Bio 430: Chemicals in the environment
Jeffrey Jenkins
Department of Environmental and
Molecular Toxicology
Oregon State University
Chemical fate:
transformation and
transport within and
between
Soil-Air-Water-Biota
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Source: U.S. Geological Survey
Chemical fate processes
wind
erosion
interception
wash
off
plant
uptake
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photodegradation
volatilization
runoff
sorption to soil
microbial or chemical
particles
degradation
leach toward
groundwater
Chemical fate processes
atmosphere
direct + indirect
photolysis
air/water
exchange
wet + dry
deposition
runoff
photodegradation
chemical + biological
transformation
groundwater
infiltration/
exfiltration
sediment/water
exchange
sorption to sediment and particles
chemical + biological
transformation
water
sediments
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outflow
Chemical fate in the environment
Molecular interactions
(physical-chemical properties, reactivities)
Environmental factors
(Temperature, pH, light intensity, ion composition and strength,
microbial activity, natural organic matter, etc.)
Environmental processes
(e.g. air/water exchange, sorption/desorption, chemical,
photochemical and biological transformation)
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Chemical fate in the environment
Transport and mixing processes
Dynamic behavior in a natural system
(mathematical models and field investigations)
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Chemicals in the Environment
Initial distribution to environment (manufacture
and use):
emission in: air-soil-water-biota compartments
Transformation: degradation/metabolism
Redistribution- transport in and between
compartments:
diffusion/advection-dispersion/mass transport
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Chemicals in the Environment
Understanding chemical fate, what scale?
Local scale: site-specific inputs, potential for
off-site transport.
Watershed scale: integration of site-specific
inputs and transport, particular emphasis on
water quality.
Regional scale: integration of watershedairshed chemical inputs and redistribution,
long range transport of persistent
compounds.
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Range of ESA Listed Salmon
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Pesticides in the Environment
Initial distribution in the
environment:
method of application
timing of application
frequency of application
amount of active ingredient
formulation (other ingredients)
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Environmental Behavior of
Pesticides in Soils
Initial distribution
sunlight
temperature
soil pH
soil texture
Persistence
and
Mobility
Environmental Fate
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organic matter
moisture
Pesticide Fate and Transport
Physical-chemical properties:
•
•
•
•
•
•
Water solubility
Vapor Pressure
Kd (soil/water partition coefficient)
Henrys Law Constant
Soil half-life
Foliar half-life
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Sorption
binding to soil or sediment particles
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Soil sorption
soil water
soil particle
concentration
of pesticide
sorbed to soil
Kd
concentration
of pesticide in
solution
K d describes the relationship between pesticide sorbed
to soil particles and pesticide dissolved in soil water.
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Soil sorption
To account for different soil types and organic
matter content the Kd is normalized for %
organic carbon.
Kd
K oc 
% organic carbon*
*
decimal equivalent
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Soil Properties that Influence
Leaching and Runoff
•
•
•
•
Permeability
Water table conditions
Organic matter content
Clay content
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Course textured
soils and other soil
conditions that
result in preferential
flow paths must
also be considered.
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Pesticides in Ground and Surface Water
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Pesticides in surface water
Mass transfer primarily in the dissolved
phase, will vary with pesticide’s solubility
in water and soil sorption.
water
soil particle
concentration
of pesticide
sorbed to soil
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concentration
of pesticide in
solution
Partitioning between soil compartments
(soil, water air)
soil water
soil particle
air
Chemical
in water
Kh
chemical
in air
Kd
Kh describes the relationship between pesticide concentration
in soil water and pesticide concentration in air.
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Volatilization
volatile loss from plant, water, or soil surfaces
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Atmospheric Transport Zones
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Volatile loss as Percent Applied
Application Rate
(kg a.i./Ha)
Vapor Pressure
(mPa @ 25 oC)
24 hr Volatile loss
as % Applied
Chlorpyrifos
1.9
2.50
16.5
Ethofumesate
2.5
0.650
6.3
Triclopyr (acid)
1.1
0.170
4.5
Triadimefon
3.1
0.060
2.1
Propiconazole
2.2
0.056
1.1
Cyfluthrin
0.2
0.004
ND
Pesticide
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Pesticide Fate
• Field dissipation: sum of chemical and
biological processes including:
– Chemical degradation1
– Biological degradation (microbial + plant)1
– Photodegradation2
– Volatilization
1Approximated
with a 1st order rate constant
2Approximated with a psuedo 1st order rate
constant
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Pesticide degradation half-life
Half-life = the amount of time it takes the
parent compound to decay to half its
original amount
Half-life in an environmental compartment:
(soil-air-water-biota) sum of all
degradation and transport pathways
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Pesticide degradation half-life
