NAFTA Guidance Document
for
Conducting Terrestrial Field Dissipation Studies
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1200 P. >
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Prepared by:
M. Corbin, W. Eckel, M. Ruhman, D. Spatz, and N. Thurman
United States Environmental Protection Agency
Office of Pesticide Programs
Environmental Fate and Effects Division
and
R. Gangaraju, T. Kuchnicki, R. Mathew, and I. Nicholson
Health Canada
Pest Management Regulatory Agency
Environmental Assessment Division
EPA
540
2006.1
March 31,2006
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Table of Contents
I. Introduction 1
A. The Conceptual Model 2
B. Additional Study Modules 5
C. Use of Terrestrial Field Dissipation Study Results 7
1. Model Evaluation 8
2. Input for Environmental Fate and Transport Models 8
3. Terrestrial Exposure Assessment 9
4. Refined Risk Assessments (RRAs) 9
D. Principle of the Study 9
E. Applicability of the Test 10
II. Description of the method 11
A. Information on the Test Substance 11
B. Field Plot Systems 12
C. Site Selection 14
D. Field Study Plot Design 14
E. Procedure 15
1, Site Characterization 15
2. Application of the Test Substance 17
3. Study Duration 19
4. Management 19
5. Irrigation 19
6. Environmental Conditions and Monitoring 20
7. Soil Sampling 21
8. Sampling of Other Media 27
9. Sampling Strategies to Increase Sensitivity 29
III. Data Analysis, Interpretation and Reporting 29
A. Statistical Analysis 29
B. Data Interpretation and Quantitative Assessment 29
C. Mass Accounting Considerations 30
D. Reporting 30
E. Study Conclusions 32
List of Abbreviations 33
Endnotes 34
Appendix I Definitions and Units 38
Appendix II Data Sheet to Characterize Test Substance Properties 40
Appendix III Analytical Method Reporting, QA/QC and Validation 41
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Appendix IV Site Characterization Data Sheet 44
Appendix V Sample Description of the Soil Profile (USDA) 45
Appendix VI Physicochemical Properties of Soil 46
Appendix VII Meteorological History Data Sheet 47
Appendix VIII Site Use and Management History for the Previous Three Years 48
Appendix IX Suggested Criteria for Module Selection 49
References 56
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I. Introduction
The harmonization of pesticide regulatory requirements being carried out under the auspices of
the North American Free Trade Agreement (NAFTA) Technical Working Group (TWO) on
Pesticides is important in achieving the goal of one North American market for pesticides. This
goal is articulated in the document known as the North American Initiative (NAI). The NAI
commits Health Canada's Pest Management Regulatory Agency (PMRA) and the United States
Environmental Protection Agency (USEPA) to harmonize pesticide regulatory tools so that
work sharing and joint review activities become routine.
This document represents the NAFTA harmonized guidance for terrestrial field dissipation
(TFD) studies, which are conducted to demonstrate the transformation, transport and fate of
pesticides under representative actual use conditions. These field studies are needed to
substantiate the physicochemical, mobility and biotransformation data from laboratory studies.
Environmental fate studies have shown that pesticide dissipation may proceed at different rates
under field conditions and may result in degradates forming at levels different from those
observed in laboratory studies.
The objective of this revised guidance document is to help ensure that TFD studies are
conducted in a manner that will provide risk assessors and risk managers with more confidence
in the data generated and with a better understanding of the assumptions and limitations of the
data and estimated half-lives of the chemical. Properly designed field dissipation studies will
also provide a feedback mechanism for testing the hypothesis generated during the problem
formulation phase of the risk assessment. Often, the interpretation of the field results relative to
the hypothesis of expected behaviour requires an understanding of the specific site conditions
under which the study was conducted. Appendices I through VIII provide examples of the data
elements EPA/PMRA believe are critical for evaluating the hypothesis.
In developing this guidance document, EPA and PMRA conducted an extensive outreach and
review program, soliciting input from stakeholders and the technical community through
several forums: three symposia (4) (5) (6), one Scientific Advisory Panel (SAP) meeting (7) and
one workshop (8). Working closely with its stakeholders, PMRA and EPA developed a
conceptual model for designing terrestrial studies that will evaluate the overall dissipation of a
pesticide in the field. The conceptual model, which is specific for each pesticide, is based on the
chemical's physicochemical properties, laboratory environmental fate studies, formulation type
and intended use pattern. It is a prediction of the relative importance of each of the
transformation and transport processes that may be involved in the dissipation of a pesticide
under field conditions and represents the sum total of all potential dissipation processes (see
Figure 1). As such, it can be used as a working hypothesis for TFD studies.
A conceptual model is developed for an individual pesticide using assumptions derived from
laboratory data in combination with the formulation type and field conditions under which the
study will be conducted; it includes only those fate processes that are "significant" to the
pesticide in question. Although the responsibility for determining which processes are
significant rests with the study sponsor, EPA and PMRA may be consulted after the
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development of the pesticide-specific conceptual model if there is a question about whether a
particular dissipation process (i.e., represented by individual study modules) should be included
in the study protocol. Through the use of the conceptual model approach, study sponsors should
be able to provide data that are useful in the assessment and characterization of exposure and
risk, fully support claims of dissipation in the final analysis and reduce the number of rejected
studies.
As ecological risk assessment evolves, so does the need for its risk assessments to be based on
more precise characterization of the data. Critical in this characterization is an understanding of
the assumptions and limitations inherent in the data. The TFD study is a keystone study that
provides the primary means for testing the hypothesis of pesticide behaviour under actual use
conditions. Although laboratory data is the foundation for the hypothesis and the basis for the
conceptual model approach, the TFD study provides the primary mechanism for testing and
refining the hypothesis for the environmental fate and transport of a pesticide under actual use
conditions.
A. The Conceptual Model
Well-designed TFD studies answer the risk assessor's basic question: "Where did the
pesticide go when applied in the field?" By using a conceptual model in the study design
phase, the study sponsor can address this question by determining which routes of dissipation
need to be evaluated in order to adequately characterize the behaviour of a pesticide in the field
under actual use conditions. The study sponsor should consider the use pattern and ensure that
the overall study design accounts for potential formulation effects. Different designs may be
necessary for multiple formulation types, such as granular and emulsifiable concentrate.
Before conducting a study, the study sponsor needs to carefully consider all potential processes
and routes of dissipation as well as determine which of these are critical to answering the risk
assessor's basic question (Figure 1). A conceptual model, based on pesticide properties,
laboratory environmental fate results, formulation type and anticipated use patterns, can focus
the studies on the major routes of dissipation. A dissipation route should be included in the
study design if it is expected to explain, in part, the observed rate of chemical dissipation from
the surface soil.
One way to approach the study design is to consider each route of dissipation as a potential
study module. Using the conceptual model, the study sponsor can determine which modules are
needed to adequately characterize the active routes of dissipation in the field. An advantage of
this approach is that it offers flexibility in addressing data needs by including modules either
concurrent with or separate from the basic field study. With this approach, not all modules need
to be performed in the same study. For example, runoff experiments may be conducted in
small-plot studies, and volatility experiments may be conducted as separate experiments in
either the field or the laboratory. Ultimately, the decision regarding when to include a module
rests with the study sponsor.
Before initiating a TFD study, the study sponsor should develop a working hypothesis of the
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pesticide-specific conceptual model. This working hypothesis can form the foundation for
optional consultations with EPA/PMRA and can be included as a section in the final report. The
working hypothesis is the foundation for the pesticide-specific conceptual model and forms the
basis for determining how well the study design captures the fate of the pesticide in the field
under actual use conditions. The working hypothesis should include the following parameters:
Estimates for each module's contribution to the dissipation process (quantitative and/or
qualitative) based on laboratory physicochemical and fate properties
Basic study modules:
Soil abiotic/biotic transformation
Leaching
Additional modules:
Volatilization
Runoff
Plant uptake
Deep leaching
Others
The conceptual model described above should then be modified based on the anticipated
conditions in the individual TFD study sites. Modifications of the laboratory estimated
contribution to dissipation for each module (both quantitative and/or qualitative) should be
described for both the basic study modules and any additional modules that are necessary based
upon a review of laboratory data. The modifications to the conceptual model should be based on
field soil properties compared to soils used in laboratory studies, weather data, water balance,
formulation type, mode of delivery, crop influence (if any), agronomic practices and other
factors.
The study sponsor should consider the following when determining if a module should be
included or excluded:
Only those routes of dissipation that are included in the field study or measured by an
acceptable guideline study can be claimed to "significantly" affect the fate of a pesticide
and/or its degradates in the field.
Additional modules should not be excluded from the study when data indicate that
associated processes may contribute to "significant" pesticide dissipation or result in any
pesticide dissipation of toxicological concern. (See I.B. for a discussion of indicators
that are used to determine inclusion of additional modules.)
Ideally, when all modules are chosen, total dissipation attributed to excluded modules
should not exceed 10-20%.
* Because drift modules are not included in the study, special equipment should be used to
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minimize any loss due to spray drift.
Ultimately, it is the responsibility of the study sponsor to establish a hypothesis of the routes of
dissipation (i.e., the conceptual model) that will affect the outcome of the TFD study. The TFD
study should test the established hypothesis, and the final report should include the hypothesis
and the results analyzed in order to confirm or modify the hypothesis (Figure 2).
Figure 1 Conceptual Model of the Factors Affecting the Field
Dissipation of a Chemical
Spray
Applied
Pesticide
Surptioii/ / Tninsfonmiiions
Retention / microbiai
chemical
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Figure 2 Iterative Process for Evaluation of TFD Results Relative to the
Pesticide-specific Conceptual Model (after Purdy, 2002)
Iterative Process of Evaluating the Conceptual Model of
Terrestrial Field Dissipation
Required
Studies
Use In Models to
f stlmate Soil
Dissipation
TFD
Develop Field
Dissipation
siwhiieife-.
Agree
Higher Tier Studies
As Needed
B. Additional Study Modules
The basic TFD study focuses on pesticide dissipation from the soil surface layer in a bareground
study; it can be used to estimate field degradation only when other major routes of dissipation
(e.g., sorption and binding, leaching, volatilization, runoff and plant uptake) are quantified and
shown to be negligible. In addition to the guidance described in this document, EPA or PMRA
may require other dissipation studies to answer specific risk assessment questions. In deciding if
an additional study module is necessary in a field study, the study sponsor should ask the
following questions:
1. What is the potential for dissipation of the parent compound and its major
transformation products by a given route (e.g., volatilization, leaching, runoff, plant
uptake, etc.)?
2. Is the potential great enough to warrant measurement under field conditions
representative of actual use?
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In most cases, using the suggested criteria found in Appendix IX or a lines-of-evidence
approach based on physicochemical properties and laboratory fate data is the best way to
answer these questions and to determine if an additional module(s) should be included in the
TFD study. Using this approach, the following modules should be considered in all phases of
the study design:
Leaching. Laboratory studies on adsorption/desorption, column leaching, solubility and
persistence can predict the possibility of leaching beneath the root zone. The basic TFD study
has traditionally incorporated a leaching component and requires analyses of soil cores
extending below the surface (generally considered as 6 in. or 15 cm) to a given depth (1) (2) (3).
If neither the parent nor degradates of concern are detected in all cores below a given depth,
analysis of deeper cores is usually not necessary. However, if leaching mechanisms other than
flow through a porous medium are suspected for the site in question (preferential flow or karst
topography), then all soil core depths should be analyzed. A conservative tracer, such as
bromide ion, should be applied to the test plot to verify the depth of water leaching over the
course of the study.
Runoff. Runoff is possible for both weakly adsorbed, highly soluble chemicals and strongly
adsorbed, slightly soluble chemicals. The former may run off in the dissolved phase, and the
latter adsorbed on the particulate phase. However, the potential for runoff depends more on the
type of formulation, cover crop, mode of application (e.g., surface application versus soil
incorporation) and site factors (e.g., slope, type of soil, infiltration capacity and rainfall
intensity) than on the chemical properties of the active ingredient(s) and transformation
product(s). Depending on the conditions of the particular field dissipation study site, loss due to
runoff may be a significant or insignificant component of pesticide dissipation from the surface.
A simple runoff collector at the downslope edge of the field may be adequate to adjust for the
amount of pesticide loss due to runoff from an unanticipated event (i.e., storm).
Volatility. Volatilization of an applied chemical is a function of partitioning of the chemical
into solid, liquid and gaseous phases in the soil environment as well as other factors (e.g., wind
speed, temperature and humidity). However, the application method of the chemical (e.g., soil-
incorporation and watering-in) may serve to suppress volatilization. For example, soil-
incorporation and watering-in are used to limit chemical losses to volatilization.
