Particle Sizes Crucially Affected the Release of Additives from Tire Wear Particles during UV Irradiation and Mechanical Abrasion

In the environment, tire wear particles (TWPs) could release various additives to induce potential risk, while the effects of particle size on the additive release behavior and ecological risk from TWPs remain unknown. This study investigated the effects and mechanisms of particle sizes (>2mm, 0.71-1mm, and <0.1mm) on the release behavior of TWPs additives under mechanical abrasion and UV irradiation in water. Compared to mechanical abrasion, UV irradiation significantly increased the level of additives released from TWPs. Especially, the additive releasing characteristics were critically affected by the particle sizes of TWPs, manifested as the higher release in the smaller-size ones. After 60 d of UV irradiation, the concentration of antioxidant N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPD) reached 10.79mg/L in the leachate of small-sized TWPs, 2.78 and 5.36 times higher than that of medium-sized and large-sized TWPs. The leachate of the small-sized TWPs also showed higher cytotoxicity. •OH and O2•- were identified as the main reactive oxygen species (ROS), which exhibited higher concentrations and dramatic attack on small-sized TWPs to cause pronounced fragmentation and oxidation, finally inducing the higher release of additives. This paper sheds light on the crucial effects and mechanism of particle sizes in the release behavior of TWPs additives, provides useful information to assess the ecological risk of TWPs. Environmental implication Tire wear particles and their endogenous additives have received much attention due to their biotoxicity. This study shows that small-sized (<0.1mm) tire wear particles release more additives in water compared to large-sized (>2mm) tire wear particles, especially under UV irradiation. The key factors contributing to this difference were the greater light absorption and ROS generation abilities of small-sized tire wear particles. These findings were crucial for understanding the environmental behavior and assessing the ecological risk of tire wear particles. More attention should be paid to the risk of small-sized tire wear particles in the future.