PFAS are present in AFFF used by the DoD and other organizations to extinguish hydrocarbon fires. Different AFFF formulations have been used, but all contain a complex mixture of PFAS, including those of greatest regulatory concern - the PFAAs and potential PFAA precursors (Field et al., 2017; ITRC, 2017). EPA has recommended a Health Advisory Level for perfluorooctanoic acid (PFOA) and PFOS, and several states have promulgated standards for PFOA, PFOS, and some of the related PFAAs (ITRC, 2018a).
SERDP has been funding research on AFFF contamination for several years to improve PFAS analysis, to develop tools for assessing the fate of PFAS in the subsurface, and to evaluate the potential for in situ remediation. A recent SERDP & ESTCP-sponsored workshop identified a number of research needs, and proposers should view the Workshop Report to obtain additional detail concerning these discussions. PFOS is of particular concern to DoD, as it is the predominant PFAS in some AFFF formulations, and a significant dead-end metabolite in others, and therefore it is typically the predominant PFAS in AFFF-impacted groundwaters (Anderson et al., 2016). PFOS appears to be particularly resistant to destructive technologies, and like the rest of the PFAAs it is generally considered nonbiodegradable (ITRC, 2018b).
Previous work has shown that several PFAS can be partially biodegraded to PFAAs under aerobic conditions, but complete biodegradation of PFAAs has not been demonstrated (e.g., Harding‐ Marjanovic et al., 2015; Liu and Mejia-Avendaño, 2013). Partial biodegradation of precursors has been observed under anaerobic conditions as well, but again, the PFAAs appear to be recalcitrant (Hamid et al., 2018).
Nevertheless, there is significant interest in the potential for biodegradation to reduce the risks posed by PFAS present in AFFF formulations, and there have been some studies suggesting biological defluorination could occur (e.g., Kwon et al., 2014). SERDP has funded prior work demonstrating that PFAA precursors were transformed to PFAAs, and confirming that PFAAs are recalcitrant under typical environmental conditions (ER-2128). Fungal biodegradation of PFAS was evaluated in project ER-2422, and enzyme-catalyzed reactions were tested as part of a possible permeable reactive barrier in ER-2127. Ongoing SERDP projects are further exploring the potential use of fungi (ER-2718), and evaluating the feasibility of combining in situ chemical oxidation (ISCO) and bioremediation to treat AFFF and its common co-contaminants (ER-2715).