Photolysis of aqueous perfluorooctanoate and perfluorooctane sulfonate

Perfluorinated chemicals (PFCs), as represented by perfluorooctanoate (PFOA: C₇F₁₅CO₂^-) and perfluorooctane sulfonate (PFOS: C₈F₁₇SO₃ ^-) have been widely used and detected over the globe. Their chemical inertness makes them highly resistant toward not only conventional treatments but also advanced oxidation processes. In this study, the hydrated electron-mediated reductive degradation of PFOX (X = A for PFOA and S for PFOS) was explored in an aqueous humic acid solution in which UV light is irradiated to excite humic acid, thereby ejecting electrons to the aqueous PFOX. The PFOX degradation was monitored with MS/MS and was further confirmed by quantifying fluorides. The quantum yield for the PFOX degradation was estimated to be as low as 10^-4. The F-index, the degree of defluorination ([F ^-]_produced / [PFOX]_degraded), was 0.7 and 2.3 for PFOA and PFOS, respectively, indicating they were partially degraded. In addition, it was determined that an electron-donating ethylenediaminetetraacetic acid (EDTA) is essentially required to inhibit the recombination between the oxidized humic acid and the hydrated electron; yet it appears to interfere with the one-electron-reduced PFOX behavior at a different degree depending on the varying ionic headgroups (carboxylate vs. sulfonate).