Biotransformation and Potential Mineralization of PFOS, PFHxS, and PFOA by Acidimicrobiaceae sp. A6 under Iron Reducing Conditions

Dr. Peter Jaffé | Princeton University

ER20-1219

Objective

This proof-of-concept project aims to improve the understanding of biodegradation processes carried out by an autotrophic bacterium (Acidimicrobiaceae sp. A6 [A6]) for degrading and potentially mineralizing per- and polyfluoroalkyl substances (PFAS) in an anoxic environment and propose pathways for this biotransformation/ mineralization process. The very promising initial data indicates defluorination of both polyfluoroalkyl substances and perfluoroalkyl acids (PFAAs), requires repetition via more comprehensive experimental work, with a critical review of the analytical evidence.

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Technical Approach

Incubations will be conducted in vials containing either perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), or perfluorohexane sulfonate (PFHxS), with pure cultures of A6 and A6 enrichment cultures. Incubations will be conducted with these cultures while oxidizing NH4+ and reducing Fe(III). The parent compound, potential degradation intermediates, as well as end products including F-, SO42- for PFOS and PFHxS, and acetate will be tracked over time. A6 numbers in both cultures and change in the microbial community of the enrichment culture will be tracked, as well as the expression of genes for key oxygenases and dehalogenases, that are thought to play a role in the degradation of these PFAS. Parallel controls that will include autoclaved samples with the PFAS, incubations with different Fe(III) reducers, controls with A6 or the enrichment culture but without NH4+ or Fe(III), and for comparison, positive A6 and enrichment culture controls (biologically active, with NH4+  and Fe(III) but without PFAS). Experiments will then be repeated over a range of concentrations to determine if there is a concentration effect in the degradation/mineralization of these compounds. The goal is to obtain, for each PFAS studied, a complete balance for C and F, plus S (for sulfonates) and to determine if they can be completely mineralized via the Feammox process or if stable intermediates do build up during the incubations. Genes for key enzymes associated with dehalogenation or the breaking of C-C bonds will be tracked to attempt linking the degradation/mineralization of these PFAS to the expression of the genes for these enzymes. Biotransformation/mineralization pathways will be proposed.

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Benefits

Preliminary results indicate that PFAS, including PFOA and PFOS, can be mineralized by A6 while oxidizing NH4+ and reducing Fe(III) (Feammox process). By conducting these experiments in a much more rigorous manner, and by stimulating the Feammox process so that ammonium oxidation stays active during the full incubation period, results will show that these PFAS can either be mineralized completely or that intermediates might build up. The Feammox process can be enhanced in constructed wetlands for the removal of NH4+ and in soil column experiments for the removal of TCE. Hence, demonstrating that this process can degrade and possibly mineralize PFOA, PFOS, and PFHxS will point to new in situ PFAS remediation technologies.

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Points of Contact

Principal Investigator

Dr. Peter Jaffé

Princeton University

Phone: 609-258-4653

Program Manager

Environmental Restoration

SERDP and ESTCP

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