xvEPA
tinted States
Protection
Agency
•Office of
Pesticide Programs
Wasmngton DC 20460
EPA-540-09 90-073
December 1989
Environmental Fate
and Effects Division
Standard Evaluation Procedure
i
Terrestrial Field Dissipation
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ENVIRONMENTAL FATE AND EFFECTS DIVISION
STANDARD EVALUATION PROCEDURE
TERRESTRIAL FIELD DISSIPATION STUDIES
Prepared by
Clinton Fletcher
Soobok Hong
Catherine Eiden
Michael Barrett
Standard Evaluation Procedures Project Manager
Catherine A. Eiden
Environmental Fate and Effects Division
Office of Pesticide Programs
United States Environmental Protection Agency
Office of Pesticide Programs
Washington, D.C. 20460
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TABLE OF CONTENTS
Page
I. INTRODUCTION
A. Objective of the Standard Evaluation
Procedure 1
B. General Theory of Terrestrial Field
Dissipation 2
II. THE SUBMITTED STUDY
A. Purpose 3
B. Study Design 3
III. THE EVALUATION PROCESS
A. Determine the Need for the Study 3
B. Read the Report .• 3
C. Prepare the Data Evaluation Record 5
1. Write the Technical Evaluation 5
2. Determine Study Acceptability 7
3. Determine Need for Deferral/Referral to
Other HED Branches 7
4. Make a Regulatory Determination 8
IV. APPENDICES
Appendix 1: General Theory 9
Appendix 2: Information to be Included in the
Registrant's Report 14
Appendix 3: Analytical Data to be Submitted by the
Registrant . 23
REFERENCE CITATIONS 28
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TERRESTRIAL FIELD DISSIPATION
I. INTRODUCTION
A. Objective of the Standard Evaluation Procedure
This Standard Evaluation Procedure (SEP) is to be used
as an aid for the Environmental Fate and Ground Water Branch data
reviewers in their evaluations of the terrestrial field dissipa-
tion studies submitted by registrants in support of pesticide
registration.
Terrestrial field dissipation studies are required by
Section 158.290 of Title 40 of the Code of Federal Regulations
(40 CFR 158.290) in support of registration of an end-use product
intended for terrestrial use or domestic outdoor use (as defined
by the Subdivision N Guidelines) and to support registration of a
manufacturing-use product which may also be legally used to
formulate such an end-use product. Section 164-1 in the Sub-
division N Guidelines describes this study (short-term field
dissipation) and provides a protocol for conducting it (_!).
This SEP introduces the concept of using a tiered
approach to requiring further field studies beyond the field
dissipation study. Specifically, the field dissipation study is
considered the first tier of field studies addressing movement
and persistence of a chemical in the field. For a description
of other field studies included in the tiered approach make
reference to Cohen et al. and the Guidance for Ground-Water
Monitoring Document(2,3).
The intention of the proposed tier approach is to
provide a step-by-step procedure in assessing ground-water and
surface-water impacts. This should ensure a gradual and consistent
approach when requiring ground water or surface water monitoring
studies. The "triggers" for further monitoring described in this
SEP will not automatically cause any new data requirements.
Results from the field dissipation study along with data from
other Subdivision N Guidelines environmental fate studies data
will be used to determine the leaching potential of a pesticide
and need for further monitoring studies. However, the field
dissipation study results are pivotal.
Currently, four field monitoring studies are a part of the
tiered approach concept. They are: the field dissipation studies
(164-1 and 164-5), the small-scale prospective ground-water moni-
toring study, the 'small-scale retrospective ground-water monitoring
study, and surface-water monitoring studies. Depending on the
results of a field dissipation study in conjunction with other
laboratory data from environmental fate studies, a ground-water
or surface-water monitoring study may be required. Depending on
the period of registration and patterns of use for a given pesti-
cide, a small-scale prospective or retrospective ground-water
study or both may be required.
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Specifically, the small-scale ground-water prospec'tive
study has been designed to address movement of pesticide residues
through the unsaturated zone and into shallow ground water for
new chemicals with a limited use history and some older chemicals
suspected of leaching. The study is conducted under conditions
providing a worst-case scenario for leaching in the field. The
small-scale retrospective ground-water study has been designed to
address the impact of a pesticide on shallow ground water after
years of past usage. Surface-water monitoring will be used to
assess the impact of pesticide residues in runoff on aquatic
environments (ponds, lakes, and streams).
The surface and ground-water studies referred to here,
as a part of the tiered approach concept, may be required to
define potential surface and ground-water impacts from the use of
pesticides. Although the toxicological significance of pesticide
residues will be considered when determining the need for and
type of field monitoring required, the toxicological significance
of residues will not be the overriding factor in determining
whether a surface or ground-water monitoring field study is
warranted.
This SEP provides a detailed sampling and analysis
procedure in Appendix 2. However, there may be specific cases
where, because of the chemical/physical properties of a pesticide,
some of the specific guidance provided in this Appendix may not
be applicable. Modifications to the detailed procedures outlined
in Appendix 2 will be considered on a case-by-case basis. For
example, a field dissipation study for a pesticide known to be
immobile, having no leaching potential, may not warrant deep
sampling throughout the entire study. Any changes to the study
design as detailed in this SEP must be formally approved by the
Agency in a protocol prior to study initiation.
B. General Theory of Terrestrial Field Dissipation
Data from field dissipation studies are used to determine
patterns of pesticide residue dissipation under actual field
conditions. These studies are required because it is likely that
patterns of pesticide degradation, such as the rate of formation
and decline of degradation products, are influenced by environ-
mental factors such as soil, climate, the presence of crops, and
other factors not duplicated in laboratory degradation studies.
As well, important information on pesticide mobility under typical
use conditions is gained.
The reviewer should be acquainted with the processes
which cause pesticides to degrade and move in the soil environment,
and is directed to Appendix 1 for a brief discussion of pesticide
dissipation processes.
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II. THE SUBMITTED STUDY
A. Purpose
The purpose of field dissipation studies for pesticides
with terrestrial uses is to determine the extent of pesticide
residue dissipation under actual use conditions. These studies
will generate data required for the evaluation of degradation,
mobility, and other avenues of residue dissipation. In addition
to parent compound, formation and decline of degradation products
are monitored under actual field conditions.
The study is an important component in assessing a
chemical's leaching potential along with laboratory data. Results
from the field dissipation study may act as a trigger to require
other field studies, specifically, ground-water monitoring studies.
The reviewer is directed to Appendix 2 for a brief discussion of
the pertinent data resulting from a field dissipation study that
may trigger the need for a ground-water monitoring study.
