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Biodegradation of PLA in surface water and its behavior towards PFOA: interactional characteristics and computational insights
Summary
After 80 days of aging in simulated surface water, biodegradable PLA microplastics became significantly rougher and more chemically reactive, increasing their capacity to adsorb the persistent pollutant PFOA by tenfold. This means so-called biodegradable plastics can actually become more dangerous environmental vectors for toxic chemicals as they weather in waterways.
The environmental impact of biodegradable microplastics (BMPs) is profoundly influenced by aging-induced surface transformations, yet their interactions with persistent organic pollutants, such as perfluorooctanoic acid (PFOA), remain poorly understood. This work investigates how aging polylactic acid (PLA), a common BMP, in simulated surface water for 80 days alters its physicochemical properties and behavior towards PFOA. Aging triggered oxidative and hydrolytic degradation, leading to pronounced morphological changes, including increased surface roughness, hydrophilicity, and oxygen-to-carbon (O/C) ratio from 0.82 to 1.28. These transformations introduced hydroxyl and carboxyl functional groups, shifting the PFOA adsorption mechanism from physisorption (in fresh PLA) to chemisorption (in aged PLA) via stronger electrostatic interactions and hydrogen bonding. Additionally, kinetic and isotherm analyses revealed a tenfold increase in PFOA monolayer adsorption capacity for aged PLA (PLA-80) compared to pristine PLA. Density functional theory (DFT) calculations corroborated these findings, demonstrating a reduced HOMO–LUMO energy gap upon PFOA adsorption, indicative of enhanced electronic reactivity and charge transfer. Topological analysis further identified multiple hydrogen-bonding sites, confirming the dominance of electrostatic forces in pollutant retention. These results underscore the critical role of aging in amplifying BMPs’ environmental reactivity, emphasizing the urgent need to incorporate aging processes into risk assessments for biodegradable plastics.