Aquatic ecosystem degradation attributed to tire wear particles in urban roadway runoff

Tire wear particles (TWP) and its antioxidant derivative N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), generated by the intensive utilization of transportation vehicles, are infiltrating aquatic ecosystems via stormwater runoff. This infiltration poses a threat to aquatic organisms and ecosystem functions within the surface water environment. Nevertheless, the phenomenon and causes of the degradation of water environments driven by urban roadway runoff remain unknown. In this study, six mesocosms were established in natural streams near Shanghai to simulate urban roadway runoff using TWP and 6PPD. We monitored physicochemical parameters, community composition, and ecosystem functions including productivity, respiration, and decomposition. NMDS analyses indicated that both TWP and 6PPD altered the community composition of phytoplankton and herbivores, with weaker but detectable shifts in benthos, and detritivores. Trophic classification analysis demonstrated that urban roadway runoff significantly decreased the abundance of phytoplankton and their herbivores, while exerting a relatively weaker impact on aquatic organisms at higher trophic levels. Urban roadway runoff also significantly reduced decomposition rates and chlorophyll a content in terms of ecosystem functions, whereas salinity increased under both TWP and 6PPD treatments. This led to a reduction in material cycling within ecosystems, impairment of primary productivity, and alteration of the osmotic pressure environment, thereby exacerbating the survival pressures on sensitive species. Structural equation modeling indicated that pollutants primarily disrupted lower trophic levels, indirectly altering ecosystem functions, particularly decomposition rates. Although short-term resilience was observed in higher trophic groups, the suppression of primary producers and grazers suggests potential long-term cascading effects that could destabilize food webs and impair ecosystem functioning. Our findings highlight the ecological risks of urban roadway runoff beyond single-species toxicity, emphasizing the need to integrate biodiversity and ecosystem function in risk assessments. This study provides a theoretical foundation for urban aquatic management frameworks that simultaneously address biodiversity conservation and ecosystem stability.