B. Study Design
The registrant's report should contain 1) a stated goal
of the study, and 2) sufficient information on the test protocol
(formulation of test material used; complete soil characterization
of the test sites; dose level and method of application; suffi-
cient description of sampling frequency, depth and methods; and
field data) and the analytical protocol (description of methods
used for quantitative and qualitative analyses and reports on the
quality control procedures used to ensure the validity of the
data).
Specific information that the registrant should include
in the report is listed in Appendices 2 and 3.
III. THE EVALUATION PROCESS
A. Determine the Need for the Study
The reviewer should initially determine whether the
study is required under 40 CFR 158.290. Normally, the study is
required to support registration of pesticide products intended
for terrestrial or domestic outdoor end uses and for manufacturing-
use products intended for use in formulating such end-use products.
B. Read the Report
Reports of field dissipation studies are first reviewed
to determine if the following information is present:
1. If an applicant's product is an end-use product, is
the test substance a product whose formulation is typical of the
formulation category?
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2. If the applicant's product is a manufacturing-use
product, is the test substance a product representative of the
major formulation category which includes that end-use product?
3. Is the formulation of the test substance (the
product) specified?
4. Is the complete soil characterization of the test
sites included? This includes pH, moisture capacity, percent
organic matter, bulk density, cation exchange capacity, textural
composition (percent sand, silt and clay), textural class - all
as a function of depth.
5. Are the field test data presented? This includes
daily climatic data including precipitation, air temperature, and
pan evaporation (if available), irrigation amounts and method,
depth to the water table and how much this varies seasonally,
slope of the test plots, soil temperature data, techniques and
times of planting and harvesting, and other information as relevant
to the specific study.
6. Was irrigation used to supplement rainfall in a dry
year?
7. Are the application rates, dates, and methods
described?
8. Is the sampling protocol, from soil core extraction
to chemical analysis, described?
9. Were the samples taken to a sufficient depth and
at close enough time intervals so that pesticide residues moving
through the soil profile would not be missed? Were the samples
collected after the immediate post-application sample taken to a
depth of 90 cm throughout the study? If not, how deeply were
the samples taken, and did the registrant receive prior approval
of shallower sample collection depths?
10. Were sufficient samples taken per sampling interval?
Were the samples composited? If so, how, and how many composite
samples were used for final residue analysis? (See Appendix 2.)
11. Are the methods used for quantitative and qualitative
analyses of the degraded compound and formation and decline of
the degradation products described?
12. Were analytical method recoveries reported? How
were they determined? Are adequate quality control measures
described for sampling techniques, sample shipment and storage,
soil extraction and cleanup, analytical instrument performance,
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13. Are the raw data (i.e., soil core concentrations)
from which a half-life can be calculated included, and is the
half-life calculated?
The reviewer should determine if there are data gaps
within the study. Failure to provide adequate information may be
sufficient reason for the reviewer to reject the study. The
Pesticide Assessment Guidelines Subdivision N, should be used as
guidance in determining the data gaps. A study that is considered
deficient in some way in comparison with the Subdivision N Guide-
lines may still be scientifically sound, and provide supplemental
information pertinent to the environmental fate of the pesticide.
This information should be reported in the review. In cases
where considerable information is missing, the reviewer should
not conduct an in-depth review of the study. Instead, a detailed
list of the deficiencies and omissions in the review should be
reported.
C. Prepare the Data Evaluation Record
After the reviewer has determined that there are no data
gaps which would cause the report to be rejected, the reviewer
prepares a Data Evaluation Record (DER) according to the Standard
Format for Preparation of Environmental Fate Reviews.
1. Write the Technical Evaluation
The reviewer should use Appendices 2 and 3 as aids
in this process. The technical evaluation should be prepared
with the following points in mind:
a. The test procedure should provide adequate
information as to how and under what conditions the study was
conducted. Consult Appendix 2.
b. The analytical procedure should provide
information on sensitivity and specificity of the analytical
method(s) used and indicate how the results were determined.
Consult Appendix 3.
c. Upon comparison with the laboratory soil
metabolism studies, the recovery of the analytical method should
be in a reasonable range, 70 to 120 percent (considering the loss
due to volatilization of parent compound and/or degradation
products).
d. The rate of disappearance of the active
ingredient of the test material provides a half-life estimate of
the active ingredient. It should answer the following questions:
o At what rate does the active ingredient of
the test material degrade and/or dissipate?
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o Is it persistent in the soil environment
under field conditions?
e. The soil degradation products identified under
aerobic and anaerobic soil laboratory conditions at 0.01 part per
million (ppm) or 10 percent of the application rate (whichever
is lower) must be analyzed for in the field dissipation studies.
As stated in the Subdivision N Guidelines (160-5), "Analysis and
identification of pesticide residues in field studies are required
only for those degradation products that were found to form in
the lab studies (.1)." Any residues present at 0.01 ppm or greater
in the lab studies should be identified and analyzed for in the
field studies. The 0.01 ppm level is suggested as a goal to be
met or surpassed. "However, registration applicants will not be
penalized for not being able to meet the 0.01 ppm goal due to
limitations of the analytical method (_1)." This is not dependent
upon the toxicological significance of the pesticide residues.
The rate of formation and decline of those compounds provides the
answers for the following questions:
o Are the degradation products persistent in
the soil environment under field conditions?
o At what rate do they decline?
f. Detection of active ingredient and/or its
degradation products in successive soil increments is an indication
of the leaching tendency of the compound. Although the laboratory
leaching studies provide information on the leaching potential of
the compound, the residue analysis in soil increments can provide
additional important information on leaching. Relevant questions
on the field data include:
o How far has the active ingredient or its
degradation product(s) leached through the
soil under field conditions? Have they
leached to greater than or equal to 90 cm?
o Were the soil increments sampled and analyzed
consistently so the pesticide residues could
be tracked with each sampling interval? Or
could the pesticide residues have leached
below the depth of sampling? This would be
indicated by significant concentrations at
the lowest depth of sampling or long time
periods (^> 1 month) between sampling. For a
pesticide known to be persistent and mobile,
extended time periods between sampling dates
may allow the pesticide residues sufficient
time to move beyond the depths sampled.
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o Were rainfall patterns and events correlated
to residue movement? Or did rainfall patterns
have little effect on the movement of residues
in the soil profile?
o If the study was conducted during a dry year,
was irrigation used to supplement natural
rainfall to provide the average amount of
rainfall expected during any given month of
the study as based on monthly averages from
sets of 10, 20 or 40 year rainfall data?
o Based upon the field dissipation tests'
results along with mobility and persistence
information, under what conditions does the
pesticide have a potential to contaminate
ground water? Is a more thorough leaching
; assessment of the pesticide necessary?
g. Quality control information provides assurance
of the integrity of the study. This information answers the
following question:
o Was the study run using Good Laboratory
Practices (GLP)?