Plant Uptake and Translocation. For systemic pesticides and transformation products whose
mode of action involves uptake through plant tissues (roots, leaves, etc.), this pathway may be a
significant route of dissipation. The study sponsor can characterize this route by conducting a
cropped-plot study in the field or by greenhouse studies on the same crop.
In summary, the process of selecting modules to include in the suite of TFD studies is the
responsibility of the study sponsor. The study design should anticipate the needs of the risk
assessor who will rely on a clear explanation of the assumptions used in the development of the
study design. Although not required, the study sponsor may consult with the risk assessor and
the risk manager on the design of the pesticide-specific conceptual model early in the process.
Early consultation will give the study sponsor time to assess the needs of the risk assessor and
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avoid unnecessary expenditure of time and resources. A well-developed pesticide-specific
conceptual model should be prepared and used as the basis for such consultation.
As noted above, the TFD study is a keystone study, in that it provides the primary means for
testing the hypothesis of environmental transformation/degradation, transport and fate
developed during the problem formulation phase of a risk assessment. The current guidance has
been developed to provide the risk assessor with a better understanding of the assumptions and
limitations inherent in the data, an improved perspective on the estimate of error in the study
results and, ultimately, better confidence in the data generated. The guidance has been written
to provide maximum flexibility for the study design while increasing confidence in the data.
Therefore, the study designer should look to the overall hypothesis of pesticide fate based on a
combination of data, including laboratory studies and physicochemical properties as well as
climate, soil, agronomic and site characteristics. Once a hypothesis is developed, the study
design may include additional modules as needed. The modules may be run concurrently with
the basic soil study or may be "plugged in" using other data, as long as the data are
scientifically valid and appropriate. One of the most important points to remember when
designing this study is that the results of the study describe the pesticide's major routes of
dissipation in the environment.
C. Use of Terrestrial Field Dissipation Study Results
The results of the TFD study are used to validate and/or refine the established hypothesis that
the pesticide dissipates in accordance with the pesticide-specific conceptual model. Differences
between field study findings and the established pesticide-specific conceptual model may
suggest the need for revision of the pesticide-specific conceptual model and possibly the need
for additional laboratory and/or field studies (Figure 2).
While this section provides examples of where the TFD study results may be used
quantitatively, the value of this study in qualitative assessments should not be overlooked. A
critical component of all risk assessments is the characterization of risk, in which the
assumptions, limitations and uncertainties inherent in the risk assessment are captured and the
potential effect of these factors on overall risk are explained. The TFD study results have been
and will continue to be a critical element of the risk characterization component of the risk
assessment; it is the only avenue by which the laboratory-based hypothesis of field behaviour
can be tested.
Results of field dissipation studies are used to estimate the field persistence of parent
compound, formation and decline of transformation products, residue carryover, and leaching
potential under representative actual use conditions. When other modules are included in the
study, results of these tests may provide important information on major dissipation routes such
as transformation, transport, volatilization, plant uptake and runoff. Although not specifically
relevant to this technical guidance document, a brief discussion of how the TFD study results
can be used in risk assessments deserves consideration. In addition to its value in characterizing
the dissipation of a pesticide in an actual field environment, field dissipation study results can
be used to evaluate the algorithms and input data for environmental fate models, and the results
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can be used to develop more refined ecological risk assessments. The following sections discuss
some of the potential uses and limitations of using TFD results quantitatively.
Model Evaluation
The results of TFD studies can be compared with pesticide estimations generated by the
Pesticide Root Zone Model (PRZM) to evaluate how well the model is performing. Although
the current field study does not always track specific routes of dissipation and identify reasons
for discrepancies, field dissipation studies can be designed to test hypotheses regarding routes
of dissipation predicted by environmental fate models such as PRZM. Not only can modelling
efforts be used to focus and interpret the results of field dissipation studies, but the study results
can also be used to evaluate the model.
Input for Environmental Fate and Transport Models
Currently, EPA and PMRA do not routinely use dissipation rates determined in the field as
degradation inputs for fate and transport modelling, such as the coupled PRZM and EXAMS
(Exposure Analysis Modeling System). Such an application is misleading when reported
dissipation half-lives (often DT50 [time for 50% dissipation of the parent chemical] values and
not true half-lives) include the combined routes of dissipation (degradation/transformation and
transport) from the surface. A rapid field dissipation rate may be due to degradation, movement
out of the surface soil, or both. Thus, the reviewer would expect a persistent, highly mobile
chemical to have a short half-life (t,/2) in the surface (provided rainfall or irrigation occur)
because it would move out of the surface.
Current models use inputs that represent the individual routes of dissipation (degradation half-
life values, rate constants, sorption/partitioning coefficients) to simulate overall dissipation.
Thus, substitution of a persistence half-life for a dissipation half-life would effectively treat
movement out of the surface (and potentially into the compartment of interest, i.e., surface
water or groundwater) as if it were degradation. It may be possible, in some instances, to
replace the route-specific model inputs with a combined dissipation rate determined in a field
study under the following conditions:
The sole focus of the modeling effort is to simulate runoff into a water body and, thus,
requires only an estimate of the amount of chemical that is available at the surface and
subject to runoff over time.
The weight of laboratory and field evidence indicates that dissipation in the field can be
confidently attributed solely to degradation/transformation (i.e., negligible loss by the
other dissipation routes, such as leaching, runoff, volatilization and plant uptake).
Terrestrial Exposure Assessment
Although terrestrial field study results can be used to determine the potential for pesticide
residues to remain in the soil from year to year, most of these studies do not provide adequate
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information on plant residue concentrations or residue concentrations in other food sources,
such as seeds or insects, in a manner that can be used in refined terrestrial exposure
assessments. However, when data are collected from foliage/food sources, they can provide
estimates of residue concentrations over time under actual use conditions in refined risk
assessments. In these cases, study results have been used to calculate estimated exposure
concentrations (EECs) in soil for buffer zone determinations in terrestrial habitats. Finally,
results from TFD studies can be used to evaluate the potential for carry-over of residues (both
parent and degradates) from one crop season to the following. This is particularly important for
persistent pesticides used in colder climates where the potential for persistence is greatest.
Evidence of from TFD studies will have implications for long-term exposure to non-target
organisms and may trigger additional studies (e.g., soil accumulation).
4. Refined Risk Assessments (RRAs)
Refined risk assessments produce a range or distribution of values instead of one fixed value
produced in a deterministic approach. Current research is focused on refining risk assessment
through the implementation of advanced probabilistic models that look at multiple pathways for
exposure and allow for sensitivity analysis to determine the significance of exposures to overall
risk. Well-designed TFD studies can provide results that are useful for interpreting and
providing feedback on model assumptions and results, and may even be considered as possible
inputs for Monte Carlo analysis.
D. Principle of the Study
Each TFD study should be designed in the context of a suite of TFD studies that identify the
route(s) and rate(s) of dissipation of the active ingredient and major degradates/transformation
products when a typical formulation/end-use product is applied under field conditions
representative of the significant area(s) where pesticides are used. The studies should quantify
the pathways of transformation and transport as well as the distribution of the parent compound
and its major transformation products in each environmental compartment. In short, the studies
should address the dissipation and fate of the active ingredient and major transformation
products in the environment.
It may not be feasible or desirable to study each of the routes of dissipation, as identified by the
pesticide-specific conceptual model, at one field site. For example, testing conditions for the
evaluation of pesticide runoff would not be appropriate for an assessment of leaching. In this
case, a modular approach is recommended in which concurrent dissipation pathways are studied
at one site, while non-concurrent pathways are evaluated in separate studies (either field or
laboratory, as appropriate). The suite of field dissipation studies may be conducted in an
iterative fashion until the results:
* provide an integrated qualitative and quantitative environmental fate assessment that
characterizes the relative importance of each route of dissipation for the parent
compound and major transformation products (greater than 10% of applied) and/or
toxicologically significant amounts of parent and transformation products. The study
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design should acknowledge the relative importance of each route may be different
depending on use pattern, formulation type and climatic conditions;
determine whether potential routes of dissipation identified in the laboratory are
consistent with field results;
characterize the dissipation rates of the parent compound and formation product as well
as decline of the major and/or toxico logically significant transformation products under
field conditions;
characterize the rates and relative importance of the different transport processes,
including leaching, runoff and volatilization;
establish the distribution of the parent compound and the major transformation products
in the soil profile;
characterize the persistence of the parent compound and major transformation products
in soil, including retention and residue carryover in the soil to the following crop season;
characterize foliar dissipation, if the compound is applied to plants; and
characterize the effect(s) of different typical pesticide formulation categories, where
applicable.
E. Applicability of the Test
TFD data are generally required by regulatory agencies (9) (10) to support the registration of an
end-use product intended for outdoor uses and to support each application to register a technical
grade active ingredient and manufacturing-use product used to make such an end-use product.
II. Description of the method
A. Information on the Test Substance
The test substance must be a typical end-use product for which TFD data are needed. (Appendix
I contains a list of definitions and units discussed throughout this guidance document.) If the
manufacturing-use product is usually formulated into end-use products from two or more major
formulation categories, separate studies should be performed with a typical end-use product for
each category (e.g., wettable powder, emulsifiable concentrate, granular).
Non-radiolabelled or radiolabelled substances can be used for the test, although
non-radiolabelled substances are preferred. The application of radiolabelled substances to field
environments is subject to pertinent national and local regulations.
The following information on the test substance should be included in the study report:
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Solubility in water (I) (3) (11) (12);
Vapour pressure (1) (3) (11) (12);
Henry's law constant;
n-octanol-water partition coefficient (1) (3) (11) (12);
Dissociation constant in water, reported as pK, or pKb (1) (11) (12);
Hydrolysis as a function of pH (1) (3) (11) (13) (14);
Photolysis on soil and in water (1) (3) (13) (15) (16);
Soil aerobic biotransformation (1) (3) (13) (15) (17);
Soil anaerobic biotransformation (1)(3)(13)(15);
Adsorption/desorption coefficients (1) (3) (13) (15).
These data are important in developing the conceptual model, identifying the potential routes of
dissipation (modules) to be studied and aiding in the experimental design with respect to the
sampling strategies, site locations, sample size and quantity, frequency of sampling, etc. The
data are also necessary to interpret the results of the study. (See Appendix II for a data sheet
that can be used in providing this information.)
An appropriate analytical method of known accuracy, precision and sensitivity for the
quantification of the active ingredient and major transformation products should also be
included in the study. In most cases, "cold" (i.e., non-radiolabelled) analytical methods that are
sufficiently sensitive to detect and monitor pesticide residues in the field are used. In order to be
useful for terrestrial exposure assessments, the limit of quantitation (LOQ) of the chosen
procedure should be between one and two orders of magnitude less than the expected
concentrations and should ideally be less than the important endpoints for non-target organisms.
The analytical methods are subject to independent laboratory validation (18). (Appendix III
contains a description of environmental chemistry information that is needed for validating
analytical methods used in conducting field dissipation studies).
B. Field Plot Systems
Plot size should be adequate to demonstrate the transformation, mobility and fate of the test
material in soil under controlled field conditions representative of actual use. The decision
concerning the plot size in field studies should be based on factors such as application methods,
crop and management factors, site characteristics and anticipated total number of samples. For
pesticides typically applied to cropped or conservation tillage plots (e.g., with at least 30% crop
residues on the surface), bareground pesticide-treated plots are necessary to help distinguish
dissipation pathways.
Large-scale studies (24) (25) (26) are conducted using normal agricultural practices
(e.g., cultivation prior to planting, etc.) and equipment. These studies may be used in
combination with other field studies, such as crop residue studies, provided the TFD studies are
not disturbed. Small plots (19) (20) (21) (22) (23) are treated using research-plot application
techniques (e.g., hand-held or backpack sprayers) that, in some cases, may reduce the variability
seen in large-scale studies. These small-plot techniques can also limit the ability to interpret
results and obtain satisfactory pesticide dissipation curves. Large-scale and small-plot studies
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have the following characteristics:
1. Large-scale studies: Large-scale studies typically cover a treated area of 8 cropped rows
by 25 m, but may range up to an entire field of several hectares, depending on the design
of the experiment and the use for which the product is intended. Typical plot sizes range
from 4 x 10 m to 10 * 40 m.
2.
Small-plot studies: Small plots (e.g., up to 2 m x 2-6 m or 4-12 m2 in area) are
preferable when pesticide dispersion is uneven and dissipation curves are difficult to
generate or interpret.
