Degradation and adsorption of fosthiazate in soil.

Adsorption and degradation behavior of a pesticide in soil has a strong effect on its environmental fate as well as efficacy for pest control. Fosthiazate is an organophosphate compound that is currently under development as a nonfumigant nematicide. In this study, we evaluated adsorption and degradation kinetics of fosthiazate in three U.S. soils with different properties. Adsorption of fosthiazate in mineral soil was negligibly weak but appeared to increase with soil organic matter (OM) content. The half-life (T(1/2)) of fosthiazate ranged from 0.5 to 1.5 months in nonsterile soils but was prolonged to 1-3 months after sterilization. Degradation of fosthiazate in soil appeared to be caused by both chemical and microbial transformations. The persistence of fosthiazate generally decreased with increasing soil pH, but increased with increasing soil OM and clay contents. This results suggest that fosthiazate may have an enhanced leaching potential in acidic soils with low OM content, and its efficacy in high pH soils may not last as long as in neutral soils because of faster degradation.