2. Determine Study Acceptability
The stated goals of the study should be appropriate
and clearly defined. The study should be conducted in a scientifi-
cally sound manner to accomplish those goals. If so, the reviewer
then determines the acceptability of the study and considers
whether the study, as it stands alone or in light of other studies
(combined testing, surrogate studies, or waivers), supports the
requested registration action. The Pesticide Assessment Guidelines
Subdivision N should be used as guidance in determining the study's
acceptability.
If the study is considered deficient in any way, a
detailed description of the deficiencies and recommendations on
how to rectify the deficiencies is prepared and included in the
DER. A study that is considered deficient in some way in compari-
son with the Subdivision N Guidelines may still be scientifically
sound, however, and provide supplemental information.
3. Determine Need for Deferral/Referral to Other HEP
Branches
If the reviewer concludes either that 1) the test
chemical or its degradates have a potential for reaching ground
or surface water due to their persistence; 2) residues may occur
in rotational crops because of their persistence and mobility;
and/or 3) there may be exposure to other nontarget organisms
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because of persistence, then the Toxicology, Dietary Exposure,
and/or Ecological Effects Branches may have to be notified. Final
decision on the need for deferral/referral is to be made after
the evaluation of the other environmental fate studies.
4. Make Regulatory Determination
Based on the technical evaluation, the reviewer
determines whether the study satisfies the data requirement for a
field dissipation study as listed in 40 CFR 158.290. As well,
the reviewer should make qualitative statements concerning persis-
tence and mobility which could influence a regulatory decision on
the pesticide, such as the need for further field monitoring
studies, if warranted.
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APPENDIX 1
General Theory
Pesticide products reaching soil either degrade (partially
or completely), are altered in varying degrees and become part
of the soil complex, or remain intact in the soil system. The
parent compound or the degradation product(s) may also migrate
to places other than the original point of application. The
major purpose of a field dissipation study is to gain insight
on transport and degradation processes of a pesticide over time
in an actual use situation.
The important difference between a study addressing
degradation and a study addressing field dissipation is that in
field dissipation studies pesticide loss is a combined result of
chemical (hydrolysis, photolysis, oxidation, and reduction) and
biological (microbial) transformation processes as well as
physi-cal migration processes (volatilization, runoff of soluble
or sorbed residue, leaching of soluble residues, plant uptake,
and drift), while degradation studies primarily examine chemical
and biological transformation processes(4). A good field
dissipation study should provide information on the vertical
transport of the pesticide in the field.
The method of application is very important for physical
transport considerations(2). For example, pesticide sprayed
onto a developing crop canopy has the potential to drift from
the site of application or be intercepted by the plant before a
portion of the application reaches the soil. Soil samples taken
immediately after application are important when the pesticide
is applied in this manner in order to estimate the amount that
reached the soil and became available for other dissipation pro-
cesses. This initial amount of pesticide reaching the soil from
application is known as the "source term." The source term can
be assumed to be, equal to the application rate when the pesticide
is sprayed onto bare soil, unless the application is made from
some distance from the bare soil (i.e., from an airplane) such
that drift processes can transport residues from the site of
application. The source term is 100 percent of application when
the pesticide is either injected or incorporated. However, these
methods of application can result in large spatial variation in
residues and care must be taken when interpreting soil core
results(2).
Physical processes which influence the dissipation of
pesticide residues following application include volatilization,
plant uptake, runoff and erosion, and diffusion and mass transport
of residues in the soil and water(5,6,7) . Volatilization refers
to the gaseous loss of residues. Residues at or near the surface
are most susceptible to volatilization, and moist conditions
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increase this process. Although the volatilization rate
generally is proportional to the vapor pressure of a pesticide,
the vapor pressure alone is not a reliable predictor of the amount
of pesticide that will be volatilized. Other properties of the-
chemical, especially water solubility, are correlated with volati-
lization rates. Volatilization is usually a very minorjnode of
pesticide dissipation if vapor pressure is less than 10~ torr,
water solubility is more than a few ppm, and the molecular weight
is less than a few hundred(S). The importance of plants in
pesticide dissipation varies with the type of pesticide and timing
of application. For pesticides which are foliarly applied, a
large fraction of the applied material is intercepted by the
foliage and losses of pesticide due to photodecomposition and
volatilization may be greater than when the pesticide is soil
applied. Dissipation via plant uptake is low, and considered
insignificant in comparison to other dissipation processes(9).
Most often, plant uptake is lumped into general "soil degradation"
estimates.
Runoff and erosion refer to the overland transport of
solubilized residues or residues adsorbed to soil particles
suspended in runoff water. Nearly all dissipation resulting from
runoff occurs with pesticides within 1 or 2 cm of the soil surface.
Therefore, injected, incorporated, or leached pesticide is gener-
ally unavailable to runoff(7). Pesticides applied below the
surface may be more extensively leached since dissipation by the
aforementioned processes is reduced and microbial degradation is
usually reduced with greater depths in the soil profile.
Whether a pesticide will leach, runoff, or be lost via
erosion is dependent upon both field and pesticide properties(5,10)
Pesticides which have a low solubility and a high adsorption
partition coefficient will tend to remain where they are applied,
with generally a small percentage of loss possible (< 5% of appli-
cation) on eroded soil. (K in mL/g is defined as C /C , where
C is the concentration of solute (pesticide) adsorbed on the
sSil in uo/g and C is the equilibrium solution concentration in
ug/mL in a soil-water complex). A more specific definition for
the adsorption partition coefficient often used is K,, which is
the value of K when C equals 1 ug/mL. Pesticides with a high
solubility and low K , will move more easily in water, and are
subject to more leaching and surface runoff.
Cohen et al.(ll) listed the following pesticide properties
which they found characteristic of some pesticides known to
leach to ground water:
o Water solubility greater than 30 ppm;
o K, less than 5.0, usually less than 1.0 or 2.0;
o K (organic carbon partition coefficient) less than
38S to 500;
o Speciation - negatively charged (fully or partially)
at ambient pH;
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o Hydrolysis half-life greater than about 25 weeks;
o Photolysis half-life greater than about 1 week; and
o Soil half-life greater than about 2 to 3 weeks.
