Occurrence of tire and bitumenwear microplastics on urban streets and in sweepsand and washwater

Tire and roadwear particles have been identified as a potentialmajor source ofmicroplastics in the environment. However, more knowledge of the emissions and their further fate in the environment is needed, and the effec- tiveness and benefits of potential measures must be investigated to support future risk management efforts. Here the concentrations of tire and bitumenmicroplastic particles (TBMP) on roads and in nearby in stormwater, sweepsand andwashwaterweremeasured for the first timewithin the same area and time period. The analysis also included plastic, paint and fiber particles. Road dustwas sampled on the road surface using awet dust sam- pler, before and after street sweeping on twooccasions. On each of these occasions, and several occasions during a four-month periodwith frequent street sweeping, sweepsand and washwater, aswell as flow-weighted sam- pling of stormwater, were collected. TBMP concentrations were operationally defined, using density separation for some samples, followed by analysis by stereo microscopy. Sodium iodide (NaI) was found to be effective for density separation of TBMP. The largest proportion of anthropogenic microplastics detected consisted of tire tread wear and bitumen. The number of TBMP ≥100 μm in the WDS samples was up to 2561 particles/L. Sweepsand andwashwater contained highamounts of TBMP ≥100 μm, up to 2170 particles/kgdwand 4500 par- ticles/L, respectively. The results showthat the sweeper collects considerableamounts of TBMP, and thusweekly sweeping might prevent further transport of TBMP to the receiving stormwater. In stormwater the number of particles ≥100 μm was up to 3 particles/L and ≥ 20 μm was up to 5900 particles/L showing the importance of analysing smaller microparticle sizes than 100 μmin all samples in future studies. This study also confirms that there is a substantial volume of TBMP generated from traffic that enters the environment.

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