The most frequently quantified polymers were polyethylene, polypropylene, and the tyre-related polymers styrene-butadiene rubber and polyisoprene. This pattern is consistent with findings from other studies of microplastics in runoff, and it points to everyday road traffic as a persistent source of plastic particles entering the water environment.

Tyre-related polymers accounted for 41 ± 24 percent of the total microplastic concentration in the samples where they were quantified, confirming tyre wear particles as an important source of microplastic pollution in this type of environment. Urban stormwater has previously been identified as a major pathway for transporting microplastics, especially tyre wear particles, into aquatic environments, and the new measurements add quantitative detail on how much rubber is actually moving off a highway surface during rain.

Interestingly, the tyre-related polymers were quantified at lower concentrations than in other studies. The researchers suggest this may indicate that true concentrations are underestimated because the analytical method used a size cut-off at 10 micrometres, meaning smaller particles were not captured. The study’s authors call for further research into standardised sampling techniques and sample preparation methods for pyrolysis-gas chromatography/mass spectrometry that can reliably identify and quantify microplastics smaller than 10 micrometres and are robust against interference from complex environmental matrices.

In addition to measuring plastic concentrations, the study examined whether microplastic levels track other common stormwater pollutants. No significant correlations were observed between microplastic concentrations and total suspended solids, volatile suspended solids, or metals.

The study was conducted on stormwater collected during rainfall events at a Swedish highway, and the authors frame the work as a contribution to understanding microplastic emissions from road runoff. They note that the findings provide knowledge for the development of methods to treat road runoff and its pollutants. Because the measurements come from a single highway system during discrete rainfall events, and because the particle size range analysed was limited to 10 to 1000 micrometres, the reported concentrations should be read within those boundaries rather than as a general estimate of road microplastic emissions everywhere.

Overall, the study quantifies what flows off a modern highway when it rains: a mixture of common commodity plastics and tyre-derived rubber, with tyre-related polymers making up a substantial share of the measured particle mass.

Subject of Research: Microplastic and tyre rubber polymer concentrations in highway stormwater runoff during rainfall

Article Title: Microplastics in a highway stormwater system: concentrations and variability during rainfall

Article References: Gaggini, E. L., Strömvall, A.-M., Rødland, E. S., Sokolova, E., Andersson-Sköld, Y., & Bondelind, M. (2026). Microplastics in a highway stormwater system: concentrations and variability during rainfall. Microplastics and Nanoplastics. https://doi.org/10.1186/s43591-026-00235-z

Image Credits: AI Generated

DOI: 10.1186/s43591-026-00235-z

Keywords: microplastics, tyre wear particles, stormwater, highway runoff, styrene-butadiene rubber, polyethylene, polypropylene, pyrolysis GC-MS, suspended solids, water pollution, Sweden, road runoff treatment