxylates with similar total carbon atom chain lengths and degree of
alcoxylation (Reekmans, 1997a). Furthermore, MBAs show unique properties when compared to conventional alcohol alcoxylates in terms of their
phase behaviour and diffusion dynamics (Table 7.7).
Other recent developments include surfactant structures using alkenyl
succinic anhydride as the hydrophobe (Reekmans, 1997a, b). Alkenyl
succinic anhydride polyethylene glycol condensates do not show a gel region, do not contain free alcohol nor free PEG, and are characterized by a
narrower polydispersity than regular alcohol ethoxylates, similar to NPE.
Structures based on this new class of hydrophobes are particularly benefical
in terms of their toxicological profile (Thomas and Hughes, 1997).
(c) Amine-, amide- and glucamide-based surfactants. Ethoxylated alkyl
(tallow and coco) amine surfactants are established products, not least
because of their use with glyphosate IPA salt. However, because of the high
degree of skin and eye irritation with fatty amines and their derivatives
when they are included in formulations at the levels needed to provide
good herbicidal performance, many are classified as an irritant, even corrosive. Major research effort has been spent to identify suitable replacements. In some, but not all, cases eye irritancy can be reduced by converting
the tertiary alkylamine to the corresponding quaternary (TV-methyl)
alkylamine. Alkoxylated tertiary or quaternary etheramines or etheramine
oxide surfactants have also been shown to be suitable replacements.
Glucamide-based surfactants, such as alkenyl succinic anhydride
diglucamides, have been shown to enhance the activity of some waterdispersible active ingredients (Callens et al, 1996) and to improve
rainfastness of concentrated glyphosate formulations (Reekmans, 1997b).
They have the additional benefit of being classified as low aquatic toxicity
wetters as well as being only slightly irritant to the skin and moderate
eye irritants (Thomas and Hughes, 1997; Reekmans, 1997b). Alcoxylated
ethylene diamines (for example the Synperonic T range) constitute another
range of toxicologically and ecologically acceptable alternatives for
the conventional alcoxylated tertiary alkyl (tallow and coco) amine
surfactants.
7.2.6 Conclusion
Environmental and regulatory pressure has led to an increased awareness
among pesticide producers to select surfactants that meet both technical
and ecotoxicological requirements, particularly with new pesticide active
ingredient formulations. Since several established surfactants, for example
nonylphenol-based chemistries, are considered to be hazardous to the environment, major research efforts have been spent on the development of
surfactant chemistries with alternative hydrophobe-hydrophile combinations. Carbohydrates such as polysaccharides and glucamides are a new
class of hydrophiles, with properties which are distinct from the conventional alcohol alcoxylates in terms of their ecological and handling profile. Speciality alcohol alcoxylates, such as the monobranched alcohol
ethoxylates (MBA), have been identified and developed to offer an alternative to nonylphenol ethoxylate (NPE) based emulsifier and dispersant
systems and, as they appear to be proper substitutes for nonylphenol
ethoxylates in different application areas, offer a more universal alternative
to NPEs than linear or methyl branched alcohol alcoxylates. The blending
of hydrophobes of different chain length and/or degree of branching is
another route for developing surfactants with an improved environmental
profile without compromising the performance. Also, recent developments
with alkenyl succinic anhydride condensates (ASAC) showed the potential
of this new class of hydrophobes, which are particularly beneficial in terms
of their toxicological profile. The combination of such hydrophobes with
polyethylene glycol, or carbohydrates such as alkyl polysaccharides and
glucamides, creates opportunities for novel combinations designed for a
particular use or application.
7.3 Enhancing biological activity using adjuvants
7.3.1 Introduction
Whilst the discovery and development of adjuvants by the agrochemical
industry has, historically, been a very empirical process, with a significant
element of chance, considerable effort is now being made to establish
a better understanding of the mechanisms that are responsible for the
beneficial effects which adjuvants can bring to a pesticide formulation.
Understanding the correlation between specific properties of the adjuvant
(and the associated physico-chemical parameters) and biological efficacy
data will allow a more rational approach when selecting adjuvants. In turn,
this will reduce the need for the empirical testing of large numbers
of adjuvant-pesticide combinations and lead to more concise, meaningful
and user-friendly technical advice and labelling (De Ruiter et al. 1988;
Holloway, 1994; Combellack, 1995; Stock, 1996).
Over the last decade, much research effort has been directed towards
eliciting knowledge about the impact of adjuvants on pesticidal activity and
the principles which govern it (Holloway, 1994). Studies with model systems
that have focused on crop species and active ingredients which are structurally representative of those used for different crops, and on the polarity
or mode of action of agrochemicals, have provided much information. The
types of surfactant under evaluation have been mainly polyethoxylates of
alcohol, alkylphenol, sorbitan and alkylamine (Coret and Chamel, 1993;
Schoenherr, 1993; Stock et al., 1993). For these structures the impact of the
degree of ethoxylation, hence HLB, has been investigated in detail, and
physico-chemical parameters such as dynamic and equilibrium surface tension, contact angles and spread factors are available (Grayson, 1995;
Hermansky and Krause, 1995; Green, 1997). Correlations between structure and effect that can provide a ranking in terms of how much efficacy is
enhanced within a given class of structurally related adjuvants have been
put forward (Briggs and Bromilow, 1994; Coret and Chamel, 1995; Bukovac
et al., 1995; Gaskin, 1995; Brumbaugh et al., 1995).
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of hydrophobes of different chain length and/or degree of branching is
another route for developing surfactants with an improved environmental
profile without compromising the performance. Also, recent developments
with alkenyl succinic anhydride condensates (ASAC) showed the potential
of this new class of hydrophobes, which are particularly beneficial in terms
of their toxicological profile. The combination of such hydrophobes with
polyethylene glycol, or carbohydrates such as alkyl polysaccharides and
glucamides, creates opportunities for novel combinations designed for a
particular use or application.
7.3 Enhancing biological activity using adjuvants
7.3.1 Introduction
Whilst the discovery and development of adjuvants by the agrochemical
industry has, historically, been a very empirical process, with a significant
element of chance, considerable effort is now being made to establish
a better understanding of the mechanisms that are responsible for the
beneficial effects which adjuvants can bring to a pesticide formulation.
Understanding the correlation between specific properties of the adjuvant
(and the associated physico-chemical parameters) and biological efficacy
data will allow a more rational approach when selecting adjuvants. In turn,
this will reduce the need for the empirical testing of large numbers
of adjuvant-pesticide combinations and lead to more concise, meaningful
and user-friendly technical advice and labelling (De Ruiter et al. 1988;
Holloway, 1994; Combellack, 1995; Stock, 1996).
Over the last decade, much research effort has been directed towards
eliciting knowledge about the impact of adjuvants on pesticidal activity and
the principles which govern it (Holloway, 1994). Studies with model systems
that have focused on crop species and active ingredients which are structurally representative of those used for different crops, and on the polarity
or mode of action of agrochemicals, have provided much information. The
types of surfactant under evaluation have been mainly polyethoxylates of
alcohol, alkylphenol, sorbitan and alkylamine (Coret and Chamel, 1993;
Schoenherr, 1993; Stock et al., 1993). For these structures the impact of the
degree of ethoxylation, hence HLB, has been investigated in detail, and
physico-chemical parameters such as dynamic and equilibrium surface tension, contact angles and spread factors are available (Grayson, 1995;
Hermansky and Krause, 1995; Green, 1997). Correlations between structure and effect that can provide a ranking in terms of how much efficacy is
enhanced within a given class of structurally related adjuvants have been
put forward (Briggs and Bromilow, 1994; Coret and Chamel, 1995; Bukovac
et al., 1995; Gaskin, 1995; Brumbaugh et al., 1995).
The next step is to examine whether these principles still hold for more
sophisticated surfactants such as carbohydrates, speciality alcohol
alcoxylates and polymers. These materials are the chemicals of the future
because of the environmental pressure being exerted on the use of
adjuvants of a previous generation, such as nonylphenol and alkylamine
ethoxylates (Knowles, 1995; Johnson, 1996). Evaluation of the properties
and associated physico-chemical parameters of these novel surfactants will
contribute to the understanding of how adjuvant behaviour may vary when
various hydrophile-hydrophobe combinations are used, and provide a
more rational approach to the preparation of synergistic blends and the
design of new adjuvants.
7.3.2 Relevance of a surfactant's properties
To understand how adjuvants affect biological efficiency when used in
pesticides, the most logical approach is to consider how the adjuvant affects
the individual processes that occur consecutively during and after the
spray application of a pesticide formulation (Briggs and Bromilow, 1994;
Holloway, 1994). The ultimate biological activity of foliar-applied agrochemicals is determined by the summation of the individual efficiencies at
each of the following stages:
• droplet adhesion and retention;
• droplet spreading and formation of deposits;
• uptake and translocation.
The impact of different surfactants on each of these distinct stages is
illustrated in the following sections. The surfactants that are considered
include 'new-generation' adjuvants, such as alkylpolysaccharides and
monobranched 'twig'-shaped alcohol alcoxylates, established materials,
such as sorbitan derivatives and linear alcohol ethoxylates, and - for reference - 'first-generation' compounds, such as alkylamine ethoxylates and
nonylphenol ethoxylates (Table 7.6). The physico-chemical parameters
associated with the different surfactant structures are listed, and some
correlations between these data and the effects on the efficacy of the
adjuvant are implied.
(a) Droplet deposition and retention. Key parameters that determine
deposition and retention of droplets are the mass (volume) and viscosity
of the droplet, its velocity in flight (kinetic energy) and the difference in
surface energy between the droplet in flight and its surface energy after
impact (Grayson etal, 1991; Tadros, 1994). The properties of the surfactant
that influence these parameters are the rate of diffusion and adsorption of
the surfactant at the spray solution-air and droplet-leaf surface interfaces,
as well as the dilational behaviour of the interface. The effects are reflected
Table 7.6 Summary of adjuvants selected to represent different chemical classes
Adjuvant
Chemical class
Structure
Alkyl polysaccharides (APS)
Atplus APS 450
C9-C11 APS
Monobranched alcohol ethoxylates
(MBA)
Atplus MBA 871
Atplus MBA 872
MBA C11 POE (7)
MBA C13 POE (15)
Linear alcohol ethoxylates
Synperonic 91/6
Synperonic A7
Lubrol 17A17
C9-C11 POE (6)
C13-C15 POE (7)
C16-C18POE(H)
Sorbitan derivatives
Tween 20
Sorbitan monolaurate POE (20)
Alkylamine ethoxylates
Atlas G-3780A
Tallow amine POE (20)
Nonylphenol ethoxylates
Synperonic NP8
Nonylphenol POE (8)
in values for the contact angle, the surface tension decay constant (TD), the
equilibrium surface tension (ye) at the air-liquid interface, and the
dilational modulus (e0); values for these parameters are given in Table 7.7.
Other factors which influence droplet adhesion and retention are the
roughness and wettability of the surface, the tilt of the leaf, the distance
between the spray nozzle and the target surface, the wind speed, and
ambient conditions (Wirth et al, 1991; Miller et al, 1995).
Dynamic surface tension. Dynamic surface tension experiments on a
0.2% (w/w) aqueous solution were carried out at 2O0C using a maximum
bubble pressure apparatus. In this technique, bubbles are generated at
different frequencies and their surface tension is determined from their
Laplace pressure. By generating bubbles at different frequencies, a plot
of surface tension against bubble frequency is obtained. As the frequency
Table 7.7 Physico-chemical parameters for the selected adjuvants (S. Davies, ICI Technology,
Wilton, UK, unpublished results, 1997)
CMC
(mol/l)a
Atplus APS 450
Atplus MBA 871
Atplus MBA 872
Synperonic 91/6
Synperonic A7
Lubrol 17All
Tween 20
Atlox G-3780A
Synperonic NP8
a
b
c
d
e
7
2.5
4
3
9
7
2
6
7
X 10"4
X 10~4
X 10"5
X 10"4
X 10"6
X W'7
X 10"5
X 10~6
X 10~5
ye
(mN/m)b
Spreading
factor on peac
TD
(ms)d
e0
(mN/m)e
26
27
32
27
28.5
37.5
36
40.7
29.3
2.27
3.3
1.63
2.86
16
7
32
7
180
1200
170
255
108
80
55
50
49
68
45
47
25
70
1.51
1.74
1.21
2.13
Critical micellar concentration (CMC).
Equilibrium surface tension (EST) of a 0.1% (w/w) solution measured at 2O0C.
Spread factor of a 0.2% (w/w) surfactant solution on pea.
Time constant from dynamic surface tension experiments (0.2% w/w).
Dilational modulus.
Surface tension (mN/m)
Time (s)
Figure 7.4 Surface tension decay curves for selected adjuvants (• = Synperonic NP8; A =
Lubrol 17A17; T - Atplus MBA 872; + - Atplus MBA 871; • - Atplus APS 450;
ft = Atlas G-3780).
of bubble formation corresponds to a certain adsorption time for the
surfactant, conversion of bubble frequencies into adsorption time data
provides a plot of surface tension against adsorption time. Figure 7.4 has to
be interpreted in this way.
The observed form of the dynamic surface tension plot depends on two
factors: first, how quickly the surfactant is adsorbed at the interface (the
dynamic adsorption), and second, how efficiently it reduces the surface
tension once it gets there. These two processes can be quantified in the
following way: first, the effectiveness of the surfactant in reducing surface
tension is given by the equilibrium value of the surface tension for the
surfactant system considered. The rate of adsorption of the surfactant may
be characterized by a time constant for the observed decay of surface
tension, TD. Most of the data show that the surface tension decay can be
related to the following expression, which is derived for diffusioncontrolled relaxation of surface tension for surfactant concentrations below
the cmc, although this equation fails at long times (Lucassen and van den
Tenpel, 1972):
It = Ye + (YO - YeJ^xpfr/TDJerfcjr/T^) 1 J
where yt is the surface tension measured at time t, ye is the equilibrium
surface tension, y0 is the zero time surface tension (that of water), t is the
time and TD is a time constant. This expression has been used to produce the
solid lines shown in Figure 7.4, which represent the best fit to the data.
From this process a value for TD is obtained. The smaller the value of TD,
the faster the rate of surfactant adsorption or the higher the dynamic
adsorption.
Values for TD are preferred to data on dynamic surface tension, which
vary with the frequency of bubble generation. Two different surfactants
may have an identical dynamic surface tension value at a given bubble
frequency, but show significantly different surface tension decay curves,
and hence dynamic adsorption properties (S. Davies, ICI Technology,
Wilton, UK, unpublished results, 1997).
Dilational modulus. Experiments were carried out by subjecting an
interface to an abrupt expansion and measuring the inital change in surface
or interfacial tension, and its subsequent decay with time. The instantaneous dilational modulus (e0) can then be calculated using the following
expression (Li et al, 1995):
80 = A dy/cL4
where A is the initial area at the interface before expansion, dy is the initial
change in surface tension and cL4 is the change in area during expansion.
The value for the dilational modulus is an equilibrium property of the
interface and at concentrations below the CMC it generally increases as the
concentration of the surfactant increases. Above the CMC the value should
not change significantly. Because of the behaviour described above, a true
comparison of the instantaneous dilational modulus of similar surfactant
systems is the measurement carried out at the CMC, which is the value
quoted for e0 in Table 7.7.
It is suggested that the dilational modulus is an influential factor affecting
the foliar retention of spray droplets. If the dilational modulus is small, it
implies that, upon impact and initial spreading of the droplet, the increase
in surface tension as the air-water interface expands, will be less than the
increase observed when a surfactant which has a higher value of e0 is used.
As the impact and capture of spray droplets on foliage take place in a
matter of milliseconds (initial spreading <10ms), the dynamic adsorption
has to be considered within this timescale. By combining dilational modulus
and DST, the variation in the surface tension of an impacting droplet with
time after impact may be modelled as shown in Figure 7.5. Within 5-10ms
of droplet impact, Atlas G-3780A and Atplus APS 450 show a similar
surface tension (50-53 mN/m), as shown in Figure 7.5, albeit that the two
surfactants show significantly distinct decay curves. For this model, a realistic rate of expansion of the droplet surface during impact was taken and
used to calculate the expected rise in surface tension on impact (S. Davies,
ICI Technology, Wilton, UK, unpublished results, 1997). The dynamic
surface tension data were then used to predict how the surface tension
Modeiled surface tension (mN/m)
time(ms)
Figure 7.5 Model decay of surface tension after droplet impaction (• = Atlas G-3780; A =
Atplus APS 450; T = Atplus MBA 871; • = Synperonic NP8).
decays with time. The value for the surface tension 10ms after impact was
used in the model.
Figure 7.6 illustrates the correlation between spray retention on pea of
the adjuvants identified in Table 7.6, and the modelled surface tension.
Aqueous solutions of sodium fluorescein (0.005% w/v) and adjuvant (lg/1)
were used to determine the retention. The quantitative assessment of the
effects was made by spectrofluorimetry of fluorescein recovered from excised foliage of each replicate immediately after the spray droplets had
dried. Results were calculated on a dry-weight basis as deposits per unit
emission (DUE) - (mgfluorescein)/(gdry weight foliage) (g fluorescein
applied) ha (Van Toor et al, 1994). The higher the DUE value, the better
the retention.
(b) Droplet spreading and deposit formation. Once spray droplets have
been retained on the surface and equilibrium has been reached, surface
tension forces will govern mainly the degree of spreading, possible coalescence and eventual coverage. To predict how an active ingredient will
spread on a target surface, data on the equilibrium surface tension (EST)
and the advancing and receding contact angles are needed (Brumbaugh
et al, 1995; Bukovac et al, 1995).
Whether greater coverage is a desirable effect or not depends on the
mode of action of the pesticide (Tadros, 1994). Good target coverage is
essential for pesticides that have a protective or residual mode of action.
With non-systemic agrochemicals the cover required depends on the mobil-
Acetone/water
1
Spray retention (DUE)
'Atplus APS
!Synperonic1 91/6
'Atplus1 MBA 872
'Atplus1 MBA
'Atlas' G
'Synperonic' NP8
Tween' 20
'LubroM7A17
No adjuvant
Modelled surface tension (mN/m)
Figure 7.6 Spray retention against modelled surface tension for peas (surfactant concentration
= lg/l).
ity and location of the pest, whereas with systemic agrochemicals the liquid
has to be brought into contact with those areas of the plant through which
the agrochemical is absorbed. As high penetration requires high concentration gradients, an optimum situation may be one in which adequate coverage of the areas where penetration occurs is achieved without too much
spreading over the surface of the leaf, since this results in 'thin deposits' and
promotes evaporation.
As water is lost from the deposit, the concentration of the surfactant
increases and different liquid crystal phases are formed. Addition of an
adjuvant may produce deposits which are solid, gel- or liquid-like, according to the structure and concentration of the surfactant (S. Davies, ICI
Technology, Wilton, UK, unpublished results, 1997). Because the main
function of a surfactant in the spray deposit is to act as a solubilizing agent
or solvent for the pesticide, the phase behaviour and the hygroscopic properties of the surfactant molecules are key factors. Thick deposits, which are
produced from droplets with limited spreading, can increase the tenacity of
the agrochemical and thus prevent the droplets or particles from being
removed by rain, thus ensuring long-term protection by the agrochemical;
this situation is often required with many systemic fungicides. The 'ideal'
physical form of the spray deposit is very much determined by the mode of
action and water solubility of the active component.
The phase behaviour of systems at higher surfactant concentrations is
likely to have an impact on biological efficiency. A significant observation is
that at low concentrations, monobranched alcohol alcoxylates (MBA),
which give cloudy solutions at room temperature, appear to form vesicles,
liposomes or a lamellar phase in water rather than conventional micelles.
Linear alcohol ethoxylates with the same number of EO groups form normal micelles at the same concentrations rather than vesicles, and upon
further 'drying' form hexagonal, cubic and then lamellar phases (S. Davies,
ICI Technology, Wilton, UK, unpublished results, 1997). The properties of
the different phases differ greatly; the hexagonal (H1) and cubic (V1) phases
have a much higher viscosity than the lamellar (L0x) phase. This has several
implications. One is that diffusion of the active ingredient through the
deposit to the surface of the leaf will be much slower if the deposit has
formed a hexagonal or cubic phase, as the molecular diffusion coefficient
depends upon the inverse of the bulk viscosity. Furthermore, large amounts
of oil, or in this case the active agent, can be solubilized in vesicles and
lamellar phases, thus preventing premature precipitation of the active component. Another effect of the higher solubilization is that the paraffinic
layer on the surface of the leaf may also be solubilized, allowing faster
penetration of the active. The presence of vesicles is also claimed to increase the transport of the active component to the surface of the leaf and
to enhance transport of the active component through membranes; both of
these effects result in systems showing a faster mode of action.
The phase behaviour for different concentrations of surfactants for the
selected surfactants (Table 7.6) is shown in Table 7.8. Liquid crystalline
structures are known to be affected by other additives in the formulation,
such as antifreeze and electrolytes. The phase behaviour upon evaporation
of a spray droplet of an agrochemical formulation should preferably be
evaluated.
Table 7.8 Phase behaviour for different concentrations of surfactants
Surfactant/surfactant
concentration
20%
30%
Atplus450
L13
L1
Atplus871
Atplus872
Synperonic 91/6
Synperonic A7
L1
L1
L1
L1
Lab
L1
L1
L1
Lubrol 17 All
Tween20
Synperonic NP8
L1
L1
L1
V1
L1
L1
H1
L1
L1
3
40%
50%
60%
70%
80%
L1
L1
L1
L1
La
V1"
L1
H1
La
H16
L1
H1
L0
H1
L1
La
L0
H1
Lac
La
L2C
L2
L2
La
H1
L1
H1
H1
L1
H1
H1
L1
La
H1 + X/
L1
L
L1
L1 = isotropic micella phase; b La = lamellar phase; c L2= inverse micellar phase; d V1 =
cubic phase; e H1 = hexagonal phase; f X1 = crystals.
7.3.3 Built-in activators and spray-tank mixtures
When considering which approach to use to optimize the activity of the
component, it must be decided whether a complete product is required, or
whether tank mixing with an adjuvant is appropriate. This decision depends
upon various factors.
(a) Route to market. In the USA, distributors are an essential route to the
market for pesticide manufacturers and are prime contacts with the end
user. As well as distributing agrochemical formulations, though, they commercialize adjuvants for tank mixes on their behalf under their own trade
name and provide recommendations on the use of such products to
growers. In Europe, national distributors are too small to carry the financial
burden of registering and marketing own-brand products. The agrochemical companies themselves market their own formulations and prefer
to avoid tank mixing where possible because of problems due to compatibility and biological activity, as well as issues surrounding national registration
(Uttley, 1995).
(b) Targeted market segment. Tank mixing allows a formulation to be
optimized for a particular market segment that may otherwise be of insufficient value to justify the development of a specifically tailored product or
niche formulation. Incorporating the adjuvant into the formulation directly
ensures product differentiation and offers a proprietary position, which
are the prime requirements for a strong position in competitive market
segments (Stock, 1996).
(c) Market developments. Because of the considerable shift towards the
rational design of agrochemical formulations, it is expected that the
emphasis with newer products to optimize formulations will reduce new
developments in tank-mix practice. However, the use of tank-mix
adjuvants to enhance many of the older pesticide formulations will
remain common practice. Furthermore, low-cost generic pesticides are
becoming increasingly popular as more active ingredients come out of
patent; such products can often provide adequate results at a much lower
cost than their more modern counterparts. Combinations of generic
pesticides and adjuvants are still usually less expensive than the latest
agrochemicals, and the opportunity offered by modern adjuvants to finetune performance can allow generic pesticides to be competitive
(Hochberg, 1996).
(d) National registrations and regulations. Regulatory and registration
requirements for adjuvants vary considerably between countries. For
example, in Germany the market for tank-mix adjuvants is virtually nonexistent because of the stringent regulatory requirements for such products
(Smith, 1993). These different, and shifting, regulatory and registration
requirements mean that multinational agrochemical companies, particularly in Europe, favour the use of activators incorporated in the formulation
(Johnson, 1996). The future viability of tank-mix products will depend upon
decisions made by the relevant regulatory authorities (Stickle, 1995; Green,
1995; Levine, 1996).
(e) Formulation type and application practice. Tank mixing allows the
efficacy of a 'standard' pesticide formulation to be adjusted and maintained
under extreme weathering conditions, as well as enabling any shortcomings
in a 'first-generation' product to be corrected. Tank-mix products that have
been evaluated by bioassays can be combined into active one-pack products
to provide enhanced 'second-generation' formulations. The downside to
the practice of using tank mixes is that there is little control over the
application: most pesticide labels are vague when it comes to recommending adjuvants. Growers using adjuvants to reduce spray rates may
forfeit their right to make claims against any pesticide manufacturer whose
products fail to work, or lead to crop damage or phytotoxicity (Green, 1995;
Stock, 1996).
Incorporating the adjuvant into the formulation ensures compatibility
and provides other benefits, such as product differentiation, lower total
cost, a proprietary position and proper application practice. The downside
to this practice is the lack of flexibility to adjust the dose as needed to cope
with adverse conditions. Furthermore, the dose needed to enhance biological efficacy is often large and it may be difficult to incorporate the quantity
required into a one-pack formulation; it may add significantly to packaging,
storage and transport costs too, particularly for pesticides that are used at
extremely low levels, such as sulphonylurea herbicides.
7.3.4 Future trends in surfactants and adjuvants
Because of the opportunities that have been, and will be, created by environmental and agricultural policies, improved product technology and the
globalization of agriculture, there is a huge incentive for agrochemical
companies to develop formulations that can be used at reduced application
rates and which contain multiple active ingredients to provide broad biological activity, with adjuvants included in the concentrate as part of the
package. Formulation science has become an advanced technology, with
sophisticated surfactants and synergistic blends developed to meet the
stringent requirements set by agrochemical producers, consumers and the
regulatory environment.
The first pesticide adjuvants were simple chemicals, such as ethoxylated
nonylphenols, ethoxylated octylphenols, ethoxylated tallow amines and
mineral oils, which contained a surfactant (in low concentrations) to emulsify the oil in the spray tank. These products, which have been used typically
as an 'insurance' to counter adverse conditions, still make up a large proportion of the adjuvant market.
The need for different adjuvants, which are highly researched and recognized as bringing added value, is increasing. A new generation of spray
adjuvants using alkyl polysaccharides, speciality or 'designer' alcohol
alcoxylates, pyrollidones, organosilicones, clathrates, acetylene diols, emulsified methylated seed oils and saponified seed oils, soya phospholipids, and
hybrids, is gaining popularity and importance (Stevens et al, 1993; Foy,
1996). Such adjuvants are more active than their older competitors.
Gradually the market is shifting towards these small-volume, high-value
products.
Enhancing the biological activity is the prime, but not sole, criterion on
which today's adjuvants are finally selected. It is the combination of
ecotoxicological and handling properties, cost-performance profile and
global availability that will make a future adjuvant successful or not. More
detail about the different requirements is given below. The relative emphasis that is placed on the individual criteria in the final selection will depend
on application (built-in or tank mix), the region, the formulation type and
its stage in the product life cycle.
(a) Enhancing biological efficacy. Enhancing efficacy was once the overriding criterion in formulation design, and obviously is still essential. However, considerations such as user safety, solvent reduction and ease of pack
disposal have triggered the development of more sophisticated types of
formulation, such as microemulsions and capsule suspensions (Beestman,
1996; Stern and Becher, 1996). Water-dispersible granules have become
popular because they virtually eliminate the risk of contamination when
mixing or loading the products into application equipment (Utz etal, 1995).
Furthermore, dry pesticide formulations are lighter and often more concentrated, and hence cheaper to package and transport (Drummond, 1996).
Unfortunately, both water-based and dry formulations tend to be less active
than solvent-based formulations, and current formulation design is as much
about incorporating adjuvants to boost the efficiency of the formulation
(Underwood et al., 1995). Modification of the physical form of the adjuvant
may be required for physical compatibility. A solid carrier may be needed,
depending on the liquidity of the product at ambient temperatures. Typically, wetters are compact molecules that have a low degree of ethoxylation,
and hence are characterized by a low pour point. They are difficult to
include in a dry formula unless adsorbents such as clays or silicas are used.
However, these solid carriers are not water soluble or biologically active
and may clog spray lines and nozzles.
A modern trend is to use spray-dried products. The morphology of such
products is a light bead that can be dissolved rapidly. With spray-dry technology a wide range of liquid and waxy surfactants can be solidified, converting them into free-flowing powders. Urea is a typical example; it can
form a crystalline solid complex or clathrate with specific surfactants and
has great potential as a component of an adjuvant. Not only is it a common
fertilizer but it has also been used in foliar sprays, with or without pesticides
or micronutrients. Consequently clathrates have excellent properties as
both a fertilizer and an adjuvant. When urea is heated in the presence of
some organic material, it recrystallizes as long hexagonal prisms to form
tunnel-like channels. The molecular ratio of urea molecules to 'guest' compound varies with molecular weight. Typical urea levels are 40-60%, and
the particle size distribution of the clathrates shows that 80% of the particles are between 200 and 600 ^m. Current production of such materials
involves melting the various components together with up to 5% water to
form a homogenous liquid, which is then sprayed into a spray tower such
that it solidifies as it falls, forming a prilled material that resembles soap
powder. The melting point of the product is essentially the spraying
temperature.
Urea adducts have many assets:
•
•
•
•
they are totally water soluble;
there are no water-insoluble carriers which may clog nozzles or pumps;
they are 100% active;
dissolution is rapid without the gelling problem associated with some
liquid systems;
• disintegration of the granule is enhanced upon dilution;
• the wetting and spreading properties of the surfactant are not affected;
• the active ingredient is not in contact with the surfactant until dilution
(extruded granules).
Urea clathrates of alcohol ethoxylates, such as Atplus S-620 and Atplus S14, can be incorporated into solid formulations. They have a dual role,
acting as a wetter/disintegrator of the granule upon dilution in the spray
tank and as a wetter/spreader of the spray solution on the surface of the
target foliage.
Other examples of growing adjuvant sophistication are microemulsions,
and technologies that are exploited in the manufacture of modern personalcare products (Loll, 1993), such as liquid crystals and liposomes. These
technologies are of interest because of the trend towards controlling
the delivery and moisturizing of active substances. The coupling of
microemulsion technology with the synergy of pyrrolidones with anionic
surfactants has led to the development of microemulsified water-insoluble
polymer concentrates (Foy, 1996). Such adjuvant systems combine spreaders, stickers and penetrants in a single adjuvant and enhance the efficacy of
a number of active ingredients by increasing uptake and reducing wash-off.
Liquid crystals can be formed in the pesticide formulation itself or by
adding surfactants to the spray-tank solution (Rogiers, 1995). Separate
emulsifier systems that are suitable for both applications have been developed. In the pesticide formulation, liquid crystals can be built up to form a
complex viscoelastic structure between the particles or droplets of the
dispersed phase, thus retarding the breakdown of the formulation and
reducing sedimentation, flocculation and coalescence. When surfactants are
tank mixed with the pesticide, a liquid crystalline phase is formed as the
spray droplet dries on the surface of the leaf. These liquid crystals may
improve rainfastness and increase pesticide activity since the active ingredient stays solubilized for a longer period.
(b) Environmental and safety considerations. To take advantage of the
opportunities created by present-day greater environmental awareness, any
new adjuvant should (Rogiers, 1995)
• meet ecotoxicological requirements, such as low groundwater contamination, no toxicity towards fish, no bioaccumulation and ready
biodegradability;
• be non-toxic to humans, fauna and flora;
• have limited effect on non-targeted organisms;
• improve the safe handling characteristics of the product for the formulator and applicator;
• improve safe disposal of product.
The proposed phase out of alkylphenol ethoxylates (APE; section 7.2.4(b))
has encouraged agrochemical companies to develop formulations without
them. Unfortunately, few surfactants are as universal in their emulsification
and dispersion performance as APE. Speciality alcohol alcoxylates, such as
the monobranched alcohol alcoxylates (MBA), have recently been identified in several applications as the preferred replacements for APE, both
as an adjuvant and an emulsifier/dispersant. Alkylpolysaccharides have
also been shown to be particularly beneficial in replacing some typical
APE-based adjuvants (Callens et al, 1996).
(c) Intellectual property. The screening of developmental products can
offer the manufacturers of agrochemical formulation and/or adjuvants the
opportunity to obtain intellectual property (patent) protection, and hence a
competitive edge. In certain pesticide applications, such as non-selective
weed control, many of the existing surfactants have been screened and
patented, and it is only when using new surfactants based on nonconventional hydrophobe-hydrophile combinations that the opportunity to
commercialize improved formulations without patent infringement
presents itself. Carbohydrate-based materials, such as glucosides and
glucamides, and the use of novel hydrophobes, such as alkenyl succinic
anhydrides (ASAC), can create such opportunities (Reekmans, 1997a).
(d) Handling. Especially when used as a tank mix, the handling characteristics of an adjuvant are very important. Properties such as good
pourability at low temperatures, low viscosity, low foaming, and no formation of gel particles at low temperatures are vital to the farmer.
Surfactants can be modified and optimized to improve handling.
Ethoxylated alkenyl succinic anhydride condensates (ASAC) are known
not to show a gel region, in contrast to the conventional linear alcohol
ethoxylates. Branched hydrophobes (MBA) are known to foam less
than the linear hydrocarbon chains, and alcoxylation will improve the cold
stability and pourability when compared to ethoxylated analogues
(Reekmans, 1997a).
Many of the older tank-mix adjuvants contain solvents to improve
handling. As the use of several of the conventional solvents is under environmental pressure because of their flash point and toxicity, and some of
the newer environmentally friendly solvents actually sell at a higher
price than the surfactant, there is a clear benefit to be gained by optimizing
the handling performance of the surfactant, rather than diluting with
solvents.
(e) Cost/performance ratio. An adjuvant must bring added value to the
formulation. In most cases the final selection of an active ingredientadjuvant combination will be based not on the cost of the adjuvant alone,
but on a cost-performance calculation. By using adjuvants, a formulator
can reduce the effects of competitive pricing because the efficacy is improved, less pesticide is required and the full cost of the formulation is
decreased; they may even give a competitive edge or advantage that will
enable a formulator to retain market share.
While the cost of the adjuvant will always be a major factor, its importance in the final selection will depend on the concentration of
adjuvant needed to obtain the desired effect, whether it is used as a
tank mix or built in, and on the type of formulation. When the aim is to
replace APE, for example, the alternative products can only carry a small
surplus.
(f) Regulatory requirements. Because of the increasingly international
nature of agriculture and the global approach and rationalization of multinational agrochemical companies, present-day formulations are often intended for use globally. Potential surfactants for these formulations need
both EINECS notification and EPA clearance. This favours the use of
established products rather than novel materials, as often the latter will not
yet be listed or exempted from the need to obtain clearance.
7.3.5 Conclusion
At present the selection of an adjuvant is based on various criteria, which
reflect the awareness of both the surfactant suppliers and pesticide manufacturers of the needs and concerns of the consumer and political circles.
Safety for the user and environmental aspects are key driving forces in
research and development, and have become prime selection criteria. A
new generation of highly researched adjuvants is available, with chemistries
such as alkyl polysaccharides, speciality alcohol alcoxylates, pyrollidones,
organosilicones and emulsified methylated seed oils which are claimed to be
more active than their older competitors. In order to meet the customer
needs and successfully promote these products, adjuvant suppliers will have
to provide empirical data recovered from field and greenhouse evaluations,
in combination with detailed information on physico-chemical properties
and associated parameters relevant to the individual unit processes and
stages for biological efficacy. Such practice will lead to an improved usage
and understanding of adjuvants and the associated effects.
Acknowledgements
The words 'Synperonic', 'Atplus', 'Atlox', Tween' and 'Lubrol' are trade
marks, the property of Imperial Chemical Industries pic.
The word 'Atlas' is a trade mark, the property of ICI Americas Inc., a
subsidiary of Imperial Chemical Industries pic.
The word 'Dobanol' is a trade mark, the property of Shell Chemicals UK
Ltd.
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8 Improving agrochemical performance:
possible mechanisms for adjuvancy
P. J. HOLLOWAY
As much as 85-90% of pesticides applied to crops never reach their target.
Instead, they disperse into the air, soil, water, animals and people.
Repetto and Baliga (1996)
8.1 Introduction
It is well known that the activity of agrochemical formulations, especially
those containing herbicides, can be improved substantially by the addition
of certain biologically inactive ingredients, known collectively as adjuvants.
Such products may be built into a formulation at the time of manufacture or
used separately for tank mixing with a formulation prior to spray application. Perhaps understandably, the discovery and commercial development
of adjuvants in the past has relied heavily on empirical or heuristic screening for enhancement effects on efficacy, with little consideration being
given to underpinning modes or sites of action for adjuvancy. However,
modern thinking on formulation design is becoming increasingly focused on
more rational approaches to adjuvant selection, based on physico-chemical
principles and a fundamental understanding of the key processes involved
in optimizing the performance of agrochemicals. Past experience has
already shown that adjuvant choice varies according to the properties of the
pesticide, its mode of action (residual, contact or systemic) and the type of
formulation used (solution, emulsion or suspension), as well as the
nature of the intended target (weed, insect or fungus).
In the present chapter the composition of adjuvants currently authorized
or approved for use with foliage-applied agrochemicals is reviewed and
then examined from a mechanistic and predictive point of view in relation
to possible effects on ultimate biological performance. Biological effects
per se will not be discussed and are dealt with elsewhere, e.g. Proceedings
of International Symposia on Adjuvants for Agrochemicals (1989, 1992,
1995).
8.2 Chemical composition of adjuvants
A large number of proprietary adjuvants are currently available worldwide.
However, despite the multitude of product names, use descriptions and
the element of commercial secrecy, they can be conveniently subdivided
into a number of broad chemical categories. The most important of
these are:
•
•
•
•
•
•
surface-active compounds (surfactants);
emulsifiable oils;
polymers;
polymer-forming compounds;
phospholipids;
inorganic salts.
Mixtures containing compounds of the same chemical class or belonging to
different classes are also often used, especially for tank mixing.
The size and content of the adjuvant market for tank mixing varies
considerably according to country (Uttley, 1995). For example, in the USA,
about 150000 tonnes were used in 1992, of which 76% were emulsifiable
oils, compared with only 20000 tonnes in Western Europe in 1993, the
major market share here being split more or less equally between
emulsifiable oils and surfactants (Figure 8.1). Demand for adjuvants worldwide is expected to increase by about 5% annually (Uttley, 1995). However,
in Germany, tank-mix adjuvants are no longer approved for use.
8.2.1 Surfactants
The majority of the surfactants used as adjuvants are based on the
polyoxyethylene (EO) hydrophile (Figure 8.2). By varying the EO content,
an oligomeric series of products having different physico-chemical properties can be produced from a given hydrophobe, reflected in the corresponding hydrophile-lipophile balance (HLB) value (Griffin, 1954). These values
typically range from 6 to 20 for adjuvants, corresponding with mean molar
EO contents of 2-20. Average MT values (relative molecular mass) are
between c. 300 and 1000, and products can vary in appearance from viscous
liquids to waxy solids; water solubility decreases with decreasing HLB.
Typical use rates for surfactant adjuvants in tank mixes are 0.1-0.5% of the
final spray volume; when built in, agrochemical/surfactant ratios may vary
from 2:1 to as much as 1:3.
Ethoxylated non-ionic surfactants with a primary alcohol or nonylphenol
hydrophobe (Figure 8.2) are employed for tank mixing with many
agrochemicals. Siloxanes (review by Hill, 1997) are a recent specialist
addition to this category of surfactant adjuvants. Alkoxylated cationic
surfactants, especially those based on tallow amines, are used mainly with
USA (148,700 tonnes)
Others 9
Vegetable oils 3
Surfactants 15
Mineral oils 73
WESTERN EUROPE (20,230 tonnes)
Vegetable oils 4
Surfactants 52
Mineral oils 43
Others < 1
Figure 8.1 Size of adjuvant markets (%) in USA (1992) and Western Europe (1993).
(Adapted from Uttley, 1995.)
the herbicide glyphosate. Anionic surfactants are not often utilized as
adjuvants, the notable exception being that (Figure 8.2) for the herbicide
glufosinate (Kocher and Kocur, 1993). Equilibrium surface tensions of
aqueous solutions of most surfactants at supramicellar concentrations
typically lie in the range 30-40 mN/m, the exception being organosilicones
which give values as low as 22 mN/m.
R - alkyl
General formula
Class
Nonionic
Primary alcohol
R — O— X
Alkylphenol
R-C 6 H 4 -O-X
Sorbitan monoester
R— CO— O— Xb
Trisiloxane
C6-C18 (linear saturated or linear + branched saturated)
C8- C10 (branched saturated)
Cj 0 -C 18 (linear saturated or linear unsaturated)
Not applicable
(Me)3Si-O-SiMe-O-Si(Me)3
Xa
Cationic
Tertiary amine
R
a
^Kv
C 2 -C 18 (linear saturated or linear saturated + unsaturated)
-<x*
Anionic
Primary alcohol sodium sulphonate
R — O — X — SO3Na
C 12 -C 14 (linear saturated)
Hydrophile X, commonly EO (C2H4O)xH, average x, range 2-20.
a
Sometimes mixed EO + PO(C3H6O)^H.
Sorbitan EO, average x = 20.
Figure 8.2 Alkoxylated surfactants commonly used as adjuvants.
Because of increasing concerns about the ecotoxicological side effects of
mainstream ethoxylated surfactants, less toxic and more readily biodegradable replacements are currently being sought. Possible alternatives now
available include alkyl polyglucosides (APs; review by Balzer, 1997) and 7Valkyl pyrrolidones (review by Login, 1995; Figure 8.3), two surfactant
classes not based on alkylene oxides. Unlike most conventional surfactants,
the product range in both cases is produced by varying the chain length of
the alkyl hydrophobe the HLB value and, consequently, water solubility
decreasing with increasing chain length. APs also have the additional
advantage of synthesis from renewable raw materials, namely starches
for the glucosyl moiety and vegetable oils for the alkyl portion.
A. ALKYLPOLYGLUCOSlDES
R = Cg-C^, saturated linear, sometimes branched
n = Average degree of glucose polymerization (1.1 - 3.0)
* Ratio between a- and P- anomers.ca 3 : 1
B. N- ALKYL PYRROLIDONES
R = C1- C-|2 . saturated linear
Figure 8.3 Surfactant adjuvants not based on alkylene oxides.
8.2.2 Emulsifiable oils
At the present time, emulsifiable concentrates (ECs) containing mineral
oils dominate this sector of the adjuvant market (Figure 8.1). Although
precise details of composition are rarely disclosed, adjuvant mineral oils are
usually described as highly refined with a low content of aromatics. Nevertheless, they will all be composed of complex mixtures of hydrocarbons
(Figure 8.4) in the range C16-C30 (Mr values 250-400). Both aliphatic and
cyclic constituents (naphthenes) are usually present and alkyl branching
is common. Mineral oils differ from one another mainly in the relative
contents of the two structural types of hydrocarbons; this has an influence
on their intrinsic viscosity.
As with certain types of surfactant, there are also environmental
concerns in several countries about the biodegradability of mineral oils.
EC substitutes based on vegetable oils (Figure 8.5) are therefore likely
to become of increasing importance in the future. Currently, two types
are available, those based on refined triacylglycerols extracted from
seed sources and those derived from short-chain alkyl esters of crude or
partially refined vegetable fatty acids. Fatty acid methyl esters are often
referred to, inappropriately, as methylated seed oils (MSOs). The most
A. ALIPHATIC HYDROCARBONS
Normal alkanes
/so-alkanes
B. CYCLIC HYDROCARBONS (NAPHTHENES)
Alkyl cyclohexanes
Alkyl decahydronaphthalenes
^ Normal and branched-chain
Contents of A and B vary according to oil source and degree of refining but usually low
amounts of aromatic hydrocarbons
Figure 8.4 Composition of mineral oil-based adjuvants.
A. TRIACYLGLYCEROLS
R R 2 ,R3 = mainly C18, 18:1 (oleic) ,18:2 (linoleic) and 18:3 (linolenic)
Acyl composition varies according to source
B. ESTERIFIED FATTY ACID DERIVATIVES
R = as in triacylglycerols
^ = C1 (methyl) to C4 (butyl)
Figure 8.5 Composition of vegetable oil-based adjuvants.
commonly used sources of adjuvant oils are from oilseed rape (canola) and
soya.
It should be noted that the three types of adjuvant oils differ considerably
in their properties. Vegetable oils are mixtures of triacylglycerols (Figure
8.5) with Mr values >850, whose composition and degree of unsaturation
varies according to source; for example, oleic acid (18:1) is the main acyl
component of rapeseed oil, whereas in soya oil it is linoleic acid (18:2). On
the other hand, fatty acid esters (Figure 8.5) are of much lower Mr (e.g.
methyl oleate 296) and less viscous than the parent vegetable oils. These
phytogenic compounds are thus more polar than the purely hydrocarbon
mineral oils. However, use rates for oil adjuvant ECs are similar, ranging
from 0.5 to 2% of the final spray volume.
Oil-based adjuvants also differ from one another in their emulsifier
content, which can vary from 1% to as high as 40%. Low-emulsifier ECs
are sometimes referred to as 'crop oils', high-emulsifier ECs as 'crop oil
concentrates'. Although emulsifier compositions are rarely specified,
most are probably blends of conventional surfactants with low HLB
values. Emulsifier composition will almost certainly vary according to oil
composition.
8.2.3
Polymers
The principal classes of polymeric adjuvants are summarized in Figure 8.6;
they are employed mainly for tank mixing and may be used in conjunction
A. POLYMERS
Synthetic latex
Polybutadiene
Polyvinyl alcohols (PVA)
R = H or a mixture of H and COCH3
Mr 20000-200000
Polyacrylamides (PAM)
B. POLYMER - FORMERS
Terpenes
Pinolene (di -1- p - menthene)
Figure 8.6 Composition of polymeric and polymer-forming adjuvants.
SOYA LECITHIN
Phosphatidylcholines
R^, R 2 = as in triacylglycerols
R 3 = -CH2- CH2- N(CH3)3,choline
Figure 8.7 Composition of phospholipid-based adjuvants.
with surfactants. Dispersions of synthetic rubber have adhesive qualities, as
do solutions of polyvinyl alcohols (PVAs) and poly aery !amides (PAMs).
The latter two classes also have viscoelastic properties which are utilized
to modify the behaviour of spray fluids, as well as their bulk viscosity if
used at high concentrations. Alkylated vinylpyrrolidone polymers and
vinylpyrrolidone-vinyl acetate copolymers have also been introduced into
the market recently (cf. Figure 8.3B).
8.2.4 Polymer-forming compounds
The main adjuvant in this category is the terpene pinolene (Figure 8.6),
which has the ability to polymerize on contact with air, forming an adhesive
and protective film over a target surface. Again, tank mixing is the principal
method of application.
8.2.5 Phospholipids
Crude soya lecithin is the chief source of phospholipids (Figure 8.7) for
the preparation of this type of adjuvant. Like vegetable oils, they are based
on glycerol but contain, in addition to unsaturated fatty acyl chains, a
hydrophilic polar phosphorylated head group, and thus possess some
surface activity. However, in water they form unique microscopic spheres,
called liposomes, consisting of concentric lipid bilayers (review by
Lasic, 1996). For agricultural use as a tank mix, the liposome dispersion is
stabilized with an organic acid, usually propionic, and the pH is c. 3.
