The overall goal of this project is to assess the transformation of polyfluorinated compounds at sites that have been historically impacted with aqueous film-forming foam (AFFF) to determine if they are a source for the long-term generation and release of perfluoroalkyl acids (PFAA). Coupling precursor transformation rates with transcriptomic analysis of source zones, this project will improve the predictive understanding of source strength for the development of conceptual site models (CSMs) at AFFF-impacted sites. Deconvoluting transformation reactions in terms of associated genes and microbial consortia with the goals of predicting transformation products from intermediates, determining how changes in conditions induce changes in transformation, and establishing treatment strategies will contribute to the predictive power of CSM. Predictive CSM will contribute to increased resource allocation efficiency when identifying mitigation strategies.

Laboratory and field data generated over the course of this project will be used to examine source strength at AFFF-impacted vadose zones. The project team hypothesizes that the maturity of AFFF-impacted sites has a significant impact on PFAA mass flux to underlying groundwater (source strength). The project team further hypothesizes that PFAA generation from source zones is reflective of the microbial consortia and expressed genes.

Five AFFF-impacted sites will be evaluated, with site selection based in part on site age (date of last AFFF release) and the type of AFFF (electrochemically derived versus fluorotelomer-based) used historically. Initial characterization efforts will focus on surface soils and shallow groundwater, where several per-and polyfluoroalkyl substance (PFAS) analytical tools (target and suspect analyses, total oxidizable precursor assay, total organic fluorine) and molecular tools will be applied. Batch systems will be used to directly measure polyfluorinated compound (precursor) biotransformation, determining the extent to which PFAA formation and release occurs in historically-impacted AFFF source areas. In situ microcosms will be strategically deployed based on batch system results. Metagenomic tools and PFAS analysis will be applied to in situ microcosms with the goal of providing mechanistic insight into the continued generation of PFAA in source zones. Considering the multiple end products and intermediates encountered in precursor biotransformation, direct measurement of rates may be challenging. However, quantifying changes in fluorine mass associated with PFAA in parallel with transcriptomic response overtime will provide excellent insight into source strength relative to various conditions.

This will be the first effort employing a coupled metatranscriptomic analysis with direct PFAS measurements to compare source zones actively generating PFAA versus those exhibiting attenuated PFAA emission. This project is expected to result in CSMs that are adapted to reflect AFFF source strength. Demonstrating how these source zones differ (or do not differ) with respect to PFAA release, site managers will have a data-driven basis on which to make decisions about site prioritization as well as mitigation strategies.

Since several studies have shown that a substantial fraction of the PFAS-related organofluorine is present as potential precursor compounds, evaluating the fate and transport of these precursor compounds in AFFF source areas is a high priority for overall site assessment. The dataset collected in this project will facilitate informed prioritization of AFFF-impacted sites, higher resolution CSM, and improved site management. Moreover, the molecular component of this work will provide mechanistic context to results, as opposed to limiting risk assessment decisions based on observational transformation data. Ancillary to the practical goal of providing better insight into the management of legacy versus nascent AFFF source zones, data collected over the course of the project will fill critical knowledge gaps in the understanding of biotransformation mechanisms underlying sustained PFAS release from AFFF source zones. (Anticipated Project Completion - 2025)