A multifactorial prioritization strategy for micropollutants in wastewater: Enhancing Indicator selection for effective monitoring and risk management

Monitoring micropollutants in wastewater remains challenging due to the large number of potential contaminants and the logistical constraints of comprehensive chemical analysis. Most existing monitoring programs focus on a limited set of priority compounds, which may overlook additional environmentally relevant substances. To address this limitation, we developed a multifactorial ranking system to select indicator micropollutants in freshwater systems affected by wastewater treatment plant (WWTP) discharges. A total of 140 micropollutants were analyzed in 54 influent and effluent samples collected over three seasons from multiple WWTPs. Multiresidue analysis confirmed the presence of 85 compounds (61% of the monitored compounds) at concentrations ranging from ng L −1 to μg L −1 . Based on a comprehensive scoring approach, we proposed an updated list of 19 micropollutant indicators to complement current monitoring efforts, inform regulatory decisions, and highlight environmental risk concerns. The ranking system incorporated multiple criteria, including environmental occurrence, detection frequency, treatment performance, and intrinsic chemical properties related to environmental behavior and potential impact. Results indicate that current regulatory indicator list (i.e indicator list from Urban Wastewater Treatment Directive), which primarily focus on evaluating quaternary treatment performance, capture only a fraction of the chemical footprint of wastewater effluents and are insufficient to account for compounds of concern when environmental risk and behavior are considered. This demonstrates the need for a comprehensive, evidence-based approach to establish monitoring priorities. Our methodology provides a transparent, flexible, and scientifically justified tool for risk-based monitoring and regulatory management of micropollutants in wastewater systems. • A multicriteria framework was developed using persistence, mobility, toxicity, bioaccumulation, occurrence and removal. • Monitoring of 140 substances showed widespread occurrence and incomplete removal in WWTP effluents. • Nineteen priority micropollutants were identified, including compounds not regulated under the Urban WWT Directive. • The framework supports risk-based monitoring and ecotoxicological evaluation of wastewater contaminants.