8.2.6 Inorganic salts
Solutions of ammonium sulphate and/or ammonium nitrate, often in
combination with a non-ionic surfactant, find specialist uses, especially with
the water-soluble herbicide glyphosate.
8.2.7 Other ingredients
Additional components may also be added to proprietary adjuvants, mainly
to improve their handling and dispensing characteristics when tank mixing.
These include organic solvents, such as isopropanol and isobutanol, especially with viscous surfactant products.
8.3 Mechanistic approaches for investigating adjuvancy
Spray application of any pesticide involves a number of discrete transfer
steps or unit processes (Young, 1986; Hall et al., 1993; Holloway, 1993),
each of which may affect the ultimate biological effectiveness. These stages
occur consecutively and in a matter of milliseconds, initially. Unit processes
are the sites of action for adjuvants, and therefore the focus of mechanistic
and predictive investigations.
The first phase is concerned entirely with spray droplets (Figure 8.8),
involving formation in the spray nozzle by atomization, transfer to and
impaction with the target, retention and coverage of the target and, finally,
evaporation to form a deposit. The deposit is the starting point for the
second phase, transfer to the biological site of action. For residual pesticides
the process stops here, but for contact and systemic active ingredients,
uptake and movement from the site of application are crucial performance
factors.
8.3.1 Atomization
Most pesticide sprays are generated by atomization through flat-fan
hydraulic nozzles, which produce a range of droplet sizes from 10 to 500 |im
in diameter, after break-up of a thin liquid sheet close to the orifice of the
nozzle (Figure 8.9). Addition of adjuvants to the spray fluid, especially
those with surface-active or viscous properties, may affect this process and
alter the droplet spectrum, the magnitude of the effect varying with the
amount added, the type of nozzle used and the position at which in-flight
measurements are recorded. In some cases, patternation may also be
changed (Chappie et al., 1993), that is, the volume distribution across the
spray swath, especially at high adjuvant concentrations.
The majority of surfactants, if used at concentrations at which they are
freely soluble in water, will decrease the volume median diameter (VMD)
SPRAY CLOUD
Droplet sizes (VMD)
IMPACTlON
Reflection
Run - off
RETENTION
COVERAGE
EVAPORATION
DEPOSIT FORMATION
Figure 8.8 Processes involved in spray delivery from hydraulic nozzles.
of droplets and increase the small droplet component (SDC; percentage in
spray volume with diameters < 100 ^m) in the spray spectrum (Arnold,
1983; Anderson et al, 1988; Holloway, 1994), when compared with water
alone. For example, using a 10 EO nonylphenol dissolved at 0.2, 1 and
5g/l, VMDs from an even-spray nozzle were decreased from 220 [im for
water to 214, 202 and 184 jum, respectively, with the SDC increasing from
7.9% for water to 8.2,10.2 and 12.5%, respectively (Holloway, 1994). However, for less soluble surfactants which form turbid dispersions in water, the
opposite effect is often observed. A striking example of this behaviour is
provided by an 8EO trisiloxane, which increased VMDs from 220 |im for
water to 283,293 and 242 (Lim when added at 0.2,1 and 5 g/1, respectively; the
corresponding SDCs were 2.3, 2.2 and 3.9%, respectively, compared with
NOZZLE
LIQUID SHEET
OSCILLATION
PERFORATION
BREAK UP
DROPLET FORMATION
VMD
DECREASE
INCREASE
Oil-in-water emulsions
Low HLB surfactants
Organosilicones
Polymers
Phospholipids
Inorganic salts
PVA
High HLB surfactants
Organic solvents
Figure 8.9 Processes involved in atomization by hydraulic nozzles and the effects of some
adjuvants on the sizes of spray droplets generated (VMD = volume median diameter).
water at 7.9% (Holloway, 1994). Analagous effects were obtained using
linear alcohols or nonylphenols with EO contents of less than 6.
Atomization of oil-in-water emulsions formed after dilution of adjuvant
oil ECs also influences the resultant spray quality (Merritt and Morrison,
1988; Butler Ellis et a/., 1997; Hall et al, 199Ib). Although, in most cases,
droplet sizes and velocities are increased substantially in comparison with
water, oil and emulsifier compositions appear to have little overall effect.
Quantitatively, the effects resemble those described above for the
trisiloxane surfactant, including the marked decrease in SDC. In addition,
EC emulsifiers, when added alone at concentrations equivalent to those in
the diluted oil EC, usually provide atomization data similar to those of the
corresponding emulsion (Hall et al., 1997b). Phospholipid adjuvants, being
liposome dispersions, also affect spray quality in a manner similar to
lipophilic surfactants and adjuvant oil emulsions (Quinn et al., 1986; Butler
Ellis et al., 1997).
Only those polymeric adjuvants which increase the viscosity of the spray
fluid alter atomization, again leading to an increase in droplet size distributions (Ozkan et al., 1993; Chappie et al., 1993; Downer et al., 1995; Dexter,
1996). Other types of water-soluble polymers (Holloway, 1994) and inorganic salts have little effect on spray quality.
Although the precise physical mechanisms for the effects of adjuvants on
atomization are unclear, photographic evidence suggests that they are probably related to differences in the distances from the nozzle at which breakup of the liquid sheet occurs (Butler Ellis et al., 1997). If the break-up point
is farther from the nozzle than that with water, the life of the sheet will be
prolonged; this will lead to the production of smaller droplets, probably by
suppression of oscillations (Figure 8.9). On the other hand, if the life of the
sheet is reduced by increased perforation, the break-up point will occur
closer to the nozzle than with water; consequently, larger droplets will be
generated from the thicker liquid sheet. However, an exception to this
hypothesis would appear to be high Mr water-soluble polymers, which
were observed to delay sheet break-up but still increased the droplet size
distributions considerably (Dexter, 1996).
It should be noted that much of the atomization data for adjuvants has
been obtained using the additives alone; further modifications to spray
quality are likely to occur if other formulation ingredients are also present
in the spray fluid. Droplet size is an important factor in the performance
of a pesticide formulation and is often overlooked; its significance
for adjuvancy is discussed in the following sections. Spray quality is also
relevant to application safety, the drift potential of a spray increasing with
an increase in SDC (Miller, 1992).
8.3.2 Retention
A major use for adjuvants is to increase the retention of pesticidecontaining spray droplets on foliage; this process is controlled by the
interactions between a number of physico-chemical factors, the most important of which are summarized in Figure 8.10. However, it is essential to
recognize that spray deposition can only be enhanced substantially on
species which are difficult to wet, such as oilseed rape and cereals. On more
easily wettable targets, for example sugar beet and field beans, adjuvant
addition usually has little effect on retention when compared with water
alone (de Ruiter et al., 1990; Holloway, 1994).
Because of their surface-active properties, most surfactants will increase
spray deposition on water-repellent foliage; this can be verified and quantified using fluorescent tracers or marker dyes (Cooke and Hislop, 1993).
DROPLET GENERATION
Number
Size
Velocity
PERFORMANCE
FACTORS
Surface tension
Viscoelasticity
Evaporation
Drift
Canopy structure
TARGET
Figure 8.10 Factors influencing droplet retention by difficult-to-wet targets.
Nevertheless, their relative efficiencies vary according to the composition
of the surfactant and are directly related to the amounts added to the
spray liquid (de Ruiter et al., 1990; Holloway, 1994). For maximum
effect, concentrations need to be well in excess of the critical micelle
concentration (CMC) of the surfactant, and therefore do not correlate with
the equilibrium surface tension values of the bulk spray solution.
Retention enhancement by EO-based surfactants is related to their EO
content. For a given hydrophobe, e.g. primary alcohol or alkylphenol, lowHLB products (EO < 6) often provide deposition inferior to those containing more hydrophilic oligomers (Holloway, 1994). Optimum retention
efficiency using APs is observed with hydrophobe chain lengths between
C8 and C12; performance on a weight-for-weight basis is equivalent to
most conventional surfactants (Hoyle and Holloway, 1996). Although the
influence of surfactant structure on spray deposition efficiency has not
been studied systematically, the shape and size of the hydrophilic and/or
hydrophobic moieties could be important. Surfactants with bulky head or
tail groups, e.g. highly branched aliphatic chains, ethoxylated secondary
alcohols, ethoxylated tertiary tallow amines (with two hydrophilic tails)
and sugars, seem to be the most efficient. From the limited quantities of
data available, the ionic properties of a surfactant would appear to be
relatively unimportant.
Improvements in spray deposition may also be achieved by tank mixing
with adjuvant oil ECs, but these are usually less than those obtained using
other deposition agents (Hall et al., 1997a,b). Oil composition does not
appear to be a major factor, performances being related more to their
emulsifier contents and the rates applied. Also, on young foliage of peas
and barley it was found that spray retention from the emulsifiers alone was
similar to the corresponding emulsions, but on older foliage, emulsions gave
superior performance to the emulsifiers (Hall et al., 1997b). The retention of
solvent-based emulsions could also be enhanced by the addition of adjuvant
oil emulsions, but efficiency was dependent on the emulsifier content in
the diluted solvent-based EC. Oil emulsions had little effect on the spray
delivery of concentrated solvent emulsions (Hall et al., 1997a).
PVAs with mean Mr values between 20000 and 100000, which have low
surface activity and do not increase bulk viscosity, are very efficient spray
deposition agents (Wirth et al., 1991; Holloway, 1994; Csorba et al., 1995),
sometimes being superior to benchmark surfactants, such as nonylphenol
10 EO and tallow amine 15EO. Similar behaviour was observed for proprietary mixtures containing other types of polymers, including PAMs (Csorba
et al, 1995).
Quantitative retention data are not available for polymer-forming or
phospholipid adjuvants. However, being dispersions, they are both unlikely
to influence spray deposition greatly. Dissolved inorganic salts would be
expected to have no effect on retention efficiency.
8.3.3 Predicting retention performance
Surfactant effects on spray deposition can often be rationalized from
knowledge of their influence on atomization and from their dynamic
surface tension (DST) characteristics. These parameters control the size
and surface tension of the droplets which will impinge on the plant surface
(Figure 8.10), and ultimately determine whether they will be retained or
reflected from it. On impact with water-repellent targets, smaller droplets
will be retained better than larger ones, as will those with surface tensions
considerably less than that of water (Hartley and Brunskill, 1958).
DST measurements on bulk surfactant solutions can be used to reveal the
increases in surface tension that occur at non-equilibrium surface ages, and
thus provide a profile of the dynamic stability of an individual surfactant;
the maximum bubble pressure method (MBPM; Franses et al., 1996)
provides a simple and relatively inexpensive technique for obtaining such
information. It should also be remembered that the surface tension of spray
droplets will not be at equilibrium, both at the moment of impact and again
immediately afterwards. It has been calculated that most surfactants take at
least 80ms to reach equilibrium at a newly formed air-liquid interface
(Brazee et al., 1994).
An example of a surfactant exhibiting poor dynamic stability (C13/C14
6EO) is given in Figure 8.11, the surface tension of its solution rising rapidly
as bubble frequency increases and surface age decreases, especially at
low concentrations, where the values approach that of water (72mN/m).
This type of behaviour is associated with increased VMDs and decreased
SDCs, in comparison with water, after atomization, leading in turn to
inferior retention-enhancing efficiency (Figure 8.11). Much better dynamic
stability is observed for the oligomeric C13/C14 15EO (Figure 8.12),
especially when the concentration of the surfactant is increased. In this
case, VMDs decrease and SDCs increase, compared with water, and as a
consequence, spray deposition also increases in a concentration-dependent
manner (Figure 8.12). The retention data shown in Figures 8.11 and
8.12 can be compared directly because they were determined in the same
experiment.
Some relationships between the spray deposition behaviour of
surfactants, their DST values and droplet spectra have been noted by
several workers (Anderson and Hall, 1989; de Ruiter et al., 1990; Wirth
et al., 1991; Stevens et al., 1993; Friloux and Berger, 1994) and mathematical
models have been proposed (Grayson et al., 1991, 1993); correlations
reported between surfactant DST and increased herbicidal activity are
likely to be serendipitous (Wales and Griffiths, 1995; Green, 1997). Absolute DST values would appear to be valid only when comparing the retention performance of a closely related series of surfactants. They are of
little use when evaluating that of different classes, where similar spray
depositions may be achieved using surfactants with widely differing DSTs,
e.g. tallow amine 15EO (54mN/m at 5Hz) and nonylphenol 10 EO (39 mN/
m at 5Hz; Holloway, 1994). In our experience, dynamic stability, indicated
simply by the slope of the DST profile, is a more meaningful predictive
parameter for surfactants, correlating well with both spray quality and
retention performance; it is also a reflection of the relative rates at which
surfactant molecules diffuse from the bulk of a drop to a freshly formed airliquid interface. We have found that these relationships are applicable to a
wide range of surface-active products, including APs (Hoyle and Holloway,
1996). Thus surfactants probably function as deposition agents mainly as a
result of their combined effects on the size and surface tension of impacting
spray droplets. Aqueous solutions of organic solvents, such as n-propanol
Surface tension (mN/m)
Bubble frequency (Hz)
Surface age (ms)
DUE
VMD
(nm)
SDC
(%)
A
Water
144
220
7.9
B
0.2g/litre
144
294
1.9
C
1g/litre
275
288
1.9
D
5g/litre
342
252
3.0
Figure 8.11 Dynamic surface tension profiles (MBPM) of a 6EO C13IC14 alcohol at three
concentrations, with the corresponding retention data on oat foliage (DUE = fluorescein
deposition per unit emission) and spray qualities (VMD: see Figure 8.9; SDC = small
droplet component, i.e. percentage of spray volume with droplets <100|im in diameter).
Equilibrium surface tension values are given at zero bubble frequency. (Adapted from
Holloway, 1994.)
and acetone, do not exhibit DST effects and retention experiments using
them (Holloway, 1994) indicate that optimum spray deposition on a
difficult-to-wet target occurs with hydraulic spray droplets with surface
tensions of c. 30mN/m. Values below this may lead to losses due to run-off.
Surface tension (mN/m)
Bubble frequency (Hz)
Surface age (ms)
DUE
VMD
fcm) (%)
SDC
A
Water
144
220
7.9
B
0.2g/litre
262
211
9.0
C
1g/iitre
580
197
10.7
D
5g/litre
773
186
13.0
Figure 8.12 Dynamic surface tension profiles (MBPM) of a 15EO C13IC14 alcohol at three
concentrations, with the corresponding retention and spray quality data (for abbreviations see
Figure 8.11). Equilibrium surface tension values are given at zero bubble frequency. (Adapted
from Holloway, 1994.)
It is impossible to record the DST of adjuvant oil-in-water emulsions
because they are two-phase systems, but workers still persist in reporting
such data in relation to their spray quality (Butler Ellis and Tuck, 1997);
this premise will also apply to any dispersed adjuvant system, e.g.
phospholipids. Nevertheless, important clues to the likely retention
performance of oil-based adjuvants are provided by their droplet spectra.
These usually show increased size distributions in comparison with water
which, by analogy with surfactant behaviour discussed above, would be
predicted to lead to moderate retention-enhancing activity.
The retention performance of polymeric adjuvants, such as PVAs, cannot
be predicted either from DST or spray quality measurements, although
they are dynamically stable with very little surface activity (Wirth et al.,
1991; Holloway, 1994). Clearly, such products have an entirely different
mode of action compared to surfactants. Although detailed structureactivity relationships have yet to be carried out, it is thought that they act
by reducing the elasticity of impacting water droplets, making them less
susceptible to reflection. This property is probably related to their ability to
form extensive 'loops and tails' in solution (Wirth et al., 1991), and consequently to modify the viscoelastic characteristics of an air-liquid interface.
Although difficult, it should be possible, using techniques such as surface
quasi-elastic light scattering (Langevin, 1992), to quantify these surface
dilatational and shear forces in bulk polymer solutions and then to examine
them in relation to deposition efficiency. Some surfactants also possess
viscoelastic properties (Sharpe and Eastoe, 1996), which might also contribute to their overall retention performance. For polymeric adjuvants
which increase bulk, as opposed to surface viscosity, it would be predicted
that droplet sizes would increase (Chappie et al., 1993; Downer et al., 1995;
Dexter, 1996); however, effects on retention have not been documented,
although spray drift is reduced.
8.3.4 Spreading and coverage
Another major application for adjuvants is to increase the spread of spray
droplets which have been retained by target foliage. This is an important
consideration for residual and contact-acting pesticides. Surfactants are
most commonly employed for this purpose and their relative spreading
potential can be predicted from equilibrium surface tension measurements. Organosilicone surfactants reduce the surface tension of water to
c. 20mN/m and are the best spreaders currently available (Stevens, 1993);
they can provide complete coverage of both wettable and water-repellent
foliage. Other surfactant classes are much less efficient (Figure 8.13) and
usually provide substantial improvements in spreading only on difficultto-wet targets (Holloway, 1994). These surfactants generally give surface
tension values in the range 30-40 mN/m. It should be noted here that surfactants which are efficient spreaders are often less effective as deposition agents and vice versa (cf. section 8.3.2), a factor to be borne in mind
for formulation design.
As observed for spray deposition, the spreading behaviour of surfactant
solutions is also concentration dependent (Figure 8.14). This phenomenon
ADJUVANTS
Sorbitan ester 2OEO
Tallowamine 15EO
Vegetable Oil
Nonylphenol 1OEO
Alcohol 6EO
Organosilicone 8EO
SPREAD FACTOR
Figure 8.13 Spread factors on oat leaves for 0.2 ul water droplets containing some adjuvants at
5 g/1; in the absence of adjuvants, droplets were repelled by the leaves. Equilibrium surface
tensions (mN/m) of the surfactant solutions were as follows: sorbitan ester 2OEO (35), tallow
amine 15EO (40), nonylphenol 10EO (30), alcohol 6EO (28) and organosilicone 8EO (22).
The vegetable oil was an EC of rapeseed oil containing 5% emulsifier. (Holloway, unpublished
results).
is not reflected by surface tension measurements on the corresponding bulk
solutions because, at most usage rates, the surfactant will be above its
critical micelle concentration. However, the situation in the spray droplet
will be different, because it is in contact with the waxy plant surface and
surfactant molecules or micelles will adsorb at this liquid-solid interface,
leading to a reduction in surfactant content in the droplet and thus its
spreadability. If organic solvents are used to reduce the surface tension of
water droplets, there are no adsorption effects. On water-repellent leaves,
surface tensions of 25-30 mN/m are required for effective spreading; these
values are similar to those necessary for optimal droplet retention
(Holloway, 1994).
Addition of oil-based adjuvants may also increase droplet spreading
on some plant species (Gauvrit, 1994), but they are not as efficient as the
best surfactants on waxy plant surfaces. Factors contributing to their
performance may also be emulsifier content and the viscosity of the oil
used. Although they undoubtedly possess surface activity, surface tension
measurements are not applicable to oil-in-water emulsions, because of their
two-phase nature.
The spreadability and covering power of other types of adjuvant formulation will also depend on their inherent surface activity; as predicted,
that of solutions containing PVAs is poor and little different from water
(Holloway, 1994).
Spread factor
Concentration (g/litre)
Figure 8.14 Concentration effects on the spreadability of 0.2 [il water droplets containing
organosilicone 8EO (A), alcohol 6EO (B) and tallow amine 15EO (C) surfactants on oat
leaves. Equilibrium surface tensions for solutions of a given surfactant were the same at the
three concentrations tested; for values see Figure 8.13. (Adapted from Holloway, 1994.)
8.3.5 Uptake and translocation
There is extensive documentation from whole-plant studies of the effects of
adjuvants on the foliar uptake of pesticides from radiolabelled formulations. Most of these data have been obtained following application of 0.21 |il droplets, which are very large in comparison with those delivered from
a spray nozzle (Figure 8.8). For example, a 0.2 ^l droplet has a diameter
of c. 750 ^m, whereas a 200 ^m diameter droplet has a volume of c. 4nl.
Nevertheless, it can be demonstrated that the addition of appropriate
surfactants will enhance the uptake of most pesticides and, as with the other
unit processes described earlier, in a concentration-dependent manner.
However, there have been comparatively few systematic studies to explore
surfactant structure-uptake enhancement relationships. For EO-based
surfactants, enhancement efficiency varies with EO content (HLB) and
the physico-chemical properties of the pesticide (water solubility and
log octanol-water partition coefficient (P) (Gaskin and Holloway, 1992;
Holloway and Edgerton, 1992; Stock et al, 1993; van Toor et al, 1995;
Sharma et al., 1996). Thus uptake of water-soluble pesticides (e.g.
glyphosate, logP -3.8) is generally favoured by adding surfactants with
high EO contents (HLB > 10), whereas that of lipophilic pesticides (e.g.
permethrin, log P 6.5) is much better in the presence of surfactants of lower
EO contents (HLB < 7). However, EO content would appear to have little
influence on the surfactant-enhanced absorption of compounds of intermediate polarity (e.g. cyanazine, logP 2.1). These relationships have been
established using alcohol, alkylphenol and tertiary amine hydrophobes.
Rates and amounts of pesticide uptake also vary considerably according to
plant species, with waxy microcrystalline surfaces often showing greater
enhancement effects with surfactants than more wettable ones.
Oil-based adjuvants can also improve the foliar uptake of pesticides,
especially herbicides (reviews by Gauvrit and Cabanne, 1993; Gauvrit,
1994; Nalewaja, 1995). Oil composition, emulsifier content and target
species all influence enhancement efficiency. Mineral oil ECs are generally
the best, but in some cases those containing vegetable oils or fatty acid
esters may provide equivalent or even better performance. Compared with
surfactants, only a few pesticides have been evaluated with oil ECs, but they
would appear to be most beneficial to the uptake of lipophilic compounds,
especially graminicides, if formulated as emulsions.
There are few reports on the effects of other chemical types of adjuvants
on pesticide uptake. Denis and Debrot (1997) found that ammonium
sulphate stimulated glyphosate uptake in a number of species. Although
polymeric or polymer-forming adjuvants would be expected to have little
influence on uptake or might even prevent it, Leaper (1996) observed
enhanced absorption of this herbicide in the presence of a PVA.
Published information suggests that currently available adjuvants have
little direct influence on the translocation of systemic pesticides (Holloway,
1995). Although they may increase the amount of pesticide that is
translocated, this is an indirect effect of increased uptake; for most mobile
pesticides, a constant proportion of the dose taken up is usually transported
subsequently. Specific transport enhancers would be a useful addition to the
adjuvant inventory.
8.3.6 Predicting uptake enhancement performance
Although some progress has been made, it is still not possible to make
precise predictions about the effect an adjuvant might have on the foliar
uptake of a pesticide. Indeed, if the wrong choice is made, pesticide absorption could be compromised (Gaskin and Holloway, 1992). Available
models (Stock et al., 1993) are only qualitative and do not accommodate
concentration and plant species parameters. Obviously more information is
needed about mechanisms of action. This might be achieved by monitoring
adjuvant behaviour using radiotracers and then using physico-chemical
modelling approaches.
Possible sites for adjuvant action are summarized in the compartmental
scheme for leaves shown in Figure 8.15. Surfactants differ considerably in
their foliar uptake characteristics with some, e.g. ethoxylated sorbitan
monoesters, showing little cuticular penetration, and thus acting mainly in
the pesticide deposit on the plant surface. Other classes of surfactants may
be absorbed, penetrating through the outer epidermal wall at different rates
and reaching the internal tissues of the leaf, where they may sometimes
cause undesirable contact phytotoxic effects (review by Gaskin, 1995).
Penetration rates of ethoxylated surfactants have been shown to be related
to EO content, with those having a low degree of ethoxylation often
being taken up rapidly, sometimes within an hour of application.
More hydrophilic products of this type are generally retained in the epidermal layer for a longer period of time before eventually reaching the
subepidermal cells.
Surfactant uptake may be impeded or increased in the presence of a
pesticide, and interactive and non-interactive mechanisms for pesticide
uptake enhancement have been proposed (Stock and Holloway, 1993).
Organosilicone surfactants are a special case, promoting almost instantaneous foliar uptake of aqueous solutions via stomatal infiltration on some
species at certain concentrations (Policello et al., 1996). Although this
is almost certainly a surface tension effect, such a mechanism has been
disputed by some workers (Roggenbuck et al., 1994).
SURFACE
A
B
C
LITTLE
PENETRATION
PENETRATION
STOMATAL
PENETRATION
CUTICLE
EPIDERMIS
SLOW
INTERNAL
TISSUES
RAPID
VERY RAPID
Figure 8.15 Summary of foliar uptake behaviour of some adjuvants. Cuticular penetration
rates vary according to species and are greater on those possessing crystalline epicuticular
deposits. (A) Ethoxylated sorbitan monoesters, polymers and polymer formers. (B) Slow:
high-EO alkylphenols and alcohols, and triacylglycerols; intermediate: alkyl polyglucosides,
tallow amine ethoxylates and fatty acid esters; rapid: low-EO alkylphenols and alcohols, and
mineral oils. (C) Organosilicones. (Adapted from Holloway and Stock, 1990, with additional
information from Stock et al., 1992; Stock and Holloway, 1993; Gauvrit, 1994 and Mercier et al,
1997.)
There are also differences in the penetration rates of adjuvant oils following foliar application as diluted ECs or as simple solutions in organic
solvents. Triacylglycerols are poorly taken up (Urvoy et al., 1992), whereas
fatty acid esters penetrate at different rates according to the chain length of
the acyl moiety (Mercier et al., 1997); for oleates, maximum uptake occurs
with the methyl ester applied to waxy leaf surfaces. Using mineral oil ECs
containing 14C-octadecane, we have also recently demonstrated rapid uptake of radiolabel by a number of plant species (K. Hall and P. Holloway,
unpublished data). However, when oils are absorbed it is not clear whether
they penetrate as far as the internal tissues or are retained in the lipophilic
cuticle and outer epidermal wall. In addition, adjuvant oil ECs contain
lipophilic surfactants as emulsifiers which are also likely to be taken up and
could contribute to the overall adjuvancy of this type of product.
Because of their high MT values, polymeric and polymer-forming
adjuvants are unlikely to penetrate the cuticle, and hence will act mainly in
the deposit or on the surface of the epicuticular wax layer. The uptake
characteristics of adjuvants containing phospholipids or inorganic salts are
unknown.
The pesticide spray deposit is clearly a major target for adjuvant action
and it is axiomatic that the presence of an adjuvant will modify its microstructure, especially if the pesticide itself is a solid. Of greater importance
is the interaction between the adjuvant and pesticide in the deposit, because
for a pesticide to penetrate it must either be a liquid or in solution
(Briggs and Bromilow, 1994). It is likely that some surfactants and oils
act as solvents or solubilizing agents for pesticides, and this will have an
important influence on the amount of pesticide available for uptake (Figure
8.16). As a predictive strategy, it might be worth while evaluating the
solubilizing capacity of adjuvants for individual pesticides from in vitro
experiments (e.g. Holloway et al., 1992). For surfactants, pesticide
solubilization will probably occur in micelles or liquid crystalline phases in
the concentrated deposit. In addition, high-HLB surfactants also possess
humectant properties which could be an additional solvency factor for
polar water-soluble pesticides. Mineral and vegetable oils would be
expected to be solvents only for lipophilic agrochemicals. It is unclear what
effect polymeric and polymer-forming adjuvants might have on pesticide
availability, other than waterproofing the deposit and thereby increasing its
persistence.
Adjuvants that are taken up by foliage will probably have additional sites
of action and their possible effects on the penetration of pesticides can be
considered in relation to the physico-chemical compartmentalized models
proposed by Briggs and Bromilow (1994; Figures 8.17 and 8.18) and
Schonherr and Baur (1994; Figure 8.19). These are concerned with rates
of diffusion and the pivotal partition parameters logPalk (alkane-water),
providing an indication of the solubility of a pesticide in epicuticular wax,
DISSOLVED
UNDISSOLVED
AVAILABLE FOR
UNAVAILABLE FOR
UPTAKE
UPTAKE
RELATIVE AMOUNTS IN FRACTIONS
• log P oct
• PKA
• Melting point
• Composition and concentration
of any adjuvants added
Figure 8.16 Physico-chemical factors influencing uptake from a solid pesticide deposit (log
Poct: log octanol-water partition coefficient; pKA: dissociation constant). (Adapted from Briggs
and Bromilow, 1994.)
and logPoct (octanol-water) of its solubility in the cuticle. Studies with a
range of unformulated radiolabelled pesticides and model compounds
suggest that there are probably 'hydrophilic' (aqueous) and 'lipophilic'
routes for cuticular penetration. Because of their very low solubilities in
epicuticular wax, as evident from their high A log P values (logPoct - logPalk),
compounds like the herbicide glyphosate would be excluded from entering
the lipophilic pathway (Figure 8.17). For the lipophilic pathway (Figure
8.18), penetration would vary inversely with A log P of the pesticide, reflecting its solubility in epicuticular wax, whilst accumulation in the cuticle
would probably occur if its logPoct was >4. Although the model of
Schonherr and Baur (Figure 8.19) does not recognize the possibility of
different penetration pathways, it provides additional information about
the driving forces for foliar uptake. The maintenance of a high concentration gradient is necessary for efficient foliar uptake of a pesticide, as well as
favourable log P values. Obviously, the same theoretical considerations can
also be applied to adjuvant absorption.
The situation where adjuvant and pesticide are present together is a more
complex system to model. Indeed, different adjuvants may be required for
pesticides entering into the leaf by the alternative pathways. Penetrant
COMPARTMENTS
FACTORS
Epicuticular wax
PENETRATION
Alkane solubility too low to
Cuticle
permit entry via epicuticular
wax : ^, log P > 6
Varies inversely log P .
Underlying
cells
Depends on log Poct and pK^
TRANSPORT
Xylem / Phloem
Figure 8.17 Physicochemical factors influencing foliar penetration of a pesticide via the
'hydrophilic' pathway (for abbreviations see Figure 8.16; A log P = logPoct - logPalk (log
alkane-water partition coefficient)). (Adapted from Briggs and Bromilow, 1994.)
adjuvants which enhance uptake of a particular pesticide could be affecting
the crucial partition processes described above, making them more favourable for uptake of the compound, or they could be interacting with components in the cuticle, making it more permeable to the compound. Although
there is a long way to go before we are in a position to predict adjuvant
effects on uptake, a general pattern is emerging that the physico-chemical
properties of the adjuvant and the pesticide need to be matched together as
closely as possible in order to achieve optimum uptake enhancement. There
would appear to be little value in mixing a lipophilic adjuvant with a highly
water-soluble agrochemical and vice versa.
8.4 Future prospects
The technical literature contains a confusing array of use descriptions
for adjuvant products, such as wetter, spreader, sticker, extender, penetrant, deposition agent, etc., as well as various combinations of such terms.
COMPARTMENTS
FACTORS
Varies inverselyAJog P
PENETRATION
Epicuticular wax
Cuticle
Accumulation log P
>4
Underlying
cells
Slow log PQct >4
Depends on log PQct and pK A
TRANSPORT
Xylem / Phloem
Figure 8.18 Physicochemical factors influencing foliar penetration of a pesticide via the
'lipophilic' pathway (for abbreviations see Figure 8.17). (Adapted from Briggs and Bromilow,
1994.)
These should be treated with caution because precise mechanisms of
adjuvancy have not been established in many cases, although pesticide
efficiency may be increased. An additional complication is that an adjuvant
may have more than one mode of action; prime examples are surfactants
which may act either as deposition agents, spreaders or uptake promoters,
or as all three.
Adjuvant chemistry and technology is now reaching an exciting stage
of development, as agrochemical manufacturers and users realize their
potential for dose reduction and improving pesticide safety. However,
the market has yet to escape from the doldrums of misconceptions, misrepresentations and extravagant claims about efficacy. Additional pressures
will arise from the need to improve the environmental safety of some
widely used adjuvants. Some suggested criteria for next generation
adjuvants are thus
• high biodegradability;
• good ecotoxicological compatibility;
PERMEANCE
Diffusion
coefficient
Path length
Size
selectivity
COMPARTMENTS
DRIVING FORCES
Epicuticular wax
Concentration
in residue
'°9 P wax
Cuticle
•°9 pcuticle
Underlying
cells
Concentration in
water phase
PENETRATION = PERMEANCE + DRIVING FORCES
Figure 8.19 Factors affecting mass transport of pesticides through plant cuticles (logPwax and
logPcuticle correspond with logPalk and logPoct, respectively, in Figures 8.16-8.18). (Adapted
from Schonherr and Baur, 1994.)
•
•
•
•
•
economic price/performance ratio;
extensive application possibilities;
equivalent or superior effectiveness compared with existing products;
manufacture mainly from renewable resources;
built into agrochemical formulations.
Acknowledgements
Research on adjuvants at lACR-Long Ashton Research Station is funded
by commissions from the Ministry of Agriculture, Fisheries and Food,
and by Industrial CASE awards from the Biotechnology and Biological
Sciences Research Council of the UK. I am also indebted to numerous
agrochemical companies and adjuvant manufacturers for their continued
financial assistance and for technology transfer. The invaluable assistance
of both past and present colleagues and postgraduate students in the
execution of the work and production of data for this chapter is gratefully
acknowledged.
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Balzer, D. (1997) Alkyl polyglucosides as surfactants, in Specialist Surfactants (ed. LD. Robb),
Blackie, London, pp. 169-207.
Brazee, R.D., Bukovac, MJ., Cooper, J.A. et al (1994) Surfactant diffusion and dynamic
surface tension in spray solutions. Transactions of the American Society of Agricultural
Engineers, 37, 51-8.
Briggs, G.G. and Bromilow, R.H. (1994) Influence of physicochemical properties on uptake
and loss of pesticides and adjuvants from the leaf surface, in Interactions between Adjuvants,
Agrochemicals and Target Organisms (eds PJ. Holloway, R.T. Rees and D. Stock),
Springer-Verlag, Berlin, pp. 1-26.
Butler Ellis, M.C. and Tuck, C.R. (1997) The effect of liquid properties on spray formation by
flat fan nozzles. Aspects of Applied Biology, 48, 105-12.
Butler Ellis, M.C., Tuck, C.R. and Miller, P.C.H. (1997) The effect of some adjuvants on sprays
produced by agricultural flat fan nozzles. Crop Protection, 16, 41-50.
Chappie, A.C., Downer, R.A. and Hall, F.R. (1993) Effects of spray adjuvants on swath
patterns and droplet spectra for a flat-fan hydraulic nozzle. Crop Protection, 12, 579-90.
Cooke, B.K. and Hislop, E.C. (1993) Spray tracing techniques, in Application Technology
for Crop Protection (eds G.A. Matthews and E.C. Hislop), CAB International, Oxford,
pp. 85-100.
Csorba, C., Hislop, E.C. and Western, N.M. (1995) Options for reduced volume 'coarse'
droplet spraying, in Proceedings of the Brighton Crop Protection Conference - Weeds,
pp. 513-20.
Denis, M.-H. and Debrot, S. (1997) Effects of salts and surfactants on foliar uptake and long
distance transport of glyphosate. Plant Physiology and Biochemistry, 35, 291-301.
de Ruiter, H., Uffing, A.J.M., Meinen, E. and Prins, A. (1990) Influence of surfactants and
plant species on leaf retention of spray solutions. Weed Science, 38, 567-72.
Dexter, R.W. (1996) Interactions of anionic surfactants and polymers used as spray tank
adjuvants, in Pesticide Formulations and Application Systems: 16th Volume (eds MJ.
Hopkinson, H.M. Collins and G.R. Goss), American Society for Testing and Materials,
Philadelphia, ASTM STP 1312, pp. 77-92.
Downer, R.A., Cooper, J.A., Chappie, A.C. et al (1995) The effect of dynamic surface tension
and high shear viscosity on droplet size distributions produced by a flat fan nozzle, in
Pesticide Formulations and Application Systems: 14th Volume (eds F.R. Hall, P.D. Berger
and H.M. Collins), American Society for Testing and Materials, Philadelphia, ASTM STP
1234, pp. 63-70.
Franses, E.I., Basaran, O.A. and Chang, C.-H. (1996) Techniques to measure dynamic surface
tension. Current Opinion in Colloid and Interface Science, 1, 296-303.
Friloux, K.M. and Berger, P.D. (1994) The relation of tallowamine ethoxylates to dynamic
surface tension and field performance, in Pesticide Formulations and Application Systems:
15th Volume (eds H.M. Collins, F.R. Hall and M. Hopkinson), American Society for Testing
and Materials, Philadelphia, ASTM STP 1268, pp. 83-97.
Gaskin, R.E. (1995) Phytotoxicity of agrochemical adjuvants, in Proceedings of the Fourth
International Symposium on Adjuvants for Agrochemicals, pp. 193-200.
Gaskin, R.E. and Holloway, PJ. (1992) Some physicochemical factors influencing foliar
uptake enhancement of glyphosate-mono(zs0propylammonium) by polyoxyethylene
surfactants. Pesticide Science, 34, 195-206.
Gauvrit, C. (1994) Methodology for determining foliar penetration of herbicides with reference to oil-based adjuvants, in Interactions between Adjuvants, Agrochemicals and Target
Organisms (eds PJ. Holloway, R.T. Rees and D. Stock), Springer-Verlag, Berlin, pp. 17191.
Gauvrit, C. and Cabanne, F. (1993) Oils for weed control: uses and mode of action. Pesticide
Science, 37,147-53.
Grayson, B.T., Pack, S.E., Edwards, E. and Webb, J.D. (1993) Assessment of a mathematical
model to predict spray deposition under laboratory track spraying conditions. II.
Examination with further plant species and diluted formulations. Pesticide Science, 37,13340.
Grayson, B.T., Webb, J.D., Pack, S.E. and Edwards, E. (1991) Development and assessment
of a mathematical model to predict foliar spray deposition under laboratory track spraying
conditions. Pesticide Science, 33, 281-304.
Green, J.M. (1997) Varying surfactant type changes quizalofop-P herbicidal activity. Weed
Technology, 11, 298-302.
Griffin, W.C. (1954) Calculation of HLB of nonionic surfactants. Journal of Society of
Cosmetic Chemists, 5, 249-58.
Hall, F.R., Chappie, A.C., Downer, R.A. et al (1993) Pesticide application as affected by spray
modifiers. Pesticide Science, 38, 123-34.
Hall, KJ., Holloway, PJ. and Stock, D. (1997a) Factors affecting the efficiency of
spray delivery onto foliage using oil-based adjuvants. Aspects of Applied Biology, 48, 11320.
Hall, KJ., Western, N.M., Holloway, PJ. and Stock, D. (1997b) Effects of adjuvant oil
emulsions on foliar retention and spray quality, in Proceedings of the Brighton Crop
Protection Conference - Weeds, pp. 549-54.
Hartley, G.S. and Brunskill, R.T. (1958) Reflection of water drops from surfaces, in Surface
Phenomena in Chemistry and Biology (eds J.F. Danielli, K.G.A. Parkhurst and A.C.
Riddiford), Pergamon Press, Oxford, pp. 214-23.
Hill, R.M. (1997) Siloxane surfactants, in Specialist Surfactants (ed. LD. Robb), Blackie,
London, pp. 143-68.
Holloway, PJ. (1993) Adjuvants for agrochemicals: why do we need them? Mededelingen van
de Faculteit Landbouwwetenschappen, Rijksuniversiteit, Gent, 58/2a, 125-40.
Holloway, PJ. (1994) Physicochemical factors influencing the adjuvant-enhanced spray
deposition and coverage of foliage-applied agrochemicals, in Interactions between
Adjuvants, Agrochemicals and Target Organisms (eds PJ. Holloway, R.T. Rees and D.
Stock), Springer-Verlag, Berlin, pp. 83-106.
Holloway, PJ. (1995) Adjuvants for foliage-applied agrochemicals: the need for more science
not serendipity? in Proceedings of the Fourth International Symposium on Adjuvants for
Agrochemicals, pp. 167-76.
Holloway, PJ. and Edgerton, B.M. (1992) Effects of formulation with different adjuvants on
foliar uptake of difenzoquat and 2,4-D: model experiments with wild oat and field bean.
Weed Research, 32, 183-95.
Holloway, PJ. and Stock, D. (1990) Factors affecting the activation of foliar uptake of
agrochemicals by surfactants, in Industrial Applications of Surfactants II (ed. D.R. Karsa),
Special Publication No.77, Royal Society of Chemistry, Cambridge, pp. 303-37.
Holloway, PJ., Wong, W.W.-C., Partridge, HJ. et al. (1992) Effects of some nonionic
polyoxyethylene surfactants on uptake of ethirimol and diclobutrazol from suspension
formulations applied to wheat leaves. Pesticide Science, 34,109-18.
Hoyle, E.R. and Holloway, PJ. (1996) Performance of alkyl polyglucosides as spray deposition
agents, in Proceedings of the Brighton Crop Protection Conference - Pests and Diseases,
pp. 441-2.
Kocher, H. and Kocur, J. (1993) Influence of wetting agents on the foliar uptake and herbicidal
activity of glufosinate. Pesticide Science, 37,155-8.
Langevin, D. (ed.) (1992) Light Scattering by Liquid Surfaces and Complementary Techniques,
Surfactant Science Series, 41, Marcel Dekker, New York.
Lasic, D. (1996) Liposones - an industrial view. Chemistry & Industry, 210-14.
Leaper, C. (1996) Rational approaches to the design of formulations of glyphosatemono(isopropylammonium). PhD thesis, University of Bristol.
Login, R.B. (1995) Pyrollidone-based surfactants. Journal of American Oil Chemists Society,
72, 759-71.
Mercier, L., Serre, L, Cabanne, F. and Gauvrit, C. (1997) Behaviour of alkyl oleates following
foliar application in relation to their influence on the penetration of phenmedipham and
quizalofop-P-ethyl. Weed Research, 37, 267-76.
Merritt, CR. and Morrison, J.R. (1988) Some physical and biological effects of spray
adjuvants, in Proceedings of the International Symposium on Pesticide Application, Paris, 1,
pp. 299-308.
Miller, P.C.H. (1992) Herbicide application, in Proceedings of the First International Weed
Control Congress, 1, pp. 150-8.
Nalewaja, J.D. (1995) Behaviour, applicability and efficacy of non-surfactant adjuvants,
in Proceedings of the Fourth International Symposium on Adjuvants for Agrochemicals,
pp. 186-92.
Ozkan, H.E., Reichard, D.L., Zhu, H. and Ackerman, K.D. (1993) Effect of drift retardant
chemicals on spray drift, droplet size and spray pattern, in Pesticide Formulations and
Application Systems: 13th Volume (eds P.D. Berger, B.N. Devisetty and F.R. Hall),
American Society for Testing and Materials, Philadelphia, ASTM STP 1183, pp. 173-89.
Policello, G.A., Stevens, P.J.G., Forster, W.A. and Gaskin, R.E. (1996) The influence of
cosurfactant and role of spreading in stomatal infiltration by organosilicones, in Pesticide
Formulations and Application Systems: 15th Volume (eds H.M. Collins, F.R. Hall and
M. Hopkinson), American Society for Testing and Materials, Philadelphia, ASTM STP
1268, pp. 59-66.
Proceedings of the First International Symposium on Adjuvants for Agrochemicals (1986) in
Chow, P.N.P., Grant, C.A., Hinshalwood, A.M. and Simundsson, E. (eds) (1989) Adjuvants
and Agrochemicals, VoIs I and II, CRC Press, Boca Raton, FL.
Proceedings of the Second International Symposium on Adjuvants for Agrochemicals (1989) in
Foy, C.L. (ed.) (1992) Adjuvants for Agrochemicals, CRC Press, Boca Raton, FL.
Proceedings of the Third International Symposium on Adjuvants for Agrochemicals (1992) in
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Proceedings of the Fourth International Symposium on Adjuvants for Agrochemicals (1995) in
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Quinn, P.J., Perett, S.F. and Arnold, A.C. (1986) An evaluation of soya lecithin in crop spray
performance. Atomisation and Spray Technology, 2, 235-46.
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Schonherr, J. and Baur, P. (1994) Modelling penetration of plant cuticles by crop protection
agents and effects of adjuvants on their rates of penetration. Pesticide Science, 42,185-208.
Sharma, S.D., Kirkwood, R.C. and Whateley, T.L. (1996) Effect of non-ionic nonylphenol
surfactants on surface physicochemical properties, uptake and distribution of asulam and
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scattering. Langmuir, 12, 2303-7.
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droplets to foliage: the role of dynamic surface tension and advantages of organosilicone
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of agrochemicals. Pesticide Science, 38, 165-77.
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uptake of some organic compounds: interactions with two model polyoxyethylene aliphatic
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9 Packaging of agrochemicals
P. D. CURLE, C. D. EMMERSON, A. H. GREGORY,
J. HARTMANN and P. NIXON
The Agrochemical Industry recognises the need for responsible and ethical care
of its products from their invention through to ultimate use and beyond
GIFAP
Viewed from a historical perspective, those engaged in development and
selection of packaging for agrochemicals were interested primarily in getting products to the point of ultimate use at the lowest cost consistent with
basic safety and shelf-life requirements. Since the mid-1980s and the substantial replacement of many metal containers by the new barrier plastics,
attention has been focused on ergonomic issues at the point of ultimate use
related to the transfer of product into application equipment. Latterly the
fate of packaging 'beyond' ultimate use has dominated considerations in
many parts of the world. Extensive collection schemes for recovery of
conventional single-trip packaging have been created in several countries
alongside the introduction of many returnable systems in appropriate markets. North America has taken a leading role in both approaches. Industry
associations have been instrumental in addressing concerns on disposal and
have agreed to cooperate and promote best practices through education
and training.
This chapter will provide a guide to the mainstream packaging materials,
methods of testing, design and performance considerations and conclude
with a review of disposal practices and returnable systems. A glossary of
technical terms is given at the end of this chapter, followed by suggestions
for further reading.
9.1 Selection of packaging types
The essential prerequisite is that there is no interaction between packaging
material and contents throughout the shelf life of the product.
9.7.7 Selection of packaging materials for solid formulations
Typical representative types of formulated products are
• wettable powders (WP);
• water-dispersible granules (WG);
• dusting powders (DP);
• granules (GR).
Polyethylene is the preferred material because it has universal application.
It is thermoplastic, and therefore an ideal sealing medium, and forms a very
good moisture barrier. The predominant requirement is the preservation
of agrochemical formulations, particularly in humid climates. Flexible
pouches or bags are preferable to rigid containers to minimize the amount
of packaging used or to be disposed of when empty. If further strength is
required, it can be obtained by the use of fibreboard outer packs.
In monolayer film constructions, a thickness of 0.1 mm will be sufficient in
most applications.
If shelf-life studies show the product to be very hygroscopic or water
sensitive, an additional moisture barrier such as aluminium will be required.
Aluminium composite foil requires a heat-sealable inner layer and external
protection against environmental influences. In addition, physical strengthening and a print carrier are required.
A typical composite foil would consist of
•
•
•
•
40gsm low-density polyethylene (LDPE) as the sealing medium;
0.012mm aluminium;
20gsmLDPE;
one of the following:
• 30gsm polypropylene (PP);
• 0.012mm polyester (PET);
• 0.015mm polyamide (PA);
• or 50gsm paper.
