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Increased Aquatic Toxicity of Tire Wear Particles Following Oxidative Aging: Mechanism Insights into Matrix Loosening and Transformation Products
Summary
Tiny bits of tire rubber wash into rivers and lakes, and this study found that sunlight and ozone exposure make them even more toxic over time, not less. As the particles break down, they release new chemical byproducts that made up nearly half of the harmful effects seen in zebrafish embryos, even at very low, real-world exposure levels. This matters because it suggests weathered tire particles in waterways could pose bigger risks to aquatic life (and potentially the food chain) than current safety testing accounts for, since most assessments don't look for these newly formed breakdown chemicals.
Tire wear particles (TWPs) are a significant component of traffic-related contaminants in aquatic environment. However, the mechanisms by which environmental aging reshapes their toxicological profile are not well understood. In this study, we mechanistically investigated the effects of ultraviolet (UV) and ozone aging on TWP leaching behavior and zebrafish embryotoxicity. UV and ozone aging enhance TWP embryotoxicity, and aged TWPs exhibit sustained developmental toxicity, even at environmentally relevant 1-10% dilutions, indicating a significantly lowered threshold for aquatic hazard. This toxicological surge is fundamentally driven by particle matrix loosening. Oxidative degradation of the polymer backbone reduces mass-transfer resistance, thereby accelerating pollutant release kinetics by up to twofold. Non-target screening (FTICR-MS) further reveals that, while legacy additives are depleted, aging generates a large suite of highly oxygenated transformation products (TPs). These newly formed compounds emerge as dominant drivers of risk, accounting for nearly half (45%) of the total calculated toxic burden in ozone-aged TWPs leachates. Together, these results demonstrate that environmental weathering transforms TWPs from relatively inert solids into highly mobile and persistent chemical vectors. This underscores the necessity of incorporating non-target oxidation products into risk assessment frameworks to prevent severely underestimating the ecological hazards posed by weathered tire-derived contaminants.