Tools for Understanding and Predicting the Affinity of Per- and Polyfluoroalkyl Substances for Anion-Exchange Sorbents

Abstract

Anion-exchange (AE) sorbents are gaining in popularity for the remediation of anionic per- and polyfluoroalkyl substances (PFAS) in water. However, it is unclear how hydrophobic and electrostatic interactions contribute to anionic PFAS retention. The goal of this study was to understand the effects of PFAS chain length and head group on electrostatic interactions between PFAS and an aminopropyl AE phase. Liquid chromatography–mass spectrometry (LC–MS) was used with an aminopropyl AE guard column to find relative retention times. The average electrostatic potential (EPavg) of each PFAS was calculated, which correlated positively with the PFAS chromatographic retention time, demonstrating the value of EPavg as a proxy for predicting electrostatic interactions between PFAS and the aminopropyl AE phase. The order of greatest to lowest PFAS AE affinity for an aminopropyl column based on chromatographic retention times and electrostatic interactions was n:3 fluorotelomer carboxylic acids (n:3 FtAs) > n:2 fluorotelomer carboxylic acids (n:2 FtAs) > perfluoroalkyl carboxylates (PFCAs) > perfluoroalkyl sulfonamides (FASAs) ∼ n:2 fluorotelomer sulfonates (n:2 FtSs) > perfluoroalkyl sulfonates (PFSAs). This study introduces a methodology for qualitatively characterizing electrostatic interactions between PFAS and AE phases and highlights that electrostatic interactions alone cannot explain the affinity of PFAS for AE resins in water treatment/remediation scenarios.

Role of Mineral–Organic Interactions in PFAS Retention by AFFF-Impacted Soil

“…This may allow for the charge(s) on their head groups to be stronger and less delocalized compared to the negative charge on anionic PFAS, thus increasing their capacity to interact with charged soil components. This hypothesis is supported by Parker et al who observed that anionic PFAS with −CH 2 – spacers between the fluorinated tail and the charged head group (e.g., a polyfluorinated fluorotelomer sulfonate) had an overall more negative electrostatic charge than those without the −CH 2 – spacer. A second possibility is that the nonfluorinated aliphatic head groups which, in contrast to the highly lipophobic fluorocarbon chain, should impart some capacity to engage in van der Waals-type interactions with hydrophobic soil components.…”

Predicted Endocrine Disrupting Activity of Unregulated Drinking Water Contaminants

“…ERα and ERβ were the most specific of the nuclear receptors, binding only 30–32% of the total UCMR1–4 organic pollutants (Figure ), respectively. This may be attributed to the presence of anionic glutamate (E353 in ERα and E305 in ERβ) in the ligand-binding domain, creating charge repulsion with carboxylates, sulfonates, and chemicals with a negative electrostatic surface potential (PFAS). , Active residues in the remaining Superfamily I class of receptors (MR, AR, GR, PR) included cationic arginine and lysine (R752 of AR; R611 and K667 of GR; R817 of MR; R766 of PR) along with mostly polar amino acids, allowing for polar/anionic pollutants (carboxylates and sulfonates) to interact. Of the proteins in Superfamily II, LXR was the most specific, binding to only 39% of the UCMR organic pollutants, while TRα and TRβ bound to the greatest number.…”

PFAS in Nigeria: Identifying data gaps that hinder assessments of ecotoxicological and human health impacts

“…Subsequently, the detection and remediation of PFAS in the environment have been subjects of significant research and technological advancement [ [128] , [129] , [130] , [131] ]. Parker et al [ 132 ] studied how chain length and head group of PFAS affect their electrostatic interactions with anion-exchange (AE) sorbents, using liquid chromatography-mass spectrometry and calculating average electrostatic potential to predict these interactions, and determining the varying affinity of different PFAS types for AE resins in water treatment scenarios. Sophisticated analytical methods have been developed for PFAS detection, including liquid chromatography-tandem mass spectrometry (LC-MS/MS), which allows for the sensitive and specific identification of individual PFAS compounds even at low concentrations in various matrices [ 133 ].…”