Aquatic Herbicide / Algaecide
Toxicity
John H. Rodgers, Jr.
2012 MN AIS Symposium
March 7-8, 2012
St. Paul, MN
Adaptive Water Resource
Management
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Risk assessment – problem or not?
Consider all available options
No decision / action vs. decision / action
Implement viable option(s)
Monitor results modify approach if
indicated
Why use herbicides or algaecides?
• Invasive and exotic species move at
unprecedented rates.
• We have changed the landscape – e.g. canals,
reservoirs, stormwater detention basins, etc.
• Human population increase – plant / people
interface.
• Changing climate – globally
• Pressure on water resources.
Myriophyllum spicatum
Didymosphenia geminata
Cylindrospermopsis raciborskii
Prymnesium parvum
Effects of a P. parvum “Bloom”
Problems Caused by Vascular and
Nonvascular (Algae) Plants
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Aesthetics
Devalue property
Disrupt transportation
Taste and odor problems/ Toxin production
Impact fisheries and endangered species
Impede irrigation
Human health
Interfere with water resource uses!
Prymnesium parvum
30-mile fish kill in Dunkard Creek
Problem?► Response
• Response “Triggers”
• No Action – Action
Consider all the “competing” water resource uses!
Factors influencing herbicide selection
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Target plant species (strain)
Water resource usages
Water body and water characteristics
Efficacy
Costs
Margin of safety for non-target species
Social acceptance (Regulatory approval)
Chemical Control Options for Aquatic
Vascular Plants and Algae
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Carfentrazone ethyl
Copper formulations
Diquat
2,4-D formulations
Dyes
Endothall formulations
Fluridone
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Glyphosate
Imazamox
Imazapyr
Penoxsulam
Peroxide formulations
Triclopyr formulations
Conditional registration:
Flumioxazin
Bispyribac Sodium
Herbicides / Algaecides can take
advantage of unique physiology
• Plants ≠ Fish, invertebrates, etc.
• Plants have “systems” that animals do
not have.
• Unique physiology!
Auxin Mimics
• 2,4-D formulations – auxin-type herbicide
(plant hormone)
• Triclopyr – auxin-type herbicide
ALS Inhibitors
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Imazapyr – inhibits ALS
Penoxsulam – inhibits ALS
Bispyribac Sodium – inhibits ALS
Imazamox – inhibits the enzyme
acetohydroxyacid synthase (AHAS) in plant
species, which is involved in the synthesis
of three branched-chain aliphatic amino
acids: isoleucine, leucine and valine
Enzyme or Biochemical Inhibitors
• Carfentrazone ethyl - protoporhyrinogen oxidase
inhibitor or 'protox' inhibitor
• Fluridone – inhibits phytoene dismutase, blocks
carotenoid biosynthesis
• Glyphosate – inhibits ESPS synthesis
• Endothall – inhibits lipid and protein synthesis
• Flumioxazin - inhibition of protoporphyrinogen
oxidase, an enzyme important in the synthesis of
chlorophyll.
Redox Reactions
• Diquat –redox reactions
• Peroxide – oxidation reactions
• Copper formulations - redox reactions,
membrane transport
Light Attenuation
• Dyes – light absorption
Toxicity – Non-target species
• Peroxide – Sodium carbonate
peroxyhydrate
• Copper formulation
• Triclopyr (TEA salt)
• Imazapyr
Animal Testing Species for Margins of
Safety for Nontarget Species
Sodium Carbonate Peroxyhydrate
Sodium percarbonate
IUPAC name : sodium carbonate—hydrogen peroxide (2/3)
other names : PCS, solid hydrogen peroxide, sodium
carbonate hydrogen peroxide, sodium carbonate
peroxyhydrate
CAS number : 15630-89-4
Properties
Molecular formula : Na2CO3·1.5H2O2
Molar mass : 157.01 g/mol
Appearance : white solid (granular)
Solubility in water : 150 g/L
What is SCP?
• Sodium carbonate peroxyhydrate
SCP Algaecide
• Made by combining 2 molecules of sodium
carbonate with 3 molecules of hydrogen
peroxide.
• Free-flowing granular.
• Stable source of alkaline hydrogen
peroxide.
• In water, produces hydrogen peroxide and
sodium carbonate.
SCP Algae Treatments
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0.3 mg/L – 10.2 mg/L H2O2
3.0 – 100 pounds / acre-foot
48 hours between applications
Large lake or heavy infestation (bloom) –
treat 1/3 – 1/2 of the area and wait 2-3 days
before treating the remaining water.
SCP Algaecide
• Algaecide – SCP concentration = 85%
• = 27.6 % hydrogen peroxide
• Registered by US EPA as algaecide for use
in ponds, lakes, reservoirs and drinking
water.
SCP Toxicity
• Pimephales promelas 96-h LC50 = 70.7 mg/L
• Pimephales promelas 96-h NOEC = 1 mg/L
• Daphnia pulex 48-h EC50 = 4.9 mg/L
• Daphnia pulex 48-h NOEC = 1 mg/L
• No bioconcentration, bioaccumulation
• Abiotic degradation
• Low toxicity of ultimate degradation products (H2O,
O2 )
Margin of Safety (MOS)
Scientific
name
Pimephales
promelas
a Lowest
96 h
LOECa
Algaecide
Cutrine®Plus
MOS c=
EC100 b
Pimephales Prymnesium
parvum
promelas
(mg Cu / L) (mg Cu / L)
0.750
0.2
Observed Effect Concentration
(Murray-Gulde et. al, 2002)
b [Cu] used to control Prymnesium parvum (EC
100)
c Margin of Safety (MOS)
LOEC of Pimephales
promelas / [Cu]
required to control
Prymnesium parvum
(mg Cu / L)
3.75
Triclopyr Toxicity
• The TEA salt is "slightly toxic" to fish with 96h
LC50 values of 552 and 891 ppm for rainbow
trout and bluegill sunfish respectively.
• The corresponding values for the
unformulated triclopyr are 117 ppm for
rainbow trout and 148 for bluegill sunfish.
• Both species were less sensitive to the TEA salt
than to the active ingredient.
Imazapyr Toxicity
• The 48- and 96-h LC50s for rainbow trout, bluegill
sunfish, channel catfish, and the water flea
(Daphnia magna) are all >100 mg/L (WSSA 1994).
• Concentrations up to 1,600 mg/L did not affect the
osmoregulatory capacity of Chinook salmon
smolts (Patten 2003).
• The 96-h LC50 for rainbow trout fry is 77,716
mg/L (ppm) ( ~22,305 ppm of the active
ingredient).
Acute, Chronic Studies
Herbicides / Algaecides can take advantage
of differences in responses to exposures
• Fish may detect and avoid herbicide or
algaecide.
• Pattern and timing of application.
• Pulse or episodic exposure vs. continuous
exposure.
• Formulation (e.g. granular vs. liquid)
Herbicide / Algaecide Fate
and Persistence
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Well Studied
Laboratory Studies
Semi-field Studies
Field Studies
Conclusions –
Aquatic Herbicides and Algaecides
• Effective for target algal species.
• MOS (margin-of-safety) for non-target
species varies.
• Research ongoing to improve and expand
data, uses and effectiveness.
• Development of new chemistries and
formulations underway.
Thank you!