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No of
½ lives
% amount
remaining
3.3
10
6.6
1
10
0.1
Sunlight photolysis of an aqueous
suspension of nitrofen
Cl
Cl
OH
OH
Cl
OH
OH
HO
OH
POLYMER
Cl
Cl
O
NO2
HO
OH
nitrofen
Cl
Cl
HO
O
NH2
HO
Cl
Cl
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HO
NH2
Cl
O
N N
O
Cl
NH2
Chemical and microbial degradation of chloroanilines
Cl
OH
Cl
CHO
OH
COOH
NH2
Cl
H2O
COOH
A. faecalis
O2
COOH
CO2
OH
Cl
OH
O
O
COOH
Ps. diminuta
NH2
Cl
O2
Cl
COOH
HOOC
Cl
O
COOH
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COOH
LD50: lethal dose
for ½ the test
animals
NOAEL
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Aldicarb degradation pathways and
LD50 values (rat acute oral)
CH3
CH3
S
N
H3C
O
O
N
O
CH3
H20
O
N OH
H3C
CH3
O
CH3
N
CH3
sulfone
24 mg/kg
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N
O
CH3
H20
H3C
O
S
N
H3C
sulfone nitrile
4000 mg/kg
CH3
S
CH3
CH3
sufoxide oxime
8060 mg/kg
O
nitrile
570 mg/kg
CH3
S
O2
S
H3C
N
N
CH3
oxime
2380 mg/kg
O
CH3
S
H3C
CH3
O
O
CH3
N OH
H3C
CH3
H3C
O
H20
O2 , fast
S
sulfoxide
0.9 mg/kg
CH3
O
CH3
Aldicarb
0.9 mg/kg
N
S
O
N OH
CH3
sulfone oxime
1590 mg/kg
CH3
S
H3C
O
N
CH3
sulfone nitrile
350 mg/kg
Pesticide Properties used to evaluate fate
in the Environment
water sol
ppm
Vapor
Koc pressure
ml/g
mm Hg
soil 1/2
life
days
foliar 1/2
life
days
Atrazine
33
100
2.90E-07
60
5
Diuron
42
480
6.90E-08
90
30
5
1000
1.50E-06
25
8
pendimethalin
28
5000
9.40E-06
90
30
triclopyr ester
23
780
1.26E-06
46
15
carbaryl
120
300
1.20E-06
10
7
chlorpyrifos
0.4
6070
1.70E-05
30
3
malathion
130
1800
8.00E-06
1
3
0.002
5300
1.10E-08
35
8
MCPA ester
esfenvalerate
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Chemical fate determines exposure
to humans and aquatic life
Chemical fate processes
wind
erosion
photodegradation
volatilization
runoff
plant
uptake
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sorption to soil
microbial or chemical
particles
degradation
leach toward
groundwater
13.4 million lbs of pesticides used annually in Oregon
What are the risks and who decides?
Federal Insecticide, Fungicide, and Rodenticide Act
regulates pesticide manufacture, use, storage, and
disposal (benefit-risk balancing statute.)
Under Authority of the Clean Water Act, ODEQ has the
authority to set pesticide water quality standards for
waters of the state (TMDLs).
Under the Endangered Species Act NMFS and USFWS
have the authority to set rules deemed necessary to
prevent more species declines under a provision
called “Four D.”
EPA, NMFS, and USFWS have “overlapping”
jurisdiction with regards to pesticide use and the
Endangered Species Act.
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EPA Risk Assessment
Risk = f (exposure, toxicity)
Source: Purdue University Pesticides Program
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Pesticide Risk Assessment
RFD: The Reference Dose is the
amount of a pesticide residue a
person could consume daily for 70
years with no harmful non-cancer
effects.
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Pesticide Risk Assessment
The RFD is determined by dividing the
NOAEL by a safety factor, usually
between 100 and 1000,
to account for uncertainty in extrapolating
from animal studies and to protect
sensitive individuals, including infants
and children.
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Quantitative Assessment of Health Risks
of Pesticides in Drinking Water
MCL - The Maximum Contaminant Level permissible in water
which is delivered to any user of a public water system
(Safe Drinking Water Act; ~50 pesticides have MCLs)
HA - Health Advisory: EPA guidance for drinking water
contaminants based on lifetime exposure and noncarcinogenic endpoints. HA is derived from the DWEL.
DWEL - Drinking Water Equivalent Level,
based on the Reference Dose (RfD) and
assuming 70 Kg person drinks 2 liters per
day over a lifetime. The DWEL has been
adjusted assuming that drinking water
comprises 20% of the allowable daily intake.
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Pesticide Risk Assessment: Wildlife
What is the toxicity of
the pesticide and it’s
degradates to wildlife?
Acute toxicity (high dose-short exposure)
Chronic toxicity (low dose-long exposure)
Most sensitive adverse effect
Sensitive sentinel species
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EPA Pesticide Aquatic Risk:
Wildlife Toxicity Assessment
• Laboratory tests are used to determine the
NOAEL in representative species.
• The hazard quotient is the ratio of the
NOAEL to the expected environmental
concentration.
• If the hazard quotient is greater than 1.0, the
potential exists for adverse ecological effects.
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Use of models for evaluating hazards
associated with chemicals in the
environment
Models use a systems approach to
understanding complex phenomenon.
Computer based environmental models
present a conceptual framework and a
mathematical formulation of fate and
transport between compartments (soil,
air, water, biota) based upon scientific
principles.
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Environmental fate models
PRZM and EXAMS (EPA)
CalTOX (California EPA)
Fugacity Model Levels I, II, III (Mackay)
Gaussian plume models (EPA, NOAA)
http://www.lanl.gov/orgs/d/d4/movies.shtml
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Fugacity Model for Biphenyl
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Fugacity Model for Biphenyl
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How Do We Assess Risk?
Follow the National Academy of Sciences (NAS)
four-step risk assessment paradigm*:
Hazard
Identification
DoseResponse
Assessment
Exposure
Risk
Characterization
* From the National Research Council’s Risk Assessment in the Federal
Government: Managing the Process, 1983.
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