Revealing overlooked per- and polyfluoroalkyl substances (PFAS) in the Pearl River estuary using a comprehensive analytical approach

Per- and polyfluoroalkyl substances (PFAS) are organofluorine chemicals with widespread global occurrence. Despite over 4700 known compounds, only a small fraction is regularly monitored, leading to potential underestimation of PFAS pollution, particularly perfluoroalkyl acid (PFAA) precursors. To address this analytical challenge, this study employed a comprehensive analytical approach, combining target analysis, oxidative conversion of PFAS precursors, and extractable organofluorine (EOF) mass balance analysis on surface sediment samples collected from the coastal South China Sea (n = 18) and eight major Pearl River outlets (n = 8) in 2021 and 2020, respectively, to investigate unidentified PFAA precursors and EOF levels for the first time. Target analysis revealed a ten-fold increase of mean PFAS concentrations in the estuary compared to a previous study on samples collected in 2018. PFAA precursors, including N-ethyl perfluorooctane sulfonamide phosphate diesters, perfluorooctane sulfonamidoacetic acids, and polyfluoroalkyl phosphate diesters, were more frequently detected at estuarine outlets. C4−C6 short-chain perfluoroalkyl carboxylic acids and perfluorooctanoic acid emerged as the predominant oxidation products, with a different composition between estuarine outlet and coastal sediment samples. Multiple regions with occurrence of C6 electrochemical fluorination precursors were identified, and 6:2 fluorotelomer sulfonic acid was detected as an unexpected oxidation product near an airport, suggesting the potential contribution from aqueous film-forming foams. A substantial fraction of extractable organofluorine was not explained by targeted PFAS analysis, indicating the presence of unidentified fluorinated compounds in the investigated coastal sediments.