NONLINEAR PESTICIDE DISSIPATION IN SOIL - A NEW MODEL BASED ON SPATIAL VARIABILITY

In both laboratory and field studies, the dissipation of pesticides in soil often fails to follow simple first-order reaction kinetics. Rather than being linear when plotted as In C versus time, the dissipation data are curved, typically concave upward. This nonlinear behavior has now been described successfully through the use of a new first-order, nonlinear kinetic model. The nonlinear model is based on the assumption of a spatially variable first-order rate constant, and it reduces to the linear case when the rate constant is spatially uniform. Excellent fits to both laboratory and field data are obtained for all pesticides modeled. Interestingly, the relative variability found for the rate constant is similar for laboratory and field studies, suggesting that the length scale of the spatial variability is very small, possibly on the order of pore-size dimensions. © 1990, American Chemical Society. All rights reserved.