Nontarget\nAnalysis Combined with TOP Assay Reveals\na Significant Portion of Unknown PFAS Precursors in Firefighting Foams\nCurrently Used in China

Firefighting\nfoam is a significant source of per- and polyfluoroalkyl\nsubstances (PFAS) pollution, yet the PFAS profiles in foam formulations,\nparticularly in China, remain unclear. Here, using target and nontarget\nanalyses, we investigated 50 target PFAS in firefighting foams currently\nutilized in China, identified novel PFAS, and discovered new end products\nthrough a total oxidizable precursor (TOP) assay. We identified a\ntotal of 54 PFAS compounds (spanning 34 classes and containing seven\nnovel PFAS) with total PFAS concentrations of 0.03–21.21 mM.\nAmong seven novel PFAS, four PFAS met persistence, bioaccumulation,\nand toxicity criteria, and another PFAS had the highest ToxPi score\namong the identified 54 PFAS. Moreover, the predominant PFAS varied\nsignificantly in the studied foams and differed markedly from those\nused in other countries. After the TOP assay, nontarget analysis uncovered\n1.1–55.5% more PFAS precursors and 8.25–55.5% more fluorine\nequivalents compared to traditional target analysis combined with\nTOP assay. Specifically, three double-bond perfluorinated alcohols\nwere identified for the first time as end products of the TOP assay.\nThis study provides crucial information for pollution control and\nrisk assessment associated with PFAS in firefighting foam applications\nand emphasizes the importance of combining nontarget analysis with\nTOP assay in uncovering unknown PFAS precursors.