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EPA-HQ-OPPT-2009-0152-0015

United States Environmental Protection Agency

Prevention, Pesticides And Toxic Substances (7101)

EPA 712-C-08-015 October 2008

Fate, Transport and Transformation Test Guidelines

OPPTS 835.2410 Photodegradation on Soil

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.

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, Subdivision N: 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 soilsurface 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 injection 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 oC.
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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)(1)).
(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/oppefed1/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 of benzoic acid 2-(2,4,6-trichlorophenyl)-hydrazide. J. Agr. Food chem. 23:1084-1088.
(3) Niles, G.P., and M.J. 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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