When and how leachate toxicity of tire wear particles peaks: quantifying its dynamics using dose-response analysis

The aquatic toxicity of tire wear particles (TWPs) depends on the leaching of various components. The leaching process is time-dependent and influenced by various environmental factors, leading to fluctuation in leachate toxicity. In this study, we quantified the temporal dynamics of leachate toxicity using the dose-response model. Meanwhile, to simulate weathering conditions, TWPs were exposed to ultraviolet (UV) irradiation and elevated temperature. The results indicated that the leachate toxicity over time fitted a biphasic pattern, with an initial increase followed by a decrease, peaking at the 11th day. The toxicity fluctuation cannot be characterized by any single component, but rather leachate should be considered as an integral whole aligning with a typical hormesis dose-response curve. High temperature of road surface increased leachate toxicity by 66%, due to elevated concentrations of 67 identified organic compounds. UV irradiation, however, mitigated this effect, acting as antagonism. These findings underline the seasonal and spatial heterogeneity in leachate toxicity. Additionally, high temperature induced the volatilization of organic compounds within TWPs, highlighting an independent exposure pathway. The methodology developed in this study will provide foundation and standard for future research on the aquatic ecotoxicity of TWPs. Environmental ImplicationThe toxicity of leachate from ubiquitous tire wear particles (TWPs) to aquatic organisms has been confirmed in field and experimental studies. However, existing researches indirectly used TWPs quantity as sole proxy for leachate toxicity, neglecting its fluctuations over leaching duration and in situ environmental factors, potentially confounding toxic effects. Herein, this study quantifies these dynamics of leachate toxicity based on measurable biological response, aiming to establish a standard scale for further quantitative assessment of TWPs ecological risk.