Perfluorooctanoic acid Degradation by UV/Chlorine

While per- and polyfluoroalkyl substances (PFAS) are recalcitrant to chemical reactions traditionally used in water treatment, we report the novel finding that combining ultraviolet (UV, 254 nm) light and chlorine can promote perfluorooctanoic acid (PFOA) degradation. About 12% removal of 100 μg/L PFOA was observed after 30 min of irradiation (6.5 × 10^–6 Einstein L^–1 s^–1) in the presence of 1.4 mM (106 mg/L) NaOCl, compared to only 1% removal by UV photolysis and no removal by NaOCl alone. UV/chlorine with 0.02 mM NaOCl (1.5 mg/L, a more common dose for water treatment) removed 6 μg/L PFOA within 30 min. To better detect defluorination, 50 mg/L PFOA was used, and UV/chlorine released significantly more fluoride (382 μg/L) than UV photolysis (0 μg/L) and dark controls (0 μg/L) over 30 min. By 60 min, this represents 32% of the maximum possible defluorination for the amount of PFOA removed by UV/chlorine versus 2% for UV photolysis. Radical scavenger tests indicated that Cl^• and Cl₂^•– play a crucial role in PFOA degradation, which we postulate is initiated by electron abstraction leading to a decarboxylation–hydroxylation–elimination–hydrolysis pathway. Whereas reaction rates were relatively slow for practical application in water treatment plants, these results underscore overlooked reactions with common water treatment constituents that may influence the fate of PFAS.