GenX is the trade name for a family of PFAS compounds developed as alternatives to PFOA by chemical manufacturers seeking to replace regulated long-chain PFAS. The primary GenX compound, HFPO-DA (hexafluoropropylene oxide dimer acid), has emerged as a contaminant of concern in surface water and drinking water near production facilities, particularly in the Cape Fear River basin in North Carolina.
Why GenX Presents Filtration Challenges
GenX compounds are short-chain ether-linked PFAS with different molecular geometry than the linear PFAS like PFOA and PFOS. Their shorter chain length and ether linkages result in lower hydrophobicity, reducing their affinity for activated carbon surfaces compared to legacy long-chain PFAS. Studies have shown that GAC provides inconsistent GenX removal, with some investigations finding removal rates as low as 40–60% under conditions where PFOA removal exceeded 95%.
Better-Performing Technologies
Carbon block filters with longer contact times perform better than GAC for GenX. Ion exchange resins with quaternary ammonium functional groups show superior GenX removal, making them increasingly preferred for treatment in affected areas. Nanofiltration and reverse osmosis also achieve effective GenX removal through size exclusion and electrostatic repulsion. For households in GenX-affected areas, RO or ion exchange is recommended over GAC alone.
Regulatory Status
HFPO-DA is regulated by EPA at a maximum contaminant level of 10 ppt under the 2024 PFAS rule — reflecting both its toxicological profile and the treatment challenges it presents. Communities and households in affected areas should ensure their treatment technology is specifically verified for GenX removal, not just for PFOA and PFOS.