Inventory and risk characterization of urban runoff pollutants in Europe

Urban runoff is a major pathway for chemical pollutants to enter aquatic ecosystems, yet the occurrences and risks of both conventional pollutants and contaminants of emerging concern (CECs) remain poorly characterized. In this study, we analyzed 34 urban runoff samples from multiple European catchment types using a combination of reversed-phase liquid chromatography (RP-LC) and hydrophilic interaction liquid chromatography (HILIC) coupled with high-resolution mass spectrometry (HRMS) for characterization of dissolved organic pollutants, alongside inductively coupled plasma mass spectrometry (ICP-MS) for quantification of trace elements. Street runoff was dominated by heavy metals and tire-derived compounds, including 6PPD-quinone (up to 0.57 µg/L) and 1,3-diphenylguanidine (up to 22.4 µg/L). Benzothiazole-2-sulfonic acid was found in 91% of samples up to 153 µg/L, significantly higher than previously reported concentrations in urban runoff. Several wastewater-associated compounds were also common, suggesting contributions from pharmaceutical residues and public urination in surface runoff, and misconnected pipes in separated sewage networks. Risk assessment revealed several compounds exceeding predicted no-effect concentrations (PNEC) with the highest risk associated with the metals Al (up to 1.1 × 10⁴ times PNEC), Cu (8.9 × 10³ times PNEC), and Zn (2.7 × 10³ times PNEC). Among CECs, clarithromycin (up to 539 times PNEC), 6PPD-quinone (49 times PNEC), and benzothiazole-2-sulfonic acid (32 times PNEC) posed the greatest risks. Our findings highlight urban runoff as an environmental concern, with metals, pharmaceuticals, and tire compounds as key drivers of ecological risks.