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Tracking microplastics across urban drainage systems and highway runoff: a snapshot assessment
Summary
Every time it rains, tiny plastic bits from tires and other sources wash off roads and city streets into our water systems—and this study found that road runoff carries especially high levels of tire-wear particles, most of it in extremely fine pieces smaller than a human hair. Standard water treatment methods only removed 14-42% of these microplastics (though adding a filtration step helped significantly), meaning much of this plastic pollution likely ends up in rivers and lakes. This matters because these tiny particles can carry chemicals and may eventually make their way into the water and ecosystems humans depend on, so better filtering technology could help reduce our
ABSTRACT Conceptual diagram of microplastic transport in urban drainage systems showing traffic-derived tire wear particles and other microplastics entering stormwater and combined sewer systems, with indicated concentrations of PE, PP, and SBR. Microplastics (MP) were quantified during an initial rainfall event in size-fractionated (63–2,000 and <63 μm) total suspended solids (TSS) from urban drainage systems and highway runoff. Polyethylene (PE), polypropylene (PP), and styrene–butadiene rubber (SBR) were quantified. At combined sewer overflow (CSO) sites, PE concentrations ranged from 0.4 to 0.5 mg L−1 in the influent and 0.3–0.4 mg L−1 in the effluent, while PP ranged from 0.04 to 0.08 mg L−1 and SBR from 0.08 to 0.25 mg L−1. Highway runoff showed the highest SBR levels, reaching 2.1 mg L−1 in the <63-μm fraction and 0.5 mg L−1 in the 63- to 2,000-μm fraction. Sedimentation-based treatment preferentially removed TSS in the coarse fraction (65–78%) compared with the fine fraction (26–37%), whereas MP removal efficiencies were generally lower (14–42%). Additional removals of 76–82% were achieved by pile cloth filtration. Ln-transformed SBR–TSS relationships at highway sites showed significant correlations and consistent slopes, supporting TSS as a potential proxy for traffic-derived tire wear particle loads. The study provides a multimatrix snapshot across CSO-related and traffic-influenced systems, enabling comparison of treatment performance and highlighting the dominance of the <63 μm fraction, particularly in road runoff.