9Cl-PF3ONS (6:2 chlorinated polyfluoroalkyl ether sulfonate, or 6:2 Cl-PFESA; CAS 756426-58-1) is the major component of the commercial mixture F-53B, a chromium-electroplating mist suppressant used almost exclusively in China. F-53B was adopted around the 1970s as a replacement for PFOS in metal plating. Despite being marketed as an alternative, peer-reviewed research found it is as resistant to degradation as PFOS, bioaccumulative, and has the longest human elimination half-life yet measured for any PFAS — roughly 15 years. The commercial product is the potassium salt; a minor congener, 8:2 Cl-PFESA, is also present.

Is 9Cl-PF3ONS in US drinking water?

Almost never. In EPA's fifth Unregulated Contaminant Monitoring Rule (UCMR 5, sampling 2023-2025), 9Cl-PF3ONS was detected in just 1 of 10,289 US public water systems — about 0.01% — at a maximum of 3.4 ng/L. It is a serious contaminant in China, where it originates from the chrome-plating industry, but it is essentially absent from US tap water. For a North American household the direct relevance is minimal.

Is F-53B regulated in the United States?

9Cl-PF3ONS is NOT one of the six PFAS with maximum contaminant levels in EPA's April 2024 National Primary Drinking Water Regulation. It IS one of the 29 PFAS monitored under UCMR 5, using EPA Method 533, so there is federal occurrence data but no enforceable limit. Internationally, PFOS, its salts, and PFOSF are listed under the Stockholm Convention (Annex B, 2009); F-53B itself is not individually listed. IARC has not evaluated F-53B or 9Cl-PF3ONS.

Where does 9Cl-PF3ONS come from?

The dominant source is the Chinese chromium-electroplating industry, where F-53B is used as a mist suppressant. The first environmental report measured it in plating wastewater at 65-112 micrograms per litre in influent and 43-78 micrograms per litre in effluent — concentrations that were not removed by treatment and passed to rivers at PFOS-comparable levels. It has since been detected biomagnifying in Bohai Sea marine organisms, in Beijing-market seafood, in the Dalian atmosphere, and in over 98% of sampled Chinese people, with the highest levels in plating workers and high fish consumers.

Is F-53B a safer alternative to PFOS?

No — it is close to the opposite, and it is often cited as a textbook example of a regrettable substitution. F-53B was adopted as a PFOS replacement, but peer-reviewed research shows it is as resistant to degradation as PFOS, clearly bioaccumulative and biomagnifying up marine food chains, thyroid-disrupting in rodents, and carries the longest human half-life measured for any PFAS to date at a median of about 15 years. Swapping one long-chain PFAS for a structurally similar alternative reproduced, and in the half-life dimension worsened, the original problem.

How long does 9Cl-PF3ONS stay in the body?

Longer than any other PFAS characterised to date. A 2016 study of exposed Chinese populations estimated a median total elimination half-life of 15.3 years, with a range of 10.1 to 56.4 years, and detected the compound in more than 98% of subjects. For comparison, PFOA and PFOS have human half-lives on the order of a few years. This extreme biopersistence is the single most striking property of the compound.

Should I worry about 9Cl-PF3ONS in my bedroom?

For a North American bedroom, the direct relevance is minimal — it was found in only 1 of 10,289 US water systems and there is no established consumer-product or indoor-dust pathway for it in North America. Its value in this Atlas is as a cautionary tale rather than a bedroom exposure: it shows that replacing one persistent long-chain PFAS with a similar alternative can reproduce or worsen the very problem the swap was meant to solve. The broader lesson applies directly to how you should read PFAS-free and safer-alternative marketing claims.

9Cl-PF3ONS (F-53B) in the Bedroom

At a glance

Chemical family	Chlorinated polyfluoroalkyl ether sulfonate (Cl-PFESA), a PFAS subclass. 9Cl-PF3ONS is the 6:2 congener and the major component of the commercial mixture F-53B; a minor congener, 8:2 Cl-PFESA (11Cl-PF3OUdS), is also present. Molecular formula C₈HClF₁₆O₄S PubChem CID 22568738
CAS number	756426-58-1 (acid form; PubChem CID 22568738). Commercial F-53B is supplied as the potassium salt
Classification	Not evaluated by IARC. NOT among the six PFAS with maximum contaminant levels in the EPA 2024 federal PFAS NPDWR; IS one of the 29 PFAS monitored under US EPA UCMR 5 (2023-2025) via EPA Method 533. Not individually listed under the Stockholm Convention (PFOS, its salts and PFOSF are listed in Annex B; F-53B is not)
Where you encounter it	Chinese chromium-electroplating industry, where F-53B is used as a mist suppressant — the source. Documented in plating wastewater, in Chinese rivers, biomagnifying in Bohai Sea marine organisms, in Beijing-market seafood, in the Dalian atmosphere, and in over 98% of sampled Chinese people. Near-absent from US drinking water (1 of 10,289 systems)
Sleep micro environment relevance	Effectively none for a North American bedroom. There is no established consumer-product, textile, or indoor-dust pathway for 9Cl-PF3ONS in North America, and it is virtually absent from US water. Its relevance here is conceptual — as evidence about how PFAS substitutions behave Inferred from the near-total absence of US occurrence and the China-specific industrial source
Activated carbon capture	Not applicable for VOC-phase capture — 9Cl-PF3ONS is a non-volatile, surface-active perfluorinated acid. Where it occurs in water, the same PFAS-certified treatment (NSF/ANSI 58 reverse osmosis; certified NSF/ANSI 53 for PFAS) used for other perfluoroalkyl acids would be the relevant control Inferred from general PFAS water-treatment performance; no 9Cl-PF3ONS-specific certification language located

