A unique characteristic of sites impacted by aqueous film-forming foam (AFFF) is that they almost exclusively arise from above-ground releases. Consequently, AFFF constituents almost always undergo significant interaction with soil in the vadose zone long before reaching groundwater. Several studies have shown that the vast majority of the mass of per- and polyfluoroalkyl substances (PFAS) derived from AFFF releases is trapped in the first few feet of the vadose zone, making the vadose zone a potential long-term reservoir of chemicals to groundwater. This shallow soil horizon generally facilitates aerobic biological processes, including the transformation of many polyfluoroalkyl compounds like fluorotelomer alcohols (“precursors”) into perfluoroalkyl acids (PFAAs). Therefore, an improved understanding of biotransformation processes that occur naturally and can be stimulated and optimized under the conditions that exist in these vadose zone PFAS mass reservoirs is a critical step to developing cost-effective management strategies for AFFF-impacted sites.
While several investigators are studying potential bacterial degradation of precursors from AFFF, many of these pathways occur anaerobically due to the oxidized nature of many PFAS. Bacterial reductive dehalogenation (including defluorination) is inherently an anaerobic process when the halogenated compound serves as an electron acceptor in metabolism. In contrast, previous work by the Mahendra group at the University of California, Los Angeles has successfully revealed the unique and largely untapped potential of fungi to degrade and defluorinate precursors (and potentially PFAAs) even under aerobic conditions, circumventing the generation of dead-end PFAA metabolites. Building on these promising findings, this project aims to systematically characterize the degradation of PFAA precursors through 1) determining fungal degradation potential, 2) identifying environmental conditions favorable to high performance, and 3) characterizing fungal metabolic pathways that biotransform precursors without the accumulation of PFAAs.
This project will result in foundational knowledge on key fungal taxa, metabolic pathways, and transformation rates for PFAA precursor degradation. Furthermore, the project team expects to determine the environmental conditions conducive for preventing the transformation of precursors into terminal PFAA. These data will also serve as a useful input into conceptual site models to predict the fate and transport of these chemicals, and help inform risk assessments and site management decisions. This project will ultimately lead to the application of fungi in field trials to degrade PFAA precursors within soil at AFFF-impacted sites. Cost effective biodegradation solutions are paramount to address environmental management of PFAS-impacted sites. (Anticipated Project Completion - 2025)