Tire and road wear particles in soils: from roadside soil to widespread impregnation

Currently, there is a lack of knowledge regarding the terrestrial fate of tire and road wear particles (TRWP) and the reliability of potential tracers. To gain insight into the widespread dispersion of TRWP, we determined the level of surface soil contamination on different spatial scales, both near different types of roads and at greater distances. The data confirmed high levels of contamination at the roadside with a sharp decrease in TRWP levels with increasing distance from the road. Beyond 20 m, general anthropogenic background contamination of 160 ± 70 mg TRWP/kg is measured. Correlation studies between TRWP content, total organic carbon (TOC) and non-exhaust and traffic metallic tracers (including Zn, Sb, Cu, Mo, Pb, …) show that the significance of correlations depends on the site and cannot be easily generalized. The studies also indicate that TOC acts as the dominant bearing phase at the roadside, whereas Al-containing fractions may dominate in surface soils at greater distances. Finally, a simple mass calculation revealed that, despite being heavily contaminated, roadsides only represent a minority of the regional terrestrial pool of TRWP. On average, >60% of the regional TRWP amount in surface soils was stored >20 m from the road, drawing attention to the widespread impregnation and impact of this pollution.