Nonideal Transport and Extended Elution Tailing of PFOS in Soil

Abstract

The objective of this research was to examine the influence of nonideal sorption/desorption on the transport of polyfluorinated alkyl substances (PFASs) in soil, with a specific focus on characterizing and quantifying potential extended, mass-transfer-limited elution behavior. Perfluorooctane sulfonic acid (PFOS) was used as a representative PFAS, and miscible-displacement experiments were conducted with two soils comprising contrasting geochemical properties. The influence of nonlinear, rate-limited, hysteretic, and irreversible sorption/desorption on transport was investigated through experiments and model simulations. The breakthrough curves measured for PFOS transport in the two soils were asymmetrical and exhibited extensive elution tailing, indicating that sorption/desorption was significantly nonideal. The widely used two-domain sorption kinetics model could not fully simulate the observed transport behavior, whereas a multirate model employing a continuous distribution of sorption domains was successful. The overall results indicated that sorption/desorption was significantly rate-limited and that nonlinear, hysteretic, and irreversible sorption/desorption had minimal impact on PFOS transport. Comparison of PFOS transport data to data reported for two hydrophobic organic contaminants (HOCs) showed that the HOCs exhibited much more extensive elution tailing, likely reflecting differences in sorption/desorption mechanisms. The projected influence of rate-limited sorption/desorption on PFOS transport at the field scale was investigated through simulation. The results of the study suggest that rate-limited sorption/desorption may affect the field-scale transport of PFOS and other PFAS for systems influenced by transient or short-residence-time conditions and in some cases could possibly increase the amount of flushing required to reduce PFOS concentrations to levels below those associated with human-health concerns.

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

“…We first present formulations of equilibrium isotherms for and . The solid‐phase adsorption can be modeled by the nonlinear Freundlich isotherm as suggested by prior experimental measurements (Brusseau et al, ; Brusseau, ; Higgins & Luthy, ; Wei et al, ) where and are fitting parameters to experimental data.…”

“…A constant temperature K is used. The parameters for the Freundlich isotherm for the Accusand and Vinton soil were reported in Brusseau () and Brusseau et al (), respectively. Note that in Brusseau () and Brusseau et al () was for PFOS aqueous concentrations in mg/L and solid‐phase adsorption concentration in mg/kg.…”

US Department of Defense–Funded Fate and Transport Research on Per‐ and Polyfluoroalkyl Substances at Aqueous Film–Forming Foam–Impacted Sites

“…Complicating factors to field‐scale predictions, however, currently are thought to include 1) lack of methods to assess the rate and extent of precursor biotransformation; 2) nonideal PFAA transport behavior attributable to complex sorption/desorption kinetics, resulting in attenuation over time (e.g., Brusseau et al 2019); and 3) greater retardation of linear versus branched isomers of a given PFAS (e.g., Kärrman et al 2011). Additional uncertainty highlighted in recent literature results from the extrapolation of experimental observations (typically performed at relatively high concentrations because of experimental constraints) down to environmentally relevant concentrations that are highly dependent on the selected sorption isotherm (Schaefer et al 2019).…”

“…(Continued ) Brusseau et al 2019); and 3) greater retardation of linear versus branched isomers of a given PFAS (e.g., Kärrman et al 2011). Additional uncertainty highlighted in recent literature results from the extrapolation of experimental observations (typically performed at relatively high concentrations because of experimental constraints) down to environmentally relevant concentrations that are highly dependent on the selected sorption isotherm (Schaefer et al 2019).…”

Interactions of Per- and Polyfluoralkyl Substances (PFAS) with Landfill Liners

“…The chemical stability of PFAS compounds means that when released, they persist in, and transport between, the atmospheric [10][11][12][13][14], terrestrial (soil and sediments) [15][16][17][18][19][20] and aquatic environments (surface and ground waters) [19][20][21][22][23][24][25][26] together with the anthropic environment (agriculture, landfills, sewage, and water treatment systems) [27]. Possible transport pathways are illustrated in Figure 1.…”