Hydrodynamic Aging Process Altered Benzo(a)pyrene Adsorption on Poly(butylene adipate-co-terephthalate) and Poly(butylene succinate) Microplastics in Seawater

The environmental behavior of biodegradable plastics under long-term hydrodynamic aging processes in seawater remains poorly understood, although plastic pollution has attracted global concern. This study obtained poly(butylene adipate-co-terephthalate) (PBAT) and poly(butylene succinate) (PBS) microplastics that endured 36-month hydrodynamic aging in seawater to elucidate their physicochemical transformations and interactions with benzo(a)pyrene (BaP). Hydrodynamic aging markedly altered surface morphology, generated cracks and pores, and enriched -C=O and -OH groups, indicating oxidative degradation. Adsorption experiments showed that BaP adsorption capacity of virgin PBAT/PBS reached 213.3/235.3 μg g−1, while it increased to 233.3/258.2 μg g−1 after hydrodynamic aging in seawater. Elevated salinity and alkaline conditions reduced BaP adsorption on microplastics. Notably, hydrodynamic aging mitigated the risk of BaP desorption from PBAT in ectothermic organisms. Gibbs free energy calculations indicated that the adsorption process was primarily driven by hydrophobic effects, hydrogen bonding, and van der Waals forces. These findings highlight that long-term hydrodynamic aging substantially modifies the interfacial properties of biodegradable plastics to alter their capacity for mediating the environmental fate of hydrophobic organic pollutants in marine ecosystems.