Formatted Title:

Potential for PFOA Defluorination in River Sediments Undergoing the Feammox Process

Background/Objectives:

Acidimicrobium sp. Strain A6 (A6 for short) is an autotropic bacterium that uses ammonium (NH₄⁺) as an electron donor and ferric iron [Fe(III)] as an electron acceptor¹ in a process that is commonly referred to as Feammox. A6 has been shown to be common in iron-rich, acidic sediments², including the Neuse River, North Carolina³. The Neuse River is acidic, iron rich, and has a high ammonium load due to the presence of many concentrated animal feeding operations (CAFOs) in its watershed, and the presence of A6 and oxidation of ammonium by this organism in its sediments has been reported previously³. A6 has also been shown to defluorinate PFAS, including perfluoro alkyl acids (PFAAs) such as PFOA and PFOS^4,5. Hence, the objective of this research was to determine, via laboratory incubations, if there is a potential for PFAA degradation in selected Neuse River sediments under natural and stimulated conditions.

Approach/Activities:

Incubations were performed on sediments of the Neuse River described previously, and for which the presence and Feammox activity of A6 was demonstrated³ and for which A6 was detected in relatively high numbers. Two incubation experiments were completed. First, three-month incubations were completed with Neuse River sediments and Feammox medium, either with or without amended PFOA (100 ppm). The objective of the PFOA ammendment was to more easily track decreases in its concentration as well as the possible production of fluoride. Incubations were also conducted without amending sediments with PFOA, which was detected at low concentrations in these sediments. This was done to assess the potential for defluorination in these sediments under environmentally relevant concentrations, and also to assess the effect of electron donor and/or electron acceptor amendment (e.g., addition of Fe(III), NH₄⁺, or both to support Feammox activity).

Results/Lessons Learned:

Results of the incubations described above reveal evidence that PFAAs such as PFOA might be defluorinated in sediments of the Neuse River where A6 is actively catalyzing the Feammox reaction. In the three-month incubations amended with 100 ppm of PFOA, approximately 20% of the PFOA was removed, accompanied by an increase in fluoride and the production of shorter carbon chain PFAAs. No fluoride buildup nor the presence of the shorter carbon chain PFAAs was detected in the non-amended controls. Oxidation of NH₄⁺and Fe(III) reduction provided evidence of active Feammox. For the incubations with environmentally relevant PFOA concentrations, degradation was evinced by fluoride production and PFOA decrease. Feammox activity was observed and measured via NH₄⁺oxidation. Collectively, these results suggest PFOA may be defluorinated in Neuse River sediment incubations containing A6 with concentrated PFOA (100 ppm) and at environmentally occuring concentrations.

References

(1) Huang, S., and P.R. Jaffé, https://doi.org/10.1371/journal.pone.0194007.

(2) Huang, S., et al., doi: 10.1016/j.soilbio.2016.04.012.

(3) Sherman, A., et al., https://doi.org/10.1007/s10533-023-01062-7.

(4) Huang, S., and P.R. Jaffé, http://dx.doi.org/10.1021/acs.est.9b04047.

(5) Jaffé, P.R., et al., https://doi.org/10.1016/bs.mie.2024.01.013.

Ariana Sherman

Affiliation

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Potential for PFOA Defluorination in River Sediments Undergoing the Feammox Process