Regulatory & certification status

Where 9Cl-PF3ONS (F-53B) stands across the major regulatory systems. Because this compound is an industrial contaminant essentially confined to China, most Western jurisdictions have no substance-specific measure for it. Where that is the case, it is stated as "no jurisdiction-specific measure identified" rather than asserted as a confirmed absence.

United States	9Cl-PF3ONS is NOT one of the six PFAS assigned maximum contaminant levels in EPA's April 2024 National Primary Drinking Water Regulation. It IS one of the 29 PFAS monitored under the fifth Unregulated Contaminant Monitoring Rule (UCMR 5), analysed by EPA Method 533, with sampling across 2023-2025. UCMR monitoring generates federal occurrence data but does not set an enforceable limit; the near-zero US detection rate (1 of 10,289 systems) is itself the key finding. Regulatory — EPA UCMR 5 · EPA PFAS
International (Stockholm Convention)	PFOS, its salts and PFOSF are listed under the Stockholm Convention on Persistent Organic Pollutants (Annex B, 2009; the acceptable-purpose and exemption framework was tightened in 2019). The metal-plating sector's historical PFOS exemption is the regulatory pressure that drove Chinese industry to adopt F-53B as a replacement in the first place. F-53B / 6:2 Cl-PFESA is itself NOT individually listed under the Convention. Regulatory — Stockholm Convention PFAS overview
IARC (cancer classification)	Neither F-53B nor 9Cl-PF3ONS has been evaluated by the International Agency for Research on Cancer. IARC's 2023 PFAS monograph (Vol. 135) covered PFOA (Group 1) and PFOS (Group 2B) only. There is therefore no IARC classification to report for this compound — an honest absence, not a clean bill of health. Regulatory — no IARC evaluation located
European Union	No F-53B-specific EU measure has been identified. PFAS as a class are the subject of a draft universal restriction under REACH and of ongoing SVHC and POPs activity, but no measure naming 9Cl-PF3ONS / 6:2 Cl-PFESA specifically was located. Treat this as "no jurisdiction-specific measure identified," not as confirmed absence — the ECHA databases are access-restricted to automated retrieval and were not read directly here. Inferred — no F-53B-specific EU instrument located; ECHA not directly consulted
Canada	No F-53B-specific Canadian measure has been identified. 9Cl-PF3ONS would fall within the scope of Canada's broad, still-developing class-based approach to PFAS under CEPA, but no substance-specific restriction naming it was located. Reported as "no jurisdiction-specific measure identified." Inferred — no F-53B-specific Canadian instrument located
Australia	No F-53B-specific Australian measure has been identified. Australia's industrial PFAS controls have focused on PFOS, PFOA and PFHxS; no measure naming 9Cl-PF3ONS / 6:2 Cl-PFESA specifically was located. Reported as "no jurisdiction-specific measure identified." Inferred — no F-53B-specific Australian instrument located
United Kingdom	No F-53B-specific UK measure has been identified. GB REACH maintains a separate SVHC and restriction process from the EU; no listing naming this compound specifically was located. Reported as "no jurisdiction-specific measure identified," not as confirmed absence. Inferred — no F-53B-specific GB instrument located
Certifications	No mainstream bedroom-product certification (CertiPUR-US, OEKO-TEX Standard 100, GREENGUARD) names 9Cl-PF3ONS specifically. As a non-volatile PFAS it would fall outside low-VOC emissions schemes entirely; textile total-fluorine / total-PFAS approaches such as OEKO-TEX's could in principle capture it, but the compound is not an expected constituent of North American bedding, so certification against it is not a practical concern. Industry — no compound-specific certification criteria located
The 72-hour test window	Not applicable. 9Cl-PF3ONS is a non-volatile, surface-active perfluorinated acid that partitions to water and surfaces rather than off-gassing, so a short VOC chamber emissions test would not capture it; it is measured instead by targeted PFAS analysis (LC-MS/MS) of water, dust or biofluids. Inferred — from the compound's volatility/emission profile versus the VOC focus of short chamber tests

What it is

9Cl-PF3ONS — 9-chlorohexadecafluoro-3-oxanonane-1-sulfonic acid, CAS 756426-58-1 — is the major component of the commercial product F-53B. Chemically it is a 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA): a perfluorinated ether sulfonic acid capped with a chlorine atom in place of the terminal fluorine you would find on a conventional PFAS such as PFOS. The commercial mixture is supplied as the potassium salt, with a minor congener — 8:2 Cl-PFESA (11Cl-PF3OUdS) — alongside the dominant 6:2 form (PubChem CID 22568738). Regulatory

F-53B is not a global commodity chemical. It has been manufactured and used almost exclusively in China, where — since roughly the 1970s — it has served as a mist suppressant in chromium electroplating. Its whole reason for existing is regulatory: PFOS, the traditional plating mist suppressant, came under international control, and F-53B was adopted as a domestic replacement. That origin story is the key to understanding it. This is not a "safer substitute" narrative. It is close to the opposite.

