Comparison and evaluation of pesticide monitoring programs using a process-based mixture model

A number of European countries run large-scale pesticide monitoring schemes in watersheds aimed at identifying and evaluating the presence of pesticide residues in the environment. These schemes provide national and regional scale assessments of pesticide concentrations within the context of environmental quality assessment, aiming to ensure some degree of ecological protection. The present study is aimed at evaluating the joint effects of the pesticide mixtures detected in monitoring programs, using a process-based mixture model that was parameterized for Daphnia magna. In total, over 15 000 samples containing over 1 million individual measurements were evaluated for effects. It was found that there are only a small number of places where one can expect to have effects on daphnids, based on measured concentrations. The most polluted samples would cause extinction of a daphnid population within only 30 h. The results show that effects are mostly triggered by a limited number of pesticide residues at locations with high emissions. It was also shown that the analytical detection limits are basically too high to exclude mixture effects. So, despite all the effort that is put into chemical monitoring programs, it remains a challenge to make statements on whether or not the environment is protected. Recommendations are offered for a different setup of monitoring programs to improve this situation. Environ Toxicol Chem 2016;35:3113-3123. © 2016 SETAC.