UV-photoaging of degradable microplastics in atmospheric and wastewater: Surface changes and enhanced antibiotic...

Aging pathways critically govern biodegradable polymer fate in the environment, yet systematic comparisons of how distinct environmental metrics alter polymer structures and contaminant sorption capacity remain unclear. This study systematically compares UV-photoaging of biodegradable microplastics in atmospheric and wastewater environments to elucidate degradation mechanisms and their impact on antibiotic sorption. Herein, we demonstrate that UV-photoaging induces markedly more severe degradation and surface changes in polybutylene succinate microplastics exposed to wastewater (W-MP) relative to those in atmospheric environments (A-MP). W-MP exhibits extensive surface damages, biofilm-driven functionalization (N/Ca/Mg enrichment and amide groups), and synergistic oxidative damage, leading to a 2.6-fold increase in surface area and significant reduction in thermal stability. This divergence results from two synergistic mechanisms. First, dissolved organic matter photosensitizes reactive oxygen species formation, which accelerates polymer oxidation. Second, biofilms colonize the plastic surface under UV stress. W-MP showed a 2.4-fold higher tetracycline adsorption capacity (576.43 μg/g) than pristine microplastics, outperforming A-MP by 1.4-fold. Adsorption was driven by hydrogen bonding and electrostatic interactions, with spectroscopic and computational analyses confirming biofilm-enhanced dual interactions. Interaction between microplastics and tetracycline peaked at neutral pH and lower temperatures, with multivalent ions reducing efficiency. Fulvic acid enhanced adsorption on W-MP by bridging the biofilm matrix, but inhibited it on A-MP. Our findings show that the aging environment influences microplastic reactivity, with wastewater systems acting as critical hotspots that convert biodegradable plastics into vectors for antibiotic persistence and spread.