Prediction of surface water input of chloridazon and chlorpyrifos from an agricultural watershed in Chile

Two compartmental fugacity-based models (Agrifug and SoilFug) for the prediction of pesticide runoff from agricultural fields were applied and experimentally validated in a river watershed, of about 106 km2, in central Chile. Chloridazon and chlorpyrifos, two of the most widely used pesticides in the study area, were selected for their different physico-chemical properties, in order to test a range of environmental fate patterns by means of these models. Theoretical values were compared with analytical determinations in river water and soil and a good predictive capability was found for both models, at least at the order of magnitude level. Value and limitations of the application of this approach at the basin scale and its usefulness for the management of pesticides are discussed.