Aqueous film-forming foams (AFFF) are complex mixtures that have been used since the 1970s. Although critical in the minimization of life and fire losses, the widespread application of AFFF has resulted in an environmental legacy of highly persistent anthropogenic chemicals. Per- and polyfluoroalkyl substances (PFAS) have also found widespread applications in various industrial processes (e.g., papermaking, oil production, mining, metal plating) and consumer products (e.g., textiles, carpets, cosmetics, food contact materials), and have therefore been commonly detected in landfill leachate, wastewater treatment plant (WWTP) effluent, and many other sources. As non-DoD-sourced PFAS in impacted ground and surface water may become co-located with DoD-sourced PFAS plumes, there is a critical need for novel forensic approaches to aid in source allocation. Non-targeted high-resolution mass spectrometry methods are critical components of PFAS characterization. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has become the prime method for complex mixture analysis due to its unrivaled mass-resolving power, high mass accuracy, and dynamic range sufficient to resolve and assign elemental compositions to tens of thousands of compounds simultaneously. The overarching objective of this project is to develop and apply ultrahigh-resolution 21 tesla FT-ICR MS for the analysis of PFAS-impacted media.
This work is being conducted in two phases. The specific objectives of the Phase I work were (1) to develop an analytical workflow for collecting and processing FT-ICR mass spectra for PFAS in aqueous samples as well as (2) to develop data reduction and chemical profiling approaches that can be used for forensic purposes. Results from Phase I are documented in the Phase I Final Report.
The specific objectives of Phase II are as follows:
The work performed during Phase I of this project consisted of collecting groundwater, WWTP effluent, and AFFF samples at three U.S. DoD sites. The samples were liquid-liquid extracted and analyzed in negative electrospray ionization mode by ultrahigh-resolution FT-ICR MS on the world’s highest performing mass spectrometer (21 tesla) at the National High Magnetic Field Laboratory. A workflow was developed to assign elemental compositions for fluorinated compounds at four confidence levels. Data and dimensionality reduction techniques were used to characterize sample composition and to develop forensic analysis approaches.
In Phase II, the project team will parallelize the computational code for spectral processing developed in Phase I, refine the PFAS identification criteria, and expand the spectral processing workflow for the identification of cationic PFAS in positive electrospray ionization mode. Product-specific marker compounds that can be targeted for future source allocation purposes will be identified based on chemometric methods, and all markers will be characterized both chromatographically and structurally using tandem MSn. All identified PFAS species will be compiled in an open-source mass spectral library, which will serve as a molecular catalogue to accelerate future PFAS identification and AFFF fingerprinting activities. Finally, the project team will validate and optimize the detection of the identified source-specific PFAS marker compounds on several lower-resolution mass spectrometers. The data will be evaluated to identify suitable precursor and product ions for routine liquid chromatography – tandem mass spectrometry (LC-MS/MS) analysis.
In Phase I, the project team discovered 300 new PFAS species and 75 novel PFAS classes that were identified at <0.2 ppm mass error and based on being members of CF2 Kendrick mass defect (KMD) series. Thousands of additional PFAS were detected at varying confidence levels. The project team demonstrated how chemical profiling approaches reveal compositional differences between samples. The forensic analysis discriminated between different samples and sources based on compositional variability. The project team highlighted PFAS that are unique to specific sources. In Phase II the project team will verify whether these analytes can be used as source-specific marker compounds after future confirmation and validation on other mass spectrometric instruments.
21 tesla FT-ICR MS achieves the highest mass resolving power and mass accuracy currently possible, far surpassing time-of-flight and Orbitrap MS systems. The development of this analytical technique for complex PFAS analysis will provide a greatly augmented mass spectral PFAS library and open-source application for assigning elemental compositions to screening data from non-targeted high-resolution mass spectrometry, assisting both DoD remedial program managers and the scientific community in chemical profiling of environmental samples, plume dating, assessing the nature and extent of PFAS impacts, and evaluating complex subsurface fate and transport processes. Furthermore, an LC-MS/MS method for product-specific marker compounds will be developed that can be widely implemented by commercial laboratories to aid in PFAS source attribution and to determine the potential liability associated with past releases. (Anticipated Phase II Completion - 2026)
Sharifan, H., M. Bagheri, D. Wang, J.G. Burken, C.P. Higgins, Y. Liang, J. Liu, C.E. Schaefer, and J. Blotevogel. 2021. Fate and Transport of Per- and Polyfluoroalkyl Substances (PFASs) in the Vadose Zone. Science of the Total Environment, 771:145427. doi.org/10.1016/j.scitotenv.2021.145427.