Comparative study on differential adsorption performance and mechanisms of alkaline vs. peroxymonosulfate aging for perfluorooctanoic acid by various microplastics

Perfluorooctanoic acid (PFOA) and microplastics (MPs) were widespread new contaminants in aquatic environments. In co-contamination scenarios, MPs could act as environmental carriers for PFOA, significantly increasing the complexity of its aquatic transport dynamics. Meanwhile, MPs aging and their interfacial interactions might induce novel combined toxicity. However, systematic studies on the differential impacts of various aging methods on interactions between different MPs and PFOA were lacking. This study examined four common aquatic MPs (polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET), Polypropylene (PP)) to investigate the effects of different aging methods (alkaline aging and peroxymonosulfate (PMS)) on the properties of MPs and their PFOA adsorption performance, and revealed the interaction mechanisms with PFOA via extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory with density functional theory (DFT) calculations analyses. Results showed both aging methods caused surface wrinkling in all MPs, damaging characteristic functional groups through hydrolysis (alkaline aging) and oxidation (PMS aging). Notably, the N-containing functional groups on PA were the main functional groups for PFOA adsorption, their damage led to a significant decrease in the adsorption capacity of aged PA, with alkaline aging having a more prominent impact than PMS aging. Furthermore, all MPs exhibited the characteristic of "physicochemical synergistic multi-layer adsorption". Specifically, PA (-C(O)NH-) and PET (-COO-) dominated chemical adsorption (γ AB -driven) due to polar groups’ strong electrostatic potential, with equilibrium capacities of 8.78 and 1.32 mg·g⁻¹ . In contrast, non-polar PE and PP mainly underwent physical adsorption (γ LW -driven), showing low capacities (0.18 and 0.54 mg·g⁻¹) and little aging impact. The findings aimed to elucidate the differential environmental impacts of various aged MPs as PFOA carriers and provide a scientific basis for assessing the combined pollution risks of these two pollutants in aquatic environments.