Per- and polyfluoroalkyl substances (PFAS) are emerging persistent organic pollutants, yet their occurrence and dynamic behavior—particularly their vertical distribution and transport mechanisms—in Antarctic coastal waters remain poorly understood. This study was based on vertical profile sampling conducted in April 2025 (austral autumn) at multiple stations within the Ross Sea shelf. The vertical distributions of legacy and emerging PFAS concentrations were analyzed.
Seven PFAS were detected in seawater samples, including PFBA, PFPeA, PFHpA, PFOA, PFOS, and two emerging PFAS—6:2 FTSA and C8 HFPO-TA. Among these, PFBA was the most abundant compound, detected at all stations. The vertical profiles of PFAS were significantly influenced by the transport pathways of cold, saline bottom water masses known as High-Salinity Shelf Water (HSSW), which are generated by Ross Sea polynyas. During sea-ice formation in polynyas, brine rejection enriches PFAS in the HSSW, which then affects PFAS concentrations at stations outside the polynya as it flows along its specific pathway. Shallow bank stations, deviating from the main HSSW transport pathway, exhibited largely uniform PFAS distributions throughout the water column. In contrast, shelf trough stations showed a trend of bottom-water enrichment, indicating substantial contributions from benthic boundary layer processes or water-mass advection. Additionally, surface PFAS enrichment observed at near-shore stations suggested inputs from atmospheric deposition and terrestrial meltwater runoff.
In autumn, the Ross Sea water column was clearly stratified, with salinity and chlorophyll-a concentration showing concurrent stratification at approximately 150 m depth, indicating a density-driven pycnocline with restricted physical exchange. However, at several stations, PFAS concentrations remained uniform across this interface, suggesting that the vertical distribution of PFAS was not governed by physical mixing alone. Instead, biogeochemical processes such as particle settling, resuspension, and desorption likely contributed to solute transport across the physical pycnocline. Anomalously elevated mid-depth temperatures observed at some stations, likely indicative of modified Circumpolar Deep Water (mCDW) intrusion, may have further influenced the redistribution of PFAS throughout the water column.
In summary, the vertical distribution of PFAS within the Ross Sea shelf is shaped by the interplay of topographically constrained water-mass transport, seasonal vertical mixing, and biogeochemical processes. This study reveals significant spatial heterogeneity in PFAS distribution over the Ross Sea shelf and provides preliminary observational evidence for the physico-biogeochemical coupling governing PFAS transport in polar marine environments.