We highlight the importance of exploring the transformation mechanisms and pathways for oxidizable PFAS molecules. The detection of TFA as the only PFCA product from Nafionrelated PFESAs is a novel example. The H-CF(CF3)-O-or -OOC-CF(CF3)-O-are oxidized and then transformed into CF3-C(O)-O-(Scheme 1), which further hydrolyzes to yield TFA. Previous studies also identified other PFAS transformation patterns under HO• oxidation, such as the exclusive formation of C7F15-COO -from C8F17-SO2NH2 and the dominating formation of - OOC-Cn-1F2n-2-COO -from H-CF2-Cn-1F2n-2-COO -(Figure ). We recommend (i) pretreating the samples with both SO4 -• or HO• before target PFAS analysis, (ii) adding more known structures (e.g., -OOC-CnF2n-COO -, ether carboxylates/sulfonates, and other commercially available PFAS chemicals) to the target list of TOP assay, (iii) using advanced mass spectrometry methodologies, data processing algorithms, and additional spectroscopy methods (e.g., F NMR) to assist structural determination, and (iv) modifying the existing methodologies with new structural transformation mechanisms. In order to satisfy the imminent need for the detection, monitoring, and treatment of "non-legacy" PFAS pollutants, it is imperative to expand our understanding of structure-transformation relationships for emerging PFAS chemicals. The elucidation of additional transformation pathways for SO4 -• oxidation is equally important and intriguing to environmental chemists. The currently unknown SO4 -• oxidation TPs might soon become the "signature" of certain PFAS pollutants. Lastly, PFAS analytical works have not adopted the widely used acidic persulfate digestion for environmental samples. We expect this report to trigger interest in testing SO4 -• oxidation (simply adjust the S2O8 2-solution pH to 2.0 and run a few additional LC-MS samples) in specific PFAS analytical scenarios to obtain more critical information on pollutant structures and profiles.