Scientists Unravel How Forever Chemical PFOA Breaks Down in Alkaline Solvent Mixtures

Perfluorooctanoic acid, better known as PFOA, has earned its place among the most notorious of the so-called forever chemicals. Its carbon-fluorine bonds are among the strongest in organic chemistry, which is precisely why the compound has persisted in soils, rivers, and drinking water supplies decades after its widespread use in non-stick coatings, water-repellent fabrics, and firefighting foams. Now, a team of French researchers led by Raphaël Tur of the French Geological Survey (BRGM), working with colleagues from Colas Environnement and the Institut de Physique du Globe de Paris, has published a detailed kinetic and mechanistic study of how PFOA can be broken down in alkaline mixtures of dimethyl sulfoxide and water. The work, published in Environmental Science and Pollution Research, offers one of the most granular pictures yet of the redox chemistry that governs the destruction of this stubborn pollutant.

The research team set out to answer a deceptively simple question: under what conditions, and through what sequence of electron-transfer events, does PFOA surrender its fluorine atoms as harmless fluoride ions? To do so, they subjected PFOA to alkaline dimethyl sulfoxide/water (DMSO/H2O) solutions under a range of carefully controlled conditions, varying the amount of sodium hydroxide, the proportion of water in the solvent blend, and the reaction temperature. The fate of PFOA and its degradation by-products was tracked using ultra-high-pressure liquid chromatography coupled with mass spectrometry, a technique sensitive enough to detect and relatively quantify the short-chain fluorinated fragments that appear as the long molecule is dismantled. Destruction efficiency, in turn, was measured by potentiometric fluoride detection with a fluoride-selective electrode, complemented by scanning electron microscopy and energy-dispersive spectroscopy to examine solid residues.

The central conceptual contribution of the study lies in how the authors frame the degradation chemistry. Rather than treating hydroxyl and hydrogen radicals as freely diffusing species that randomly attack PFOA molecules, the researchers describe the entire process through redox couples involving only the carbon atoms within PFOA and its by-products. In this framework, the hydroxyl radical paired with hydroxide (OH·/OH⁻) and the hydrogen radical paired with water (H·/H2O) act as transient redox intermediates associated with discrete electron-transfer events. The electron donor in the system is hydroxide, while the electron acceptors are molecular oxygen, PFOA itself, and water. This carbon-focused redox description allows the team to explain why certain reactions proceed readily while others stall, simply by examining the oxidation state of each carbon atom in the molecule.

A key insight emerging from this analysis is that the nucleophilic or electrophilic character of each redox reaction depends on the oxidation state of the carbon atom involved. Carbons bearing multiple fluorine atoms sit at high oxidation states and behave as electrophilic targets, while carbons that have been partially reduced become susceptible to different modes of attack. The most favorable degradation pathway identified by the team involves the stepwise oxidation of carbon driven solely by the OH·/OH⁻ redox couple. Through this repeated sequence, the molecule is progressively shortened, with each cycle eliminating one –CF2– unit from the chain in the form of two fluoride ions and one carbonate ion. In effect, the perfluorinated backbone is unzipped two fluorine atoms at a time, converting the once-inert fluorocarbon chain into benign inorganic products.

The study also reveals that degradation is not purely an oxidative affair. The OH·/OH⁻ and H·/H2O redox couples together mediate secondary electron-transfer pathways in which two different carbon atoms within the same PFOA-derived molecule are simultaneously oxidized and reduced. This coupled oxidation-reduction within a single molecule helps explain the variety of by-products observed chromatographically, including shorter-chain perfluorinated species that retain some of their fluorine content. Understanding these parallel pathways matters for remediation engineering, because incomplete mineralization can leave behind shorter perfluorinated acids that are themselves persistent and, in some cases, more mobile in groundwater than the parent compound.

Perhaps the most practically important finding concerns the role of water. Although water is a participant in the redox chemistry, the researchers found that both the initial water content of the solvent mixture and the water continuously formed during the reactions actually limit the destruction process. The mechanism is subtle: water enhances the solvation of hydroxide ions, and a heavily solvated hydroxide is a weaker electron donor. Because the oxidizing capacity of the OH·/OH⁻ redox couple depends on the availability of unsolvated, reactive hydroxide, excess water effectively throttles the reaction. This finding provides a clear chemical rationale for why DMSO-rich mixtures outperform more aqueous media, and it suggests that managing water activity will be essential in any attempt to scale the chemistry beyond the laboratory bench.

