Discerning the inefficacy of hydroxyl radicals during perfluorooctanoic acid degradation

Abstract Perfluorooctanoic acid (PFOA) is a recalcitrant contaminant of emerging concern, and there is growing interest in advanced oxidation processes to degrade it. However, there is ambiguity in the literature about the efficacy of hydroxyl radicals ( OH) for degrading PFOA. Here, we resolve this controversy by comparing PFOA degradation by UV photolysis (254 nm, 6 × 10−6 E/L.s) versus UV + H2O2, which produces OH. We optimized OH production in a UV + H2O2 system using nitrobenzene (NB) as a OH probe, but even under optimized conditions (i.e., 5 g/L H2O2), no significant difference occurred in PFOA removal by UV photolysis (21.1 ± 0.4%) versus UV + H2O2 (19.7 ± 0.7%) after 1-day treatment. Both treatments also resulted in similar daughter by-product concentrations and defluorination efficiencies (9.5 ± 1.7% for UV photolysis and 6.8 ± 1.0% for UV + H2O2), which indicates that OH is ineffective towards PFOA degradation and infers that other degradation mechanisms that are independent of OH production should be explored.