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Limitations of Current Approaches for Predicting Groundwater Vulnerability from PFAS Contamination in the Vadose Zone
Citation:
Rovero, M., D. Cutt, R. Griffiths, U. Filipowicz, K. Mishkin, B. White, S. Goodrow, AND Richard T. Wilkin. Limitations of Current Approaches for Predicting Groundwater Vulnerability from PFAS Contamination in the Vadose Zone. GROUNDWATER MONITORING AND REMEDIATION. National Ground Water Association, Westerville, OH, 41(4):62-75, (2021). https://doi.org/10.1111/gwmr.12485
Impact/Purpose:
Perfluoroalkyl and Polyfluoroalkyl Substances (PFASs) are a current research priority due to their widespread distribution in the environment, toxicity, potential for bioaccumulation, and limited knowledge regarding their fate and transport properties. EPA Regions and many state environmental agencies use soil-water partition models developed by the EPA to determine soil remediation criteria that are protective of groundwater. However, these models may not be well suited for PFAS sites since little is known about the sorption behavior of the anionic, zwitterionic, and cationic PFASs in relation to soil physical properties and groundwater chemistry. Practitioners need a more robust, and easy-to-use tool that will aid in better predicting the complex behavior of PFASs in different geochemical and physical environments. The work is of interest to the international environmental community, including EPA’s regional, program, and local partners.
Description:
Contamination of soil and groundwater by per- and polyfluoroalkyl substances (PFAS) is a growing area of concern, yet there is limited understanding of the factors that control PFAS sorption and desorption in soil. We reviewed published literature for reported sorption coefficients (Kd) of eight anionic PFAS in soil to assess whether the use of a constant Kd value to estimate sorption, as is frequently done with contaminants such as chlorinated solvents, is predictive of groundwater vulnerability. Kd values spanned three to five log units for each of the PFAS reviewed, indicating that no single value would be appropriate for use in predicting PFAS impacts to groundwater using existing soil-water partition equations. No soil partitioning data were available for hexafluoropropylene oxide dimeric acid (HFPO-DA, also called GenX). Regression analysis was used to determine if the soil or solution parameters reported in literature might be used to predict Kd values for PFAS. Our analysis determined that none of the 15 experimental parameters collected could individually explain variability in reported Kd, and the data were insufficient to allow for robust multiple linear regression. Significant associations between Kd and soil calcium and sodium content were found for many of the selected PFAS, which suggests that soil cation content may be more important to sorption than commonly considered, while organic carbon (OC) content was significant only at elevated levels (>5%). Unexplained discrepancies between the results from studies in which PFAS is introduced to soil and desorbed within the laboratory and those which collected material from PFAS-impacted sites suggest that laboratory experiments may be overlooking some aspects critical to PFAS sorption. Future studies of this nature would benefit from the development and use of standardized analytical methods to improve data quality and the establishment of a set of soil parameters appropriate for collection to produce more complete data sets for analysis.
URLs/Downloads:
DOI: Limitations of Current Approaches for Predicting Groundwater Vulnerability from PFAS Contamination in the Vadose Zone
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