Environmental risk assessment of organic micropollutants in public wastewater treatment plants in Flanders, Belgium

The widespread occurrence of organic micropollutants (OMPs) is a growing concern due to potential adverse effects on aquatic wildlife. WWTP effluent is a major source of OMPs that have been found in the form of complex chemical mixtures. The prioritization of concerned OMPs and WWTPs is a useful approach for water quality management, which can be done by using environmental risk assessment (ERA). In this study, the ERA was performed using the Flanders Environment Agency database of measured environmental concentration (MEC) of OMPs in 40 Belgian WWTP effluents from 2000-2021. The effect data were annual average environmental quality standards (PNEC) from NORMAN database to derive risk quotients (RQ). The 38 OMPs from the database included pharmaceuticals, personal care products, pesticides, PFAS, and others, which had MECs ranging from 2.35 ng/L to 360 µg/L. Pesticides dominated among groups of concerned OMPs. The majority of WWTP effluents were at high risk of mixture effects with the sum of RQs exceeding 10. PFAS and pharmaceuticals were the main contributors to WWTP effluents' predicted environmental risk. Based on this observation, we wanted to validate the prediction of the environmental risks from the database with ecotoxicity testing of real-world wastewater treatment plant effluents. WWTP effluents with high predicted risk were selected to perform whole effluent toxicity testing with freshwater green algae (Raphidocelis subcapitata) and cyanobacteria (Microcystis aeruginosa), which are sensitive test organisms to herbicides. Our study highlights the importance of using ERA for the selection of candidate compounds and toxicity test systems to focus on future effect-based monitoring campaigns