These criteria were derived from an examination of the
available environmental chemistry data on the pesticides alachlor,
aldicarb (including sulfoxide and sulfone degradates), atrazine,
bromacil, carbofuran, DBCP (1,2-dibromo-3-chloropropane), DCPA
(dimethyl tetrachloroterephthalate), 1,2-dichloropropanef dinoseb,
EDB (1,2-dibromoethane), oxamyl, and simazine. Cohen et al. set
their criteria such that these pesticides, all of which were
found in ground water at the time, each met most or all of them.
At this time, a larger number of pesticides have been
detected in ground water. An examination of the larger data
base, now available on the environmental chemistry of these
pesticides detected in ground water, indicates that these criteria
when used individually are poor predictors of potential groundwater
contamination. For example, the solubility of the commonly used
triazine herbicides varies widely, from 3 to 160 ppm. Triazine
compounds have been found in ground water including those with
solubilities lower than 30 ppm.
Perhaps the most important criteria used by Cohen et al. in
examining le'aching potential were the soil persistence and soil
adsorption measurements. A pesticide must be sufficiently stable
in the soil environment (persistent) and available for hydrologic
transport (mobile) below the zone of active microbial degradation.
Movement of pesticide residues to greater than or equal to 90 cm
is considered a field indicator of a pesticide's potential to
reach shallow ground water.
The rate of dissipation of pesticide residues by surface
runoff is related to the same chemical characteristics. Whether
a pesticide runs off or leaches is a function of formulation,
application method, and soil and climatic factors. Factors which
result in storm water leaching through the profile rather than
running off the field include: "sandy" soil, low water holding
capacity, little slope (< 2%), and a dense crop or plant residue
cover. The reverse conditions (heavy clay soil, bare soil condi-
tions, etc.) favor water running off the field. In general,
storm events near the time of application are most likely to
cause significant dissipation of residues via runoff. Residues
will dissipate, adsorb and/or leach with time so that later storms
will not have any residue available for transport in the top few
centimeters. In the same way, recharge events near the time of
application are most critical for leaching pesticides, since they
may transport the pesticide below the zone of active microbial
decay(7 ).
Numerous factors are known to influence degradation of
pesticides in the soil environment, including the chemical nature
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of the pesticide in combination with environmental factors.
Laboratory studies (anaerobic and aerobic soil metabolism, hydro-
lysis, photolysis, etc.) help define the chemical reactivity of
the pesticide and the rate of reaction under different conditions.
Environmental factors of importance include soil pH, organic
matter content, soil moisture, soil temperature, cation exchange
capacity, and aeration(S). Since environmental conditions vary
in both time and space, rates of degradation in the field also
vary widely, being either slower or quicker than what is measured
in the laboratory.
Under normal field conditions, aerobic microbes are
predominantly responsible for the degradation of pesticide
residues within the root zone (the few feet of soil below the
surface). Under conditions of saturation (i.e., during flooding),
however, the oxygen supply may be consumed and anaerobic organisms
take precedence(12). In this condition, the rate of degradation
may be similar to laboratory-determined anaerobic degradation.
Additionally, if a pesticide shows a tendency to photodegrade,
and the pesticide is applied to the canopy surface or to a bare
soil surface, then photochemical degradation can become the major
mode of degradation.
Microorganisms, including heterotrophic bacteria,
actinomycetes and fungi, and obligate and facultative photoauto-
trophic algae, comprise up to 80 percent of the living biomass in
soil(13). Microbial populations are most concentrated in the
upper few centimeters of soil and decline with depth in parallel
with the decline in soil organic matter. Most pesticides degrade
more slowly with increasing depth in the soil, presumbly largely
because of decreased microbial metabolism. This does not
necessarily mean, however, that microbial degradation of pesticides
below the A or B soil horizon is inconsequential. Direct micro-
scopic observation of soils provides evidence that many slow-
growing organisms exist which cannot be cultured and studied
further by traditional techniques, and which may be quite different
in their metabolic characteristics from those organisms which
have been identified. It is possible that some microorganisms
existing below the root zone are more efficent utilizers of some
pesticides as carbon energy sources and therefore substantially
contribute to the degradation of these compounds even though they
have a slow metabolic rate. Microbial degradation of pesticides
will depend on what kind of organisms are present under the field
conditions and the ability of these organisms to adapt to the
chemical. In general, high organic matter, moist conditions
(60 to 80 percent of the field capacity) and warm temperatures
are favorable for microbes and enhance the microbial degradation
of the pesticide. Other factors which influence microbial degra-
dation include pH and cation exchange capacity. The reader is
directed to the Standard Evaluation Procedures for Aerobic Soil
Metabolism and Anaerobic Soil Metabolism for further information
on the microbial degradation of pesticides.
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Many pesticides are partially degraded in soil by
nonbiological processes and some reactions can be brought about
either by microbial enzymes or strictly by chemical reactions. ;.
Usually these two processes work in conjunction(14,15). The
most complex process by which pesticides are degraded in soils
involves microbial utilization of the pesticide as an energy
source(16). It appears, however, that microbial degradation of
most organic chemicals at low concentrations applied to soil
occurs primarily via co-metabolism by soil organisms using soil
organic matter as their main source of energy(16).
The method of application and the formulation can also
affect the degradation in soil. For example, incorporation into
soil can reduce volatilization (a physical process) as well as
photodegradation (a chemical process). Pesticide formulations
include dusts, wettable powders, granules, microcapsules, seed
dressings, emulsions, mtscible liquids, and solutions. In general,
the more surface area available for decay processes, the more
rapid will be the rate of degradation. The use of granules
usually increases the persistence of pesticides, because the
pesticide only becomes slowly available for microbial degradation,
volatilization, etc. Emulsions tend to be more persistent as
well. Wettable powders and dusts have the most surface area, and
hence have the tendency to degrade the quickest of all
formulations(17).
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APPENDIX 2
Information to be Included in the Registrant's Report
Section 164-1 in the Subdivision N Guidelines describes the
short-term field dissipation study and gives a protocol for
conducting this study(1). Also, Section 160-5 in the Subdivi-
sion N Guidelines describes general reporting and evaluation
requirements for this study(l).
