Perfluorohexane sulfonate (PFHxS) is a 6-carbon sulfonate PFAS compound regulated under EPA’s 2024 rule as part of a hazard index alongside PFNA and PFBS. PFHxS has been used in industrial applications and firefighting foam, and its presence in drinking water supplies presents specific filtration considerations due to its intermediate chain length.
Removal Characteristics
As a 6-carbon compound, PFHxS falls between the readily removed long-chain PFAS (8+ carbons) and the more challenging short-chain compounds (4 carbons and below). Activated carbon removal of PFHxS is generally good — typically 85 to 95% with carbon block systems — but lower than for PFOA and PFOS under equivalent conditions. Ion exchange resins designed for PFAS removal show strong PFHxS performance, often exceeding 95%.
RO Performance
Reverse osmosis provides reliable PFHxS removal through membrane exclusion, with most certified systems achieving 95 to 99% reduction. Given PFHxS’s regulatory status and moderate chain length, RO is the most conservative treatment choice for households with detected PFHxS, particularly when concentrations are elevated and achieving concentrations well below the 4 ppt hazard index threshold is desired.
Practical Recommendations
Households in areas with detected PFHxS should test their source water, then select a treatment system that covers intermediate chain length compounds. Requesting specific PFHxS performance data from filter manufacturers — rather than relying solely on PFOA/PFOS certification — ensures the system will perform adequately for the actual compounds present. Annual post-filter verification testing is particularly important for compounds with intermediate removal characteristics.