Specific agrochemical formulation properties, e.g. a strong odour or volatile components, require a composite film which consists of LDPE and an
additional barrier, not necessarily aluminium. PA or PET are ideal reinforcements for larger packages, e.g. 10-20 kg.
Typical constructions are
• 0.015mm PA (external), which provides the gas barrier and physical
strength;
• 0.050-0.100mm LDPE (internal), which provides moisture protection
and sealing.
The principle in designing multilayer films is to combine barrier properties.
A comparison of LDPE, PA and a laminate of LDPE-PA illustrates this
(Table 9.1).
Film or composite foil packages for powders or granules are usually
tubular form-fill-seal (FFS) pouches, prefabricated bags or lined cartons. It
is essential that seals are designed to minimize the retention of formulation
after emptying and rinsing.
Table 9.1 Permeation rates of films
Film
LDPE 0.100mm
PA 0.015mm biaxially orientated
LDPE/PA biaxially orientated,
0.05/0.015 mm
Oxygen permeation rate
(cm3/(m2 day bar))
at 230C and 75% RH
Water vapour
transmission rate
(g/m2 day)
at 230C and 85% RH
(DIN 5312 2)
800
15
0.7
40
25
1.9
The choice of packaging must also take account of cost. Container size
has considerable influence on the economics of packaging, as does the filling
operation. Higher packaging material costs can be absorbed by more economical filling costs.
(a) Water-soluble films. A special type of packaging suitable for
agrochemical formulations, such as wettable powders (also gels and solvent
based liquids) is the water-soluble bag. Typically made of polyvinyl alcohol
(PVAL), a variety of grades are available to combine optimum product
compatibility with rapid dissolution in cold water.
These packages do not protect the formulation in the usual sense, as the
film itself requires protection from moisture or rain. They protect the
operator applying the product by preventing dermal contact or inhalation
and contain premeasured doses, leaving outer packages clean.
The polyvinyl alcohol material dissolves to become part of the spray
liquid. Sometimes the physical properties of the spray liquid may be altered
and need to be checked. An industry test method for determination of the
rate of dissolution in water has been published by CIPAC as MT 176. The
method was designed to evaluate the dissolution of seams and it can be
included in appropriate FAO specifications for water-dispersible and
water-soluble powders and granules.
The recommended film thickness is 0.040mm. Films selected should be
free from pinholes. The solubility of standard grades of PVAL is reduced if
coapplied with boric acid and borax micronutrients.
Care has to be taken with the storage of film (or prefabricated bags)
prior to packing a product. The instructions of the supplier should be
followed.
Water-soluble bags may be designed to contain between a few grams of
a formulation and approximately 25 kg. They must be printed with watersoluble or water-dispersible inks for identification purposes. A suitable
outer bag of polyethylene film or paper-polyethylene-aluminium foil laminate is necessary to protect the water-soluble film.
9.7.2 Selection of packaging materials for liquid formulations
Liquid agrochemicals nearly always consist of an active ingredient and a
solvent system, which may include water. A surfactant system is usually
present where the preparation is not water miscible, and dilution in water is
required. All formulation components can influence the packaging choice.
Therefore compatibility studies have to be performed in order to prove the
suitability of a package (preferably in sales packs). It is essential to evaluate
the proposed closure for its suitability.
The most common types of liquid formulations are
• emulsifiable concentrates (EC), soluble liquids (SL) and ultra-low volume (ULV): the presence of hydrocarbon solvents may adversely affect
compatibility with certain plastics such as HDPE;
• suspension concentrates (SC) and emulsions in water (EW): usually
HDPE compatible.
The most common packaging materials used for liquid agrochemicals are
plastics and metal (aluminium, tinplate or mild steel), or combination containers with removable plastic liners. Some glass is still present in some
markets but its use is diminishing.
9.13 Plastics
Blow-moulded containers of high-density polyethylene (HDPE) offer a
wide flexibility in design and construction, and good moisture barrier properties, but poor resistance to hydrocarbon solvents.
An improvement in chemical compatibility with solvent-based liquids
can be obtained by fluorination. As an in-line process, the treatment is
carried out during the blow moulding of the container. The alternative is to
apply the fluorine gas in a vacuum chamber after blow moulding, resulting
in a treatment of the internal and external surface of the containers. Different levels of treatment are available and it is therefore important to specify
the required level. The barrier to non-polar hydrocarbon solvents is created
by the formation of polar C—F bonds in the non-polar polyethylene surface. Fluorinated HDPE is in principle available in any size, e.g. 10001 IBCs
(intermediate bulk containers).
Other possibilities are offered by coextruded, multilayer plastic containers, which are available up to 101 capacity. Here, plastics with different
properties can be combined to produce multilayer packages, ideally 'tailored' to suit the product requirements. A typical construction of a 11 bottle
is HDPE with a minimum layer thickness of 0.7mm, a bonding agent of
minimum thickness 0.010mm and an internal layer of EVOH (ethyl vinyl
alcohol) or PA of minimum thickness 0.020mm. Reground material from
the manufacturing process can be blended with virgin HDPE and used as
a fourth layer between the external PE and the bonding agent, without
increasing the container weight.
Biaxially oriented polyester (PET) is available up to 51 in capacity and
widely used for packaging of solvent and aqueous-based liquid products
(Figure 9.1). The transparency of PET offers advantages in relation to
rinsing, and the quantity of plastic requiring disposal after use for a given
packed volume is less than for other rigid plastics. However, its water
vapour transmission rate is higher than that of HDPE. This can adversely
affect compatibility with certain moisture sensitive agrochemicals. PET is
also not compatible with highly alkaline environments or with certain very
polar solvents.
Combination packs of flexible plastic film liners in corrugated cases
(bag in box) may be suitable for certain agrochemical markets, providing
Figure 9.1 Examples of PET containers in the range 0.5-51. (Courtesy of Dow AgroSciences.)
they meet performance requirements. Their advantage is disposal of
the contaminated lightweight liner separately from the clean outer
container.
9.1.4 Metal
Metal containers, made from aluminium or tinplate or steel with or without
internal lacquer linings, are well established.
Aluminium has the advantage that it can be converted into one- or twopiece containers, if a suitable alloy is used. Although its purity should be a
minimum of 99.5% (as per DIN 1712.3 or other international standards), an
internal protective lining is required for many products.
Tinplate is a low-carbon mild-steel sheet coated on both surfaces with tin
either by dipping or electrodeposition. The grade of tin, weight/thickness
ratio of the tin coating, passivation (treatment to stop further chemical
reaction), performance specification, formability and grain direction should
be borne in mind when specifying tinplate.
The tinplate container is built from three pieces (body, top and base)
which are joined together by seaming, soldering, glueing, welding or a
combination of any of these techniques. A benefit with rectangular-shaped
containers is that distribution costs are minimized.
Internal lacquer linings are generally required for tinplate, using a roller
application to achieve a uniform coating. Freedom from pinholes and good
adherence of the lacquer are among the factors which need to be considered. However corrosion, leakage from seams or closures and denting can
cause customer resistance to tinplate. It is also difficult to pass the UN
performance tests with sizes over 300ml. For these reasons the trend has
been to replace tinplate with plastic containers where possible.
Closures for metal packages must have equally good barrier and compatibility properties.
9.1.5 Glass
In spite of its universal product compatibility and availability, glass is not
recommended for commercial packaging for safety reasons as it shatters on
impact. Dimensional tolerances are not well controlled and neck thread
engagement is frequently variable. However, it is accepted that for bottles
below 200ml they are acceptable where alternatives are not immediately
available, providing the closure is leak-free.
9.1.6 Recommended tests to be carried out on the main types of containers
Irrespective of the type of the final container, in addition to regulatory
performance testing, the following tests should always be carried out on
filled packs before and after storage at elevated temperatures, as a minimum requirement (Table 9.2):
• mass loss or gain;
• appearance of the container (including internal surface);
• appearance and functioning of the closure system.
Table 9.2 Recommended tests on final sales packs
Package/component type
Containers
Tinplate
Visual/physical checks
Longer-term
storage
observations
Tin layer (thickness)
Quality of seams
Corrosion
Tinplate with protective lining
Porosity, adhesion
Elasticity
Aluminium
Corrosion
Aluminium with protective
lining
Porosity, adhesion
Elasticity
High-density polyethylene
(HDPE)
Polyethylene terephthalate
(PET)
Deformation/wall thickness
Odour barrier properties
Internal pressure (head space)
Oxygen content
Colour changes
Drop stability
Stress cracks
Coextruded plastics (multilayer)
As for HDPE, additionally
thickness of single layers and
homogeneity/porosity of the
barrier
Closure systems
Caps
Gaskets
Sealing disks
Films
Laminated films/foils
Water-soluble films
Torque
Differences in dimensions
Weight differences
Differences in dimensions
Corrosion
Adhesion of laminates/
delamination
Leaks
Stress cracks
Odour barrier properties
Tightness of seals
Brittleness
Adhesion of laminates/
delamination
Deformation
Corrosion
Porosity
Water solubility
Tear resistance
Total penetration energy (freefalling dart)
Brittleness
Elongation
Spray properties
(with product)
9.7.7 Specifications
Detailed specifications are necessary to ensure the consistent performance
of the complete package. Each of the packaging material components must
be precisely specified on a separate sheet. It is also important to give clear
'packaging instructions' to the filling plant, independent of package specifications, describing how to assemble the package components.
(a) Package specifications. The package specification describes what has
been agreed between the packaging plant and the supplier. It must define
all parameters of raw materials, dimensions and physical properties. Drawings need to be self-explanatory. A typical example showing the basic
specification content for a 11 bottle is described in Table 9.3.
Specifications should be revised from time to time in the light of technical
developments in packaging materials or conversion processes.
9.1.8 Packaging instructions
These list the quantities of individual packaging and label components
required per pallet of product and describe their method of assembly and
standards to be used. They provide the filling and packaging plant with vital
information and are also used for planning and logistics, quality assurance
(in-process and final goods control) and accounting. Packaging instructions
Table 9.3 Specimen package specification
Definition of the item
Nominal volume
Code no.
Description
Raw material
Colour
Print
Total volume
Weight
For further technical details refer to drawing no.
Test programme/AQL procedures
Delivery instruction
Date/signatures
HDPE bottle
1 litre
7123456
Cylindrical bottle, extrusion blow
moulded, neck 50mm
Polymer, grade reference virgin
material
Regrind only from the same process
(closed loop recommended)
Natural transparent
Neutral
1.1 litres
85g ± 3.4g
3353g
03, dated 01.05.1990
Palletized 1.2 X 1.0 X 1.8m
Each layer packed on trays securely
wrapped
Table 9.4 Packaging instructions
Category
Details
Parts list
Code numbers of bottle, closure,
label shipping case, tape, pallet,
shrink film
Torque, type of glue, type and
width of tape
Mean weight, tolerance limits
Numbers and positions of hazard
label, UN coding
Method of application, position
Size of pallet, arrangement of
cases, number of layers per
pallet, means of securing, gross
volume and weight per pallet
Maximum height for stacking
pallets. Annual colour (first in,
first out), identification of pallet
load
Instruction for packaging plant
Weight accuracy
Marking and labels
Batch number, release date
Pallet stacking pattern
Warehousing instructions, annual colour code,
pallet label
also contain warehouse handling information for product distribution. The
structure shown in Table 9.4 is a useful guideline.
9.2 Closures
9.2.7 Prevention of leakage
The primary function of any container is containment of the product until
it is needed for use. With some exceptions, the closure is that part of the
container which is left open to permit filling with product and then closed
for transport and storage. It is finally reopened to dispense the product. In
some designs it may be reclosable to permit subsequent storage of a partused container without risk of spillage. Reclosability is particularly important for liquids if there is any possibility of only partial use of the container
contents in an application. It is essential that the closure remains secure and
resists leakage. Mating surfaces which form the effective seal and which
come into contact with the product must be resistant to it, and not incorporate materials which may react dangerously or lead to softening, weakening
or failure of the closure. Induction heat sealing has become the standard
method for closing plastic containers holding liquids due to its suitability for
use in conjunction with flammable solvents and adaptability for both lowand high-speed filling lines with varying levels of automation.
9.2.2 Tamper evidence
Tamper evidence is a desirable feature of pesticide containers demanded by
many users. It may be divided into two basic types: internal and external.
Inner membranes which are induction heat-sealed to rigid plastic containers for liquids provide internal tamper evidence. This means that screw
caps must be removed to permit visual inspection of the inner membrane to
establish if the package has been tampered with. An additional benefit of
inner membranes is that the container remains closed after removal of the
screw cap, and therefore a natural platform is provided for coupling with
closed transfer systems where these are in use.
Internal tamper evidence is provided in a similar manner on small
tinplate containers where a tinplate neck plug (shive) is fitted so that it
cannot be removed without being damaged.
External tamper evidence may be provided in a variety of ways and a few
examples are described below.
(a) Steel drums. Metal overseals crimped over the traditional screwthreaded bung must be destroyed to permit access to the bung. This type of
overseal may also be used on HDPE drums and aluminium containers with
internal screw-threaded bungs.
Retractable plastic pourspouts are available for steel drums with a ringpull cover which must be destroyed in order to remove the screw cap. Such
spouts also provide internal tamper evidence, as the neck of the spout may
be sealed with a ring-pull plastic membrane.
(b) Fibre drums. Lever locking bands are provided with a loop of wire
which passes through adjacent holes in the band and which is closed with a
motto or logo indicating the origin of the product. The wire must be cut to
open the band.
(c) Cartons. Cartons sealed with external adhesive tape or with adhesive
between overlapping flaps are not reclosable without leaving some evidence of damage caused by any previous opening. Some designs include
perforated tear strips which are automatically tamper evident if used.
(d) Bags and pouches (flexibles). Seams may be sewn, glued or heat
sealed, which make it necessary to tear, cut or otherwise pierce the container material to obtain the contents.
(e) Rigid plastic containers. Various designs of plastic and metal screw
caps are available with break-off rings. The ring may be designed to break
from the cap by rupture of fragile bridges between the cap and ring as the
cap is unscrewed. Alternatively it may have a tear-off band which utilizes
more robust connecting bridges that cannot be ruptured simply by unscrewing the cap. Both types require the container neck to have an interference
feature below the threaded portion which engages the ring or band and
prevents removal of the cap without rupture of the connecting bridges. The
major diameter of the interference feature is greater than the major diameter of the screw thread, and it may be in the form of a smooth ring known
as a bead or a saw-toothed ratchet. The choice between bead and ratchet
may be limited by the material of construction of the container neck and
cap or by the method of rupture required. In the case of tear-off bands, care
is required during design and selection to ensure that users wearing gloves,
which may be wet, will have no difficulty grasping the tab and removing the
band. Similarly, care is needed to ensure that the length of container neck
is sufficient to permit simple break-off rings to fall away from the cap after
rupture of the bridges. It is also necessary to ensure that the ring is retained
by the interference feature whilst the container is inverted for pouring.
Both types of cap should be designed with an external profile providing a
firm grip, bearing in mind the level of physical effort required to rupture
connecting bridges.
These methods of tamper evidence may also be used in conjunction with
small aluminium, steel or tinplate containers.
In a particular variant employing metal caps, the cap is delivered to the
filling location without preformed screw threads. These are formed after
application of the cap using a system of rollers which presses the cap wall
into the thread form of the container neck. This produces the roll-on
pilferproof closure (ROPP) when a break-off ring is also present.
It is important during design or selection to assess the ergonomics and
efficacy of tamper evidence in use before and after ageing the containers
with product.
9.2.3 Closure diameter - liquid products
The maximum closure diameter of rigid tight-head containers for liquid
pesticides transported without outer secondary packaging and which are
subject to international transport regulations is 70mm. Closure diameters
of inner packaging transported as combination packaging (e.g. in a corrugated fibreboard outer case) do not normally exceed 70mm for liquids. It is
recognized that it becomes more difficult to prevent leakage as closure
diameters increase above 70mm. The main exception is where a large
diameter is needed on a bi-compartment container to accommodate two
openings within one neck.
Many agrochemical manufacturers have reached a consensus to standardize neck diameters on plastic packaging (single compartment and bicompartment with two necks) in order to help to facilitate good neck
Table 9.5 Main neck diameters for rigid plastic containers
Major (crest) diameter of
screw thread3
(mm)
Bore diameter
of opening3
(mm)
50-55b
42 or 39C
39
28-3Qb
63
50
45
38^
3
0
Nominal values; b depending on source and neck detail;
depending on source. Not in Europe.
designs, better operation of filling lines and the introduction and acceptance
of closed transfer systems. Some diameters are being phased out over a
period. Those expected to remain in long-term use are shown in Table 9.5.
A major effort is being made to maximize the use of 63 mm diameter where
possible. ECPA has issued a standard neck drawing (Figure 9.2) with the
following key dimensions:
Major diameter
Bore diameter
Minimum through bore diameter
63.4mm
54.7mm
50.0mm
9.2.4 Dispensing liquid products from packs designed for pouring
Non-refillable containers for liquid pesticides up to 101 should be capable of
providing smooth pouring without splashing given a reasonable degree of
care, when product is dispensed without the aid of a closed transfer system,
pump or tap. Experimental work has established that necks in the range 4563mm (bores 39-55 mm) give more controlled pouring and less spillage
from 51 and 101 containers than smaller diameters. It has also been demonstrated that, for a given neck bore and capacity, cylindrical containers
provide a wider arc of smooth pouring than jerricans. Also, the smooth
pouring arc obtainable with a jerrican varies according to the direction of
pouring in relation to its geometry (major axis perpendicular to the direction of pouring is better). Larger containers (e.g. 20-2101) require the use of
dispensing pumps or taps to ensure satisfactory performance.
Special attention should be given to pouring and overall ergonomics
when designing or selecting bi-compartment containers with either one or
two necks. The possibility that neck bore diameters above 55 mm may give
increased spillage should be evaluated. Also, the relationship between position and shape of each compartment and its opening should be considered
together with the effect of differing attitudes of such containers during
pouring.
NECK THREAD
SCALE 1:1
THREAD PROFILE
SCALE 10:1
DETAIL A
SCALE 5:1
Mod
Figure 9.2 ECPA industry standard neck thread.
Drawn
MAW
Date
Figure 9.3 Typical pictograms demonstrating use of cutter.
Mention has been made of the role of inner heat-sealed membranes to
preserve the closed system concept. Where closed transfer systems are not
used it is necessary to cut open the inner membrane by more manually
intensive methods. It is common practice, particularly in Europe, to include
an external cutting feature (e.g. a cutting thorn) on the screw cap. A
pictogram illustrating the use of the cutter feature is often provided on the
external surface of inner membranes (Figure 9.3).
After removing the cap, it is inverted and the cutter feature rotated
against the membrane to first pierce and second cut the membrane away
from the neck circumference. It is important to limit the rotation of the cap
to approximately 150-270°, for example a single turn of the wrist, since a
complete 360° rotation may result in loss of the membrane inside the
container. After achieving the desired degree of cutting, a gloved finger
may be used to press the membrane carefully against the internal neck wall.
Smooth pouring is achieved provided care is taken with respect to the
attitude of pouring in relation to the position of the membrane attached to
the neck, and the angle and rate of pouring. This should ensure that liquid
does not catch the membrane, which could result in partial obstruction
of the neck opening. The need for separate handling and disposal of a
detached membrane is avoided by this procedure.
Various designs of cutter feature are available. Cutting efficiency should
be evaluated to ensure reliability using the appropriate container before
and after prolonged storage with the product.
9.3 Labelling
The product label is a prime source of technical information concerning the
product, its areas of use, methods and timing of application, and safety
precautions to be observed. It may also carry the formal authorization
number issued by a national registration authority, indicating that the product has been approved for sale in a particular country and that the label text
has also been formally approved. Advice on writing label text and recommended sizes of font is available in a GIFAP Monograph and the basic
responsibilities of companies are covered in the FAO Code of Conduct and
the FAO monograph on good labelling practice. The use of appropriate
GIFAP pictograms should also be considered.
In order to fulfil its function, the label must remain firmly affixed and
clearly legible throughout the container's life until its final disposal, particularly if the label is exposed on a continuous daily basis to direct sunlight
during this period, which could cause inks to fade. It is essential that
appropriate adhesives are selected for good bonding. Both pressuresensitive and aqueous-based adhesives are in common use.
Leaflet labels which may contain several pages of extended text are
available from certain specialized suppliers. Leaflet labels are useful where
a product has several uses and also in bilingual countries such as Belgium,
Canada and South Africa.
9.4 Shelf life
Limited persistence in the environment is a desirable characteristic of many
pesticides. However, this beneficial characteristic can cause products to
undergo chemical and physical changes. The rate at which this happens
depends very much on the nature of the active ingredient(s), the formulation, the packaging and, notably, the storage conditions. The product
remains fit for use as long as these changes have no adverse effects
on application and biological performance, or on operator, consumer and
environmental safety.
The period during which the product remains fit for use is known as the
'shelf life'. This should be established as at least 2 years. Shelf life is
determined by intense storage stability testing under a variety of short- and
long-term storage regimes. These regimes are selected having due regard to
the geographical regions and climates to which the product and packaging
will be exposed during transport, intermediate warehousing and storage by
the final user.
Guidelines on the recommended studies and storage regimes to be
undertaken in order to determine shelf life are given in GIFAP Monograph
No. 17. Procedures for good storage practice which can give a significant
benefit in preserving both the product and container are described in
GIFAP Monograph No. 10. This monograph includes advice on dealing
with a product which has exceeded its shelf life or been stored under
unfavourable conditions.
Some national registration authorities and the Commission of the
European Communities require that applications for product registration
include information demonstrating the shelf life of the product. Applicants
for product registration may also be required to obtain approval for the
type of packaging proposed and demonstrate that the packaging is resistant
to its contents.
9.5 Pack design with regard to easy rinsing and disposal
The majority of pesticide products are designed for mixing in water prior to
application to the crop or target species. There are economic and environmental benefits to be gained from effective rinsing of containers of these
products prior to disposal. However, these benefits are only realized in full
when water used for rinsing is transferred into the sprayer and delivered to
the target. Effectively rinsed containers may be classified as non-hazardous
(subject to local regulations) and are therefore preferred for subsequent
storage prior to final disposal.
It is important when designing or selecting a container that due consideration is given to avoiding design features, such as recesses or an
integral hollow handle, which are liable to impede easy effective rinsing.
Steel and plastic drums should include optimum draining features in their
design.
As a general rule it may be assumed that rinsing efficiency will decrease
with increasing viscosity of liquid products. This in turn increases the potential contribution of container design and materials of construction to efficient rinsing.
Primary packaging for solids, including flexible materials, should be
capable of being rinsed with pressurized water without disintegrating.
An exception to this is when water-soluble film is a component of the
primary package.
The three main rinsing methods recommended are described in section
9.8.
9.6 Types of secondary packaging
The most usual form is corrugated fibreboard cases, made from boards
consisting of two or more flat parallel sheets of paper liners separated by a
fluted or corrugated sheet. They are held together with adhesive applied to
the crest of the flutes, which have considerable strength. The air spaces
within the board help to cushion the contents of cases during an impact.
The types of pulp used to manufacture the liners are:
• Pure kraft;
• Multi-ply test or jute (which has one or more plies of recycled fibre,
bonded to a kraft facing);
• Chip or straw (made from low-quality waste paper with short fibres and
locally indigenous materials).
The material base weight is defined as mass per unit area (gsm). The fluting
or middle ply is corrugated during the conversion process and consists of
kraft, semi-chemical (65% wood pulp plus waste paper) or straw (25-75%
straw pulp plus waste pulp). The wave-like shape of the flute form can be
varied in height and width. The four standard variations are designated as
A, B, C or E flute. A comparison of board properties when using the
different flute forms is shown in Table 9.6.
Specific flute profiles exhibit individual performance characteristics.
Flute forms separated by a liner can be combined to form double-wall
board or even triple-wall for heavy-duty cases, combining the advantages of
each flute form.
Case design, construction and sealing methods used for closing the filled
pack all contribute to its final performance. Internal fitments such as sleeves
or dividers improve the strength considerably, but care should be exercised
to ensure that cases are not overspecified. Design and construction options
are illustrated in the International Fibreboard Case Code.
The main disadvantage of corrugated fibreboard is its loss of rigidity
when wet or stored in high humidity conditions. Various treatment processes and barrier layers are available to minimize this effect. The effectiveness of materials to resist water is measured by the Cobb absorbency test.
The compression strength of cases should be measured and simulated stacking tests carried out, particularly where packed products have little strength
of their own, to ensure the required performance qualities can be met. Flaps
are sealed with adhesive and/or plastic pressure-sensitive tape.
Ensuring that cases do not overhang the edge of pallets prevents a loss
of between 25 and 40% in stacking strength. Software is available for
optimizing pallet stacking patterns using a personal computer.
Table 9.6 Comparison of board properties with different flute
forms
Flute form
A
B
C
E
Flat crush
resistance
Stiffness
Cushioning
Machinability
Print quality
*
***
**
****
****
****
*
*
**
**
***
***
***
***
**
**
*
*
****
****
Key: **** best; *** intermediate; ** acceptable; * worst.
9.6.1 Unit cartons
Unit cartons are occasionally used within outer cases to collate primary
packs together to form a sales unit. They consist of single-thickness cartonboard or E-flute fibreboard.
9.6.2 Combination with primary pack
Each of the secondary pack components described above has to combine
with the primary pack to give the level of performance required to comply
with local or international standards related to the packaging of hazardous
goods, established by agencies such as United Nations.
9.6.3 Methods for protection of unit loads
Further strength and protection for complete pallet loads can be provided
where transport and storage conditions are particularly severe by the use of
corner posts, cages, overcovers or interleaves made from plastic, wood,
fibreboard or metal. Load security and stability can be improved by film
stretch wrapping or tensile strapping around the palletized goods.
9.7 United Nations performance tests
Most national and international transport legislation is now based on the
Recommendations of the Committee of Experts on the Transport of Dangerous Goods published by the United Nations. Packages must pass the relevant performance tests to obtain a United Nations certificate when the
contents they are intended to carry are classified as hazardous. The performance tests are a drop test, a leakproof test, an internal pressure (hydraulic) test and a stacking test as summarized in Table 9.7.
The procedures and level of severity for these tests depend on whether
the product is a solid or a liquid, on its density at 2O0C and vapour pressure
at 50 or 550C, on the design and construction of the package and, finally, on
the degree of hazard to which the product has been assigned.
Combination packages (primary packs collated in a secondary or outer
pack) are only subjected to the drop and stacking tests.
The detailed performance criteria and hazard classifications may differ
between the various transport authorities. For example, the United States
Department of Transport specifies a vibration test in addition to those given
above. The authorities in New Zealand will only grant certificates for
combination packs when the inner packages have already passed the requirements for primary packages shipped without outer packaging (solo
requirements).
Table 9.7 UN package performance tests
Test
Drop
Leakproofnessb
Internal pressure15
(hydraulic)
Stacking
Applicable to
All packs: drop height 0.8, 1.2 or 1.8 ma
Liquids only: test pressure 20 or 3OkPa for 5min
Liquids in metal, plastic and composite containers: test
pressure 100 kPa min for 30minc
All packs except bags and sacks
Minimum stacking load: equivalent to 3 m height of stackd
a
Drop height to be increased pro rata for relative densities above 1.2. Temperature of plastic
drums and jerricans, composite packagings (plastic material) and combination packaging with
plastics inner packagings, other than plastic bags for solids or articles, to be reduced to -180C
or lower prior to the drop test.
b
Not required for combination packages.
0
Higher test pressures may be needed for some products. Test duration of 5 min required for
metal packaging and composite packaging (glass, porcelain and stoneware).
d
Plastic drums and jerricans and composite packaging (plastics receptacle with outer plastics
drum or box) to be maintained under the load at not less than 4O0C for 28 days. Other packages
to be tested for 24 h: temperature not specified.
NB Every packaging intended to contain liquids (but excluding inner packaging of combination packaging) should successfully undergo a suitable leakproofness test, and be capable of
meeting the appropriate test level indicated above:
1. before it is first used for transport;
2. after remanufacturing or reconditioning, before it is reused for transport.
Proof of the compatibility of plastics packaging materials with the proposed contents must also be established in accordance with the regulations,
but again the detailed requirements may vary between authorities.
UN marks are displayed on packages which have passed the UN performance tests and for which a UN certificate has been issued. The authorized mark is provided with the certificate. Its use on a package containing
hazardous products means that the package must be representative of the
design type tested. Use of a UN mark also places an obligation on the
person consigning goods for transport to abide by the terms of the full test
documentation attached to the certificate.
The number of countries with the ability to carry out the UN protocols
at accredited test stations with UN certificates issued under Competent
Authority approvals is increasing annually. This is essential to enable all
UN signatory countries to meet the legal requirement for UN certification
of dangerous goods, particularly for export or shipment to neighbouring
islands.
For parcel shipments via groupage carriers, particularly in the USA,
certification by the International Safe Transit Association (ISTA) may also
be required. Unlike UN testing, ISTA testing is sequential in nature, starting with a vibration test followed by a drop test and completed with an
optional stacking test on the same test specimen. Detailed test methods may
be selected from prescribed alternatives for each of these parameters.
9.8 Rinsing methods
The great majority of agrochemicals are designed for dilution in water at
the point of use, and effective on-farm rinsing of these products is good
agricultural practice and one of the cornerstones of all management strategies for single-trip containers. The three main methods of rinsing, manual,
integrated pressure and pressure, are described below.
Manual rinsing is usually known as 'triple rinsing' to indicate that the
operation should be carried out three times with three portions of clean
water (each portion 10-25% of container volume). The procedure consists
of adding clean water, refitting the closure and shaking or rolling the container to rinse all internal surfaces. After emptying and two repetitions
of this procedure, the final rinsate is drained for 30s before refitting the
closure.
The integrated-pressure method requires purpose-built equipment attached to or adjacent to a crop sprayer which diverts clean water at 3-5 bar
pressure into used containers inverted over a rinsing nozzle and then collects the rinsate for piping into the spray tank (Figure 9.4). Although
suitable for rinsing both rigid and flexible containers which may have contained solids or liquids, it is a prerequisite that the minimum opening (bore)
of the container neck is not less than 39mm diameter. This is essential to
permit insertion of the rinsing nozzle which may be up to 35 mm in diameter. Closed transfer systems normally include a facility for integrated
pressure rinsing of non-refillable containers as a standard feature. Integrated rinsing is the only method which guarantees that rinsate is delivered
to the crop or target species. It was developed initially in the Netherlands,
where it has been a legal requirement to install the necessary equipment on
sprayers since 1990. As a result of the Dutch initiative, sprayers throughout
Europe have been equipped for integrated rinsing. Some countries have
issued standards covering the construction and/or performance of such
equipment.
In the pressure method, pressurized water is delivered via a hosepipe
through the container neck, or alternatively a device is fitted to the
hosepipe which is capable of penetrating the base of containers to create a
'straight-through' method of rinsing.
Each of these techniques requires the use of clean water (not diluted
working spray mixtures) to achieve effective rinsing. However, some modern sprayers have the facility to divert spray mixture into the container for
an initial rinse before switching to a secondary rinse using clean water.
Further details have been published by ECPA and other trade associations.
No attempt should be made to use water for rinsing where the product is
not designed for mixing with water, such as dustable powders (DP) and
ultra-low volume liquids (UL). Where the product is diluted in organic
solvent prior to application, for example oil-miscible liquids (OL or OF)
Figure 9.4 Integrated rinsing of 5-1 HDPE container with isolated handle. (Courtesy of Dow
AgroSciences.)
and oil-dispersible powders (OP), it may be possible to rinse containers
with the diluting solvent. However, this should not be done without a prior
and detailed assessment of hazards which may arise. In particular, the
electrical safety of any equipment, including any static hazards, must be
thoroughly reviewed. If the solvent cannot be safely vented from the container or presents a greater hazard than the pesticide being used, then
rinsing should be avoided.
Where containers have not been rinsed or there is any doubt over the
efficacy of rinsing (e.g. due to the presence of significant visible residues),
such containers should be stored separately from well-rinsed containers
prior to disposal. It may be necessary to arrange a different method of
disposal for such containers, taking account of local laws or regulations and
local disposal facilities if any. Where specific instructions are provided on
the label, these should of course be followed.
9.9 Closed transfer systems
Closed transfer systems have been prescribed by law for specific classes of
agrochemicals in California since 1973. More recently, general safety legislation in the United Kingdom encompassing all classes of agrochemicals
(and also general industrial chemicals) has encouraged sprayer manufacturers and others to consider engineering controls as a first line of personal
protection ahead of personal protective equipment (PPE). As a result a
number of economically priced closed and enclosed transfer systems with
provision for integrated rinsing have become available which offer a choice
of technical attributes. Chemlok and Multi-Tran® are examples of the
former type, whereas CTR is an example of the latter (Figures 9.5 and 9.6).
Figure 9.5 Chemlok closed transfer system, manufactured under licence by Fluid Systems
(UK) Limited. (Courtesy of Fluid Systems.)
Figure 9.6 CTR Chemical Transfer Rinse from Martin Lishman with 1-1 PET container,
((a) Courtesy of Silsoe Research Institute, (b) Courtesy of Martin Lishman.)
For some users loading large sprayers, a benefit which may not be
obvious is a significant saving of a rather precious commodity: time. Appropriate PPE should still be worn as specified on the agrochemical label (or
by, for example, an assessment of the working situation which is mandatory
in the UK). The reduced level of dependency on PPE should prolong the
service life of such equipment and may offer further savings in time. However, there are no circumstances in which protection for eyes, hands and
feet can be safely overlooked during loading and mixing operations.
9.10 Collection of containers after use
Although disposal of used containers on the farm or via municipal landfill
remains as a fact of life in many regions of the world, in the last 10 years a
credible and growing alternative has been created: collection followed by
either energy recovery or material recycling. Pioneered in North America,
agrochemical manufacturers have collaborated on an unprecedented scale
with each other and with dealers and waste contractors to create not-forprofit organizations which administer the entire collection and recovery
process and ensure that safety standards and controls are maintained. In the
USA many state governments also take an active role in the running of
collection sites, inspection of containers and provision of shredding equipment. In the State of Illinois, for example, there were 82 sites in 1996 of
which four are permanent; 18 of the temporary sites were operated by the
Department of Agriculture.
Typical schemes request farmers to bring rinsed containers on a voluntary basis to appointed collection sites for inspection to ensure visible
product residues are absent (Figure 9.7). Temporary sites may be open at a
given location for a few days or perhaps only 1 day, so a successful
programme requires farmers to schedule container disposal above other
tasks when the nearest site is open. Once accepted, ownership is transferred
and plastic containers are shredded to reduce bulk prior to onward
shipment.
In Germany there is a second size-reduction step at a central location, as
the collected plastic is supplied to the steel industry for use as a reducing
agent, replacing primary hydrocarbons in blastfurnace operations. Since
most of the collected plastic is used for its reactivity properties rather than
its energy value, the programme meets the legal definition of material
recycling in Germany instead of energy recovery.
In Belgium all types of packaging waste arising in agriculture, including
2001 steel drums, corrugated board and containers which cannot be rinsed,
are taken to a waste-to-electricity facility which is uniquely operated as a
joint venture between one of the regional governments and 33 enterprises
drawn mainly from the chemical, metal and automobile industries. The
Figure 9.7 Mobile plastic shredder, Illinois, USA. (Courtesy of Dow AgroSciences.)
facility has joined the Responsible Care* initiative operated by the Belgian
Federation of Chemical Producers. The Belgian Government has set the
agrochemical industry a collection target of 80% in 1997, up from 60% in
the previous year. This is well above the recovery target of 50-65% contained in the European Union Directive on packaging and packaging waste
(94/62/EC). In 1996 Canada was the leading country, with a recovery rate
for plastic of nearly 70%.
Although recovered plastic in the USA is accepted as a replacement fuel
in cement kilns due to its high calorific value, as well as in some municipal
waste-to-energy plants, considerable work has taken place in Canada and
the USA to identify alternative applications for the material. Various proposals have been extensively evaluated over the past few years to ensure
both operator safety and the absence of adverse environmental effects
before endorsement and large-scale adoption of specific options. Fence
posts and pallets are now available on a semi-commercial basis for use in
agriculture and related industries. Tiles for use in agricultural field drainage
and car parking are nearing approval.
Collection programmes are also at various stages of evolution in parts of
South America, the Pacific region and elsewhere in Europe.
* Registered service mark of Chemical Manufacturers Association, USA.
9.11 Summary of key design criteria
GIFAP issued design criteria for single-trip primary and secondary (outer)
packaging in 1994. These criteria will assist those involved in the design,
selection or use of packaging for agrochemicals to improve ergonomics and
safety features whilst reducing the environmental burden of container
manufacturing processes and distribution. In 1996 ECPA issued a series of
guidance notes under the overall title of 'Container Management Strategy',
which should be consulted by those readers wishing to pursue the subject
matter in more detail.
9.12 Returnable packaging systems
During the last few years many types of returnable packaging systems for
liquid and granular products have been introduced. North America has
again played a leading role in this development with Australia and parts of
Europe and South America also being involved. Although the same principles apply, the sector is divided into 'mini-bulk' (intermediate bulk in
European parlance) covering 212-30001 (c. 56-750 US gallons) and 'smallvolume returnable' (SVR) below 2121. The dividing line arises from an
EPA ruling that only registration holders or third parties under contract to
registration holders are permitted to refill containers with a capacity of 56
US gallons or less. Given the typical distances between primary manufacturing sites in the USA and the areas of final use, this ruling reduces the
efficiency which might otherwise be obtainable from SVRs. As most but by
no means all agrochemicals are applied in only one season per calendar
year, it is necessary to review specific applications critically and in depth to
ensure that a net benefit is delivered to the customer-supplier partnership.
Detailed considerations applicable to SVRs are outlined below but these
also apply in some degree to mini-bulk systems.
9.12.1 Small-volume returnable containers
SVR containers have been developed as a means of reducing the quantity
of used empty agrochemical packaging for disposal, often into landfill sites.
SVRs are normally fitted with some form of sealed coupling which minimizes dermal contact with the formulation when using such containers.
The US Environmental Protection Agency gives high priority to the use
of SVRs (together with water-soluble packaging when appropriate) in their
hierarchy of environmentally acceptable container classes. SVRs are typically made of stainless steel or plastic materials. They are designed for use
with closed transfer systems, offering high standards of operator protection.
Industry agreements have enabled the introduction of a common agrochemical interface between the container and the spraying system. Other
coupling systems are under consideration.
SVRs work by allowing product to be extracted via a standard coupler,
using a pump, suction or gravity flow system. Formulations are measured or
metered before being discharged into a sprayer or nurse tank. A SVR forms
an ideal reservoir for direct-injection application systems. The system is
protected by tamper-evident seals and one-way valves which restrict access
by the user.
When the container is empty it is returned to the agrochemical manufacturer via a designated distributor for inspection, cleaning and refilling.
9.12.2 SVR design criteria
Small-volume returnable containers for pesticides must be approved under
local regulations. The USA and UK have developed their own guidelines
for SVR design which stipulate that they must meet the following criteria:
• contain the product and prevent loss due to spillage, leakage, permeation
(of plastic) or corrosion (of steel) during handling or storage;
• give physical protection to the product and resist normal external forces
to which the container will be subjected during normal filling, storage,
transport and use;
• preserve the activity of the contents by preventing direct or indirect chemical decomposition and provide protection against climatic
conditions;
• provide a safe and effective means of dispensing and reclosure;
• allow instructions for safe product handling and use to be fixed securely
and protected from deterioration due to weather or product staining;
• provide user safety and convenience during storage, handling and
dispensing.
9.12.3 Stewardship
Refilling of SVRs will be subject to the requirements of local health and
safety/environmental legislation. It will be conducted to agreed standards
for filling agrochemical containers, whether on a manufacturer's or an
authorized contractor's site.
Within the distribution chain, SVR containers can be used for single
dedicated product use, in which case no internal cleaning may be necessary
between filling cycles. When used for a variety of products, rigorous decontamination and relabelling are required. The service history of each SVR
container is documented.
The materials of construction must be chemically compatible with the
contents.
9.12.4 Closures
The closure for a SVR container is tamper evident and eliminates the risk
of accidental contamination of the product. The closure needs to be compatible with existing or future closed transfer systems for pesticide application equipment. Existing designs include the ECPA agreed standard
interface based on a Micro Matic Macrovalve which is detailed below.
9.12.5 Labelling and marking
The product label for a SVR container is similar to that for a non-returnable
equivalent. Additional information covers:
• the method of coupling and emptying;
• returning and refilling;
• rinsing and product substitution.
The label will carry a batch number and date of product release to comply
in all respects with Article 10 of the FAO International Code of Conduct on
the Distribution and Use of Pesticides. Unless detached, labels may survive
several refilling cycles. Many SVRs are labelled with a unique serial number
and are bar coded to facilitate tracking through the supply chain and return
loop.
9.12.6 Handling
The SVR container must be easy to lift and manipulate, even when wet.
Suitable handles or grips will be incorporated where required by the shape
or weight of the container. There must be no sharp edges or projections on
the SVR container or closure.
9.12.7 Disposal
SVR containers which have reached the end of their life or which are no
longer fit for service will be disposed of in accordance with current guidelines. The precise determination of the timing of disposal of steel SVRs is
controlled by the registration holder or its authorized agent operating under a formal contract. A stainless steel container may last 20 years, whereas
the lifespan of a plastics container is restricted to 5 years by law.
9.13 ECPA standard SVR interface*
9.13.1 Container interface/extractor valve
It should have two key way options (Figure 9.8):
• The only interface agreed so far.
Key 3D.
Key 3F.
Figure 9.8 ECPA industry standard SVR Macrovalve keys, manufactured by Micro Matic Inc.
(Courtesy of Micro Matic.)
• For non-pressurizable containers (designated 3D);
• For pressurizable containers (designated 3F).
Note that in Europe ECPA recommends the adoption of the 3F key way as
this permits emptying by pressure or suction. However, the use of pressure
may not be permitted for some hazard categories such as Flammable
Liquids. It is essential to check local regulations and take all necessary
steps to ensure the suitability of specific methods of operation.
The container interface should have the following performance
characteristics:
• the extractor valve must be positively installable and be retained in the
neck of the container so that no leakage occurs;
• it cannot be removed by unscrewing it - removal should only be possible
by using a special tool;
• on removal it will first safely vent any excess pressure from the container;
• the extractor valve must be constructed from materials compatible with
solvents in common use;
• the flange surface must be marked 3D or 3F as appropriate.
9.73.2 Coupler
It must be dimensionally compatible with the extractor valve defined above.
In addition, it should have the following performance characteristics:
• must be robust enough to withstand a drop on to a solid unyielding
surface from 1.2m;
• must allow no leakage during the transfer process;
• must have a pressure relief safety device if used for pressure dispense
(3F);
• must be operable with a gloved hand;
• must be capable of being attached with no more than a quarter turn and
possess a lock-down feature making it impossible to remove without
following the correct disconnection procedure: this feature must also
prevent accidental disconnection by a dropping or tugging action;
• must allow use of either a vacuum, pump or transfer apparatus in accordance with key way specification 3D or 3F, as appropriate;
• must be capable of being fully cleaned and decontaminated;
• must not leak on inversion when connected;
• must be constructed from materials compatible with commonly used
solvents;
• must connect to extraction equipment via a lin (25.4mm) BSP male
thread;
• a pressure inlet to the coupler should be fitted: an M18 female thread
connection when used for pressure dispensing (3F);
• must be marked 3D or 3F.
9.13.3 Extractor valve and coupler combined
This should have the following characteristics:
• should have a one-way valve to prevent access to the container;
• all entry points to be protected by tamper-evident devices;
• must allow flow of a standard material at no less than ;tl/min when a
vacuum of y bar is applied;
• must perform within the criteria of a 'dry-disconnect' mechanism;
• the coupler must connect to extraction equipment via 1 in (25.4mm) BSP
male thread;
• must not permit leakage in the normal closed position.
Alternative couplings which can in principle be used with any SVR are the
Micro Matic Drumvalve, which utilizes a three-pin bayonet coupling in
agrochemical and some other applications, and the Van Leer Closed Dispense System (CDS).
One example of a stainless steel SVR employing a Micro Matic
Macrovalve coupling is the 7.5 USG Voyager* container introduced by
DowElanco in North America. In Europe, The Cyanamid Ecomatic® System consists of a plastic SVR employing the Micro Matic Drumvalve coupling and Vac-Tran® transfer system from Wisdom® Systems (Figure 9.9).
• Trade mark of Dow AgroSciences. ® Registered trade marks of Cyanamid and Wisdom
Agricultural respectively.
Figure 9.9 Vac-Tran® vacuum-powered high-speed closed transfer and volumetric measurement equipment from Wisdom® Systems being connected to an Ecomatic® container from
Cyanamid. (Photograph courtesy of Crops magazine.)
A similar system is being used by AgrEvo under the trade mark Echo.*
Novartis has pioneered a 101 SVR in F-HDPE known as LinkPak.1 This
system employs instead a two-pin bayonet-type interface which couples
directly to the sprayer, usually via the induction bowl cover. Product transfer is by gravity, and metering is achieved using graduated scales on the
container wall.
9.14 Future direction
During the last 15 years there has been a sea change in the packaging
of agrochemicals which is unprecedented in the history of the industry.
Packaging technology is no longer taken for granted but has become an
integral and critical part of product development. The potential consequences across entire businesses of an ill-judged choice are now well
recognized.
Recent legislation has placed additional constraints on the selection of
packaging and the overall cost of servicing the final customer, and this trend
will clearly continue. However, until scientifically valid methods of calculating what is known as the 'life cycle assessment' become available and
accepted, the relative merits of this or that delivery system will continue to
be the subject of intense debate. In the meantime the current volume split
between single-trip and returnable containers is likely to stabilize. Demands for new materials and innovation in design to deliver unique selling
propositions will continue unabated. Conversely there is also a need to
maintain vigilance on the standardization of certain components in order to
minimize the hassle factor at the point of ultimate use.
Consistent with many other human activities, each proposal for change
will be challenged to meet and surpass ever-higher standards of technical,
environmental and financial performance in order to compete in the modern world of global markets.
Glossary of terms and definitions
Definitions of relevant words and phrases appearing in these guidelines are
given as follows:
Active ingredient(s) The biologically active part of the pesticide present in
a formulation.
AQL (acceptable quality level) The maximum proportion of defective
items which can be accepted in a delivery.
* Trade mark of AgrEvo. f Trade mark of Novartis.
Bi-compartment A container divided into two separate fillable chambers.
Carton A container made from paperboard (0.3-1.1 mm) and delivered flat
for erection before filling.
Case A container made from corrugated fibreboard or occasionally wood.
Closed transfer system A system whereby the product pack is connected
directly to the spray equipment and product is metered into the spray tank,
avoiding the need for user contact.
Closure A device which closes an opening in a receptacle.
Coextrusion The process of forming a multilayer container or sheet
material by extruding two or more layers simultaneously through a single
die.
Collation A gathering and fastening together of packages to form a larger
unit.
Combination pack One or more inner packagings secured in an outer
packaging for transport purposes.
