Combined contamination of tire and road wear microplastics with heavy metals in expressway tunnels: occurrence characteristics and risk assessment.

Tire and road wear microplastics (TRWMPs), as an important type of microplastics, have attracted increasing attention. However, current studies on their contamination within expressway tunnels remain limited. Therefore, we investigated the occurrence characteristics of TRWMPs in dusts from various tunnels, and combined contamination with heavy metals (HMs). The results showed that the abundance of TRWMPs in expressway tunnel dust (53,778 n/kg) was much higher than that sampled from other land use types (1360-4960 n/kg) in the same region. A large amount of polyamide was released into the environment along with wear particles from the vehicles. Also, the abundance of TRWMPs inside tunnels was greater than outside, and the proportion of large-size TRWMPs was higher inside tunnels. TRWMPs was symmetrically distributed with respect to the center of expressway tunnel. The pollution load index (PLI) and ecological risk index (H) indicated that study area was heavily contaminated with TRWMPs. There was a significant positive correlation between the abundance of TRWMPs and concentration of Cr (p < 0.01) in dust, and their risk assessment and health risk fluctuations were almost identical. Thus, the study is of great significance for elucidating the synergistic contamination and potential risk of TRWMPs and HMs in expressway tunnels.