Pavement wear generates microplastics in stormwater runoff.

Tire and road wear particles are a major source of microplastics to urban stormwater. They are composed of hetero-aggregates of abraded tire and pavement particles that are difficult to distinguish. While tire wear is a known source of microplastics, little is known on the contribution of pavement wear. This two-year field study with complementary lab testing evaluates the effects of pavement degradation on microplastic generation in stormwater from different pavement types: asphalt, concrete, and recycled rubber pavers. Pavement specimens from each site were collected and underwent degradation testing. We directly demonstrated that pavement wear is a source of microplastics in stormwater separate from tire wear. We showed that the rubber pavement released the most microplastics in lab testing, suggesting that the formulation of such novel recycled-tire pavers must undergo thorough testing before wide application. The asphalt pavement was the most susceptible to rutting and released the most microplastics in the field, including a large proportion of tire wear particles. Both land-use and pavement surface characteristics influenced microplastic generation. These results demonstrate the need to consider microplastic generation during pavement material selection and mitigate the spread of microplastics from pavement wear to nearby environments.