Advanced understanding of the natural forces accelerating aging and release of black microplastics (tire wear particles) based on mechanism and toxicity analysis

Currently, tire wear particles (TWPs), a typical type of black microplastics (MPs), are frequently overlooked as the major source of MPs in aquatic environments. TWPs are widely distributed and exhibit complex environmental behaviors. However, how natural forces affect the aging and release behavior of TWPs at the nano(micro)scale remains inadequately explored. This study systematically investigated the aging behavior and mechanism of TWPs under the action of simulated natural light and high-temperature in both dry and wet environments, as well as the effect of aging treatment on the released leachate. The findings demonstrated that aging treatment significantly altered the physicochemical properties of TWPs, including chain scission and surface oxidation, and facilitated the release of heavy metals and organic additives in the meantime. In particular, the leaching concentration of Zn exhibited a positive linear relationship with exposure time. In the thermal-aging process, the oxidation of TWPs was primarily caused by superoxide anion (O