Tyre wear particles in a highway stormwater system during rain: quantification by automatic sampling and pyrolysis-GC/MS, and correlations with metals and solids

Abstract

Tyre wear particles (TWP) are a major microplastic pollutant in road runoff, yet their transport dynamics in stormwater remain poorly understood. This study investigates the abundance and dynamic behaviour of TWP during rain events in a highway stormwater system between March and May 2023. Road runoff was collected from gully pots and stormwater wells using automatic samplers during rain events and analysed for TWP, elements, total suspended solids (TSS), volatile suspended solids (VSS) and turbidity. Quantification of TWP was performed using pyrolysis-gas chromatography/mass spectrometry for size fractions of 1.6–20 μm and 1.6–500 μm. Results show that TWP concentrations ranged from 9–170 mg L⁻¹ for the larger size fraction, and 8–150 mg L⁻¹ for the fine size fraction, with higher concentrations at the beginning of the rain event, suggesting a first-flush effect or sediment resuspension. The majority, 87 ± 13% on average, of TWP were quantified in the fine size fraction (1.6–20 μm). The findings indicate that TWP are mobilised from road surfaces and resuspend from gully pot sediments, thus resulting in low retention of TWP in the stormwater system. Additionally, high concentrations of metals, such as Cr, Cu, and Zn, were measured. Strong correlations were observed between TWP, TSS, VSS, and metals, suggesting shared transport pathways. These findings contribute to understanding the dynamic TWP transport behaviour during rain events, supporting better design of stormwater treatment systems targeting this emerging contaminant.