Generally, cropped plots are not required in TFD studies. However, if a crop is expected to
significantly influence the rate and/or route of pesticide dissipation (e.g., runoff from turf,
accumulation in the turf layer, accumulation into the crop, or abiotic degradation and
volatilization from leaf surfaces), then specific greenhouse or small-plot field studies (using the
same crop) are needed to address these routes of dissipation. In some cases, though, the studies
conducted to satisfy other environmental fate or human health data requirements may fulfill
these data needs. In the case of foliarly applied pesticides that are systemic, the test substance
should be applied to the intended crop, as specified on the label, to characterize the influence of
plant uptake and subsequent foliar metabolism and to provide a complete picture of the
dissipation of the pesticide from the terrestrial system. The influence of plant uptake and
subsequent dissipation should also be characterized in the case of pre-plant and pre-emergent
pesticides as well. When foliar processes interfere with the characterization of soil dissipation
processes, a bare study plot (i.e., not sown to intended crops and maintained plant free) should
be run in parallel to the cropped study. This analysis can be conducted either within the field
design or using suitable laboratory or greenhouse data. However, the use of laboratory or
greenhouse data will require an explanation of the conditions under which the data were
collected and how any differences between conditions in the laboratory/greenhouse and the
field study results and laboratory hypothesis may influence the evaluation of the field results.
While the bare plot study may be an artificial system, it is useful in providing an interpretable
pesticide dissipation curve in the soil.
Cropped plot field studies are needed when plants are an important factor in controlling field
dissipation of the pesticide. Assessing the importance of plant processes in pesticide dissipation
requires an examination of the mode of action of the pesticide, application timing relative to
canopy development, target crop or environment, and an evaluation of data from confined
rotational crop studies and foliar wash-off studies. Consideration of these factors requires
integration of the data into the overall hypothesis testing on probable routes of dissipation.
Cropped plots should be considered in the design of field studies when one or more of the
following criteria have been met:
Systemic pesticides, which are designed to move into and through the plant, are used.
This type of pesticide is expected to become incorporated into the plant either through
active or passive uptake.
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c.
* Foliar-applied pesticides applied at half to full canopy of the plant are expected to be
predominantly deposited on leaf surfaces. Under these conditions, foliar dissipation is
expected to be the dominant process in the field, although washoff can lead to increased
loadings to soil.
Pesticides applied to pasture, foliage crop, grass and turf are expected to strongly
influence dissipation pathways of pesticides.
Evidence of high foliar wash-off fractions or uptake of parent compounds (30-day
emergency crop rotation interval) from rotational crop studies indicate plant processes
may control pesticide dissipation. These studies should be conducted on the same crops
as the TFD study crop(s).
Execution of a study using a cropped plot should be conducted concurrently with a bare ground
study. Analyses of the data collected from the two plots should be similar except that plants
should be sampled and analyzed for pesticide residues in the cropped plots. The separate
collection, compositing and analyses of soil samples collected within and between the rows of
the row crop(s) may also be necessary. Whole plant residues should be designed to capture
either dissipation or accumulation in the plant. It is recommended that foliar wash-off half-lives,
if available, and potential plant accumulation rates be considered for designing sampling
frequency. Crop residues should be expressed as concentrations on both a dry weight and wet
weight basis. Additionally, crop yields, expressed as the total crop mass (g) / unit area (m2),
should be determined at each sampling time. Recording crop growth stage and area coverage
can prove useful in the overall interpretation of the results.
Site Selection
Field study sites should be representative of the soil, climatic and management factors under
which the pesticide will be used. The following factors should be considered in selecting field
study sites:
Number of uses/crops
Geographic extent and acreage of the crops/use patterns
Soil characteristics
Climate (including temperature, amount and distribution of precipitation, solar exposure
and intensity)
Use and management practices
Crop impacts on pesticide dissipation
Pesticide formulation
« Timing, frequency and method of pesticide application
Label restrictions regarding usage, sites or conditions
Differences between the field study sites and the use patterns of one or more of these factors
could affect the fate properties and dissipation processes of the pesticide, thus reducing the
applicability of field study results beyond the conditions of the study. Tools, such as the
13
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PMRA/EPA geographic information system (GlS)-based decision support model or other GIS-
based vulnerability assessment tools that account for the critical factors affecting pesticide
dissipation, can be used to determine the most appropriate field sites (27) (28). The GIS
decision support model utilizes ecological regions (e.g., the Ecological Regions of North
America), geospatial soil and agricultural crops databases, climatic information, and pesticide
properties, including laboratory fate data. Comparable field study area selection is based on
environmental conditions and the conceptual pesticide dissipation model developed from
laboratory fate studies.
The TFD study should include multiple field sites, generally four to six study sites. The actual
number of sites needed depends on such factors as the number of formulations, the geographical
extent of the use pattern, the number of uses and management practices as well as the range in
soil and climatic conditions within the geographic extent of the uses. If pesticide use is limited
geographically and/or to minor crops, a reduced number of field studies may be proposed.
D. Field Study Plot Design
An assessment of the fate of the pesticide in the terrestrial environment should include all
processes that can affect the fate of the chemical, including transformation, leaching,
volatilization, runoff, sorption to soil and plant uptake (1). Terrestrial field studies should be
designed, conducted and evaluated to assess the most probable routes and rates of pesticide
dissipation under conditions representative of actual use. The physicochemical properties of the
pesticide, laboratory environmental fate data, application techniques and site characteristics
should be considered in designing the study.
The basic field study design evaluates field dissipation in soil at a bareground site. If the
pesticide-specific conceptual model suggests that volatilization, leaching, runoff or plant uptake
are potentially important dissipation routes, then a modular approach is recommended whereby
dissipation pathways that can be studied concurrently at one site are included, while those
pathways that are incompatible are evaluated in separate studies.
The study design should encompass the range of practices and conditions that reflect the actual
usage of the test substance. For all field dissipation studies, non-cropped (bareground) plots
must be included. If the proposed use pattern includes application of a systemic pesticide on a
standing crop and it is believed that uptake may be an important route of removal from the field,
the trial should be conducted with a cropped soil in addition to the non-cropped (bareground)
plots. Data generated from laboratory or greenhouse studies may be used to supplement the
field data. However, the use of laboratory or greenhouse data will require an explanation of the
conditions under which the data were collected and how any differences between conditions in
the laboratory/greenhouse the field study results and laboratory hypothesis may influence the
evaluation of the field results. The studies should also include an untreated control plot.
Because of field-scale variability, the experimental units in each TFD study should be
replicated. Replication serves the following functions (29):
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Providing an estimate of experimental error
Improving precision by reducing standard deviation of a mean
Increasing the scope of inference of the experiment by selection and appropriate use of
variable experimental units
Effecting control of the error variance
Allowing statistical comparisons of intra- and inter-site variability
E. Procedure
1. Site Characterization
Assessing pesticide dissipation requires detailed description of the site characteristics as well as
characterization of "representative" soils at each test site. Ideally, the site selected for the TFD
study should be represented by a single soil type in order to reduce variability in the field. Such
information is critical to assess in situ chemical and physical properties of the test soil.
a. Site Description
The study site should be described according to geographic coordinates (e.g., latitude,
longitude), location on a map (topographic map, aerial photograph or soil survey map), location
within the watershed, landforms, landscape position, land surface configuration (e.g., slope
length and gradient, aspect and direction, micro-relief, roughness, shape, elevation) and depth to
groundwater. A suggested site description sheet can be found in Appendix IV.
b.
Soil Characterization
At each site, a representative soil pedon should be identified, and a minimum of one soil profile
should be described by soil horizons (preferably 2 m in depth) using standard soil
morphological properties (depth to and thickness of horizons or layers, Munsell color, texture,
structure, macroporosity, depth to a root restricting layer, etc.). Soil profiles will be described
and classified to family or series level according to an internationally recognized system
representative of the areas where the study is conducted. Examples of internationally
recognized systems are the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS), Canadian or the Food and Agriculture Organization of the
United Nations (FAO). In addition to the description of soil morphology, information on the
soil parent material, vegetation, erosion class, natural drainage class, surface runoff, infiltration
and saturated hydraulic conductivity should be reported. A suggested soil profile description
can be found in Appendix V.
Soil samples from each horizon should be collected and characterized by determining the
physicochemical properties in the laboratory. The physical properties should include particle
size distribution (i.e., % sand, % silt and % clay, with size fractions specified), textural class
(USDA), undisturbed bulk density, and soil moisture characteristic curve (0-15 bar) to help
determine the soil water balance throughout the study. The soil chemical properties should
include pH, percentage of organic carbon and cation exchange capacity. Standardized methods
15
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should be used and referenced for the determination of these properties. (See (30) and (31) for
examples.) Depending on the chemical properties or use site, additional analyses, such as clay
mineralogy, specific surface area, and anion exchange capacity (especially in soils dominated
by low activity clays or derived from volcanic materials) of the surface soil layer or epipedon
and the subjacent horizon (layer), may be helpful for determining sorption potential at the field
site. A suggested format for reporting the soil properties is given in Appendix VI.
c.
Environmental Conditions
Measurement of meteorological variables is necessary to understand pesticide dissipation in the
field. Daily records of maximum, minimum and mean temperature (air and soil), total
precipitation, mean wind speed and potential evapotranspiration are recommended from five
days prior to the first application of the pesticide through to the conclusion of the study. When
irrigation is used to supplement rainfall, timing and amounts of irrigation water should also be
reported. Historical climatological data should be obtained to help evaluate site data with
respect to long-term regional variation, and the source and location of the historical data should
be specified. Historical climatic information should include monthly average rainfall, average
monthly minimum and maximum temperatures, and the dates and the number of days in the
average annual frost-free period. A suggested format for reporting the historical meteorological
conditions is given in Appendix VII.
d. Management History
Information on the use of the study site, for example, crops grown, pesticides and fertilizers
used, should be provided for the previous three years. The site selected should not have a
history of the use of the study pesticide or other pesticides of similar nature (chemical class,
common nonvolatile transformation products, etc.) for at least three years prior to the study.
This requirement is necessary to reduce analytical interferences and potential microbial
adaptations for the test. Management factors, such as tillage and cultivation methods, irrigation
practices, etc., should be described in detail. A suggested format for reporting the land use and
management history can be found in Appendix VIII.
2. Application of the Test Substance
The TFD study should address the effect of pesticide formulation on dissipation. Different
formulations are expected to change the fate or transport properties of the pesticide. For
example, granular or microencapsulated formulations may release the active ingredient more
slowly than emulsifiable concentrate formulations. For this reason, separate studies should be
performed on at least one representative formulation from each of the applicable formulation
groups listed below. If the various commercial formulations of a given pesticide are not
expected to change the fate of the active ingredient, the applicant should provide the necessary
data in support of this assumption within the body of the study report. In general, it may be
possible to compare a field study conducted using water soluble liquids/water soluble
powders/emulsifiable concentrates with water dispersible liquids/wettable powders/water
dispersible granules. However, separate field studies will be needed for microencapsulated and
16
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granular formulations.
The recommended groupings of pesticide formulations are as follows:
Water soluble liquids, water soluble powders and emulsifiable concentrates
The release of an active ingredient into the environment is controlled by the formulation type
and the site-specific environmental conditions. Water soluble liquids and powders form true
solutions when mixed with water, and emulsifiable concentrates consist of oil soluble pesticides
and emulsifiers. These formulations are expected to have little effect on the transport of the
pesticide in soil (32).
Water dispersible liquids, wettable powders and water dispersible granules
Water dispersible liquids, wettable powders, and dispersible granules consist of finely ground
solids of various dimensions. Various studies indicate that these formulations may affect the
transport of pesticides in soil (33) (34) (35). For example, Ghodrati and Jury (33) showed
wettable powder formulations may be more resistant to preferential flow than emulsifiable
concentrates and technical grade material dissolved in water.
Granules
After precipitation or irrigation, granular formulations release the active ingredient gradually as
a function of diffusion or leaching (36). Therefore, this formulation may have a significant
effect on transport of the active ingredient if a rain event or irrigation occurs after application.
Microencapsulated pesticides
Microencapsulated/controlled-release formulations can reduce the potential of leaching through
soil (32) but may result in higher surface losses of a chemical when compared to other
formulations (37). Available literature on the effects of microencapsulated and controlled-
release formulations is inconsistent, and testing of this formulation type needs to be evaluated
on a case-by-case basis.
In the TFD study, the pesticide product should be applied at the maximum proposed use rate
utilizing the same application method(s) as stated on the label. In limited instances (e.g., for
ultra-low application rates), it may be necessary to apply the pesticide at a rate greater than the
maximum proposed use rate due to analytical detection limits.
Recommended equipment for pesticide delivery in the TFD study should be of high precision,
suited for the particular pesticide formulation (some pesticides may need to be homogenized by
a continuous mixing device in the tank) and outfitted with a device to keep drift loss to a
minimum.
The pesticide application, including timing and the number of applications, should be consistent
with labelling. The pesticide application should:
occur at the typical time(s) of the year and stage(s) in crop development when it is
normally used;
17
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be performed according to label instructions for the specific formulation (e.g., a granular
pesticide typically applied as a band should be applied as a band in the field dissipation
study);
be incorporated if the pesticide is typically incorporated; and
be measured by spray cards or similar verification techniques and related to the target
application rate and measured concentration in the spray tank.
