There are many materials laden with per- and polyfluoroalkyl substances (PFAS) that require treatment to reduce possible exposure risks. Thermal treatment approaches are widely utilized despite concerns regarding the fate of fluorine species produced during such treatment. The primary objectives of this project are to (1) investigate and improve low temperature thermal treatment approaches for PFAS and (2) develop and expand infrared (IR) spectroscopy approaches for quantifying the performance of thermal treatment with respect to off-gas characterization. This work will account for the fate of fluorine species including hydrogen fluoride and volatile organic fluorine species (VOF), and evaluate treatment additives that may improve low temperature thermal treatment. A vetted IR spectral library of relevant VOF species will be developed to help users assess thermal treatment efficacy, and state-of-the art IR analytical tools will be investigated for their ability to quantify low concentrations of VOF.

The objectives of this project will be achieved through a variety of laboratory experiments probing the thermal decomposition of PFAS with different headgroups, perfluoroalkyl chain length, and degree of fluorination. Further, experiments will evaluate candidate alkali and alkali earth metal amendments that have been shown in preliminary testing to enhance decomposition of PFAS. Experiments will also support the development of IR spectroscopic approaches for measuring VOF. In particular, IR reference spectra for a variety of relevant VOF will also be generated using well-vetted methodologies. The following technical tasks will be performed during the project:

• Task 1. Evaluate thermal decomposition of representative PFAS.
• Task 2. Evaluate alkali and alkali earth metal additives for enhancing decomposition.
• Task 3. Develop an IR spectral library of VOF gases related to PFAS decomposition.
• Task 4. Evaluate advanced IR detection and quantification methods for VOF.
• Task 5. Evaluate PFAS thermal decomposition under simulated field conditions.

A PFAS Spectral Library was constructed to provide quantitative infrared spectra of PFAS in the gas phase. This database supports PFAS investigations where gas-phase infrared signatures may be measured (e.g., during treatment by thermal decomposition). The database currently contains infrared spectra for 15 compounds; these were selected based on the potential of these compounds being thermal degradation products of manufactured chemicals. 

Additional compounds will be added to the database in the future. Additional information about the database may be obtained from Baker et al., 2023.

This project will provide the Department of Defense (DoD) with improved understanding of PFAS thermal decomposition processes, and improved tools for evaluating gaseous products of decomposition. Novel treatment additives that facilitate low temperature PFAS treatment will be evaluated and IR reference spectra of VOF will be measured and disseminated to the community. This effort will improve the DoD’s ability to manage PFAS-laden materials more cost-efficiently and sustainably, and will ultimately allow for better protection of human and ecological well-being while preserving our communal resources. (Anticipated Project Completion - 2024)

Baker, T.J., R.G. Tonkyn, C.J. Thompson, M.K. Dunlap, P.G. Koster van Groos, N.A. Thakur, M.J. Wilhelm, T.L. Myers, and T.J. Johnson. 2023. An Infrared Spectral Database for Gas-Phase Quantitation of Volatile Per- and Polyfluoroalkyl Substances (PFAS). Journal of Quantitative Spectroscopy and Radiative Transfer, 295: 108420. doi.org/10.1016/j.jqsrt.2022.108420.

Baker, T.J., R.G. Tonkyn, C.J. Thompson, T.L. Myers, and T.J. Johnson. 2023. SERDP & PNNL Database of Quantitative Infrared Spectra of PFAS in the Gas Phase. doi.org/10.25584/PNNLDH/1884308. 

Thompson C.J., N.B. Gallagher, K.D. Hughey, M.K. Dunlap, T.L Myers and T.J. Johnson. 2023. An Interactive Spectral Analysis Tool for Chemical Identification and Quantification of Gas-Phase Species in Complex Spectra. Applied Spectroscopy, 77(6): 557-568. doi.org/10.1177/00037028231169304.

Wilhelm M.J., T.J. Johnson, and T.L Myers. 2023. Disentangling the Confounding Spectroscopy of C1 Molecules: Without Symmetry as a Guide, Everything is Allowed. AIP Advances, 13(3): 055133. doi.org/10.1063/5.0155054.

Zhao, Y., P.G. Koster van Groos, N. Thakur, M.E. Fuller, A. Soto, and P.B. Hatzinger. 2024. Formation of Volatile Chlorinated and Brominated Products During Low Temperature Thermal Decomposition of the Representative PFAS Perfluorohexanesulfonate (PFHxS) in the Presence of NaCl and NaBr. Environmental Pollution, 348:123782. doi.org/10.1016/j.envpol.2024.123782.