From roads to water organisms? – Sequential extraction indicates high bioavailability of Cd, Zn and Pb from tire and road wear particles from a highway tunnel and go-kart tracks

Tire wear particles (TWP) are a rising issue with emerging ecotoxicological concerns, so that the new Euro 7 regulation is going to set emission limits for tire abrasion. On road surface, TWP incorporate various (non-)traffic related particles (containing heavy metals) forming tire and road wear particles (TRWP). During rainfall, these composite particles are mobilized via drainage systems into the aquatic environment, where TRWP may release incorporated and adsorbed heavy metals from the road into the surrounding water. Consequently, these heavy metals may become bioavailable to aquatic organisms. To evaluate the potential release of heavy metals from TRWP and their bioavailability, we applied a sequential extraction (Community Bureau of Certified References, BCR) to TRWP samples from a highway tunnel and go-kart lanes. For TRWP samples in the aquatic environment, sequential extraction indicated high bioavailability for Cd, Zn (> 50 % under aerobic conditions) and Pb (> 70 % under anaerobic conditions). The relative mobility of the investigated trace elements followed the order: Zn > Pb > Cd >> Cu > Co > As >> Ni > Cr. Furthermore, experiments using river water from the Freiberger Mulde showed that newly adsorbed Cd and Zn on TRWP from the surrounding water are only weakly bound and thus readily bioavailable (Cd > 95 %, Zn > 85 %). These findings indicate that TRWP can significantly influence the mobility and bioavailability of heavy metals in aquatic systems, which is crucial for assessing ecological risks and predicting the potential impact of TRWP as carriers of toxic metals to aquatic biota.