Pesticide metabolites in soil: Estimation of formation & degradation rates

Understanding the behaviour of pesticide metabolites is an important aspect of assessing the environmental fate of pesticides. The formation and degra dation of pesticide metabolites in soil is examined here for a simple situa tion, to examine how to estimate the rates of these processes. A key diffic ulty is that the rate of metabolite degradation depends on the rate of meta bolite formation via parent pesticide degradation. This difficulty can only be taken into account with the use of models, some of which are demonstrat ed here. Fits of these models to actual data show that very different estim ates of degradation rate can result, even though the fits are similar due t o different combinations of metabolite formation and degradation rate. The paper raises important issues about deciding which estimates of metabolite degradation rate are the most accurate, and defining which combinations of parent-metabolite properties are appropriate for environmental fate assessm ents. The example used here demonstrates that models of pesticide metabolit e transformations need further review and development to resolve these issu es, particularly for more complex situations.