Identification of organic micropollutants and transformation processes in an agricultural and urban river catchment applying target and non-target analysis

The presence of organic micropollutants in highly modified lowland rivers is a growing concern for the environment and human health. This study employs both target and non-target analysis over two years with high spatiotemporal resolution in the Münstersche Aa River which is influenced by both agricultural and urban land use to identify major stressors, their input pathways and the impact of low-flow conditions. Treated wastewater is the major input pathway for pharmaceuticals, illicit drugs as well as for pesticides and biocides. Moreover, urban and agricultural non-point sources contribute to the input of organic micropollutants. Database search identified sartans as a therapeutic class of pharmaceuticals of interest in the river and spatiotemporal analysis for two years showed wastewater treatment plants as the major input source with highest concentrations of >1 μg/L in summer at low-flow conditions for the sartans. Thereby, mean concentrations of candesartan and valsartanic acid as well as the carbamazepine metabolite 10,11-dihydro-10,11-dihydroxycarbamazepine exceeded health orientation values. For the first time, the UV protection agent 2-[4-(Diethylamino)-2-hydroxybenzoyl] benzoic acid (DHHB) was tentatively identified in a river. Fold change analysis at Lake Aasee, which is a small, shallow reservoir lake in the Münstersche Aa River system, stagnant at low and flowing at high discharge, revealed that elimination and associated formation processes are responsible for the changing occurrence of features at the inflow and outflow of the lake. The exact mechanisms need to be further evaluated. The present study provides valuable insights to stressors in high modified water bodies and shows that fold change analysis after non-target data processing is a valuable tool to gain insights into transformation processes in lakes and rivers which can aid in prioritizing research in the future.