b Including both oxidation-released F -and all C-F bonds in the remaining parent PFAS and targeted TPs. A significant gap from 100% suggests the formation of unknown TPs. Second, for the -COO -containing PFESA structures without a C-H bond, the degradation became more difficult. The ratios of [S2O8 2-]:[NBP-COOH] and [S2O8 2-]:[TP1] needed to be 200:1 to achieve >95% degradation of the parent structures. In particular, the degradation of NBP-COOH and NBP-H by SO4 -• only differed in the first step (i.e., decarboxylation versus Habstraction, Scheme 1b), but the defluorination from NBP-COOH with all S2O8 2-doses were lower than from NBP-H (Table , zone C versus B). TP1 from NBP-COOH or as the starting material (Table , zone D) also showed higher recalcitrance than from NBP-H.