Polymer-dependent accumulation of PFASs on microplastics in Xiamen Bay: field evidence and laboratory partitioning

Per- and polyfluoroalkyl substances (PFASs) are widespread in coastal waters, yet evidence for PFASs carried by microplastics (MPs) remains limited in semi enclosed bays. A method was optimized to extract and quantify MP associated PFASs and applied to Xiamen Bay. With MP standards spiked with 15 PFASs, 0.1% ammonia in methanol yielded recoveries of 76.83-109.15%. Field MPs contained eight PFASs (52.10 ± 15.79 ng g^-1 of ΣPFAS) and were dominated by foamed polystyrene (PS, 78.73%) and PE/PP (21.27%). PFAS burdens were higher on PS, with PFOS contributing disproportionately. Paired surface waters contained 13 PFASs (mean: 80.19 ng L^-1) dominated by short chain PFCAs (PFHxA and PFPeA). MPs-water partitioning indicated moderate enrichment (1.93-3.73 of log K_d-WM) and slightly stronger partitioning to PS, and correlation and multivariate patterns showed PS associated compositions tracked dissolved phase variability more closely than PE/PP. Batch sorption experiments with pristine and UV aged PS confirmed stronger PFOS than PFOA sorption and enhanced uptake after aging. Spatial patterns were consistent with stronger river influence on short chain acids and more localized coastal inputs for long chain sulfonates, suggesting that aged buoyant MPs can intensify MP associated PFAS co-contamination in semi-enclosed coastal waters.