Where multiple applications are allowed, an experimental design that enables assessments of
dissipation should be used. The study design should include collection and analysis of samples
prior to and after each application with a full set of samples collected after the final application
in order to estimate a dissipation rate. Replicated treatment plots will evaluate both single and
multiple applications. This guidance acknowledges that the use of multiple applications can
complicate the analysis of data generated during the course of the study. However, a critical
aspect of the TFD study is that the conditions under which it is conducted reflect actual use
conditions for the pesticide as closely as possible. Also, the use of a seasonal maximum amount
of pesticide in a single application can alter the conditions of soil microbial populations which
may alter the results of the study. Given these factors, it is recommended that the TFD study be
conducted using multiple applications at the maximum allowable rate specified on the labels for
that compound.
3. Study Duration
The duration of the TFD study, which has historically taken up to two years to complete, should
be sufficient to determine the DT75 of the parent compound as well as the pattern of formation
and decline of major transformation products in the soil. In determining the decline of the major
transformation products, the study duration should be sufficient to determine the time required
for major transformation products to dissipate to 25% of their maximum detected values in the
soil. A major transformation product is one accounting for £ 10% of the applied amount at any
time during the laboratory studies, or one that has been identified as being of potential
toxicological or ecological concern.
4. Management
The management (e.g., fertilization, seed bed preparation, weed control, sowing and tillage) of
the field dissipation study site should be carried out in accordance with good agricultural
practices. Tillage practices (conventional tillage, conservation tillage or no-till) should be
typical of those used for the particular crop and label recommendations.
5. Irrigation
It is essential that the study design include sufficient water to meet the crop need in quantity and
timing. If the use pattern includes irrigation to supplement the water requirements of the plant,
18
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6.
then the study should be conducted under irrigated conditions. In this case, the study design
should ensure appropriate timing and sufficient water to meet 110% to 120% of the crop need.
Also, in the case of bare plots, the site should receive sufficient water at the appropriate time to
meet the crop water need for the intended crop in that use pattern. In other words, a bare plot
site conducted for a corn use should receive 110% to 120% of the water need for corn in that
use area. Alternatively, if the use pattern does not involve irrigation, then the field studies do
not necessarily have to be conducted with supplemental irrigation. However, it may be
necessary to prepare the site for irrigation in case of drier than normal conditions. For non-
irrigated sites, the study design should ensure that 110% to 120% of normal monthly rainfall is
delivered to the site.
Environmental Conditions and Monitoring
The following environmental conditions should be recorded daily at the study site:
Precipitation
Mean air temperature
Potential evapotranspiration or pan evaporation (can be determined from a nearby site,
or evapotranspiration may be calculated from other environmental data)
Hours of sunshine and intensity of solar radiation
Mean soil temperature
Soil moisture content
a.
Soil Water Balance
Soil water content can affect the mode of degradation, degree of microbial activity, potential for
volatization, plant growth and potential for movement (i.e., up or down in the soil profile). To
interpret routes and patterns of dissipation of the test substance, the soil water content needs to
be measured on a regular basis to adequately determine the flux of soil water. Continuous or
daily measurements are preferred, but, at a minimum, readings should be collected at each
sampling time. Various methods of measuring soil water include tensiometers, time domain
reflectometry (TDR), neutron probes, gypsum blocks and direct measurement of the moisture
content of the soil samples (30).
b. Using Tracers to Track the Potential Depth of Leaching
A conservative tracer can be applied along with the test chemical to help determine the
direction, depth and rate of soil water movement through the vadose zone. Tracer selection
should consider the chemistry of the tracer, including potential sources of interference,
background/baseline levels, analytical detection limits and potential losses such as plant uptake.
If a tracer is used, background concentrations need to be analyzed prior to the study.
c. Soil Temperature
The soil temperature can also affect the rate of degradation, degree of microbial activity,
19
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potential for volatilization, plant growth, and potential for and direction of water movement
(i.e., up or down in the soil profile). Modern on-site weather stations typically include readily
available measurements of soil temperature, which should be used in interpreting the results of
field dissipation studies.
7. Soil Sampling
Soil samples for residue analysis should be representative of each replicate plot at each
sampling time. Replicate plots can be defined as repetitive, homogeneous sections of a field
treated with the test pesticide in a similar manner to allow comparison between treatments.
Sampling procedures can have a major effect on variability of pesticide concentrations in soil;
accurate and consistent sampling is vital for meaningful results. Variables such as plot size, soil
variability, crop management practices, pesticide application method and existing knowledge of
the behaviour of the pesticide in the environment should be considered in designing an
appropriate soil-sampling protocol.
a. Sampling Patterns
Soil core holes should be marked after sampling. Plugging holes with soil from untreated areas
of the site will prevent the cross-contamination at greater depths and subsequent anomalous
results.
A random or systematic soil sampling pattern (38) may be followed, depending on the type of
pesticide application and other variables listed above. For example, the soil may be sampled
in-row only (e.g., seed furrow or band treatment) or by a random pattern that covers the entire
treatment area (i.e., broadcast application). Because it may be difficult to obtain interpretable
results using an in-row sampling pattern, extreme care should be taken in the application and
sampling procedures.
In order to avoid variability resulting from possible under-coverage, drift or edge effects,
outside rows of treated areas should be excluded from sampling.
In small plots, systematic sampling is preferred to ensure that all treated sectors of the plot are
represented and to make it easier to avoid sampling in a previous core hole or in zones where
spray patterns in successive passes of the application equipment may have overlapped or failed
to cover the surface adequately.
Larger diameter cores are expected to reduce variability in the field. Typically, a core of one to
two inches in diameter has been used in TFD studies, but use of larger diameter cores should be
considered in the field design.
b. Depth of Soil Sampling
In order to fully demonstrate the fate and transport of the pesticide under study, soil should be
collected from a depth sufficient to encompass the vertical distribution of the pesticide and its
20
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major transformation products at each sampling time. Data from laboratory studies
(physicochemical properties, mobility and transformation) can be used in conjunction with
water recharge estimates (e.g., average rainfall data and expected irrigation coupled with
evapotranspiration estimates) and soil permeability properties to establish appropriate core
depths. Soil sampling should proceed to at least a depth of one metre, particularly for pesticides
with laboratory fate characteristics that indicate leaching is an important route of dissipation.
The major transformation processes usually occur within the "biologically active" zone of the
soil. For sampling purposes, this zone can be defined as the maximum depth of tillage, rooting
depth of agronomic plants or the depth of an impermeable soil layer, whichever is deepest. If
the laboratory studies indicate a low potential of a pesticide to leach, the emphasis of soil
sampling designs should be placed on this zone of soil rather than subsoils. The "biologically
active" soil zone concept will allow flexibility in experimental design because of different
agronomic practices, types of soil and site characteristics.
For most studies, soil cores should be collected to 1 m in depth and divided into six or more
depth increments for analysis (e.g., 15 cm, 15 cm, 15 cm, 15 cm, 20 cm and 20 cm). For low
application rate pesticides or where the results of the laboratory studies indicate very low
mobility of the parent chemical and its major transformation products in soil, core depths could
be sectioned into shorter increments to circumvent dilution of the chemical residues with excess
soil. In all cases, analysis of the sectioned cores should clearly define the extent of leaching of
the parent chemical and its major transformation products in the soil profile.
Soils should be sampled to a sufficient depth such that the lowest section of the sampled cores
does not contain detectable amounts of the active ingredient or major transformation products.
In the absence of rainfall or irrigation, the initial or zero time samples can be taken to at least
one sample increment below the depth of incorporation. For example, a pesticide incorporated
to 3 inches below the surface should be sampled from 0 to 6 inches and from 6 to 12 inches,
assuming a 6-inch interval.
c. Times of Soil Sampling
Soil sampling should be carried out prior to treatment, immediately after treatment (zero time)
and at increasing intervals (daily, weekly, monthly) between sampling times. If more than one
application is made, then soil sampling should be done before and immediately after each
application and then at increasing intervals after last application. Time intervals should be based
on the results of laboratory studies and other field studies, if available. Sampling frequency
should consider laboratory half-life estimates with increased frequency of sampling for shorter
half-life compounds. Other factors that may affect sampling frequency include compound
mobility and site-specific environmental conditions (e.g., rainfall and micro-climate). The
frequency of sampling should be concentrated after each application time to characterize the
dissipation of the test substance. However, the number and distribution of sample times should
also be sufficient to adequately characterize the formation and decline of the transformation
products.
21
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The dissipation of a product used in multiple applications over a season should be studied
through a full cycle of applications (22).
Residue data should be obtained until at least 75% of the pesticide and/or its major
transformation products have dissipated from the soil profile or the pattern of dissipation has
been clearly delineated (4!) (42). The study sponsor should determine the DT50 and DT7S from
the initial concentration because the dissipation rate constant often decreases with time (i.e., the
half-life is not constant as in first-order kinetics). If 75% dissipation is not reached by the time it
freezes in the fall, the study should be continued in the following year(s).
The plot should be sampled at the end of the growing season to determine residue carryover to
the next season; sampling in subsequent years may be necessary. Long-term studies may be
recommended if dissipation is slow to occur. This is particularly important for persistent, low
mobility pesticides or for those chemicals that show pesticidal activities at low concentrations.
If a control plot is included in the study design, then soil sampling need only be conducted
during the early stages of the study with a limited number of samples. The intention of the
control sample is to ensure that the pesticide is not present prior to application and to provide
information concerning potential loss of the pesticide from drift.
d. Time Zero Sampling
The time zero concentration lays the foundation for all subsequent sampling and is used to build
confidence that the pesticide was applied uniformly and accurately. The following points should
be considered in developing a time zero sampling protocol for a single application on bare
ground:
Availability of an appropriate analytical method with limits of quantitation low enough
to detect the parent and key degradates at relevant concentrations
Handling of all fortification samples in the same manner as soil samples
Testing of verification devices before use to provide confidence in compatibility with
the test substance
Application of reasonable correction factors provided they are within 10% to 20%,
although correction is not necessary
Verification of the actual rate applied
Calculation of an expected concentration in the field
Comparison of time zero concentrations with the expected concentration
For multiple applications, each application should be treated as time zero, and concentrations
prior to and immediately after application should be determined.
For cropped plots, the time zero sampling strategy should be modified to measure the portion of
pesticide reaching foliage as well as the portion reaching the ground surface.
The initial concentration in the soil immediately after treatment ("time zero") is a crucial
22
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benchmark value. Time zero sampling is recommended to verify residue concentrations
reaching the target and confirm uniformity of its distribution. The pesticide residues in all
subsequent soil samples are evaluated in relation to this value. An initial residue value that is
significantly lower than the value found for a subsequent sample may jeopardize the utility of
the study by rendering estimation of dissipation times (DT50 and DT75) meaningless. It cannot
be emphasized enough how critical the accurate delivery and accounting of a pesticide at time
zero are for the evaluation of the study results. Ideally, a study should utilize techniques that
maximize the delivery of the pesticide to the field at the target rate and keep corrected time zero
(time zero concentration after applying corrections related to delivery efficiency and field
monitoring results) results within 10% of that rate. However, it is recognized that this is a
"goal" and that may not always be obtainable.
Determination of time zero concentration involves the following steps:
* Analysis of the spray tank mixture before and after application
Use of collection devices such as filter paper, spray cards, etc.
Soil sampling immediately after application
Preferably, time zero sampling is conducted in duplicate, and the two sets of soil samples are
processed separately to provide two estimates of the mean time zero concentration. Time zero
sampling data should be used to confirm that the pesticide was uniformly applied to each plot at
the intended rate. Techniques used and any deficiencies associated with the delivery of the
pesticide to the field should be described and accounted for when analyzing the study results.
Although not routinely required, there may be instances where a cropped plot should be
sampled concurrently with a bare soil plot. In this case, the following factors should be
considered in the sampling strategy of a well-designed protocol:
Time zero samples
Types of sample (i.e., soil versus plant) and sampling frequency
Sample locations (e.g., between rows, under rows)
Accounting for plant uptake versus foliar dissipation
Residues in roots
Chemical factors such as formulation and application method
Crop characteristics
e. Number and Pooling of Samples
The purpose of soil sampling in the TFD study is to measure the mean concentration of the
pesticide (and its degradates or transformation products) so that dissipation may be followed
quantitatively over time. In order to generate a reliable estimate of the mean concentration that
represents the entire treated plot, a sufficient number of core samples should be taken to achieve
acceptable variability in the concentration across the plot. The number of cores needed to
estimate the mean concentration (statistically, the sample size) will then depend on the desired
precision (i.e., standard deviation around the mean) and the variability of the pesticide
23
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concentration in the field (the field or population variability).
