United States Prevention, Pesticides EPA712-C-08-015
Environmental Protection And Toxic Substances October 2008
Agency (7101)
&EPA Fate, Transport and
Transformation Test
Guidelines
OPPTS 835.2410
Photodegradation
on Soil
• -Jl
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INTRODUCTION
This guideline is one of a series of test guidelines that have been
developed by the Office of Prevention, Pesticides and Toxic Substances
(OPPTS), United States Environmental Protection Agency for use in the testing
of pesticides and toxic substances, and the development of test data to meet the
data requirements of the Agency under the Toxic Substances Control Act (TSCA)
(15 U.S.C. 2601), the Federal Insecticide, Fungicide and Rodenticide Act
(FIFRA) (7 U.S.C. 136, et seq.), and section 408 of the Federal Food, Drug and
Cosmetic (FFDCA) (21 U.S.C. 346a).
OPPTS developed this guideline through a process of harmonization of
the testing guidance and requirements that existed for the Office of Pollution
Prevention and Toxics (OPPT) in Title 40, Chapter I, Subchapter R of the Code
of Federal Regulations (CFR), the Office of Pesticide Programs (OPP) in
publications of the National Technical Information Service (NTIS) and in the
guidelines published by the Organization for Economic Cooperation and
Development (OECD).
For additional information about OPPTS harmonized guidelines and to
access this and other guidelines, please go to http://www.epa.gov/oppts and
select "Test Methods & Guidelines" on the left side menu.
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OPPTS 835.2410 Photodegradation on Soil
(a) Scope—(1) Applicability. This guideline is intended for use in meeting testing
requirements of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) (7 U.S.C. 136, et
seq.). It describes procedures that, if followed, would result in data that would generally be of
scientific merit for the purposes described in paragraph (b) of this guideline.
(2) Background. The source materials used in developing this OPPTS guideline are OPP
161-3 Photodegradation studies on soil, OPP 160-4 General test standards, OPP 160-5Reporting and
evaluation of data (Pesticide Assessment Guidelines, Subdivision N - Chemistry: Environmental
Fate, EPA report 540/9-82-021, October 1982) and OPP Addendum 4 on Data Reporting to Pesticide
Assessment Guidelines, SubdivisionN: Chemistry: Environmental Fate, Photolysis Studies, January
1988.
(b) Purpose. Pesticides are applied to the surface of soil and/or on the exposed surfaces of
plants, and are then subject to photodegradation. Photodegradation studies on soil provide data on
photolytic pesticide dissipation and on the nature and persistence of photoproducts formed by soil-
surface catalyzed photolysis. Information from these studies enables the Agency to determine the
stability of the pesticide when exposed to sunlight and to predict the likelihood of the pesticide
persisting in the environment, the photoproducts that are likely to be produced, and their stability
when exposed to sunlight.
(c) General considerations. Data from a photodegradation study on soil surfaces support
end-use products intended for terrestrial and forestry uses with the exception of uses involving
application to soils solely by inj ection of the product into the soil or by incorporation of the products
into the soil upon application. Data from such studies also support manufacturing-use products
which may legally be used to formulate such end-use products.
(d) Test method.—(1) Test substance. Studies should be conducted with the technical or
purer grade of each active ingredient in the product, or where radioisotopic analytical techniques are
used (they are preferred), studies should be conducted with the analytical grade of each active
ingredient in the product.
(2) Test procedures.—(i) Concentrations. One or more concentrations of the test
substance should be used for this study at levels that will permit isolation and identification of
photoproducts formed.
(ii) Light sources. Soil samples should be exposed to a spectrum of light providing or
simulating expected use conditions. If an artificial light source is used, its intensity, wavelength
distribution, and the length of the exposure should be comparable to sunlight, as the rate of
photolysis is dependent on these factors and will vary if the artificial light source is different from
the natural sunlight.
(iii) Temperature. Temperature should be held constant (±1°C) between 18 and 30 °C.
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(iv) Soil types. One of the soils (e.g., sandy loam, silt loam, or other soil appropriate to the
application site) specified in OPPTS 835,4100 (Aerobic soil metabolism study) should be used, if
data from that study are also submitted. Soil from foreign sources may be used, providing the
foreign soil will have the same characteristics as soil in the United States common to the proposed
use area. Additional information on use of foreign soils may be obtained from the document
"Guidance for Determining the Acceptability of Environmental Fate Studies Conducted with
Foreign Soils," at the U.S. Environmental Protection Agency's Environmental Fate and Effects
Division, Office of Pesticides (see paragraph (f)(l)).
