Potential deterioration of chemical water quality due to trace metal adsorption onto tire and road wear particles – Environmentally representative experiments

Tire wear particles are an increasing issue in particle emissions to the environment. Germany-wide approximately 100,000 t tire wear particles are emitted every year into the environment which are estimated to be one third of the microplastic emissions. Up to 20% are estimated to reach inland surface waters. Their behavior in the aquatic environment is understudied. Tire wear particles have an overly hydrophobic surface that is capable of adsorbing substances like trace elements. In this study we investigated the adsorption and desorption of trace metals onto and from the particle surface of tire-related samples in water samples of the Freiberger Mulde, a river with naturally elevated concentration of trace elements. The priority trace metals Cr, Ni, Zn, Cd and Pb show a significant adsorption onto the particle surface of tire-related samples. Tire wear particles themselves revealed adsorption of mainly Ni, Cd and Pb. Regarding the German classification for suspended matter in freshwaters, an endangering of the chemical water quality is expected due to the adsorption process and not due to the particles themselves. Upcoming electromobility is expected to increase the Zn (increased tire abrasion) and decrease the Cu amount (reduced brake abrasion) released to freshwaters.