The Co-Transport of PFAS and Cr(VI) in porous media
Graphical abstract
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.
References (27)
- et al.
Physical and chemical factors affecting the adsorption of Cr(VI) via humic acids extracted from brown coals
Desalination
(2010) Adsorption of heavy metal ions on soils and soils constituents
J. Colloid Interface Sci.
(2004)Estimating the relative magnitudes of adsorption to solid-water and air/oil-water interfaces for per- and poly-fluoroalkyl substances
Environ. Pollut.
(2019)- et al.
PFAS concentrations in soils: back- ground levels versus contaminated sites
Sci. Total Environ.
(2020) - et al.
The precautionary principle and chemicals management: the example of perfluoroalkyl acids in groundwater
Environ. Int.
(2016) - et al.
Predicting partitioning of radiolabelled 14C-PFOA in a range of soils using diffuse reflectance infrared spectroscopy
Sci. Total Environ.
(2019) - et al.
Per- and polyfluorinated substances (PFASs): environmental challenges
Curr. Opin. Colloid Interface Sci.
(2015) - et al.
Sorption behavior of perfluoroalkyl substances in soils
Sci. Total Environ.
(2015) - et al.
Column versus batch methods for measuring PFOS and PFOA sorption to geomedia
Environ. Pollut.
(2021) - et al.
Transport of PFOS in aquifer sediment: transport behavior and a distributed-sorption model
Sci. Total Environ.
(2021)