Vitamin B12 (CoII) initiates the reductive defluorination of branched perfluorooctane sulfonate (br-PFOS) in the presence of sulfide

Abstract

Due to the extremely high stability of perfluorooctane sulfonate (PFOS), effective defluorination is difficult. Previous studies indicated that PFOS can be decomposed under the catalysis of vitamin B12 (VB12) with strong artificial reductants such as Ti(III)-citrate and nZn 0 . In this study, we explored if naturally occurring reductant like sulfide (S 2− ) could initiate the reaction. In S 2− /VB12 system, branched PFOS (br-PFOS) can undergo effective decomposition and defluorination at the temperature of 70 • C and pH greater than 12. The degradation of br-PFOS fits pseudo-first-order kinetic with a rate constant of 0.0984 ± 0.0034 d -1 in the presence of 30 mM Na 2 S and 300 μM VB12, while linear PFOS (L-PFOS) remained stable during 30 d reaction process. UV-Vis spectral characterization indicates that S 2− reduces VB12(Co III ) to Co II , which is able to initiate the reductive defluorination. Based on the product analysis, HF/2F elimination followed by C-C scission is the dominant degradation pathway of br-PFOS instead of stepwise H/F exchange. The primary products include F − and polyfluorinated sulfonates and carboxylates. The degradation of br-PFOS is strongly dependent on temperature due to a relatively high apparent activation energy of 62.86 kJ/mol. Strong alkaline condition can greatly enhance the decomposition efficiency since S 2− is the primary reactive form. This study provides new insights into the VB12-catalyzed defluorination of PFOS and a feasible approach for future natural or engineered remediations of br-PFOS.

Adsorption and Reductive Defluorination of Perfluorooctanoic Acid over Palladium Nanoparticles

“…Other destruction methods, such as sonication, plasma treatment, thermal treatment, and chemical oxidation, are able to break the C–F bonds, but they generally require high investment costs and a high requirement for energy, temperature, or pressure, and they often give rise to hazardous secondary pollution . Only a few studies reported the alternative reductive defluorination using chemical reducing agents like ZVI (zero-valent iron) or titanium­(III) citrate , for PFAS removal. These reductive methods are hindered by low efficiency or activity, secondary contaminants, and poorly understood mechanisms.…”

Bacterial transformation of per- and poly-fluoroalkyl substances: a review for the field of bioremediation

“…27 It is likely that a reduced corrinoid, specically B12, as well as a reducing agent, such as Ti(III) or HS − , are required during the reported enzymatic deuorination of branched poly-uorinated compounds. 131,132 The same enzymatic reactions do not deuorinate similar linear polyuorinated PFAS. 131,132 Overall, the enzymatic mechanism(s) of PFAS deuorination are not well understood and remain the subject of intense investigation.…”

“…131,132 The same enzymatic reactions do not deuorinate similar linear polyuorinated PFAS. 131,132 Overall, the enzymatic mechanism(s) of PFAS deuorination are not well understood and remain the subject of intense investigation. This research will likely determine the long-term potential for PFAS bioremediation.…”

Nothing lasts forever: understanding microbial biodegradation of polyfluorinated compounds and perfluorinated alkyl substances

“…Enzymes have been purified, structures determined, and reactions shown to be dependent on reduced low‐potential cobalt‐corrinoid cofactors (Neumann et al ., 1996 ; Kräutler et al ., 2003 ; Payne et al ., 2015 ). To this author’s knowledge, none of these well‐characterized dechlorinating and debrominating enzymes have been shown to catalyze reductive defluorination, but reduced corrinoids have been demonstrated to have defluorination activity with polyfluorinated compounds (Ochoa‐Herrera et al ., 2016 ; Liu et al ., 2018 , 2018 , 2018 , 2018 ; Sun et al ., 2021 ).…”