Tire Additives and Transformation Products (TATPs) in Roadside Soils along Southern California Highways

In highly urbanized areas, heavy vehicular traffic generates large amounts of tire wear particles (TWPs) and tire additives and transformation products (TATPs), which are released into roadside environments. TATPs can cause acute and sublethal toxicities to nontarget organisms, but their levels and distribution in roadside soils are poorly understood. This study assessed TATP contamination in roadside soils along busy highways in Southern California. Representative TATPs (15) were monitored, and the total concentrations (ΣTATPs) ranged from 33.6 to 1747.5 ng/g. Compounds such as 1,3-diphenylguanidine (DPG) and benzothiazole and its derivatives (BTHs) were consistently detected at higher levels. The TATP contamination profile was influenced by season and surface runoff with higher levels in summer. TATP levels decreased with increasing distance from the road. Traffic volume positively correlated with total TATP levels, while the proportion of trucks contributed to elevated levels of paraphenylenediamine antioxidants (PPDs). These findings highlight the significant presence of TATPs in roadside soils, posing risks as secondary pollution sources for downstream ecosystems. Research is urgently needed to understand the transformations of TATPs in roadside soils, their transport potential to sensitive environments, and the mitigation role of natural and engineered infrastructures along highways.