Characterisation and spatial distribution of tyre wear particles in Swedish highway snow: Loads into roadside ditches and risk of emissions with snowmelt

Tyre wear particles (TWP) are a significant source of microplastic pollution that can accumulate in road-adjacent snow. This study investigates characteristics, abundance and spatial distribution of TWP for two size fractions: <500 µm and 1.6–20 µm in the near-road environment of a highway. Quantification was done using Pyrolysis–Gas chromatography/Mass spectrometry (PYR-GC/MS), alongside morphological and elemental analyses by Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM-EDX). Transport behaviour of TWP was investigated through comparison with selected stormwater related parameters (conductivity, nano-sized particle concentration, total and dissolved carbon and organic carbon, ions, total and dissolved metals). Results show that TWP concentrations in snow ranged between 7.8 and 1300 mg/L and concentrations decreased with distance from the highway. An abundant and varying proportion of TWP was found in the fine fraction 1.6–20 µm, ranging from 0.3% to 98% with an average of 48%. TWP strongly correlated with concentrations of solids and metals, suggesting similar transport processes. SEM-EDX+ML analyses showed that bitumen and tyre wear particles were the second and third most abundant components in the solid material in the snow, with minerals being the most abundant. Tyre and bitumen wear particles appeared less elongated than in road dust previously analysed from the same highway. These findings advance the understanding of TWP transport and distribution in near-road snow environments. Given the potential for acute release during snowmelt, mitigation measures limiting TWP emissions and spread, including better snow management and disposal practices are needed.