Abstract
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.
Highlights
Increased concentrations of plastic in oceans, lakes and watercourses is a growing environmental problem that has been recognized in the past decade (Auta et al, 2017; Barboza and Gimenez, 2015; Jiang, 2018)
The aim of the study was to: 1) investigate the concentrations of microplastics/tire and bitumen microplastic particles (TBMP) on road surfaces in an urban area, and in stormwater collected from the catchment area during a period with weekly street sweeping; 2) estimate the potential contribution of micro-sized tire wear from an urban street area to water recipients; and 3) to investigate the uptake of TBMP by street sweeping
To be able to estimate the total amounts of TBMP and TWP in stormwater and road particle matrices, a broad size spectrum of particles should be analysed, which includes particles at least ≤100 μm and preferably smaller
Summary
Increased concentrations of plastic in oceans, lakes and watercourses is a growing environmental problem that has been recognized in the past decade (Auta et al, 2017; Barboza and Gimenez, 2015; Jiang, 2018). For practical reasons bitumen has often been included when traffic related particles are studied. Recent studies indicate that tire and road wear particles (TRWP), may be one of the major sources of microplastics in the environment (Kole et al, 2017; Sommer et al, 2018). Based on a compilation of results from existing models, Sommer et al (2018) suggested that 30 vol% of all microplastics that pollute rivers and oceans relate to tire wear. TRWP that end up in waterways may be transported large distances from their source, and Kole et al (2017) have estimated that 5–10% of all plastics in the oceans originate from TRWP
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