An overview of the key topics related to the study of tire particles and their chemical leachates: From problems to solutions

The environmental contamination and biological impacts of tire particles and their associated chemicals is of great concern. Variously termed as tire wear particles (TWP), tire and road wear particles (TRWP), and end-of-life tires (ELTs) to differentiate between possible compositions and sources in the environment, these rubber particles are a major source of plastic pollution. The array of added chemicals that leach into the environment presents an additional environmental, toxicological and regulatory challenge. In this review, we define several topic areas that are relevant to the study of tire particles, outlining the current state and ongoing challenges. Emissions estimates needed to establish environmental loads are based on dated, summarised dataset rather than measured data, but determining the environmental presence of tire particles is hampered by a lack of standardised sampling methods. Several techniques for the analysis of tire rubber and associated chemicals are available, but the variability in tires model composition makes the selection of analytical markers challenging, as does a lack of commercial standards. Toxicologically, there remains a need to delineate particle and leachate effects and, in addition, to investigate emerging chemicals of concern and their transformation products. Such knowledge is required to feed into regulatory processes which currently regulate tire constituents separately rather than as the whole tire. Technological solutions to capture or replace tire rubber are progressing, often outside of academia, and it is important that the scientific community collaborate with those attempting to reduce the environmental impact of tires, including the tire industry.