Combustion The action or process of burning.
Competent authority The person in a national government's civil service
whose responsibility it is to administer the international modal codes based
on the United Nations Recommendations for the Transport of Dangerous
Goods.
Composite pack An integration of an inner receptacle with an outer packaging, remaining as a single unit for filling, storage, transportation and
emptying.
Compression strength The maximum load (static or dynamic) carried by a
case at a standard temperature and relative humidity before collapsing.
Corrugated fibreboard One or more sheets of fluted paper adhering to flatfacing plies.
Dangerous goods Articles or substances which are capable of significant
risk to health, safety or property.
Distribution The process by which pesticides are supplied through trade
channels in local or international markets.
Environment Surroundings, including water, air and soil and their interrelationship, and all relationships between them and living organisms.
Flammables Substances which give off flammable vapour at temperatures
of up to 610C (closed-cup test).
Formulation The combination of various ingredients designed to render
the product useful and effective for the purpose claimed; the form of the
pesticide as purchased by users.
gsm g/m2.
Hazard A function of effect (toxic or other) and exposure (i.e. hazard
equals effect times exposure), and as such demonstrates a potential for risk
rather than a actual risk.
IBC Intermediate bulk container. The term includes capacities of 25030001. The construction of rigid IBCs normally includes a fixed pallet base
or equivalent feature to permit mechanical handling.
Label The written, printed or graphic matter on, or attached to, the pesticide; or the immediate container thereof and the outside container or
wrapper of the retail package of the pesticide.
Packaging The primary container together with the secondary protective
wrapping(s) used to carry pesticide products via wholesale or retail distribution to users.
Pallet A platform of wood, metal or plastic onto which containers are
stacked in a regular pattern to form a unit load. This platform allows
mechanical handling equipment to be used.
Permeation The process of diffusion or migration of odours, vapours, gases
or liquids through the material of construction of plastic containers, films or
laminates.
Personal protective equipment (PPE) Any clothing, materials or devices
designed to protect operators from pesticides when they are handled or
applied.
Pesticide Any substance or mixture of substances intended for preventing,
destroying or controlling any pest, including vectors of human or animal
disease, unwanted species of plants or animals harming or interfering with
food, agricultural commodities or wood; substance(s) administered to animals for the control of insects, arachnids or other pests on or in their bodies.
The term includes plant growth regulators, defoliants, desiccants, fruit thinning or sustaining agents, and substances to protect crops from deterioration during storage and transport.
Pesticide legislation Any laws or regulations introduced to regulate the
manufacture, marketing, storage, labelling, packaging and use of pesticides
in their qualitative, quantitative and environmental aspects.
Pictogram A symbol which conveys a message without the use of words.
Poison A substance that can cause disturbance of structure or function,
leading to injury or death when absorbed in relatively small amounts by
humans, plants or animals.
Primary pack The packaging which comes into direct contact with the
formulation. In the case of water-soluble films, some registration authorities consider this primary pack material is part of the formulation and the
overpack becomes the primary one.
Product The pesticide in the form in which it is packaged and sold; it
usually contains an active ingredient plus adjuvants and may require dilution prior to use.
Recovery A process whereby destruction or landfill of used packaging is
avoided and value is recovered. Recovery of calorific value is one example.
Recycling A process whereby pesticide packaging material, following rinsing and cleaning, is reused for other acceptable uses.
Registration The process whereby the responsible national government
authority approves the sale and use of a pesticide following the evaluation
of comprehensive scientific data demonstrating that the product is effective
for the purposes intended and not unduly hazardous to human or animal
health or the environment.
Repackaging The transfer of pesticide from any commercial package into
any other, usually smaller, container for subsequent sale.
Residue Any specified substances in food, agricultural commodities or
animal feed resulting from the use of a pesticide. The term includes any
derivatives of a pesticide, such as conversion products, metabolites, reaction products, and impurities considered to be of toxicological significance.
The term 'pesticide residue' includes residues from unknown or unavoidable sources (e.g. environmental) as well as known uses of the chemical.
Rinsing Decontamination of the inner surfaces of an empty, used package
by application of water or appropriate solvents.
Risk A quantitative or qualitative measure of hazard. The likelihood or
probability of a hazard or harm actually occurring.
Shelf life The period of time during which the chemical and physical properties of a pesticide remain sufficiently unchanged as to maintain its biological activity and application properties at the required level.
SVR (Small-volume returnables/refillables) Containers less than 56 USG
in capacity, designed to be filled, emptied, returned and refilled many times.
Tamper evidence A device to indicate that a pack has been opened or
interfered with in an unauthorized manner.
Toxicity A physiological or biological property which determines the capacity of a chemical to do harm or produce injury to a living organism other
than by mechanical means. It is an intrinsic property of a substance (i.e. the
compound is toxic at a given concentration).
Ullage The space in a filled container above the product.
Wad (liner) The disc of material(s) inside a closure forming a seal.
Water-soluble film A flexible sheet of material which dissolves on contact
with cold water. It can be heat sealed to form a bag or pouch. The most
commonly used water-soluble polymer is partially hydrolysed polyvinyl
alcohol (PVAL).
FAO
CIPAC
GIFAP
Food and Agriculture Organisation of the United Nations
Collaborative International Pesticides Analytical Council Ltd
Groupement International des Associations Nationales de
Fabricants de Produits Agrochimiques. Renamed as GCPF:
Global Crop Protection Federation
ACPA
American Crop Protection Association
CPI
Crop Protection Institute (Canada)
ECPA
European Crop Protection Association
LACPA
Latin American Crop Protection Association
UNIDO
United Nations Industrial Development Organisation
IMO
International Maritime Organisation
GESAMP Joint Group of Experts on the Scientific Aspects of Marine
Pollution
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10 Application techniques for agrochemicals
G. A. MATTHEWS
The majority of pesticide formulations are diluted in water and applied
under pressure through hydraulic nozzles, while some specialized formulations are used with a petrochemical diluent, undiluted as ultra-low volume
sprays, or dry as granule or dust treatments. In this chapter the different
types of nozzles and the portable, tractor-drawn and aerial equipment are
described, followed by information on alternative methods of application.
More detailed description of application techniques is given by Matthews
(1992). A recent trend in the developed countries has been the health and
safety legislation leading towards linking packaging of pesticides, described
in the previous chapter, with the application equipment to provide a closed
transfer system minimizing operator exposure. With the trend towards
adoption of integrated pest management (IPM) to minimize the use of
pesticides, more accurate and timely application is of increasing importance
(van Emden and Peakall, 1996). In particular, training is needed to ensure
better choice of equipment, especially the nozzles, and calibration to ensure
the correct dosage is applied.
10.1 Hydraulic nozzles
The key part of the atomization of liquid sprays into droplets is the nozzle.
Liquid passing through a small orifice in the nozzle tip forms a sheet, which
subsequently breaks into droplets. The process of break-up includes rim
disintegration where droplets are thrown from the edge of the sheet, but
most droplets are formed by perforated sheet disintegration. An increasing
number of holes develop in the sheet, separated by thin ligaments of liquid
that are unstable. These ligaments break up into droplets and smaller
ligaments, which ultimately produce smaller satellite droplets. In some
cases under turbulent conditions, wavy sheet disintegration occurs where
sections of the sheet may break away. The break-up of the sheet is also
influenced by the physical properties of the formulation, including dynamic
surface tension and viscosity of the liquid. If the sheet disintegrates closer to
the nozzle, larger droplets are formed, whereas if the sheet remains coherent and stretches to form a very thin film before break-up, smaller droplets
are produced (Butler Ellis etal., 1997; Figure 10.1). Irrespective of the mode
of break-up, hydraulic nozzles produce droplets of a wide range of sizes.
Figure 10.1 Spray from 110 degree 04 nozzle hydraulic nozzle to show effect of pressure and
addition of certain surfactants, (a) Water sprayed at 1 bar pressure; (b) as (a) at 3 bar pressure;
(c) water plus 0.5% LI-700 at lbar pressure; (d) as (c) at 3 bar pressure; (e) water plus 0.5%
Ethokem at 1 bar pressure; (f) as (e) at 3 bar pressure. (Photographs supplied by P. Miller,
Silsoe Research Institute.)
Figure 10.1 Continued
Figure 10.1 Continued
The subsequent trajectory of the droplets will be influenced not only by
their size, but also by the air flow generated by the spray and the passage of
the sprayer, as well as any natural air movement. Larger droplets with a
high terminal velocity will be influenced predominently by gravity and fall
more or less vertically onto horizontal surfaces; in contrast the smaller
droplets, generally regarded as those below 100 |im in diameter, will be
winnowed from the spray and become airborne immediately. Such droplets
are effectively collected on thin vertical surfaces, such as some leaves and
stems. Spiders' webs are also efficient collectors of small droplets (Samu
et al., 1992). Downwind dispersion of these droplets beyond the treated
field, referred to as spray drift, can cause unacceptable effects on non-target
organisms elsewhere in the environment (Cooke, 1993).
The extent to which such droplets move downwind will be affected by the
height of the nozzle above the soil or crop, the wind velocity and turbulence, and the filtering effect of the crop or other vegetation at the field
edge. A wind speed of 2-5 m/s is preferred to improve impaction of droplets
on vegetation and reduce the volume of spray remaining airborne. Drift has
been most noticeable from ground sprayers, when hot convective air movement lifts the smallest droplets away from a crop, a process exacerbated by
the evaporation of the water carrier so that droplets decrease in size during
transport. After a spray, movement of vapour from deposits on foliage can
also occur (Elliott and Wilson, 1983). Aerial spraying is considered to cause
more drift because of the greater release of sprays and turbulence created
in the wake of the aircraft increasing the transit time between the nozzle
and the crop. In consequence in the USA, a 'Spray Drift Task Force' has
been examining droplet spectra from different nozzles and types of formulation used in aerial sprays (Hewitt et a/., 1994). Orchard spraying where
sprays are directed upwards can also increase the risk of drift. Regulatory
authorities now demand 'buffer' or 'no-spray' zones downwind of a treated
area for some pesticides to minimize adverse effects on the environment.
Ideally, sprays are applied when a wind is blowing away from a sensitive
area. The width of the barrier needed will depend on many factors, and is
generally much wider for aerial treatments. On some ground field-crop
sprayers a downward directional air flow is imposed to project droplets
more effectively into a crop canopy and reduce drift (Taylor and Andersen,
1997). Similarly some growers use tunnel sprayers to protect spray from the
wind while treating tree crops (Matthews et al., 1992).
The extent of drift is also affected by the droplet spectrum, especially the
proportion of droplets smaller than lOOjLim diameter. A spray classification
system was developed, based on the spectrum of selected reference nozzles
(Doble et al., 1985; Southcombe et al., 1997) measured by equipment using
a laser-light diffraction technique, phase Doppler or imaging equipment
(Young, 1991; Parkin, 1993). Stating specific droplet sizes is avoided by
referring to the spectrum measured for the reference nozzles, as the actual
Table 10.1 Reference nozzles used to categorize spray quality
Nozzle3
Spray quality boundary5
Fl 10/0.48/4.5
F110/1.2/3
F110/1.96/2
F80/2.92/2.5
Very Fine/Fine
Fine/Medium
Medium/Coarse
Coarse/Very Coarse
a
See text for explanation of the nozzle code.
Figure 10.1 shows the spectra obtained for these reference
nozzles.
b
data will vary between each type of measuring instrument, depending on
the method of sampling the spray and the characteristics of the measuring
technique. The reference nozzles are shown in Table 10.1 and the spray
classification in Figure 10.2. Spray quality will be affected by the pressure,
thus an increase in pressure will produce a finer spray. Most agricultural
Droplet diameter, /zm
VERY COARSE
COARSE
MEDIUM
FINE
VERY FINE
Cumulative % volume
Figure 10.2 Spray quality. (BCPC Spray Classification Scheme, as modified).
sprays on arable crops are applied using a medium spray quality, but where
there is a risk of drift, farmers are advised to use a coarse or very coarse
nozzle. Some spray drift will still occur with a coarse nozzle, but the volume
of spray liable to drift is very much less than with a medium or fine nozzle.
Where there is a selective pesticide or low risk of damage downwind, then
a fine spray may be preferred to improve coverage on foliage. In large areas
of cereal crops it may be possible to use a fine spray initially, but then
change to a coarser spray when close to the field boundary, especially where
tractor equipment is fitted with a turret-type nozzle holder to facilitate
changing to a different nozzle tip. Very fine sprays are normally not recommended for arable crops, although there are situations where they are used
in combination with appropriate less volatile formulations. These very fine
sprays are subdivided into mists and fogs when used in protected cropping
and stores, in relation to the risk of inhalation of extremely small droplets.
Measurement of the droplet spectra of fan types of hydraulic nozzles is
relatively straightforward, but sampling of cone, twin-fluid and rotary atomizers is more complex, so recent research has included measurements of
spray drift under standardized wind tunnel conditions (Miller et al., 1993).
As there is a range of droplet sizes in a spray, the measurements frequently
used to describe sprays are the volume median diameter (VMD) and the
number median diameter (NMD). Other parameters are discussed by
Lefebvre (1989, 1993).
10.1.1 Types of hydraulic nozzle
There is a vast range of different hydraulic nozzles with different outputs,
spray angles and patterns. They can be identified by a code which indicates
the type/spray angle/flow rate (l/min)/pressure (bar) (Table 10.2). An example of a fan nozzle would be F110/1.2/3. These are held in a nozzle body by
a cap which may be a screw or bayonet fitting. Directly upstream of the tip
there should be a filter with a mesh size smaller than the final orifice size to
prevent blockages of the nozzle during spraying. Most agricultural sprayers
will require a 50-mesh filter at the nozzle. The nozzle body should also
incorporate a non-drip valve (Figure 10.3). This is usually a diaphragm type,
but there are now available valves which will control the pressure at the
nozzle as well.
(a) Fan nozzles. These nozzles have a V-shaped slot that intersects with a
hemispherical cavity obtained by drilling a circular orifice from the opposite
side of the nozzle tip. The detailed configuration of the elliptical orifice
produced will determine the angle of the emerging spray sheet, the volume
of spray emitted and the pattern of the spray of a stationary nozzle. Most
nozzles produce a normal distribution across the spray, so that by overlapping adjacent nozzles on a spray boom an even distribution of pesticide is
Table 10.2 Nozzle code
Letter code
D
F
FE
RD
LP
HC
OC
AI
Nozzle type
Deflector
Fan - standard
Even spray fan
Pre-orifice (reduced drift)
Low pressure
Hollow cone
Offset fan
Bubble jet (air inclusion)
Spring
Valve
Liquid flow
Filter
Nozzle
Figure 10.3 Hydraulic nozzle showing diaphragm check valve and filter.
obtained across the swath. In practice, air movement from the forward
speed of the nozzle, particularly at high tractor speeds, will create vortices
at the edge of the spray sheet and affect the dispersal of the droplets
(Young, 1991; Richards et al., 1997). Some nozzles are designed to be used
in isolation and produce a more rectangular distribution or 'even' spray for
band treatments.
Traditionally these nozzles were made in brass or stainless steel, but most
are now produced by injection moulding with a hard-wearing polymer.
Erosion of the nozzle orifice is caused if poor-quality water containing
abrasive sand particles is used, but generally the lifetime of plastic nozzles
is as good as if not better than brass. Some manufacturers provide ex-
Table 10.3 Colour code for hydraulic nozzles
Colour
Flow rate
(1/min at 3 bar)
Orange
Green
Yellow
Blue
Red
Brown
Grey
White
0.4
0.6
0.8
1.2
1.6
2.0
2.4
3.2
tremely hard ceramic nozzle tips, usually in a plastic mounting, but these are
more expensive. The use of polymers has allowed nozzles to be colour
coded for flow rate (Table 10.3). Irrespective of the material of construction, the output and pattern of nozzle tips need to be checked regularly and
replaced if necessary to avoid overdosage.
The flow rate of these standard flat-fan nozzles is determined at 3 bar
pressure, but there is a range of low-pressure fan nozzles which are calibrated at 1 bar pressure. The low-pressure nozzles are used for herbicide
applications to minimize drift. Arable spraying of crops such as wheat is
often with fan nozzles having a 110° angle, rather than 80° or 65° nozzles, so
that the boom can be set close to the crop. However, increasing the angle
produces a thinner sheet, and the VMD is smaller for the same volume
output (Arnold, 1983). The VMD of a fan nozzle is usually slightly larger
than a cone nozzle for the same flow rate and pressure. Fan nozzles are
considered ideal for spraying relatively flat surfaces.
(b) Twin-fan nozzles. Fan nozzles are often pointed directly down
towards the soil or crop, but deposition on cereal stems can be improved by
angling the nozzles (Hislop et al., 1995). In some cases a farmer may use a
nozzle tip with two separate identical orifices to spray 30° forwards and 30°
backwards. With two orifices and the possibility of blockage if these are too
small, the volume application rate is usually higher with these nozzles.
(c) Pre-orifice nozzles. The proportion of spray in small droplets
(<100^im) is reduced if the operating pressure is reduced. This is achieved
automatically when a fan nozzle is fitted with a small orifice on the inlet side
(Barnett and Matthews, 1992; Castel, 1993). These nozzles have been used
to reduce the risk of spray drift (Csorba et al., 1995), but the larger droplet
size may affect coverage on the crop.
(d) Deflector nozzles. A fan pattern can be obtained by directing a jet of
liquid from a circular orifice onto a flat surface which deflects the trajectory
Figure 10.4 Deflector nozzle. (Photograph courtesy of Spraying Systems Co.)
of the spray. In contrast to the elliptical orifice on a flat-fan nozzle, the
deflector nozzle, sometimes referred to as an anvil or impact nozzle, is less
likely to block. A new type of deflector nozzle projects spray in the same
direction as a standard fan and can be used easily on a tractor boom (Figure
10.4; Csorba et al., 1995). Most deflector nozzles, however, project spray at
an angle to the inlet opening. The VMD of a deflector nozzle is slightly
larger than from a standard flat-fan nozzle as there is more rim disintegration from the edge of the liquid sheet.
(e) Twin-fluid deflector nozzles. On some equipment compressed air is
introduced into the spray liquid in the nozzle. The Airtec nozzle enables
lower volumes of spray to be applied with less risk of blockages. The
balance between the pressure of liquid and air pressure is important to
obtain the required spray quality. Young (1991) gives the BCPC spray
quality for certain settings. Droplets from these nozzles contain small
bubbles of air.
(f) Bubble jets. A recent development has been the use of hydraulic
nozzles with a small inlet on the side to allow air to be sucked into the spray
by a venturi action. The larger droplets formed are less likely to bounce
from certain types of leaf surface due to the air bubbles entrapped in the
spray.
(g) Cone nozzles. In these nozzles the liquid is channelled into a vortex
before it emerges from a circular orifice. The nozzle may contain a separate
swirl plate with between one and four tangential slots around the periphery
to impart the swirling flow of the liquid, and produce a hollow cone pattern.
Choice of swirl plate and orifice disc will affect the spray angle and flow
rate. An additional central hole in the swirl plate will produce a full cone.
On some cone nozzles there is a slot cut on the inside of the orifice disc to
create the swirl; with these nozzles there is a standard insert behind the
orifice disc. Cone nozzles direct the spray at the crop at different angles, so
coverage of irregular surfaces such as a mass of foliage may be better than
when using a fan spray in a single plane. A variable-cone nozzle is fitted on
some of the cheaper sprayers; in these the distance between the orifice and
the swirl plate can be adjusted so that the spray pattern can be changed
from a very narrow jet to a wide-angled fine spray. A disadvantage of these
nozzles is that they have to be adjusted by hand and, apart from the extreme
settings, it is difficult to return to a particular setting.
(h) Offset nozzles. The orifice on these nozzles directs the spray to one
side. They are most often used to treat the sides of roads with herbicides,
but may also be useful for treating under low branches of some tree crops.
10.2 Portable sprayers
Many farms, especially in the tropics, are quite small with a range of crops,
so versatile portable equipment is needed to apply pesticides. Some crops,
such as irrigated lowland rice, are difficult to access with vehicular equipment and, like areas with crops on steep slopes or uneven terrain, will
require portable equipment. Small or large farms, inside greenhouses and
experimental areas may also be treated with manually carried equipment,
certain types of which are described in sections 10.5-10.8.
The smallest sprayers are simple syringes, but are arduous to operate and
liable to cause excessive operator contamination. The most common small
sprayers are known as compression sprayers, with a 1-101 tank. Spray liquid
can occupy about two-thirds of the tank capacity, and when sealed an air
pump is used to pressurize the tank. This pressure forces the spray to the
nozzle and atomizes it. As spray is produced, pressure inside the tank will
fall, so droplet size increases unless a pressure control valve is fitted to the
outlet, usually a trigger valve and lance with a single nozzle. Compression
sprayers are widely used in vector control since the operator does not need
to pump while spraying. Small compression sprayers are also commonly
used in pest control operations for control of cockroaches and other domestic pest problems.
More widely used in agriculture are the lever-operated knapsack
sprayers which require continuous steady pumping while spraying (Figure
10.5). These are either fitted with a piston or diaphragm pump which is
operated manually by an under-arm or over-arm lever. Spray from the
pump enters a pressure chamber to even out fluctuations in pressure with
individual pump strokes. The pressure built up in this chamber forces the
spray liquid through a hose to a trigger valve and lance. The spray tank,
usually of 151 capacity, is carried on the operator's back using two or three
straps. The third waist strap is advantageous as it keeps the tank more
firmly in position, so that the energy operating the lever is fully utilized.
Specifications for this type of equipment have been published in an effort to
improve the quality and durability of equipment and reduce operator contamination. Pressure at the nozzle will vary unless a pressure control valve
is used (Matthews and Thornhill, 1993).
Figure 10.5 Lever-operated knapsack sprayer. (Photograph courtesy of Cooper Pegler/Hardi
International.)
Unfortunately with manually operated equipment, operators invariably
use a lance in front of their body and walk directly into the spray and
through treated foliage (Thornhill et al., 1996). When highly toxic insecticides have been applied, operators have become poisoned as few in the
tropics will afford appropriate personal protective clothing. Efforts have
been made to train users to direct the spray downwind away from their
body. Furthermore, equipment has been designed to mount nozzles on a
boom mounted on the rear of the tank so that the operator walks away from
the spray. Such equipment, designed initially for spraying cotton, can be
adjusted in relation to the height of the crop so that the amount of pesticide
applied is proportional to leaf area.
Application with manually operated equipment is more variable, as the
rate of pumping, speed of walking and nozzle height affecting the swath
width will depend on each individual using the equipment. As mentioned
earlier, a pressure control valve reduces the variation due to speed of
pumping. In view of these variables it is important that equipment is calibrated for each individual. As an aid to calibration, a container referred to
as a 'Kalibottle' can be fitted to a nozzle to collect spray applied to 25m2.
The user then can see on the scale the volume applied per hectare.
In addition to knowing the volume application rate, the user needs to
calculate the amount of pesticide to add to each tankload. For some crops
and pesticides this has been facilitated by providing formulated products in
water-soluble sachets or tablets so that the user adds one of these to each
tankload. Most pesticides, however, are still marketed for the small-scale
user in simple containers and liquid has to be poured into the container cap
to measure small volumes. Containers with a built-in measure are preferred
(Figure 10.6), especially with the more toxic pesticides, to eliminate contamination of the user's fingers. So far there has been no commercial
development of a system designed for direct injection on manually operated
sprayers (Craig et al, 1993).
Unfortunately, too often the cheapest sprayer has been purchased, and as
such equipment is not very durable, this has resulted in leakages and excessive operator contamination. Availability of spare parts is often difficult,
especially as many of the rural farmers do not have access to equipment
suppliers. This emphasizes the importance of avoiding the most toxic pesticides when using manually operated equipment.
In some countries, because of the effort needed to use a manually operated knapsack, it is being replaced by those fitted with a two-stroke engine
or electrically driven pump. The latter have an in-built rechargeable battery, and have sufficient capacity for only one or two nozzles on a lance. The
other type of motorized knapsack is the mistblower fitted with a two-stroke
engine to drive a centrifugal blower to create a high-velocity (60-80 m/s)
airstream. The knapsack mistblower was developed originally for treating
cocoa in West Africa, but has become very widely used in some countries
Figure 10.6 Pesticide container with built-in measure.
for row crops as well as trees. These machines usually have a simple airshear nozzle with a variable restrictor upstream to control the volume
application rate. Too often the restrictor is used at maximum flow rate, and
this leads to a larger droplet size and significant fallout on the ground.
Modifications to the nozzle include various designs to distribute the liquid
in a thin film into the airstream or the use of a rotary atomizer (Hewitt,
1993). The main difficulty with two-stroke engines is usually their maintenance, particularly when users leave the engine idling for long periods. The
velocity of the airstream at the nozzle is soon dissipated, so if tall trees need
treatment, the nozzle should be mounted at the end of an extended delivery
tube. For smaller bushes such as coffee, a spinning disc mounted in front of
a propeller fan carried on the back of the operator has been designed
(Povey et al., 1996).
10.3 Tractor sprayers
Larger arable farms use either a boom sprayer mounted on the three-point
linkage of the tractor, a trailed sprayer or a larger self-propelled sprayer.
Some sprayers have an axial fan to provide an air curtain along the boom.
Equipment for treating orchards is considered separately below. The tank
capacity on modern tractors can be up to 10001, but larger tanks must be
trailed. In some cases an auxiliary tank is mounted on the front of a tractor.
Increasing tank size is a disadvantage as increased compaction of soils
should be avoided.
The basic layout of the field crop sprayers, in terms of a pump, controls
and boom with nozzles, has not changed very much, but to meet increasingly strict regulations, the ancillary equipment on these sprayers has
changed dramatically over the last decade (Figure 10.7). The emphasis on
reduction of operator contamination to meet requirements of health and
safety regulations has led to the use of low-level induction hoppers. The top
of these must not be more than 1 m above the ground so that pesticide
drums are not lifted on to the top of a sprayer (Figure 10.8). Some problems
have been experienced with new formulations, such as dispersible granules
in water-soluble packs, especially when several sachets are placed in a lowlevel induction hopper and the plastic is slow to break down at low temperatures. With containers having a standard 63mm opening, there is
Filling
injector
control
Liquid chemical Clean water
induction tank container
Injector „
Powder
chemical
induction
bowl
Control
Tank
lid
Tank suction
control
Pump
Sprayboom
Chemical
container
Suction line
Return line
Pressure line
Suction hose with
floating strainer
Figure 10.7 Layout of tractor sprayer. (Courtesy of Allman Limited.)
Figure 10.8 Low-level-induction bowl.
also increasing use of closed transfer systems, and the use of refillablereturnable containers is expected to increase to eliminate the problem of
disposal of a large number of small contaminated containers. Sprayers
should now have a separate water tank for the user to wash gloves and
hands if contaminated with pesticide while adjusting the sprayer in the field.
Two separate containers for personal protective equipment (one for clean
items and the other for contaminated clothes) are also advised, particularly
as some items, such as a face shield and apron, may be required only while
preparing the spray.
The choice of pump design and capacity will depend to a great extent on
the width of the boom and thus the number of nozzles operated, and have
surplus capacity to provide a return flow to the tank for agitation. Boom
width was formerly generally about 12m, but many large farms now have
18, 24 or even 36m booms, which fit with multiples of the equipment used
to sow the crop. On the larger equipment these booms are hydraulically
operated. The trend towards wider booms is to increase work rate, provided
fields are relatively flat.
There are generally four types of pump which may be used, namely the
piston, diaphragm, roller vane and gear pumps. Centrifugal pumps may be
used to speed the filling of a sprayer. Piston pumps are suitable for high
pressure, but as the pressure at the nozzle need not exceed 4 bar, most
farmers now prefer diaphragm pumps which are less likely to wear. These
consist of between two and six diaphragms arranged around the crankshaft
drive, since the volume displaced by each diaphragm is relatively small.
Associated with each diaphragm is an inlet and outlet valve. Both the piston
and diaphragm pumps should have an air chamber to even out pulses in
spray pressure. The less-expensive roller-vane pump is used on smaller
sprayers. These consist of a rotor with a series of rollers around its periphery that contact the eccentric housing so that spray is pushed between the
rollers in one direction. The rollers and seals around the drive shaft are
likely to wear, but can be replaced to renovate the pump. Gear pumps are
no longer used on these sprayers.
Upstream of the pump there should be a large-capacity filter to prevent
any material damaging the pump. This main filter may have a backflushing
system so that it only needs to be cleaned once a day when spraying has
been completed. Filters should also be located in the line to the boom as
well as at individual nozzles to minimize stoppages due to blocked nozzles.
A pressure-regulating valve is needed to control the pressure delivered to
the boom. The surplus liquid is directed through a series of nozzles
mounted in the bottom of the tank to provide agitation. This is especially
important with particulate formulations to ensure they remain in suspension. Care is needed when the tank is nearly empty, otherwise air in the
spray will cause foaming. More complex valves are used on some sprayers
so that the volume of spray applied compensates for changes in forward
speed. These usually operate by affecting the pressure; because the droplet
spectrum will be altered, the variation in tractor speed should be limited. To
avoid taking pesticide into a tractor cab, controls are ideally electrically
operated switches linked to solenoid valves. Apart from a main valve, there
are usually individual valves to control flow to each section of the boom.
Normally a boom will be in three sections so that the right or left side can
be shut off if necessary at the edge of the field. In order to avoid having
surplus spray liquid when the field has been treated, it is important to know
the exact size of the field and accurately calibrate the sprayer. It is considered better to run out of spray on the last swath than to have to dispose of
surplus spray. Modern electronic equipment is available to monitor the
application rate and keep an accurate record of the volume applied (Jahns
and Rietz, 1996).
Any of the hydraulic nozzles described above can be fitted to a tractor
boom. Some manufacturers fit a three-way turret at each nozzle position so
that different types of nozzle can be quickly selected depending on the type
of pesticide and volume of application needed. In general, nozzles for cereal
crops are spaced 50cm apart and the boom height adjusted to give an
overlap and provide even coverage across the swath. On some crops such as
potatoes, the nozzles may be mounted on a vertical dropleg so that spray
can be directed laterally and upwards into the crop canopy. On some
sprayers a plastic sleeve along the boom directs an airflow provided by an
axial fan to distribute spray into the canopy (Figure 10.9). This will reduce
Figure 10.9 Tractor sprayer with air-sleeve. (Photograph courtesy of Hardi International.)
downwind drift provided there is sufficient foliage to collect the spray
(Young, 1991; Taylor and Andersen, 1997). On a bare soil surface the
rebound of air from the soil surface could increase the extent of spray drift.
The passage of a tractor sprayer through a row crop can be readily
determined by counting the rows, but on a closely spaced crops, such as
wheat, damage caused by the passage of the tractor is avoided by leaving
some rows unsown to provide 'tramlines' across the fields. It is important,
therefore, to match the boom width of the sprayer with the width of the
planter.
Instead of spraying a whole field to control weeds, experiments have
shown that it is possible to map the distribution of important weeds using a
hand-carried Global Positioning System (GPS) and programme a computer
on the tractor to spray an appropriate herbicide using a direct injection
system (Frost, 1990) only on the infested parts of a field (Paice et al., 1995).
Modelling of the potential savings by patch spraying of black grass infestations indicated savings of up to £207/ha over 10 years (Rew et al., 1997).
Further development of direct injection systems is needed so that only the
required amount of pesticide is mixed as it is needed, but the range of
formulations available makes such a system difficult to produce.
As with all sprayers, equipment should be thoroughly cleaned after use
and any pesticide flushed out of the pipework with clean water. Any pesticide left in the sprayer may have an adverse effect on valves and other
components. In particular, individual nozzles should also be very carefully
cleaned without damaging the orifice. Management of water contaminated
with pesticides is discussed in Chapter 13.
10.3.1 Portable lines
In some countries many growers use a mechanized pump, either on a
tractor or a wheeled trolley from which the spray is pumped through a long
hose to a hand-operated lance. These sprayers usually apply a very high
volume, often over 10001/ha, so that spray runs off foliage. This type of
spraying is therefore extremely wasteful as well as time consuming. Where
the pesticide label indicates a dosage per hectolitre, it is based on 10001/ha,
so the spray is very dilute and the effect of the surfactant in some formulations is negligible, thus hydrophobic foliage is not effectively wetted. Some
growers do use a vertical boom mounted on a trolley to pull between rows
of crops such as tomatoes in greenhouses, and may use lower volumes of
spray.
70.3.2 Orchard sprayers
The portable line technique formerly used in orchards has been replaced by
air-assisted sprayers. The most common design has an axial fan, usually
mounted at the rear of a trailed tank. An arrangement of vanes directs the
air flow laterally and upwards to project the spray, normally from a series of
hydraulic nozzles, into the tree canopy. Some growers use rotary nozzles
and have reduced the volume of spray in some cases to as low as 501/ha,
which is usually considered satisfactory for commercial use provided
dosage rates are maintained (Cross and Berrie, 1990). As any spray leaving
the top of the canopy can drift over long distances, tree crop spraying is generally regarded as polluting the area. Major changes have led to growing
smaller trees and this has allowed alternative sprayers to be considered. In
some countries the air from an axial fan is ducted so that it is directed
laterally into the trees (Figure 10.10). Other equipment uses centrifugal
fans with several ducts to direct spray to different parts of the canopy, or
crossflow fans mounted vertically to direct spray laterally into the canopy.
Other equipment has various systems of recycling the spray (Gohlich et a/.,
1996). The most advanced technique is to enclose the trees in a mobile
tunnel while spraying to reduce drift and soil contamination, but nozzles
need to be directed upwards to ensure underleaf coverage (Cross and
Berrie, 1995). Tunnel sprayers require single rows of trees on relatively
level ground.
The trend has been to reduce the volume of spray applied to reduce the
wastage caused by runoff, in some cases as low as 601/ha, although in hot,
dry climates a higher volume is recommended to prevent droplets drying
too quickly and reducing penetration of systemic pesticides. The problem is
Figure 10.10 Modified axial fan sprayer for orchards.
to obtain good distribution of pesticides to control the range of pests and
diseases that occur during the season. The amount of foliage increases at
the start of the crop season, so accurate timing of early sprays is crucial and
repeat sprays may be required to protect new growth.
Instead of hydraulic nozzles, some sprayers use air-shear nozzles, especially with centrifugal fans, or rotary atomizers (Raisigl and Felber, 1991).
The high velocity of air needed for shear nozzles contrasts with the need to
have a sufficient air volume to displace air within the canopy with aircarrying spray droplets. However, the important factor is to achieve airturbulence within the canopy so that the movement of the leaves filters out
the spray. Walklate et al. (1996) suggested that it may be possible to increase the work rate using an air-assisted orchard sprayer and reduce drift
by increasing the forward speed, provided it gives sufficient deposition with
the available air flow to achieve control of the pests and diseases.
10.4 Aerial application
Aerial application is important in forestry, over large irrigated areas and
where an extensive area of infestation must be controlled very rapidly, as
over 200 ha can be treated per hour. The increase in the use of agricultural
aircraft and the area treated since the 1950s is presented by Rowinski
(1996). However, where ground equipment can be used, it is now increasingly preferred in order to reduce environmental pollution. Nevertheless,
with appropriate choice of droplet size and formulation, aerial spraying can
be very effective and fast. In pine plantations, small droplets of insecticide
in a low-volatile ULV carrier are more effectively filtered by the foliage
than when larger droplets are used at 201/ha as a water-based spray. In
contrast for fruit fly control, where an attractive bait is included with the
insecticide, large droplets are required to minimize the impact on nontarget organisms. Large droplets are also essential with aerial herbicide
treatments.
A range of aircraft types has been used for aerial application. Ideally a
single-engined low-wing aircraft specially designed for pesticide application, such as the Turbo-Thrush, should be used. In an emergency it is
possible to attach a tank to the undercarriage of small aircraft, normally
used in air-taxi services. In large-scale operations, twin-engined or larger
aircraft have been employed, especially in forestry work. At the other
extreme a large microlight aircraft with a cockpit to protect the pilot has
also been used for ULV applications (Figure 10.11; Bateman, 1997). Helicopters have also been widely used because of their manoeuvrability, ability
Figure 10.11 Microlight aircraft with Micronair atomizers applying ULV myco-pesticide
against locusts. (Photograph courtesy of Roy Bateman.)
to land without an airstrip and operate at lower flying speeds. Higher
operating costs can be compensated for by high work rates. They are
sometimes used with a sprayer slung on a hook under the aircraft.
The basic spray gear is somewhat similar to that used on a tractor,
although the pump is usually a centrifugal pump either driven by a small
propeller mounted in the slipstream of the main engine propeller, or by a
hydraulic power take-off from the engine. The older propeller system produces more drag on the aircraft. The tank on agricultural aircraft is built
into the fuselage and is normally immediately in front of the cockpit. The
tank has a dump valve to release the spray contents rapidly in an emergency, and is normally filled through a rapid coupling system mounted on
the fuselage behind the cockpit.
Nozzles, always with a non-drip valve, are usually mounted on a boom
just below the trailing edge of the wing. The boom does not extend to the
end of the wing, in order to avoid spray being carried in the wing-tip
vortices, as this increases the risk of spray drift. Hydraulic nozzles of various
types have been used on aircraft. By adjusting their position relative to the
airflow, the spray droplet spectrum is finer if the nozzles are directed
forwards and coarser if directed backwards (Spillman, 1982). One development of a deflector nozzle, which is popular in the USA, is the CP nozzle
with three different angles of deflection and easily changed flow rates, but
droplet sizes tend to be larger with the deflector nozzles. Instead of a large
number of hydraulic nozzles, it is possible to fit between one and ten rotary
atomizers, depending on their size and the volume application rate required. One version is the Micronair AU5000, on which the speed of rotation can be changed by adjusting the pitch of its propeller blades. An
electrically driven version is also available. Rotary atomizers have been
particularly used for very fine sprays and ultra-low volume application, for
example in forestry insect and locust control operations, but the Micronair
units can be used for sprays at 201/ha. Data on droplet spectra with an
AU3000 mounted in a wind tunnel enabled derivation of a model to predict
field performance (Parkin and Siddiqui, 1990). Data for ULV fenitrothion
sprayed against locusts have been reported by Hooper and Spurgin (1995).
For very large droplets a cone nozzle with an additional orifice, the Rainjet
nozzle, and similarly the Microfoil, which contains a series of needle orifices
directed backwards, have been used, where the airspeed does not exceed
150km/h, otherwise the droplets shatter.
While ULV sprays are applied at usually less than 31/ha, most agricultural sprays use water-based formulations at 20-301/ha with a VMD of
200 |im. Spraying should cease if the ambient air temperature exceeds 360C
or the depression of the wet bulb of a thermometer exceeds 80C. Adjuvants
to reduce the evaporation or increase the droplet size are needed if treatments are needed in hot, dry climates, although increase in droplet size may
be counterproductive if coverage is inadequate.
The track spacing of aircraft used to be dependent to a large extent on
ground markers, either flagmen or fixed boards, but with the development
of the Global Positioning System (GPS), pilots can use a laptop computer to
determine their position and record their flight path. Accuracy is improved
with a differential GPS. Computer models, such as the AGDISP (Agricultural DISPersal) and FSCBG (Forest Service Cramer-Barry-Grim) are
available to predict downwind dispersion of spray, including the effects of
evaporation, meteorology, canopy penetration and ground and canopy
deposition (Barry, 1993; Teske et al., 1993). The effects of the near wake of
an aircraft on droplet dispersion has been visualized by using LIDAR
technology in which pulses of laser light are directed into the cloud of spray
droplets and the intensity and time delay of reflected light impulses are
measured (Mickle, 1993; Payne, 1998).
With the need for rapid refilling of an aircraft, preparation of sprays prior
to loading should be facilitated by the type of formulation, and foaming
avoided.
10.5 ULY and CDA ground application
Ultra-low volume (ULV) application, the minimum volume to obtain economic control, was initiated with oil-based sprays of dieldrin to control
locusts, using the exhaust gases of a vehicle to atomize the spray. Subsequently the development of hand-carried spinning-disc sprayers has
enabled ULV sprays to be applied to field crops. These sprayers have a
small 12V DC motor powered by batteries. The ULV formulation is fed by
gravity through a restrictor to the spinning disc, which is held above the
crop downwind of the operator so that air turbulence distributes the spray
within the crop canopy (Figure 10.12). Extensive areas of cotton have been
treated with insecticides using this technique, but the availability and cost of
specially formulated oil formulations has led to adoption of very-low volume (VLV) spraying. This enables farmers to use less expensive formulations diluted in 10-151 of water per hectare. With an adjuvant to reduce the
effect of evaporation, as low as 51/ha has been applied. In particular, molasses has been used as an adjuvant with insecticides as it also attracts the moth
stage of the noctuid pests of cotton.
When extremely low volumes are applied, droplet size becomes more
critical, otherwise a high proportion of the spray is wasted. With insecticides
used against foliar pests, the mist range (50-100 jim) was considered most
suitable to minimize inhalation hazards and excessive drift downwind, while
avoiding excessive deposition on the nearest horizontal surface. However,
where herbicides need to be applied, drift downwind must be avoided, so
a larger droplet size (usually about 250 |im) was recommended. The need
for a particular droplet size within narrow limits led to the concept of
Next Page
Previous Page
The track spacing of aircraft used to be dependent to a large extent on
ground markers, either flagmen or fixed boards, but with the development
of the Global Positioning System (GPS), pilots can use a laptop computer to
determine their position and record their flight path. Accuracy is improved
with a differential GPS. Computer models, such as the AGDISP (Agricultural DISPersal) and FSCBG (Forest Service Cramer-Barry-Grim) are
available to predict downwind dispersion of spray, including the effects of
evaporation, meteorology, canopy penetration and ground and canopy
deposition (Barry, 1993; Teske et al., 1993). The effects of the near wake of
an aircraft on droplet dispersion has been visualized by using LIDAR
technology in which pulses of laser light are directed into the cloud of spray
droplets and the intensity and time delay of reflected light impulses are
measured (Mickle, 1993; Payne, 1998).
With the need for rapid refilling of an aircraft, preparation of sprays prior
to loading should be facilitated by the type of formulation, and foaming
avoided.
10.5 ULY and CDA ground application
Ultra-low volume (ULV) application, the minimum volume to obtain economic control, was initiated with oil-based sprays of dieldrin to control
locusts, using the exhaust gases of a vehicle to atomize the spray. Subsequently the development of hand-carried spinning-disc sprayers has
enabled ULV sprays to be applied to field crops. These sprayers have a
small 12V DC motor powered by batteries. The ULV formulation is fed by
gravity through a restrictor to the spinning disc, which is held above the
crop downwind of the operator so that air turbulence distributes the spray
within the crop canopy (Figure 10.12). Extensive areas of cotton have been
treated with insecticides using this technique, but the availability and cost of
specially formulated oil formulations has led to adoption of very-low volume (VLV) spraying. This enables farmers to use less expensive formulations diluted in 10-151 of water per hectare. With an adjuvant to reduce the
effect of evaporation, as low as 51/ha has been applied. In particular, molasses has been used as an adjuvant with insecticides as it also attracts the moth
stage of the noctuid pests of cotton.
When extremely low volumes are applied, droplet size becomes more
critical, otherwise a high proportion of the spray is wasted. With insecticides
used against foliar pests, the mist range (50-100 jim) was considered most
suitable to minimize inhalation hazards and excessive drift downwind, while
avoiding excessive deposition on the nearest horizontal surface. However,
where herbicides need to be applied, drift downwind must be avoided, so
a larger droplet size (usually about 250 |im) was recommended. The need
for a particular droplet size within narrow limits led to the concept of
Figure 10.12 Spinning disc sprayer applying insecticide on cotton in West Africa.
controlled droplet application (CDA; BaIs, 1975). The narrow droplet spectrum has been obtained principally by using rotary atomizers, as droplet
size can be decreased as the rotation speed of the disc increases.
The formation of the spray is also affected by flow rate; thus at very low
flow rates, individual droplets can be produced, but as flow rate increases,
ligaments are formed (Figure 10.13) which break into smaller main and
much smaller satellite droplets. There is thus a period between single and
ligament droplet formation where the range of droplet sizes is increased.
Once ligaments are formed, there is a bimodal distribution of droplets, and
the size will increase as the flow rate increases, until the disc is flooded and
a sheet of liquid leaves the disc and breaks up in much the same way as that
from a hydraulic nozzle. Rotary atomizers therefore need to be used
with relatively low flow rates, which makes them ideal for ULV and VLV
applications.
The design of the disc is important. Initially BaIs (1970) used peripheral
teeth to provide the least area on which liquid could attach itself, thus
enhancing the production of individual droplets. Later, grooves were added
to the inside of the disc to channel the flow to the teeth (Clayton, 1992).
While a smoothed edged disc will produce a spray, the combination of teeth
and grooves gives better control of droplet size for a wider range of flow
rates (Matthews, 1996).
ULV formulations need be relatively involatile, so oil carriers, especially
light paraffinic oils as well as vegetable oils such as soyabean and cottonseed
Figure 10.13 Ligament formation from a spinning disc. (Photograph courtesy of Micron
Sprayers Limited.)
oil, have been used, but viscosity can affect the flow rate and also influence
subsequent activity of the spray deposit. As many pesticides do not mix
adequately in oil, solvents have been used in the oil formulations. Some of
these solvents proved to be very phytotoxic, so in some formulations containing, for example, isophorone, other additives, including beeswax and
woolfat, were incorporated in the formulation to reduce the phytotoxicity
(Maas, 1971). However, oil carriers have proved particularly important in
developing formulations of mycopesticides. In the control of locusts with
the fungus Metarhizium flavoviride (IMI 330189), conidial spores are suspended in purified mineral or vegetable oils (Bateman, 1997).
The technique of using the spinning disc is to determine a track separation based on the crop canopy, as wind speed will vary during spraying.
Commencing near the downwind side of the field, successive passes are
made through the field progressively upwind, so the operator, spraying
downwind, never walks through treated foliage. Track spacings of up to 6m
have been used on small plants, but on cotton as the season progresses, the
track spacing should be reduced to apply a higher volume in relation to the
crop leaf area. With the water-based formulations applied at VLV, a larger
droplet (100-150 ^m) is needed to compensate for evaporation of the water
from droplets, so the track spacing is generally no more than 3 m, narrowing
to every row in the case of cotton spraying.
10.6 Fogs, mists and aerosols
Space treatments inside glasshouses and in warehouses require very small
droplets with a low terminal velocity so that they remain airborne for as
long as possible. Fogs are normally considered to be when the droplets are
smaller than 15\im and visibility is reduced, but in this chapter fogs are
considered to be all applications with a VMD less than 50 ^m and more than
5% of the volume smaller than SO^im. Mists have a VMD between 50 and
100 jim and less than 5% by volume smaller than 30 ^m. 'Aerosol' is a term
also used for small droplets, but here is confined to those produced by
pressure packs. Fogs have been used outside buildings to control pests in
forests and for mosquito control, but should be used only if there is a
temperature inversion and no wind.
Fogs are produced either by heat, i.e. thermal fogs or by an air shear and
vortex referred to as cold fogs. Thermal fogs use a dilute concentration of
pesticide diluted in an oil or odourless kerosene. In some cases a waterbased formulation is used with an adjuvant to assist in the production of the
fog. Cold fog is usually produced with a ULV formulation.
