Assessing the ecotoxicity of pesticide transformation products

Once released to the environment, pesticides may be degraded by abiotic and biotic processes. While parent compounds are assessed in detail in many regulatory schemes, the requirements for the assessment of transformation products are less well developed. This study was therefore performed to explore the relationships between the toxicity of transformation products and their parent compounds and to develop a pragmatic approach for use in the risk assessment of transformation products. Data were obtained on the properties and ecotoxicity of transformation products arising from a wide range of pesticides. Generally, transformation products were less toxic to fish, daphnids, and algae than their parent compound. In instances where a product was more toxic, the increase in toxicity could be explained by either (1) the presence of a pesticide toxicophore; (2) the fact that the product is the active part of a propesticide; (3) the product is accumulated to a greater extent than the parent compound; or (4) the product has a more potent mode of action than the parent. On the basis of the findings, an approach has been proposed to estimate the ecotoxicity of transformation products based on chemical structure and data on the toxicity of the parent compound. The assessments can be performed at an early stage in the risk assessment process to identify those substances that require further testing.