Abstract

A simple model is described for assessing the ground water contamination potential of pesticides. This model, based on simple processes of linear, equilibrium and singular partition between solution and soil organic matter, steady convective flow, and first-order degradation, calculates fractions of pesticides remaining in the soil as they leach to greater depth. Possible effects by preferential flow that may be present in structured soils are ignored. The soil profile is divided into a number of layers which may differ in bulk density, moisture content at field capacity, organic C content, and degradation half-life. The leaching depths predicted by this model generally agreed with the mean leaching depths measured in a field study, and with those predicted by the CALF model. The leaching depths by the simple model were also statistically related to those simulated by the LEACHM model, although the values by LEACHM were found to be much higher than those by the simple model and by CALF. Under the soil and environmental conditions given, the simple model predicted that chlorpyriphos and chlorthal dimethyl would not leach to any noticeable depth before being completely degraded, that metribuzin, prometryne, propyzamide and simazine would mostly degrade to insignificant concentrations before reaching 500 cm, and that traces of fenamiphos, metalaxyl and linuron might reach beyond 1000 cm.