Pesticide Mixtures in Surface Waters of Two Protected Areas in Southwestern Germany

Pesticides enter non-target surface waters as a result of agricultural activities and may reach water bodies in protected areas. We measured in southwestern Germany pesticide concentrations after heavy rainfalls in streams of a drinking water protection area near Hausen (Freiburg) and in the catchment of the Queich (Landau), which originates from the biosphere reserve Palatinate Forest. On average, 32 (n = 21) and 21 (n = 10) pesticides were detected per sample and event in the area of Hausen (n = 56) and in the Queich catchment (n = 17), respectively. The majority of pesticides detected in > 50% of all samples were fungicides, with fluopyram being detected throughout all samples. Aquatic invertebrates exhibited highest risks with 16.1% of samples exceeding mixture toxicity thresholds, whereas risks were lower for aquatic plants (12.9%) and fish (6.5%). Mixture toxicity threshold exceedances indicate adverse ecological effects to occur at half of sites (50%). This study illustrates the presence of pesticide mixtures and highlights ecological risks for aquatic organisms in surface waters of protected areas in Germany.