There are several types of thermal fogger. One type uses the pulse jet
engine (Figure 10.14) to create an exhaust temperature of 50O0C into which
the pesticide is injected. There is vaporization, followed by condensing
of the vapour on contact with the much lower ambient temperature to form
Figure 10.14 Thermal fogger.
the dense white cloud of fog. Small hand-carried versions of these machines
have either a piston, bellows or electrical pump initially to pressurize the
fuel tank to deliver petrol plus air to the combustion chamber. Once the
engine has started, a spark from the plug in the combustion chamber is no
longer required because the exhaust gases ignite the incoming fuel. Larger
versions are trolley or truck mounted. Routine maintenance is essential to
ensure the foggers can be started quickly, and they should be used only by
trained staff. As a flame can be produced, equipment is designed to stop the
flow of insecticide to the nozzle if the engine stops. As a safety precaution,
a fire extinguisher should be readily available when these foggers are used.
Alternative hand-carried foggers usually have a two-stroke engine and use
a friction plate and/or the exhaust gases to provide the heat. Larger types of
thermal fogger have a motor and blower unit. Fuel is pumped into a combustion chamber and the hot air is blown into a mixing nozzle where the
pesticide is vaporized.
Cold foggers use an air shear to create the small droplets. In some the air
is rotated to form a vortex into which the pesticide is injected. The size of
machine can vary from a hand-carried unit with an electrical or two-stroke
engine to larger trolley- or truck-mounted versions. Many used indoors
have electrical motors and controls so that they can be operated while the
building is unoccupied (Van Zuydam and van de Zande, 1996). Treated
areas need to be well ventilated before staff can re-enter. A particular
problem with some horticultural crops is the extent to which plants are
handled, exposing staff to surface deposits.
Whether a thermal or cold fog is used the concentration of pesticide
formulation within a building should not exceed 2.71 per 100Om3. Care must
be taken to ensure that gas or oil pilot lights are turned off to avoid a spark
which could cause an explosion. In large buildings, care is needed to ensure
adequate distribution of the pesticide. If hand-carried or trolley equipment
is used, the operator should wear full personal protective equipment and
start treatment farthest from the exit door, moving along a clear path to the
door. If remotely controlled, adequate circulation of a fog may require fans
operated with totally enclosed motors. Fogs will eventually settle, so most
of the pesticide will be deposited on the upper surface of horizontal surfaces. There will be very little deposited on the lower surface of foliage. The
dosage applied in a fog is generally quite low to achieve killing of insects
that are actively flying or stimulated to fly at the time of treatment, so
retreatment may be required if the area becomes reinfested from outside
the building or immature stages are not controlled.
10.6.1 Mists
Slightly larger droplets (50-1OO [xm VMD) with less risk of inhalation are
also used inside buildings, especially for more selective treatments on pro-
Figure 10.15 Hand-carried mist applicator in glasshouse. (Photograph courtesy of Micron
Sprayers Limited.)
tected crops, rather than fill the complete air space with a fog. An electric or
two-stroke engine-driven motor is used with a fan to project droplets from
a spinning disc (Figure 10.15). The choice of fan and motor unit will depend
on the scale of the operation and whether delicate foliage has to be treated,
but penetration into a thick canopy will depend on air turbulence. Special
ULV formulations have been used with this type of equipment. In some
glasshouses the sprayer is mounted on a monorail to traverse the crop.
Alternatively some growers have used a motorized knapsack mistblower
with an air-shear nozzle.
10.7 Electrostatically charged applications
The aim of improving spray deposition, especially on the undersurface of
leaves, with less drift has led to several attempts to use an electrostatic
charge on droplets. In many cases an electrostatic charge is added to spray
from a hydraulic nozzle or spinning disc, by induction, ionized field or direct
charging of the spray (Marchant, 1980; Matthews, 1989). In the USA, Law
(1980) developed an induction charging system for an air-shear nozzle
which has been used on both tractor-mounted booms and for a hand-held
lance portable line system in glasshouses (Giles et al., 1995). An induction
charging system on air-shear nozzles is commercially available on
mistblowers. Arnold and Pye (1980), Cayley et al. (1984) and Marchant
(1985) examined the use of spinning discs with electrostatic sprays, and a
commercial sprayer was developed for treating potato tubers with
fungicides (Cayley et al., 1987). All these sprayers used conventional pesticide formulations, but Coffee (1979), following the development of the
hand-held spinning disc sprayers for applying insecticides on cotton, developed the principle of electrodynamic spraying with oil-based formulations.
Subsequently the handheld 'Electrodyn' was used commercially on cotton
by small-scale farmers with prepackaged ULV insecticides in 'Bozzle' containers (Smith, 1989). The Bozzle cap was colour-coded to indicate different
flow rates. The technique used a high-voltage generator powered by four
1.5V batteries to charge the nozzle at 24kV. Emerging under gravity, the
charged liquid formed regular ligaments and produced a very narrow droplet spectrum. At the fixed voltage, increasing flow rate increased the droplet
size. The limited number of pesticides that could be formulated at less than
31/ha and have the required resistivity was one of the factors that prevented
continued commercial development of this system.
While spray drift can be reduced by electrostatic charging, especially with
fine sprays (Western and Hislop, 1997), the distribution of a charged spray
within a crop may be unsatisfactory. Charged droplets are deposited on the
nearest earthed surface, so when a crop canopy meets between the rows
there is little penetration to the lower foliage. Using air assistance with
electrostatically charged sprays will improve penetration; thus Abdelbagi
and Adams (1987), using 18|im droplets in a 2m3/s airflow, obtained
underleaf coverage and improved whitefly control in a glasshouse. Allen
et al. (1991) reported improved deposition on apple trees and reduced
incidence of powdery mildew by using an induction charging system with
air-assisted cone nozzles.
10.8 Chemigation
Pesticide application in all types of irrigation system is referred to as
chemigation. This system of treating crops has increased in popularity,
especially where sprinkler-type irrigation, such as centre-pivot equipment,
is used. Drip and subsurface irrigation is suitable for soil-applied pesticides.
When injecting chemicals into the flow of water, it is essential that equipment has control valves to prevent any backflow to the source of water.
Sprinkler irrigation may apply more than 50001/ha, so foliar chemicals are
very dilute and only a small proportion of the pesticide may be retained on
the crop, especially as sprinkler systems tend to produce very large droplets
(Kohl and DeBoer, 1984). Systemic pesticides that are taken up through
the roots will be more effective. The large dilution factor may also affect
pesticidal activity if the active ingredient is readily hydrolysed or affected
by pH. Wind can affect the distribution from sprinklers and as centre pivots
can take a long time to cover a field, some pest damage may occur before
treatment is completed. Dowler (1993) has reviewed the equipment used in
chemigation.
10.9 Granule, dust and seed treatments
The application of dusts has declined, although the use of sulphur dust
is still popular in some areas. The extremely small particle size of dusts
(mostly <30^im) makes them prone to inhalation, and particles are
readily blown by the wind or dislodged from foliage. The larger granule
formulations are preferred to dusts, but these are mostly confined to soil
treatments. One exception is the use of granules for stem borer control in
maize.
Dry particle formulations are often applied by simple hand-held equipment such as a pepper-pot type of container, but for accurate application
over large areas, the irregular shape of the inert clay or other particles
makes dispensing more difficult than the pumping of liquid spray through
nozzles. Improvements in formulation using polymer and graphite coatings
can produce more spherical particles that flow by gravity from a hopper to
a metering system and outlet. Hoppers, with a rainproof lid, usually have a
sloping floor so that the particles roll down to the metering system. Various
adjustable gates have been used on some applicators, but for granule application a positive displacement rotor is preferred as this will deliver a constant volume for each revolution. On tractor-mounted equipment the rotor
is usually driven by a trailing wheel, so that application is proportional to
the actual forward speed. The speed of rotation and width of the rotor can
be adjusted to provide different application rates, but care has to be taken
in setting up the rotor so that granules are not ground into a dust. This is
particularly important as the most toxic pesticides, such as aldicarb, are
often formulated only as a granule.
Granules are often applied at the time of sowing, so equipment is then
mounted on the toolbar with the seed drill. The delivery tube from the
metering rotor is then fitted alongside the seed coulter to drop the granules
to the side or below the seed to enhance uptake of the pesticide through the
roots. For broadcast soil surface treatments, the end of the delivery tube can
be fitted with a 'fishtail' or deflector plate to spread the granules over a
wider area. On some equipment, instead of having several hoppers, the
granules are distributed across the swath in an airflow from a blower unit.
Granules are also applied from aircraft, for example when treating irrigated
rice fields in the USA.
10.9.1 Seed treatment
Localized use of pesticides is important in IPM (integrated pest management). Seed treatment is one technique, albeit prophylactic, which can
protect young seedlings during the often crucial stage of crop establishment. Seed treatment is also possible at a central unit operated by seed
merchants. The main problem is providing sufficient active ingredient uniformly on a batch of seeds without causing phytotoxicity. The process of
pelleting seeds with inert materials, one or more pesticides as required and
nutrients can give a large pellet which is easier to sow. Clayton (1993)
reviews the different types of equipment used in seed treatment. On some
of these a spray is applied to seed as it is tumbled in a rotating chamber,
while in others a spray is applied as seed is carried up an auger. Rotary
atomizers and twin-fluid nozzles are used to keep the volume of spray
applied to a minimum. Other information on seed treatment is given by
Jeffs (1986). Film coating is also used for some seed treatments.
10.10 Miscellaneous
10.10.1 Weed wiper
Translocated herbicides, such as glyphosate, can be applied to foliage using
a 'weed wiper'. This consists of a container to drip feed a liquid to an
absorbent surface so that it remains wet without dripping. It has been used
in plantations for isolated patches of weeds and, when mounted on a tractor, is used to treat weeds that are higher than the crop. It has also been
used in set-aside land to control thistles and certain other tall weeds, where
spray drift must be avoided.
10.10.2 Lure and kill
Instead of broadcast treatments, the insect pest is lured by an attractant to
a surface treated with a persistent insecticide. In one example in the USA,
'sticks' with the pheromone grandlure and an insecticide have been used to
check boll weevil populations.
10.10.3 Tree injection
A systemic insecticide has been used on certain types of palm tree by
drilling a small hole, angled 45° downwards in the stem, and using a small
hand-operated injector. The hole is covered with a fungicide paste or filled
with a pesticide impregnated plastic plug. About 3 ha/day can be treated by
one person.
While sprays applied through hydraulic nozzles remain the dominant
method of pesticide application, a wide range of other application techniques are available to suit particular circumstances. As indicated at the
beginning of this chapter, training to get present systems to be used more
accurately is needed worldwide, so that pesticides are applied more judiciously within integrated crop management programmes and environmental pollution is minimized. Similarly, further research is essential if
improved technology is to provide more accurate dose transfer to manage
pest populations.
10.11 Standards
There are now specifications on the performance of pesticide application
equipment, including those published by ISO, WHO, FAO, CEN and national standards organizations. A scheme to classify equipment according to
its potential contamination hazard to the user and the environment was
proposed by Parkin et al. (1994). In addition, in Europe there is a trend
towards regular inspection of sprayers on farms, which is or will become
mandatory (Heestermans, 1996). In Germany mandatory checks at 2-year
intervals were introduced in 1993 following an attempt to have a voluntary
scheme (Ripke, 1996). Only about 20% of the farmers used the scheme and
on these farms only 50% of the equipment was considered to be in a
satisfactory condition (Wehmann, 1993). In the UK following the Food and
Environmental Protection Act 1985, users of pesticides have had to have
training and in some cases certification before they can legally use pesticides. A pesticide user training scheme has been developed by the Agricultural Training Board and the testing is carried out under the National
Proficiency Test Council.
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performance based on wind tunnel assessments of spray drift, in ANPP-BCPC 2nd International Symposium on Pesticide Application Techniques, Strasbourg, pp. 109-16.
Paice, M.E.R., Miller, P.C.H. and Bodle, J.D. (1995) An experimental sprayer for spatially
selective application of herbicides. Journal of Agricultural Engineering Research, 60, 10716.
Parkin, C.S. (1993) Methods for measuring spray droplet sizes, in Application Technology for
Crop Protection (eds G.A. Matthews and E.G. Hislop), CABI, Wallingford, pp. 5784.
Parkin, C.S. and Siddiqui, H.A. (1990) Measurement of drop spectra from rotary cage aerial
atomisers. Crop Protection, 9, 309-22.
Parkin, C.S., Gilbert, A.J., Southcombe, E.S.E. and Marshall, CJ. (1994) The British Crop
Protection Scheme for the classification of pesticide application equipment by hazard. Crop
Protection, 13, 281-5.
Povey, G.S., Clayton, J.S. and BaIs, T.E. (1996) A portable motorised axial fan air-assisted
CDA sprayer: a new approach, in Proceedings of the Brighton Crop Protection Conference,
pp. 367-72.
Raisigl, U. and Felber, H. (1991) Comparison of different mistblowers and volume rates for
orchard spraying. BCPC Monograph, 46,185-96.
Rew, L.J., Miller, P.C.H. and Paice, M.E.R. (1997) The importance of patch mapping resolution for sprayer control. Aspects of Applied Biology, 48, 49-55.
Richards, M.D., Hislop, E.G. and Western, N.M. (1997) Static and dynamic patternation of
hydraulic pressure nozzles. Aspects of Applied Biology, 48, 201-8.
Ripke, P.O. (1996) Testing of field sprayers already in use in Germany. EPPO Bulletin, 26,4751.
Rowinski, R.S. (1996) The use of aeroplanes for plant protection in and out of Europe, EPPO
Bulletin, 26, 123-30.
Samu, F., Matthews, G.A., Lake, D. and Vollrath, F. (1992) Spider webs are efficient collectors
of agrochemical spray. Pesticide Science, 36, 47-51.
Smith, R.K. (1989) The 'Electrodyn' sprayer as a tool for rational pesticide management in
smallholder cotton, in Pest Management in Cotton (eds M.B. Green and DJ. de B. Lyon),
Ellis Horwood, Chichester, 227-46.
Southcombe, E.S.E., Miller, P.C.H., Van de Zande, J.C. etal (1997) The international (BCPC)
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11 Regulatory requirements in
the European Union
W. K. DE RAAT, I. A. VAN DE GEVEL,
G. F. HOUBEN and B. C. HAKKERT
11.1 Introduction
It has been realized for many decades that the use of chemical plant protection products (PPPs) does not have only beneficial sides. Various adverse
effects on humans and the environment may occur as well, which is not
surprising, as the mode of action of PPPs is virtually always based on
toxicity. Although the art of developing PPPs is very much concerned with
specificity, it is often not possible to restrict completely the toxicity of PPPs
to the target organism. Moreover, most PPPs are xenobiotic by nature, and
may therefore have toxic effects not related with their mode of action.
Exposure of non-target organisms to PPPs, including humans, cannot be
ruled out completely. By reducing persistency and improving application
techniques, it is attempted to minimize this exposure. However, effective
control often requires a certain degree of persistency, while bringing a
sufficient amount on the target is generally accompanied by some spillage.
The adverse side effects of PPPs form the major impetus for the regulation of their use by governments. In addition there exists another, and in
many countries, older impetus. The application of PPPs needs to be sufficiently efficacious. Farmers have to be sure that they are using a product
that indeed protects the valuable crop against pests and diseases, while it
does not affect the quality of the crop. When a product is allowed for use,
it should perform as promised on its label.
Adverse side effects and efficacy are not fully independent aspects of the
regulation of PPPs. They are increasingly becoming two sides of a coin.
Efficacy is often measured in terms of the amount needed for a good result.
It goes without saying that the amount used is also an important aspect of
the problem posed by possible side effects. On the other hand, efficacy and
prevention of adverse side effects may be competitive aspects of PPP regulation. Very efficacious PPP applications may still not be deemed acceptable, because a less efficacious one is available, which is more acceptable as
regards its environmental side effects. The regulation of PPPs is ultimately
aimed at achieving a balance between efficacy and side effects which is
acceptable for society.
The regulation of PPPs has a great economic impact on agriculture,
consumer and chemical industry. It strongly influences efficiency of
plant production, prices of plant-derived products, and costs and risks
of the development of PPPs. This, combined with its significance to the
quality of human and environmental health, makes it clear that the regulation of PPPs is of paramount importance for society. Thus all developed
countries have more or less elaborated regulatory systems. These virtually always consist of a registration or authorization process. Some PPPs
are allowed for well-defined applications (combinations of pests, crops
and application conditions). These combinations are included in positive
lists, i.e. they are registered. Other combinations are not allowed in those
countries.
It has been recognized by the governments of the Member States (MS)
of the European Union (EU) that the regulation of PPPs should not be
dealt with by them independently, but that collaboration between the
MS is necessary in this field, and that part of the regulatory framework
should be placed at the EU level. The legislative starting point for this
collaboration is Council Directive 91/414/EEC 'concerning the placing of
plant protection products on the market', here referred to further as 91/414/
EEC. This directive is the basis of a still-expanding regulatory framework.
The most important reason for regulating PPPs on the EU level is put into
words as follows in the preamble of 91/414/EEC: 'Whereas, in view of the
hazards, there are rules in most Member States governing the authorization
of plant health products; whereas these rules present differences which
constitute barriers not only to trade in plant protection products but also to
trade in plant products, and thereby directly affect the establishment and
operation of the internal market; Whereas it is therefore desirable to eliminate such barriers by harmonizing the provisions laid down in the Member
States;'.
This chapter tries to provide insight into the regulation of PPPs in the EU
as far as it is based on 91/414/EEC. The chapter mainly concentrates on
chemical PPPs, leaving biological PPPs aside. However, as the latter are
falling under the same directive, much of what will be put forward pertains
to them as well. Sections 11.2 and 11.3 present an overview of basic features
of 91/414/EEC in concise form. Some regulations and consequences are
dealt with in more detail in the subsequent sections. It is pointed out here
that the framework of EU legislation consisting of 91/414/EEC and associated directives, regulations and guidelines (see Appendix 11.A), is still not
complete and fully established. The implementation only started a few
years ago, when there were still clear gaps in the legislative framework.
Practice has led and will lead to changes and additional legislation. The art
is, so to speak, learned by doing. So this chapter can only present an outline
based on the situation as it is fixed in presently accepted and notified
directives, regulations and guidelines. In the future we will learn, to what
extent the plans and ideas, as they are reflected in these documents, show
themselves to be feasible.
11.2 Some basic features of 91/414/EEC
11.2.1 Which plant protection products?
91/414/EEC pertains to all plant protection products (PPPs) to be used in
the EU. PPPs are defined by 91/414/EEC (Article 2) as active substances
(ASs) or preparations containing ASs intended to:
• protect plants and plant products against all harmful organisms;
• influence the life processes of plants, other than as a nutrient (for
example growth regulators);
• preserve plant products, insofar as they are not subject to special provisions on preservation;
• destroy undesired plants (i.e. herbicides);
• destroy parts of plants, or check or prevent undesired growth of plants.
These include all PPPs, the active 'substance' of which is a microorganism
or a virus.1 The authorization of PPPs is solely based on the relevant
properties of the AS and the preparation. Directive 91/414/EEC is only
concerned with adjuvants as integral components of PPPs. The relevant properties of these compounds are not considered separately. Moreover, adjuvants are not authorized separately, irrespective of them being
added during the production process to the PPP or immediately prior to
use.
Directive 91/414/EEC does not pertain to pesticides not used for plant
protection purposes. For instance, an insecticide used to control cockroaches in houses is not regulated through 91/414/EEC, but through the
(draft) Biocide Directive, which is still in preparation. The same insecticide
may, however, be used to protect the harvest against losses caused by insect
damage, an application which falls under 91/414/EEC.
11.2.2 Authorization of active substances and plant protection products
A key feature of 91/414/EEC is the separate authorization of ASs and the
PPPs which derive their efficacy from these ASs, or which may solely
consist of an AS. ASs are authorized for the whole of the EU and placed on
a list attached to 91/414/EEC: Annex I. Annex I also lists conditions and
restrictions associated with the inclusion of the ASs. The authorization of
ASs is applied for with, and prepared by an MS, the so-called Rapporteur
1
This chapter is only concerned with chemical ASs and PPPs based thereon.
MS. However, it is finally decided upon, not by the competent authorities of
the Rapporteur MS, but by the Commission of the EU, after consultation
with experts from all MSs. Although ASs are authorized separately from
PPPs,2 authorization of the ASs is not solely based on their own relevant
properties, but also on relevant properties of at least one of the PPPs based
on them. So the applicant for the authorization of an AS has to submit a
dossier containing information on the relevant properties of the AS as well
as at least one PPP based on that AS. The authorization of PPPs containing
one or more ASs remains in the hands of the MSs, although it has to
occur along the lines made explicit in Annex VI of 91/414/EEC, the socalled Uniform Principles (Council Directive 94/43/EC). Obviously, these
authorizations pertain only to the use of the PPPs in the MS granting
authorization. Separate applications have to be made by the notifier
for authorization in another MS. However, as the JVISs must to a certain
extent recognize each other's authorization (the principle of mutual recognition, which is discussed later in this section), authorizations in other MSs
should at least require substantially less new data to be generated by the
notifier.
A MS can only authorize PPPs with active ingredients which are included
in Annex I of 91/414/EEC. This means that no data on the relevant properties of the AS have to be submitted in the context of a national authorization.3 These have already been submitted, summarized and evaluated in the
context of the inclusion of the AS in Annex I.
A notifier will hardly ever strive for the authorization of a new AS alone.
This means that the first authorization of a PPP in a MS will virtually always
go with the authorization of its AS at the EU level, the MS competent
authorities deciding on the PPP and the Commission on the AS.
11.2.3 Existing and new active substances
Directive 91/414/EEC distinguishes between
• existing ASs, which were already on the market within the EU 2 years
after the notification of 91/414/EEC (marketed before 25 July, 1993); and
• new ASs, the authorization of which is applied for after that date.
The existing ones are subject to a review programme, which must lead to a
decision as to whether they can be placed on Annex I. As long as they have
not passed this review programme, PPPs with these ASs will be dealt with
largely according to national authorization procedures, independently of
2
It is emphasized that a PPP can consist of an AS as the only component. This means that ASs
have to be included in Annex I (i.e. have to be authorized on the EU level), and at the same
time may be authorized as a PPP by a MS for use only in that MS.
3
Exposure data may be asked.
the provisions of 91/414/EEC and its associated legislative framework.
However, when they have passed the review programme and failed to be
placed on Annex I, PPPs based on them may no longer be used in the whole
of the EU. If the Commission decides to include them in Annex I, the
national authorizations have to be adapted accordingly. This means that it
has to be decided whether or not the current national authorizations already comply with 91/414/EEC. If not, the authorization has to be cancelled
or changed, possibly after the submission of additional data.
11.2.4 Harmonization of methods and procedures
Directive 91/414/EEC explicitly prescribes the studies required to obtain
insight into the relevant properties of ASs and PPPs, as well as the guidelines to be followed for their execution. The studies concerned with the
relevant properties of ASs are listed in Annex II of 91/414/EEC, and those
concerned with the relevant properties of PPPs are listed in Annex III. In
the original Directive these annexes consist of lists in which the studies are
merely mentioned; they are further elaborated in a series of amendments
of 91/414/EEC by the Commission (93/71/EEC, 94/37/EC, 94/79/EC,
95/35/EC, 95/36/EC, 96/12/EC, 96/46/EC).
Directive 91/414/EEC is further aimed at harmonization of the
• interpretation of the relevant properties;
• criteria for reaching decisions based on the relevant properties;
• administrative procedures.
This is put into effect by means of various additional directives and guidelines, the most notable being the Uniform Principles (Annex VI, Council
Directive 94/43/EC).
77.2.5 Quality standard
Directive 91/414/EEC is aimed at the establishment of a quality standard
for PPP authorization in the whole of the EU. This is illustrated by the
following citations from the preamble of 91/414/EEC:
Whereas the provisions governing authorization must ensure a high standard of
protection, which, in particular, must prevent the authorization of plant protection products whose risks to groundwater and the environment and human
and animal health should take priority over the objective of improving plant
production;
Whereas it is necessary at the time when plant protection products are authorized, to make sure that, when properly applied for the purpose intended, they are
sufficiently effective and have no unacceptable effect on plants or plant products,
no unacceptable influence on the environment in general, no harmful effect on
human or animal health or on groundwater;
The quality standard is defined by the whole of prescribed methods and
procedures, in particular in Annexes II, III and VI of 91/414/EEC.
11.2.6 Mutual recognition
The preamble of 91/414/EEC states
Whereas it is in the interests of free movement of plant products as well as
of plant protection products that authorization granted by one Member
State,... should be recognized by other member states, unless certain agricultural, plant health and environmental (including climatic) conditions relevant to
the use of the products are not comparable in the regions concerned;
In other words, the authorization of a combination of a PPP and application
in one MS should imply a registration of this combination in all other MSs,
provided that specific conditions in the other MSs do not lead to unacceptably different adverse side effects or an unacceptably reduced efficacy (see
Articles 10 and 11 of 91/414/EEC). Restriction or prohibition of an authorization by a MS based on 'specific conditions' can be overruled by the
Council of the European Communities.
This mutual recognition of PPP authorizations depends heavily on harmonization of methods and procedures and on the defined quality standard.
Directive 91/414/EEC and its associated legislation assure the other MSs
that the MS which initially granted the authorization did so, in principle
based on known, adequate and mutually accepted methods and procedures.
Furthermore, mutual recognition depends on the definition of 'conditions
relevant to the use of the products (which) are not comparable in the
regions concerned'. Whereas the harmonization of methods and procedures is made explicit by 91/414/EEC and its associated legislation, it is
often less clear when 'non-comparability of conditions' justifies forgoing the
recognition by one MS of the authorization by another MS.
11.2.7 Data protection
The following is stated in Article 13 of 91/414/EEC: 'In granting authorizations, Member States shall not make use of the information referred to in
Annex II for the benefit of other applicants:'. The same is stated about the
information referred to in Annex III. Thus 91/414/EEC seeks to guarantee
that the valuable data submitted by companies to support the authorization
of a PPP, with or without the concurrent authorization of the AS(s) present
in this PPP, cannot be used by competitors for authorization purposes. This
data protection expires after 10 years. In case of an existing, i.e. preDirective, AS, meanwhile included in Annex I, the 10 years start from the
date of authorization under the pre-Directive national regimens in each
MS, whereas data submitted to support the authorization of a 'new' AS are
protected for 10 years from the date the AS in question is included in
Annex I.
The attention of the reader is drawn to the fact that the 10-year period for
existing ASs may expire on different dates in the MSs depending on the
date of authorization under the pre-Directive national regime, while the 10year period expires for all MS at the same date in case of 'new' ASs. Data
submitted with the purpose of changing an inclusion in Annex I or extending it, are protected for a period of 5 years.
PPPs, i.e. preparations containing one or more ASs, are dealt with
slightly differently. When they are based on ASs already included in Annex
I, the data protection period (pertaining to Annex III data) lasts for 10
years, starting with the date of the first authorization in any MS. In cases
where PPPs have been authorized under the pre-Directive national regimens, but do contain ASs meanwhile included in Annex I, the data protection period (pertaining to Annex III data), is equal to that stipulated by the
national regimen, with a maximum of 10 years.
Data protection concerning ASs not included in Annex I, or PPPs containing such ASs,4 is not altered as long as the ASs are indeed not included
in Annex I. In other words, it is not regulated by 91/414/EEC.
11.2.8 Exemptions from the 'standard' authorization procedures
As has been set forth above, ASs which were authorized in any MS up to 2
years after the notification of 91/414/EEC, are exempted from the requirements for authorization set by 91/414/EEC, as long as no decision has been
reached as to their inclusion in Annex I in the framework of the review
programme. After this decision has been reached, the national authorization should be adapted so as to conform the authorization to the requirements set by 91/414/EEC.
Moreover, 91/414/EEC discerns certain situations in which 'Member
States must be enabled to authorize plant protection products not complying with the above mentioned conditions when it is necessary to do so'. The
reason explicitly mentioned is the occurrence of an 'unforeseeable danger
threatening plant production which cannot be countered by other means;'.
Such authorization should be evaluated retrospectively by the EU.
MSs are also allowed to authorize provisionally a PPP with an AS not yet
included in Annex I, i.e. not yet authorized for use in the EU, for a limited
period. However, the company seeking registration should then submit a
dossier which conforms to the requirements for such dossiers set by 91/414/
EEC, while the MS may only grant authorization when it expects the AS
and the PPP to satisfy the conditions for authorization set by 91/414/EEC.
During the provisional authorization term, a decision should be reached as
4
Which are thus authorized according to pre-Directive national legislation.
to the inclusion of the AS in Annex I. If such a decision has not been
reached at the end of the provisional authorization term, a new provisional
term is decided upon.
11.3 Overview of authorizations
Directive 91/414/EEC discerns the following types of authorizations.
• Active substances:
• Provisional authorization of a new (post-Directive) AS by a MS (Article 8.1 of 91/414/EEC). Pertains only to the MS in question. The
maximum term is 3 years. This term can be extended, if no decision is
reached by the Commission as to the inclusion in Annex I within 3
years. The term ends when such a decision is reached. If the AS is not
included in Annex I, the authorization cannot be extended; if it is,
authorizations of PPPs based on the provisional authorization of the
AS, must be adapted to the conditions associated with the inclusion in
Annex I by the Commission.
• Initial authorization of a new (post-Directive) AS by the Commission,
i.e. inclusion in Annex I (Article 5 of 91/414/EEC). It pertains to the
whole of the EU. The maximum term is 10 years. It forms the basis of
the authorizations of all PPPs which derive their activity from this AS
in every MS. Authorizations of PPPs may not conflict with the conditions associated with the inclusion in Annex I.
• Initial authorization of an existing (pre-Directive) AS by the Commission according to the review programme (Article 8 of 91/414/EEC;
Commission Regulation (EEC) No 3600/92), i.e. inclusion in Annex I.
It pertains to the whole of the EU. The maximum term is 10 years.
Existing national authorizations of PPPs should be adapted to the rules
of 91/414/EEC and the conditions associated with the inclusion in
Annex I. See further in section 11.6.
• Renewal of the authorization of an AS by the Commission, i.e. renewal
of the inclusion in Annex I (Article 5.5 of 91/414/EEC). It pertains to
the whole of the EU. The maximum term is 10 years. See further in
section 11.6.
• Transitional authorization to allow a decision by the Commission on
the renewal of an authorization of an AS (Article 5 of 91/414/EEC). It
pertains to the whole of the EU. It is valid for not longer than is
necessary for a decision to be reached by the Commission, provided
that the application for renewal is made 2 years before the current
authorization expires. See further section 11.6.
• National authorization of an existing (pre-Directive) AS after the
notification of 91/414/EEC (Article 8.2 of 91/414/EEC). It pertains
only to the MS in question. It is valid until the AS has passed the review
programme, but not longer than 12 years, as the review programme is
planned to be completed within 12 years upon the notification of
91/414/EEC. If the AS fails to be included in Annex I, the authorization cannot be extended; if it is, authorizations of PPPs based on the
authorization of the AS by the MS must be adapted to the conditions
associated with the inclusion in Annex I by the Commission.
• Plant protection products:
• Authorization for 'limited and controlled use of a preparation in a MS
because of unforeseeable danger which cannot be contained by other
means' (Article 8.3 of 91/414/EEC), irrespective whether or not the AS
is included in Annex I. It pertains only to the MS in question. The
maximum term is 120 days. During this period a decision is reached by
the Commission as to whether, and under which conditions this period
may be extended.
• Initial authorization by a MS of a PPP containing an AS included in
Annex I, following the Uniform Principles (Article 4 of 91/414/EEC;
Council Directive 94/43/EC). It pertains only to the MS in question.
The maximum term is 10 years.
• Renewal by a MS of the authorization of a PPP containing an AS
included in Annex I, following the Uniform Principles (Article 4.5 of
91/414/EEC; Council Directive 94/43/EC). It pertains only to the MS in
question. The maximum term is 10 years.
• Transitional authorization by a MS, to allow a decision on the renewal
of an authorization of a PPP containing an AS included in Annex I
(Article 4.5 of 91/414/EEC). It pertains only to the MS in question. The
term is the period necessary for a decision to be reached by the MS.
• National authorization of a PPP containing an existing (pre-Directive)
AS, after the notification of 91/414/EEC. It pertains only to the MS in
question, until the AS has passed the review programme. The maximum term is 12 years, as the review programme is planned to be
complete within 12 years upon the notification of 91/414/EEC.
• National authorization of a PPP existing before the notification of
91/414/EEC. It pertains only to the MS in question, until national
authorization expires.
11.4 Data requirements
The situation with respect to data requirements has changed in the EU with
the notification of 91/414/EEC. Since the end of July 1993 the data requirements set by 91/414/EEC, as defined by Annex II and Annex III of 91/414/
EEC, have been in force in all member States for ASs not yet placed on the
market in the EU at that time and for PPPs containing such ASs. For ASs
already on the market in the EU at the end of July 1993 and for the PPPs
Table 11.1 Amendments to Annex II and Annex III of Directive 91/414/EEC
Directive
Commission
Commission
Commission
Commission
Commission
Commission
Commission
Commission
Subject
Directive 93/71/EEC
Directive 94/37/EC
Directive 94/79/EC
Directive 95/35/EC
Directive 95/36/EC
Directive 96/12/EC
Directive 96/46/EC
Directive 96/68/EC
Introduction and efficacy
Physical and chemical properties
Mammalian toxicology
GLP requirements
Fate and behaviour
Ecotoxicology
Analytical methods
Residues
containing them, the Member States continue to apply their pre-Directive
national rules concerning data requirements, as long as the ASs have not
been re-evaluated at the EU level (i.e. have not passed the Review Programme; see section 11.8).
Annex II is only concerned with the relevant properties of the ASs,
whereas the relevant properties of the PPPs form the subject of Annex III.
However, as set forth in section 11.5, the inclusion of ASs in Annex I is not
based solely on Annex II information. Together with Annex II information,
Annex III information on at least one PPP containing the AS to be included
should be submitted. In a survey on data requirements for pesticide registration in OECD countries5 it was concluded that some EU countries already follow 91/414/EEC closely in their national legislation, while other
countries differ from 91/414/EEC on this point. It may be concluded that
the 91/414/EEC data requirements are comparable to the requirements of
MS as the Netherlands, the United Kingdom and Germany, with respect to
the range of relevant properties covered and the thoroughness with which
these topics have to be investigated. In general, the data requirements have
not become more lenient in the EU by the implementation of 91/414/EEC.
On the whole, standardization on a strict level is achieved.
The data requirements as put forward in the two annexes have been
amended by several Commission Directives which are presented in Table
11.1. While the original annexes merely list the requirements, these amendments provide a more detailed description of the information required, the
conditions under which it is required and the way it should be presented.
The scope of the present chapter does not permit a full presentation of
the contents of Annex II and Annex III and the amendments listed in Table
11.1. Nevertheless, the main subjects covered by the annexes are presented
in Table 11.2.
5
OECD, Organisation for Economic Co-operation and Development (1994) Data requirements for pesticide registration in OECD member countries: survey results. Environment
Monograph No. 77, Paris.
Table 11.2 Subjects covered by Annex II and Annex III for chemical active substances and
plant protection products
No. in Anne?L
Annex II
1
2
3
4
5
6
7
8
9
10
Annex III
1
2
3
4
5
6
7
8
9
10
11
12
Required data
Identity of the active substance
Physical and chemical properties of the active substance
Further information on the active substance (function, field of use, mode of
action, emergency measures in the case of an accident, etc.)
Analytical methods
Toxicological and metabolism studies on the active substance (acute
toxicity, short-term toxicity, long-term toxicity, reproductive toxicity,
metabolism studies in mammals, supplementary studies, medical data)
Residues in or on treated products, food and feed
Fate and behaviour in the environment (fate and behaviour in soil, fate and
behaviour in water and air)
Ecotoxicological studies on the active substance (effects on birds, aquatic
organisms and other non-target organisms)
Summary and evaluation of points 7 and 8
Proposals including justification for the proposals for the classification
and labelling of the active substance according to Council Directive
67/548/EEC (hazard symbols, indications of danger, risk phrases, safety
phrases); in most cases guideline 93/21/EEC is used for this purpose
Identity of the plant protection product
Physical, chemical and technical properties of the plant protection product
Data on application
Further information on the plant protection product (packaging, re-entry
periods, procedures for destruction or decontamination of the plant
protection product and its packaging, etc.)
Analytical methods
Efficacy data
Toxicological studies (acute toxicity, operator exposure)
Residues in or on treated products, food and feed
Fate and behaviour in the environment
Ecotoxicological studies (effects on birds, aquatic organisms and other nontarget organisms)
Summary and evaluation of points 9 and 10
Further information (information on authorizations in other countries,
information on established maximum residue limits in other countries,
proposals including justification for the classification and labelling
proposed in accordance with Directive 67/548/EEC and Directive
78/631/EEC)
Directive 91/414/EEC requires a full description of the studies conducted, including the methods applied, or bibliographical references to
studies and methods. The requested information should be obtained from
studies which are performed in accordance with test methods described in
Annex V to Directive 79/83 I/EEC or, in the event of a method being
inappropriate or not described, other methods used should be justified.
Moreover, guidelines should be used as proposed by Council Directive
67/548/EEC and its annexes (such as 87/302/EEC and 92/69/EEC). These
guidelines set out test methods for the determination of physico-chemical,
toxicological and ecotoxicological properties and are mainly based on
OECD guidelines. For residues, a draft guideline is available ('Guideline
for the establishment of community maximum residue levels of plant protection products in food and feedstuff of plant and animal origin'}. Tests must
be conducted in accordance with the requirements of Directive 86/609/EEC
(animal health care) and the principles laid down in Directive 87/18/EEC
(good laboratory practice).
Not all the information mentioned in Annex II and Annex III needs to be
submitted for authorization. Depending on the nature of the substance, its
proposed use, scientific necessity or technical feasibility, some information
may be omitted. However, in such cases, a justification for the absence
should be submitted. When, and on which basis, the information should be
provided for authorization of the active substance and PPP is described in
the amendments of 91/414/EEC (Table 11.1).
11.5 Dossier preparation
For the inclusion of an active substance, either new or existing, in Annex I
(sections 11.6 and 11.8), a dossier should be submitted which satisfies the data
requirements specified by Annex II and Annex III. This dossier should not
only contain study reports or other primary documents concerned with the
requirements of the two annexes, but also a number of additional documents,
which are specified in Document 1663/VI/94, revision 7.2. These documents
include summary reports for individual studies and 'primary information' as
well as summary reports covering the different topics of the annexes on
differents levels of integration. Moreover, the notifier has to submit information on the scope and purpose of the dossier and an evaluation which shows
why the inclusion is regarded as being justified. The content and structure of
the Annex I inclusion dossier is described in this section.
For authorization of a PPP which is based on ASs already included in
Annex I by an MS (section 11.7), a dossier has to be submitted to that MS
which contains the information required by Annex III of Directive 91/414/
EEC. As no explicit Community rules exist for such dossiers, they may
differ from MS to MS, as long as they indeed are based on Annex III.
However, in many cases, the Annex I inclusion dossier may also be used for
the authorization of PPPs, as it should cover Annex III information on at
least one PPP containing the AS. The dossier should contain the following
documents.
(a) Document A.
is submitted.
Contains statement of the context in which the dossier
(b) Document B. Contains contacts with other notifiers.
(c) Document C. Contains copies of existing labels for each of the new
preparations for which an Annex III dossier is submitted.
(d) Document D. Contains details of approvals held for the active ingredient issued by the Competent Authorities of the MS.
(e) Document E. Contains details of uses and conditions of use: good
agriculture practice.
(f) Document F. Commission regulation (EEC) No 3600/92 Notification.
In case of existing ASs, a copy of each notification submitted to the Commission in the context of the programme of work undertaken for the examination of existing ASs.
(g) Document G. Contains coformulant information: permitted uses in
food, animal feeding stuffs, medicines and cosmetics in accordance with
community legislation.
(h) Document H. Contains coformulant information: safety data sheets in
accordance with directive 67/548/EEC.
(i) Document I. Contains coformulant information: further information.
(j) Document J. Contains confidential information.
(k) Documents K-II and K-III. Original test and study reports (and other
primary informations) should be submitted, to provide the required information on the relevant properties of the AS (Annex II) and at least one
PPP (Annex III). All reports should be divided into six sections, as presented in Table 11.3.
(I) Documents L-II and L-III. Summaries of Annex II and Annex III
dossiers should contain a report on the acceptability of the quality of each
individual test and study submitted. These summaries represent the first
summarizing tier (Tier I). Those reports should be assembled in six sections, as presented in Table 11.3, and should take the form as specified in
Document 1663/VI/94, revision 7.2,1996. In Tier I attention should be given
to the following subjects.
• When methods are used, other than those specified in Annex II and
Annex III, a detailed description of these methods, the reason for their
choice, and their scientific validity and comparability with the methods
specified in Annex II and Annex III should be provided.
Table 11.3 Main headings of the sections in Documents L-II/III (Tier I), and M-II/III (Tier II)
Section
1
Headings and corresponding Annex II and Annex III points3
Identity (IM, III-l)
Physical and chemical properties (II-2, III-2)
Data on application (III-3)
Further information (II-3, III-4)
Efficacy data (III-6)
Proposals for the classification and labelling (IMO, III-12.3)
Proposals for risk and safety phrases and proposed label (II-5.1 and 5.2)
2
Analytical methods (II-4.1 and 4.2, III-5.1 and 5.2)
3
Toxicological and metabolism studies (II-5)
Toxicological studies (III-7)
4
Residues in or on treated products, food or feed (II-6, III-8 and 12.2)
5
Fate and behaviour in the environment (II-7, III-9)
6
Ecotoxicological studies (II-8, 111-10)
a
Indications in parentheses show the annex by which the information is required as well as the
points of the annex addressed.
• Reference to the compliance with requirements of GLP (good laboratory
practice) or reasoned justification in the case of non-compliance.
• Residue data from supervised field trials should be compiled using the
standard EC form, ensuring that data relevant to all critical GAPs for
which community MRLs are proposed, are included. The data should
be grouped by crop and within crops by country in which trials were
conducted.
• A list of all tests and study reports, test guidelines and published papers
submitted with the dossier or other test and study reports or published
papers of which the notifier is aware, form the final part of Tier I. Within
the six sections, the documents should be listed alphabetically by author.
• In case of tests and studies known to the notifier but not submitted, a
separate list of these documents, listed alphabetically by author, should
be attached at the end of each of the six sections (see Table 11.3).
(m) Documents M-II and M-III. Summaries of the Annex II and Annex
III dossier for each section (Table 11.3). These summaries represent the
second summarizing tier (Tier II). The Tier II summaries should contain a
discussion and interpretation of the results of all Annex II and Annex III
studies, and within each of the six sections (Table 11.3) conclusions are
reached.
A concise summary of each individual test and study should be included.
Each summary should include the following elements, when applicable:
• the reference number of the test or study;
• the appropriate test or study reference;
•
•
•
•
•
the test guideline and method used;
relevant GLP and GEP information;
a brief description of the methodology used;
a concise tabular presentation of the findings with supporting text;
the conclusions reached.
Within each section a reasoned statement should be included of the conclusions reached by the notifier on the basis of the data and information
submitted, taking into account:
• the weight of evidence of the data available (quality and consistency of
the data);
• the criteria specified in Article 5 of Directive 91/414/EEC;
• the criteria and guidelines for evaluation and decision making with respect to the inclusion of active substances in Annex I;
• the evaluative and decision-making criteria specified in Annex VI, where
they are relevant.
(n) Document N. An overall assessment of all the information in the
dossier. This Document represents the third tier (Tier III). The Tier III
summary includes an integration of the results obtained and the conclusions
reached by the notifier on the basis of the Annex II and Annex III tests,
studies and information provided. This information should be integrated
and presented in a standard order as shown in Table 11.4.
The information presented should:
• address and interpret all important elements (as presented in Table
11.4) taking into account the quality and consistency of the data base as
well as the criteria and guidelines referred to in previous tiers of the
dossier;
• include proposals relating to the necessary conditions and restrictions for
the inclusion in Annex I;
• include proposals for the comparability of the conditions under which
studies were conducted in one region to the conditions in other regions,
together with the reasoning for the extrapolations proposed;
• include proposals for the classification and labelling of the active
substance;
• establish the rationale for the proposed inclusion of the active substance
in Annex I.
(o) Document O. Document O consists of forms used by the competent
authority of the MS for the completeness check of the dossier (initial
valuation; section 11.6). The forms should be completed by the notifier and
should be submitted as part of the application for inclusion in Annex I. The
following forms should be submitted.
Table 11.4 Document N (Tier III); order in which the reasoned statement of the conclusions
reached should be presented
Chapter
Contents
1
Identity
2
Physical and chemical properties
3
Details of uses and further information
4
4.1
Impact on human and animal health
Effects arising from exposure to the active substance or their transformation
products
ADI
AOEL
Drinking water limit
Impact arising from exposure to the active substance or to impurities contained
in it
4.2
4.3
4.4
4.5
5
5.1
5.2
5.3
Methods of analysis
For the active substance as manufactured
For the formulation
For the residues
6
6.1
6.2
Definition of residues
Relevant to MRLs
Relevant to environment
7
7.1
7.2
7.3
7.4
Residues
Relevant to consumer safety
Relevant to worker safety
Proposed EU MRLs and compliance with existing EU MRLs
Proposed EU import tolerances and compliance with existing EU import
tolerances
8
8.1
8.2
8.3
Fate and distribution in the environment
Fate and behaviour in soil
Fate and behaviour in water
Fate and behaviour in air
9
9.1
9.2
9.3
9.4
9.5
9.6
9.7
Effects on non-target species
Effects on terrestrial vertebrates
Effects on aquatic species
Effects on bees and other arthropod species
Effects on earthworms and other soil macroorganisms
Effects on soil microorganisms
Effects on other non-target organisms (flora and fauna)
Effects on biological methods of sewage treatment
10
Classification and labelling
11
Overall conclusions
12
Proposed decision
13
Further information to be submitted
• Evaluation form 1, for checking that the required supporting documentation has been provided (Documents A-J).
• Evaluation form 2, for checking that the required Annex II and Annex
III dossier summaries and an overall assessment have been provided
(Tier I, Tier II and Tier III).
• Evaluation form 3, for checking that all test and study reports required in
accordance with Annex II have been provided (Documents K-II).
• Evaluation form 4, for checking that all test and study reports required in
accordance with Annex III have been provided (Documents K-III).
In addition Document O consists of forms for checking the acceptability of
the quality of individual test and study reports. It is not necessary to submit
these forms completed.
• Evaluation form 5, for checking that the Tier I quality checks for individual test and study reports are themselves of acceptable quality.
• Form 6, listing of the test guidelines specified and the requirements
relating to compliance with GLP and GEP for individual Annex IIA tests
and studies.
• Form 7, listing of the test guidelines specified and the requirements
relating to compliance with GLP and GEP for individual Annex IIIA
tests and studies.
Moreover, in Document 1663/VI/94, revision 7.2, 1996, some guidance is
provided for the required presentation and format of the documents to be
submitted.
