Simultaneous Analysis of Ultrashort- to Long-Chain PFAS in Multisalinity Aquatic Systems: Methodology, Spatial Profiling, and Risk Prioritization

Ultrashort-chain per- and polyfluoroalkyl substances (PFAS) have attracted increasing attention due to their rising concentrations and high mobility in environmental contexts, yet their incorporation into routine multianalyte workflows remains challenging. This study established a multidimensional liquid chromatography-tandem mass spectrometry platform for the simultaneous quantification of 60 PFAS spanning ultrashort- to long-chain homologues. Large-volume direct injection achieved satisfactory limits of quantification (≤1 ng/L) for most PFAS, without complex sample pretreatment. The method was applied to surface waters across a freshwater-marine salinity gradient from the Xiaoqing River and Laizhou Bay during two sampling campaigns in 2023 and 2024. Trifluoroacetic acid (TFA) dominated the PFAS profile, accounting for 87-99% of total PFAS (∑₆₀PFAS), with a maximum concentration of 1 467 000 ng/L. In 2024, median concentrations of TFA and most PFAS decreased by 33-78% downstream of a fluorochemical industrial park, whereas perfluoro-2,5-dimethyl-3,6-dioxo-heptanoic acid (C7 HFPO-TA) increased by 170%. An environmental hazard prioritization index (EHPI) based on persistence, mobility, bioaccumulation, ecotoxicity, and human health hazards was applied to the 60 target PFAS using in-house and open-source predictive models, yielding a prioritized pollutant ranking in Laizhou Bay. TFA and C7 HFPO-TA emerged as the highest-priority chemicals, indicating an urgent need for strengthened monitoring and regulatory management.