Dissipation and degradation are fundamental processes governing pesticide environmental fate. It has become standard practice to describe rates using single first-order kinetic equations (SFO). In SFO the time for a decrease of a certain fraction of the compound remains constant; thus dissipation rate data can be conveniently described by the compound's soil half-life (t1/2). SFO equations are simple to use, inherently conservative, and are used almost exclusively in regulatory pesticide assessments. However, there are numerous published studies that demonstrate that SFO might not be the most appropriate kinetic model to describe pesticide dissipation kinetics. In this presentation, we will describe some of our experiences in using SFOs and alternate models. Model use when adapted degradation conditions develop in soils will be highlighted. In almost all cases biphasic models that incorporate dissipation rates that change with time provide better fits to the data.

Interpreting kinetic data during adapted degradation

244th National Meeting (2012)

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