11.6 Inclusion of active substances in Annex I of 917414/EEC
11.6.1 Introduction
The following general requirements are mentioned in Article 5 of 91/414/
EEC for the inclusion of ASs in Annex I of 91/414/EEC:
an active substance shall be included in Annex I . . . , if it may be expected that
the plant protection products containing the active substance will fulfil the following conditions:
(a) their residues, consequent on application consistent with good plant protection practice, do not have any harmful effects on human or animal health or
on groundwater or any unacceptable influence on the environment, and the
said residues, in so far as they are of toxicological or environmental significance, can be measured by methods in general use;
(b) their use, consequent on application consistent with good plant protection
practice, does not have any harmful effects on human or animal health or any
unacceptable influence on the environment as provided for
This citation makes it clear that the inclusion in Annex I does not depend
solely on the toxicological and other relevant properties of the ASs. Also
relevant is to what extent these properties are expected to lead to undesired
effects when PPPs with these ASs are actually applied. We see here that the
Annex III information plays a dual role: it supports both the Annex I
inclusion of the AS in question on the EU level, and the authorization of the
PPPs based on this AS on the MS level. However, the same holds for the
Annex II information. In addition to its role in the inclusion procedure,
this information is also used when PPPs are authorized by the MSs,
although in the form of an extensive summary, the so-called monograph
(section 11.7).
One AS can be a component of many different PPPs, which may be used
for different purposes and in different manners. An AS may give rise to
undesired effects when involved in one combination of PPP and application, while being devoid of such effects in case of another combination.
However, 91/414/EEC explicitly states that for a new AS the general
requirements cited above are 'deemed to be satisfied where this has been
established for at least one preparation containing the said active substance'. This means that the choice of the first PPP-application combination
by the notifier is very important with respect to the possibilities of inclusion
of the AS.
It may be expected that inclusion in Annex I of a new AS will always be
applied for together with an application for the authorization of use of one
or more PPPs containing these ASs in one or more MSs. It is hardly useful
for a notifier to apply only for an inclusion of the AS in Annex I, while
postponing the application for use in the MSs. Consequently, the dossier
submitted will always serve both purposes. This section deals only with
what is done with the dossier to reach a decision on the inclusion of the AS
in Annex I.
Annex I does not just list compound names; conditions for inclusion can
also be defined. These conditions are, of course, mentioned in Annex I as
well. They may pertain to purity, identity and levels of impurities, types of
PPP which may contain the AS, manner of use, and agricultural, plant
health and environmental conditions. Thus Annex I may confine possible
applications of ASs by specifying binding conditions. Authorizations of
PPPs by a MS can only be granted if these conditions are not violated. For
instance, PPPs shall not be authorized for use under environmental conditions, by means of application techniques, in crops, against target organisms, or in regions or on soils which are explicitly excluded in Annex I for
one of the ASs on which their effectivity is based. Moreover, the ASs have
to be as pure as required by Annex I, while levels of certain impurities may
not be higher than required. Annex I may also restrict the ASs to certain
types of PPPs, or may exclude certain types of PPPs from containing an AS.
In this way the inclusion of ASs anticipates the authorization of PPPs by
MSs for applications under conditions which are deemed incompatible by
the EU in view of the desired protection of humans and the environment.
Recent developments point to the possibility of including the submission
of additional information within a certain term as a condition for the Annex
I inclusion of an AS. In other words, it seems that an AS can be included
while all the information deemed necessary for a full evaluation of its
relevant properties has not yet been submitted, as long as this submission
occurs within a certain period of time. The Annex I inclusion procedure
consists of three basic phases:
1. checking the adequacy for evaluation of the dossier (initial evaluation)
by the competent authorities of the MS;
2. detailed evaluation of the dossier by the competent authorities of the
MS, resulting in a summary report with recommendations: the monograph;
3. the decision phase, which occurs at the EU level and which is largely
based on the monograph.
77.6.2 Initial evaluation
The initial evaluation consists of a careful check by the competent
authority of the Rapporteur MS, as to whether the dossier actually contains
the information required by 91/414/EEC. It must cover all the points
listed in Annex II and Annex III. Furthermore, the various summaries
required should be present in the dossier (Document 1663/VI/94; section
11.5).
To facilitate the initial evaluation, the notifier has to fill in a number of
separate initial-evaluation forms which are part of Document O of the
dossier (Appendix 4 of Document 1654/VI/94; section 11.5). The initial
evaluation is largely based on these forms. In addition, it is suggested that
a limited number of Tier I summaries be examined for compliance with the
guidelines for summarization (Document 1663/VI/94). Tier I is also used to
check whether:
• the necessary studies have been carried out;
• justifications for not performing the relevant studies are present;
• it is indicated when missing information will become available.
When the dossier is found to be inadequate for reaching a decision on
inclusion in Annex I, the notifier is informed accordingly and given the
opportunity to fill the gaps. When adequate:6
• the initial-evaluation forms are sent to the Commission and to the other
MSs;
6
Possibly after a revision.
• the Commission officially establishes the adequacy of the dossier (Article
6.3 of 91/414/EEC);
• the dossier is sent to the Commission and the other MSs;
• the Rapporteur MS starts to prepare the monograph.
11.6.3 Detailed evaluation and the preparation of the monograph
The detailed evaluation of the dossier starts with the preparation of the
monograph by the Rapporteur MS. Document 1654/VI/94 (Revision 5)
states that 'Monographs should be sufficiently comprehensive to permit
decisions to be made without the need for further reference to individual
study reports and supporting documentation.' This citation reveals the
pivotal role of the monograph. It can justly be regarded as the corner stone
of the Annex I inclusion procedure, because it virtually replaces the dossier
after its completion. Moreover, as will be set forth in section 11.7, the
monograph also plays an important role in the authorization of PPPs based
on the AS in question according to the Uniform Principles (Annex VI of
91/414/EEC; Directive 94/43/EC).
The preparation of the monograph places much influence and
reponsibility in the hands of the competent authority of the Rapporteur
Table 11.5 Standard outline of the monograph (from Document 1654/VI/94, Revision 5)
Part
Contents
Volume 1 Level 1
Level 2
Level 3
Level 4
Statement of subject matter and purpose for which the monograph
was prepared
Reasoned statement of the overall conclusions which the
Rapporteur MS believes should be reached on the basis of the
data and information provided, or available, taking account of
relevant evaluative and decision-making criteria
Proposed decision with respect to the application for inclusion of
the active substance in Annex I, the proposed conditions and
restrictions to be associated with any inclusion, together with a
reasoned statement as to the reasons therefor, taking into
account relevant evaluative and decision-making criteria
Statement of the studies and information believed necessary to
permit a decision to be made, or a statement of the studies and
information necessary for the removal of any conditions or
restrictions associated with the the inclusion in Annex I
Volume 2 Annex A
Listing of the available data and information
Volume 3 Annex B
Summary, evaluation and assessment of data and information
submitted or available, in the light of relevant evaluative and
decision-making criteria, providing the scientific background to
the conclusions reached and proposals made at levels 2 to 4,
together with a list of the tests and studies relied upon for
conclusions reached
Volume 4 Annex C
Confidential information
MS. Although the monograph is discussed in, and may be amended by
several EU expert groups, the scene has, so to speak, been set by the
monograph, which is prepared by the Rapporteur MS. The notifier strongly
depends on the competent authority of the Rapporteur MS for a wellbalanced summary and interpretation of its valuable data in the form of the
the monograph. The monograph consists of so-called levels, in which the
overall results and conclusions of the detailed evaluation and the recommendations based thereon are reported, and annexes which contain details.
The standard outline is presented in Table 11.5 (Document 1654/VI/94).
Table 11.5 indicates that the outline of the monograph resembles the
structure of the dossier (section 11.5). The relation between monograph
and dossier is further illustrated by Table 11.6. This table shows the documents in the dossier on which the various parts of the monograph are based.
(a) Level 1: subject matter and purpose. The first part of the monograph
serves to answer questions regarding
• the purpose of the monograph;
• the identity of the AS and the PPPs concerned;
• the intended use of the PPPs.
With respect to the first question, five answers are possible:
• a first inclusion of a new AS, i.e. an AS not yet on the market in the EU
2 years after the notification of 91/414/EEC;
• a first inclusion of an existing AS, i.e. an AS already on the market in the
EU 2 years after the notification of 91/414/EEC;
• a modification or removal of restrictions or conditions associated with the
first inclusion;
• a special review of the inclusion because the conditions of inclusion are
no longer met;
• the renewal of the inclusion.
The question regarding the identity of the AS and the PPPs based
thereon should be answered not only in terms of names, codes, chemical
Table 11.6 Relationship between monograph and dossier
Part of monograph
Documents in dossier
Volume 1 Level
Level
Level
Level
A, C-E, J-L
G-I, N and O
O
G-J, L and M
1
2
3
4
Volume 2 Annex A
I-L
Volume 3 Annex B
C and E, G-M
Volume 4 Annex C
B and J
formulae and compositions, but also by providing information on purity,
impurities, methods of chemical analysis and methods of manufacture.
The third question requires information on the type of target organism,
mode of action, the crop, plant products, and existing authorizations (in
case of existing ASs).
(b) Level 2: conclusions of the detailed evaluation. The detailed evaluation is presented in Annex B of the monograph (section 11.6.3(f)). Level 2
serves as a summary of this annex in the form of a series of concise conclusions regarding the various points addressed by Annex II and Annex
III. These conclusions should make it clear which effects ('nature and
significance') are to be expected under normal and worst-case conditions
determining exposure, based on a weight-of-evidence analysis ('extent,
quality and consistence of the data concerned').
Obviously, the conclusions should in particular be concerned with the
criteria specified in Article 5 of 91/414/EEC. Furthermore, Annex VI of 91/
414/EEC (the Uniform Principles; Directive 93/43/EC) should be used as a
guidance, as far as the PPPs are concerned. Finally, Document 1654/VI/
94 Revision 5 mentions 'criteria and guidelines for evaluation and decision
making with respect to the inclusion of active substances in Annex I,
where available'. However, such criteria and guidelines have not yet been
published.
The conclusions are not solely based on Annex II and Annex III. Document 1654/VI/94 Revision 5 states that the assessment of the notifier of the
data (Documents N and O of the dossier) should be taken into account. In
the case of non-active substances (formulants or adjuvants), their use in
food, animal feed, medicines and cosmetics in accordance with EU legislation, relevant safety data sheets and other relevant toxicological information should be considered (Documents G, H and I of the dossier).
Moreover, relevant information available to the evaluators which is not
present in the dossiers should be taken into account.
(c) Level 3: proposed decision concerning inclusion, conditions and
restrictions. The competent authority of the Rapporteur MS proposes the
decision to be taken as regards the inclusion. This decision is presented in
Level 3 of the monograph, together with its rationale in the form of 'a full
and reasoned statement'. It can be proposed to include or not to include the
AS, to remove the AS or, in case of existing ASs, to postpone a decision
pending additional information. Obviously, the rationale should be based
on the criteria specified in Article 5 and Annex VI (the Uniform Principles)
of 91/414/EEC, and specific Annex I inclusion guidelines and criteria yet to
be published. When it is decided to include the AS in Annex I, the conditions and restrictions are mentioned together with a reasoned statement.
The conditions may include 'specified tests and study reports to be submitted by specific deadlines' .
(d) Level 4: additional information necessary. In case the decision is postponed, it is stated in Level 4 which additional information is required to
enable a decision on inclusion or removal to be taken. Moreover, the
information necessary for the removal of conditions or restrictions associated with an inclusion is indicated here.
(e) Annex A: list of the available information. Annex A of the monograph consists of a detailed list of all the information present in the
dossier or otherwise available to the Rapporteur MS, including references
of documents, study reports and publications, the guidelines followed,
whether or not studies comply with GLP, and the owner of study
reports.
(f) Annex B: summary, evaluation and assessment of information. Annex
B is by far the bulkiest part of the monograph. It represents the core
of the detailed evaluation by the competent authorities of the MSs. It is
the scientific basis of the decision as to the inclusion of the AS. It consists
of
• summaries of all the study reports as well as other submitted or otherwise
available information;
• overall summaries for each of the headings in Annex II and Annex
III.
Moreover, the quality of the information is assessed. Important in this
respect are:
• the completeness of the information in view of what is required by Annex
II and Annex III;
• the execution of studies according to the prescribed guidelines;
• the validity of studies which deviate from these guidelines;
• the validity and value of studies and other information not specifically
required by Annex II and Annex III;
• the execution of studies according to quality guidelines such as GLP;
• the validity of justifications for not providing required information;
• the acceptability of studies and other information for evaluation
purposes.
For each heading of Annex II and Annex III, the information is evaluated
in the light of the criteria defined in
• 91/414/EEC (Article 5);
• Annex VI of 91/414/EEC (the Uniform Principles);
• additional Annex I inclusion criteria and guidelines which are yet to be
published.
This evaluation is based on a weight-of-evidence analysis by Annex II and
Annex III headings. The whole of the information is thereby taken into
account, allowing questionable information to be compensated by goodquality information.
Annex B also contains the derivation of the acceptable daily intake
(ADI), the acceptable operator exposure level (AOEL), the drinking-water
limit and the maximum residue level (MRL).
(g) Annex C: confidential information. All information claimed to be confidential by the notifier and recognized accordingly by the Rapporteur MS
is included in Annex C, together with the rationale for this inclusion. Annex
C pertains in particular to detailed specifications of PPPs, manufacturing
details and to medical data. Moreover, this annex presents all steps taken by
notifiers of an existing (pre-Directive) AS to submit a collective dossier in
the framework of the review programme (section 11.8) when they failed to
do so.
The information in Annex C is not present in other parts of the monograph or in published versions of the monograph.
Table 11.7 Summary of the Annex I inclusion procedure for new active substances (according to 91/414/EEC, Commission Regulation (EEC) 3600/92, and Document 1654/VI/94,
Revision 5)
Order
Activity or decision
Remarks
1
Submission of dossier with Annex II data for
the As and Annex III data for at least one
PPP based on the As
2
Completeness check by the Rapporteur MS is 'Without excessive delay'
sent to the Commission and other MSs.
3
Submission of additional data until
completeness has been reached
No term specified
4
Dossier is sent to the Commission and all
other MSs
'Without excessive delay'
5
The Commission sends the dossier to the
Standing Committee on Plant Health (SCPH)
6
Decision on acceptability of dossier by
Commission or Council
Within 3-6 months after the SCPH
has received the dossier
7
Composition of monograph by the
Rapporteur MS
Within 12 months after the dossier
has been found to be acceptable
(see 6)
8
Decision upon inclusion in Annex I by
Commission or Council
9
Submission of additional data, if requirement
is a condition of the inclusion
Term specified in decision (see 8)
10
Composition of revised monograph by the
Rapporteur MS
Within 9 months of the submission
of the additional data
11
Decision upon inclusion in Annex I by
Commission or Council
The notifier chooses a MS to which
the dossier is submitted. This MS
acts as Rapporteur MS
11.6.4 Procedure
The Annex I inclusion procedure is presented in summarized form in Table
11.7, as far as it is explicitly described in 91/414/EEC and associated legislation. The Standing Committee on Plant Health (SCPH) consists of representatives from all MSs and advises the Commission on questions regarding
plant health, among them questions in the context of the authorization of
ASs.
Decisions are normally taken by the Commission following the advice of
the SCPH. When the Commission does not agree with the Committee, it
submits a proposal to the Council of Ministers, which makes a decision.
However, when the Council does not reach a decision within a specified
term, the decision is automatically taken according to the proposal of the
Commission. In the case of the Annex I inclusion, the Council has a period
of three months to decide.
11.7 Authorization of plant protection products
11.7.1 General requirements
PPPs are authorized separately by the competent authorities of each MS for
use in its national territory. No general authorization procedure for the
whole of the EU exists, although the principle of mutual recognition ought
to make authorizations a lot easier after an authorization has been granted
by one MS. The European competent authority (Commission, Council or
Standing Committee on Plant Health) does not take an active part in the
authorization of PPPs, but leaves the procedure and the decision in the
hands of the competent authority of the MS. It has only established
the prior conditions in the form of 91/414/EEC and associated EU
legislation.
According to 91/414/EEC, PPPs can either be pure ASs, or PPPs the
effectiveness of which is due to the presence of one or more ASs. Inclusion
of ASs in Annex I of 91/414/EEC should not be regarded as an authorization of their use as PPPs. It only represents the fulfilment of the first of a
series of requirements for the authorization of the use of PPPs, whether
they consist solely of ASs or contain ASs in addition to other, non-active
substances, such as adjuvants. In addition, the following general requirements are listed in 91/414/EEC:
•
•
•
•
sufficient effectivity;
no unacceptable effects on plant or plant products;
no unnecessary suffering and pain to vertebrates to be controlled;
no harmful effects on human and (domestic) animal health, by direct
exposure or through drinking water, food or fodder;
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11.6.4 Procedure
The Annex I inclusion procedure is presented in summarized form in Table
11.7, as far as it is explicitly described in 91/414/EEC and associated legislation. The Standing Committee on Plant Health (SCPH) consists of representatives from all MSs and advises the Commission on questions regarding
plant health, among them questions in the context of the authorization of
ASs.
Decisions are normally taken by the Commission following the advice of
the SCPH. When the Commission does not agree with the Committee, it
submits a proposal to the Council of Ministers, which makes a decision.
However, when the Council does not reach a decision within a specified
term, the decision is automatically taken according to the proposal of the
Commission. In the case of the Annex I inclusion, the Council has a period
of three months to decide.
11.7 Authorization of plant protection products
11.7.1 General requirements
PPPs are authorized separately by the competent authorities of each MS for
use in its national territory. No general authorization procedure for the
whole of the EU exists, although the principle of mutual recognition ought
to make authorizations a lot easier after an authorization has been granted
by one MS. The European competent authority (Commission, Council or
Standing Committee on Plant Health) does not take an active part in the
authorization of PPPs, but leaves the procedure and the decision in the
hands of the competent authority of the MS. It has only established
the prior conditions in the form of 91/414/EEC and associated EU
legislation.
According to 91/414/EEC, PPPs can either be pure ASs, or PPPs the
effectiveness of which is due to the presence of one or more ASs. Inclusion
of ASs in Annex I of 91/414/EEC should not be regarded as an authorization of their use as PPPs. It only represents the fulfilment of the first of a
series of requirements for the authorization of the use of PPPs, whether
they consist solely of ASs or contain ASs in addition to other, non-active
substances, such as adjuvants. In addition, the following general requirements are listed in 91/414/EEC:
•
•
•
•
sufficient effectivity;
no unacceptable effects on plant or plant products;
no unnecessary suffering and pain to vertebrates to be controlled;
no harmful effects on human and (domestic) animal health, by direct
exposure or through drinking water, food or fodder;
• no harmful effects on groundwater;
• no unacceptable influence on the environment, with particular regard to
• fate and distribution in the environment;
• impact on non-target species;
• the possibility to determine the nature and quantity of ASs in the PPP, as
well as any toxicologically or ecotoxicologically significant and relevant
impurities and coformulants (including adjuvants);
• the possibility to determine residues caused by authorized use, as far as
these are (eco)toxicologically significant;
• the provisional establishment and notification for approval to the Commission of maximum residue levels (MRLs).
11.7.2 The Uniform Principles
The authorization of PPPs by the MSs has to proceed along the lines
presented in the Uniform Principles (UP) (Annex VI of 91/414/EEC; Council Directive 94/43/EC). A discussion on the UP, at the time of writing, has
to start with informing the reader that these principles were annulled by the
European Court of Justice in 1996 on formal grounds, not related to the
contents itself. This means that they are not valid at the time of writing. It
lies beyond the scope of this chapter to go into details regarding the reasons
why. It is assumed here that the annulment will be undone, after as yet
unknown alterations of the UP. It was not possible to anticipate these
alterations, and thus this section proceeds as if the UP have not been
annulled. The UP are concerned with the evaluation of the data on the
relevant properties (evaluation phase of the authorization) and the criteria
for granting or refusing the authorization (decision phase of the authorization).
The starting point for the evaluation and the decision on the authorization consists of
• the Annex III data submitted to the competent authorities (section 11.4);
• the monograph prepared in the course of the inclusion of the AS in
Annex I (sections 11.6 and 11.8);
• all relevant technical and scientific information which can reasonably be
regarded as accessible and which pertains to efficacy and adverse side
effects;
• argumentations by the notifier for the omission of data required by
Annex III.
Additional data and argumentations may be submitted after the submission of the initial dossier by the notifier during the evaluation phase. The
UP prescribe that during this phase, the competent authority should cooperate with the notifier to
•
•
•
•
solve problems as regards the adequacy of the dossier;
identify gaps in the dossier at short notice;
allow changes of the proposed uses;
allow changes of the PPP.
This is to facilitate adaptation of the dossier to the requirements during the
evaluation phase. No adaptation of the dossier is possible during the decision phase.
The UP stipulate that, taking into account information provided in a later
phase as well as argumentation for omitting the submission of data, the
whole application for authorization should be turned down when it is not
adequate for at least one of the proposed sub-applications.7
The decision on the authorization has to be reached 12 months from the
date when the dossier reaches compliance with Annex III, i.e. the decision
phase may not last longer than 12 months. No maximum term is prescribed
by the UP for the evaluation phase.
11.7.3 Evaluation
The UP discern two evaluation levels:
• an initial evaluation based on the best and most relevant data and estimations, based on realistic conditions of use;
• a repeated evaluation which is in particular concerned with the remaining
uncertainties and doubts, and is based on realistic worst-case scenarios as
regards the conditions of use.
The evaluation must take into account the aspects listed hereunder. It
should to be emphasized that the scope of the present chapter does not
allow a complete treatment of the aspects evaluated. A selection was made
of the major aspects, but various obvious ones were omitted.
• Aspects concerning the effects of the PPP on organisms to be controlled,
plants (crops) and plant products:
• crop or plant-product improvement achieved through the application
of the PPP;
• damage to crops or plant products caused by the organism to be
controlled;
• consequences of not using the PPP when it is not aimed at the control
of a pest or disease organism;
• damage to crops or plant products caused by the PPP due to its
phytoxicity;
• effects on crops or plant products not meant to be treated;
7
An application may include different uses (here referred to as sub-applications) of one PPP.
• effects due to residues in soil or on the crop or plant product;
• comparison with 'reference' PPPs;
• in case a vertebrate has to be controlled: effects on behaviour, health,
time between treatment and death, conditions under which the animals
die (suffering).
• Aspects concerning the exposure of persons applying the PPP:
• exposure actually measured or estimated with models;
• toxic effects of the ASs;
• the acceptable operator exposure limits (AOELs) of the ASs (section
11.6);
• toxic effects of the complete PPP;
• skin absorption of toxic components when skin exposure is anticipated;
• operation instructions (techniques), including time and frequency of
application;
• maximum dose;
• conditions during application (climate);
• size and quality of packing (risk of exposure due to handing of the
packing);
• proposed exposure-reduction measures;
• proposed protective measures (next to effectivity, convenience, accessibility and costs).
• Aspects concerning the exposure of bystanding persons and persons
handling, or working in, the treated crops:
• toxic effects of the ASs;
• the acceptable operator exposure limits (AOELs) of the ASs (see
section 11.6);
• toxic effects of the complete PPP;
• skin absorption of toxic components when skin exposure is anticipated;
• residues on the treated crop;
• occupational activities not directly concerned with application;
• re-entry times.
• Aspects concerning the exposure of the general population to residues in
food:
• residue levels in crops and animals fed with them;
• distribution of residues over edible and non-edible parts of the
plant;
• possibility of extrapolation between crops;
• exposure of the consumer via food or otherwise, taking into account
exposure due to the application of other PPPs containing the same
ASs;
• the acceptable daily intakes of the ASs (ADI) (section 11.6);
• the formation and presence of breakdown and reaction products and
metabolites in plants and plant products;
• behaviour of ASs and their metabolites between treatment and harvest
(crops) or post-harvest use;
• waiting periods between treatment and harvest (crop) or post-harvest
use;
• good agricultural practice.
• Aspects concerning environmental fate:
• pollution of soil, groundwater used as a source for drinking water,
ambient air, surface water and sediment with ASs or their metabolites,
degradation (also at 1O0C) and reaction products; evaluation based on
measurements or adequate models;
• identity of metabolites, degradation products and reaction products;
• degradation routes and rates (e.g. microbial, photochemical or
hydrolysis), persistence;
• mobility and evaporation;
• proportion dissolved in water and particle bound;
• proportion extractable and non-extractable in soil and sediment;
• production and treatment of drinking water in the region of
application;
• presence in groundwater of the ASs or degradation products due to use
of PPPs in the past;
• application of other PPPs with the same ASs in the region;
• drift, atmospheric deposition, discharges, leaching, runoff;
• methods for decontamination, disposal and elimination of the PPP and
its packing.
• Aspects concerning exposure of non-target organisms:
• the risk of exposure of birds, other terrestrial animals, aquatic organisms, honeybees, other beneficial arthropods, and macro-organisms in
the soil;
• estimation of exposure with adequate models;
• short-term and long-term toxicological risks for these non-target organisms, based on the most sensitive organisms used in the toxicity tests;
• ratios between exposure estimates and measures for acute, short-term
and long-term toxicity;
• effects on microbial activity in the soil;
• use of other PPPs in the region with the same ASs;
• environmental fate (soil, water, sediment and air);
• bioaccumulation and bioconcentration;
• biodegradation in the aquatic environment;
• mechanisms of action of the ASs.
• Aspects concerning chemical analysis:
• adequacy (specificity, sensitivity, reproducibility and recovery) of
proposed methods;
• stability during storage.
11.7.4 Authorization criteria
The scope of the present chapter does not allow a complete treatment of all
the criteria formulated in part C of the UP for granting, changing or refusing an authorization. Only a selection of the less obvious ones will be
presented concisely.
(a) General aspects. Authorization of PPP is not a question of 'either-or'.
It may be subjected to conditions and limitations not proposed originally by
the notifier, which may be related to the agronomic, phytosanitary and
environmental conditions and climate in the region where the application is
proposed. The MS may even exclude certain regions of their territory from
the authorization, while granting authorization for others.
The intensity of the treatment of crops (dose and frequency) should be as
low as is necessary to achieve the desired effect, even when higher
intensities do not lead to unacceptable risks to humans, animals or the
environment, provided that this does not lead to resistance to the PPP of
the organisms to be controlled. Different maximum intensities can be prescribed for different regions, depending on the agronomic, phytosanitary
and environmental conditions and climate.
Basically, an authorization may only be granted when all specific criteria
(see below) are met. However, the UP provide for some escape possibilities
on this point. A risk-benefit evaluation is allowed in some cases when not
all specific criteria for authorization are met. When these specific criteria
pertain to efficacy, effects on crops or plant products, suffering of vertebrates to be controlled, or physical and chemical properties, exemption
is possible if disadvantages or risks are counterbalanced by advantages
concerning
•
•
•
•
•
stimulation of, or compatibility with integrated control systems;
prevention of resistance of the organisms to be controlled;
prevention of too rapid degradation of ASs in the soil;
reduction of risks for workers involved in the application, and consumers;
reduction of environmental pollution and effects on non-target
organisms.
When the state-of-the-art in analytical chemistry does not yet allow
criteria to be met which pertain to the chemical analysis of ASs,
adjuvants and other relevant compounds, the authorization may be granted
for a restricted term, during which the notifier may develop an adequate
method. The authorization is reconsidered at the end of this restricted
term.
After an authorization has been granted, the MS may take measures to
increase efficacy or reduce adverse side effects, where possible in close
consultation with the notifier.
(b) Efficacy and disadvantageous effects on crops and plant products. No
authorizations may be granted for PPPs aimed at the control of organisms
which are not deemed harmful, or at achieving effects not deemed
beneficial. In other words, notifiers have to convince the competent
authority of the MS that they are trying to solve a real problem. If not, the
PPP is not regarded as a PPP. This criterion is less trivial than it seems,
as the occurrence and harmfulness of organisms causing pests and diseases may depend on the region and the climate. The criterion may not
hamper authorization for one region, while leading to a refusal for another
one.
However, solving a real problem is not enough. The PPP must be competitive in its improvement of the crop or the plant product with reference
PPPs. If no reference PPPs are available, the application of the 'aspirant'
PPP must have unambiguously advantageous results.
Application of the PPP according to the instructions for use, in compliance with the information on the label and when relevant in view of the use
of the crop or the plant product, should not lead to
•
•
•
•
•
relevant phytotoxicity;
reduced reproductive capacity of the plants;
reduced quality of the crop or the plant product;
reduced quality of crops cultivated after the harvest of the treated crop;
reduced quality of adjacent crops.
A quantitative decrease of the crop yield must be compensated by a clearcut improvement of its quality.
(c) Effects of the PPP on human health. No authorization is granted when
the exposure of the operator involved in the application of the PPP exceeds
the acceptable operator exposure limit (AOEL) and other occupational
threshold exposure levels established by the EU (Council Directive
80/1107/EEC and Council Directive 90/394/EEC). The same holds for
bystanders and workers handling or entering the crop after treatment.
Whether levels are deemed to have been exceeded depends also on the
effectivity, accessibility and availability, and feasibility of protective measures and protective clothing, re-entry and waiting times (re-entry intervals)
and measures to prevent exposure of bystanders.
(d) Effects of residues on human health. The authorization should guarantee that the lowest possible amount of PPP is used which is necessary to
achieve the desired efficacy, and that further measures (waiting time and
storage time) ensure the lowest possible residue levels in food crops and
animals fed these crops or parts thereof. An authorization can be refused if,
within the limits set by the desired efficacy, no optimization has been strived
for as regards this criterion.
Maximum residue levels (MRLs) may already have been established
in the framework of Council Directives 76/895/EEC, 86/362/EEC, 86/363/
EEC, 90/643/EEC, 91/132/EEC and Council Regulation 2377/90, or on
the occasion of an earlier authorization of an AS or PPP in the framework
of Council Directive 91/414/EEC. If they are not yet established, the
MS does so during the decision phase. It is also possible for a 'new' MRL
to be established, based on the Annex II/Annex III dossier. The establishment of a new MRL is based on the acceptable daily intake (ADI)
and an assessment of exposure via food based on all authorizations so
far.
Authorization is refused if the new application of the PPP does not
comply with the conditions attached to the establishment of existing MRLs,
unless the notifier proves that the existing MRLs are indeed not exceeded.
Obviously, authorization is refused if 'new' MRLs may cause an intake
exceeding the ADI.
The MSs only propose MRLs; the Commission decides whether this
proposal is acceptable in the light of all other possible exposures of the
consumer to the ASs via the food.
Residues present in animal fodder may not affect the health of the
animals.
(e) Criteria concerning soil, water and air pollution. Explicit authorization
criteria are defined in the UP regarding the presence of the ASs in the soil
and in groundwater which serves as a source for the preparation of drinking
water. After 3 months the concentrations in the soil should have been
reduced to 50% and after 1 year to 10%. If the reduction is proceeding
more slowly, no authorization may be granted, unless it can be demonstated
by the notifier that no accumulation can occur in the soil to concentrations
which are so high as to
• give rise to unacceptable residue levels in the crops; or
• cause phytotoxic effects; or
• affect non-target organisms.
The expected or measured concentrations in groundwater which serves
as a drinking-water source should not exceed either the levels established in
Council Directive 80/778/EEC concerning the quality of drinking water, or
the maximum drinking water levels derived from the ADIs when the ASs
were included in Annex I.
If the first above-mentioned levels are lower than the second, while there
are no monitoring data on the concentrations in groundwater, the authorization may only be granted provisionally for a period of 5 years. Authorization may then be normalized (i.e. lose its provisional status and extended to
the normal term) if a monitoring programme carried out during the provisional authorization period shows that the levels of Council Directive
80/778/EEC are not expected to be exceeded, if necessary after the implementation of conditions for, and restrictions of, use.
If the 80/778/EEC levels are the lowest and are expected to be exceeded
based on monitoring data which are submitted with the application, while
the ADI-based data are not expected to be exceeded, a provisional authorization of 5 years is granted. This authorization may be normalized if the
risks to human health of this situation are further evaluated, and if measures (restrictions of, or conditions for, use) are taken in the MS to ensure
that the 80/778/EEC levels will not be exceeded in practice.
The provisional authorization can be renewed, i.e. a new provisional term
of 5 years can be granted, if the monitoring programme shows that the 80/
778/EEC levels are approached in practice, while it may be expected that
the concentrations will become lower than these levels in the second period
of provisional authorization.
In other words, ultimately, i.e. after the period of provisional authorization of 5 years, no exceeding of the 80/877/EEC levels is allowed, if they are
lower than the ADI-based levels. If they are higher than the ADI-based
levels, while the latter are expected to be exceeded, no provisional authorization is warranted.
As regards the pollution of surface water, the UP stipulate that authorization is refused if one of the following conditions is not met:
• the concentrations are lower than those allowed by Council Directive 75/
440/EEC in surface water which serves as source for the preparation of
drinking water;
• the concentrations are not so high as to lead to unacceptable effects on
non-target organisms.
The criteria are much simpler for air than for soil and, in particular, water.
Air concentrations should not lead to an exceeding of the acceptable operator exposure level (AOEL).
(f) Effects on non-target organisms. The authorization criteria concerning
the effects on non-target organisms are explicitly defined in the UP. In the
case of birds, vertebrates, aquatic animals, algae and honeybees, the ratio
between expected exposure in the field and exposure causing effects in the
laboratory is determined. Authorization requires a certain margin of safety
between these exposure levels. For instance, birds and other vertebrates
should not be exposed to levels higher than one-tenth of the LD50 value
(exposure level at which 50% of the animals die). Furthermore,
bioaccumulation is deemed important. For instance, the concentrations in
aquatic organisms of easily biodegradable ASs should not exceed the concentration in the water by more than a factor of 1000, while for more
persistent ASs this factor may not be higher than 100. The criterion for the
microflora in the soil is the reduction of carbon and nitrogen mineralization
after 100 days. If these processes are inhibited by more than 25% at the end
of this period, no authorization may be granted.
The UP provide for a number of possibilities to escape from these strict
criteria. In essence they all require convincing evidence from field studies
that no adverse effects are to be expected in the environment, even if the
results of the standardized laboratory studies do point to the occurrence of
such effects. In other words, the standardized laboratory studies are overruled by the more expensive and elaborate field studies which provide a
better impression of what may be expected to occur in reality.
(g) Methods of chemical analysis. State-of-the-art methods of chemical
analysis should be used. A number of strict criteria are defined as to the
quality (specificity, sensitivity, reproducibility and recovery) of the methods
for the determination of residue levels.
(h) Chemical and physical properties. The PPP should meet the specification established by the Food and Agricultural Organisation (FAO) of the
United Nations as regards its chemical and physical properties. If this
specification is not available, the composition of the PPP should lie within
ranges which are explicitly defined in the UP, also after storage. Moreover,
the Manual on the development and use of FAO specifications for plant
protection products applies.
11.8 Transitional measures and the review programme
11.8.1 Transitional authorizations
Article 8 of 91/414/EEC is concerned with the transition from the old
situation in the EU, when PPPs, including their ASs, were regulated separately and independently by each MS, to the situation when all PPPs are
authorized according to 91/414/EEC and its associated EU legislation. In
between, the following transitional authorizations are possible.
(a) Existing national authorizations, i.e. pre-Directive authorizations of
PPPs. A pragmatic solution has been chosen. Existing authorizations
remain valid until they expire following the pre-Directive national legislation, irrespective of the inclusion in Annex I of the ASs concerned.
(b) Renewal of pre-Directive authorizations of PPPs. Pre-Directive
authorizations may be renewed for a period no longer than the Review
Programme (section 11.8.2), i.e. until 12 years after the notification of 91/
414/EEC (July 2003). This renewal is granted following MS legislation,
largely independently from the rules set by 91/414/EEC and associated EU
legislation. Directive 91/414/EEC only prescribes the general requirements
for such an authorization. These general requirements are the same as those
applied for authorization of a new PPP under 91/414/EEC (section 11.7.1).
After the new term has expired, a second renewal has to follow the rules
of 91/414/EEC completely. This means that the second renewal is only
possible if the ASs of the PPPs have been included in Annex I in the
framework of the Review Programme, while the authorization of the PPPs
has to follow the Uniform Principles (Annex VI of 91/414/EEC; section
11.8). If the ASs have not passed the review programme, or if they have, but
have failed to be included in Annex I, no renewal is possible.
Renewals of pre-Directive authorizations terminate when one of the ASs
in the PPP has passed the review programme, but was denied the inclusion
in Annex I. If, however, all the ASs in a PPP have reached Annex I, the
existing authorizations have to be adapted to the new situation. This means
that these have to meet the conditions attached to the inclusion in Annex I.
As long as one of the ASs in a PPP has not passed the review programme,
while the others were not denied inclusion, no adaptation to the new
situation is required.
(c) Authorizations of new PPPs with existing (pre-Directive) ASs.
Authorizations of new PPPs with existing ASs (see below) are granted for
a period no longer than the Review Programme. The same rules apply to
these authorizations as to the renewal of pre-Directive authorizations (see
above).
11.8.2 Review programme
Directive 91/414/EEC provides for the gradual examination of all existing
ASs, i.e. all ASs in use in the EU before 23 June 1993, with regard to the
possibility of their inclusion in Annex I. This so-called 'Review Programme'
(RP) has been worked out in Commission Regulation (EEC) 3600/92. The
RP will be carried out in phases. Each phase consists of the examination of
a group of ASs which are selected by the Commission, taking into account
aspects of human health, environmental health, residue problems, the
number of PPPs which contain the ASs, and the availability or lack of
important biological and chemical data. In fact, the Commission prioritizes
the existing ASs for examination. The first prioritized group has been
published as Annex I of Regulation 3600/92.
The RP is planned to last 12 years from the date 91/414/EEC was notified.
However, 10 years after the notification of 91/414/EEC, it may be decided
by the Commission, the Standing Committee on Plant Health or the Council to extend this period for certain ASs.
Not all prioritized ASs are indeed examined. Notifiers must have such an
interest in the ASs as to notify the Commission of their preparedness to
submit the data necessary for evaluation within 6 months of the notification
of the Regulation in which the list of the prioritized ASs is published. When
during this period no notifications by notifiers have been received by the
Commision, the MS have the opportunity to notify their preparedness
during a further 6 months. As notifiers, the MS have the same obligations as
the notifying notifiers. When no notifiers or MSs have notified their preparedness to 'defend' an AS in this 1-year period, this AS will not be
included in Annex I. The notified ASs are divided among the MS by the
Commission, each MS acting as the 'rapporteur' for a series of ASs (see
Commission Regulations (EC) 933/94 and 2230/95). Then the notifiers have
12 months to prepare a dossier.
The procedure by which the decision is reached about inclusion of existing ASs in Annex I of 91/414/EEC is in many aspects similar to the procedure followed for new ASs (sections 11.5 and 11.6). The dossier submitted
must be equivalent to a dossier submitted for a new AS (section 11.5). This
means that the data must yield information equivalent to the information
required in Annex II of 91/414/EEC for the AS and in Annex III of 91/414/
EEC for at least one of the PPPs based on the AS (section 11.4). Subsequently, the competent authority of the Rapporteur MS composes a monograph on the AS (section 11.6), which must be ready 12 months after the
submission of a dossier which is deemed complete. It has to include one of
the following recommendations:
• to include the AS in Annex I, whereby it must be stated under which
conditions;
• to remove the AS from the market;
• to remove the AS from the market temporarily, pending the submission
of additional data;
• to postpone a decision, pending the submission of additional data.
The monograph is evaluated at several meetings of expert representatives
of MSs. Together with the remarks of these experts and the proceedings of
their meetings, the monograph serves as the basis for the decision taken by
the Standing Committee on Plant Health, the Commision or the Council. In
case additional data are required, the Rapporteur MS has to evaluate these
within 9 months of their submission, whereupon a new decision is taken.
Also, this second decision may include the requirement of additional data.
If so, a new 9-month period is started, and so on
• until it can be decided whether or not the AS should be included in
Annex I; or
• until the notifier does not submit the required data, in which case the AS
is denied inclusion.
The basic steps of the RP are listed in Table 11.8.
Table 11.8 Overview of the basic steps of the Review Procedure (according to Commission
Regulation (EEC) 3600/92)
Order
Activity or decision
Remarks
1
Composition of a list of prioritized
ASs by the Commision
Annex I of Regulation (EEC) 3600/92
2
Notification of interest in Annex I
inclusion by producers
6 months upon the notification of
Regulation (EEC) 3600/92
3
Notification of interest in Annex I
inclusion by the MS
Next period 6 months
4
Composition of list of notified ASs
and Rapporteur MSs by the
Commission or the Council
Regulations (EC) 933/94 and 2230/95
5
Submission of dossier by notifier
Within 12 months of the composition of
the list of notified compounds
6
Submission of missing data, followed
by sending of revised dossier to the
Commision and all MSs
Within 12 months of submission of the
dossier
7
Composition of monograph by the
Rapporteur MS
Within 12 months of the submission of the
dossier
8
Decision upon inclusion in Annex I or
the requirement of additional data by
the Commission or Council
9
Submission of additional data
Term specified in decision (see 8)
10
Composition of revised monograph by
the Rapporteur MS
Within 9 months of the submission of the
additional data
11
Decision upon inclusion or the
requirement of additional data by
the Commission or Council
12
In case of requirement of additional
data, go to 9
Notifiers can submit a dossier independently of each other. In that case,
only the notifiers submitting a sufficiently complete dossier can make use of
the inclusion in Annex I for the authorization of PPPs. A recent development points to the possibility that notifiers submitting an incomplete dossier
can make use of an inclusion if they can show within a certain period that
they have regular access to the data lacking in their dossiers but present in
the dossiers which enabled the inclusion. Notifiers can also submit a dossier
together. In fact, they are stimulated to do so by 91/414/EEC. In that case,
all the participants can make use of the inclusion for authorization
purposes.
Parties (producers or trading companies) not notifying, not submitting a
separate dossier, or not participating in a dossier, can only make use of an
inclusion in Annex I, if
• their PPP complies with the FAO specifications; and
• they have access to the data submitted by the original notifiers.
11.9 Adjuvants
Since there is no European regulation for adjuvants, each MS currently
regulates adjuvants in its own way. The main areas where information and
data may be required as part of the authorization procedure include physical
and chemical data, toxicology, environmental data, efficacy and residues.
The requirements for data in each category may well vary with each Member State, but the basic requirements will be broadly similar. The differences
between the Member States originate to a great extent from the question as
to whether adjuvants include coformulants, i.e. substances that are added by
the PPP manufacturer at the formulation stage of a PPP, or whether they
also, or only, include the products that are added by the user to the PPP in,
for example, the spray tank immediately before application. The currently
proposed EU definition refers solely to tank-mix adjuvants: 'Formulants
and preparations containing two or more formulants put up in the form in
which they are supplied to the user and placed on the market with the
objectives shown by the label to be added by the user to a PPP or a mixture
of PPPs at a diluted or ready to use stage, for the purpose of changing its or
their properties or effects' (Working Document 2772/VI/92, Revision 3, 30
January 1993). However, in several Member States, a different definition of
adjuvants is used. Thus the requirements and methods for authorization of
an adjuvant depend entirely on the definition chosen. Moreover, it depends
on the Member State in which authorization is requested.
In 1992 the EU issued a working document suggesting amendments to
the scope of 91/414/EEC. This document basically inserted the word 'coadjuvant' alongside 'active substance', wherever the latter term appeared.
This proposal would have had the effect of virtually treating adjuvants as
ASs from a regulatory point of view. However, the working document is
still under revision.
The main principle underlying the regulation of the use of adjuvants is
the following: 'Adjuvants or non-active substances should be adequately
regulated to ensure their use is safe for human health and the environment'.
Therefore the Commision started preparatory work for an amendment to
Directive 91/414/EEC to include more specific requirements for adjuvants.
Acknowledgements
The authors thank Dr H.E. Falke and Ir. JJ. Meeussen of the Dutch
Pesticide Authorization Board and Dr H. de Heer of the Dutch Ministry of
Agriculture, Conservation of Nature and Fisheries for their valuable
comments.
Appendix ll.A An overview of European Community general
legislation associated with plant protection products
1. Council Directive 75/440/EEC of 16 June 1975 concerning the quality required of surface
water intended for the abstraction of drinking water in the Member States.
2. Directive 76/895/EEC relating to the fixing of maximum levels for pesticide residues in and
on fruit and vegetables.
3. Council Directive 80/778/EEC of 15 July 1980 relating to the quality of water intended for
human consumption.
4. Council Directive 80/1107/EEC on the protection of workers from the risks related to
exposure to chemical, physical and biological agents at work.
5. Council Directive 86/362/EEC of 24 July 1986 on the fixing of maximum levels for pesticide residues in and on cereals.
6. Council Directive 86/363/EEC of 24 July 1986 on the fixing of maximum levels for pesticide residues in and on foodstuffs of animal origin.
7. Council Directive 90/394/EEC on the protection of workers from the risks related to
exposure to carcinogens at work.
8. Commission Directive 90/643/EEC of 26 November 1990 amending the annexes to Council Directive 70/524/EEC concerning additive in animal feedstuffs.
9. Council Directive 91/132/EEC of 4 March 1991 amending directive 74/63/EEC on undesirable substances and products in animal nutrition.
10. Council Regulation (EEC) No 2377/90 laying down a Community procedure for the
establishment of maximum residue limits of veterinary medicinal products in foodstuffs of
animal origin.
11. Council Directive 91/414/EEC of 15 July 1991 concerning the placing of plant protection
products on the market, OJ. No. L 230,19.8.1991, p. 1.
12. Commision Regulation (EEC) No. 3600/92 of 11 December 1992, laying down the
detailed rules for the implementation of the first stage of the programme of work
referred to in Article 8 (2) of Council Directive 91/414/EEC, OJ. No. L366, 15.12.
1992.
13. Commission Directive 93/37/EC of 22 July 1993 amending Council Directive 91/414/EEC
concerning the placing of plant protection products on the market, OJ. No. L 221,
31.8.1993, p. 27.
14. Commission Directive 93/71/EEC of 27 July 1993 amending Council Directive 91/414/
EEC concerning the placing of plant protection products on the market.
15. Commission Regulation (EC) No. 933/94 of 27 April 1994, OJ. No. L 107 of 28 April
laying down the active substances of plant protection products and designating the
rapporteur Member State for the implementation of Commission Regulation (EEC) No.
3600/92, OJ. No. L 107, 28.4.1994.
16. Commission Directive 94/37/EC of 22 July 1994 establishing Annex VI to Directive 91/414/
EEC concerning the placing of plant protection products on the market, OJ. No. L 194,
29.7.1994, p. 65.
17. Council Directive 94/43/EC of 27 July 1994 establishing Annex VI to Directive 91/414/
EEC concerning the placing of plant protection products on the market, OJ. No. L 227
1.9.1994, p. 31.
18. Commission Directive 94/79/EC of 21 December 1994 amending Council Directive 91/414/
EEC concerning the placing of plant protection products on the market, OJ. No. L 354,
31.12.1994, p. 16.
19. Commission Document 1663/VI/94, revision 7.2. Guidelines and criteria for the preparation and presentation of complete dossiers for the inclusion of active substances in Annex
I of Directive 91/414/EC.
