Several countries use one or a few scenarios to evaluate the leaching of pesticides. This, however, can be too strict for some substances while being too lenient for others, because of the wide ranges in pesticide properties. In a GIS approach the variability is explicitly taken into account and more accurate results are expected. This research has been carried out to compare the two approaches.
The PEARL model was used to calculate the leaching in 8 FOCUS scenarios and the Dutch standard scenario (NLS). A number of pesticides was included, covering wide ranges in properties. The spatially distributed model GeoPEARL was used to calculate the 90th percentile leaching concentrations for the Netherlands, taking into account information on a.o. soil properties and climatic conditions. None of the scenarios is capable of representing realistic worst-case conditions in the Netherlands for the broad range of pesticides. Six FOCUS scenarios appear to be more vulnerable. Using the FOCUS approach, the NLS and GeoPEARL results agree well, except for volatile and acidic substances. When using single applications, NLS-results appear to be lower: the ratio (GeoPEARL/NLS) ranges from 1 to 385. We conclude that tools such as GeoPEARL should replace single scenarios in evaluation studies.