The statistics of this estimation were developed several years ago (Gilbert, 1987) and have been
made into a calculator (DQO-PRO) by EPA's Superfund program to support the development
of Data Quality Objectives (DQOs). The DQO process is an experimental design exercise
intended to quantitatively define the sampling effort, given the data precision needed to support
decision-making.
In the case of the TFD study, the major DQO is measurement of the mean concentration at each
sampling time with a small enough error (standard deviation) that the means at different
sampling times over the course of the study can be used to calculate a statistically significant
rate of dissipation from the soil. Data presented by Jones et al. in 2004 (47) at the 227"1
American Chemical Society National Meeting suggest that the standard deviation among 16
samples individually analyzed from a variety of TFD studies is about 110%. (This analysis
provides an estimate of field or population variability.) Further analysis by industry (I. van
Weesenbeck, 2004 (48)) suggests that the variability in calculated half-lives is less than the
variability of the mean concentrations from which they are calculated (assuming constant
variability of the soil means over the course of the study), and that standard deviations of up to
100% in the mean concentration result in tolerable error for half-lives up to one year in length.
The following table, based on calculations with DQO-PRO, provides the number of individually
analyzed cores needed to estimate, at a 95% confidence level, the mean concentration at any
time, within a known error (standard deviation), given various assumptions about the population
variability. Using the assumption of 110% for a population, a sample size of 15 or 16 cores is
expected to estimate the mean concentration to within 60% standard deviation. (The actual
number of cores calculated by DQO-PRO was 16, but 15 facilitates the use of 3 replicate
subplots.)
The TFD study sponsor may use 15 cores per sampling episode as a minimum, although this
minimum number implies that the mean concentration calculated from the 15 cores is no more
precise than the 60% coefficient of variation (CV). If the cores are composited before analysis,
the standard deviation of the results should be corrected for compositing. (Note: If the standard
deviation calculated from the core analysis is greater than the expected 60%, the assumption of
110% CV in the field population may not be valid, and a larger number of cores should be
collected.)
If greater precision is desired to support more quantitative uses of TFD study results, or if
greater than 110% variability in the field is expected, then the study sponsor should use the
table provided in Il.FJ.e. (Table 1) or the DQO-PRO calculator to find the number of cores
necessary to achieve the desired level of precision.
In Table 1, the shaded area indicates the tolerable error that can be achieved in estimating the
mean concentration (top row) when 30 to 45 cores are taken from fields having variability in
concentration indicated by CV figures in the left-most column (population). These calculations
assume that samples are analyzed individually or that a correction for compositing is made. For
24
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example, if a 200% population (field) CV is assumed, 34 cores will estimate the mean
concentration to within 70% error, and 46 cores will estimate it to within 60% error, after
correction for compositing. If a 100% population (field) CV is assumed, then 46 cores will
estimate the mean concentration to within 30% error, after correction for compositing.
Table 1
Tolerable Error in Estimation of Mean Concentration
Population
(field)
%CV
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18
Finally, certain principles apply to the study design, regardless of the intended use of the study
results. The number and diameter (typically 3 to 12 cm) of soil cores should be based on the
size of the plot, the type of soil and the amount of soil necessary for analysis. Corresponding
depths of soil cores from a single replicate plot can be pooled and mixed thoroughly to produce
one representative composite sample that can be analyzed. An adequate number of cores per
25
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plot should be collected at each sampling time to ensure the sample is representative of the plot.
For example, a composite sample from a 2-m * 1-m small plot may consist of 15 soil cores (3-
cm diameter) per sampling time over a period of one year (19) (20) (39) (40). In large plots,
cores of greater diameter are usual (24) (38). The variability within a large plot is typically
greater than in a small plot because of less uniform pesticide application and soil spatial
variability. For field studies of longer duration with small plots, the plot area should be
increased to accommodate collection of a greater number of cores, resulting from an increased
number of sampling times. If a large-scale plot contains areas of different types of soil, soil
organic matter content, etc., or knolls/depressions, then representative cores from areas of
different soil types should be pooled and analyzed separately from other samples.
f. Handling of Samples
Soil samples should be handled in the following manner.
Soil samples should be frozen if they cannot be extracted immediately.
Air-drying of soil samples before extraction is not recommended because of possible
loss of chemical residues from the samples via volatilization.
To check the stability of pesticide residues during storage, untreated soil samples should
be fortified in the field with analytical standards (parent chemical and major
transformation products), stored, and then extracted and analyzed within the same time
period and in the same manner as samples from treated field plots (21). Recovery results
from field-fortified samples are preferred to recovery data from more conventional
storage stability studies such as laboratory-fortified samples.
8. Sampling of Other Media
Measuring pesticide residues in soil over time provides direct information on a limited number
of dissipation routes, e.g., transformation, sorption and leaching. Other dissipation routes that
often play major roles in the environmental fate of a compound include accumulation and
metabolism in plants; volatilization from soil, water and/or plant surfaces; soil binding; runoff;
and spray drift. To meet the objectives of the TFD study and to determine where the pesticide
goes in the environment, the study sponsor may need to design the sampling scheme to account
for routes of dissipation that cannot be accounted for through soil core sampling alone.
a. Sampling Plants and Foliage
When the pesticide is applied to cropped plots, plant material should be sampled. The sampling
scheme should be designed to track the decline in pesticide residues from foliage with time, and
foliage sampling should include a time zero residue level. Pesticide residues may also be
affected by abiotic degradation (hydrolysis and/or photolysis), be translocated into plant foliage
and volatilize from foliage more readily than from soil. If any of these processes from foliage
are a likely route of dissipation, the study design should ensure that appropriate measurements
26
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are made. In contrast to soil sampling times, foliage samples need to be collected more
frequently at the beginning of the study in order to adequately characterize foliar dissipation.
It may be appropriate to use existing laboratory and/or greenhouse plant studies as a substitute
for a full scale field sampling of plant material. However, when relying on
laboratory/greenhouse data to support a route of dissipation in the field study, the registrant
needs to characterize any differences between the conditions under which the
laboratory/greenhouse studies were conducted relative to the field dissipation study. These
laboratory/greenhouse studies should be conducted using similar conditions as those present in
the field study, e.g., plants, application, treatment, etc., if possible. The registrants should
consider collecting a set of benchmark samples from the field study to determine how much of
the pesticide was removed by the crop and for comparison with the laboratory/greenhouse
studies.
b. Air Sampling
Monitoring studies have found pesticide residues in the atmosphere, demonstrating that some
pesticides have the potential to volatilize from the field (43). Many pesticides are
soil-incorporated, though, to retard volatilization and enhance efficacy. In cases where the
vapour pressure and Henry's law constant of the pesticide or site-specific environmental
conditions (e.g., warm temperatures, windy conditions) suggest potential volatilization, the TFD
study should provide meaningful data on volatilization losses from the field. In this case, air
sampling, with methods that measure pesticide residues in the vapour phase, may be needed to
determine whether volatilization is a route of dissipation. Air samples need to be collected more
frequently at the beginning of the study to adequately characterize the volatilization of the test
substance.
c. Sampling for Pesticide Residues in Runoff
Laboratory studies may indicate the potential for pesticide residues to move offsite dissolved in
runoff water or through erosion. Typically, the TFD study is conducted on a site that is
essentially flat. However, if the use pattern suggests that the pesticide will be used in areas of
significant slope (e.g., orchard uses) or that there are significant risks associated with aquatic
exposures from runoff, then a runoff component may
be necessary (44).
9. Sampling Strategies to Increase Sensitivity
Strategies that could be used to increase the detection sensitivity of pesticides in TFD study
samples include the following:
Decreasing the thickness of sample soil depth (thinner increments)
Increasing the area of soil or foliage samples
Increasing the volume of runoff water or air samples
Increasing the application rates
27
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Increasing the number of replications
Refining/improving analytical methods for parent and major transformation products
Improving recovery efficiencies
III. Data Analysis, Interpretation and Reporting
A. Statistical Analysis
Data gathered from the study should be analyzed by statistical methods that describe the
pesticide's rate of dissipation. Methods should be specified and consistent with the study
design; goodness of fit of the data to the statistical analysis should be provided. Analysis should
emphasize the dissipation of the pesticide from the upper soil layer to which the pesticide is
applied, as well as comparisons of within-site and among-site variability.
B. Data Interpretation and Quantitative Assessment
An evaluation of the data collected in the field dissipation study and interpretation of the results
should include the following considerations:
Half-life and times for 50% and 75% dissipation of the parent chemical (DT50 and DT75,
respectively) under field conditions, determined from the residue data
Dissipation parameters of the major transformation products (e.g., quantities and rates of
formation and decline, including DT50)
Mobility of the parent compound and the major transformation products under field
conditions
A comparison of the dissipation and mobility parameters from the field studies with
corresponding results from laboratory studies and predictions based on the pesticide's
physical/chemical properties (e.g., solubility in water, vapour pressure, Henry's law
constant, dissociation constant and n-octanol-water partition coefficient)
Plant uptake of pesticide residues in the field compared with that under laboratory or
greenhouse conditions, within the context of the experimental parameters at the field
site, e.g., application, climatic (precipitation and temperature), edaphic (soil properties
and moisture conditions) and cropping parameters
Identification and discussion of discrepancies between the results of field studies and
laboratory studies
C. Mass Accounting Considerations
The residue data for the parent chemical, each of the major transformation products and the
total major chemical residues should be expressed in terms of equivalent amounts of parent
28
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chemical on a dry-weight basis, and then as percentages of the 0-day concentration. These
percentages can then be summed for the sampled environmental compartments (e.g., soil
depths, air, water, plants) and plotted versus time to estimate an overall mass account. If the
overall mass accounting is unexpectedly low, major route(s) of dissipation were possibly not
adequately addressed in the field study design.
D. Reporting
The study report should be clear and succinct with definitive conclusions regarding the
environmental fate and transport of the pesticide after field application. Soil samples results
should always be reported on a dry-weight basis along with percent moisture. The study
conclusion should be discussed both in terms of the data developed in the field study and in
terms of the expected route(s) of dissipation suggested by the laboratory studies. Discussion of
how the study compares with other field studies of this active ingredient should be included.
The report should clearly identify those aspects of the study having a direct bearing on the
author's conclusions and the validity of the study results.
In addition to a full description of the analytical methods used, the following data should be
reported:
Information on the test substance and relevant transformation products:
Formulation of the test substance
Limits of analytical detection/quantification
Physicochemical and environmental fate properties
* Specific activity and labelling positions (if appropriate)
Information on the field study site:
Location
Climatic conditions and history
Soil taxonomic classification and properties with depth
Hydrologic setting
Size and configuration of the treatment and control plots
Crop, management and pesticide-use history
Depth to the water table
Application of the test substance:
Time(s) of application
Rate(s) of application
Method of application
Confirmation of application rate
Field condition at the time of application
Meteorological conditions at the time of application
Tracer(s) used, if any:
Typeoftracer(s)
Rate and method of application
29
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E.
Maintenance activities:
Type of vegetation
Agricultural practices (date of seeding, time of harvest, yields, etc.)
Weed control
Conditions during test:
Daily air temperature (minimum, maximum)
Daily precipitation and irrigation (reporting of single rainfall events), intensity
and duration
Irrigation technique
Weekly and monthly sums of precipitation and irrigation
Weekly mean soil temperature
Soil water content
Daily evapotranspiration or pan evaporation
Movement of tracers (if used)
Residues in soil (as mg/kg dry weight and % of applied amount) at each sample interval:
Concentration of test substance in each soil depth
Concentration of transformation products in each soil depth
Concentration of extractable radioactivity in each soil depth, if applicable
Concentration of non-extractable radioactivity in each soil depth, if applicable
Total amounts of test substance, transformation products, other unidentified
extractable residues and non-extractable radioactivity, if appropriate
Residues on and in plants (in mg/kg fresh weight and % of applied amount) at each
sample interval, if appropriate. In addition, plant residues should be reported based on
how much of the pesticide was removed from a unit-area of the field in order to be
useful in mass accounting.
Residues detected via other avenues of dissipation (e.g., volatility, runoff, leaching), if
appropriate
Mass accounting (recovered percentage of applied test substance) at each sample
interval
Appropriate statistical analyses of the collected data
Protocol deviations and amendments
Data should be presented in both tabular and graphical forms.
Study Conclusions
After an extensive outreach and review program involving stakeholders and the technical
community, EPA and PMRA developed harmonized guidance for conducting a TFD study.
Central to this guidance is the development of a conceptual model, using assumptions derived
30
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from laboratory data along with the intended use pattern and physicochemical properties of the
pesticide. As such, the conceptual model is a prediction or working hypothesis for the TFD
study.
Although laboratory data is the foundation for the hypothesis and the basis for the conceptual
model approach, the TFD study provides the primary mechanism for testing and refining the
hypothesis for the transformation, fate and transport of a pesticide under actual use conditions.
