Fluorotelomer Sulfonates: The Firefighting Foam Legacy
Fluorotelomer sulfonates (FTS)—including 6:2 FTS and 8:2 FTS—are PFAS compounds present in firefighting foams as both intentional components and degradation products. They are among the most frequently detected PFAS in groundwater near military installations and airport firefighting training areas, where AFFF use has contaminated underlying aquifers.
Treatment Challenges for FTS Compounds
6:2 FTS has intermediate adsorption affinity on activated carbon—better than short-chain carboxylates but less reliably removed than PFOS. Studies show 60–80% GAC removal for 6:2 FTS under optimal conditions, with significant variability based on competing PFAS, natural organic matter, and contact time. 8:2 FTS, with its longer chain, shows somewhat better GAC performance at 80–90% removal.
Transformation to Terminal PFAS
A complicating factor for FTS compounds is their potential transformation to terminal PFAS through aerobic biodegradation. 6:2 FTS can biotransform to 5:3 FTCA, 5:3 FTUCA, and ultimately to PFPeA—regulated compounds. Treatment systems that remove FTS while allowing precursor transformation may be creating a delayed regulated PFAS problem in treated water.
Monitoring and Compliance Implications
Utilities treating AFFF-contaminated water should include fluorotelomer sulfonates in comprehensive monitoring programs even though they are not directly regulated by EPA MCLs. Their presence indicates PFAS contamination scenarios where GAC provides only partial protection across the full suite of relevant compounds.