Behaviour of pesticides in topsoil and subsoil in relation to possible contamination of groundwater

The PESTLA model is among the most sophisticated models that are now used for assessing pesticide leaching in a registration procedure. The calculated percentage leached is almost pathologically sensitive to a few sorption and tranformation parametersat leaching levels relevant in the registration. A theory was developed to calculate the influence of spatial variability in sorption and transformation parameters with simple analytical expressions. The model tended to overestimate the rate of transportof sorbing pesticides in a field study. Studies on the transformation rate of a few pesticides in water-saturated subsoil materials indicate that such rates may be significant to assessing leaching to deep groundwater