As the keystone environmental fate study, the TFD study allows the risk assessor to directly
compare the laboratory hypothesis of the transformation, fate and transport of the pesticide with
those processes measured in the field. Without the terrestrial field study, the assessor will not
have a feedback mechanism to evaluate the laboratory hypothesis of environmental behaviour.
Well-designed TFD studies characterize the transport, transformation and biological
assimilation processes of a pesticide in the field as well as the dissipation rates of the parent
compound and major breakdown products. In contrast to laboratory studies, TFD studies
highlight the potential simultaneous processes that may occur in the field. For example,
biodegradation can occur during leaching or runoff. Hydrolysis and photolysis can be enhanced
by certain soil components in the field that may be absent during laboratory studies. Also, initial
products of hydrolysis and photolysis can serve as substrates for microbial degradation.
As pesticide risk assessment moves from a deterministic approach to a more sophisticated
probabilistic approach, the need for better characterization of the data used in a risk assessment
increases. In characterizing the data, the risk assessor needs to understand the assumptions,
limitations and error in the study results. This guidance has been developed to address this need
and to provide the study sponsor with flexibility in designing a study without increasing the cost
of conducting the study.
31
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List of Abbreviations
List of Abbreviations
CV coefficient of variation
DQO data quality objectives
DTj0 see Appendix I
DT75 see Appendix I
EEC estimated exposure concentration
EPA United States Environmental Protection Agency
EXAMS Exposure Analysis Modeling System
FAO Food and Agriculture Organization of the United Nations
GIS geographical information system
NAFTA North American Free Trade Agreement
NRCS Natural Resources Conservation Service, USDA
PMRA Pest Management Regulatory Agency
PRZM Pesticide Root Zone Model
RRA refined risk assessment
tl/2 see Appendix I
TDR time domain reflectometry
TFD terrestrial field dissipation
USDA United States Department of Agriculture
32
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Endnotes
Endnotes
(1) Cheng, H.H. 1990. Pesticides in the Soil Environment: Processes, Impacts, and Modeling. Soil
Sci. Soc. Amer. Book Series #2, Madison, WI.
(2) Fletcher, C., S. Hong, C. Eiden, and M. Barrett. 1989. Standard Evaluation Procedure:
Terrestrial Field Dissipation Studies. EPA-540/09-90-073. EPA, Office of Pesticide Programs,
Washington, DC.
(3) Agriculture Canada, Environment Canada, and Department of Fisheries and Oceans. 1987.
Environmental Chemistry and Fate Guidelines for Registration of Pesticides in Canada. Trade
Memorandum T-1-25 5. Ottawa, Canada.
(4) Mastradone, P.J., J. Breithaupt, P.J. Hannan, J.A. Hetrick, A.W. Jones, R.D. Jones, R.J. Mahler,
S. Syslo, and J.K. Wolf. 1995. Critical assessment of terrestrial field dissipation guidelines. In
M.L. Leng, E.M.K. Leovey and P.J. Zubkoff (eds.). Agrochemical Environmental Fate Studies:
State of the Art. Lewis Publishers, Boca Raton, FL. p. 93-98.
(5) American Society of Agronomy, Division of Environmental Quality (A5), Symposium
"Integrating Environmental Fate and Transport Data from Laboratory to Field Studies." A.G.
Hornsby, Division Chair; J.K.. Wolf, and J.A. Hetrick, Symposium Chairs. St. Louis, MO, 1995.
Abstracts published in Agronomy Abstract (1995).
(6) American Chemical Society, Agrochemical Division Symposium "Pesticide Risk Assessment:
From a Conceptual to a Quantitative Exposure Model." Al Barefoot, and Don Wauchope, Co-
chairs. Anaheim, CA, 2004. Abstracts published in ACS National Meeting Technical Program.
(7) FIFRA Scientific Advisory Panel (SAP) Meeting, "Review of Proposed Revised Guidance for
Conducting Terrestrial Field Dissipation Studies." October 1998, Arlington, Virginia.
www.epa.gov/oscpmont/sap/1998/index.htm
(8) Terrestrial Field Dissipation Workshop, OPP/PMRA. Arlington, Virginia, 2002.
(9) United States Code of Federal Regu lations. Part 15 8 of Title 40, Protection of the Environment.
(10) Canada. Pest Control Products Regulations. Section 9.
(11) Organisation for Economic Co-operation and Development. 1993. OECD Guidelines for the
Testing of Chemicals. OECD, Paris.
(12) United States Environmental Protection Agency. 1988. Pesticide Assessment Guidelines.
Subdivision D: Product Chemistry. EPA-540/09-82-018. EPA, Office of Pesticide Programs,
Washington, DC.
(13) United States Environmental Protection Agency. 1982. Pesticide Assessment Guidelines.
Subdivision N, Chemistry: Environmental Fate. EPA-540/9-82-021. EPA, Office of Pesticide
Programs, Washington, DC.
33
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Endnotes
(14) Creeger, S.M. 1985. Standard Evaluation Procedure: Hydrolysis Studies. EPA-540/9-85-013.
EPA Office of Pesticide Programs, Washington, DC.
(15) SETAC-Europe. 1995. Procedures for Assessing the Environmental Fate and Ecotoxicity of
Pesticides. Society of Environmental Toxicology and Chemistry.
(16) Whetzel, N.K., and S.M. Creeger. 1985. Standard Evaluation Procedure: Soil Photolysis
Studies. EPA-540/9-85-016. EPA Office of Pesticide Programs, Washington, DC.
(17) Fletcher, C.L., and S.M. Creeger. 1985. Standard Evaluation Procedure: Aerobic Soil
Metabolism Studies. EPA-540/9-85-015. EPA Office of Pesticide Programs,
Washington, DC.
(18) Marlow, D.A., D.D. McDaniel, A.E. Dupuy, Jr., and E.M. Leovey. 1995. Data Reporting
Guideline for Environmental Chemistry Methods. Subdivisions N, E, and K. EPA Office of
Pesticide Programs, Washington, DC.
(19) Chapman, R.A., and C.R. Harris. 1982. Persistence of isofenphos and isazophos in a mineral
and an organic soil. J. Environ. Sci. Health. B17: 355-361.
(20) Harris, C.R., H.J. Svec, and W.W. Sans. 1971. Toxicological studies on cutworms. VII.
Microplot field experiments on the effectiveness of four experimental insecticides applied as
rye cover crop and soil treatments for control of the dark-sided cutworm. J. Econ. Entomol.
64: 493-196.
(21) Harvey, J., Jr. 1983. A simple method of evaluating soil breakdown of 14C-pesticides under field
conditions. Residue Rev. 85: 149-158.
(22) Hill, B.D. 1981. Persistence and distribution of fenvalerate residues in soil under field and
laboratory conditions. J. Agric. Food Chem. 29: 107-110.
(23) Walker, A., and P.A. Brown. 1985. The relative persistence in soil of five acetanilide
herbicides. Bull. Environ. Contam. Toxicol. 34: 143-149.
(24) Birk, L.A., and F.E.B. Roadhouse. 1964. Penetration and persistence in soil of the herbicide
atrazine. Can. J. Plant Sci. 44: 21-27.
(25) Hunter, J.H., and E.H. Stobbe. 1972. Movement and persistence of picloram in soil. Weed Sci.
20: 486-489.
(26) Khan, S.U., H.A. Hamilton, and J.E Hogue. 1976. Fonofos residues in an organic soil and
vegetable crops following treatment of the soil with the insecticide.
Pestic. Sci. 7: 553-558.
(27) Kroetsch, D., R. Gangaraju, W. Effland, I. Nicholson, N. Thurman, and D. Pagurek. 1998. A
34
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Endnotes
spatial decision support system for the selection of target areas for pesticide field dissipation
studies. Paper presented at First International Conference on Geospatial Information in
Agriculture and Forestry, 1-3 June 1998, Lake Buena Vista, FL.
(28) Soil Survey and Land Research Centre (SSLRC), Cranfield University (1998). SEISMIC, A
unique national spatial information system for environmental modelling. SSLRC, Cranfield
University, Silsoe, Bedford, UK. Internet WWW page, URL
www.silsoe.cranfield.ac.uk/nsri/
(29) Steel, R.G.D., and J.H. Torrie. 1980. Principles and Procedures of Statistics: A Biometrical
Approach. McGraw-Hill Book Company, New York, NY.
(30) Klute, A. 1986. Methods of Soil Analysis - Part 1: Second Edition, Physical and Mineralogical
Methods, American Society of Agronomy, Madison, WI,
ASA Monograph No. 9.
(31) Page, A.L. 1982. Methods of Soil Analysis - Part 2: Chemical and Microbiological Properties,
American Society of Agronomy, Madison, WI, ASA Monograph No. 9.
(32) Flury, M. 1996. Experimental evidence of transport of pesticides through field soils - a review.
J. Environ. Qual. 25: 25^*5.
(33) Ghodrati, M., and W.A. Jury. 1992. A field study of the effects of soil structure and irrigation
method on preferential flow of pesticides in unsaturated soil. J. Contain. Hydro. 11:101-125.
(34) Hurto, K., and M. Prinster. 1993. Dissipation of turfgrass foliar dislodgeable residues of
chlorpyrifos, DCPA, diazinon, isofenphos, and pendimethalin. In: K. Racke and A. Leslie
(eds.). Pesticides in urban environments: fate and significance. American Chemical Society,
Washington, DC. pp. 86-99.
(35) Wauchope, R. 1987. Tilted-bed simulation of erosion and chemical runoff from agricultural
fields: II. Effects of formulation on atrazine runoff. J. Environ. Qual. 16(3):212-216.
(36) Furmidge, C. 1984. Formulation and application factors involved in the performance of soil
applied pesticides. In: R. Hance (ed.). Soils and crop protection chemicals. Monogr. 27. British
Crop Protection Council, Croydon, UK. p. 49-64.
(37) Kenimer, A., J. Mitchell, A. Felsot, and M. Hirschi. 1997. Pesticide formulation and application
technique effects on surface pesticide losses. Trans. ofASAE. 40(6):1617-1622.
(38) Roadhouse, F.E.B., and L.A. Birk. 1961. Penetration and persistence in soil of the herbicide
2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). Can. J. Plant Sci. 41: 252-260.
(39) Chapman, R.A., and C.R. Harris. 1980a. Insecticidal activity and persistence of terbufos,
terbufos sulfoxide, and terbufos sulfone in soil. J. Econ. Entomol. 73(4): 536-543.
35
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Endnotes
(40) Chapman, R.A., and C.R. Harris. 1980b. Persistence of chlorpyrifos in a mineral and an organic
soil. J. Environ. Sci. Health B15(l): 39^6.
(41) United States Environmental Protection Agency. 1975. Field dissipation studies. Guidelines for
registering pesticides in the United States. 40 FR (123): 26894-26896.
(42) Smith, A.E. 1971. Disappearance of triallate from field soils. Weed Sci, 19(5): 536-537.
(43) Taylor, A.W., and W.F. Spencer. 1990. Volatilization and Vapor Transport Processes. In H.H.
Cheng (ed.). Pesticides in the Soil Environment: Processes, Impacts, and Modeling. Soil Sci.
Soc. Amer. Book Series #2, Madison, WI. pp. 213-270.
(44) Smith, C.N., D.S. Brown, J.D. Dean, R.S. Parrish, R.F. Carsel, and A.S. Donigan, Jr. 1985.
Field Agricultural Runoff Monitoring (FARM) Manual. EPA 600/3-85/043. United States
Environmental Protection Agency, Athens, GA.
(45) Gilbert, R.O. 1987. Statistical Methods for Environmental Protection Monitoring. Van
Nostrand Reinhold, pp. 30-34.
(46) Keith, L.H, G.L. Patton, and P.O. Edwards. Radian International LLC, Austin TX. DQO-PRO
2.0: Calculator for estimating numbers of environmental samples and associated QC samples.
Public domain software available at American Chemical Society Division of Environmental
Chemistry website: www.envirofacs.org/dqoprQ.htm
(47) Jones, R.L., et.al. 2004. Suitability of field data for determining degradation rates in
environmental risk assessments. Presented at the 227th American Chemical Society National
Meeting, Anaheim, CA, March 2004.
(48) van Wessenbeck, I. 2004. Comparison of lab and field DT50 PDFs and PRZM-3 soil and water
concentration predictions. Presented at the 227* American Chemical Society National Meeting,
Anaheim, CA, March 2004.
36
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Appendix I
Appendix I Definitions and Units
50% dissipation time (DT^): The amount of time required for 50% of the initial pesticide
concentration to dissipate. Unlike the half-life, the dissipation time does not assume a specific
degradation model (e.g., a first-order degradation).
