Car tire particles and their additives: biomarkers for recent exposure in marine environments

Car tire particles represent an important category of microplastics that is difficult to alleviate. The particles stem from abrasion during driving, so-called tire wear particles (TWPs), down-cycled end-of-life tire granulate, popular as low-cost infill on sports fields, or degradation products from discarded tires. The material contains a variety of additives and chemical residues from the manufacturing process, including metals, especially high concentrations of zinc, polycyclic aromatic hydrocarbons (PAHs), and benzothiazoles, but also para-phenylenediamines (PPDs) and numerous other organic chemicals. In urbanized areas, TWPs are emitted from roads, and granulates disperse from artifical sports fields and other urban surfaces to the environment, suggesting that runoff to coastal systems is likely and a route of exposure to marine organisms. Recent experimental studies show tire rubber particles in marine animals from different functional groups in addition to uptake of tire-related organic chemicals into biological tissues. These include bivalves, crabs, and fish, representing different body sizes, marine habitats, and feeding modes, and thus varying exposure scenarios. Our findings from GC-HRMS SIM chromatography demonstrate that different marine species ingest tire rubber particles, and that several tire additives are taken up into tissues post-ingestion. Although the organic chemicals do not seem to bioaccumulate, they are specific and bioavailable chemicals in tire materials. Mapping of tire rubber particle distributions in coastal systems, dose-response toxicity testing and risk assessments of environmental concentrations are thus warranted, also with a view to potential trophic transfer and implications for human health.