Transformation products and reaction mechanisms of UV/sulfite remediation of PFOS, PFOA, PFBS, and GenX desorbed from carbon nanotubes

Abstract:

Per- and polyfluoroalkyl substances (PFAS) are highly persistent, bioaccumulative, and toxic contaminants that are ubiquitous at trace levels in many environmental matrices, including surface water and drinking water. Conventional water treatment strategies are ineffective against PFAS or are expensive, so novel remediation approaches are required. Reduction via the hydrated electron has been well-studied but is prohibitively slow and inhibited by interferences, since PFAS concentrations are low relative to the more reactive species in the matrix. Sorption of PFAS to activated carbon or anion exchange resins is another common remediation tactic. However, this is expensive and creates PFAS-laden sorbent that must still be dealt with.

To advance PFAS remediation approaches, we investigated the feasibility of combining sorption and reduction, in order to capitalize on the best attributes of each strategy. Solutions of four PFAS (PFOS, PFOA, PFBS, and GenX) were treated with hydrated electrons generated by UV photolysis of sulfite. Experiments were repeated both with and without sorption of PFAS to carbon nanotubes. The de/sorption could be controlled by changing the solution pH. Reduction only occurred when PFAS was not sorbed and this could be described using a combined kinetics sorption model. Liquid chromatography coupled to high-resolution mass-spectrometry was performed and a nontarget analysis approach was used to identify PFAS reductive transformation products. The effect of sorbent on the transformation products formed was also investigated. Novel cyclic perfluorosulfonate products not previously described in the PFAS-hydrated electron literature were detected. These findings present the opportunity to successfully concentrate PFAS from water through sorption, desorb it as a concentrate, and then employ reductive degradation.