A comprehensive study on the impact of UV aging time on the adsorption and desorption behaviors of antibiotics on degradable and non-degradable microplastics

The extensive use of microplastics (MPs) and antibiotics has not only exacerbated environmental pollution, but the composite pollutants formed by them also pose escalating ecological risks. This study investigated the impact of aging time on the biodegradable polylactic acid (PLA) and non-degradable polyvinyl chloride (PVC), as well as the adsorption/desorption behavior of norfloxacin (NOR), ciprofloxacin (CIP), and sulfamethoxazole (SMZ) onto these MPs. The effects of ultraviolet (UV) aging (30, 60, and 90 days) on MPs’ physicochemical properties and adsorption performance were systematically evaluated. The results showed that UV aging altered MPs’ surface morphology, crystallinity, and surface charge, enhancing their adsorption capacity. Adsorption kinetics followed the pseudo-second-order model, while isotherms aligned with the Freundlich model, indicating multilayer adsorption governed by physical and chemical interactions (e.g., hydrogen bonding, electrostatic, hydrophobic, and π-π interactions). The adsorption capacities followed the order NOR > CIP > SMZ, with aged PLA exhibiting superior performance (PLA-90d > PLA-60d > PLA-30d > pristine PLA > PVC-90d > PVC-60d > PVC-30d > pristine PVC). PLA exhibited a higher adsorption capacity for antibiotics than PVC, indicating that biodegradable MPs have a stronger ability to adsorb organic pollutants. Desorption experiments were conducted in different pH and waters. The results revealed that PLA-90d and PVC-90d exhibited the highest NOR release rates (30.43 % and 24.64 %, respectively) at pH 11, with seawater promoting greater desorption than lake or ultrapure water due to ionic competition. These findings highlight the critical role of aging in amplifying MPs’ environmental risks as carriers of antibiotics.