A. Information to be Included
1. Dates on which the study began and ended;
2. Name and address of the laboratory or institution
performing the test;
3. Location where the test was performed;
4. Names of the principal investigators;
5. Signatures of each of the senior personnel responsible
for the study;
6. Certification by the registrant that the report is a
complete and unaltered copy of the report provided by the testing
facility;
7. The report should reference or identify the test
substance, formulation statement, formulation category, and
include the chemical name and purity of active ingredient,
molecular structure, manufacturer and lot and sample number(s)
(including physical state, solubility in water, vapor pressure,
and pH) if not reported elsewhere;
8. Description of the test sites including soil
characteristics (as a function of depth), the approximate water
table location, area and field slope, previous pesticide/crop
history;
9. Weather data on a daily basis including air temperature,
precipitation (rain and snow), irrigation water, and soil
temperature on an infrequent basis;
10. A detailed report in tabular form of the residue data
from the treated soil (usually expressed as ppmW). Graphs are
often included to expand on the data given in tabular form; and
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11. A complete discussion of the results of the study which
should include a discussion of the following:
a. Percent recovery for the analytical method (A);
b. Dissipation rate and half-life estimate of the parent,
including regression analysis to indicate how well the dissipation
rate is described by a first-order model;
c. Rate of formation and decline of the degradation
products;
d. Identity of residues occurring at levels equal to or
greater than 0.01 ppm or 10 percent of the application rate,
whichever is lower. ThTs is not dependent upon the toxicological
significance of the pesticide residues;
e. Residue decline curves; and
f. Vertical mobility of parent compound and degradation
products.
B. Detailed Discussion
1. The Test Substance
The test substance must be a typical end-use product.
The test substance must also be a product whose formulation is
typical of the formulation category to which the product belongs.
If the applicant's product is a manufacturing-use product
that legally could be used to make an end-use product for which
terrestrial field dissipation data are required, the test substance
must be a product representative of the major formulation category
which includes that end-use product. (If the manufacturing-use
product is usually formulated into end-use products comprising two
or more major formulation categories, a separate study must be
performed with a typical end-use product for each such category.)
The pesticide product shall be applied at the maximum
proposed use rate utilizing the same application method(s) as
stated on the label.
2. The Test Sites
Field dissipation studies should be conducted in at
least two different sites in the United States which are represen-
tative of the areas where the pesticide is expected to be used.
For restricted use patterns where only one typical area is involved,
data from two similar sites are needed. Studies at additional
locations may be needed if the product is intended for a terres-
trial crop use, and the sites of application vary appreciably in
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-16-
climate or other pertinent characteristics. Therefore, a
sufficient number of field dissipation test sites will be necessary
as needed to represent all different uses. For each representative
test site, a control and a cropped plot will be needed. The
cropped plot should be treated with all applicable agricultural
practices, e.g., irrigation, fertilizer, etc. In situations
where a dense crop cover exists, and normal application procedures
result in an insufficient amount of pesticide reaching the soil,
a study using a bare soil plot may be necessary to determine the
half-life of a parent compound and the patterns of formation and
decline of degradates. Test sites which have not received prior
pesticide application of the test pesticide are preferred. If
the soil has received prior treatment of the same or similar type
of compound, then the microbial enrichment or adaptation to that
type of compound may have occurred. Subsequent pesticide
applications may then degrade more rapidly(18).
The location of the test sites, slope, field area,
location of water table, and complete information on the soil
properties (textural characterization of soil, pH, and organic
matter as a function of depth) should be provided.
A rain gauge should be installed as an integral part of
every test site to determine if supplemental irrigation will be
needed as the study progresses. Monthly rainfall averages based
on 10-, 20-, or 40-year sets of data should be used to determine,
if in any given month of the study, supplemental irrigation is
needed to bring the natural rainfall up to the expected monthly
average.
3. Test Procedures
a. Application
The test plots are prepared and maintained for the
intended crop and/or noncrop uses in the same manner as for
ordinary practices. The test substance should be applied using
the method of application stated in the directions for use on the
product label and at the highest rate recommended.
b. Sampling Scheme
"The timing of sampling and number of sampling dates
should be adequate to describe the degradation of the pesticide
and the pattern of formation and decline of the degradates.
o Pesticides which are persistent and immobile
need fewer sampling dates than pesticides which
degrade quickly or are mobile. An appropriate
sampling schedule for persistent.and immobile
pesticides (soil metabolism half-lives of 6 months
to 1 year) would be monthly for 6 months near
the beginning of the study, then bimonthly until
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-17-
12 months, and quarterly until the termination
of the study. For mobile and less persistent
pesticides (half-lives of greater than 1 week to
6 months) sampling at weekly intervals for a
month or more following application, and then
biweekly for several months, then monthly sampling
until the pesticide has dissipated, may be
appropriate. The sampling schedule can be tailored
to suit the degradation rate of the pesticide.
The sampling schedule should be described and
explained in a protocol prior to study initiation.
o For a pesticide with a very short half-life, less
than 1 week, the sampling scheme may include
samples on day 1, 3, 5, and then sampling emphasis
should be directed toward the major degradate(s).
c. Number and Compositing of Soil Samples
A study by Smith et al. suggests that 15 to 20 soil
cores taken per sampling interval per test site will be adequate
to determine pesticide residue concentrations, with an expected
coefficient of variation for those residues of 50 to 100 percent,
with a standard deviation (relative error) of ^ 50 percent around
the mean(19,20).
o For a small field plot approximately 15 meters
square (225 m ) a minimum of 15 soil cores per
field plot (or application site) per sampling
interval after pretreatment per sampling depth
increment must be taken. A one time sampling of
15 soil cores is recommended at pretreatment.
o For a field plot as typically used in field
dissipation studies, 15 soil cores per sampling
interval per 15 cm depth, increment are adequate
to characterize the pesticide residues in the
field. Individual depth increments from these
15 cores may be composited to a smaller subset
of samples for analysis.
For example, for each depth increment, three
composite samples consisting of five cores each
are acceptable. However, all cores should not
be composited to one sample for analysis. The
Agency finds it necessary to have some idea of
the variation in the concentrations of pesticide
residues in the field for determining a half-
life range.
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-18-
Samples may be composited as follows: All A cores
(A , A , A3, etc.)2and all B cores (B,, B2, B3, etc.) and
all C cores (C,, C , C,, etc.) are pooled, homogenized and
subsamples analyzed. A minimum of three composited samples must
be available for analysis in any plot for any time increment.
The figure below is illustrative; other sample collection schemes
are possible.
Al
Bl cl
A-?
B r
2 2
(2) 2
B
A
^i^
B,
d. Soil Sampling Depths
Soil from the test areas should be sampled following
treatment for the purpose of ascertaining the extent of pesticide
dissipation.
