The influence of molecular structure on the adsorption of PFAS to fluid-fluid interfaces: Using QSPR to predict interfacial adsorption coefficients

Abstract

Per-and poly-fluoroalkyl substances (PFAS) are emerging contaminants of critical concern for human health risk. Assessing exposure risk requires a thorough understanding of the transport and fate behavior of PFAS in the environment. Adsorption to fluid-fluid interfaces, which include airwater, OIL-water, and air-OIL interfaces (where OIL represents organic immiscible liquid), is a potentially significant retention process for PFAS transport. Fluid-fluid interfacial adsorption coefficients (K i) are required for use in transport modeling and risk characterization, yet these data are currently not available for the vast majority of PFAS. Surface-tension and interfacial-tension data sets collected from the literature were used to determine interfacial adsorption coefficients for 42 individual PFAS. The PFAS evaluated comprise homologous series of perfluorocarboxylates and perfluorosulfonates, branched perfluoroalkyls, polyfluoroalkyls, alcohol PFAS, and nonionic PFAS. The K i values vary across eight orders of magnitude, and are a function of molecular structure. The results of quantitative-structure/property-relationship (QSPR) analysis demonstrate that a model employing molar volume (V m) as a descriptor provides robust predictions of log K i values for air-water interfacial adsorption of the wide range of PFAS. The model also produced good predictions for a limited set of data for OIL-water interfacial adsorption. The predictive capability of the QSPR model for a wide range of PFAS with greatly varying structures reflects the fact that molar volume provides a reasonable representation of the influence of molecular size on cavity formation/destruction in solution, and thus the hydrophobic-interaction driving force for interfacial adsorption. The QSPR model presented herein provides a means to incorporate the fluid-fluid interfacial adsorption process into transport characterization and risk assessment of PFAS in the environment. This will be particularly relevant for determining PFAS mass flux in the Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Influence of Water Concentrations of Perfluoroalkyl Acids (PFAAs) on Their Size-Resolved Enrichment in Nascent Sea Spray Aerosols

“…The EF SML increased with increasing NPC and revealed an S-shape trend (see PFCAs in Figure S8 ). In contrast, some other parameters that characterize the surface activity of PFCAs, for example, the CMCs, the surface/bulk water distribution coefficient (C surface /C water – 1) reported by Reth et al, 20 as well as the interfacial adsorption coefficient (the ratio of surface excess (mol/cm 2 ) to C water ) reported by Brusseau, 41 all demonstrated log–linear relationships with the number of perfluorinated carbons. Bias in the glass plate sampling method used in the present study may be one of the causes for the discrepancy, since highly surface-active substances such as PFDoDA may be adsorbed to the glass plate resulting in an underestimation of the EF SML .…”

“…Theoretically, at environmentally relevant concentrations (generally <0.1 mg L –1 ) the ratio of surface excess (mol cm –2 ) to aqueous concentration (mol cm –3 ) of a fluorinated surfactant should be constant. 41 Consequently, the amounts of chemical substance scavenged on the air–water interface of air bubbles as well as the amounts aerosolized after bubbles burst should be proportional to their concentrations in the water. Tseng et al 51 found that the amount of surface active organic compounds transferred to air by bubble bursting was linearly proportional to the amount in the SML.…”

“… 40 PFAA concentrations in the open ocean were reviewed in the previous study by Johansson et al 17 Despite the large variation in water concentrations, the influence of PFAA water concentration on the EFs is unknown. According to Brusseau, 41 the ratio of surface excess of a PFAA (i.e., the amount adsorbed at the interface, mol cm –2 ) to its aqueous concentration (mol cm –3 ) is constant at environmentally relevant levels. Thus, theoretically, when air is entrained in seawater, the amount of PFAAs adsorbed on the bubbles’ air–water interface and aerosolized should be proportional to the concentrations of PFAAs in seawater.…”

PFAS removal from groundwaters using Surface‐Active Foam Fractionation

“…However, as indicated in Section 6.1, SAFF is less effective in removal of shorter-chain PFAS molecules that exhibit lower adsorption coefficients. This is demonstrated by the results in Table5, from which it is also clear that an AIX Percentage removal of individual PFAS species due to SAFF treatment versus the adsorption coefficient reported byBrusseau (2019). Note the logarithmic scale on the abscissa.…”

A Mathematical Model for the Release, Transport, and Retention of Per‐ and Polyfluoroalkyl Substances (PFAS) in the Vadose Zone

“…The impact of fluid‐fluid interfacial adsorption on PFAS retention and transport in soil was examined initially by Brusseau (), who employed surface tension data for PFAS including two of primary concern—perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)—and measured air‐water interfacial areas along with a comprehensive retention model to conduct a theoretical assessment. Additional surface‐tension‐based theoretical analyses of PFAS retention have since been reported (Brusseau, , ; Brusseau & Van Glubt, ; Costanza et al, ; Silva et al, ). Miscible‐displacement laboratory experiments demonstrating that adsorption of PFAS at air‐water and NAPL‐water interfaces can be an important retention process in soil and sand materials have also been reported (Brusseau et al, ; Lyu et al, ).…”