The widespread use of aqueous film-forming foams (AFFF) for hydrocarbon fuel firefighting has created an environmental legacy throught the U.S. as per- and polyfluoroalkyl substances (PFAS) continue to cause sustained groundwater plume development. However, PFAS have been widely used in industrial and consumer products due to heat, oil and water resistance, and PFAS leaching from landfills, wastewater treatment plants (WWTP) and other sources may lead to co-located plume development. The overarching objective of this project was to apply ultrahigh-resolution Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) to identify compounds in AFFF at the molecular level that can be used to guide the development of novel analytical approaches to identify unique marker compounds for AFFF “fingerprinting” and PFAS source allocation, and catalogue PFAS associated with AFFF releases.
Groundwater, WWTP effluent, and AFFF samples were collected at three DoD sites. The samples were liquid-liquid extracted and analyzed 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 fingerprint the sample composition and to develop forensic analysis approaches.
First, 300 new PFAS species and 75 novel PFAS classes were discovered that were unambiguously 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. Second, the project team demonstrated how sample fingerprinting approaches reveal compositional differences between samples. Third, the forensic analysis was able to discriminate between different samples and sources based on compositional variability. Fourth, the project team highlighted PFAS that are unique to specific sources. These analytes can potentially be used as source-specific marker compounds after future confirmation and validation on other mass spectrometric instruments.
FT-ICR MS achieves the highest mass resolving power and mass accuracy, far surpassing quadrupole time-of-flight (QTOF) and Orbitrap MS systems, sufficient to identify and resolve PFAS compounds without prior chromatographic separation. Consequently, FT-ICR MS can reveal complex sample composition and molecular features that would remain unresolved on lower-performance instruments. This first-of-its-kind application of FT-ICR MS and the workflow developed here are a critical first step in cataloguing PFAS associated with AFFF and non-AFFF sources as well as in identifying unique marker compounds for fingerprinting that can be targeted in the future on more widely accessible mass spectrometric instruments. Ultimately, this information will provide critical guidance to DoD remedial program managers to (1) track transformation and retardation processes of AFFFs, (2) date plumes, (3) understand the extent of PFAS impact, and (4) to determine the potential liability associated with past releases.
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. https://doi.org/10.1016/j.scitotenv.2021.145427