Modelling ethoprophos and bentazone fate in a sandy humic soil with primary pesticide fate model PRZM-2

Primary pesticide fate models are powerful tools for ranking pesticides within an environmental contamination risk analysis context. The performance of primary pesticide root zone model PRZM-2 to analyse ethoprophos and bentazone transport and dissipation is assessed. The evaluation was performed within the framework of an European modelling validation exercise, which enabled us to use a high quality data set and to adopt a standardised modelling protocol. Within this paper PRZM-2 was evaluated by four different users using the Vredepeel data set. Simulations were carried out with and without calibration of some parameters, as identified by the independent model users. Finally, a simulation with a consensus parameter set was performed. The model did not accurately describe the behaviour of ethoprophos and bentazone. However the model gave predictions of chemical concentration that were within an order-of-magnitude. It is clear from this exercise that, given exactly the same data, different model users will parametrise a model in very different ways which in turn will lead to very different model output. Control of model input and guidance for the selection of inputs is therefore vital if a model is to be used to predict the fate of pesticides in the environment.