Pesticides from wastewater treatment plant effluents affect invertebrate communities

Abstract We quantified pesticidecontamination and its ecological impact up- and downstream of seven wastewater treatment plants (WWTPs) in rural and suburban areas of central Germany. During two sampling campaigns, time-weighted average pesticideconcentrations ( c TWA ) were obtained using Chemcatcher® passive samplers; pesticidepeak concentrations were quantified with event-driven samplers. At downstream sites, receiving waters were additionally grab sampled for five selected pharmaceuticals. Ecological effects on macroinvertebrate structure and ecosystem function were assessed using the biological indicator system SPEAR pesticides(SPEcies At Risk) and leaf litter breakdown rates, respectively. WWTP effluents substantially increased insecticide and fungicide concentrations in receiving waters; in many cases, treated wastewater was the exclusive source for the neonicotinoidinsecticides acetamipridand imidaclopridin the investigated streams. During the ten weeks of the investigation, five out of the seven WWTPs increased in-stream pesticidetoxicity by a factor of three. As a consequence, at downstream sites, SPEARvalues and leaf litter degradation rates were reduced by 40% and 53%, respectively. The reduced leaf litter breakdown was related to changes in the macroinvertebrate communities described by SPEAR pesticidesand not to altered microbial activity. Neonicotinoidsshowed the highest ecological relevance for the composition of invertebrate communities, occasionally exceeding the Regulatory Acceptable Concentrations (RACs). In general, considerable ecological effects of insecticides were observed above and below regulatory thresholds. Fungicides, herbicides and pharmaceuticals contributed only marginally to acute toxicity. We conclude that pesticideretention of WWTPs needs to be improved.