20. Commission Document 1654/VI/94, revision 6. Guidelines and criteria for the preparation
of complete dossiers for the inclusion of an active substance in Annex I of Directive 91/
414/EEC.
21. Commission Regulation (EC) No. 491/95 of 3 March 1995 amending Regulation (EC) No.
933/94, in particular with regard to the integration of the designated public authorities and
the producers in Austria, Finland and Sweden in the implementation of the first stage of
the programme of work referred to in Article 8 (2) of Council Directive 91/414/EEC
concerning the placing of plant protection products on the market.
22. Commission Directive 95/35/EC of 14 July 1995 amending Council Directive 91/414/EEC
concerning the placing of plant protection products on the market, OJ. No. L 172,
22.7.1995, p. 6.
23. Commission Directive 95/36/EC of 14 July 1995 amending Council Directive 91/414/EEC
concerning the placing of plant protection products on the market, OJ. No. L 172,
22.7.1995, p. 6.
24. Commission Regulation (EC) No. 2230/95 of 21 September 1995 amending Regulation
(EC) No. 933/94, laying down the active substances of plant protection products and
designating the rapporteur Member States for the implementation of Commission Regulation (EEC) No. 3600/92, OJ. No. L 225, 22.9.1995, p. 1.
25. Commission Directive 96/12/EC of 8 March 1996 amending Council Directive 91/414/EEC
concerning the placing of plant protection products on the market, OJ. No. L 65,
15.3.1996, p. 20.
26. Commission Directive 96/46/EC of 23 August 1996 amending Council Directive 91/414/
EEC concerning the placing of plant protection products on the market, OJ. No. L 214,
23.8.1996, p. 18.
27. Commission Directive 96/68/EC of 21 October 1996 amending Council Directive 91/414/
EEC concerning the placing of plant protection products on the market, OJ. No. L 277,
30.10.1996, p. 25.
12 Regulatory requirements in the USA
J. M. WAGNER
12.1 Introduction
According to the American Crop Protection Association, pesticide chemical development, testing and US Environmental Protection Agency (EPA)
approval takes 8-10 years and costs manufacturers between $35 million and
$50 million for each new pesticide [I]. Achieving EPA registration is costly
and time consuming, requiring a working knowledge of the many federal
regulations, policies and guidelines that control the process.
This chapter provides a review of the key features of the federal registration process with discussion of state requirements as well. It can serve as a
general guide to those developing, testing, marketing or registering pesticides in the USA. A comprehensive review of reference sources is provided
and includes many that are available on the World Wide Web of the
Internet.
Throughout this chapter the term 'pesticide' is used to mean the biologically active ingredient in a product which produces an effect on a target
pest. The terms 'pesticide' and 'active ingredient' are used interchangeably.
The terms 'product' and 'formulation' are used interchangeably to refer to
the combination of active ingredient, diluents and adjuvants as a packaged
mixture.
Regulatory requirements in the USA are continually changing and evolving. Each year EPA issues new or revised regulations or policies that affect
the pesticide industry. To the extent possible, the most relevant and up-todate sources of information and references available at the time of this
writing have been used. When considering registration decisions, one must
be sure to consult the most current version of any EPA regulation.
12.2 Federal pesticide laws
In the USA there are two laws which must be considered when seeking a
federal license to sell, also known as a pesticide registration. The Federal
Insecticide, Fungicide, and Rodenticide Act (FIFRA) regulates the manufacture, distribution and sale of pesticides, whether in high-strength technical grade products or in formulations. The Federal Food, Drug, and
Cosmetic Act (FFDCA) regulates the distribution and sale of crops and
food items containing residues of pesticides and of inert ingredients used in
pesticide formulations. The FIFRA is contained in Title 7 of the US Code
of Laws [2]. That portion of the FFDCA which regulates pesticide and inert
ingredient residues in or on food and crops is contained in Title 21 of the US
Code, Sections 321-409 [2]. FIFRA in its entirety and the previously mentioned portion of the FFDCA are administered by the US Environmental
Protection Agency (EPA). It is EPA's responsibility to provide detailed
guidance to the regulated community on how to comply with both laws.
This guidance is provided principally in Title 40 of the Federal Code of
Regulations (CFR), Parts 150-189. One must have an in-depth knowledge
and understanding of the these regulations and how EPA interprets and
applies them to be successful in obtaining pesticide registration approvals.
12.2.1 Federal Insecticide, Fungicide, and Rodenticide Act
The Federal Insecticide, Fungicide, and Rodenticide Act was established
as US law in 1947 to regulate pesticides, denned in the law as substances
'intended for preventing, destroying, repelling, or mitigating any pest or
intended for use as a plant regulator, nitrogen stabilizer, defoliant, or desiccant.' Intent is determined by claims on the product label and/or composition or mode of action of the product as distributed or sold. In 1947
FIFRA was primarily a law which set standards for product labeling. Since
then FIFRA has been amended and its scope broadened many times. The
1972 amendment expanded the standards for product labeling and required
that pesticide manufacturing sites should be licensed. The 1974 amendment
established standards, based on dermal toxicity, to protect agricultural
workers who enter pesticide-treated crops. The 1975 amendment created
the Scientific Advisory Panel, an independent body of scientists selected by
EPA, to assist in deciding critical scientific issues.
The 1978 amendment was especially important to the agrochemical industry, adding several key components to form today's modern law. It gave
EPA authorization to grant 'conditional' registrations, thereby allowing the
possibility of earlier market entry with an earlier financial return on investment. It also granted manufacturers 10 years of exclusive-use protection of
their registration data. This amendment also created a formalized process
for revoking registrations of products where the risks exceed the benefits
of use.
The next amendment in 1988 required EPA to accelerate the rate of
product reregistration. This required industry to replace older safety studies
which did not satisfy current requirements with studies conducted to
modern standards. For many agrochemical companies this process placed a
financial strain on research and development resources in order to comply
with EPA deadlines for submitting these new studies. This amendment
affected approximately 1138 active ingredients. In its annual report for
1996, the EPA reported that it had completed the reregistration of only
39% of the eligible active ingredients [3]. EPA does not expect to complete
the reregistration process, started in 1988, until sometime after the year
2000.
The most recent amendment occurred in 1996. It is referred to as the
Food Quality Protection Act of 1996 (FQPA), and greatly expanded the
safety standards which are set forth in FIFRA and FFDCA. Because of its
broad implications for the agrochemical industry, FQPA deserves special
consideration and is discussed in section 12.2.3.
12.2.2 Federal Food, Drug, and Cosmetic Act
Pesticides that are registered for use on food crops must also have federal
tolerances established to permit residues of the pesticide in raw and processed foods. This requirement for tolerances was initiated in 1954 with the
enactment of Section 408 of the Federal Food, Drug, and Cosmetic Act.
Residues of a pesticide that exceed a tolerance, or for which no tolerance
has been established, are considered unsafe and the food is classified as
adulterated and unlawful.
The authority to establish pesticide tolerances is delegated to the
Environmental Protection Agency. The EPA issues rules and regulations
regarding the data required to support petitions to establish tolerances. The
tolerance-setting procedures, as well as the standards of safety for setting
tolerances, have recently been extensively revised by the Food Quality
Protection Act of 1996.
12.2.3 Food Quality Protection Act, 1996
On 3 August 1996 the FQPA was signed into law with immediate effect.
Since there was to be no phase-in period, the EPA was forced to begin
quickly the process of writing and issuing interpretative policies and rules.
In order to focus itself to accomplish this, EPA declared a moratorium on
most registration activities. Lasting about 6 months, it provided EPA with
time to establish the broad principles whereby it could develop the detailed
policies for the administration of FQPA. While a thorough assessment of
all components of FQPA is beyond the scope of this work, those of most
significance are reviewed. The FQPA amended both the FIFRA and
FFDCA laws.
The more significant changes to the FIFRA include the following [2].
• Reregistration and re-evaluation of pesticide tolerances. Within 10 years,
EPA is required to re-evaluate the tolerances for each active ingredient
to determine if the tolerances meet the new safety standards of FQPA.
• Periodic review of registrations. EPA is required to establish rules for,
and to start the periodic review of all registrations. The old FIFRA
requirement that all registrations automatically expire every 5 years was
eliminated. In practice, this 5-year expiration was never implemented.
EPA is now encouraged to review a pesticide's registration every 15
years.
• Minor-use crops. In terms of the safety data required for registration, the
1988 amendment to FIFRA treated pesticides for smaller-area crops,
such as avocados and strawberries, the same as pesticides for larger-area
crops, such as corn and soybeans. EPA is now permitted to provide
certain incentives to encourage industry to pursue registrations for use on
minor crops. The incentives include increasing the time period for exclusive use of data, granting data waivers and granting time extensions
for meeting study deadlines. FQPA generally defines a 'minor use' as one
where the total area for the crop in the USA is less than 300000 acres
(c. 120000ha).
• Expedited registration of reduced-risk pesticides. FQPA directs EPA to
develop procedures and guidelines for expediting the registration of pesticides that qualify as 'reduced-risk' or 'safer' pesticides. A safer pesticide
is defined as one which (1) reduces pesticide risks to humans, (2) reduces
pesticide risks to non-target organisms, (3) reduces the potential for
contamination of valued environmental resources or (4) broadens the
adoption of integrated pest management strategies.
The more significant changes to FFDCA include the following [2].
• The Delaney Clause. Prior to FQPA, pesticide residues in processed
foods were considered 'food additives' regulated under Section 409 of
FFDCA. When pesticide residues in a processed food, such as flour,
exceeded a tolerance established for the raw agricultural commodity, in
this example wheat, under Section 408, a separate food additive tolerance
for flour was required under Section 409. However, the Delaney Clause
of Section 409 prohibited the establishment of food additive tolerances
for those chemicals classified by EPA as carcinogenic. Paradoxically,
EPA was permitted to set a tolerance in the raw food wheat, but not in
flour, for the same carcinogenic chemical if the risk was acceptable.
Under FQPA, pesticide residues are excluded from the definition of
'food additive', and therefore the Delaney Clause no longer applies to
the establishment of pesticide tolerances. Both raw and processed
foods are now regulated under the same standard of safety regarding
carcinogens.
• Standards for establishment of tolerances for pesticide residues in food.
Under FQPA, EPA may establish a tolerance if there is 'a reasonable
certainty that no harm will result from aggregate exposure to the pesticide chemical residue, including all anticipated dietary exposures and all
•
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other exposures for which there is reliable information' [2]. This requires
that the total amount of human exposure to a pesticide chemical be
determined from residues in food, drinking water and uses in or around
the home. The total potential exposure is then compared to the safe level
of exposure determined from toxicity studies. Tolerances may be established if the total exposure level will not exceed the safe level.
Safety standards for infants and children. This requires EPA to apply
an additional ten-fold safety factor for allowable exposure to a pesticide
chemical to protect against a potential threshold effect observed in
animal toxicity testing. The standard safety factor of 100-fold can be
increased by a factor of ten when reliable data are not available to assess
pre- or post-natal toxicity to infants and children. A safety factor of ten is
used to account for the variation in sensitivity among the members of the
human population, and an additional factor of ten is used to account for
the uncertainty in extrapolating animal data to humans, which together
gives the standard 100-fold factor.
Dietary exposure - percentage of food actually treated with a pesticide.
When assessing chronic dietary risk to a pesticide, EPA may consider the
percentage of a crop that is actually treated with the pesticide for the
purposes of calculating human exposure through the diet. In practice,
EPA has already been doing this in those cases where an assumption of
100% results in an unacceptable risk.
Tolerances for use of pesticides under an emergency exemption. If EPA
grants an emergency exemption from registration for a pesticide for a
crop use under FIFRA Section 18, it must also establish a tolerance for
residues of the pesticide on the crop. These tolerances are subject to the
same standards of safety as other pesticide tolerances under FFDCA. An
exemption under Section 18 is generally requested by a state to address
a pest problem where registered pesticides are not achieving adequate
control. The exemption is for a specific amount of product, for a specified
number of acres of the crop, for usually no more than a single growing
season.
Reregistration fees. FQPA extends EPA authority to collect registration
maintenance fees from 1997 to 2001 at the rate of $14 million per year. It
allows EPA to collect an additional $2 million per year in each of years
1998, 1999 and 2000. This is discussed in more detail in the section
'Registration Fees'.
Consumer right-to-know. This provision requires industry to provide
EPA with informative summaries of safety data submitted in support of
petitions to establish pesticide tolerances on food and exemptions from
tolerances for inert ingredients on food. EPA is to publish the summaries
and make them publicly available.
Estrogenic substances screening program. FQPA requires EPA to develop a screening program within 2 years to determine if pesticide chemi-
cals may have endocrine-disrupting effects. The screening program is to
be implemented within 3 years.
• Schedule for review of tolerances. This provision requires EPA to review
the pesticide tolerances and inert ingredient tolerance exemptions that
were in effect on 3 August 1996, according to the following schedule:
complete 33% within 3 years, 66% within 6 years and 100% within 10
years. EPA must evaluate the tolerances and exemptions to determine if
they meet the safety standards of FQPA and revoke those that do not.
At the time of FQPA's enactment, there were 9728 tolerances and
exemptions for active and inert ingredients that are subject to the FQPA
reassessment [4]. Of the tolerances and exemptions for active ingredients
subject to the reassessment schedule, 8190 are tolerances and 712 are
exemptions from tolerances. Also subject to reassessment are 826 exemptions for inert ingredients.
Pesticides groups. In order to comply with FQPA reassessment priorities
and reregistration scheduling requirements, EPA has divided pesticides
with tolerances and exemptions into three groups [4]. In general, Group 1
pesticides will be subject to reassessment first, followed by Groups 2 and 3.
Group 1
Risk- and hazard-based priorities. Group 1 includes those tolerances
and exemptions associated with the following types of pesticides, which
according to EPA appear to pose the greatest risk to the public health.
• Pesticides of the organophosphate, carbamate and organochlorine
classes (EPA intends to conduct tolerance reassessments for organophosphate pesticides in the first 3 years of the schedule).
• Pesticides that EPA has classified as probable human (Groups Bl and
B2) carcinogens, and possible human (Group C) carcinogens for which
EPA has quantified a cancer potency.
• High-hazard inert ingredients.
• Any pesticides which, based on the best available data at the time of
scheduling, exceed their reference dose (RfD). The term 'reference dose'
refers to an estimate of a daily exposure to the human population that is
likely to be without an appreciable risk of harmful effects during a lifetime. It is generally derived from dose levels used in standard chronic
feeding studies with laboratory animals.
Reregistration priorities. Because EPA must, in addition to meeting
the tolerance reassessment schedule, also complete the reregistration
program by 2002, tolerance reassessments for those pesticides for which
Registration Eligibility Decisions (REDs) were substantially complete
prior to FQPA's enactment are also included in Group 1, even though the
tolerances for these pesticides may not be among those that appear to pose
the greatest risk to public health. For the sake of completeness and for
tracking purposes, those food-use pesticides for which REDs were issued
after 3 August 1996 are also listed in Group 1, even though EPA has
completed their FQPA tolerance reassessments.
Tolerance revocations. EPA has also placed in Group 1 those pesticides
for which tolerances and exemptions are in the process of being proposed
for revocation. These tolerances and exemptions are included in the total
9728 subject to reassessment. In 1997 EPA began to issue a number of
proposed rules to revoke over 1000 tolerances and exemptions: one notice
proposes to revoke tolerances and exemptions associated with pesticides
for which all registrations have been canceled, a second notice proposes to
revoke tolerances for uses that have been deleted from pesticide registrations, a third notice proposes to revoke tolerances for uses canceled in order
to reduce theoretical risks to levels below the reference dose, and a fourth
notice proposes to revoke tolerances for uses no longer considered to be
significant livestock feed items.
Group 2. Possible human carcinogens not included in Group 1 will be
reassessed as part of Group 2. Because EPA intends to complete the
reregistration program in 2002, tolerances and exemptions for all remaining pesticides subject to reregistration will also be reassessed as part of
Group 2.
Group 3. Group 3 includes the biological pesticides, as well as those
inert ingredients referenced in 40 CFR part 180 that EPA has not identified
as high-hazard inert ingredients. Also included in Group 3 are, as part of the
registration renewal program, those post-1984 pesticides with tolerances
and/or exemptions not yet reassessed under FQPA.
12.3 EPA Office of Pesticide Programs
According to the EPA, there are about 20000 federally registered pesticide
formulations, containing approximately 675 active ingredients and 1835
inert ingredients [5]. About 470 active ingredients are used in agriculture
and EPA has established more than 9000 tolerances (maximum residue
limits) for pesticides in foods. To administer this enormous inventory of
registered products and tolerances and to process new requests, the EPA
have a staff of approximately 800 people in 1997. They include scientists,
regulatory specialists, information specialists, attorneys, managers and administrative staff.
12.3.1 Organization
The Office of Pesticide Programs (OPP) has been reorganized many times
since it was first created. Currently it is composed of nine divisions (Table
12.1) [5].
The Antimicrobials Division is responsible for registering the disinfectant products used in medical facilities, as well as those used around the
home.
The Biopesticides and Pollution Prevention Division was formed in 1994.
It reviews all registration applications for (1) microbial pesticides - bacteria, fungi, protozoans and viruses, (2) biochemical pesticides - naturally
occurring compounds that have a non-toxic mode of action, and (3) plant
pesticides - pesticide substances introduced into plants along with the
genetic material necessary for the production of the substance within the
plant.
The Biological and Economic Analysis Division is made up primarily of
economists, statisticians and scientists who provide analyses of the economic benefits of pesticides. These analyses are often used where potential
benefits of use are balanced against the concern for potential risks. The
Division is also a source of information about farming practices and all
types of pesticide usage.
The Environmental Fate and Effects Division is composed of scientists
who evaluate environmental and ecological data submitted to support registrations. From these evaluations scientists characterize the nature of any
risk to non-target plants and animals, and the potential of a pesticide to be
present in drinking water.
The Field and External Affairs Division provides a range of services,
including (1) the coordination of the development of OPP regulations and
policies, (2) serving as primary communications link to states, American
Indian tribes and foreign governments, (3) administering the pesticide applicator certification and worker protection programs, and (4) serving as
external communication link for major OPP decisions and policies.
Table 12.1 EPA Office of Pesticide Programs: organization
structure, 1997
Director's Office
Antimicrobials Division
Biopesticides and Pollution Prevention Division
Biological and Economic Analysis Division
Environmental Fate and Effects Division
Field and External Affairs Division
Health Effects Division
Information Resources and Services Division
Registration Division
Special Review and Reregistration Division
The Health Effects Division is comprised of scientists who evaluate toxicology and residue data, and perform human health risk assessments.
The Information Resources and Services Division provides OPP with its
information technology systems. This division is playing a major role in the
advance towards a paperless submission process where all data and information will be in electronic format.
The Registration Division has been at the center of the pesticide regulatory program from the beginning of registrations in 1947 as part of the US
Department of Agriculture. Responsible for all registration matters, this
Division functions around a product manager system where groups of similar products are assigned to specific managers and their teams. The teams
are the primary contact to those seeking registrations. Registration Division
and its product managers are a key link in the registration process.
The Special Review and Reregistration Division ensures that existing
pesticide registrations and tolerances meet current regulatory requirements. This includes identifying data gaps and requiring that modern
studies be submitted to support an existing registration or tolerance. This
Division evaluates the risks of continued use of older pesticides and decides
the future of these products, which may include denial of continued registration and use.
12.3.2 Operating objectives
The Legislative Branch of the Federal Government writes the environmental laws and EPA, as part of the Executive Branch, carries them out. The
statutory language of a law provides broad mandates to EPA regarding the
law's intent and purpose. They do not provide the detailed process information of how to achieve the law's objectives. This process is created by EPA,
based on a number of inputs:
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how it interprets the intent of the legislators who created the law;
the prevailing public opinion regarding the law;
the views of those who are being regulated;
the views of special interest groups;
EPA's own opinion of how it should do its job.
Taking these factors into account, invariably giving more weight of importance to some and less to others, EPA formulates its objectives and policies.
The EPA has proposed a set of objectives for pesticides for the year 2005
and has made them available for public comment [6]. These objectives are
likely to determine, or at least influence, the detailed day-to-day policies of
how EPA regulates pesticides in the years leading up to 2005.
The objectives are to [6]
• reduce by 50% the use of pesticides that have been classified as having
the highest potential to cause cancer;
• reduce by 100% the use of pesticides on foods that do not meet the
FQPA standard of 'reasonable certainty of no harm';
• double the number of registrations for safer chemicals and biopesticides;
• reduce by 50% the area of agricultural land treated with pesticides that
have carcinogenic and neurotoxic characteristics;
• complete the reregistration for all pesticides initiated under FIFRA 1988
amendment;
• complete 90% of the tolerance reassessment for all pesticides required
under FQPA;
• provide adequate protection for all endangered plant and animal species
on pesticide labeling;
• develop or revise 100% of the regulations, policies and guidelines for
registering safer pesticies and biopesticides to improve and streamline
the registration process;
• improve, develop and use risk assessment tools that address the aggregate exposure or risk, and common mechanisms of toxicity provisions of
FQPA.
Most of these objectives will continue to put pressure on the older compounds. As EPA approves more of the safer compounds, those products
with undesirable characteristics will be selected for deregistration. Thus
manufacturers are focusing their invention efforts towards discovery of
products considered by EPA to be safer.
12.4 Product registration: obtaining a license to sell
All product registrations are approved under the authority contained in
FIFRA. It provides for several types of registrations. This section describes
the general administrative procedures which must be followed for each
type. Applicants should refer to the detailed guidance documents published
by EPA when preparing petitions for registration. One of the better references for this is EPA's registration information manual [7].
12.4.1 Experimental Use Permit
Experimental Use Permits (EUPs) are issued under Section 5 of FIFRA.
EPA regulations regarding this type of temporary approval for use of a
pesticide are contained in 40 CFR Part 172.
EUPs allow the generation of information and data needed to support
the future registration of a product. Distribution and use of a product under
an EUP is tightly controlled by EPA. Only participants in the experimental
program may distribute or receive the product, for use only at sites approved by EPA, and only under the terms and conditions of the permit.
EUPs are generally not required for testing conducted in a laboratory,
greenhouse or small-scale field trials. They are also not required for field
testing if limited to a cumulative total of 10 acres (c. 4 ha) or less against a
specific pest species. An exception to this is the testing of certain genetically
altered and non-indigenous microbial pest agents where small-scale testing
may require an EUP. Direct consultation with the Agency is needed to
determine whether an EUP is needed in this instance.
The preparation of an application should include the following
information:
• a completed EPA Form 8570-17: Application for Experimental Use
Permit;
• the purpose or objective of the proposed testing;
• a detailed description of the testing program:
• test parameters;
• the amount of product to be used in testing;
• identification of the crops, fauna, flora, sites, modes, dosage rates and
situation of application in the testing;
• identification of the states and counties within states where the testing
will occur;
• the number of acres by state and county involved in the testing;
• the expected dates or time period when the testing will take place;
• the manner in which supervision of the testing will occur;
• a completed EPA Form 8570-4: Confidential Statement of Formula;
• the data specified in 40 CFR Part 158 for an EUP, formatted according to
EPA Pesticide Regulation (PR) Notice 86-5 [8].
If the EUP testing is to be done on a food or animal feed crop, then the
applicant must also do one of the following:
• provide evidence that a tolerance for residues of the pesticide has been
established by EPA on the food or feed item;
• certify to EPA that all food or feed treated in the EUP will be destroyed;
• petition EPA to set a temporary tolerance for residues of the pesticide on
the food or feed item based on submitted data.
12.4.2 Registration
By definition in FIFRA, a pesticide that is used to control or mitigate any
pest that can damage or destroy food, feed or fiber crops must be registered
with EPA. Definitions for 'pesticide' and 'pest' are found in FIFRA and in
40 CFR Part 152.
The inert ingredients in a pesticide formulation, whether added to the
product by the manufacturer or to a tank mixture of products by the user,
are not required to be registered as separate chemical entities. They are,
however, subject to the tolerance-setting requirements of FFDCA when
applied to food or feed crops. This is discussed in section 12.4.3(b).
EPA places an application for pesticide registration in one of three main
categories: (1) a new chemical application, (2) a new use application or (3)
a 'me-too' application. A new chemical application is made for a product
containing a new active ingredient that has not previously been registered
by the EPA. A new use application is made for a currently registered active
ingredient where the applicant wants to add a new use site, e.g. an additional crop, or wants to register a new formulation of the active ingredient.
A 'me-too' application is for a product that is substantially similar or identical in its uses and chemical composition to products that are currently
registered.
EPA may grant a 'conditional registration' under Section 3(c)(7)(C) of
FIFRA for a new active ingredient, where certain data are lacking, on
condition that such data are received by the end of the conditional registration period, and that:
• the data do not meet or exceed the risk criteria set forth in 40 CFR
154.7;
• use of the pesticide during the conditional registration period will not
cause unreasonable adverse effects;
• use of the pesticide is in the public interest.
(a) Contents of application. Each application for a new chemical,
new use, or formulator's exemption must include all of the following
information.
• Completed EPA Form 8570-1: Application for Registration.
• Completed EPA Form 8570-4: Confidential Statement of Formula.
• Draft labeling for the product. The product label is the written, printed,
or graphic material on, or attached to, the product container. Detailed
information on labeling requirements, such as the ingredient statement,
precautionary statements and directions for use are discussed in section
12.9.
• Supporting data as specified in 40 CFR Part 158.202.
• FIFRA Section 3(c)(l)(F) Data Compensation forms as appropriate
(EPA Form 8570-29 or 8570-27).
If the submitter owns or has rights to the data being submitted, this
should be indicated on the Certification with Respect to Citation of Data,
Form 8750-29. If the submitter is relying on data owned by others, and the
data is within the 10-year exclusive use window provided to the owner, then
the submitter must provide written authorization from the data owner for
EPA to reference the data. If the data are clear of the 10-year window, then
the submitter must indicate to EPA that an offer to pay reasonable compen-
sation has been provided to the data owner. All of these options are available on the Form 8570-29, and discussed further in section 12.7.
Under FIFRA Section 3(c)(2)(D) an applicant is excused from the
requirement to submit or cite data on the active ingredient if the source of
the active ingredient is an EPA registered product and is purchased from
another manufacturer. This section of FIFRA is referred to as the 'formulator's exemption'. In this instance the applicant must submit EPA Form
8570-27, Formulator's Exemption Statement. While the applicant is excused from data requirements on the active ingredient, the data requirements for the formulated product are still required.
(b) EPA priority system for processing applications. During the mid1990s, the regulated industry found that increasing amounts of time were
being required by EPA to process registration applications. EPA has
claimed that, despite increased productivity, it has not been able to keep
pace with an increasing number of applications [1O]. To manage the workload created by industry, EPA instituted a priority registration process in
1996. This process was formalized in a 1997 PR Notice to industry [1O]. It
provides for the scheduling of each manufacturer's applications for new
chemical and new use registrations, tolerance petitions, experimental use
permits, and exemptions from tolerance for inert ingredients.
Applications for registration of microbial, biochemical and plant
pesticides and submissions to the Antimicrobial Division are not subject to
this PR Notice. These types of applications are generally not subject to
the delays incurred for conventional chemical pesticides for two reasons:
(1) they are handled by a dedicated staff in the Biopesticide Division and
the Antimicrobial Division, and (2) they are generally subject to fewer data
requirements compared to conventional chemical pesticides.
For products subject to the priority system, manufacturers are permitted
to submit a total of five registration actions into the system. The five are to
be ranked by the manufacturer in order from the most to the least important. It is anticipated that EPA will complete the processing of these five
actions within 12-18 moths, at which time EPA is expected to invite industry to rank and submit its next five requests.
Applications for registration of new formulations of active ingredients
that are currently registered, and for changes in use patterns that do not
require supporting data, are generally not subject to the priority system.
These types of actions are generally processed on a 'first in, first out' basis.
(c) Reduced-risk (safer) products. EPA put its 'reduced-risk' pesticides
strategy into effect in 1993 (Federal Register, Volume 58, Number 5854). Its
intent is to encourage the development, registration and use of lower-risk
products. Guidance on preparing reduced-risk rationales is in PR Notice
93-9.
EPA defines a safer pesticide as one which (1) reduces pesticide risks
to humans, (2) reduces pesticide risks to non-target organisms, (3) reduces
the potential for contamination of valued environmental resources or (4)
broadens the adoption of integrated pest management strategies.The major
advantage of achieving a reduced-risk status is that EPA will expedite the
registration review process for safer products.
According to PR Notice 93-9, a reduced-risk rationale must address all of
the following: human health effects, environmental fate and effects, other
hazards, risk discussion, and pest resistance and management.
The rationale must substantiate a claim for reduced risk by showing how
the product is inherently safer, and also how it is safer compared to alternative, competitive products. All competitive products registered by EPA for
the same use should be considered in the rationale. The guidance provided
in PR Notice 93-9 should be closely followed when preparing and submitting a rationale for safer status of a product. This and other PR notices can
be obtained directly from EPA or from its internet site (Appendices 12.A
and 12.B).
(d) Biopesticides. EPA considers products of biotechnology and natural
products to be inherently safer than conventional chemical pesticides.
To encourage the development and registration of biopesticides, EPA
has simplified the registration process. First, it developed the registration
data requirements around a tiered testing concept. Generally, each
category of data, e.g. toxicology, has Tiers I, II and III. The complexity,
duration and cost of studies generally increases with each tier of testing.
If significant adverse effects are observed in Tier I studies then Tier II
studies will be required. Results at one level determine if testing at
the next higher level is needed. Often, only Tier I studies are necessary.
Second, in 1994, EPA created its Biopesticide Division to process
biopesticide registrations exclusively. Thus biopesticides have lower regulatory costs and a faster regulatory review process, compared to chemical
pesticides.
EPA places biopesticides in one of three categories: microbial, biochemical and plant pesticides.
Microbial pesticides include bacteria, fungi, protozoans and viruses. The
EPA data requirements are published in 40 CFR Part 158.740. The basic
requirements for registration include
• a thorough taxonomic description of the active microbial ingredient;
• information on the pathogenicity and toxic components of the
microoganism and toxins associated with its growth;
• a description of the manufacturing process with emphasis on quality
control procedures;
• acute toxicity and pathogenicity studies.
By late 1995, EPA concluded that safety data for microbial pesticides
submitted up to that time did not raise any human health concerns. As a
result, EPA has been granting exemptions from the requirement for tolerances for this category [U].
Biochemical pesticides are naturally occurring compounds that have
a non-toxic mode of action. The EPA data requirements are published in
40 CFR Part 158.690. Natural lepidopteran insect pheromones and plant
growth regulators such as auxins, gibberellins and cytokinins are, by definition, biochemical pesticides [12]. When used as pesticides, commonly
recognized foods or their components, e.g. garlic and cinnamon, are also
considered biochemical pesticides. If a synthesized chemical is structurally
similar to, and functionally identical to, a naturally occurring biochemical,
then the synthesized chemical is also considered to be a biochemical. Insect
pheromones and pheromone traps are exempt from FIFRA registration in
40 CFR Part 152.25, 'Exemptions for pesticides of a character not requiring
FIFRA regulation'.
The basic Tier I requirements for registration include:
• product chemistry data;
• Tier I toxicity studies:
• acute toxicity;
• genotoxicity;
• immunotoxicity;
• 90-day feeding study;
• developmental toxicity;
• Tier I non-target organism and environmental expression:
• avian acute oral toxicity;
• avian dietary toxicity;
• freshwater fish acute toxicity;
• freshwater invertebrate acute toxicity;
• non-target plant studies.
Plant pesticides (transgenic plants) are pesticide substances introduced
into plants along with the genetic material necessary for the production of
the substance within the plant. EPA has published the data requirements
for plant pesticides in the Federal Register, Volume 59, No. 225, pp. 60496547. At the time of writing, EPA has proposed numerous changes to the
regulations which will probably affect registration of transgenics. Those
involved with plant pesticide registrations should contact EPA for the most
up-to-date policies and regulations.
EPA acknowledges that there are compounds in all plants that provide
resistance to insect or microbial damage, and that they occur in many food
crops without presenting a human dietary hazard [9]. However, EPA
justifies the regulation of plant pesticides on the basis that some pesticidal
traits from microbes, animals or from other plants may represent a new
exposure and risk for humans. EPA has decided that it will not concern
itself with the plant per se, but rather with the pesticidal substance produced
in the plant, and the novel human exposure that the plant may offer for the
pesticidal substance.
Basic registration requirements include
• product characterization:
• identification of the donor organism and the gene sequence inserted
into the recipient plant;
• identification and description of the vector or delivery system used to
move the gene into the recipient plant;
• identification of the recipient organism, including information on the
insertion of the gene sequence;
• data and information on the level of expression of the pesticidal
substance;
• product analysis and residue chemistry:
• proposed mode of action of the pesticidal substance;
• range or estimate of concentrations of the substance in the plant and
plant parts and the analytical method used, if toxicity or expression
data are required;
• toxicity:
• proteinaceous;
• acute oral toxicity;
• observed dermal effects;
• non-proteinaceous:
• oral studies (acute, subchronic or chronic feeding studies);
• observed dermal effects;
• pulmonary studies.
The limited routes for significant exposure to plant pesticide substances
should limit the amount of toxicity testing needed for registration. The
proteinaceous substances have the least amount of testing, on the basis
of expected degradation of these substances to amino acids with passage
through the intestinal tract.
In addition to regulation by EPA, some biopesticides are also subject to
regulation by the Animal and Plant Health Inspection Service (APHIS) of
the US Department of Agriculture, and by the US Food and Drug Administration (FDA). APHIS is concerned with an organism that has been
genetically engineered using recombinant DNA techniques, which is a plant
pest as defined in 7 CFR Part 340 [13]. The definition of 'plant pest' includes
bacteria, viruses and any other infectious agent or substance which can
injure or cause disease to any plant. APHIS announced in 1997 that a
number of organisms have no potential for plant pest risk and would no
longer be regulated [14]. These include
•
•
•
•
•
insect-resistant corn (Northrup King Company);
herbicide-tolerant cotton (DuPont Agricultural Products);
herbicide-tolerant soybean (AgrEvo);
insect-resistant cotton (Calgene);
insect-resistant corn (Monsanto).
Those developing biopesticides should consult with the Biotechnology
Evaluation Unit of Biotechnology and Scientific Services of APHIS, located at 4700 River Road, Riverdale, Maryland, telephone 301-734-7612.
APHIS maintains current information about its biopesticide regulations at
its internet site (Appendix 12.A).
FDA is concerned about the unexpected effects of genetically engineered
substances in food. Their major concern is for potential allergenicity to the
food containing the substance. FDA works with industry under a voluntary
review program. Those developing transgenic plant pesticides may wish to
consult with FDA about this program.
12.4.3 Tolerances and exemptions from tolerances
The Federal Food, Drug, and Cosmetic Act requires that tolerances are
established for maximum permissible pesticide residues resulting in or on:
• raw agricultural commodities or processed food;
• meat, milk, poultry and eggs - from direct treatment or from transfer of
residues through treated animal feed;
• rotational crops - from transfer of residues in the soil from previously
treated crops;
• imported food commodities.
Maximum permissible levels are established based on the results of EPArequired residue data submitted by industry. These data are submitted as
part of a 'pesticide tolerance petition'. Generally, a tolerance petition and
an application for registration are submitted together.
(a) Procedures for filing tolerance petitions. There are no forms to complete for tolerance petitions; however, EPA requires certain kinds of information and data to be submitted, in a format described in Section 408 of
FFDCA. In summary the petition must include all of the following.
• Section A: Product Chemistry Data. The name, chemical identity and
composition of the pesticide. This includes a description of the manufacturing process, chemical analysis of typical production batches of the
chemical, certified limits for ingredients of a product, and an analytical
method for the active ingredient.
• Section B: Proposed Product Labeling. Labeling submitted must contain
the directions for use of the product. This includes treatment or dosage
•
•
•
•
•
rates, the maximum number of applications per crop, the interval
between treatments, and use restrictions such as the minimum interval
between the last treatment and crop harvest, also known as the preharvest interval.
Section C: Full Reports on Toxicity Studies with the Chemical. The types
of toxicity data required to support a petition are identified in 40 CFR
Part 158.340, Toxicology Data Requirements.
Section D: Dietary Exposure Data. Information on testing for the
amount of pesticide residue remaining on the crop or processed food
item when the crop is treated according to label directions. The types of
data required are identified in 40 CFR Part 158.240, Residue Chemistry
Data Requirements.
Section E: Practical Methods for Removing Residue that Exceeds a
Proposed Tolerance. Although not always required by EPA, this information would include how to reduce residues to levels at or below the
tolerance by methods such as washing a food item.
Section F: Proposed Tolerance Level. The petition should generally propose the maximum residue level seen in field crop residue trials as the
tolerance level.
Section G: Reasonable Grounds in Support of the Petition. This section
of the petition should include a technical rationale which explains how
the submitted data support the proposed tolerance level.
(b) Inert formulation additives. Simply stated, an inert ingredient is any
ingredient that is not an active ingredient, as defined in 40 CFR 153.125, and
includes, but is not limited to, the following types: attractant, binder, buffer,
carrier, coating agent, defoaming agent, diluent, dispersant, dye, emulsifier,
encapsulating agent, flocculating agent, preservative, propellant, solvent,
stabilizer, surfactant, synergist, thickener and wetting agent.
In April 1987, EPA published a policy statement intended to discourage
the use of toxic inerts (Federal Register, Volume 52, Number 77). The policy
categorized the approximately 1200 inert ingredients on file with EPA at
that time into four lists. The lists were created to set EPA priorities for
regulatory action. EPA has focused primarily on the compounds in List 1.
EPA Toxicity Categories for Inert Ingredients (1987) are as follows:
•
•
•
•
List 1: inert ingredients of toxicological concern;
List 2: potentially toxic inert ingredients with a high priority for testing;
List 3: inert ingredients of unknown toxicity;
List 4: inert ingredients of minimal concern.
About 50 inert ingredients were placed in List 1 based on carcinogenicity,
adverse reproductive effects, neurotoxicity, other chronic effects, developmental toxicity, ecological effects, or potential for bioaccumulation.
EPA placed another 60 inert ingredients in List 2 based on structural
similarity to chemicals known to be toxic to humans. Inert ingredients were
put on List 4 if they were genererally regarded as innocuous. These included substances classified as 'generally recognized as safe' (GRAS) by the
FDA (21CFR Part 182). An inert ingredient was placed on List 3 if there
was no basis for listing it on any of the other three lists. There were about
800 ingredients placed on List 3.
EPA's policy encourages industry to substitute inert ingredients in Lists
1 and 2 with those from List 3 or 4, or with newer and safer compounds. The
policy also allows EPA to require additional safety studies for inert ingredients on Lists 1 and 2.
When developing formulations for use on growing or stored crops, or for
use on animals, chemists should refer to the list of inert ingredients that are
currently exempt from the requirement for a tolerance (40 CFR Part 180).
No safety data on these exempt inert ingredients are required. The inert
compounds that are exempt from tolerances are published by EPA as
follows:
• 40 CFR Part 180.1001 (c) - inert ingredients used in formulations applied
to growing crops or to raw agricultural commodities after harvest;
• 40 CFR Part 180.1001 (d) - inert ingredients used in formulations applied
to growing crops only;
• 40 CFR Part 180.1001 (e) - inert ingredients used in formulations applied
to animals.
EPA's 1992 'List of Pesticide Product Inert Ingredients' is also a useful
reference. It is a comprehensive list of inert ingredients and their associated
Chemical Abstract Service Registry Numbers [15].
If an inert ingredient is not exempt from a tolerance, a petition must be
submitted to EPA requesting an exemption. If the inert compound is included in the FDA GRAS list then, generally, no safety data are needed
with the petition. If it is not on the GRAS list, then the petition may need
safety data on the inert ingredient, such as acute toxicity studies, subchronic
toxicity data and product chemistry data. Safety studies in the scientific
literature that are supportive could be cited. It is best to consult with EPA
if there is any question of whether data are required.
(c) Registration fees. Registration maintenance fees are specified in
FIFRA Section 4(i)(5). EPA requires those holding pesticide registrations
to pay an annual fee, according to the number of registrations held and the
size of the business. A summary of the fee schedule is given in Table 12.2.
In 1997, FIFRA authorized EPA to collect fees in an aggregate amount of
$14 million. In the years 1998 to 2000, EPA may collect $16 million in
aggregate. If EPA expects a shortfall from the aggregate amount author-
Table 12.2 Registration maintenance fees
Category
Amount
Annual Fee
First registration - $650
Each additional registration up to 200 - $1300
Maximum Annual Fee
Up to 50 registrations - $55000
Greater than 50 registrations - $95000
Maximum Annual Fee for Small Business3
Up to 50 registrations - $38500
Over 50 registrations - $66500
a
Small Business is denned as having 150 or fewer employees and average annual gross
revenues not more than $40 million.
ized, it may adjust upwards the amount required for individual product
registrations.
(d) Tolerance fees. EPA is charged with administration of Section 408
of the Federal Food, Drug, and Cosmetic Act (FFDCA). Section 408
authorizes EPA to establish tolerance levels and exemptions from the
requirements for tolerances for food commodities. Section 408(o) requires
that the EPA collect fees that will be sufficient to cover the costs of processing petitions for pesticide products (Table 12.3). This fee schedule is
changed annually by the same percentage as the change in the Federal
General Schedule pay scale. A new fee schedule is published annually in the
Federal Register [16].
Table 12.3 EPA Tolerance Petition Fees Schedule (1997)
Category
Amount
Petition for
Tolerance
New tolerance or an increase in
the level of an existing tolerance
Lower numerical level than a
tolerance already established
for the same pesticide
Tolerance on additional food
commodities at the same
numerical level as a tolerance
already established for the
same pesticide
$64025, plus $1600 for each food
commodity greater than nine
$14650 plus $975 for each food
commodity on which a tolerance
is requested
$14 650 plus $975 for each
food commodity on which a
tolerance is requested
Exemption
from Tolerance
Exemption from the requirement
of a tolerance
$11800
Temporary
Tolerance
New tolerance
Renew or extend
Same numerical level or at a
higher numerical level
$25575
$3625
$12750 plus $975 for each food
commodity
Fee type
Next Page
12.5 Registration and tolerance data requirements
The studies needed to support registration and tolerance submissions are
listed in 40 CFR Part 158.202, Data Requirements Tables. The majority of
the data requirements for a pesticide can be determined by consulting these
tables.
EPA places all use patterns in one of the following categories for purposes of determining data requirements:
•
•
•
•
•
•
Terrestrial: (a) Food Crop and (b) Non-food use;
Aquatic: (a) Food Crop and (b) Non-food use;
Greenhouse: (a) Food Crop and (b) Non-food use;
Forestry;
Domestic Outdoor;
Indoor.
Tables 12.4-12.8 provide an inventory of most of the EPA data requirements. Which specific studies are required by EPA for a particular product
depends upon (1) the product's use pattern, (2) the type of registration
being sought, (3) the physico-chemical characteristics of the pesticide and
(4) whether the submitter is relying on existing data or generating new
studies. Guidance on the conduct of each study is provided by EPA in its
testing guidelines. An index of these guidelines and how to obtain copies
are provided in Appendix 12.A.
12.6 Data evaluation
With the potential for over 100 separate registration studies to be required
to support the registration of a new active ingredient, and with aggregate
costs for these studies running into the millions of dollars, it is imperative
that industry knows in advance what EPA expects in terms of study conduct
and reporting, and what principles of interpretation EPA will use in evaluating the data. EPA has provided industry with this guidance in the form of
three sets of information:
• Pesticide Assessment Guidelines (PAG);
• Standard Evaluation Procedures (SEP);
• Data Reporting Guidelines (DRG).
The PAGs provide detailed information necessary to design study
protocols that will meet EPA requirements. Studies are evaluated by EPA
against the PAGs to determine if the specifications given in the PAGs have
been followed. Major deviations from the PAGs can be grounds for rejecting the study and causing delays in product registration approval.
The SEPs provide EPA scientists with a checklist of criteria that each
study must satisfy, in order to be acceptable, and provide guidance on
Table 12.4 Product chemistry data requirements
Data requirement
Guideline no.
Group A: Product Identity, Composition, and Analysis Test Guidelines
Product identity and composition
Description of materials used to produce the product
Description of production process
Description of formulation process
Discussion of formation of impurities
Preliminary analysis
Certified limits
Enforcement analytical method
61-1
61-2
61-2
61-2
61-3
62-1
62-2
62-3
Group B: Physical/Chemical Properties Test Guidelines
Color
Physical state
Odor
Melting point/melting range
Boiling point/boiling range
Density/relative density/bulk density
Dissociation constant in water
Partition coefficient (n-octanol-water)
pH
Stability to normal and elevated temperatures, metals and metal ions
Oxidation-reduction: chemical incompatabiity
Flammability
Explodability
Storage stability
Viscosity
Miscibility
Corrosion characteristics
Dielectric breakdown voltage
Submittal of samples
Water solubility
Vapor pressure
63-2
63-3
63-4
63-5
63-6
63-7
63-10
63-11
63-12
63-13
63-14
63-15
63-16
63-17
63-18
63-19
63-20
63-21
64-1
63-8
63-9
EPA's interpretive policies. This helps ensure consistency of evaluation
among the many EPA scientists reviewing similar types of studies.
After evaluating a study against the appropriate PAG and SEP, the EPA
scientist will determine the significance of any inconsistencies in the test
procedures, and categorize the study as to its usefulness for regulatory risk
assessment. The three study categories as described in the SEPs are as
follows [17].
• Core Guideline: all essential information was reported and the study was
performed according to recommended protocols. Minor inconsistencies
with standard methodologies may be apparent; however, the deviations
do not detract from the study's soundness or intent. Studies within this
category fulfill the basic requirements of 40 CFR Part 158 of the regulations and are acceptable for use in a risk assessment.
• Supplemental: studies in this category are scientifically sound; however,
they were performed under conditions that deviated substantially from
Table 12.5 Toxicology data requirements
Data requirement
Guideline no.
