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9Cl-PF3ONS

9-chlorohexadecafluoro-3-oxanone-1-sulfonic acid

2-(6-chloro-1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexoxy)-1,1,2,2-tetrafluoroethanesulfonic acid

Also known as 9Cl-PF3ONS6:2 Cl-PFESA
2-((6-chloro-1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexyl)oxy)-1,1,2,2-tetrafluoroethanesulfonic acidPerfluoro(2-((6-chlorohexyl)oxy)ethanesulfonic acid)9Cl-PF3ONS2-(6-chloro-1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexoxy)-1,1,2,2-tetrafluoroethanesulfonic acid2-((6-chloro-1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexyl)oxy)-1,1,2,2-tetrafluoroethane-1-sulfonic acidClOPFLSA n=66:2 Cl-PFAES6:2 Cl-PFESA

A chlorinated perfluoroether sulfonic acid (6:2 Cl-PFESA), the major component (~90%) of the Chinese-made F-53B chromium-plating mist suppressant. Persistent, bioaccumulative, and detected at low ppt levels under UCMR 5.

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 In utero

Vulnerable populations

Pregnant Infants Children

Overview

9-chlorohexadecafluoro-3-oxanone-1-sulfonic acid (9Cl-PF3ONS), also known as 6:2 Cl-PFESA, is a chlorinated perfluoroether sulfonic acid and the major component (~90%) of F-53B — a chromium-electroplating mist suppressant developed in China in the 1970s as a 'safer' replacement for PFOS in metal-finishing applications. The minor component of F-53B (~10%) is its longer-chain sibling 11Cl-PF3OUdS (8:2 Cl-PFESA). 9Cl-PF3ONS has been detected in surface water, drinking water, and human serum across multiple continents and was found in 42 U.S. public water systems serving roughly 130,000 people under EPA's UCMR 5 monitoring program, with the highest concentration (11.7 ppt) measured at Lincoln, Alabama.

Pollution sources

Industry Manufacturing Consumer products

Sources

9Cl-PF3ONS enters drinking water primarily through industrial discharges from metal-finishing operations that historically used F-53B as a chromium mist suppressant. Although F-53B production and use have been concentrated in China, atmospheric long-range transport, imported consumer goods, and U.S. industrial emissions have produced detectable contamination in multiple regions. UCMR 5 detections so far cluster in Alabama, Oklahoma (Ponca City area), Massachusetts, and New York. As with other Cl-PFESAs, 9Cl-PF3ONS is highly mobile in groundwater and resists degradation indefinitely, allowing contamination plumes to migrate far from the original release sites.

Health risks

9Cl-PF3ONS has not been formally classified as a carcinogen by IARC or NTP, but it shares the structural and toxicological profile of other PFAS of concern. In animal and human studies, Cl-PFESAs have been linked to hepatotoxicity, thyroid hormone disruption, immune suppression, and adverse developmental effects. Occupational studies of F-53B-exposed Chinese electroplating workers documented serum elimination half-lives on the order of 15 years for 6:2 Cl-PFESA — substantially longer than PFOA (~2.4 years) or PFOS (~5.4 years), and among the longest measured for any PFAS in humans. This analyte is monitored under UCMR 5 but is not currently subject to a federal MCL.

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. Ion exchange Resin beads that swap unwanted ions (lead, calcium, certain PFAS, perchlorate) for harmless ones like sodium. Common in water softeners and PFAS treatment columns.

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

9Cl-PF3ONS is removed effectively by granular activated carbon (GAC), anion exchange resin, and high-pressure membranes including reverse osmosis and nanofiltration. Its perfluorinated chain and chlorine substituent contribute to strong adsorption on GAC media. 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

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Related contaminants

11-chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (11Cl-PF3OUdS) A chlorinated perfluoroether sulfonic acid (8:2 Cl-PFESA), the minor component of F-53B chromium-plating mist suppressant. Persistent and bioaccumulative; detected at low ppt levels in U.S. drinking water under UCMR 5.

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