GenX (HFPO-DA) and other per- and polyfluoroalkyl ether acids (PFEAs) are next-generation PFAS compounds developed as replacements for legacy perfluorooctanoic acid (PFOA); they have been detected in drinking water sources near fluorochemical manufacturing facilities and are now subject to EPA maximum contaminant levels under the 2024 PFAS National Primary Drinking Water Regulation. Unlike long-chain PFAS, PFEAs have shorter environmental half-lives but still bioaccumulate in aquatic organisms and raise liver and developmental toxicity concerns at parts-per-trillion concentrations. Granular activated carbon, high-pressure membranes, and anion exchange resins are the primary removal technologies validated against this compound class.

Hopkins, Z. R.; Sun, M.; DeWitt, J. C.; Knappe, D. R. U.

Journal – American Water Works Association, 110 (7):13-28; 10.1002/awwa.1073 2018

Abstract:For several decades, a common processing aid in the production of fluoropolymers was the ammonium salt of perfluorooctanoic acid (PFOA). Because PFOA is persistent, bioaccumulative, and toxic, its production and use are being phased out in the United States. In 2009, the US Environmental Protection Agency stipulated conditions for the manufacture and commercial use of GenX, a PFOA replacement. While GenX is produced for commercial purposes, the acid form of GenX is also generated as a byproduct during the production of fluoromonomers. The discovery of high concentrations of GenX and related perfluoroalkyl ether acids (PFEAs) in the Cape Fear River and in finished drinking water of more than 200,000 North Carolina residents required quick action by researchers, regulators, public health officials, commercial laboratories, drinking water providers, and consulting engineers. Information about sources and toxicity of GenX as well as an analytical method for the detection of GenX and eight related PFEAs is presented. GenX/PFEA occurrence in water and GenX/PFEA removal by different drinking water treatment processes are also discussed. © 2018 American Water Works Association.

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Source: Water Feed

GenX and PFAS Ether Acids: The Emerging Contaminant Landscape

The phase-out of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) under the Stockholm Convention and U.S. TSCA stewardship agreements led chemical manufacturers to introduce shorter-chain and structurally modified PFAS alternatives. GenX chemicals — specifically hexafluoropropylene oxide-dimer acid (HFPO-DA) and its ammonium salt — were one of the first commercially deployed replacements, used primarily in fluoropolymer manufacturing. Subsequent environmental monitoring revealed that GenX and structurally related PFEAs migrate into surface water and groundwater at detectable concentrations, particularly downstream of manufacturing discharge points.

Detection in Drinking Water Sources

PFAS ether acids were first detected in the Cape Fear River watershed in North Carolina at concentrations ranging from sub-ng/L to several hundred ng/L, depending on proximity to the Chemours Fayetteville Works facility. Subsequent national-scale surveys have identified PFEAs in surface water intakes across the Southeast, Midwest, and industrial corridor states. The EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR5) requires all large systems and a representative sample of small systems to monitor for 29 PFAS, including GenX, between 2023 and 2025.

Health Effects and Toxicological Basis for Regulation

Animal studies on HFPO-DA show hepatotoxicity, developmental effects, and immune system impacts at low-dose exposures. While the compound shorter chain length results in more rapid elimination from human tissue compared to PFOA, the effective replacement dose required to substitute for PFOA industrial function means higher manufacturing volumes and consequently greater environmental loading. The EPA finalized MCLs for individual PFAS and a combined hazard index for PFAS mixtures in April 2024, establishing enforceable limits for PFOA, PFOS, PFNA, PFHxS, HFPO-DA (GenX), and PFBS.

Removal Technologies and Performance Data

Treatment efficacy against PFEAs varies by compound chemistry and system design:

• Granular activated carbon (GAC): Effective for longer-chain PFAS; short-chain PFEAs break through GAC beds faster, requiring more frequent regeneration or higher carbon contact time (EBCT greater than 15 minutes) to achieve consistent removals above 80%.
• High-pressure membranes (nanofiltration/RO): Achieve greater than 95% rejection of most PFAS including PFEAs due to size exclusion and charge repulsion. Concentrate stream management is a key consideration.
• Single-use anion exchange resins (SIEX): Single-use resins designed for PFAS can achieve effluent concentrations below 1 ng/L for GenX and are increasingly cost-competitive for systems where GAC contact time is limited by infrastructure constraints.