Demonstrating the near-complete defluorination of individual PFAS and AFFF is the only evidence that can be used to confirm PFAS mineralization and mitigated risk. In this study, the PFAS destruction efficiency and degree of defluorination were based on the decay in PFAS concentrations and the quantitative yield of F -measured in extract solvents using both F -and total organic fluorine (TOF). The defluorination efficiency (DeF) was calculated as: