ABSTRACT
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.
ABSTRACT
This study aims to examine tire and road wear particle (TRWP) emissions under realistic conditions in order to provide some valuable insights into understanding their sources and fate in the environment. TRWP emissions were evaluated with a fully instrumented vehicle driving on five representative road types: urban, ring road, suburban, highway, and rural. Multiple vehicle dynamic variables were recorded to assess the factors influencing these emissions. For the first time, emitted particles were collected on filters and analyzed by means of pyrolysis coupled with gas chromatography-mass spectrometry to determine the polymeric content of tires, in specifically quantifying styrene-butadiene rubber (SBR) and butadiene rubber (BR) pyrolytic markers. The measurements obtained from the five road types revealed similar size distributions for SBR + BR emissions, with maxima found in the (ultra)fine fraction (< 0.39 µm). Upon applying an SBR + BR-to-TRWP conversion factor, (ultra)fine fraction TRWP emissions proved to be the highest for suburban (64 ± 5 µg/km), followed by highway, urban, ring road and rural routes. The output represents up to 480 tons of TRWP per year emitted in the EU27, thus suggesting a widely impregnated atmospheric compartment capable of threatening human health. Furthermore, an analysis of variables revealed that acceleration, tire constraints, and constant sustained driving factors had specific impacts on TRWP emissions.