HFPO-DA

Hexafluoropropylene oxide dimer acid

2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)propanoic acid

Also known as HFPO-DA GenX

2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)propanoic acid2,3,3,3-Tetrafluoro-2-(heptafluoropropoxy)propionic acidPropanoic acid, 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-236-236-82,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acidPERFLUORO(2-METHYL-3-OXAHEXANOIC) ACIDGenXPerfluoro-2-methyl-3-oxahexanoic acid

A perfluoroether carboxylic acid (GenX) developed by DuPont/Chemours as a PFOA replacement for fluoropolymer manufacturing. Federally regulated under EPA's 2024 PFAS NPDWR at MCL 10 ppt; widely detected in U.S. drinking water.

Chemistry

CAS 13252-13-6

Formula C6HF11O3

Mol. weight 330.05 g/mol

Group PFAS · perfluoroether-carboxylic-acid

Chemistry — what these mean

CAS: CAS Registry Number — a unique numeric ID assigned by the Chemical Abstracts Service. Every chemical has one, and it's the universal lookup key across regulatory and scientific databases.
Formula: The contaminant's molecular formula — the count of each atom in one molecule (e.g. C8HF15O2 means 8 carbon, 1 hydrogen, 15 fluorine, 2 oxygen atoms). Used to identify the compound in chemistry references.
Mol. weight: Molecular weight — the total mass of one molecule in grams per mole. Used to convert between mass-based and concentration-based measurements.
Group: The chemical family this contaminant belongs to — e.g. PFAS, disinfection byproducts, heavy metals. Contaminants in the same group often share treatment options and regulatory approach.

Regulatory limits

Values in ppt (parts per trillion)

EPA MCL 10 ppt

EPA MCLG 10 ppt

Status: Under review

Compliance by Apr 25, 2029

Detection limit 5 ppt

Regulatory limits — what these mean

EPA MCL: Maximum Contaminant Level — the highest amount of a contaminant legally allowed in drinking water, federally enforced by the EPA. Above this level, the utility must take corrective action and notify customers.
EPA MCLG: Maximum Contaminant Level Goal — the level the EPA considers safe with no known or expected health risk. Non-enforceable: it sets the health-based target, while the enforceable MCL sits above it where treatment costs make hitting the goal impractical.
Proposed status: Where the regulation sits in the EPA process — enforced (in force), proposed (awaiting finalization), under review, or withdrawn. A proposed limit is not legally binding yet, but it signals where regulation is heading.
Compliance by: The date utilities must meet a new or updated limit. Until then, the prior limit (or no limit) applies. Recent PFAS rules in particular phase in over multiple years.
Detection limit: The lowest concentration testing equipment can reliably measure. A "non-detect" result does not mean zero — it means below this threshold. Important for ultra-trace contaminants like PFAS, where the legal limit sits near what labs can actually measure.

Occurrence

UCMR 5

2023 – 2025

Occurrence — about this data

The Unregulated Contaminant Monitoring Rule — the EPA program that tests public water systems for contaminants that are not yet federally regulated. Each cycle (UCMR 1 through 6, roughly every five years) targets a different shortlist; UCMR 5 focused on PFAS. The data informs whether the EPA later regulates those contaminants.

External databases

PubChem 114481 EPA CompTox DTXSID70880215 EPA code HFPO-DA

External databases — what these mean

PubChem 114481: PubChem CID — the unique compound ID in the NIH's PubChem chemical database. Tap the pill to open the substance record: structure, physical properties, safety data, and links to related research.
EPA CompTox: The EPA's research-side chemical registry — the CompTox Chemicals Dashboard. Each substance gets a DTXSID identifier that links it to bioactivity data, exposure estimates, and regulatory programs.
EPA code: Internal EPA code used in SDWIS (the EPA's drinking-water records system) to identify a contaminant across compliance reports and violations. Useful for cross-referencing against state monitoring data.