(v) Test samples. Samples of soil should be exposed to either natural or simulated sunlight
conditions.
(vi) Controls. Samples of soil treated with the pesticide at the same application rate as
irradiated soil samples and maintained in darkness should be used as experimental controls.
(vii) Test duration and sampling intervals. Soil samples should be taken for analysis at
four or more sampling time intervals, with at least one observation made after one-half of the test
substance has degraded or 30 days, whichever comes first. The maximum duration of the study need
not exceed 30 days.
(viii) Methodology. Procedures for photolysis of thin film of pesticide by artificial light are
described by Koshy et al in paragraph (f)(2). General procedures for photolysis in aqueous solution,
on soil and as a thin film are described by Niles and Zabik in paragraph (f)(3).
(e) Reporting and evaluation of data. Reporting units should be in the metric system.
(1) Test method. Each report should contain a statement regarding the test method used,
including a full description of the experimental design and procedures.
(2) Test substance, (i) The report should identify the test substance, and should include
chemical name of the active ingredient, molecular structure of the active ingredient, and qualitative
and quantitative description of the chemical composition.
(ii) If radiolabeled material is used, the chemical and radiochemical purity of the material, its
activity in Curies/mole and disintegrations per minute per gram (dpm/g) or other standard unit, the
site of radiolabeling, the isotope used, and the source when appropriate.
(iii) Manufacturer, and lot and sample numbers of the test substances.
(iv) Properties of the test substance, including physical state, pH, and stability.
(3) Light source. If sunlight is used as the light source, a record of the intensity of incident
sunlight, time of exposure, and other major variables which affect incident light such as latitude,
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time of year, and atmospheric cover. If artificial light is used as the light source, the nature of the
source, intensity, wavelength, distribution, and time of exposure, as well as the relationship of the
light intensity employed to that of natural light should be reported.
(4) Photoproducts. Identification of each photoproduct produced in greater than 10 percent
yield at any point during the course of the study, and material balance and half-life estimates for the
parent substance.
(5) Soil, (i) Describe the soil, its source and characteristics (textural class, percent sand,
percent silt, percent clay, percent organic matter, pH, moisture capacity, and cation exchange
capacity).
(ii ) Any preparation (such as sieving) or modification (such as milling) done to the soil.
(iii) How the pesticide was applied to the soil.
(6) Test equipment. The report should include a description of the test equipment used, and
photographs or detailed descriptions of nonstandard equipment.
(i) The identity of the instrumentation, equipment and reagents used, and the operating
conditions of the instrumentation.
(ii) A description of the equipment used to measure the wavelength range and intensity of the
incident light.
(7) Analytical method. A full description of each method used in this study, the method
validation data, recovery and method detection limit data, quality control procedures and results,
sample chromatograms, sample calculations, and a material balance. A detailed description of the
procedures used in preparation and handling of the sample throughout the method.
(8) Results/discussion. This section should contain the scientific results of the study. Each
report should contain the principal mathematical equations used in generating and analyzing data, as
well as representative calculations using these equations. Data regarding rates of formation and
decline of parent compounds or their degradates should be expressed as amounts, concentrations,
and corresponding percentages. Rate constants should be reported in conjunction with rate data.
Tabular data, as well as graphs for decline curves, should be submitted.
(f) References. The following references should be consulted for additional background
information on experimental procedures for conducting soil photolysis studies:
(1) U.S. Environmental Protection Agency (2006). Guidance for Determining the
Acceptability of Environmental Fate Studies Conducted with Foreign Soils. Environmental Fate
and Effects Division, Office of Pesticide Programs, USEPA. Washington DC. This document
can be found at: http://www.epa.gov/oppefedl/ecorisk_ders/soils_foreign.htm
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(2) Koshy, K.T., A.R. Friedman, A.L. van der Slik, and D.R. Graber. 1975. Photolysis
ofbenzoic acid2-(2,4,6-trichlorophenyl)-hydrazide. J. Agr. Food chem. 23:1084-1088.
(3) Niles, G.P., and MJ. Zabik. 1975. Photochemistry of bioactive compounds.
Multiphase photodegradation and mass spectral analysis of basagran. J. Agr. Food Chem.
23:410-415.
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