Seasonal Contrast in Oceanic Regulation of Traditional and Emerging Per- and Polyfluoroalkyl Substances in the Coastal East China Sea

Traditional and emerging per- and polyfluoroalkyl substances (PFAS) are widespread in coastal environments influenced by intense anthropogenic activity. However, their spatiotemporal dynamics in response to seasonal oceanographic processes remains insufficiently understood. By integrating basic hydrological and biogeochemical data, this study systematically compares the occurrence and behavior of traditional and emerging PFAS in full-depth seawater and surface sediments across the coastal East China Sea (ECS) during summer and winter. Waterborne PFAS consistently exhibited nearshore-to-offshore decreasing gradients and surface enrichment in both seasons, highlighting persistent terrestrial inputs. Notably, summer concentrations were generally lower, with weaker negative correlations with salinity, likely due to enhanced freshwater discharge during the wet season, which diluted and dispersed PFAS more effectively. Seasonal reversal of coastal currents driven by the monsoon further modulated the contaminant transport pathways. In contrast, sediment PFAS concentrations were generally higher in the summer, which can be attributed to stronger vertical mixing in the winter that facilitates the remobilization of contaminants. Enhanced sediment resuspension during the winter also promoted greater partitioning of PFAS, especially hydrophilic short-chain compounds, into the aqueous phase. These findings offer valuable insights into the seasonal variability and environmental behavior of PFAS in coastal marine systems.