UV-aged tire wear particles and their leachates jointly enhance antibiotic resistance gene dissemination.

Tire wear particles (TWPs) represent a major source of environmental microplastics, yet how ultraviolet (UV) aging influences their effects on the transfer of antibiotic resistance genes (ARGs) remains unclear. Here, the promoting effects and underlying mechanisms of UV-aged TWPs and their leachate on bacterial conjugative transfer were investigated. Aging significantly increased the specific surface area and oxygen-containing functional groups of TWPs, and promoted the release of heavy metal ions and organic additives into leachate. In conjugation assays, 60-day-aged TWPs enhanced the transfer frequency of plasmid RP4 by 15.3-fold; whereas the corresponding leachate alone caused a 62.0-fold increase. Mechanistically, aged TWPs acted primarily as a physical oxidative stressor, promoting conjugative transfer through reactive oxygen species (ROS) generation and disruption of cell membrane integrity. Aged leachate acted mainly as a chemical signaling stressor, inducing biofilm formation and collective behavioral responses that created a protective microenvironment conducive to plasmid exchange, although they also contributed to oxidative stress. Combined exposure further produced a response greater than that of either pathway alone, establishing a physicochemical dual-stress framework that drives ARGs transfer. Collectively, these findings suggest that environmental aging critically shapes the ecological risks of microplastics, positioning aged TWPs as potential vectors for ARGs dissemination and underscoring the need to consider both particle-associated and leachate-mediated pathways in future risk assessments.