Occurrence patterns, spatial heterogeneity, and compositional variation of PFASs in deep-sea cold seep sediments from...

The occurrence and compositional variation of per- and polyfluoroalkyl substances (PFASs) in deep-sea cold seep sediments remain poorly characterized. Here, 25 target PFASs were analyzed in 40 sediment layers from six cores collected in the northern South China Sea. A tiered reporting scheme distinguished quantified concentrations (≥LOQ), detections between LOD and LOQ, and trace-level responses below the method LOD. Quantified ΣPFASs ranged from 0.13 to 6.12 ng g^-1 dw, with an overall mean of 1.39 ng g^-1 dw; the highest whole-core station-mean concentration occurred at station F (3.06 ng g^-1 dw). The dominant contributors to quantified ΣPFASs were PFPeA, PFDS, PFHxA, and 6:2 FTSA, accounting for 40.8%, 26.9%, 13.3%, and 8.1%, respectively. PFDS had a lower quantification frequency than the dominant PFCAs but made a disproportionately high contribution, mainly reflecting elevated PFDS concentrations in selected horizons, including the 4-8 cm interval at station F. Quantified PFASs were dominated by PFCAs (58.3%) and PFSAs (33.6%), whereas Other target PFASs accounted for 8.1% and were almost entirely represented by 6:2 FTSA. PERMANOVA indicated that inter-station variability (R² = 0.510, p < 0.001) exceeded depth-band effects (R² = 0.064, p = 0.017). Ordination further linked chain length and functional-group composition to multivariate compositional differences. These results establish a baseline record of PFAS occurrence and compositional heterogeneity in cold seep sediments and provide an occurrence-based context for future testing of chromatographic-like retention during burial.