Discerning the Relevance of Superoxide in PFOA Degradation

Perfluorooctanoic acid (PFOA) is a widely distributed recalcitrant contaminant. In recent years, advanced oxidation processes have been explored for PFOA degradation, yet factors influencing their efficacy and degradation mechanism are not fully understood. Here, we resolve ambiguity in the literature regarding the role of superoxide in PFOA degradation (e.g., by nucleophilic attack) by considering three pure superoxide-producing systems: KO 2 in dimethyl sulfoxide, xanthine oxidase with hypoxanthine, and WO x /ZrO 2 catalyst with H 2 O 2 . Superoxide production was confirmed in all systems by electron paramagnetic resonance spectroscopy and by precipitation of nitroblue tetrazolium, a common superoxide probe. Positive control experiments showed that the produced superoxide degrades ∼48% of bisphenol A within 1 day, corroborating the fact that superoxide was sufficiently stable and available for reaction in the test systems. However, no PFOA degradation was observed, which was corroborated by the absence of fluoride and degradation byproducts in all three systems. Therefore, other reaction pathways should be explored for PFOA degradation.