Bioaccessibility, bioaccumulation and effects of tire-associated chemicals for aquatic and soil-dwelling organisms

Tire and road wear particles (TRWP) are produced by the friction between the tires and road and consist of polymer-containing tread with pavement encrustations. There are many data gaps remaining regarding their fate and potential toxicological impact on the aquatic and terrestrial environment. This study aimed to (i) investigate the solubilization and bioaccessibility of 11 tire-associated chemicals into fish gastric and intestinal fluids using an in vitro digestion model. The effect of food co-ingestion on the bioaccessibility of the chemicals was also assessed by introducing ground Gammarus pulex as a food surrogate in the digestion vessels. We also (ii) explored the effects of tire particles at environmentally relevant soil concentrations on survival, growth and reproductive output of an earthworm species, Eisenia fetida. The bioaccumulation potential of several commonly used tire-related chemicals was established and their bioaccumulation kinetics were determined. Our results show that the targeted compounds were rapidly solubilized into fish simulated digestive fluids within an average gut transit time of 3h in gastric fluid and 24h in intestinal fluid. Only a small percentage (0.06%) of hydrophobic tire-associated chemicals was found to be solubilized in the simulated fluids compared to more hydrophilic chemicals for which up to 44% of the total concentration in tire particles was solubilized. The effects of food co-ingestion on the solubilization of tire-associated chemicals was compound-specific and either lowered or stimulated their solubilization into the gut fluids. Our experiments also indicate that tire-associated chemicals were bioavailable to earthworms in natural soil spiked with tire particles albeit with a significant chemical increase in the organisms only in a highly contaminated soil (5% tire particles). The chemicals investigated did not show strong bioaccumulation potential: the Biota-Soil Accumulation Factor was