Occurrence of tire and bitumen wear microplastics on urban streets and in sweepsand and washwater

Tire and road wear particles have been identified as a potential major source of microplastics in the environment. However, more knowledge of the emissions and their further fate in the environment is needed, and the effectiveness and benefits of potential measures must be investigated to support future risk management efforts. Here the concentrations of tire and bitumen microplastic particles (TBMP) on roads and in nearby in stormwater, sweepsand and washwater were measured for the first time within the same area and time period. The analysis also included plastic, paint and fiber particles. Road dust was sampled on the road surface using a wet dust sampler, before and after street sweeping on two occasions. On each of these occasions, and several occasions during a four-month period with frequent street sweeping, sweepsand and washwater, as well as flow-weighted sampling 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 and washwater contained high amounts of TBMP ≥100 μm, up to 2170 particles/kg dw and 4500 particles/L, respectively. The results show that the sweeper collects considerable amounts of TBMP, and thus weekly 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 μm in all samples in future studies. This study also confirms that there is a substantial volume of TBMP generated from traffic that enters the environment. [Display omitted] •Traffic related microplastics is one of the major sources to microplastic emissions•Samples were collected at the road surface, in the stormwater and from a sweeper•Microplastics have been analysed and quantified with light microscopy•The majority of identified microplastics in all media consist of tire and bitumen•The measured emissions seem to be we`ll in line with theoretical values