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NFDHA

Nonafluoro-3,6-dioxaheptanoic acid

2,2-difluoro-2-[1,1,2,2-tetrafluoro-2-(trifluoromethoxy)ethoxy]acetic acid

Also known as NFDHA
Perfluoro-3,6-dioxaheptanoic acid671-204-0nonafluoro-3,6-dioxaheptanoic acidC5HF9O4NFDHA (dimer)DOPFLCA n=5PPWRLPJIHGWGFH-UHFFFAOYSA-NTYD-03561

A short-chain perfluoroether carboxylic acid; toxicology dataset is limited but assumed PFAS-class persistent. Low-prevalence UCMR 5 analyte detected in 14 U.S. public water systems serving 376K people at very low ppt levels.

Group
PFAS
Regulatory status
UCMR
Unregulated Contaminant Monitoring Rule
Top removal tech
Activated carbon

Primary concern: Immune and liver toxicity

Affected organ systems

Liver Immune Developmental Endocrine Affecting the body's hormone system — thyroid, adrenal, reproductive, or metabolic hormones. Thyroid

Health effects

Immunotoxin Suppresses or alters the immune system. Can increase risk of infection or reduce vaccine effectiveness. Endocrine disruptor Mimics or blocks the body's hormones (estrogen, thyroid, testosterone). Can affect development, reproduction, and metabolism at very low doses. Developmental toxin Causes harm during development before birth or in early childhood — birth defects, low birth weight, delayed growth, or learning problems later in life. Hepatotoxin Damages the liver. Effects range from elevated liver enzymes on a blood test to fatty liver disease and, with prolonged exposure, liver cancer.

Exposure routes

Drinking water Dietary Occupational

Vulnerable populations

Pregnant Infants Children

Overview

Nonafluoro-3,6-dioxaheptanoic acid (NFDHA) is a short-chain perfluoroether carboxylic acid built from a 2-carbon perfluoroalkyl tail, two ether oxygens, a perfluoromethyl head, and a terminal carboxylic acid (C5HF9O4, MW 296). It is structurally smaller than either of its UCMR 5 perfluoroether siblings — HFPO-DA (GenX, MW 330) and ADONA (MW 378). The compound has been used and studied primarily as an industrial fluorochemical processing intermediate and as a known biotransformation product of larger perfluoroether-ether precursors. Its independent commercial use is small, and the published toxicology dataset is correspondingly thin. UCMR 5 places NFDHA among the lowest-occurrence analytes in the program: detected in only 14 U.S. public water systems across four states (New York, Rhode Island, Texas, and Minnesota), serving roughly 376,000 people, with even the highest measured concentration (0.00394 ppb / 3.94 ppt at Clute, Texas) sitting well below NFDHA's own UCMR 5 Minimum Reporting Level of 20 ppt — every reported NFDHA value is an EPA-J-flagged estimate below the formal quantitation limit.

Pollution sources

Industry Manufacturing

Sources

Documented sources of NFDHA in U.S. drinking water are limited. Two source patterns are consistent with the observed geography: (1) industrial discharges and atmospheric deposition from fluoropolymer or specialty-chemical manufacturing — likely explaining the Clute / Richwood / Hemphill clusters in coastal Texas where the petrochemical and fluorochemical industries are concentrated; and (2) PFAS-precursor degradation in groundwater at known multi-PFAS impact sites — likely explaining the Rhode Island Newport-area detections (Naval Station Newport co-occurs with documented AFFF impact) and the Long Island, NY detections (regional groundwater PFAS plume). Because NFDHA can arise as a transformation product of larger perfluoroether ethers, its appearance can also signal the presence of unmeasured upstream precursors in the same source water.

Health risks

There is no NFDHA-specific Reference Dose, Health Reference Level, or carcinogen classification from EPA, IARC, or NTP. Risk assessment is therefore class-extrapolated from the better-studied perfluoroether carboxylic acids (HFPO-DA / GenX, ADONA) and broader PFAS: the carbon-fluorine and ether-oxygen backbone is environmentally and biologically persistent, and the structural similarity to HFPO-DA implies likely hepatotoxic and immunotoxic potential at sufficient exposures. Pharmacokinetic data in humans is essentially absent — no defensible serum half-life has been published — so EPA included NFDHA in UCMR 5 precisely to build the occurrence dataset that future toxicology work will need.

Effective treatments

Activated carbon Granular or block carbon that traps organic contaminants as water flows through. The most common point-of-use filter media — handles chlorine taste, VOCs, pesticides, and many PFAS. Reverse osmosis A semipermeable membrane that pushes water through under pressure, leaving most dissolved contaminants behind. Removes a very broad range — PFAS, lead, arsenic, nitrate, salts — at the cost of slower flow and some wastewater.

Does not remove

UV Ultraviolet light that disrupts the DNA of bacteria, viruses, and protozoa as water flows past the lamp. Disinfects but doesn't remove chemicals or particles. Chlorination Adds chlorine or hypochlorite to kill bacteria and viruses. The most common disinfection method in US water systems; leaves a residual that keeps water protected through the distribution pipes. Boil Kills bacteria, viruses, and protozoa after a one-minute rolling boil. Does NOT remove chemicals like lead, nitrate, or PFAS — boiling actually concentrates them as water evaporates.

NSF certifications

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

Water treatment

NFDHA is removed by the same processes that handle other short-chain perfluoroether acids: granular activated carbon (GAC), anion exchange resin, and high-pressure membranes (reverse osmosis, nanofiltration). The short perfluorinated chain and small molecular weight mean GAC adsorption is weaker than for long-chain PFAS like PFOA or PFOS — utilities sizing GAC for NFDHA should expect earlier breakthrough and shorter media life relative to legacy PFAS, mirroring the operational pattern observed with HFPO-DA and ADONA. 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 general PFAS reduction; NSF/ANSI 58 covers RO systems.

Gallery

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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. Hexafluoropropylene oxide dimer acid (HFPO-DA) 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 + classification data sourced from public databases (PubChem, EPA CompTox, IARC monographs); 3D molecular models from 3d.nih.gov where available.