75% dissipation time (DT7S): The amount of time required for 75% of the initial pesticide
concentration to dissipate. Unlike the half-life, the dissipation time does not assume a specific
degradation model (e.g., a first-order degradation).
Dissipation: Overall process leading to the eventual disappearance of substances from the site of its
application or an environmental compartment. Dissipation comprises two main types of processes:
transport processes, such as volatilisation, leaching, plant uptake, runoff or erosion that transfer
substances to different environmental compartments; and transformation processes such as microbial
degradation, hydrolysis and/or phototransformation that produce transformation products.
First-order kinetics: A model that assumes that the rate of degradation/dissipation is
proportional to the concentration of the reactant and remains constant during the reaction time
period.
The single first-order model is derived from the differential equation:
dM
dt
= -kM
with
M = mass of the compound
MO = initial mass of the compound
k = rate constant for the compound
The integrated form of the above equation is a simple exponential equation with two parameters (Mand
M = M,e~kt
with
A/= mass of the compound at time t
Half-life (tJ/2): The time required for a concentration of a pesticide to be reduced (i.e., degrade,
metabolize or otherwise dissipate) to one-half. With each half-life period, half of the remaining
concentration of pesticide will disappear from the system.
37
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Appendix I
Half-life versus 50% dissipation time: When the reaction follows first-order degradation kinetics, the
half-life will be equivalent to the 50% dissipation time. In this case, the reaction rate is proportional to
the reactant concentration and constant over time. However, when the degradation rate is not first-
order, the half-life and the 50% dissipation time will differ. In this situation, the half-life is usually
greater than the 50% dissipation time. Discrepancies between the t1/2 and the DT50 may suggest that
pesticide degradation follows something other than a first-order reaction model.
Ideal application and planting techniques: The use of specially adapted application machinery to
accurately apply a pesticide in small plot field trials in a manner approximating field methods.
Major transformation products: Degradation products/metabolites of the parent compound that are
observed at any time in the laboratory or field studies at a level equal to or greater than 10% of the
initial concentration of the parent compound. In addition, major transformation products may include
other compounds of toxicological significance.
Plot: A single experimental unit, e.g., a control plot, a treated plot.
Replicate plot: One of two or more plots treated in an identical manner at one site.
Site: Exact geographical location of a study.
us.
iv,.
38
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Appendix II
Appendix II Data Sheet to Characterize Test Substance Properties
This table contains the physicochemical properties of the test substance and the environmental fate
laboratory studies necessary to design a TFD study.
* ^^^:Propei^r/lab::«ttidy
Solubility (mg/L)
Vapour pressure (Pa)
Henry's law constant
(atnvmVmol)
Dissociation constant (pKa or
pKb)
w-octanol-water partition
coefficient (ATOW)
Hydrolysis (half-life)
Major transformation products
Soil photolysis (half-life)
Major transformation products
Soil aerobic biotransformation
(half-life and persistence)
Major transformation products
Soil anaerobic biotransformation
(half-life and persistence)
Major transformation products
Adsorption/desorption
(A.andAJ
Mobility class
Others
'4^fe5yji
Classification
-,-. Rdferdii$K-~r:,--
39
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Appendix I
Appendix III Analytical Method Reporting, QA/QC and Validation
Environmental chemistry information that is needed for the independent validation of analytical
methods used in conducting field dissipation studies is listed below.
Documentation. A full description of the analytical methods used in all steps of the analytical protocol
should be submitted, including the following information:
1. Name and signature, title, organization, address and telephone number of the person(s)
responsible for the planning and supervision/monitoring and laboratory procedures/analyses
2. Analytical method(s) title/designation/date
3. Source of analytical method(s) [e.g., Pesticide Analytical Manual (PAM), Vol. II, scientific
literature, company reports]
4. Principles of the analytical procedure (description)
5. Copy of the analytical method(s) detailing the following procedures:
a) extraction
b) clean-up
c) derivatization
d) determination and calculation of the magnitude of the residue
6. Reagents or procedural steps requiring special precautions to avoid safety or health hazards
7. Identification of the chemical species determined
8. Modifications, if any, to the analytical method(s)
Extraction efficiency
9.
10.
Instrumentation (e.g., GC)
a) make/model
b) type/specificity of detectors
c) column(s) packing materials and size
d) gas carrier and flow rates
e) temperatures
f) limits of detection and sensitivity
g) calibration procedures
Interferences, if any
40
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Appendix I
12. Confirmatory techniques
a) other column packings
b) detectors
c) mass spectrometry
d) nuclear magnetic resonance
13. Date(s) of sampling, extraction and residue analyses
14. Sample identification (coding and labelling information)
15. Residue results (examples of raw data, laboratory worksheets, stepwise calculation of residue
levels, dilution factors, peak heights/areas, method correction factors applied [e.g., storage
stability and method validation recovery values], standard curve(s) used, ppm of total residues
and of individual components if they are of special concern, range of residue values,
representative chromatograms, spectra of control and treated samples)
16. Statistical treatments of raw data
17. Other additional information that the study sponsor/researcher considers appropriate and
relevant to provide a complete as well as thorough description of residue analytical
methodology and the means of calculating the residue results
Quality Assurance/Quality Control. A complete description of the measures taken to ensure the
integrity of the analytical results should include information on the following:
1. Logbooks and/or record keeping procedures, representative instrument printouts, such as
chromatograms, spectral analyses, etc.
2. Sample coding
3. Use of replicate samples and control blanks
4. Use of written and validated analytical methodology for residue analyses involved in all test and
analytical procedures, including modifications 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
9. Good laboratory practices in handling the test substance(s)
10. Quality assurance project plan
41
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Appendix 111
11. Internal and external auditing schedule established by the study director using an independent
quality assurance unit
Independent Laboratory Method Validation. A full description of the method validation procedures
performed by an independent laboratory should be submitted and include the following information:
1. 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 test applied, including 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 the results
6. Discussion and conclusions of the results
42
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Appendix IV
Appendix IV Site Characterization Data Sheet
This table can be used to describe the pertinent site characteristics that can influence the dissipation of
the test substance in terrestrial environments.
Parameter! ;
Geographic coordinates
Latitude
Longitude
Data Source
FIPS Code for State, County
Location within watershed
Landforms
Landscape position
Land surface
Slope gradient
Slope length
Direction
Micro-relief
Roughness
Elevation
Data source(s)
Depth to groundwater
Average rainfall (yearly/monthly)
Average air temperature
(daily/weekly/monthly)
Minimum
Maximum
Average soil temperature
(daily/weekly/monthly)
Minimum
Maximum
Average annual frost-free period
Dates
Number of days
Others
Site Description
Information Source :
43
-------
Appendix V
Appendix V Sample Description of the Soil Profile (USDA)
TAXONOMIC CLASS: Fine-loamy, mixed, thermic Aridic Paleustalfs; Amarillo Series
PEDON DESCRIPTION: Amarillo fine sandy loamgrassland. (Colours are for dry soil unless
otherwise stated.)
A 0 to 11 inches; brown (7.5YR 4/4) fine sandy loam, dark brown (7.5YR 3/4) moist; weak fine
granular structure; hard, very friable; many fine roots; many fine and medium pores; many
wormcasts; mildly alkaline; clear smooth boundary. (5 to 19 inches thick)
Bt 11 to 27 inches; reddish brown (SYR 4/4) sandy clay loam, dark reddish brown (SYR 3/4)
moist; moderate coarse prismatic structure parting to weak medium subangular blocky
structure; very hard, friable; many fine and medium pores; thin patchy clay films on faces of
prisms; clay bridged sand grains throughout; common wormcasts; mildly alkaline; gradual
wavy boundary. (8 to 25 inches thick)
Btkl 27 to 38 inches; yellowish red (SYR 4/6) sandy clay loam, moist; weak medium subangular
blocky structure; hard, friable; clay bridged sand grains; common films and threads of calcium
carbonate on faces of peds; interiors of peds noncalcareous; moderately alkaline; gradual wavy
boundary. (8 to 30 inches thick)
Btk2 38 to 56 inches; pink (SYR 7/3) sandy clay loam, light reddish brown (SYR 6/3) moist; weak
medium subangular blocky structure; hard, friable; estimated 60 percent calcium carbonate
equivalent; 30 percent by volume is concretions of calcium carbonate less than 1 inch in
diameter; calcareous, moderately alkaline; gradual wavy boundary. (6 to 36 inches thick)
Btk3 56 to 85 inches; yellowish red (SYR 5/6) sandy clay loam, yellowish red (SYR 4/6) moist; weak
very coarse prismatic structure parting to weak medium subangular blocky structure; slightly
hard, friable; thin patchy clay films and clay bridging of sand grains; few, mostly vertical
stringers of soft bodies of calcium carbonate are concentrated along faces of prisms; few
calcium carbonate concretions less than 1 inch in diameter; calcareous, moderately alkaline;
gradual wavy boundary. (8 to 50 inches thick)
Btk4 85 to 99 inches; light reddish brown (SYR 5/4) sandy clay loam, yellowish red (SYR 4/5) moist;
weak very coarse prismatic structure parting to weak medium subangular blocky structure; hard,
friable; thin patchy clay films and bridged sand grains; few soft bodies of calcium carbonate are
concentrated in vertical columns along faces of prisms; calcareous, moderately alkaline.
44
-------
Appendix VI
Appendix VI Physicochemical Properties of Soil
:.;> ;b;iligliP!s?:ri- .-' 1 . '[- f:
, r1 v^zlsBWWny; :/.;. '!i!,-x-:
. y "~c'^.r,?'-.vV!:i iJ~M - -f--; -
Depth
Texture
% sand
% silt
% clay
Textural class (USDA)
Bulk density
Soil moisture characteristic
Obar
0.1 bar
a bar
1 bar
5 bars
10 bars
15 bars
pH
Organic carbon (%)
Cation exchange capacity
(meq/lOOg)
Base saturation (%)
Clay mineralogy
Specific surface
Anion exchange capacity
Others
js,=tgjsg?4>:s ;
fe JsttliFji :
?!:8JLi
rtpjLiJ:.^
Asllf-^ !'i:*
fit-';
^"^i^K^^S:^^
P^BB
pfi?!|'y|«-
iipftJifCi^r.;'
fl-^:'.
i£\?^$
''":"-''.&
a.
i]liiiiiNiiii»uj ' ' c
;:;i:2:;:r;:::::Wl*tDOa .
:;-.- -;7;-:.-,
45
-------
Appendix VII
Appendix VII Meteorological History Data Sheet
This table can be used to describe the pertinent meteorological factors that can influence the dissipation
of the test substance in terrestrial environments.
Parameter
Site Description
Information Source
Average monthly rainfall
January
February
March
April
May
June
July
August
September
October
November
December
Average minimum/maximum air
temperature
January
February
March
April
May
June
July
August
September
October
November
December
Average annual frost-free period
Dates
Number of days
Others
46
-------
Appendix VIII
Appendix VIII Site Use and Management History for the Previous
Three Years
^IfipctWi;-''^!!1:--''
Crops grown
Pesticide and fertilizer use
Cultivation methods
Tillage
Irrigation practices
Others
T:.|,: . .-.-.
YXrei^y*^
47
-------
Appendix IX
Appendix IX Suggested Criteria for Module Selection
Field Study Indicators
In deciding what modules to incorporate into a field study, the study sponsor should ask the following
questions:
1. What is the potential for dissipation of the parent compound and major transformation by a
given route (e.g., volatilization, leaching, runoff, etc.)?
2. Is the potential great enough to warrant measurement under field conditions representative of
actual use?
In many cases, several criteria or a weight-of-evidence approach based on physicochemical properties
of the test substance and laboratory studies is the best way to answer these questions. No single
laboratory study by itself can absolutely predict transformation, transport or dissipation in the field.
Laboratory data can, however, provide quantitative or semi-quantitative indices of the inherent
persistence and mobility under field conditions.
Volatilization Potential
Important physicochemical properties influencing volatilization are vapour pressure and solubility in
water. The partitioning of a chemical between air and water is described by Henry's law and can
increase or decrease the volatilization potential. Adsorption to soil is an important process that reduces
volatilization. When needed, volatilization from soil and water may be specially studied under
laboratory conditions to gain additional knowledge. Quantification of trapped volatile organics in
standard laboratory studies of biotransformation/metabolism in soil and aquatic systems also addresses
volatilization of the parent compound and transformation products.
Other factors that may be considered include method of application (e.g., foliar versus soil surface
versus soil incorporated, injected and watered-in), temperature, soil moisture content, soil organic
carbon content, soil texture, soil porosity, residue persistence and leaching.
