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Review

Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) Adsorption onto Different Adsorbents: A Critical Review of the Impact of Their Chemical Structure and Retention Mechanisms in Soil and Groundwater

by
Mehak Fatima
1,
Celine Kelso
2 and
Faisal Hai
1,*
1
Strategic Water Infrastructure Laboratory, School of Civil, Mining, Environmental and Architectural Engineering, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia
2
School of Science, Faculty of Science, Medicine & Health, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia
*
Author to whom correspondence should be addressed.
Water 2025, 17(9), 1401; https://doi.org/10.3390/w17091401
Submission received: 7 April 2025 / Revised: 28 April 2025 / Accepted: 28 April 2025 / Published: 7 May 2025
(This article belongs to the Special Issue The PFAS (Perfluoroalkyl and Polyfluoroalkyl Substances) Challenges: Environmental Impact and Alternative Treatments)
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Highlights

  • PFOA/S sorption depends on pH, ionic strength, and co-existing ions in solution.
  • PFOS consistently showed higher adsorption than PFOA on all adsorbents.
  • PFOA/S adsorption occurs in the following order: AER> single-walled CNTs> AC.
  • Sorption capacities for PFOA/S on all adsorbents decreased above pH 5.
  • 1-2 year of in situ treatment adequately reduces PFOA/S concentrations in groundwater.

Abstract

Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are emerging contaminants of concern as they persist in natural environments due to their unique chemical structures. This paper critically reviewed the adsorption of PFOA and PFOS, depending on their chemical structure, by different adsorbents as well as soil. Adsorption of PFOS generally surpasses that of PFOA across various adsorbents. Despite having the same number of carbons, PFOS exhibits greater hydrophobicity due to two major structural differences: firstly, it has one extra CF2 unit and secondly, the sulfonate group in PFOS, being a relatively hard base, readily adsorbs on oxide surfaces, enhancing its adsorption compared to the carboxylate group in PFOA. While comparing activated carbon (AC) adsorption performance, powdered activated carbon (PAC) demonstrates higher adsorption capacity than granular activated carbon (GAC) for PFOS and PFOA. Anion exchange resin (AER) outperforms other adsorbents, with a maximum adsorption capacity for PFOS twice that of PFOA. Carbon nanotubes (CNTs) exhibit two-fold higher adsorption for PFOS compared to PFOA, with single-walled CNTs showing a distinct advantage. Overall, the removal of PFOS and PFOA under similar conditions on different adsorbents is observed to be in the following order: AER > single-walled CNTs > AC. Moreover, AER, single-walled CNTs, and AC exhibited higher adsorption capacities for PFOS than PFOA. In situ remediation studies of PFOA/S-contaminated soil using colloidal activated carbon show a reduction in concentration to below acceptable limits within 12–24 months. The theoretical and experimental studies cited in this review highlight the role of air–water interfacial adsorption in retaining PFOA and PFOS as a function of their charged head groups during their transport in unsaturated porous media.
Keywords: PFOA; PFOS; adsorption; ion exchange; PFAS functional head groups PFOA; PFOS; adsorption; ion exchange; PFAS functional head groups
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MDPI and ACS Style

Fatima, M.; Kelso, C.; Hai, F. Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) Adsorption onto Different Adsorbents: A Critical Review of the Impact of Their Chemical Structure and Retention Mechanisms in Soil and Groundwater. Water 2025, 17, 1401. https://doi.org/10.3390/w17091401

AMA Style

Fatima M, Kelso C, Hai F. Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) Adsorption onto Different Adsorbents: A Critical Review of the Impact of Their Chemical Structure and Retention Mechanisms in Soil and Groundwater. Water. 2025; 17(9):1401. https://doi.org/10.3390/w17091401

Chicago/Turabian Style

Fatima, Mehak, Celine Kelso, and Faisal Hai. 2025. "Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) Adsorption onto Different Adsorbents: A Critical Review of the Impact of Their Chemical Structure and Retention Mechanisms in Soil and Groundwater" Water 17, no. 9: 1401. https://doi.org/10.3390/w17091401

APA Style

Fatima, M., Kelso, C., & Hai, F. (2025). Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) Adsorption onto Different Adsorbents: A Critical Review of the Impact of Their Chemical Structure and Retention Mechanisms in Soil and Groundwater. Water, 17(9), 1401. https://doi.org/10.3390/w17091401

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