Preapplication Sampling
o Soil cores should be taken to a minimum depth of
90 cm. (Modifications may apply on a case-by-
case basis. All modifications must be detailed
in an approved protocol prior to study initiation.)
o Soil samples serving as test controls should be
obtained from the intended application sites
immediately prior to application of the test
substance and, if possible, from adjacent untreated
areas to check for any background residues of
pesticide in the soil. A single pretreatment
sample consisting of 15 soil cores each taken to
90 cm should be taken and analyzed from the
intended application sites to establish the
presence or absence of residues, and for soil
characterization down to 90 cm before study
initiation. The 15 soil cores may be composited
in increments greater than 15 cm down to 1 sample
for analysis.
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-19-
Postapplication Sampling
o Samples must be taken immediately following each;
application. Therefore, when multiple applica-
tions are made, immediate postapplication samples
should be taken after every application.
Depending on the length of time between applica-
tion intervals, the exact sampling depth and
schedule for immediate postapplication samples
may be negotiated. Samples taken immediately
postapplication should be sampled to 15 to 30 cm.
A shallower sampling depth is considered adequate
immediately after application, as long as no
significant rainfall or irrigation events have
occurred between the application and the sampling.
Immediate postapplication samples should be taken
the day o.f the application (day zero). However,
if the pesticide is soil-incorporated beneath 15
to 30 cm, the immediate postapplication sample
must be taken to the depth of incorporation.
Initial shallower sampling may reduce the possi-
bility of contaminating deeper soil layers during
the sampling process with high levels of pesticide
residues.
o For all samples collected after the immediate
postapplication samples, soil samples will be
consistently taken to a depth of 90 cm. The
soil cores will be divided or taken in the
following increments: 0 to 15 cm (plow/disc
depth) and then in additional 15 cm increments
to a minimum depth of 90 cm for each sampling
interval.
e. Field Study Design
The use of a grid or regularly-spaced pattern to
define possible sampling points within a test plot is recommended.
The actual grid points selected may be chosen randomly at the
center of grid sections, at grid intersection points, or at
opposite corners of grid sections. Instructions on setting up
regularly-spaced sampling patterns using subplots within a field
and collecting cores within the subplots for compositing are
available in the open literature(20,21). Random number routines
may be used to select sampling points(22).
f. Analysis Regime
o The single pretreatment sample consisting of 15
soil cores collected before pesticide application
will be analyzed throughout the 90 cm depth to
establish the background conditions for the
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-20-
field plots and to characterize the soil profile.
The one time sampling is necessary to determine
the presence or absence of residues and establish
background conditions.
Day zero samples taken immediately after final
pesticide application should be collected and
analyzed to a 15 to 30 cm depth to establish day
zero conditions in the field. When multiple
applications are made, all immediate post-
application samples prior to the final application/
must be sampled and analyzed to a 15 to 30 cm
depth. Sampling and analysis depths should be
discussed in a protocol for Agency approval
prior to study initiation. (If the pesticide is
incorporated into the soil, soils must be sampled
to a depth which allows for the injection depth.)
All samples taken after the immediate
postapplication sample must be collected down to
90 cm in 15 cm increments, and each set of 15 cm
increments may be composited into subgroups for
a minimum of three, composites for analysis as
previously explained. Increments may be frozen
and stored and analyzed sequentially as residues
are detected in successively deeper soil increments.
Increments must be analyzed to a minimum depth
of 30 cm (two successive 0 to 15 cm increments)
below the deepest increment in which residues
are found.
The parent and major degradates as identified
from aerobic soil metabolism studies should be
tracked in the field dissipation study. Any
degradate identified .in the aerobic soil metabo-
lism study at greater than or equal to 0.01 ppm
(10 ppb) or 10 percent of the application rate,
whichever is lower, should be tracked in the
field dissipation studies. The 0.01 ppm and 10
percent of application rate levels are intended
as goals to be met or surpassed. A registrant
will not be penalized for not being able to meet
the 0.01 ppm goal because of limitations with
the analytical method. However, the registrant
is expected to try to reach these goals. There
are new compounds in use that are applied at use
rates less than 10 ppb. Because of possible
toxic effects on humans and the environment, the
ability to detect these low use compounds and
their degradates becomes necessary.
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o Important evidence that sampling has not gone
deep enough include:
- Significant concentrations at the lowest depth
of sampling; and
- A significant amount of time between sampling
dates (£ 1 month) and prior information
indicating that the pesticide and/or its
degradation products may be leachers.
Soil samples should be analyzed as soon as possible
after being taken. If samples are stored before extraction and
analysis, it must be shown that the pesticide residues will not
degrade under the storage conditions. Freezing the soil samples
at or lower than 0 degrees C (preferably -18 degrees C) as soon as
possible after collection until analysis is an acceptable means
of storage. (A temperature of 0 degrees C) it is given as a set
standard unless the registrant can show that there was no degradation
at a higher temperature through a storage stability study. Storage
stability must be determined using pesticide-fortified samples
stored for as long as test samples are stored before residue
analysis (see below).
g. Storage Stability
It is recommended that a number of soil samples from
the various depth increments be field spiked with the pesticide
in order to ascertain the storage stability of the pesticide and
degradates during transport for the longest storage period.
A storage stability study is required as a part of
the field dissipation studies. Field soil should be spiked in
the lab and kept under storage conditions identical to those used
for the field samples. The storage stability study should indicate
if the pesticide is degrading during storage. Periodically, a
storage sample should be removed and analyzed for this purpose.
Storage stability samples should be kept for analysis for as long
a period as the field samples are held under storage prior to
analysis.
h. Test Duration
Reaction kinetics of dissipation of pesticides are
concerned primarily with the decline in concentration of the
pesticide over time(5,22,23). However, the Guidelines(1) also
require information on the degradation products. Therefore,
residue data should be collected until patterns of decline of the
active ingredient of the test substance and patterns of formation
and decline of degradation products are established in soil or to
the time periods specified below, whichever comes first:
o Field and vegetable crop uses: 18 months;
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-22-
o Orchard crop and pastureland uses: 12 months;
o Domestic outdoor, park, ornamental, and turf x
uses: 4 months; and
o Rights-of-way, shelter belts, and related uses:
2 months.
i. Triggering Ground-Water Monitoring Studies
If the pesticide is shown to have a potential of
moving into or is detected in the 75 to 90 cm increment, a ground-
water monitoring study may be required. The following points
should be considered when assessing the significance of any finding
of residues at 75 to 90 cm:
1) Is the detection consistent with trends observed
at earlier times in the experiment and with behavior exhibited at
other sites (after allowing for differences in soil type and
precipitation intensity)?
2) Is the apparent mobility consistent with
laboratory measurements of the soil-water partition coefficient
for the pesticide on similar soils?
3) Can sample contamination (as a result of coring
or analytical procedures) be eliminated as a potential cause of
detection?