Vapour Pressure
The measured vapour pressure of a chemical compound is a guide to its volatility and to the probability
of its movement into the atmosphere. A volatility classification based solely on vapour pressure is best
suited to dry, non-adsorbing surfaces. In general, pesticides with vapour pressures ^ 1 * 10"6 mm Hg
(1.33 x 10'4 Pa= 1.33 * 10'! mPa) are considered relatively non-volatile under field conditions,
whereas pesticides with vapour pressures > 3.9 x 10'5 mm Hg (5.20 x 10° Pa = 5.2 mPa) are
considered to be of intermediate to high volatility under field conditions (Kennedy and Talbert, 1977).
Thus, a vapour pressure > 3.9 x JO"5 mm Hg or 5.2 mPa at 25°C raises concern regarding potential
volatilization and vapour drift of the active ingredient.
Henry's Law
Henry's law addresses the partitioning of a compound between water and air, a process that can
increase or decrease the overall volatilization of the compound from a water or moist surface. A
unitless water/air distribution ratio can be calculated by the following equation (Burkhard and Guth,
1981; EPA, 1975):
48
-------
Appendix IX
SxTx82.08x760>
PxQMWxIO6 ,
where: Cwater = concentration of the compound in water [ug/mL]
C^ = concentration of the compound in air [ug/mL]
S = the solubility of the compound [ug/mL]
T = absolute temperature [°K = °C + 273.15]
82.08 = gas constant, R, [(mL x atm) / (°K x mol)]
760 = mm/atm
P = vapour pressure [Torr] of the compound
GMW = gram molecular weight of the compound [g/mol]
A volatility classification from a water surface based on CwatH/Cajr is found in the following table (EPA,
1975)
<102
Rapidly lost from a water surface
102-103
Volatile from a water surface
103-105
Slightly volatile from a water surface
>105
Non-volatile
Soil Adsorption Effects
Because adsorption to soil can significantly reduce volatilization, volatilization from a moist soil is
assumed to be volatilization from water modified by adsorption. The distribution ratio between wet soil
and air can be calculated by the following equation (Burkhard and Guth, 1981; EPA, 1975):
wher
e: r_ » C __ ( 1 ^
WBtor+soi vwter I I
c.
-"water
Moil
T + ".
'Ir
conce
ntration of the compound in wet soil (w/w on a dry weight basis)
Qvater = concentration of the compound in water (w/v),
Cji, = concentration of the compound in air (w/v),
r = (weight of soil)/(weight of water), and
Kd = linear adsorption coefficient
Although no generic classification of volatility from moist soil was presented by EPA (1975) and
Burkhard and Guth (1981), several non-fumigant compounds were categorized as volatile, slightly
volatile and non-volatile from moist soil, based on their wet soil/air distribution ratios and assuming a
49
-------
Appendix IX
standard soil containing 2% organic carbon and a value of 6 for r, the soil/water weight ratio.
Estimated Tendency of Compounds to Volatilize from Water and Moist Soil
(Burkhard and Guth, 1981, and EPA, 1975)
CompfHUd
^J^V^^wr^l:;^;;
,-: - .. v.^ :^,f - .:=*-,:.
cis-\,3-D
trans-l,3-D
EDB
DBCP
2.5 x 10
1.85 x 10
7.7 x 10-'
5.8 x 10'1
Soh^ttjy
v; . ^V];
«
-..»
lydto'-^F- '- :i'^- '- ''"-& "v : "~
2700
2800
3370
1230
1.77x 10
2.49 x 10
4.33 x 10
1.67 x IO2
0.51
0.56
0.65
2.58
1.2 x 10
1.81 x 10
3.54 x 10
4.59 x IO2
: ... . Volatile from moist soil J
chloroneb
EPIC
dichlobenil
disutfoton
diazinon
gamma-HCH
isazophos
DDT
3.0 x 10'3
1.97x 10'2
5.5 x 10'4
2.62 x IO3
7.32 x 10
8
370
18
SUghtty volatile from it
1.8x 10"4
-
3.2 x 10'5
1.9 x IO7
9.71
4.26
4.26
2.53 x 10'2
15
40
10
150
0.0012
^mwiiitef^ii&sou m ?: : ' iH»M- : irtf tr - = +
parathion
metolachlor
chlorpropham
atrazine
methidathion
monuron
metalaxyl
3.8 x 10'5
1.0 x 10'5
8.9 x 10'7
5.0 x lO'7
5.05
1.73
1.33 x id'1
6.65 x 10'2
2.93 x 10'1
20
530
88
33
240
230
7100
2.35 x IO2
1.84 x IO3
3.48 x IO3
5.55 x IO3
3.29 x IO4
1.96 x IO4
2.73 x IO5
3.26 x IO2
23.2
5.66
3.28
5.49 x IO3
1.07 x IO4
1.2 x IO4
'-,', " ^'"tp;"' : r. T:''-;F:"" ' : .' '- '::' 7-'
42.6
10
26.8
2.06
4860
2.37 x 10s
3.34 x 10s
5.29 x 10s
6.08x10'
1.58x IO6
HT ; -il*;;;. 'S^- #, ",%
3.3 x IO4
2.63 x IO6
8.0 x IO5
3.2 x IO6
1.45 x IO7
4.2 x IO7
2.11 x 10"
209
2.73
11.8
3.44
3.71
1.66
0.75
6.9 x 10*
7.62 x IO6
l.Ox IO7
1.2x IO7
5.62 x lO7
7.67 x IO7
1.93x 10s
soil adsorption coefficient corrected for a standard soil containing 2% organic carbon
soil to soil water (w/w) = 6; soil water to soil air (v/v) = 1
Considering the values calculated for Cwater+soll/Cair in the previous table, the following categorization
seems reasonable for volatilization from moist soil with 2% organic carbon and a soil to water ratio
50
-------
Appendix IX
(w/w)of 6.
Volatility classification from moist soil based on CwateT+!oil/Cair
^i^jii
''.';£:; \ ; ff JVIiii^i^ '.y'" ;
< 1 x 103
1 x 103-1.5
1.5 x 104- 1
1 x 105-2x
x 104
xlO5
106
>2x 106
,.* - \
Rapidly lost from moist soil
Volatile from moist soil
Intermediately volatile from moist soil
Slightly volatile to non-volatile from moist soil
Non-volatile from moist soil
2% soil organic carbon, soil to soil water (w/w) = 6 and soil water to soil air (v/v) = 1
Based on the above data and categorization, volatilization of chemicals from soil under laboratory
conditions should be investigated for chemicals with a volatility (Csoi1 + waIet/Cair)-value < 106.
Furthermore, values <, 105 indicate the need for volatility studies under field conditions.
Leaching Potential
The movement of a chemical through soil is dependent on several factors including rainfall and
irrigation and the properties of the chemical and the soil. In general, leaching is faster and more
extensive in coarse-textured soils and soils that have low organic matter and clay content. An
assessment of leaching potential at sites in specific use areas should also consider the likelihood of
potential preferential flow through relatively large soil voids, e.g., cracks, root channels and Karst
topography.
A mobility classification based on soil column leaching was developed by Guth and Hdrmann (1987).
Monuron has been proposed as the reference compound.
Relative mobility factors1 (RMF) from soil column leaching studies and corresponding mobility classes
for a variety of pesticides are presented in the table below (adapted from Guth and H6rmann, 1987):
. A^ft^-^iilLiilSiifiinB^i-^i' ,
-, '^/,»3^.S~JHJ.»JUE;'pSIUlllJBBr'Er;-,;,-.i ' *'-"
<0.15
0.15-0.8
0.8-1.3
i ;.'
fluorodifen (< 0.1 5), parathion
(<0.15)
profenophos (0.18), propiconazole
(0.23), diazinon (0.28), diuron (0.38),
terbuthylazin (0.52), methidathion
(0.56), prometryn (0.59), alachlor
(0.66), metolachlor (0.68)
monuron (1 .00), atrazine (1 .03),
simazin (1 .04), fluometuron (1.18)
^&*'i&H*liiim.\i ,^l
I immobile
II slightly mobile
III moderately mobile
51
-------
Appendix IX
1.3-2.5
2.5-5.0
>5.0
prometron (1 .67), cyanazin (1 .85),
bromacil (1.91), karbutilate (1.998)
dioxacarb (4.33)
monocrotophos (> 5.0), dicrotophos (>
5.0)
IV fairly mobile
V mobile
VI very mobile
The relative mobility factor is calculated as follows:
I leaching distance of test compound (cm)
{ leaching distance of reference compound (cm
Adsorption of a chemical to soil, expressed as the adsorption coefficients, Kd and Koc, is a major
determinant of leaching potential. The following mobility classification of McCall et al. (1981) is based
on the soil organic carbon adsorption coefficient, Koc, and is best suited to non-ionic chemicals.
The following table describes the classification of soil mobility potential of chemicals based on HPLC
retention times (McCall et al., 1981).
- K*: : * -»!= *- sf r> '$ ' ^ii^^W^:''^""-1* : "*
0-50
50-150
150-500
500-2000
2000-5000
>5000
Very high
High
Medium
Low
Slight
Immobile
Leaching potential is indicated by a mobility classification of medium to very high.
Dissociation of ionic compounds in response to the ambient soil pH affects adsorption and, therefore,
mobility in soil. Anionic species that have a negative charge at ambient soil pH are likely to have a
very high leaching potential. The effects of soil pH on the adsorption of acids and bases by soil is
summarized by Tinsley (1979).
Effect of pH on Adsorption of Acids and Bases by Soils (Tinsley, 1979)
di=:. omponnd r^fe;
Strong acid
Weak acid
" 'iilfv . ":.13:ij^^ ,: {Wf>. :";-
.^'liiriiiv^-
Anion
Neutral molecule
' ^ifflSSfiB^^
6- ". :. .!'"; «"
Anion
Anion
LiibKi& -
Small
Large effect: less
adsorption at
PH>PK8
52
-------
Appendix IX
Strong base
Weak base
Polar molecule
Non-polar molecule
Cation
Cation
Neutral molecule
Neutral molecule
Cation
Neutral
Neutral molecule
Neutral molecule
Decrease at very low
pH
Increasing adsorption
to pH = pKa,
decreasing with pH
30 ppm
Kd < 5 and usually < 1 or 2
Koc<300to500
Henry's law constant < 10"2 atnvm3/mol
Negatively charged (either fully or partially) at ambient pH
Hydrolysis half-life > 25 wk
Photolysis half-life > 1 wk
Half-life in soil > 2 to 3 wk
Note that all of these criteria should be considered together, not individually, in the assessment of
leaching potential.
Gustafson (1989) developed the following leaching potential index, based on persistence in soil and
adsorption:
Gl/S =
where: t)
)/isoil
50% decline time in soil under field conditions
soil organic carbon adsorption coefficient
This index is best suited for non-ionic compounds. More importantly, it is better to use laboratory soil
metabolism / biotransformation values for t,7, ^ as field values include decline via leaching (which is
what is being assessed). In any case, based on the calculated GUS score, the leaching potential of
compounds can be categorized as follows:
Classification system based on calculated GUS scores (Gustafson, 1989)
- _. .
-------
Appendix IX
>2.8
> 1. 8 and < 2. 8
<1.8
Leacher
Borderline leacher
Non-leacher
The leaching potential of compounds with GUS scores > 1.8 should be investigated further.
54
-------
References
References
Burkhard, N., and J.A. Guth. 1981. Rate of volatilisation of pesticides from soil surfaces; comparison
of calculated results with those determined in a laboratory model system. Pestic. Sci. 12(1):
37-44.
Cohen, S.Z., S.M. Creeger, R.F. Carsel, and C.G. Enfield. 1984, Potential for pesticide contamination
of groundwater resulting from agricultural uses. In R.F. Krugger and J.N. Seiber, (eds.). Treatment
and Disposal of Pesticide Wastes. ACS Symposium Series No. 259. American Chemical Society,
Washington, DC. pp. 297-325.
Gustafson, D.I. 1989. Groundwater ubiquity score: A simple method for assessing pesticide
leachability. Environ. Toxicol. Chem. 8: 339-357.
Guth, J.A., and W. D. Hermann. 1987. Problematik und Relevanz von Pflanzenschutzmittel-Spuren in
Grund(Trink-)Wasser. Schr.-Reihe Verein WaBoLu, 68: 91-106.
Kennedy, J.M., and R.E. Talbert. 1977. Comparative persistence of dinitroaniline
type herbicides on the soil surface. Weed Sci. 25(5): 373-381.
McCall, P.J., R.L. Swann, and D.A. Laskowski. 1983. Partition Models for Equilibrium Distribution of
Chemicals in Environmental Compartments. In R.L. Swann and A. Eschenroder (eds.). Fate of
Chemicals in the Environment. American Chemical Society, pp. 105-123.
Tinsley, I.J. 1979. Chemical concepts in pollutant behaviour. John Wiley and Sons, New York.
United States Environmental Protection Agency. 1975. Volatilization studies. Guidelines for
registering pesticides in the United States. 40 FR(123): 26889-26891.
Li.S-1
12.00
55
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