The degradation rate of a test substance is one of the processes governing its persistence in the environment. Degradation rate studies are performed in soils that are representative of agricultural fields, following the requirements and methods as specified in the test guidelines, such as those published by the U.S. EPA, OECD, JMAFF, and EU/EC. To briefly summarize, the aerobic transformation in soil study is intended to provide information on (1) the rate and route of degradation of the test substance in representative soils, (2) the patterns of formation and decline of transformation products, if possible, and (3) the identification of major transformation products formed during the incubation period. Information gained from this study may be used for predicting the concentration of the parent compound and transformation products in aerobic soil environments. These studies are conducted under controlled laboratory conditions, and not in an environment exposed to naturally-occurring weather conditions and other factors that could impact the degradation rate of the test substance. The objective of this presentation is to assess the impact of soil characteristics on the degradation rate of pesticides and active pharmaceutical ingredients (APIs), utilizing historical data generated at Smithers within the past 8 years, which includes various soil types with different USDA texture classifications. The presentation will demonstrate how persistence of chemicals (described as their DT50) may be influenced by soil characteristics, such as particle size and makeup (i.e., clay, silt, and sand content), organic matter content, microbial biomass, cation exchange capacity, and pH, which are inherent to the characterization of the soil type. Correlations between the calculated DT50 and any of the soil characteristics, as well as their regulatory implications and impact on persistence will be discussed.

Assessing the impact of soil characteristics on the rate of chemical degradation under aerobic conditions

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