An in vitro comparison of the toxicological profiles of ground tire particles (TP) and actual tire and road wear particles (TRWP) emissions

There is currently limited data on the potential effects of tire and road wear particles (TRWP) on human health. TRWP include tire fragments, but also road wear materials, dust, adsorbed gaseous pollutants and different types of inclusions that could affect their hazard profiles. Due to their availability and lower complexity, ground tire particles (TP) are often used in toxicological studies. However, this makes it difficult to draw firm conclusions about the potential hazard of actual TRWP. Here, we compared the in vitro toxicological profile of ground TP and actual TRWP emissions of similar size collected from road traffic. For this purpose, TP and TRWP were separately incubated with alveolar macrophages for 24 h, and the cellular response was evaluated in terms of cytotoxicity, proinflammatory response and oxidative stress. Both TP and TRWP induced neither significant cytotoxicity nor oxidative stress, but triggered a concentration-dependent proinflammatory response, as evidenced by increased TNF-α production. The level of TNF-α production was slightly higher with TRWP than with TP, independent of the particle dose. All in all, the pulmonary toxicity of TRWP could be due primarily to the tire tread inclusions and only marginally to other particle components (i.e. road wear materials, dust …). Although these preliminary results need to be confirmed by further analysis, they could be useful for tire manufacturers in the production of safer-by-design tires.