Risk characterization of organic micropollutants in public wastewater treatment plant effluents in Flanders, Belgium.

This study investigates the ecological risks posed by organic micropollutants (OMPs) in wastewater treatment plant (WWTP) effluents in Flanders, Belgium, based on single-compound risk characterization. Utilizing a 5-year monitoring dataset from the Flemish Environment Agency (VMM) and seven ecological threshold values types, this research characterizes the risk of 207 OMPs, including pharmaceuticals, pesticides, industrial chemicals, and other pollutants. Several OMPs persist in effluents at concentrations that pose significant ecological risks after secondary and tertiary treatment processes in the region of Flanders (Belgium). This study identified 32 OMPs with regional risk quotients (RQregion) exceeding 1, with 24 of these showing RQregion values over 10, marking them as high-priority pollutants. Notable high-risk substances include chlorpyrifos, benzo(b)fluorene, and several herbicides. The findings highlight the necessity for investment in advanced treatment processes to enable compliance with the updated Urban Wastewater Treatment Directive (UWWTD), which mandates an 80% reduction in a fixed set of micropollutant indicators in relation to their load in WWTP influent by 2045. Based on our prioritization of high-risk OMPs, the fixed set of indicators mandated by the UWWTD does not fully represent the range of harmful contaminants in WWTP effluents, indicating a need for a broader monitoring framework and a more inclusive indicator set. These results underscore the necessity for an expanded approach to monitoring and regulating OMPs to ensure comprehensive protection of aquatic environments.