Exposure and the potential for adverse effects to non-target organisms following pesticide application is a function of several factors including: application rates and frequency, resulting concentrations in the environment (i.e., air, water, soil and sediment) and food web bioaccumulation processes, including trophic position. Pesticide bioaccumulation in an organism (e.g., fish) is a function of competing rates of uptake via different exposure pathways and elimination. Key processes governing the elimination of the parent chemical from an aquatic organism include transfer to the water and the feces and metabolic biotransformation. Bioaccumulation and time to approximate steady-state are determined by the total elimination half-life. For many hydrophobic chemicals the total elimination half-life is strongly influenced by the first-order, primary metabolic biotransformation rate constant (kB). Few in vivo measured kB data exist. Methods have been developed to obtain in vivo kB estimates from laboratory bioaccumulation tests. This method has been applied to develop a kB database of approximately 700 organic chemicals for fish. The database has subsequently been used to develop and validate screening-level kB QSARs including a model in the BCFBAF module of the US EPA's EPI Suite program. Biotransformation rate constant databases and QSARs have also been developed for mammals. Here we review the concepts of the kB estimation methods and databases and QSAR developments. We illustrate case study examples of the key role kB has on the bioaccumulation of pesticides in fish and in food webs. Examples include steady-state assumptions typically used for bioaccumulation hazard assessment (i.e., bioaccumulation factors, biomagnification factors and trophic magnification factors) and dynamic exposure conditions, as typically occurs after pesticide applications in the environment.

Role of biotransformation rates in food webs in pesticide bioaccumulation and risk assessment

248th National Meeting (2014)

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