Pesticide mixtures in streams of several European countries and the USA

Abstract Given the multitude of pesticides used in agriculture, adjacent streams are typically exposed to pesticide mixtures. Previous studies analysed the ecological risks of a few pesticide mixtures or were limited to an individual region or crop, whereas a large scale analysis of pesticide mixtures is missing. We analysed routine monitoring data from Germany, France, the Netherlands and the USA comprising a total of 4532 sites and 56,084 sampling occasions with the aim to identify the most frequently detected pesticides, their metabolites and mixtures. The most frequently detected compounds were dominated by herbicides and their metabolites. Mixtures mostly comprised of two up to five compounds, whereas mixtures in the USA and France had clearly less compounds than those of Germany and the Netherlands. The number of detected pesticides and thereby the size of mixtures is positively correlated to the number of measured pesticides (r = 0.57). In contrast, a low relationship was found to the ratio of agricultural areas within the catchment (r = 0.17), and no relationship was found to the size of the catchment (r = 0.06). Overall, our study provides priority mixtures for different countries that may be used for future ecotoxicological studies to improve risk assessment for stream ecosystems.