Innovative Sorbents for Stabilizing Per- and Polyfluoroalky Substances (PFAS) in Soil Contaminated by Aqueous Film-forming Foam (AFFF)

Project Summary/Abstract: Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals consisting of thousands of synthetic organic compounds in which the hydrogen atoms bound to the carbon backbones are fully or partially substituted with fluorine. Due to their widespread use, PFAS are detected ubiquitously. Owing to the nature of PFAS being persistent, bioaccumulative, and toxic, cleaning up PFAS contaminated environments has been an urgent task globally. While numerous technologies, for example chemical, biological, thermochemical, sonochemical, etc. have been studied and used for removing PFAS from contaminated environments, none of these are without any drawbacks. In many cases, the intentional remediation processes that are often cost- and/or energy intensive, lead to generation of un-desired degradation products and/or secondary contamination. To avoid these potential negative effects, stabilization that seeks to retain PFAS in its original environment for long-term has gained momentum in recent years. To promote the formation of bound residues (BR) between PFAS and soil, different sorbents have demonstrated different capabilities. Even the best sorbent on the market, however, is not able to bind PFAS stable enough to withstand extraction by basic methanol. Additionally, sorption of short-chain PFAS and precursors has been a huge challenge for all sorts of sorbents. We propose here to test our newly synthesized sorbents with respect to forming stable BR in the soil-sorbent-plant systems. Our preliminary studies have shown that the three top-performing sorbents have higher sorption capacity and faster rate than those commercially available. In this Phase I proposal, we plan to understand the leachability and bioavailability of three types of PFAS in the near real-world mesocosms. Besides mass balance of the PFAS, correlations between BR and other parameters, such as soil total organic carbon content, PFAS chain length and functional group, precursor transformation, and growth of and uptake of PFAS by alfalfa will be established. In addition to having a deep understanding of PFAS transformation, distribution, and stabilization in the target systems, we propose to elucidate the BR structure and dynamics at the atomic level. This will benefit from a combination of chemical analysis and 19F solid-state NMR. Insights gained from these deep studies will enable us to fully understand the mechanisms controlling binding between PFAS, soil, and sorbent; pinpoint the deciding factors and parameters contributing to the formation of the strongest possible BR; and guide us in designing and engineering the next generation sorbents. Success of this project will lead to a cost-effective, scalable, and green approach for remediating sites contaminated by PFAS, reveal the binding mechanisms underlying BR formation, and result in novel sorbents for not only stabilizing PFAS in soil, but also for removing PFAS from contaminated water and beyond.