The repeated historic use of aqueous film-forming foam (AFFF) in firefighting has resulted in impacted groundwater at many sites throughout the country. Further, per- and polyfluoroalkyl substances (PFAS) are often commingled with hydrocarbons and solvents. This integrated experimental and modeling research was designed to address the data gaps associated with the processes that control the transport (e.g., sorption, interphase partitioning, interfacial accumulation) and aerobic/anaerobic transformation of PFAS in natural subsurface environments. In addition, an additional goal of this project was to develop models and decision tools that could aid site managers in the assessment of PFAS mobility and persistence in complex AFFF source areas.  

A matrix of experiments of increasing scale and complexity was undertaken with individual PFAS and mixtures, employing reference media and natural aquifer materials collected from PFAS-impacted sites. Experiments encompassed air-water and nonaqueous phase liquid (NAPL)-water interfacial tension and soil sorption measurements, biotransformation microcosm experiments for selected PFAS precursors, and single and multiphase column transport experiments. These experiments supported the development and calibration/validation of mathematical modeling tools, which were then used to explore potential PFAS transport and fate under representative field conditions and to formulate a decision matrix for use by site managers.

Research findings revealed that PFAS migration is greatly influenced by interfacial processes. Air-water interfacial accumulation was shown to: (1) be a strong function of ionic strength; (2) lead to substantial mass retention in unsaturated soils; and (3) be a nonlinear function of concentration, with a limiting capacity at higher concentrations. Under conditions consistent with AFFF releases, competitive sorption effects were found to be pronounced, with more surface-active PFAS enhancing the transport of other PFAS. At AFFF field application levels, spill conditions were shown to have a strong influence on PFAS mobility and mass fluxes at the water table and to have the potential to reduce soil moisture and mobilize entrapped NAPLs.

The biotransformation of three PFAS precursors, perfluoro-1-octanesulfonamide (FOSA), 8:2 fluorotelomer alcohol (8:2 FTOH), and 6:2 fluorotelomer sulfonic acid (FTS), also constituents of a legacy AFFF, was explored. The extent and rate of biotransformation of FOSA and 6:2 FTS were found to be strongly influenced by environmental factors, such as soil sorption capacity, availability of sulfur sources, and native microbial community composition. 8:2 FTOH was transformed rapidly by indigenous microbial communities from AFFF-impacted surface soils under aerobic conditions, and its biotransformation rates and pathways were found to be highly dependent upon redox conditions. Sixteen classes of PFAS in a historically used 3M AFFF formulation were identified, and multiple classes of electrochemical fluorination (ECF)-based precursors and a wide range of homologues were demonstrated to be transformed under biotic and/or abiotic conditions.

This research has improved our understanding of interfacial retention mechanisms of PFAS and supported the development/validation of mathematical models for prediction of PFAS transport at AFFF-impacted sites. Representative model applications led to development of a meta-analysis table for use by practitioners that depicts the extent of correlation of important transport metrics with AFFF release parameters and site conditions. This project also improved the understanding of the potential for biotransformation of fluorotelomerization (FT)- and ECF-based precursors in AFFF-impacted soils under various environmental conditions. Results provide insight into the structure-relevant stability of PFAS and a starting point for screening microbes and functional genes engaged in PFAS biotransformation. (Project Completion - 2023)

Arshadi, M., J. Costanza, L. M. Abriola, and K. D. Pennell. 2020. Comment on “Uptake of Poly- and Perfluoroalkyl Substances at the Air−Water Interface” by Schaefer et al. (2019), Environmental Science & Technology, https://dx.doi.org/10.1021/acs.est.0c01838   

Costanza, J., M. Arshadi, L. M. Abriola, and K. D. Pennell. 2019. Accumulation of PFOA and PFOS at the Air-Water Interface. Environ Sci and Technol Letters, 6(8): 487-491. https://pubs.acs.org/doi/full/10.1021/acs.estlett.9b00355.

Costanza, J., L. M. Abriola, and K. D. Pennell. 2020.  Aqueous Film-Forming Foams Exhibit Greater Interfacial Activity than PFOA, PFOS, or FOSA. Environmental Science & Technology, 54(21):13590-13597. https://doi.org/10.1021/acs.est.0c03117

Liao, S., Z. Saleeba, J. D. Bryant, L. M. Abriola, and K. D. Pennell. 2021. Influence of Aqueous Film Forming Foams on the Solubility and Mobilization of Non-Aqueous Phase Liquid Contaminants in Quartz Sands. Water Research, 195(116975). https://doi.org/10.1016/j.watres.2021.116975