Rapid quantitative analysis and suspect screening of per-and polyfluorinated alkyl substances (PFASs) in aqueous film-forming foams (AFFFs) and municipal wastewater samples by Nano-ESI-HRMS

Abstract

A rapid analytical method for per- and polyfluoroalkyl substances (PFASs) combining nano-electrospray ionization and high-resolution mass spectrometry (Nano-ESI-HRMS) was developed and applied to aqueous film-forming foams (AFFFs) and wastewater samples collected from three local wastewater treatment plants (WWTPs). This method exhibited high sensitivity with lower limits of detection (LODs) of 3.2∼36.2 ng/L for 22 target PFAS analytes. In AFFF formulations, Nano-ESI-HRMS enabled the first-time detection of trifluoromethanesulfonic acid (TFMS), perfluoroethyl cyclohexanesulfonate (PFECHS), 6:2 fluorotelomer sulfonyl amido sulfonic acid (6:2 FTSAS-SO2), N-ammoniopropyl perfluoroalkanesulfonamidopropylsulfonate (N-AmP-FASAPS, n = 3–6), ketone-perfluorooctanesulfonic acid (Keto-PFOS), fluorotelomer unsaturated amide sulfonic acid (FTUAmS, n = 7), and 6:2 fluorotelomer amide (6:2 FTAm). Their structures were verified by the tandem MS analysis using collision-induced dissociation. Further, the combination of absolute and semi-quantification results revealed 16 PFASs from 9 PFAS classes as dominant AFFF constituents, accounting for 88.2∼96.5% of the total detected anionic and zwitterionic PFASs, including perfluorinated sulfonic acids (PFSAs, n = 1,4∼8), 6:2 fluorotelomer sulfonates (6:2 FTS), fluorotelomer thioether amido sulfonic acid (FTSAS, n = 6,8), fluorotelomer sulfinyl amido sulfonic acid (FTSAS-SO, n = 6,8), N-AmP-FASAPS (n = 6), 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB), perfluoroalkylsulfonamido amino carboxylate (PFASAC, n = 6), 2-((perfluorooctyl)thio)acetatic acid (Thio-8:2 FTCA), and 6:2 FTAm. At WWTPs, aerobic and anaerobic biotransformation of PFAS precursors at the aeration tanks and secondary clarifiers were evident by the generation of mid/short-chain perfluoroalkyl acids, such as perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluoropentanoic acid (PFPeA), as well as the emergence of ultrashort trifluoroacetic acid (TFA) and TFMS and several novel fluorotelomer carboxylic acids (FTCAs). Overall, Nano-ESI-HRMS enabled comprehensive PFAS quantitative analysis and suspect screening, applicable for rapid investigation and assessment of PFAS-related exposure and treatment in environmental matrixes. Our results also revealed that AFFFs and municipal wastewaters are two key sources contributing to the prevalent detection of ultrashort-chain PFASs (e.g., TFMS and TFA) in water.