Tire wear particle and leachate exposures from a pristine and road-worn tire to Hyalella azteca: Comparison of chemical content and biological effects

Tire emissions have emerged as an environmental contaminant of concern. To fully understand their effects to biota, research is needed from different stages of a tire's lifecycle. In this study we exposed freshwater Hyalella azteca to tire wear particles (TWPs) as particle suspensions or their respective chemical leachates (the chemicals released from tire particles into water) from a pristine (P-TWP) and worn (W-TWP) tire of same make and model. Acute and long-term toxicity experiments on H. azteca showed that P-TWP suspensions were more toxic than W-TWP suspensions with estimated LC values of 364 ± 64 particles (0.19 ± 0.03 g L) and 3073 ± 211 particles (0.91 ± 0.06 g L), respectively. However, leachates from W- and P-TWPs appeared equally toxic, but did not conform to a sigmoidal dose-response pattern and LC values could not be derived. In long-term tests (21 d) P-TWP suspensions showed no significant effects on H. azteca mortality (p = 0.970) or reproduction (p = 0.123), but growth was significantly reduced (p = 0.003) at the highest concentration tested (250 particles mL or 0.127 g L). Chemical analysis of both particle types and their leachates showed that four compounds, benzothiazole, 1-indanone, aluminum and zinc, consistently leached from TWPs into water. Analysis of the two TWPs showed a difference in the concentration of the various compounds. Specifically, P-TWPs contained significantly more 1-octanethiol, phenanthrene, anthracene and aluminum than W-TWPs, suggesting that they are possible candidates for the increased toxicity observed following P-TWP exposure.