Modeling pesticide fate in soils:: Verification of local scale models and transfer from local to regional scale

Mathematical models play an increasing role in the prediction of the fate of chemicals in soils and groundwater. Registration procedures of pesticides in Europe accept e.g. the use of mathematical models to predict their leaching potential. But also predicting the fate of xenobiotics introduced by accident or diffuse pollution in soils and groundwater relies nowadays strongly on modelling. Given the importance of protecting water resources, these models should reflect the best of knowledge regarding the environmental fate of chemicals but also the quality of these models should be unquestioned. The paper consists of three parts. In the first part we will present the outcome of a benchmarking study of models used in pesticide registration in Europe. Model calculations are compared with exactly known solutions of selected scenarios. In a second part we will highlight the importance to consider heterogeneity when dealing with the prediction of solute transport at lysimeter and field scale based on models. In a third part we will present results from a regional study of the evolution of pesticide concentrations in subsurface waters using mathematical models.