Group A: Acute Toxicity Test Guidelines
Acute oral toxicity
Acute dermal toxicity
Acute inhalation toxicity
81-1
81-2
81-3
Group B: Specific Organ /Tissue Toxicity Test Guidelines
Acute eye irritation
Acute dermal irritation
Skin sensitization
81-4
81-5
81-6
Group C: Subchronic Toxicity Test Guidelines
90-Day oral toxicity
Subchronic nonrodent oral toxicity - 90-day
Repeated dose dermal toxicity - 21/28 days
Subchronic dermal toxicity - 90 days
Subchronic inhalation toxicity
Prenatal developmental toxicity study
Reproduction and fertility effects
82-1
82-1
82-2
82-3
82-4
83-3
83-4
Group D: Chronic Toxicity Test Guidelines
Chronic toxicity
Carcinogenicity
Combined chronic toxicity/carcinogenicity
83-1
83-2
83-5
Group E: Genetic Toxicity Test Guidelines
Escherichia coli WP2 and WP2 uvrA reverse mutation assays
Gene mutation in Aspergillus nidulans
Mouse biochemical specific locus test
Mouse visible specific locus test
Gene mutation in Neurospora crassa
Salmonella typhimurium reverse mutation assay
Sex-linked recessive lethal test in Drosophila melanogaster
Detection of gene mutations in somatic cells in culture
In vitro mammalian cytogenetics
In vivo mammalian cytogenetics tests: spermatogonial chromosomal
aberrations
In vivo mammalian cytogenetics tests: bone marrow chromosomal
analysis
In vivo mammalian cytogenetics tests: erythrocyte micronucleus assay
Rodent dominant lethal assay
Rodent heritable translocation assays
Bacterial DNA damage or repair tests
Unscheduled DNA synthesis in mammalian cells in culture
Mitotic gene conversion in Saccharomyces cerevisiae
In vitro sister chromatid exchange assay
In vivo sister chromatid exchange assay
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
84-2
Group F: Neurotoxicity Test Guidelines
Delayed neurotoxicity of organophosphorus substances following
acute and 28-day exposure
Neurotoxicity screening battery
Developmental neurotoxicity study
Schedule-controlled operant behavior
Peripheral nerve function
81-8, 82-7, 83-1
83-6
85-5
85-6
Group G: Special Studies Test Guidelines
Metabolism and pharmacokinetics
Dermal penetration
Immunotoxicity
85-1
85-3
85-7
81-7, 82-5, 82-6
Table 12.6 Residue chemistry data requirements
Data requirement
Chemical identity
Directions for use
Nature of the residue - plants, livestock
Residue analytical method
Multiresidue method
Storage stability data
Water, fish and irrigated crops
Food handling
Meat, milk, poultry and eggs
Crop field trials
Processed food/feed
Proposed tolerances
Reasonable grounds in support of the petition
Submittal of analytical reference standards
Confined accumulation in rotational crops
Field accumulation in rotational crops
Guideline no.
171-2
171-3
171-4a,b
171-4c,d
171-4m
171-4e
171-4f,g,h,
171-4i
171-4J
171-4k
171-41
171-6
171-7
171-13
165-1
165-2
Table 12.7 Environmental fate data requirements
Data requirement
Hydrolysis
Photodegradation:
In water
On soil
In air
Metabolism studies (laboratory):
Aerobic soil
Anaerobic aquatic
Aerobic aquatic
Mobility studies (laboratory)
Leaching and adsorption/desorption
Volatility:
Laboratory
Field
Dissipation studies - field
Soil
Aquatic (sediment)
Soil, long-term
Accumulation studies
Rotational crops:
Confined
Field
Irrigated crops
In fish
In aquatic non-target organisms
Guideline no.
161-1
161-2
161-3
161-4
162-1
162-3
162-4
163-1
163-2
163-3
164-1
164-2
164-5
165-1
165-2
165-3
165-4
165-5
Table 12.8 Ecological effects data requirements
Data requirement
Guideline no.
Group A: Aquatic Organism Test Guidelines
Aquatic inverebrate acute toxicity, test, freshwater daphnids
Oyster acute toxicity test (shell deposition)
Mysid acute toxicity test
Penaeid acute toxicity test
Bivalve acute toxicity test (embryo larval)
Fish acute toxicity test, freshwater and marine
Daphnid chronic toxicity test
Mysid chronic toxicity test
Fish early-life stage toxicity test
Fish life cycle toxicity
Oyster BCF
Fish BCF
Aquatic food chain transfer
Field testing for aquatic organisms
72-2
72-3
72-3
72-3
72-3
72-1
72-4
72-4
72-4
72-5
72-6
72-6, 165-4
72-6
72-7, 165-5
Group B: Terrestrial Wildlife Test Guidelines
Avian acute oral toxicity test
Avian dietary toxicity test
Avian reproduction test
Wild mammal acute toxicity
Field testing for terrestrial wildlife
71-1
71-2
71-4
71-3
71-5
Group C: Beneficial Insects and Invertebrates Test Guidelines
Honeybee acute contact toxicity
Honeybee toxicity of residues on foliage
Field testing for pollinators
141-1
141-2
141-5
Group D: Non- target Plants Test Guidelines
Target area phytotoxicity
Terrestrial plant toxicity, Tier I (seedling emergence)
Terrestrial plant toxicity, Tier I (vegetative vigor)
Seed germination/root elongation toxicity test
Seedling emergence, Tier II
Early seedling growth toxicity test
Vegetative vigor, Tier II
Terrestrial plants field study, Tier III
Aquatic plant toxicity test using Lemna spp. Tiers I and II
Aquatic plants field study, Tier III
121-1
122-1
122-1
122-1
123-1
123-1
123-1
124-1
122-2, 123-2
124-2
Group E: Toxicity to Microorganisms Test Guidelines
Algal toxicity, Tiers I and II
122-2, 123-2
recommended guideline protocols. Results do not meet regulatory requirement; however, the information may be useful in a risk assessment.
• Invalid: these studies provide no useful information. They are not scientifically sound, or they were performed under conditions that deviated so
significantly from recommended protocols that the results will not be
useful in a risk assessment.
After the assessment of the study is completed, it is documented as a
study review which will be forwarded to the Registration Division Product
Manager. The Product Manager will in turn provide the applicant with a
copy of the review. If there are any deficiencies in the study, the applicant
will be asked to address them within a specified period of time.
12.6.1 EPA risk assessment process
The principal purpose for generating most registration data is to enable the
assessment and characterization of potential risks to humans, non-target
animals or to the environment from the pesticide use. Under FIFRA sections 3(c)(5)(C) and (D), EPA must determine that the pesticide will not
generally cause unreasonable adverse effects on the environment, taking
into account the economic, social and environmental costs and benefits of
the use of the pesticide.
To make this determination EPA uses established principles of risk assessment and risk management. A risk assessment will consider the potential of a pesticide to cause an adverse effect in a test species, the lowest dose
level at which the adverse effect occurs and the dose level where no adverse
effect is observed. Next, consideration is given to the amount of exposure
which may occur, from the pesticide to people, or to the environment, and
the duration and route of the exposure. When integrated, these components
provide an estimate of the probability that an adverse effect, observed in
laboratory or field studies, may occur in an exposed population of people,
animals or in the environment.
Risk assessments are carried out for a variety of reasons and include the
following.
• Human health risk assessments for various routes of exposure including
acute and chronic dietary exposure, and dermal and inhalation exposure
to assess the risk of cancer, chronic effects, developmental toxicity, reproductive toxicity, neurotoxicity and mutagenicity. FQPA requires EPA to
evaluate these risks from the aggregate exposure to a pesticide, i.e. from
both dietary and non-dietary routes.
• Ecological risk assessments based on acute and chronic exposure to
residues of a pesticide to aquatic organisms and mammals and birds.
• Environmental risk assessments based on the potential of a pesticide to
be persistent in soils and/or leach to groundwater.
After determining the potential risk of occurrence for an adverse effect in
an exposed population or in the environment, EPA will then make risk
management decisions. These decisions compare and consider the potential
risks with the political, social and economic factors regarding a pesticide
and its use.
It is important that registrants have a working knowledge of EPA risk
assessment procedures so that they may conduct their own 'EPA-style'
assessments. These assessments should be carried out as data become avail-
able, to understand as early as possible which products will meet EPA
safety standards, and can then be confidently taken to full commercial
development.
12.6.2 Industry interaction with EPA: practical advice
Frequent contact with EPA, especially the Registration Division, is advantageous. Contact EPA prior to submission to determine which Product
Manager will handle your application. Discuss any uncertainties about
preparing the submission with the Product Manager. If the issues warrant,
a meeting at the EPA offices may be desirable; contact the Product Manager to arrange such a meeting. A list of EPA contacts is provided in
Appendix 12.C.
Be patient, but expectant, with EPA regarding progress on an application. They have a tremendous work load and must adhere to many rules,
policies and regulations to process each application. You can and should
request verbal reports from the EPA Product Manager on progress. How
frequently you contact the Product Manager depends on the type of application. For example, an application for registration of a new formulation of
a pesticide previously registered should generally take no more than 6-12
months to process. In this case it would be reasonable to ask for progress
reports about every 2-3 months. In the initial contact, about 3-4 weeks after
submission, ask for a projected completion date from the Product Manager.
The timing of subsequent contacts should be based on the expected completion date. On the other hand, an application for registration of a new active
ingredient can require 24 months or more to process. In this case, less
frequent contact would be appropriate, perhaps every 4 months or longer,
again dependent on the expected completion date. In any case, do not
depend on EPA to initiate contact and provide progress reports. EPA will
expect an applicant to periodically make requests for updates.
Invariably, EPA will have a concern of some kind regarding an application, perhaps with the administrative information or with the study conduct
or results, requiring resolution before the registration approval is granted.
First, determine if EPA is correct in its position, taking into account all the
EPA rules, guidelines or policies which may impact the issue. If they are
correct, discussion with EPA may be desirable to ascertain what is needed
to rectify the problem, especially if a study is involved. If EPA are incorrect,
a technically sound rebuttal should be prepared and submitted. On a caseby-case basis, a meeting with EPA scientific staff may also be warranted to
resolve issues regarding studies. Often, rejected studies can be upgraded or
repaired to an acceptable 'Core' status.
Some companies use consultants to do some or all of their regulatory
work. Consultants can conduct or arrange for the conduct of registration
studies, prepare and submit the registration application and carry out the
follow-up work with EPA personnel.
12.7 Data protection and compensation
Protection against the unauthorized and uncompensated use of proprietary
registration data was added to FIFRA in section 3(c)(F) in 1978. The
regulations for these provisions of FIFRA are found in 40 CFR Part 152.83.
For those submitting data, FIFRA provides for
• a 10-year period of exclusive right to the use of 'exclusive-use' data
submitted to support the initial registration of an active ingredient;
• a 15-year period of the right to compensation for use by others of
'compensable' data.
The term 'exclusive-use' study means that all of the following conditions
apply:
• the study pertains to a new active ingredient first registered after 30
September 1978;
• the study was submitted in support of the application which resulted in
the first registration of the new active ingredient, or in support of an
application to amend the registration to add a new use;
• the study was not submitted to satisfy a data requirement imposed under
FIFRA section 3(c)(2)(B), also known as a 'Data Call-In'.
The 10-year period of exclusive use commences with the date of EPA
issuance of the initial registration of the active ingredient. The term
'compensable' data applies to any study submitted after 31 December 1969.
The 15-year period of the right to compensation commences on the date the
study is submitted to EPA.
For those citing the data of others, FIFRA provides that
• citation of 'exclusive use studies' is acceptable only if the original data
submitter has given written authorization under the terms outlined in
40 CFR Part 152.93;
• citation of studies which are not 'exclusive-use' data are acceptable provided that
• an offer-to-pay compensation has been provided to the original data
submitter under the terms of FIFRA section 3(c)(l)(F); or
• the study was originally submitted to EPA on or before 31 December
1969; or
• the study was originally submitted to EPA 15 years or more before the
date of the application citing the study.
EPA must receive confirmation that an 'offer to pay' has been submitted
to the original data submitter; however, EPA does not get involved in
determination of the amount of the compensation. This is left to negotiation between the two parties. If they cannot agree, the amount is determined according to binding arbitration as described in FIFRA section
3(C)(I)(F).
FIFRA section 3(c)(2)(D) exempts applicants from the requirement to
submit or cite data, for any ingredient contained in their products, which are
derived from an EPA-registered product which the applicant purchases
from another producer. This exemption is referred to as the 'formulator's
exemption'. The terms and conditions for the exemption are outlined in
40 CFR Part 152.85.
12.8 Reregistration and product defense
FIFRA section 3(g) requires that all pesticides first registered before 1
November 1984, undergo reregistration. This process requires that older
studies are replaced with studies carried out to modern scientific standards.
In 1988 the Agency began to accelerate the reregistration process. At that
time, EPA categorized the 1150 active ingredients into 600 groups of
related pesticides. They further divided the categories in four lists: A, B,
C and D [18].
List A consists of 194 chemical groups containing 350 active ingredients
in total for which EPA had already started reregistration prior to 1988. Lists
B, C and D contain the remainder of the active ingredients with those of
highest regulatory concern in List B and those of least concern in List D.
Each active ingredient must pass through five phases to complete
reregistration [18]:
• Phase 1: Listing of Active Ingredients. In 1989, EPA published the four
lists and asked companies to announce their intentions about supporting
each product through the process.
• Phase 2: Declaration of Intent and Identification of Studies. This phase
was completed in 1990. Registrants were required to commit to the
reregistration process, to the conduct and submission of replacement
studies where needed, and to pay the first installment of the reregistration
fee.
• Phase 3: Summarization of Studies. During this phase registrants were
required to reformat, summarize, and submit those studies considered
acceptable, recommit to satisfying data gaps, and to pay the final
installment of the reregistration fee. This phase was completed in late
1990.
• Phase 4: EPA Review and Data Call-Ins. EPA reviewed all Phase 2 and
3 submissions and required registrants to satisfy all data gaps within four
years. This phase was completed in 1993.
• Phase 5: Reregistration Decisions. During this phase EPA evaluates the
replacement studies, conducts risk assessments based on these data and,
where needed, requires mitigation measures or regulatory controls to
reduce a pesticide's risks. EPA then reregisters those pesticides that can
be used without posing unreasonable risks to human health or the environment. When a pesticide is eligible for reregistration, EPA explains the
technical and regulatory basis for its decision in a Reregistration Eligibility Decision (RED) document. As the RED documents are issued, EPA
makes them publicly available. A list of completed documents are available at the EPA Internet site in 'PDF' format, where they can be read
using Adobe® Acrobat® Reader software.
In its annual report for 1996 [3], the Office of Pesticide Programs indicated that of the 614 groups of active ingredients eligible for reregistration
in 1988, 232 are no longer supported by industry. REDs have been issued
for 148, leaving 234 to be completed. Registrants have submitted over
21000 studies in this process and EPA has reviewed over 14500. EPA does
not expect to complete the reregistration process, which started in 1988,
until after the year 2000.
72.8.1 Data Call-In and industry task force groups
FIFRA section 3(c)(2)(B) allows EPA to require additional data to support
currently registered products. If EPA determines that a new type of study
is needed to judge the safety of a class of compounds or of a single compound, it will issue a 'Data Call-In' to all registrants of products containing
the compounds of concern. FIFRA allows for the formation of an industry
task force, whereby all the registrants required to conduct the new study
may jointly share the cost of developing the data. For example, EPA required spray drift studies to support most agricultural products. This requirement affected a total of 38 companies that joined together in 1990 as
members of the Spray Drift Task Force, and generated the required spray
drift studies. The multimillion dollar cost of conducting these studies has
been divided among the members, which has considerably reduced the
financial impact for any single company.
The formation of industry task groups has become the standard mechanism for the generation of data of a generic nature that is applicable to two
or more companies. The approach is embraced by EPA as a more efficient
use of its resources compared to working separately with many individual
companies.
12.8.2 Special review process and cancellation of registrations
The current process used by EPA to identify and cancel registrations for
pesticides that may cause unreasonable adverse effects to people or to the
environment, is referred to as the 'special review' process. A pesticide may
be considered for special review if any of the following criteria are met
(40 CFR Part 154.7):
•
•
•
•
•
acute toxicity to humans or domestic animals;
potential chronic or delayed toxic effects in humans;
potential hazards to non-target organisms;
risk to the continued existence of any threatened or endangered species;
risk of destruction or other adverse modification of a critical habitat of
any threatened or endangered species;
• any other adverse effect to humans or the environment which may outweigh the benefits that justify initial or continued registration.
For those pesticides identified as meeting any of these criteria, registrants
may be notified that the EPA is considering a special review, and given
opportunity to rebut the EPA's findings. If EPA agrees with the registrant
that the pesticide does not pose a significant risk, it will explain its decision
in a Federal Register notice. If it disagrees, a notice of special review will be
published in the Federal Register, which starts a lengthy process often
lasting several years.
If EPA determines, through the special review process, that a product has
risks associated with its use that exceed the benefits to society of such use,
then EPA may start cancellation proceedings under 40 CFR Part 164.
Currently, EPA tries to avoid costly and lengthy special review and
cancellation proceedings by using a more informal approach to achieving
risk reduction. Usually, EPA will contact a registrant and discuss its concerns about risks for a particular product. It will seek to negotiate an
agreement, whereby a product's use is modified in a way that reduces
exposure to the product, thereby reducing the associated risk to an acceptable level. This informal process takes far less time and resources compared
to a special review.
12.9 Product labeling
The contents of pesticide labels have increased substantially over the past
10 years. The label has become an extensive collection of information about
a product and includes sections with warnings about its potential hazard to
people, animals, plants and the environment; requirements for users to
wear protective clothing and equipment; prohibitions on the use of the
product; practical first aid measures in case of exposure; requirements for
disposal of unused product and empty containers; and detailed directions
for use of the product. The typical agricultural product label with all of its
length and complexity takes considerable time and effort to understand in
its entirety.
The FIFRA defines the term 'label' as the written, printed or graphic
matter on, or attached to, the pesticide or any of its containers or wrappers.
It includes all written, printed or graphic information accompanying the
pesticide or device at any time, or to which reference is made on the label
or in literature accompanying the pesticide. EPA has published the requirements for pesticide labels in 40 CFR Part 156. The EPA has also published
an excellent practical guide for those writing pesticide labels, EPA Label
Review Manual, 2nd edition (1996) [19]. The manual is also available electronically at the EPA Internet site (Appendix 12.A).
The basic format for all labels includes the following sections [19]:
• Ingredient Statement: identifies the active ingredient (s), the percentage
by weight of each active ingredient and the percentage by weight of inert
ingredients in a product;
• Restricted Use Pesticide Statement: identifies those products under
FIFRA Section 3(d) considered highly toxic to people or to the environment, which may only be applied by persons certified as trained and
competent by EPA or by a State to use them;
• 'Signal Word' and 'Keep Out of Reach of Children' Statement: appears
on almost all end-use pesticide products. The signal word is determined
by the most severe toxicity category (Table 12.9) assigned to the five
acute toxicity studies. Signal words are as follows:
• Toxicity Category I - 'DANGER';
• Toxicity Category II - 'WARNING';
• Toxicity Categories III and IV - 'CAUTION';
Table 12.9 EPA Acute Toxicity Categories (40 CFR Part 156.10)
Study
Category I
Category II
Category III
Category IV
Acute oral
(mg/kg)
^5O
>50-500
>500-5000
>5000
Acute dermal
(mg/kg)
^2OO
>200-2000
>2000-5000
>5000
Acute inhalation
(mg/1)
^0.05
>0.05-0.5
Eye irritation
Corrosive (irreversible
destruction of ocular
tissue) or corneal
involvement or
irritation persisting
for more than 21 days
Corneal
involvement
or irritation
clearing in
8-21 days
Skin irritation
Corrosive (tissue
destruction into the
dermis and/or
scarring)
Severe
Moderate
irritation at
irritation
at72h
72 h (severe
erythema or
(moderate
edema)
erythema)
>0.5-2
>2
Minimal
Corneal
involvement
effects
clearing in
or irritation
clearing in
less than
7 days or less 24 h
Mild or slight
irritation
(no irritation
or slight
erythema)
• 'Skull and Crossbones' Symbol and the word TOISON': these symbols
identify pesticide products which are determined to be in Toxicity Category I based on at least one of the following acute toxicity studies: acute
oral, acute dermal or acute inhalation;
• Statement of Practical Treatment: provides information to the pesticide
user concerning appropriate first aid for the various routes of exposure if
accidental exposure occurs;
• Environmental Hazards: identifies any hazards to the environment and
any necessary precautions to protect the environment;
• Physical or Chemical Hazards: identifies any hazards such as flammability
or explodability;
• Directions for Use: provides the instructions concerning how to use the
product, the pests controlled, the application sites, and any application
equipment to be used;
• Re-entry Statement: identifies any time period following treatment when
entry into a treated area is restricted;
• Product Name: brand name chosen by the manufacturer;
• Warranty Statement: a disclaimer statement included voluntarily on
most pesticide products by the registrant to reduce the company's
liability concerning any damage caused by the use of a pesticide
product;
• Storage and Disposal: identifies the precautions necessary for storing unused product and disposing of any unused product or its
container;
• Registrant Name and Address: identifies the registrant of the product;
• Net Contents: identifies the amount or weight of pesticide in the
container;
• EPA Product Registration Number and Establishment Number: each
product has a unique registration number assigned by EPA; the establishment number, also assigned by EPA, identifies the manufacturing
site.
12.10 State registration requirements
Sections 24 and 26 of FIFRA are the principle sources of authority for state
regulation of pesticides. Section 24(a) provides that
A State may regulate the sale or use of any federally registered pesticide or device
in the State, but only if and to the extent the regulation does not permit any sale
or use prohibited by this Act.
All states have some arrangement for registration for pesticides. After a
federal registration is obtained, applications must be submitted and approved by each state before a product may be sold in that state. Many states
require only that the appropriate forms be completed and submitted along
with the necessary fees and proof of EPA registration. However, according
to Lawyer [20], 'some states, such as California, Arizona, New York, and
Florida almost always require additional documentation or data, particularly for new active ingredients, novel formulations and agricultural-use
products'.
In these states it is usually necessary to submit the same studies and study
summaries that were filed for the federal EPA registration. A copy of the
EPA study evaluations is also required in some cases. In their evaluation of
the data, state scientists occasionally reach a substantially different interpretation of the study results than reached by EPA. This is particularly
frustrating for an applicant who has passed the stringent federal EPA
requirements, but fails to pass the state data reviews, thus delaying sales of
a product.
Generally, labeling approved by EPA for federal registration will be
acceptable for state registration. In some instances, however, a specific
concern may lead a state to require additional label language not on the
federal label. The applicant must then go back to EPA to seek approval for
the additional language. If the applicant refuses to do so, the state will
probably withhold issuance of the state registration.
More states are requiring data to be submitted to support pesticide
registrations. In a few states, data requirements are actually more stringent
than EPA's requirements. Manufacturers must have a working knowledge
of each state's policies with special attention to the more demanding states
of Arizona, California, Florida and New York. As the state with the most
technically complex and demanding registration process, California deserves special mention. The California Department of Pesticide Regulation's (DPR) Internet home page (see Appendix 12.A) describes the
magnitude of their requirements:
pesticide manufacturers must submit studies of toxicology, efficacy,
phytotoxicity, environmental fate, product chemistry, and residue methodology
before DPR can register a product. DPR scientists, including toxicologists, entomologists, biologists, plant physiologists, chemists, and physicians evaluate the
elaborate testing data. Much scrutiny focuses on the acceptability of studies and
any potential for the pesticides to cause adverse health or environmental effects,
to ensure the proper, safe, and efficient use of pesticides.
Also worth noting, is California's strategic pesticide plan, issued in 1997
[21], which includes certain goals and objectives which will be of interest to
those pursuing registrations in this state. By March 1998, DPR plans to
establish itself as an essential participant in US EPA's national and international pesticide agenda. By December 1999, DPR plans to reduce the
median time period between the federal registration of a pesticide contain-
ing a new active ingredient and registration of the product for use in
California. Its strategies for achieving these goals include
• expanded participation in harmonization efforts with US EPA and,
through US EPA, harmonization efforts under North American Free
Trade Act;
• expanded participation in Organization for Economic Cooperation and
Development harmonization through US EPA, including analysis of the
dossier/monograph system;
• implementing concurrent acceptance of applications for registration of
all pesticide products containing new active ingredients;
• coordinating the review of pesticides containing new active ingredients
with US EPA;
• using new technologies to communicate with registrants and applicants
for registration of pesticide product and to process registration
information.
It is apparent from these strategies that California intends to be a leader
in pesticide regulation in the USA and emphasizes its desire to improve
harmonization of the pesticide requirements at the federal and state level.
Harmonization that eliminates unnecessary data requirements will be welcomed by industry. Reducing the time between submission and registration
would also be welcomed. The chances of achieving this latter goal will be
increased with the use of new technologies which allow electronic submission of data, a concept under serious consideration by EPA, California,
Canada and other governments.
For information about registering products in California contact the
Department of Pesticide Regulation, Division of Registration and Health
Evaluation, 1020 N Street, Sacramento, CA 95814-5624, telephone 916-4453980, or visit their Internet web site at the address given in Appendix 12. A.
Information on contacts in other states are available at the American Crop
Protection Association's Internet home page (Appendix 12.A).
12.11 Conclusions
The federal and state requirements for pesticide registration have greatly
increased in scope and technical complexity since their inception in 1947.
As an industry, pesticide manufacturing is among the most heavily regulated in the USA. For basic manufacturers, registration costs are a significant portion of research and development expenses.
Government controls for pesticides have created a need for highly
trained specialists who can provide a manufacturer with all of the technical
and administrative data and information needed to obtain registrations.
These specialists must be knowledgeable about governments' regulations,
rules and policies and skilled in complying with their requirements.
Environmental groups and governments are placing heavy pressure on
manufacturers to invent safer products to replace older pesticides that have
been tools of agriculture, in some cases, since the 1960s. Some successes
have been achieved using traditional synthetic chemistry and some in the
relatively new field of biotechnology. Heavy investment in biotechnology in
the 1990s, by a number of manufacturers, will undoubtedly pay big dividends in the next millennium.
Acknowledgements
The author acknowledges with thanks, colleagues in Zeneca Ag Products
who read and commented on the manuscript, R. Ridsdale, B. Kaminski and
A. Davidson, and his wife Cheryl, for proof-reading and correcting the text
and providing her support for this project.
Appendix 12.A Index of EPA study guidelines
The EPA harmonized testing guidelines are organized in the following 10
series:
810
830
835
840
850
860
870
875
880
885
Product Performance Test Guidelines
Product Properties Test Guidelines
Fate, Transport and Transformation Test Guidelines
Fate and Transport Field Studies Test Guidelines
Ecological Effects Test Guidelines
Residue Chemistry Test Guidelines
Health Effects Test Guidelines
Occupational and Residential Exposure Test Guidelines
Biochemicals Test Guidelines
Microbial Pesticide Test Guidelines
Final guidelines series are available from the US Government Printing
Office, Washington, DC 20402, or call 202-512-1530 for disks or paper
copies. In addition, all final guidelines will be available on the EPA Internet Site at URL: http://www.epa.gov/OPPTS_Harmonized/830_Product_
Properties_Test_Guidelines, in PDF (portable document format; Table
12.A.1).
Appendix 12.B Sources of registration information
There are many sources of information on pesticides that may be of regulatory value. Some of the best sources are listed here. These are the same
Table 12.A.1 The World Wide Web of the Internet
Reference
Internet URL address
EPA documents published in the Federal
Register
http://www.epa.gov/fedrgstr/
EPA Office of Pesticide Programs Home Page
http://www.epa.gov/internet oppts/
EPA Label Review Manual
http://www.epa.gov/oppfead/labeling/lrm
EPA, OPP, Organization and Contacts
http://www.epa.gov/oppfod01/oppinfo/
EPA, OPP, PR Notices
http://www.epa.gov/docs/PR_Notices
EPA, OPP, Harmonized Testing Guidelines
http://www.epa.gov/OPPTS_Harmonized/
EPA, Models for Evaluating Exposure to
Pesticides and Risk
http://www.epa.gov/epahome/models.htm
EPA, List of Chemicals Registered during
1971-1994
http://www.epa.gov/oppbeadl/newais.htm
EPA, 40 CFR Part 180: List of Tolerances and
Exemptions from Tolerances
http://www.epa.gov/pesticides/regstat.htm
EPA, Public Docket
htt://www.epa.gov/docs/PublicDocket
EPA, List of Completed Registration Eligibility
Documents
http://www.epa.gov/oppsrrdl/REDs/
USDA, APHIS Biotechnology and Scientific
Services Home Page
http://www.aphis.usda.gov/bbep/bp/
The National Technical Information Service
Home Page
http://www.ntis.gov
NTIS Database Search Engine - search for
documents/publications in the NTIS catalogue
http://www.ntis.gov/advance.htm
California Department of Pesticide Regulation
Home Page
http://www.cdpr.ca.gov
Florida Division of Agriculture and
Environmental Services Home Page
http://www.Fl-ag.com
American Crop Protection Association Home
Page
http://www.acpa.org/
sources recommended by EPA in PR NOTICE 94-3: How to Obtain Information from OPP.
(a) Freedom of Information, US Environmental Protection Agency, 401 M
Street, SW, Washington, DC 20460; Fax (202) 260-0295. Most of EPA's
records not specifically prepared for routine public distribution may be
obtained under the Freedom of Information Act (FOIA). FOIA is the
statutory mechanism for providing the public access to Agency records. The
types of pesticide records available include FIFRA health and safety data,
internal data reviews or memoranda, administrative files for registered
products, and policy and guidance documents. FOIA requests should in-
elude any known EPA identifiers, such as the EPA Registration Number,
active ingredient or chemical code, Master Record Identification Number
(MRID), submitter, subject, etc.
(b) Communications Branch, FOD, Office of Pesticide Programs (7506C),
US Environmental Protection Agency, 401 M Street, SW, Washington, DC
20460; Telephone (703) 305-5017; Fax (703) 305-5558. The Communications Branch provides information on recent pesticide announcements and
copies of non-technical brochures, booklets, and fact sheets on a variety of
pesticide topics.
(c) EPA Docket Office, Environmental Protection Agency, Office of Pesticide Programs, OPP Public Docket (7506C), 1921 Jefferson Davis Highway,
Crystal Mall 2, Room 1132, Arlington, VA 22202, Telephone (703) 305-5805.
EPA makes many of its documents available to the public through its
Docket Office.
(d) National Technical Information Service, 5285 Port Royal Road,
Springfield, Virginia 22161; Telephone (703) 487-4650; Fax (703) 321-8547.
The official resource for government-sponsored US and worldwide scientific, technical, engineering, and business-related information. Many EPA
technical documents are available through NTIS: Position Documents,
Registration Standards, Reregistration Eligibility Documents (REDs), Fact
Sheets, the compact label file, and Standard Evaluation Procedures. Information is available in various formats: printed reports, CD-ROMs, computer tapes and diskettes, on-line, audio cassettes, video cassettes and
microfiche. The NTIS Web site includes product listings on more than 375
subject areas from more than 200 US government agencies. Send mail
orders to: NTIS, 5285 Port Royal Road, Springfield, VA 22161. E-mail
orders to NTIS orders@ntis.fedworld.gov.
(e) National Pesticide Information Retrieval System (NPIRS) at Purdue
University, Project Manager, Telephone (317) 494-6616. The National
Pesticide Information Retrieval System (NPIRS) on-line database is available by annual subscription through Purdue University. NPIRS allows
users to access information on registered pesticide products, pesticide
tolerances, chemical information Fact Sheets, Pesticide Document Management System (PDMS) study listings, and Material Safety Data
Sheets. Selected NPIRS information is also available in CD-ROM or book
format.
(f) National Pesticides Telecommunications Network (NPTN), Telephone
(800) 858-7378. A toll-free telephone service, provides general infor-
mation to the public about pesticides. Using a number of data bases,
NPTN has access to the most recent literature published on virtually
any pesticide.
Appendix 12.C Office of Pesticide Programs: senior EPA contacts
The following is a listing of the senior managers within the Office of Pesticide Programs (OPP) as of May 1997. All OPP telephone area codes are
703.
Daniel M. Barolo, Director - 305-7090
Stephen L. Johnson, Deputy Director - 305-7092
Antimicrobials Division
Frank T. Sanders, Director - 308-6411
William L. Jordan, Associate Director - 308-6411
Biological and Economic Analysis Division
Allen L. Jennings, Director - 305-8200
Sherry Sterling, Associate Director - 305-8200
Biopesticides and Pollution Prevention Division
Janet L. Andersen, Director - 308-8712
Kathleen Knox, Associate Director - 308-8712
Environmental Fate and Effects Division
Joseph J. Merenda, Director - 305-7695
Denise M. Keehner, Associate Director - 305-7695
Field and External Affairs Division
Anne E. Lindsay, Director - 305-7102
Jay Ellenberger, Associate Director - 305-7102
Health Effects Division
Margaret J. Stasikowski, Director - 305-7351
Stephanie R. Irene, Associate Director - 305-7351
Information Resources and Services Division
Linda A.Travers, Director - 305-5440
Richard D. Schmitt, Associate Director - 305-5440
Registration Division
James Jones, Director - 305-5447
Peter P. Caulkins, Associate Director - 305-5447
Special Review and Reregistration Division
Lois A. Rossi, Director - 308-8000
Jack Housenger, Associate Director - 308-8000
References
1. National Agricultural Chemicals Association (1993) From Lab to Label, The Research,
Testing and Registration of Agricultural Chemicals, Washington, DC.
2. Office of Pesticide Programs (1997) The Federal Insecticide, Fungicide, and Rodenticide
Act (FIFRA), and Federal Food, Drug, and Cosmetic Act (FFDCA) As Amended by the
Food Quality Protection Act (FQPA) of August 3, 1996. EPA Document 730L97001,
United States Environmental Protection Agency, Washington, DC.
3. Office of Pesticide Programs (1996) EPA Office of Pesticide Programs Annual Report for
1996. EPA Document 735R96001, United States Environmental Protection Agency,
Washington, DC.
4. United States Environmental Protection Agency (1997), Notice: Raw and Processed Food
Schedule for Pesticide Tolerance Reassessment, Federal Register, Volume 62, Number 149,
August 4, page 42019, US Government Printing Office, Washington, DC.
5. Office of Pesticide Programs (1997) EPA OPP Pulse, EPA-730-X-97-002. United States
Environmental Protection Agency, Washington, DC.
6. Office of Pesticide Programs (1997) Goals 2005 Project. United States Environmental
Protection Agency, Washington, DC.
7. Office of Prevention, Pesticides and Toxic Substances (1992) General Information on
Applying for Registration of Pesticides in the United States, EPA/737/b-92-001, United
States Environmental Protection Agency, Washington, DC.
8. Office of Pesticides and Toxic Substances (1986) PR Notice 86-5 Notice to Producers,
Formulators, Distributors and Registrants. United States Environmental Protection
Agency, Washington, DC.
9. Kough, J.L. (1995) Regulatory Requirements for Plant-Pesticides. Proc. USDA IR-4/EPA
Minor Use Biopesticdes Workshop, 7-8 November 1995, National Foundation for Integrated Pest Management Education, Washington, DC.
10. Office of Pesticides and Toxic Substances (1997) PR Notice 97-2 Notice to Producers,
Formulators, Distributors and Registrants. United States Environmental Protection
Agency, Washington, DC.
11. Sjoblad, R.D. (1995) Regulatory Requirements for Microbial Pesticides. Proc. USDA IR4/EPA Minor Use Biopesticdes Workshop, 7-8 November 1995, National Foundation for
Integrated Pest Management Education, Washington, DC.
12. McClintock, TJ. (1995) Regulatory Requirements for Biochemical Pesticides. Proc. USDA
IR-4/EPA Minor Use Biopesticdes Workshop, 7-8 November 1995, National Foundation
for Integrated Pest Management Education, Washington, DC.
13. US Code of Federal Regulations, Title 7, Part 340, Restrictions on the Introduction of
Regulated Articles, US Government Printing Office, Washington, DC.
14. Animal and Plant Health Inspection Service (1997) BSS Biotechnology Update July 1997,
Internet address http://www.aphis.usda.gov/bbep/bp/newsleter.html, United States Department of Agriculture, Washington, DC.
15. Office of Pesticide Programs (1992) List of Pesticide Product Inert Ingredients, United
States Environmental Protection Agency, Washington, DC.
16. United States Environmental Protection Agency (1997) Tolerance Processing Fees. Federal Register, Vol. 62, No. 90, pp. 25524-5, May 9, US Government Printing Office,
Washington, DC.
17. Office of Pesticide Programs (1985) Hazard Evaluation Division Standard Evaluation
Procedure, United States Environmental Protection Agency, Washington, DC.
18. Office of Prevention, Pesticides, and Toxic Substances (1994), Status of Pesticides in
Reregistration and Special Review, EPA 738-R-94-008, United States Environmental Protection Agency, Washington, DC.
19. Office of Prevention, Pesticides and Toxic Substances (1996) Label Review Manual, 2nd
edn, EPA737-B-96-001, United States Environmental Protection Agency, Washington,
DC
20. Lawyer, A.L. (1993) Update on the State Regulation of Pesticides, in The 15th Annual
Pesticide Regulation Conference, Washington, Z)C, Executive Enterprises, Inc., New York,
NY.
21. California Department of Pesticide Regulation (1997) Department of Pesticide Regulation
Strategic Plan 1997, California Environmental Protection Agency, Sacramento, California.
13 Waste management and disposal of
agrochemicals
K. S. JOHNSON
13.1 Introduction
The formulation and packaging of agrochemical products involves the use
of relatively clean process technologies. These, for the most part, incorporate active ingredients and adjuvants usually manufactured elsewhere and
should not generate large quantities of wastes for disposal. A strong emphasis within the industry is now directed to point-source initiatives for waste
minimization, recycling and reuse, which has further reduced waste outputs.
However, despite these initiatives, it is inevitable that various types of
non-recoverable wastes will continue to arise and require safe disposal.
The disposal of all waste types arising from the production of agrochemicals
involves an area of extreme environmental sensitivity. Strict legislative
controls now exist in many countries for the storage, movement, treatment
and disposal of all waste types. The onus of 'duty of care' is firmly
placed upon the waste producer to ensure that all wastes are disposed of
legally, safely and responsibly without adverse impact on the receiving
environment.
This chapter offers a practically orientated systems approach for day-today on-site management, handling and selection of disposal options for
agrochemical waste types. The on-site treatment and disposal of aqueous
effluents arising from both process and plant cleaning operations is separately addressed in the final stage of this chapter. Finally, references are
made, and in some instances examples given, of waste handling and process
equipment. These are intended solely for the purpose of illustration and not
for the advertisement of specific items of proprietary plant or equipment.
13.2 Site management responsibilities
Site waste management is a highly sensitive operation equal in importance
to other site operations and in essence is an extension of manufacturing
process activities. A senior manager should be fully responsible for all
aspects of waste management and disposal. These duties will normally be
delegated or assigned to a responsible line manager for implementation and
control. It is essential therefore that the designated manager, as a minimum,
has received adequate training appropriate for the job.
A number of short- and medium-term waste management training
courses are now provided by universities and institutions.1'2 These courses
provide the essential elements of waste management including current
legislation, interpretation and implementation, systems controls and selection of disposal options, as a necessary supplement to equally important
on-site management experience and expertise. Waste disposal activities
involve a direct interface with controlling authorities and professional
waste disposal contractors. It is vitally important that the manager has both
the status and experience to interact professionally as a company representative with such authorities or organizations. Similarly, it is equally
important that adequate resources and personnel are provided for this
essential site-service operation.
13.3 Waste minimization
The most effective measures for the implementation of a waste minimization programme are dependent upon a planned strategy of waste reduction
and reuse at source with clearly defined objectives against which improvements and performance may be assessed. These include:
• full commitment, participation and support of senior management;
• longer-term waste minimization plans integrated into production and
business strategies involving joint accountability for waste minimization
performance;
• training and motivation of staff at all levels whose commitment to
achievement of the objectives is essential to the success of the waste
minimization programme;
• assessment and quantification of waste streams;
• selection of options for waste minimization, reduction, recovery and
reuse;
• implementation of minimization initiatives;
• data recording of recovered materials and cost benefits including reduction in waste disposal costs as a result of overall reduction in nonrecoverable waste residues.
13.3.1 General principles and definitions
The concept of waste minimization in the agrochemical industry involves
a combination of the principles of waste source reduction and waste
1
Loughborough University of Technology, Loughborough, Leicestershire, LEIl 3TU, UK.
Institute of Waste Management, 9 Saxons Court, St Peters Gardens, Northampton, NNl ISX,
UK.
recycling. These effectively reduce either the volume or toxicity of the potential waste outputs and so reduce the overall impact upon the environment. Of the two approaches, waste source reduction, where practicable, is
preferred to recycling. However, both options should be considered.
Source reduction options include:
•
•
•
•
good operating practices;
technology changes;
input material changes;
product changes.
Recycling options include:
• use and reuse of wastes;
• reclamation.
13.3.2 Examples of source reduction options
(a) Good operating practices (housekeeping). These can usually be
improved with in-house reorganization at minimal cost and include the
following.
• Material handling and inventory control. For example, stock control to
ensure that large quantities of raw materials and finished products are not
held in store for lengths of time, particularly for slow-moving products.
• Records for waste streams. This will allow, for example, the identification
of the waste streams from particular process areas and the monitoring of
fluctuations with time.
• Spill prevention and control. This will prevent the generation of waste
from the spill and clean-up of the spillage.
• Maintenance procedures. For example, setting and improving maintenance schedules will help avoid spillages and leakages.
• Waste stream segregation. This will avoid cross-contamination and may
allow the waste stream to be recycled.
• Product scheduling. For example, this will avoid the production of quantities of stock that are in excess of requirements.
• Waste management cost allocation. This will allow the true costs of
producing a product to be determined.
• Personnel training and supervision. For example, the basic principles of
reducing waste at source, reuse and recycling and the importance of each
individual's role in reducing waste generation.
(b) Technology changes. These concern the process itself, the plant and
the equipment involved. Costs can range from minor modifications to major
capital projects and include
•
•
•
•
automated process control;
improved design of equipment;
process water conservation and recycling;
in-process recycling.
All new and refurbished plant projects must critically address each area
of potential waste creation and make provision for these to be reduced
to the minimum. This is incorporated in the hazard and operability process
(HAZOP). A number of options exist for in-process recycling, including
• end of campaign washings collected from pipes and vessels;
• drum rinse liquors;
• dusts recovered from dedicated extraction units.
(c) Authorized changes in process raw materials. Changes in raw material
active ingredients and formulation adjuvants may produce more environmentally acceptable product types. They may also lead to a reduction in
certain hazardous substances which could beneficially influence recycling or
the ultimate disposal of product residues or outdated products. Any change
must be authorized. Examples include
• substitution of solvent-based formulations with water-based emulsion
suspensions;
• replacement of dust-based products with water-soluble or dispersible
grains and slow active-release granules.
These product types are safer options for field application and use, produce
less waste during manufacture and will be more amenable to reprocessing
on expiry of shelf life.
(d) Review and rationalization of product range including product types and
pack sizes. A wide range of common product types, with varying active
ingredient concentration, exists along with a multiplicity of pack sizes particularly in the horticulture and retail market areas. On expiry of shelf life,
practical problems emerge in the removal of materials from packages for
recycling or reprocessing, often resulting in the creation of quantities of
unwanted product requiring disposal as toxic waste. Strict stock control to
limit the number of packs of a given type stored, and regular reviews of
stock to ensure storage times do not exceed shelf life would enable reductions in non-recoverable waste outputs.
73.3.3 Example of recycling, use and reuse of waste and reclamation
Opportunities for the use and reuse of wastes should be investigated. One
example is given below.
Product liquid wastes, for example washings containing colloidal
suspensions or valuable active ingredients, are too dilute for direct recycling
into the parent process. Dewatering techniques using ultrafiltration
membrane technology can effectively concentrate suspensions to volumes
suitable for direct process reuse. The aqueous liquors passing the
membrane are easily treated in the standard site effluent system. Benefits
include
• complete recovery of valuable product hitherto discharged to effluent
drain;
• elimination of a serious and expensive effluent treatment problem.
13.4 Waste types
Despite the initiatives for point-source waste reduction, it is inevitable that
some waste materials will be generated for disposal.
These may be classified into three broad types and will include the
following.
• Non-Toxic Wastes. Clean package waste and office paper.
• Lightly Contaminated Wastes. Emptied, discarded, bags, bottles, cans
and drums containing small residual quantities of the original contents of
active ingredients, adjuvants or products.
• Toxic and Hazardous Wastes. Non-recoverable production materials,
outdated or unwanted stocks of finished products and raw materials,
effluent treatment sludges and laboratory wastes.
13.5 Waste handling
A system for the collection, assembly, packaging and labelling of wastes
must be established at each manufacturing site. Responsibilities for these
duties must be clearly defined and adequately resourced to ensure regular
clearance of wastes from workplace areas.
13.5.1 Operator safety
Operators working in areas of waste collection, packaging and assembly
will be subjected to the same degree of exposure and contact risk as corresponding plant areas producing wastes. It is essential, therefore, that similar
safety procedures, provision and use of personal protective equipment are
applied along with training and supervision.
13.5.2 Workplace designated waste collection areas
A designated area in each plant or work area should be allocated for the
deposition and subsequent collection of wastes for disposal. It is recommended that colour-coded bins or drums are provided within the area to
allow, so far as possible, at source, the segregation or specific waste types
prior to collection.
A suggested colour-code for adoption is
green: clean, uncontaminated waste;
grey: lightly-contaminated waste;
red: toxic and hazardous waste.
13.5.3 Site waste collection
Normally, a two-tier system will be necessary.
1. Daily collection of clean and lightly contaminated wastes for routine
disposal.
2. A less frequent collection of toxic waste types requiring advance
notification for preparation and safe storage prior to disposal.
Often these waste types originate from valuable feedstock and it is
essential to ensure that every option for recycling or recovery has been
explored.
13.5.4 Secure waste storage
Regulations in many countries now require secure areas for the preparation
and storage of wastes awaiting final disposal. Depending upon the quantities of waste undergoing processing and storage, it may be necessary to
license this facility with the controlling authority. This area should be
enclosed within a security fence at least 2m high. Access gates should be
wide enough to admit fork-lift trucks and lorries for waste movement and
collection. The floor area should be constructed in concrete and bunded to
contain spillage and contaminated runoff water. Drainage from this area
should be routed to an interceptor vessel within the site effluent system. If
possible, the area should be roofed over to provide operator protection and
minimize runoff of rainwater. Clean roof-waters should be piped via sealed
drains to the site surface-water drains to avoid overloading the effluent
treatment system.
73.5.5 Waste preparation prior to disposal
Legal, safety and economic factors require that all wastes be assembled
reasonably compacted, contained and labelled before disposal.
Figure 13.1 Drum crusher. (Photograph courtesy of Rodan Engineering Ltd.)
(a) Standard items of equipment. Standard items of equipment are available and are often essential for this purpose.
Drum crusher. All pesticide containers must be rendered unusable before off-site disposal as waste. Consideration should be given to the installation of a proprietary drum-crushing unit.3 An example of a standard drum
crusher capable of processing steel drums of up to 2051 capacity is shown in
Figure 13.1.
Waste compactor. Large volumes of clean and contaminated lowdensity wastes (paper and plastic) are generated regularly for disposal.
Much of this can be recycled or landfilled. It is essential therefore that the
waste is compacted to smaller volume and where appropriate overpacked
to minimize dust exposure risks to operators at both the production and offsite disposal stages of the operation.
Each site should consider the acquisition of a proprietary waste
compactor as part of the waste processing unit (Rodan Engineering Co.
3
Rodan Engineering Co. Ltd, Unit 5 Millbrook Business Park, Jarvis Brook, Crowborough,
West Sussex, TN6 3JE, UK.
Figure 13.2 Waste compactor. (Photograph courtesy of Rodan Engineering Ltd.)
Ltd). An example of a waste compactor for processing plastic, paper, cardboard and bottles of up to 251 capacity is shown in Figure 13.2.
Waste shredder. Large quantities of contaminated plastic bottles and
other waste materials arise for disposal, particularly from product decanting
operations. These must be re