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.

Pesticide occurrence in protected surface waters in nature conservation areas of Germany.

A complete ban on pesticide use in sensitive areas, such as nature conservation areas (NCA), is currently being debated in the EU as part of the Sustainable Use Regulation. NCA are strictly protected landscapes in Germany with minimal agricultural activity (<4.5 %) that serve as vital ecological refuges. However, it is largely unknown whether surface waters in German NCA are contaminated by pesticides. The current study uses extensive monitoring data (n = 3,822,553 measurements, 1998-2020, 208 pesticides) from the federal state of Saxony (18,416 km2), Germany, to characterize pesticide occurrence, contamination levels and risks (defined as exceedance of regulatory threshold levels) for surface waters in NCA (n = 68,277 measurements, mean size = 2.5 km2) in comparison to unprotected areas (n = 3,754,276). Pesticide detection frequencies show strong correlation between NCA and unprotected areas (UPA, R2= 0.70-0.92), but concentrations to be ∼40 % lower in protected areas. Ecological risk distributions for three major species groups are similar between NCA and UPA (fish = 79.8 % overlap in density distribution, invertebrates = 78.6 %, plants = 81.9 %). Threshold exceedances differ greatly among groups (fish = 0.9 %, aquatic invertebrates = 14.7 %, plants = 20.4 %). Based on principal component analysis, ecological risks for aquatic plants and aquatic invertebrates are strongly correlated with upstream agricultural land use (80.5-82.4 %) and are negatively correlated with upstream (semi)-natural land cover (90.1-97.3 %). Fluvial transport appears to be the most important pathway for contaminants into NCA surface waters, likely due to small conservation area size. Overall, surface waters in NCA are exposed to numerous organic contaminants causing ecological risks, highlighting the need to improve protection of these valuable water resources.