Potential Transport and Degradation of “Aged” Pesticide Residues In Soil.

“Aging” has been shown to affect the sorption-desorption of pesticides in the soil, which in turn can control transport and degradation processes. Aging effects have been characterized by batch sequential extraction methods, in which sorption coefficients (i.e. Kd) are determined for the chemical remaining after a given equilibration period. Kds have been shown to increase with aging time for many classes of pesticides. Mechanisms that result in aging effects on sorption processes are unclear, but may be due changes in binding mechanisms or the result of decreased amounts of remaining pesticide in the soil (when Freundlich 1/n < 1.0). Regardless of the mechanisms involved, aging may affect the prediction of potential pesticide transport and degradation processes, and subsequent environmental risk. For instance, observed increases in sorption during pesticide aging should be taken into account during characterization of the sorption process for mathematical models of pesticide transport. Potential transport in would be over predicted for some pesticides if ‘fresh’ Kds were used to predict transport rather than ‘aged’ Kds, which in turn, would result in a prediction of increased environmental risk. Possible aging affects on pesticide availability for degradation is still unanswered. In spite of increased Kd values, aging had no effect on some pesticides’ degradation by specific degrading microorganisms.