The toxicological significance of pesticide residues
present at the 75 to 90 cm depth in the soil profile will not
play a role in determining if further small-scale prospective or
retrospective ground-water monitoring studies are warranted.
j. Triggering Surface-Water Monitoring Studies
If the pesticide is shown to have a potential of
moving from the site of application into surface waters, a surface-
water monitoring study may be required. [Note: the exact criteria
for surface-water monitoring studies have not been established.]
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-23-
APPENDIX 3
i
Analytical Data to be Submitted by the Registrant
A_. Analytical Procedures
1. Analytical Methods
•
A full description of the analytical methods used in all
steps of the analytical protocol must be submitted, including the
following information:
a. Name (and signature), title, organization, address
and telephone number of the person(s) responsible for the planning
and supervision/monitoring and laboratory procedures/analyses;
b. Analytical method(s) title/designation/date;
c. Source of analytical method(s) [e.g., Pesticide
Analytical Manual (PAM), Vol. II, scientific literature, company
reports);
d. Principles of the analytical procedure (description);
e. Copy of the analytical method(s) detailing in stepwise
fashion the procedures (extraction, clean-up, derivatization,
determination, calculation of the magnitude of the residue);
f. Reagents or procedural steps requiring special
precautions (to avoid safety or health hazards, explain);
g. Identification of the chemical species determined;
h. Describe modifications, if any, of the analytical
method(s);
i. Extraction efficiency;
j. Instrumentation [make/model, type/specificity of
detectors, column(s) packing materials, size, gas carrier, flow
rates, temperatures, limit of detection and sensitivity, calibration
procedures, etc.;
k. Interference(s), if any;
1. Confirmatory techniques [e.g., other column packings,
detectors, mass spectrometry, nmr, etc.];
m. Date(s) of sample taking, extraction and residue
analyses;
n. Sample identification [coding and labeling information];
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-24-
o. Residue results [examples of raw data, laboratory
worksheets, stepwise calculation of residue levels,
dilution factors, peak heights/areas, method correc-
tion factors applied (e.g., storage stability and
method validation recovery values, standard curve(s)
used, ppm found of "total" residues and of individual
components if of special concern, range of residue
values, representative chromatograms, spectra of
control and treated samples)];
p. Statistical treatments of raw data;
q. Other additional information the registrant/researcher
considers appropriate and relevant to provide a complete and
thorough description of residue analytical methodology and the
means of calculating the residue results.
B. Method Validation
A full description of the method recovery validation
procedures must be submitted and include information on the
following:
1. The recovery level(s) of the test compounds from the
soil (substrate) at various fortification level(s) using the
residue analytical methodology;
2. A validated method sensitivity level;
3. Results of the study and statistical tests applied, a
stepwise presentation of the procedure for calculating percent
recovery from the raw data;
4. All the data/information necessary to independently
verify the results;
5. Summary of data results; and
6. Conclusions drawn from the data results.
C. Quality Assurance
A complete description of the measures taken to ensure the
integrity of the test and analytical protocols should include
information on the following:
1. Logbooks and/or recordkeeping procedures; representative
instrument printouts (chromatograms, spectra, etc.);
2. Sample coding;
3. Use of replicate samples and control blanks;
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-25-
4. Use of written and validated analytical methodology for
re.sidue analyses involved in all test and analytical procedures,
including modification(s) made;
5. Skills of laboratory personnel;
6. Laboratory facilities;
7. Use of high quality glassware, solvents, and test
compounds to ensure minimal contamination;
8. Calibration and maintenance of instruments; and
9. Good laboratory practices in handling the test
substance(s).
D- Residue Analysis
1. Extraction of Soil Residues
Soil samples from each depth increment should be subdivided
and extracted with appropriate solvents, filtered, and reextracted
if necessary. Exhaustive extraction methods are sometimes neces-
sary. The reviewer should determine that an appropriate extracting
solvent was used in the study. The reader is directed to Chesters,
et al.(24) for a general overview on the subject of pesticide
axtraction and analysis of soil without elaboration on specific
orocedures and to Hance and McKone for specific procedures for
nerbicides(25). Extractable residues are considered as those
oeing immediately available for uptake by rotational crops, expo-
sure to nontarget organisms, and for leaching into the ground
vater. They are also available for further degradation.
2- Qualitative Identification of the Extracted Residues
Thin-layer chromatography (TLC) of extracted residues
vith cochromatography of known standards (identified as degradation
products from the laboratory soil metabolism studies), preferably
in more than two solvent systems, is adequate for tentative quali-
tative identification. Other spectroscopical analysis such as
}as chromatography/mass spectrometry (GC/MS) may be needed for
positive identification.
Analysis of Residues
Quantitative analysis of the extracted residues can be
3one either by GC or high performance liquid chromatography (HPLC)
\11 analytical methods must be examined for their specificity,
sensitivity, and recovery.
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-26-
E. Persistence and Mobility
1. Field Mobility Determination
Based on the residue analysis in soil increments, the
extent of leaching and potential for ground water contamination
of the test material or its degradation product(s) is examined.
A qualitative judgment can be made on the mobility of the parent
and degradation products based on criteria described earlier
(solubility, K., etc.) and this judgment is compared with results
of the field dissipation study, i.e., how much pesticide leached
below the treated zone, how fast it leached, and how far it
leached? Movement of residues to the 75-90 cm depth is an imme-
diate indicator of potential to reach shallow ground water in
the absence of other data. Field data which indicate leaching
in combination with laboratory data indicating mobility and per-
sistence are sufficient grounds to conclude that the pesticide
and/or its degradation products have the potential to contaminate
ground water.
2. Half-Life Estimation
Although dissipation of pesticides under field conditions
is not only due to loss by degradation but also due to loss by
other means (e.g., volatilization, runoff, etc.), first-order
degradation rate equations are useful for describing approxi-
mately the rate of dissipation of pesticides. Caution must be
used, however, since dissipation can be misunderstood and thought
of as disappearance. In fact, the disappearance of residues from
soil can mean appearance in another media, such as ground or
surface water or air.
As mentioned earlier, the reaction kinetics of pesticide
degradation in soil are concerned primarily with the decline in
concentration of the pesticide with time. For pesticides that
are not strongly sorbed to soil, rates of degradation often
approach first-order kinetics at low concentrations and zero-
order at high concentrations. At field application rates, the
degradation rates of most pesticides approach first-order
kinetics. That is, the concentration of the pesticide in soil
(which is usually low compared to the other reacting materials
in soil) determines the rate of the reaction(26). However,
rates tend to decrease with time more than would be expected
which suggest adsorptive forces are still active in the soil(16).
