PFAS Analysis with Ultrahigh Resolution 21T FT-ICR MS: Suspect and Nontargeted Screening with Unrivaled Mass Resolving Power and Accuracy.

Per- and polyfluoroalkyl substances (PFASs) are a large family of thousands of chemicals, many of which have been identified using nontargeted time-of-flight and Orbitrap mass spectrometry methods. Comprehensive characterization of complex PFAS mixtures is critical to assess their environmental transport, transformation, exposure, and uptake. Because 21 tesla (T) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers the highest available mass resolving power and sub-ppm mass errors across a wide molecular weight range, we developed a nontargeted 21 T FT-ICR MS method to screen for PFASs in an aqueous film-forming foam (AFFF) using suspect screening, a targeted formula database (C, H, Cl, F, N, O, P, S; ≤865 Da), isotopologues, and Kendrick-analogous mass difference networks (KAMDNs). False-positive PFAS identifications in a natural organic matter (NOM) sample, which served as the negative control, suggested that a minimum length of 3 should be imposed when annotating CF2-homologous series with positive mass defects. We putatively identified 163 known PFASs during suspect screening, as well as 134 novel PFASs during nontargeted screening, including a suspected polyethoxylated perfluoroalkane sulfonamide series. This study shows that 21 T FT-ICR MS analysis can provide unique insights into complex PFAS composition and expand our understanding of PFAS chemistries in impacted matrices.

Spatial Trends of Anionic, Zwitterionic, and Cationic PFASs at an AFFF-Impacted Site.

Soil and groundwater from an aqueous film-forming foam (AFFF)-impacted site were sampled at high resolution (n = 105 for soil, n = 58 for groundwater) and analyzed for an extensive list of anionic, zwitterionic, and cationic poly- and perfluoroalkyl substances (PFASs). Spatial trends for perfluoroalkyl acids and many precursors enabled a better understanding of PFAS composition, transport, and transformation. All PFASs without analytical standards were semi-quantified. Summed PFAS and individual PFAS concentrations were often higher at depth than near the surface in soil and groundwater. Zwitterionic and cationic compounds composed a majority of the total PFAS mass (up to 97%) in firefighter training area (FTA) soil. Composition of PFAS class, chain length, and structural isomers changed with depth and distance from the FTA, suggesting in situ transformation and differential transport. The percentage of branched perfluorooctane sulfonate increased with depth, consistent with differential isomeric transport. However, linear perfluorooctanoic acid (PFOA) was enriched, suggesting fluorotelomer precursor transformation to linear PFOA. Perfluorohexane sulfonamide, a potential transformation product of sulfonamide-based PFASs, was present at high concentrations (maximum 448 ng/g in soil, 3.4 mg/L in groundwater). Precursor compounds may create long-term sources of perfluoroalkyl acids, although many pathways remain unknown; precursor analysis is critical for PFAS fate and transport understanding.

Evaluation of a drop-in waste volume reduction method for liquid investigation derived waste containing per- and polyfluoroalkyl substances.

Development of on-site treatment strategies for PFAS-containing investigation derived waste (IDW) will decrease the potential for secondary release following off-site disposal, lower disposal costs, and promote more effective long-term management of PFAS-laden waste. Herein, we report the application of a simple, drop-in treatment that utilizes one of two PFAS sorbents: bituminous granular activated carbon (GAC) or strong base anion exchange resin (IX) and a small circulation pump to adsorb and concentrate PFAS impacted mass from liquid IDW collected from two sites with disparate water chemistries and synthetic IDW amended with PFAS-containing aqueous film forming foam (AFFF). Bench scale intermittent circulation experiments revealed that bituminous granular activated carbon (GAC, 0.5 mg/mL) removed up to 97.0 ± 1.4% and 96.4 ± 0.5% of PFOS and PFOA, respectively, in both site-derived IDW sources. Improved performance was observed in experimental treatments containing a strong base anion exchange resin (IX, 0.5 mg/mL), where up to 99.4 ± 0.1% and 96.7 ± 0.2% of PFOS and PFOA were removed, respectively. High chloride concentrations (20 g/L) reduced removal of short chain perfluorocarboxylates (PFBA and PFHxA) using GAC or IX, but high salt concentrations had negligible effects on the removal of PFOA, PFBS, PFHxS, or PFOS. Excellent scalability was observed in mesoscale experiments, where the majority of amended PFAS mass was removed from synthetic IDW within five days of vessel circulation using two different PFAS-capture configurations. Combined PFOS and PFOA concentrations were reduced to levels below 0.07 µg/L using either GAC or IX for both configurations. Results generated in this study support the application of this approach as an economical strategy for potential waste volume reduction in IDW destined for off-site disposal.

Mass-Based, Field-Scale Demonstration of PFAS Retention within AFFF-Associated Source Areas.

Transport of poly- and perfluoroalkyl substances (PFAS) at aqueous film-forming foam (AFFF)-impacted sites is limited by various processes that can retain PFAS mass within the source area. This study used concentration data obtained via a high-resolution sampling and analytical protocol to estimate the PFAS mass distribution in source and downgradient areas of a former firefighter training area. The total PFAS mass present at the site was approximately 222 kg, with 106 kg as perfluoroalkyl acids (PFAAs) and 116 kg as polyfluorinated precursors. Zwitterionic and cationic PFAS represented 83% of the total precursor mass and were found primarily in the source and up/side-gradient areas (75%), likely due to preferential hydrophobic partitioning, electrostatic interactions, and diffusion into lower-permeability soils. Based on the release history and the high percentage of total PFAS mass represented by precursors (primarily electrochemical fluorination-derived compounds), the estimated conversion rate of precursors to PFAAs was less than 2% annually. Eighty-two percent of the total PFAS mass was encountered in lower-permeability soils, which limited the potential for advection and transformation. This contributed to a 99% decrease in the mass discharge rate at the far-downgradient plume (0.048 kg/yr compared to the near-source area (3.6 kg/yr)). The results provide field-scale evidence of the importance of these PFAS retention processes at sites where AFFF has been released.

Enhanced Extraction of AFFF-Associated PFASs from Source Zone Soils.

Poly- and perfluoroalkyl substances (PFASs) derived from aqueous film-forming foam (AFFF) are increasingly recognized as groundwater contaminants, though the composition and distribution of AFFF-derived PFASs associated with soils and subsurface sediments remain largely unknown. This is particularly true for zwitterionic and cationic PFASs, which may be incompletely extracted from subsurface solids by analytical methods developed for anionic PFASs. Therefore, a method involving sequential basic and acidic methanol extractions was developed and evaluated for recovery of anionic, cationic, and zwitterionic PFASs from field-collected, AFFF-impacted soils. The method was validated by spike-recovery experiments with equilibrated soil-water-AFFF and analytical standards. To determine the relative importance of PFASs lacking commercially available analytical standards, their concentrations were estimated by a novel semiquantitation approach. Total PFAS concentrations determined by semiquantitation were compared with concentrations determined by the total oxidizable precursor assay. Finally, the described method was applied to two soil cores from former fire-training areas in which cations and zwitterions were found to contribute up to 97% of the total PFAS mass. This result demonstrates the need for extraction and analysis methods, such as the ones presented here, that are capable of quantifying cationic and zwitterionic PFASs in AFFF-impacted source zone soils.