Atlas of pesticide concentrations in Dutch surface waters: a pilot study

A pilot study was conducted to explore the potential for geographically mapping concentrations of individual pesticides in Dutch surface waters and compiling these maps into a National Pesticide Atlas. This atlas could be used for various purposes: 1) To see where specific pesticides are monitored, observed and find out whether these are problematical. 2) To explore the relationship between environmental pesticide levels and land use, using the results as feedback to improve national pesticide admission procedures (post-registration review) 3) To review the quality of the present Dutch pesticide monitoring system. For the study we used measured data for the years 1997 and 1998, preparing maps for six illustrative pesticides. The data are presented on a grid scale of 5x5 km2. Pesticide concentrations are compared with three standards: the EU drinking water standard, the maximum tolerable risk (MTR) level and the admission standard set by the Dutch Pesticide Admission Board (CTB). The results show that all these pesticides can be satisfactorily mapped at the national level and that for most of the compounds investigated a useful relationship can be established between environmental concentration and land use. The maps also serve to show up gaps in the present pesticide monitoring system. The study yielded several new insights, among them that standards were found to be exceeded in areas and at times of the year not anticipated on the basis of land use and pesticide use statistics. As a follow-up to this pilot study a new project has been started to develop an internet version of the pesticide atlas for all measured pesticides in The Netherlands.