The rate of loss is proportional to its concentration in the soil
and can be expressed by the equation:
- dc K n (1)
dt ~ c
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-27-
where c = the concentration of the pesticide, K = the rate
constant, t = time, and n is the order of the reaction. For
first-order kinetics, n = 1, therefore,
_ _d£ . (2)
' KC
dt
where c is the amount of pesticide present in soil at time t.
Here, the first-order reaction means that the disappearance of
the pesticide is proportional to the amount left in the soil.
The dissipation of most pesticides from soils can be
considered as following a first-order reaction at least over a
portion of the degradation curve (5,1_9,2_4). It is reported that,
overall, the reaction kinetics involved~Tn decomposition of pesti-
cides follow mostly the zero-, first-, and second-order reaction
systems (2j>) . However, it is doubtful that any one single rate
eguation will ever be found which is applicable to all or most
pesticides in soil (5) . Data summarized show that the relation-
ships imply that the proportion of the chemical degraded with
time decreases as the concentration of the chemical decreases
(2_4). The rate at which the last traces of a chemical disappears
can be very slow ( 27) .
With these caveats, the first-order rate of reaction can be
determined as:
K = (- ln(c/cQ))/t (3)
where c = soil concentration at time t, c = initial concentra-
tion immediately following application, t = time in days.
The half-life, t, ,~, that is, when C = Co/2, can then
easily be determined as:
t1/2 = 0.693/K . (4)
where K = reaction rate, day , as determined by Equation (4).
The reviewer should use judgment when applying this equa-tion,
since each date on which soil residues were determined would
imply a different half-life. Computer programs are available
which fit all the residue data to a first-order rate equation.
If possible, these should be used to determine a reaction rate
which best fits all the data available.
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REFERENCE CITATIONS
1. U.S. Environmental Protection Agency. Pesticide Assessment
Guidelines Subdivision N. Chemistry: Environmental Fate.
EPA-540-982-021. Washington, DC, 1982.
2. Cohen, S.Z.; Eiden, C.; Lorber, M.N.; to be published in ACS
Symposium Series #315, Evaluation of Pesticides in Ground
Water, W.Y. Garner, R.C. Honeycutt, and H.N. Nigg, ed.,
American Chemical Society, Washington, DC, 1986.
3. Eiden, C.; Lorber, M.; Holden, P.W.; DeBuchananne, G.;
Cohen, S.; Guidance for Ground-Water Monitoring Studies,
(technical document in draft) 1988.
4. Laskowski, D.A.; Swann, R.L.; McCall, P.J.; Dishburger,
H.J.; Bidlack, H.D.; in Test Protocols for Environmental
Fate and Movement of Toxicants, Proc. Symp. of A.O.A.C.,
94th Ann. Meet., October, 1980.
5. Goring, C.A.I.; Laskowski, D.A.; Hamaker, J.W.; and Meikle,
R.W.; in Environmental Dynamics of Pesticides, R. Haque and
V. H. Freed eds., Plenum Press, New York, 1974, p. 135.
6. Bailey, G.W.; White, J.L.; Residue Reviews, 32, 29-92, 1970.
7. Stewart, B.A.; Woolhiser, D.A.; Wischmeier, W.H.; Caro, J.H.;
Frere, M.H.; Control of Water Pollution from Cropland Volume
II An Overview?"EPA Report No. 600/2-75-026b. 1976.
8. J. Adams, U.S. EPA, personal communication.
9. Edwards, C.A.; in Organic Chemicals in the Soil Environment,
C.A.I. Goring and J.W. Hamaker eds., Dekker, New York, 1972,
p. 513.
10. Leonard, R.A.,; Bailey, G.W.; Swank, R.R.; from Land
Application of Waste Materials by Soil Conservation Society
of America, 1976.
11. Cohen, S.Z.; Creeger, S.M.; Carsel, R.F.; Enfield, C.G.;
from Treatment and Disposal of Pesticide Wastes, ACS Symposium
Series #259, R.F. Krueger and J.N. Seiber, ed., American
Chemical Society, Washington, DC, 1984.
12. Alrichs, J.L., in Organic Chemicals in the Soil Environment,
C.A.I. Goring and J.W. Hamaker eds., Dekker, New York, 1972,
p. 40.
13. Odum, E.P., Fundamentals of Ecology, 3rd ed., W.B. Saunders
Co., Philadelphia, 1971.
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14. Zimbahl, R.L.; Freed, V.H.; Montgomery, M.L.; Furtick, W.R.;
Weed Res., 10, p. 18, 1970.
15. Skipper, H.D.; Volk, V.V.; Weed Sci., 20, p. ~344, 1972.
16. Goring, C.A.I., in Organic Chemicals in the Soil Environment,
CAI. Goring and J.W. Hamaker eds., Dekker, New York, 1972,
p. 793.
17. Young, W.R.; Rawlins, W.A.; J. Econ. Entomol., 51, p. 11,
1958.
18. Audus, L.J., in The Physiology and Biochemistry of Herbicides,
L.J. Audus ed., Academic, London, 1964.
19. Smith, C.N., Parrish, R.S., and Carsel, R.F., "Estimating
Sample Requirements for Field Evaluations of Pesticide Leaching,
Environmental Research Laboratory, U.S. EPA, April 4f 1986.
20. Cline, Marlin G., "Principles of Soil Sampling," Soil Science,
1944.
21. Tourtelot, Harry A. and Miesch, A.T., "Sampling Designs in
Environmental Geochemistry," Geological Society of America,
Special paper 155, 1975, pp. 107-117.
22. Jones, Russell L., "Pesticides in Groundwater: Conduct of
Field Research Studies," Rhone-Poulenc Ag Company, April 15,
1988, P.O. Box 12014, Research Triangle Park, NC.
23. Hamaker, J.W., in Organic Chemicals in the Soil Environment,
Goring, C.A.I, and J.W. Hamaker eds., Dekker, New York,
1972, p. 253.
24. Chesters, G.; Pionke, H.B.; Daniel, T.C.; in Pesticides in
Soil and Water, W.D. Guenzi ed., Soil Science Society of
America, Inc., Madison, WI, 1974, p. 451.
25. Hance, R.J.; McKone, C.E.; in Herbicides, L.J. Audus, Ed.;
Academic, 1976, p. 393.
26. Kearn H.J., Pflanzensch.-Nachr. Bayer 30, 1977, p. 98-117.
27. Graham-Bryce, I.J., in The Chemistry of Soil Processes, D.J.
Greenland and M.H.B. Hayes eds., Wiley, 1981, p. 621.
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