The European Union under FOCUS introduced guidance for calculating degradation kinetics of pesticides in 2006 and the U.S. and Canada released their guidance at the end of 2012.  The guidance issued by FOCUS is scientifically rigorous but quite complex (over 400 pages of instructions).  The goal of the U.S and Canada guidance was simplicity and this was achieved, although this resulted in first order kinetics rarely being considered an acceptable fit.  Experience with these two schemes has allowed the development of a simplified approach for degradation kinetics.  This approach preserves the scientific rigor of the FOCUS approach and allows use of first order kinetics when it adequately describes the degradation of the compound over most of the study period.  A variety of approaches can be used to estimate degradation rates of metabolites.  Sometimes combining separate compounds into a single compound for kinetic analysis may be inappropriate when there are significant differences in properties such as degradation rates and sorption coefficients.  Also, the estimated degradation rate for a metabolite can be influenced by the degradation rate of the parent or predecessor metabolite.

Determining degradation kinetics of pesticides and their metabolites for regulatory assessments

248th National Meeting (2014)

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