Group

PFAS

Regulatory status

Primary

NPDWR — federally enforced MCL

Top removal tech

Activated carbon

Primary concern: Liver and immune toxicity

Affected organ systems

Liver Immune Developmental Endocrine Thyroid

Health effects

Immunotoxin Endocrine disruptor Developmental toxin Hepatotoxin

Exposure routes

Drinking water Dietary Occupational In utero

Vulnerable populations

Pregnant Infants Children

Overview

Hexafluoropropylene oxide dimer acid (HFPO-DA), marketed by Chemours under the trade name GenX, is a perfluoroether carboxylic acid introduced around 2009–2010 as a replacement for PFOA in fluoropolymer manufacturing. The GenX process is used at the Chemours Fayetteville Works site in North Carolina to produce fluoropolymer resins for cookware coatings, food packaging, semiconductor components, and other industrial applications. Despite manufacturer claims of a shorter biological half-life than PFOA, HFPO-DA is extraordinarily persistent in the environment, mobile in groundwater, and has been detected in 163 U.S. public water systems serving roughly 2.7 million people under EPA's UCMR 5 monitoring. In April 2024 EPA finalized a Maximum Contaminant Level of 10 ppt for HFPO-DA as one of six PFAS regulated under the National Primary Drinking Water Regulation.

Pollution sources

Industry Manufacturing Consumer products

Sources

HFPO-DA enters drinking water primarily through industrial discharges and atmospheric deposition from fluoropolymer manufacturing plants. The two principal U.S. sources are the Chemours Fayetteville Works facility, which contaminated the Cape Fear River and downstream public water systems in southeastern North Carolina (Brunswick County, Wilmington), and the legacy DuPont Washington Works plant in Parkersburg, West Virginia, which has produced detectable contamination in Lubeck PSD (WV), Little Hocking (OH), and other Ohio River communities. UCMR 5 results show the highest concentrations clustering in Kentucky, South Carolina, North Carolina, and the Ohio River valley, with South Point Village (OH) measuring 39.1 ppt average — nearly four times the federal MCL.

Health risks

EPA's 2024 PFAS NPDWR set the HFPO-DA MCL of 10 ppt based on liver toxicity observed in animal studies — the underlying Reference Dose was derived from increased liver weight and hepatocellular hypertrophy in mouse oral dosing studies. HFPO-DA has not been formally classified as a carcinogen by IARC or NTP, but it has been associated with immune suppression, thyroid disruption, and adverse developmental effects in laboratory studies, and crosses the placenta in humans. Chemours-funded studies have reported a human serum elimination half-life on the order of days-to-weeks — much shorter than PFOA — but independent confirmation is limited and the environmental persistence is undiminished.

Effective treatments

Activated carbon Reverse osmosis Ion exchange

Does not remove

UV Chlorination Boil

NSF certifications

NSF/ANSI 53 Health-related contaminants NSF/ANSI 58 Reverse osmosis systems

Water treatment

HFPO-DA is removed effectively by granular activated carbon (GAC), anion exchange resin, and high-pressure membranes including reverse osmosis and nanofiltration. Because HFPO-DA is a shorter-chain perfluoroether acid, it adsorbs less strongly to GAC than long-chain PFAS such as PFOA — GAC breakthrough occurs sooner, so utilities meeting the new federal MCL must monitor media life closely and replace it more frequently than for legacy PFAS. Conventional treatment processes — coagulation, sand filtration, disinfection, UV, and ozonation — do not remove it. Boiling concentrates rather than removes it. NSF/ANSI 53 and NSF P473 certify point-of-use filters for PFAS reduction; NSF/ANSI 58 covers RO systems.

Gallery

Related contaminants

4,8-dioxa-3H-perfluorononanoic acid (ADONA) A perfluoroether carboxylic acid developed by 3M/Dyneon as a PFOA replacement for fluoropolymer manufacturing. Persistent in the environment; detected at low ppt levels in U.S. drinking water under EPA's UCMR 5 monitoring program.

Chemistry + classification data sourced from public databases (PubChem, EPA CompTox, IARC monographs); 3D molecular models from 3d.nih.gov where available.