Rainfall, seasonal variation, and stream type governing the multi-media fate and ecological risks of tire additives and their transformation products in mega-urban streams.

Tire additives and their transformation products (TATPs) are increasingly recognized for their toxicity and widespread environmental presence. However, the interplay of rainfall, seasonal variation, and stream type in governing their multi-media partitioning and risks remains largely unexplored. This study investigated the spatiotemporal distribution, environmental drivers, and ecological risks of 21 TATPs in three distinct urban streams (general road, expressway, and rural road-adjacent). Seventeen, 19, and 14 TATPs were quantified in water (514-6541 ng/L), suspended particulate matter (SPM, 12.8-244 ng/L), and sediment (1.71-248 ng/g), respectively. Rainfall significantly altered aqueous TATP levels, while stream type and seasonal variation influenced TATP pollution in SPM and sediment. Multiple linear regression identified pH, temperature, and road area as key aqueous-phase drivers, whereas precipitation and road area controlled the levels of TATPs in SPM and sediment, respectively. Hydrophobicity was a key determinant in TATP multi-media partitioning. High ecological risks were found across all water samples, primarily associated with 1,3-diphenylurea (DPU), 1,3-dicyclohexylurea (DCU), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q), and hexa(methoxymethyl)melamine (HMMM). Eight TATPs exhibited persistence, bioaccumulation, or toxicity traits, warranting prioritized regulation. These insights are crucial for crafting effective environmental policies to mitigate =TATP impacts and protect urban aquatic ecosystems.