The biphasic behavior of pesticide degradation in soils is currently determined by fitting the data for the parent to a simple first-order (SFO) and a biphasic (DFOP, FOMC, and IORE) kinetic model. If SFO fit is rejected by visual and statistical assessment, degradation is considered biphasic. However, in some cases, SFO fit is acceptable, but a biphasic model provides a better fit, leading to very different degradation endpoints. The purpose of this study is to explore the feasibility of using a pathway kinetic fit approach to verify biphasic behavior of parent degradation. The basic premise is that the degradation behavior of parent must be kinetically consistent with formation of metabolites. Thus, a kinetic model for the parent can only be considered as a best-fit model, if it simulates both parent degradation and formation of metabolites in a pathway fit with all metabolites included. This approach can help discern a pseudo-biphasic behavior that does not correspondingly generate metabolites and avoid selecting over-conservative degradation endpoints for exposure modeling, although more datasets are needed to confirm its feasibility. The approach is illustrated with a real kinetic data set in this study.

Biphasic behavior of pesticide degradation in soils: Verification by pathway kinetic fits

246th National Meeting (2013)

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