In situ biofilm development on microplastics and its impact on PFAS adsorption in aquatic environment

Microplastics (MPs) in aquatic environments are rapidly colonized by microorganisms, leading to biofilm formation that alters their physicochemical properties and pollutant interactions. This process strongly affects the transport, transformation, and fate of coexisting contaminants, raising ecological concerns given the widespread abundance of MPs in natural waters. In this study, in situ exposure experiments were conducted in the Chishui River (Southwest China) to examine biofilm development on polypropylene (PP) and polystyrene (PS) over 60 days. Biofilm colonization significantly modified MP surface hydrophobicity, charge distribution, and functional groups, with biomass increasing by 4.40-5.70-fold. PS exhibited stronger microbial attachment and colonization, likely due to its rougher morphology and aromatic structure. Biofilm growth also enhanced the adsorption of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), increasing uptake by 1.12-1.45 and 1.16-1.39 times, with maximum capacities of 1.48-3.35 µg/g and 2.00-5.36 µg/g, respectively. Mechanistic analyses indicated hydrophobic and electrostatic interactions as dominant drivers, complemented by hydrogen bonding and surface complexation. Overall, these findings provide field-based evidence that biofilm development markedly strengthens MP-pollutant interactions, underscoring the ecological risks of biofilm-mediated contaminant transport in natural waters.