Environmental Sciences Seminar:
Reductive Defluorination of PFAS by Acidimicrobiaceae sp. A6 while Oxidizing Ammonium or Hydrogen under Iron Reducing Conditions
The oxidation of ammonium (NH4+) to nitrite (NO2–) under iron-reducing conditions is referred to as Feammox. The genome of an organism responsible for this process, Acidimicrobiaceae sp. A6 (referred to as A6), has been sequenced, and contains reductive dehalogenase-like genes (RDases). Hence, 100-day incubations were conducted with a series of PFAS over a concentration range from 0.1 mg/l to 100 mg/l, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Either NH4+ or hydrogen (H2) were used as the electron donor for A6 to reduce Fe(III) during these incubations. Results show that all of the PFAS examined, including perfluorinated compounds such as PFOA and PFOS were defluorinated with either electron donor. Independent of the initial concentration, after 100-day incubations ~ 60% of PFOA or PFOS was degraded during the incubations. Analyses of fluorinated intermediates, fluoride ions produced, as well as Fe(II) produced and NH4+ oxidized during these incubations, indicate that that the process is a reductive defluorination. Buildup of acetate, in combination with a carbon balance shows that at least a partial production of completely defluorinated degradation products did occur. RDases were not expressed when either NH4+ or H2 were oxidized under iron-reducing conditions in the absence of PFAS, but they were expressed in both the pure A6 culture and the A6 enrichment culture in incubations when PFAS were present and fluoride was produced. While incubations with the pure A6 culture produced little if any fluorinated compounds with shorter carbon chains, production of such intermediates was observed during incubations using the A6 enrichment culture, indicating that once A6 partially defluorinates these PFAS, other organisms present in the enrichment culture can then break the carbon-carbon bond. To our knowledge this is the first reported anaerobic mineralization of perfluorinated compounds such as PFOA and PFOS.