Experimental and molecular dynamic simulation study of perfluorooctane sulfonate adsorption on soil and sediment components

Abstract

Soil and sediment play a crucial role in the fate and transport of perfluorooctane sulfonate (PFOS) in the environment. However, the molecular mechanisms of major soil/sediment components on PFOS adsorption remain unclear. This study experimentally isolated three major components in soil/sediment: humin/kerogen, humic/fulvic acid (HA/FA), and inorganic component after removing organics, and explored their contributions to PFOS adsorption using batch adsorption experiments and molecular dynamic simulations. The results suggest that the humin/kerogen component dominated the PFOS adsorption due to its aliphatic features where hydrophobic effect and phase transfer are the primary adsorption mechanism.Compared with the humin/kerogen, the HA/FA component contributed less to the PFOS adsorption because of its hydrophilic and polar characteristics. The electrostatic repulsion between the polar groups of HA/FA and PFOS anions was attributable to the reduced PFOS adsorption. When the soil organic matter was extracted, the inorganic component also plays a non-negligible role because PFOS molecules might form surface complexes on SiO 2 surface.The findings obtained in this study illustrate the contribution of organic matters in soils and sediments to PFOS adsorption and provided new perspective to understanding the adsorption process of PFOS on micro-interface in the environment.

Transport of GenX in Saturated and Unsaturated Porous Media

“…It is notable that while Vinton soil has a very low organic-carbon content, it has by far the largest metal-oxide content. The greater proportion of oxides likely supports adsorption via additional mechanisms beyond hydrophobic interaction, such as electrostatic interactions and the formation of complexes by ligand exchange with metal oxides, as has been observed in prior studies for PFAS and hydrocarbon surfactants. − This additional adsorption is lumped into the log K oc value. A similar observation of greater adsorption by Vinton compared to Eustis soil was reported for PFOS …”

Assessing the potential contributions of additional retention processes to PFAS retardation in the subsurface

“…Research investigating PFAS adsorption by solids has become a focus over the past decade, with investigations examining water treatment applications (as reviewed in Du et al, 2014 and Merino et al, 2016) and subsurface porous media--- soils and sediments (Liu and Lee, 2005, 2007, Higgins and Luthy, 2006, 2007, Johnson et al, 2007, Carmosini and Lee, 2008, Chen et al, 2009, Pan et al, 2009, Ferrey et al, 2012, Guelfo and Higgins, 2013, Zhao et al, 2014, Milinovic et al, 2015, Zhang et al, 2015, Hellsing et al, 2016). Adsorption of PFAS by solids is complex due to the nature of the molecular structure of PFAS.…”

“…As would be anticipated, research has shown that PFAS sorption by subsurface media is greatly affected by the geochemical properties of the solid, particularly with respect to specific components present. Critical factors investigated for PFAS include the magnitude and nature of organic carbon, magnitude and type of metal oxides, and clay mineralogy (Higgins and Luthy, 2006, Liu and Lee, 2007, Ferrey et al, 2012, Milinovic et al, 2015, Zhang et al, 2015). In addition, it is well known that the adsorption of surfactants is sensitive to water chemistry.…”

Molecular dynamics simulation of organic contaminant adsorption on organic‐coated smectite clay

“…we previously characterized adsorption on pristine smectite using MD simulations. Other previous atomistic simulation studies of the adsorption of similar contaminants on organic-coated minerals have modeled PFAS adsorption on organic-coated silica surfaces and within an organic-coated Na-smectite nanopore, but these studies simulated very short time scales (2.1 ns or less) and did not quantify the free energy of adsorption of the organic contaminant (Yan et al, 2020;R. Zhang et al, 2015).…”

“…We focus on two contaminants, dimethyl phthalate (DMP), an uncharged polar chemical plasticizer, and perfluorobutanesulfonic acid (PFBS), a short chained anionic surfactant in the family of per‐ and polyfluoroalkyl substances (PFAS), for which we previously characterized adsorption on pristine smectite using MD simulations. Other previous atomistic simulation studies of the adsorption of similar contaminants on organic‐coated minerals have modeled PFAS adsorption on organic‐coated silica surfaces and within an organic‐coated Na‐smectite nanopore, but these studies simulated very short time scales (2.1 ns or less) and did not quantify the free energy of adsorption of the organic contaminant (Yan et al., 2020; R. Zhang et al., 2015). Previous experimental studies have observed significantly enhanced adsorption of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) on smectite clay in the presence of cationic surfactants such as hexadecyltrimethylammonium bromide (Tian et al., 2016; Zhou et al., 2010), whereas humic acid, tannic acid, and Suwannee River natural organic matter coatings resulted in decreased PFOS and PFOA adsorption compared with pure smectite surfaces (Jeon et al., 2011).…”