Transformation of 6:2 fluorotelomer sulfonic acid in laccase-mediator systems

Per- and polyfluoroalkyl substances, better known as PFAS, have earned the nickname forever chemicals for good reason. Their carbon-fluorine backbones are among the most chemically stable structures ever synthesized, which made them indispensable in everything from non-stick pans to fire-extinguishing foams, but also means they refuse to break down in the environment. Now a team at the University of Georgia, working with a colleague at the University of Padova, has reported a proof-of-concept that a fungal enzyme called laccase, paired with humble soybean meal extract, can chip away at one stubborn PFAS precursor: 6:2 fluorotelomer sulfonic acid, or 6:2 FTS. The findings, published in Frontiers in Environmental Engineering, hint at a cost-effective, enzyme-driven route to remediate contaminated croplands and pastures.

6:2 FTS is a polyfluorinated compound with a six-carbon fully fluorinated tail and a two-carbon hydrogenated linker. It was introduced as a replacement for perfluorooctane sulfonate (PFOS) after that legacy chemical was banned, serving as a chrome mist suppressant in electroplating, an emulsion aid in fluoropolymer processing, and a co-formulant in aqueous film-forming foams. But the swap came with a catch: 6:2 FTS degrades slowly under aerobic conditions and barely at all under anaerobic ones. Worse, it acts as a precursor to persistent perfluoroalkyl acids, the terminal breakdown products that accumulate in water, soil, and living tissue. PFAS exposure has been linked to liver and kidney disease, reduced fertility, neurological dysfunction, and thyroid cancer, making the search for effective remediation techniques urgent.

The Georgia team turned to a process called enzyme-catalyzed oxidative humification reactions, or ECOHRs. White-rot fungi secrete extracellular enzymes like laccase under nutrient starvation to break down lignin, and these enzymes generate highly reactive, non-specific intermediates that can also attack xenobiotics. Laccase is particularly attractive for remediation because it uses molecular oxygen as its terminal electron acceptor, unlike peroxidases that require hydrogen peroxide. Previous studies showed that laccase-mediator systems could transform roughly 50 percent of PFOA and 59 percent of PFOS, but how a PFAA precursor like 6:2 FTS would behave during ECOHRs remained untested.

The researchers set up reactors with two laccase sources, a purified enzyme from Aspergillus sp. and a crude preparation from Pycnoporus sp. SYBC-L3, and two mediators: the synthetic chemical 1-hydroxybenzotriazole (HBT) and soybean meal extract (SBMe), which contains natural mediator compounds like vanillin, apocynin, and daidzein. They also tested the effect of copper sulfate, which acts as a bridge between negatively charged PFAS and the enzyme. The most effective combination, crude laccase with SBMe and 10 mM CuSO4, reduced 6:2 FTS concentration by 23.8 percent relative to its control over 119 days.

High-resolution mass spectrometry revealed a suite of tentative transformation products ranging from C8 down to C3, including a previously unreported candidate formula C3F7O3S that could be consistent with perfluoropropanesulfonate. The team also measured a 34.8 percent drop in adsorbable organic fluorine, supporting the idea that transformation, and potentially degradation, had occurred. Interestingly, the crude laccase system yielded fewer unique products (12) than the purified system (38), possibly because co-factors in the crude preparation drove deeper transformation and backbone cleavage.

To explain why 6:2 FTS is so recalcitrant compared to PFOS, the team calculated bond dissociation energies (BDEs) of its C-C and C-S bonds. The BDE profile showed a significant energy spike at the junction between the perfluorinated tail and the hydrogenated linker, exceeding even the uniform BDE profile of PFOS. Applying Bent’s rule, the extreme electronegativity of fluorine forces the junction carbons to inflate s-character into the adjacent C-C bond, shortening and dramatically strengthening it. This localized bond stabilization, compounded by structural mismatch between the rigid helical tail and the flexible zigzag linker, raises the thermodynamic barrier to cleavage and could explain the variable degradation observed across different studies.

The soybean meal extract proved remarkably durable as a mediator. Amended only once at the onset of the experiment, it sustained phenolic compounds across the entire 119-day period, outperforming HBT, which had to be supplemented weekly. The low cost of soybean meal, roughly $0.15 per pound, combined with the elimination of about 80 percent of downstream enzyme purification costs when using crude laccase, makes this system potentially cost-effective for field-scale application.

The authors caution that this is a proof-of-concept with limitations. The single-reactor setup lacked independent replicates, so statistical significance could not be assessed, and several tentative products were identified without MS/MS fragmentation data to confirm structures. Conventional terminal PFCAs like PFHxA and PFBA were not detected, though structurally similar precursors were. Future work should focus on transformation in environmentally relevant soil matrices, quantify degradation products, define the pathway, and assess ecotoxic effects of copper sulfate before recommending practical application.

Still, the study opens a compelling window on ECOHRs as a potentially cost-effective remediation technique for vast croplands and pastures contaminated with PFAS precursors. If enzyme-driven humification can be scaled and refined, the humble soybean and a fungal enzyme might become unlikely heroes in the fight against forever chemicals.

Subject of Research: Transformation of 6:2 fluorotelomer sulfonic acid in laccase-mediator systems

Article Title: Transformation of 6:2 fluorotelomer sulfonic acid in laccase-mediator systems

Article References: Munir, U., Wang, Y., Zhu, X., Ji, Y., Habteselassie, M. Y., Squartini, A., & Huang, Q. (2026). Transformation of 6:2 fluorotelomer sulfonic acid in laccase-mediator systems. Frontiers in Environmental Engineering, 5, Article 1948940. https://doi.org/10.3389/fenve.2026.1948940

Image Credits: AI Generated

DOI: 10.3389/fenve.2026.1948940

Keywords: 6:2 FTS, PFAS, laccase-mediator system, ECOHRs, soybean meal extract, bioremediation, transformation products, bond dissociation energy, PFAA precursors, environmental engineering, Transformation, fluorotelomer