Characterization of tire and road wear microplastic particle contamination in a road tunnel: From surface to release

Road pollution is one of the major sources of microplastic particles to the environment. The distribution of tire, polymer-modified bitumen (PMB) and tire and road wear particles (TRWP) in different tunnel compartments were explored: road surface, gully-pots and tunnel wash water. A new method for calculating TRWP using Monte Carlo simulation is presented. The highest concentrations on the surface were in the side bank (tire:13.4 +/- 5.67; PMB:9.39 +/- 3.96; TRWP:22.9 +/- 8.19 mg/m2), comparable to previous studies, and at the tunnel outlet (tire:7.72 +/- 11.2; PMB:5.40 +/- 7.84; TRWP:11.2 +/- 16.2 mg/m2). The concentrations in gully-pots were highest at the inlet (tire:24.7 +/- 26.9; PMB:17.3 +/- 48.8; TRWP:35.8 +/- 38.9 mg/g) and comparable to values previously reported for sedimentation basins. Untreated wash water was comparable to road runoff (tire:38.3 +/- 10.5; PMB:26.8 +/- 7.33; TRWP:55.3 +/- 15.2 mg/L). Sedimentation treatment retained 63% of tire and road wear particles, indicating a need to increase the removal efficiency to prevent these from entering the environment. A strong linear relationship (R2-adj=0.88, p < 0.0001) between total suspended solids (TSS) and tire and road wear rubber was established, suggesting a potential for using TSS as a proxy for estimating rubber loads for monitoring purposes. Future research should focus on a common approach to analysis and calculation of tire, PMB and TRWP and address the uncertainties related to these calculations.

Automated summary

This study explores the distribution of tire, polymer-modified bitumen (PMB), and tire and road wear particles (TRWP) in different tunnel compartments. It presents a new method for calculating TRWP and investigates the effectiveness of sedimentation treatment. The results reveal the importance of addressing road pollution as a major source of microplastic particles.