The control test using SiO2 as the only co-milling reagent to treat 200 μL AFFF shows that the target PFAS concentrations increased after BM treatment (Figure ). This result implies that the SiO2-BM can only break down precursors to target PFAS, while further mineralization was nonexistent or very slow. Consequently, the defluorination was insignificant (DeF < 10%; Figure ).