The objective of this proof-of-concept project is to experimentally measure and validate several critical physical and chemical properties (i.e., acid-dissociation constant (pKa), aqueous solubility, and diffusion coefficients) for select per- and polyfluoroalkyl substances (PFAS) to improve the understanding of partitioning in the subsurface and subsequent fate and transport.

The objective of the project will be accomplished using nuclear magnetic resonance (NMR). NMR is advantageous due to its relative ease, speed, and little to no sample preparation. Oregon State University’s 800 MHz instrument provides structural, as well as quantitative, data for PFAS. The pKa values for a series of select PFAS will be determined by monitoring the chemical shift of fluorine on carbons bonded to ionizable head groups (e.g., carboxylate, sulfonate, sulfonamide acetic acids) as a function of pH from pH -1 to 11. As needed, pKa experiments for very acidic PFAS (e.g., pKa < 2) will be performed in varying levels of organic solvent in order to shift the pKa up into the pH range of -1 to 11 and then back-extrapolating to 0% organic solvent. Solubility experiments will be performed with neat solids using aqueous solutions at low and high ionic strength and a known pH (e.g., 7). Diffusion coefficients will be determined for PFAS that lack aqueous diffusion coefficients including substituted and unsubstituted sulfonamides, nonionic fluorotelomer alcohols, and zwitterionic PFAS.

The project will result in an extensive dataset of chemical properties for a homologous series of PFAS of varying headgroups and chain lengths. The pKa data will inform PFAS speciation as a function of pH, which determines many partitioning properties. Diffusion coefficients for low and high ionic strength will be useful for PFAS movement through sediments and to interfaces. The chemical properties data will be submitted into the PubChem database, ensuring accessibility and scalability of research findings. Successful completion of this effort will ultimately improve the cost effectiveness of PFAS treatment technologies, directly benefiting the warfighter and installation communities. (Anticipated Project Completion - 2027)