Novel per- and polyfluoroalkyl substances in an active-use C6-based aqueous film forming foam

Studies have identified hundreds of per- and polyfluoroalkyl substances (PFAS) in aqueous film forming foam (AFFF) using high resolution mass spectrometry (HRMS), and there is increasing reliance on HRMS with suspect screening in areas such as PFAS fate and transport. Characterization of active-use AFFF formulations is crucial for maintaining representative lists of PFAS for such efforts. Herein, targeted analysis, total oxidizable precursor assay (TOP), suspect screening, and non-targeted analysis were used to characterize PFAS in an AFFF currently certified for use by the U.S. military. The sum of PFAS identified during targeted analysis and suspect screening was compared to TOP, demonstrating that > 90% (20.2 mM) of the estimated total PFAS concentration (22.4 mM) was comprised of ''unknown'' PFAS. Tandem and multi-stage tandem mass spectra were used to annotate 10 PFAS within 9 classes, 8 of which have never been reported. A subset are fluorotelomer-based isomers of legacy, electrochemically synthesized PFAS. Thus, suspect screening efforts that rely solely on accurate mass matching may mis-annotate PFAS presented here as isomers that will have key differences in properties such as biotransformation pathways. The total estimated concentration of the 10 PFAS was ~20 mM, which agrees with the ''unknown'' fraction (20.2 mM) identified by TOP.