What GenX Is
GenX is the common name for HFPO-DA (hexafluoropropylene oxide-dimer acid), a short-chain PFAS compound developed and marketed by Chemours as a substitute for PFOA. Chemours has produced GenX at its Fayetteville Works facility in North Carolina since 2009. Contamination of the Cape Fear River downstream from the facility — the drinking water source for Wilmington, North Carolina — was reported in 2017 and sparked national attention to short-chain PFAS as a replacement chemical class.
Why Short-Chain Compounds Are Harder to Treat
Short-chain PFAS compounds — those with fewer than six carbons in the fluorinated chain — present distinct treatment challenges compared to long-chain compounds like PFOA and PFOS. Their shorter chains mean weaker interactions with activated carbon adsorption sites. Studies consistently find that granular activated carbon achieves lower removal rates for GenX, PFBS, and PFNA than for longer-chain compounds, often requiring higher media doses or more frequent replacement.
EPA Regulatory Action on GenX
The EPA’s 2024 PFAS National Primary Drinking Water Regulation established a 10 ppt maximum contaminant level for HFPO-DA (GenX) as part of a hazard index alongside three other PFAS compounds. This represents the first federal drinking water regulation specifically targeting short-chain PFAS substitutes — a regulatory development that closes the substitution loophole that drove GenX adoption in the first place.
Treatment Implications
Water systems and households seeking comprehensive PFAS protection cannot rely solely on standard activated carbon systems. Addressing the full spectrum of regulated PFAS — including short-chain compounds — requires either high-performance adsorptive media with demonstrated short-chain efficacy, reverse osmosis with its non-selective membrane rejection, or anion exchange resin with strong-base functional groups. Treatment selection should be guided by site-specific PFAS compound profiling.