Integrated assessment of tire and rubber wear-derived compounds in wastewater treatment systems and receiving environments

Abstract

Tire and rubber wear-derived compounds (TRDCs) are emerging contaminants released through tire abrasion and transferred mainly by urban runoff, with environmental relevance concern. Since wastewater treatment plants (WWTPs) act as point sources by treating combined urban runoff and wastewater, this study assessed 25 TRDCs across an integrated water cycle, including wastewater, sewage sludge and surface water from one of Europe's longest river basins. Widespread occurrence was observed, highlighting the impact of urban and industrial activities on aquatic ecosystem. Benzothiazoles (BTHs) and benzotriazoles (BTRs) dominated the pollution profile, while the highly toxic 6PPD-quinone (6PPD-Q) was frequently detected at lower concentrations. Surface water (346 ng/L, median; 1.68-1510 ng/L, min-max) showed significant lower (p < 0.01) levels than wastewater (3923 ng/L, 422-23422 ng/L), while sludge accumulated notably high TRDC concentrations (424 ng/g, 184-2257 ng/g), acting as a reservoir and potential source for agricultural soils. Although some compounds (2-OH-BTH, MBTH, 6PPD-Q) showed high removal efficiencies (>75%), conventional WWTPs were not fully effective. Surface water concentrations were significantly higher (p < 0.01) in urban and high-traffic areas, confirming road runoff as a key source. Ecotoxicological assessment indicated substantial acute risks in aquatic ecosystem associated with PPDs, particularly 6PPD-Q, and moderate chronic risks under cumulative exposure scenarios. Potential risks for soil organisms were also observed considering annual sludge amendments (from 1 to 100 years) to agricultural soil at agronomic conditions. These findings underscore the need for continuous monitoring, mitigation strategies, and regulatory consideration, adopting a One Health approach within the European Water Framework Directive.