Regulation of terrestrial input and ocean processes on the occurrence and transport of traditional and emerging per- and polyfluoroalkyl substances in the inner shelf of the East China Sea

Coastal oceans, serving as transitional zones between land and sea, possess unique geographical features and complex hydrological conditions, functioning as regional reservoirs and crucial transport pathways for anthropogenic pollutants such as per- and polyfluoroalkyl substances (PFASs) to the open ocean. This study comprehensively investigates traditional perfluoroalkyl carboxylic and sulphonic acids (PFCAs and PFSAs) and emerging perfluoroalkyl ether carboxylic and sulfonic acids (PFECAs and PFESAs), fluorotelomer sulfonates (FTSAs) in seawater columns and surface sediments from the inner shelf of the East China Sea, by integrating hydrological and biogeochemical data. Comparable levels of traditional and emerging PFASs were observed in seawater samples, in contrast to higher concentrations of traditional PFASs in surface sediments. Waterborne PFASs exhibited a nearshore-to-offshore decreasing trend and a surface enrichment pattern in offshore waters, typically influenced by terrestrial inputs and oceanic processes. Significant terrestrial inputs for waterborne PFASs were identified, including large rivers like the Changjiang River (Yangtze) and semi-enclosed coastal bays such as Xiangshan Port and Sanmen Bay, where prolonged hydraulic retention times contribute to PFAS accumulation. The source apportionment model demonstrated that emerging fluorochemical manufacturing, textile production, and high-performance fluoropolymer materials are primary sources, consistent with PFAS releases from commercial products and industrial processes along the Changjiang River and in Xiangshan County. Hydrologically, the offshore transport barrier effect created by river plume fronts, and the vertical stratification of different water masses were significant for PFASs. Sediment inputs and resuspension also played a crucial role, with surface sediment-bottom water partitioning behavior primarily regulated by the hydrophobicity of PFASs and salting-out effects. While the overall ecological risks of PFASs were low, elevated risks associated with legacy perfluorooctanoate (PFOA), perfluorooctane sulfonate (PFOS), and emerging hexafluoropropylene oxide dimer acid (HFPO-DA) warrant closer attention due to their accumulation in the environment. The methodologies and findings of this research provide valuable insights into PFAS cycling in coastal oceans worldwide.