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Biodegradation and Surface Reconfiguration Triggered the Adsorption–Desorption of Phenanthrene on Biodegradable Polylactic Acid Microplastics in the Marine Environment
Original title: Biodegradation and Surface Reconfiguration Triggered the Adsorption–Desorption of Phenanthrene on Biodegradable Polylactic Acid Microplastics in the Marine Environment
Summary
"Biodegradable" plastics, often marketed as eco-friendly alternatives, aren't necessarily harmless once they hit the ocean: this study found that as PLA (a common plant-based plastic) breaks down in seawater over years, its surface becomes rougher and more chemically "sticky," allowing it to soak up much higher levels of a toxic pollutant called phenanthrene compared to fresh, unweathered plastic. This matters because these aged plastic particles could act as carriers that concentrate pollutants and transport them through the marine food chain, meaning "biodegradable" plastics may still pose environmental and
The virgin polylactic acid (V-PLA) microplastics did not adsorb phenanthrene (PHE), while the adsorption capacity of 36-month bioaged PLA microplastics (BA-PLA 36M ) increased to 94.5 μg g –1 for PHE, a common organic pollutant in marine environments. The adsorption capacity for PHE increased to 102 μg g –1 after the removal of the surficial biofilm from the BA-PLA 36M, indicating that the bioaged surface, but not the biofilm of PLA microplastics, served as the predominant driver affecting the interfacial performance of organic pollutants. The maximum adsorption of PHE on BA-PLA 36M reached 259.7 μg g –1 at pH 7.0, and high salinity could sharply decrease the PHE adsorption capacity of BA-PLA 36M microplastics (26.8 μg g –1 ). Compared with the V-PLA, long-term biodegradation of BA-PLA 36M in seawater led to porous surface structures with increased specific surface area and −C═O and −OH contents on the surface of PLA microplastics. Density functional theory calculation and molecular dynamics simulation indicated that bioaging could trigger the initial adsorption of a small amount of PHE, and the adsorbed PHE induced in situ surface reconfiguration of the BA-PLA 36M surface to further promote PHE adsorption. The biodegradation coupled with in situ surface reconfiguration caused by preadsorption triggered the adsorption–desorption of PHE on biodegradable microplastics.