Risk implications induced by behaviors of artificial and pavement-generated TWPs in river water: Role of particle-self properties and incubation aging

Here, we investigated the pristine properties of three typical tire wear particles (TWPs) and their aging properties after incubation in runoff (primary aging) and sewage (further aging), and captured the differences in the behavioral characteristics of nine TWPs in river water, with a view to paving the way for revealing the intrinsic mechanism of the hydroecological effects of TWPs. Our results highlight that the generation modes of three pristine tire wear particles (TWPs), stemming from typical tire and road wear processes—specifically, rolling friction (R-TWPs) and sliding friction (S-TWPs), alongside cryogenically milled tire treads (C-TWPs)—significantly impact their pristine physicochemical properties. This impact encompasses surface structure, particle size (D [4,3]: 8.5–121.3 μm), surface potential (−10.4 ∼ −1.8 mV), contact angle (95.2–129.8°), density (1.09–1.75 kg/m3), etc., consequently, these differences significantly influence their migration capability and sorption capacity during the incubation and aging in runoff and sewage. Interestingly, after incubation and aging in the migrating aqueous phase, particularly with additional aging in sewage, not only do distinctions in the aforementioned physicochemical properties (namely, particle size (5.6–6.6 μm), surface potential (−18.4 ∼ −18.1 mV), contact angle (124.5–125.4°), density (1.05–1.16 kg/m3)) among various types of TWPs diminish, but the environmental behaviors (encompassing, desorption capacity, aggregation kinetics, photochemical activity—formation of persistent free radicals, and exudation—derivative (6PPD-Quinone) of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine: 6PPD) exhibited by this array of TWPs demonstrate a remarkable coherence within the downstream river water. Concerningly, the aforementioned features of aquatic system behaviors appear to be predisposed towards exacerbating the heightened toxicity of TWPs, for example, the leaching concentration of 6PPD-Q increased by two to three times after aging, aligning with established precedents regarding the toxicological causes associated with the quinone derivatives of antioxidants in rubber contaminants.