The objective of this project is to assess the fate of per-and polyfluoroalkyl substances (PFAS) after their release to soil and sediments in locations where aqueous film-forming foam (AFFF) has been released. Specifically, this project aims to provide a better understanding of the sorption and subsequent biotransformation and release of cationic, zwitterionic, and neutral PFAS from source zones under environmentally relevant conditions. The project team hypothesizes that biotransformation of these polyfluorinated compounds, which are often referred to as perfluoroalkyl acids (PFAAs) precursors, will result in the release of more mobile anionic PFAS species, including PFAAs. The project team also hypothesizes that the physicochemical properties of the soil and sediments, as well as the redox conditions of the source zone, will affect relative rates of chemical release.

To provide mechanistic insight into the effects of surfaces, water composition, and redox conditions on relative rates of biotransformation and chemical release from source zones, the project team will study the release of representative precursors in AFFF that are well retained by soils. After these compounds are adsorbed onto well-characterized solids, they will be incubated in microcosms with different terminal electron acceptors (i.e., oxygen, ferric iron, sulfate). Rates of conversion of precursors to mobile species including perfluoroalkyl sulfonates, carboxylates, and negatively charged polyfluorinated alkyl substances will be measured under different conditions (e.g., varying pH, salinity, organic carbon content) comparable to those likely to be encountered in source zones. Transformation products identified in aerobic and anaerobic microcosm experiments will be compared to those detected in samples from source zones where AFFF has been released. Lastly, the project team will investigate biomarkers indicative of precursor biotransformation or toxicity to provide a better means of determining when precursor biotransformation and mobile chemical release are likely to occur.

Long-term release of PFAS and mobile precursors from source zones represents a significant challenge for site managers attempting to protect impacted aquifers. The potential for biotransformation of precursor compounds to release mobile PFAS has yet to be thoroughly investigated. Therefore, results from this research will support the development of effective strategies for managing precursors and prioritizing locations where additional remediation may be necessary. By developing an understanding of the impact of soil type, water chemistry, and redox conditions on the biotransformation of AFFF precursors, the project team will advance fundamental knowledge about the factors controlling these processes, enabling site managers to predict environmental fate and identify strategies for minimizing future chemical releases. (Anticipated Project Completion - 2027)