The kinetic data translate into a straightforward recipe for maximizing defluorination. The higher the molar ratio of sodium hydroxide to PFOA, at 62:1 or greater, the lower the water content, with DMSO/H2O volume ratios of at least 3.87:1, and the higher the temperature, at 120 °C or above, the greater the extent of defluorination achieved. Each of these parameters pushes the chemistry in the same direction: abundant hydroxide supplies the electron donor that fuels the redox chain, a DMSO-rich environment keeps hydroxide minimally solvated and maximally reactive, and elevated temperature accelerates the electron-transfer steps that cleave the carbon-fluorine bonds. The conditions are demanding, but they remain far milder than the incineration temperatures, often exceeding 1000 °C, required to destroy PFAS thermally.

The significance of this work is best appreciated against the backdrop of the broader PFAS remediation challenge. Thousands of per- and polyfluoroalkyl substances are in commercial use, and their chemical inertness, which made them so valuable in industry, renders them essentially immune to conventional water treatment. Adsorption onto activated carbon or ion-exchange resins merely concentrates the problem rather than solving it, transferring the chemicals from water to a spent sorbent that still requires destruction. Advanced oxidation processes, which have proven effective against many organic pollutants, often fail against fully fluorinated compounds because hydroxyl radicals preferentially attack electron-rich moieties that perfluorinated chains simply do not possess. Reductive approaches using hydrated electrons have shown promise, but they too face structural and practical constraints. Chemical destruction in solvent systems, exemplified by the low-temperature mineralization of perfluorocarboxylic acids reported in Science in 2022, has emerged as one of the most exciting frontiers in the field.

The new study adds mechanistic depth to this frontier by explicitly mapping the electron-transfer choreography that underlies solvent-phase destruction. Prior work in alkaline DMSO systems had established that hydroxide can act as a one-electron reducing agent in aprotic solvents, generating superoxide and other reactive intermediates, and that DMSO itself participates in the radical chemistry of such mixtures. What the French team contributes is a unified, carbon-centered accounting of where electrons flow during PFOA degradation, showing that the apparent complexity of the product distribution can be rationalized by the oxidation states of individual carbon atoms and the redox couples that address them. This level of mechanistic resolution is precisely what engineers need to design reactors that push reactions down the most productive pathways while suppressing the side reactions that generate problematic intermediates.

Challenges remain before such chemistry can treat real-world contamination. The solvent volumes, hydroxide loadings, and temperatures required are substantial, and contaminated environmental matrices introduce water, dissolved oxygen, co-contaminants, and sorbed phases that the pristine laboratory solutions do not contain. The research was conducted under the European Union’s Horizon 2020 PROMISCES project, which targets the monitoring and elimination of emerging contaminants in soil and water, suggesting that the authors view the work as a step toward applied solutions rather than pure curiosity. Even so, the study’s message is ultimately an optimistic one: the carbon-fluorine bond, long considered an insurmountable barrier, yields predictably to a well-understood sequence of electron transfers when the solvent environment is engineered to keep hydroxide in its most reactive form. For a class of pollutants whose very name, forever chemicals, encodes despair, that predictability is a genuinely hopeful development, turning the destruction of PFOA from an empirical art into a science that can be rationally optimized.

Subject of Research: Chemical defluorination kinetics and redox mechanisms of perfluorooctanoic acid (PFOA) in alkaline dimethyl sulfoxide/water solutions

Article Title: Defluorination of perfluorooctanoic acid in alkaline dimethyl sulfoxide/water solutions: kinetics and carbon-focused redox mechanism insights

Article References: Tur, R., Betelu, S., Colombano, S., Davarzani, D., Bristeau, S., Grandclément, J., Perrault, A., Lions, J., van Hullebusch, E. D., & Ignatiadis, I. (2026). Defluorination of perfluorooctanoic acid in alkaline dimethyl sulfoxide/water solutions: kinetics and carbon-focused redox mechanism insights. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38216-7

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38216-7

Keywords: PFOA, PFAS, forever chemicals, defluorination, DMSO, redox chemistry, hydroxide, electron transfer, water treatment, environmental remediation, reaction kinetics, fluoride