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

Abstract

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.

Monitored Natural Attenuation to Manage PFAS Impacts to Groundwater: Scientific Basis

“…In general, sites with more retention will likely be more amenable to using MNA to manage PFAS in the subsurface. Two examples of this general PFAS MNA retention framework are presented herein; first, a hypothetical PFAS site with a PFAS mass distribution based in part on partitioning data from Brusseau (2018), and second, an actual site described by Adamson et al (2020) and Nickerson et al (2021). The scientific basis for PFAS MNA detailed in this paper was used to develop potential guidelines for implementing PFAS MNA, which are presented in a companion paper ).…”

“…These mechanisms include hydrophobic and electrostatic interactions, which are a function of pH, ionic strength, organic carbon content, the charge of soil particles, chain lengths, and charge of the functional group of the PFAS (Nguyen et al 2020). The relative importance of these processes has been documented at PFAS field sites (Weber et al 2017;Adamson et al 2020;Nickerson et al 2021). For example, a field-scale evaluation of a former fire training area where aqueous film-forming foam (AFFF) had been released showed that zwitterionic and cationic precursors were strongly retained within the source area relative to PFAAs due to preferential sorption characteristics (Adamson et al 2020;Nickerson et al 2021).…”

“…The relative importance of these processes has been documented at PFAS field sites (Weber et al 2017;Adamson et al 2020;Nickerson et al 2021). For example, a field-scale evaluation of a former fire training area where aqueous film-forming foam (AFFF) had been released showed that zwitterionic and cationic precursors were strongly retained within the source area relative to PFAAs due to preferential sorption characteristics (Adamson et al 2020;Nickerson et al 2021). Differences in PFAS distribution among solid and liquid phases as a function of carbon chain length were also noted.…”

“…A second example is the PFAS site delineated by Adamson et al (2020) and Nickerson et al, (2021). At this site, PFAS concentrations in surface soils were measured, and the mass in the vadose zone was included in the total PFAS mass estimate for the site.…”

Environmental Sources, Chemistry, Fate, and Transport of Per‐ and Polyfluoroalkyl Substances: State of the Science, Key Knowledge Gaps, and Recommendations Presented at the August 2019 SETAC Focus Topic Meeting

“…Branched and linear isomers will have different physical and chemical properties (water solubility, sorption, transport behavior, and bioaccumulation potentials) and, hence, are expected to show different fate and transport behavior (Kärrman et al, 2011). The isomer Environmental sources, chemistry, fate, and transport of PFAS-Environmental Toxicology and Chemistry, 2021;40:3234-3260 profiles present at the source of contamination will change and redistribute after a certain distance from the source, and in addition, the transformation of different precursor isomers may be different (Adamson et al, 2020;Anderson et al, 2016;Guelfo & Higgins, 2013;Liu, Zhong, et al, 2019;Nickerson et al, 2021). Therefore, measuring PFAS at a distance from the source may show different isomer profiles compared with the source, resulting in misinterpretation of sources.…”