Elsevier

Chemosphere

Volume 286, Part 3, January 2022, 131834
Chemosphere

The Co-Transport of PFAS and Cr(VI) in porous media

https://doi.org/10.1016/j.chemosphere.2021.131834Get rights and content

Highlights

  • Cr(VI) can increase the migration potential of PFOS in soil and groundwater.

  • Cr(VI) may compete with PFOS for both organic-carbon and inorganic domains.

  • PFOS sorption is controlled by the geochemical composition of the porous media.

Abstract

PFAS and Cr are present at some sites as co-contaminants. The objective of this research was to investigate the co-transport behavior of per- and polyfluoroalkyl substances (PFAS) and hexavalent chromium (Cr(VI)) in porous media. Miscible-displacement experiments were conducted using two soils and an aquifer sediment with different geochemical properties. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were employed as model PFAS. The retardation of PFOS was decreased in the presence of Cr(VI). Conversely, the transport and retardation of PFOA was not affected by the presence of Cr(VI). The reduction of PFOS retardation caused by Cr(VI) is likely due to sorption competition for both organic-carbon and inorganic (metal-oxides and clay minerals) domains. The relative contributions of the three soil constituents to PFOS sorption and the potential for competition between PFOS and Cr(VI) is a function of the geochemical composition of the porous media (i.e., organic carbon, metal-oxides and clay minerals). The PFAS had minimal impact on the retention and transport of Cr(VI). To our knowledge, the results presented herein represent the first reported data for PFOS and Cr(VI) co-transport in porous media. The results of this study indicate that the presence of Cr(VI) has the potential to increase the migration potential of PFOS in soil and groundwater, which should be considered when characterizing electroplating facilities, leather tanning facilities, and other co-contaminated sites.

Introduction

Per- and polyfluoroalkyl substances (PFAS) have been widely used in many industrial, commercial, and military applications. The strong carbon-fluorine bond provides PFAS with high thermal, chemical, and biological stability. PFAS are contaminants of critical concern because of their persistence and widespread distribution in the environment (e.g., Ahrens, 2011; Krafft and Riess, 2015; Cousins et al., 2016; Wang et al., 2017). As a result, the transport and fate behavior of PFAS in soil and groundwater has become a recent focus of research.

Hexavalent chromium has recently received renewed attention as a contaminant of concern. One of the primary sources of hexavalent chromium is the chromic acid mist from the chrome plating industry (U.S. EPA, 1998). Perfluorooctane sulfonate (PFOS), one of the most common PFAS, was employed as a mist suppressant for many years to minimize the release of chromium during the chrome-plating process. The PFOS served to reduce the surface tension of the solution and thereby control chromium emission (U.S. EPA, 2009; Danish EPA, 2011). Hexavalent chromium is also detected at leather tanning sites, where trivalent chromium is employed to stabilize the leather by cross linking the collagen fibers during the chromium-tanning process (Hedberg, 2020). The trivalent chromium can be oxidized to hexavalent when released to the environment. PFAS are used in the leather tanning process as protective coatings on leather, and the industrial wastes such as sludge and scraps from leather tanneries are sources of PFAS and Cr(VI) (KEMI, 2015; Wang et al., 2017).

The potential exists for co-release of chromium and PFOS into the surrounding environment at electroplating facilities, leather tanning facilities, and other sites, creating a co-contaminated system. Understanding the co-transport behavior of chromium and PFOS in porous media is important for characterizing the potential health risks associated with these co-contaminated sites. To the best of our knowledge, there have been no prior published investigations of PFOS and Cr(VI) co-transport behavior in porous media. The objective of this study is to investigate the co-transport of PFAS and Cr(VI) in natural porous media. Miscible-displacement transport experiments are conducted using two soils and an aquifer sediment that comprise a range of geochemical properties. PFOS and perfluorooctanoic acid (PFOA) are employed as model PFAS. The results of the experiments are used to evaluate the impact of co-contaminant presence on retardation and transport of each contaminant.

Section snippets

Materials and methods

PFOS (ACS# 1763-23-1, ~40% in H2O), PFOA (ACS# 335-67-1, 95% purity) and potassium dichromate (ACS# 7778-50-9, 99% purity) were purchased from Sigma-Aldrich. 2,3,4,5,6-pentafluorobenzoic acid (ACS# 602-94-8, Sigma-Aldrich, 99% purity) was used as the nonreactive tracer (NRT) to characterize the hydrodynamic conditions of the packed columns. This compound is not a PFAS. A synthetic groundwater (SGW) solution was used for all experiments. Three air-dried porous media were employed for the

Solute transport in single-solute systems

The breakthrough curves (BTCs) for the NRT are presented in Fig. SI1. They are sharp and symmetrical, with retardation factors (R) of 1. Recoveries were within measurement uncertainty of 100%. The ideal transport behavior observed for all three media indicates that the columns were well packed and not measurably influenced by nonuniform flow.

The speciation of Cr(VI) is a function of pH and other solution conditions. Cr(VI) occurs as CrO42− under the conditions of these experiments (pH = 7.1, C0

Conclusions

The objective of this research was to investigate the co-transport behavior of per- and polyfluoroalkyl substances (PFAS) and hexavalent chromium (Cr(VI)) in porous media. Miscible-displacement experiments were conducted using two soils and an aquifer sediment with different geochemical properties. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were employed as model PFAS. The retardation of PFOS was decreased in the presence of Cr(VI). Conversely, the transport and

Credit author statement

Dandan Huang: Investigation, Analysis, Writing- Original draft preparation. Naima A. Khan: Analysis, Writing- Review & Editing. Guangcai Wang: Resources, Supervision, Writing- Review & Editing. Kenneth C. Carroll: Resources, Supervision, Writing- Review & Editing. Mark L. Brusseau: Conceptualization, Methodology, Resources, Supervision, Investigation, Analysis, Writing- Review & Editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was supported by the NIEHS superfund Research Program (grant #P42 ES 4940) and the China Scholarship Council (CSC). Additional support was provided by the USDA National Institute of Food and Agriculture (Hatch project 132356), and partial support was also provided by the Department of Energy (DOE) Minority Serving Institution Partnership Program (MSIPP) managed by the Savannah River National Laboratory.

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