Where you encounter it

The Chinese chrome-plating industry — the source

F-53B enters the environment overwhelmingly through metal-plating wastewater. The first environmental report, by Wang and colleagues in 2013, measured it in electroplating wastewater in Wenzhou at 65–112 micrograms per litre in influent and 43–78 micrograms per litre in effluent — and found it was not removed by the plant's treatment, passing to receiving rivers at PFOS-comparable concentrations on the order of tens of nanograms per litre. Peer-reviewed In other words, the same properties that make PFAS useful and persistent carried straight through conventional treatment.

Biomagnifying through the food chain

Once in the aquatic environment, 9Cl-PF3ONS behaves like the long-chain PFAS it was meant to replace. Liu and colleagues 2017 found that 6:2 Cl-PFESA is the dominant Cl-PFESA congener in Bohai Sea marine organisms and that it biomagnifies up the marine food chain, much like PFOS. Peer-reviewed It has also been detected in seafood sampled from Beijing markets and in the atmosphere over Dalian — evidence that it has moved well beyond the immediate plating-plant footprint into food and air.

In the Chinese population — but not in US water

Human biomonitoring tells the same story. The compound has been detected in more than 98% of sampled Chinese people, with the highest burdens in plating workers and high fish consumers. Contrast that with the United States: in EPA's UCMR 5, 9Cl-PF3ONS turned up in a single water system out of 10,289, at a maximum of 3.4 ng/L. Regulatory That near-total absence is not an accident — F-53B was never a US or European industrial product, so the exposure that dominates in China simply has no counterpart pathway in a North American home.

What the research says

As persistent as PFOS — the original warning

Wang and colleagues 2013 titled their paper "First report of a Chinese PFOS alternative overlooked for 30 years" — and their central finding was that F-53B is "as resistant to degradation as PFOS." Peer-reviewed They reported a 96-hour zebrafish LC50 of 15.5 mg/L and confirmed it was not removed by wastewater treatment. The framing mattered: a chemical adopted specifically to get out from under PFOS regulation shared PFOS's defining hazard — environmental persistence.

The longest human half-life measured for any PFAS

The most striking single result comes from Shi and colleagues 2016, who studied elimination kinetics in exposed Chinese populations. They estimated a median total-elimination half-life of 15.3 years (range 10.1–56.4 years) and described 6:2 Cl-PFESA as "the most biopersistent PFAS in humans reported to date," detecting it in over 98% of subjects. Peer-reviewed For comparison, PFOA and PFOS have human half-lives on the order of a few years. On the single axis that matters most for a persistent pollutant — how long it stays in the body — the "alternative" is worse than the chemical it replaced.

Bioaccumulation and toxicity in fish

Wu and colleagues 2019 examined toxicokinetics and effects in adult zebrafish, reporting bioaccumulation (log bioconcentration factor 2.36–3.65), slow elimination, liver damage, and oxidative stress. Peer-reviewed These are the hallmarks of a bioaccumulative, biologically active PFAS rather than an inert substitute.

Thyroid disruption in mammals

The mammalian evidence points the same direction. Hong and colleagues 2020 ran a 28-day oral study in rats and found a dose-dependent decrease of roughly two-fold in serum T3 and T4, thyroid follicular hyperplasia at doses of 5 mg/kg/day and above, and a disrupted TSH feedback response — a clear signature of thyroid endocrine toxicity. Peer-reviewed Thyroid hormones govern metabolism and development, so this is not a trivial endpoint.

Putting it together

Across five peer-reviewed studies the picture is consistent: persistence comparable to PFOS, clear bioaccumulation and biomagnification, the longest human half-life measured for any PFAS to date, and thyroid toxicity in rodents. There is no dimension in which 9Cl-PF3ONS reads as a meaningful improvement over the compound it replaced. Inferred synthesis of the cited studies; no head-to-head risk assessment of F-53B versus PFOS was located

What this means for your bedroom

Directly, very little. 9Cl-PF3ONS is not an expected constituent of North American mattresses, bedding, or household dust, and it is virtually absent from US drinking water. If you live in North America, you are not being exposed to it through your sleep environment in any way this Atlas can document. There is no filter to buy, no label to check, no take-home protocol specific to this compound.

Indirectly, it is one of the most useful entries in the Atlas — because it is a clean, well-documented example of a regrettable substitution. A long-chain PFAS (PFOS) came under regulatory pressure; industry reached for a structurally similar alternative (F-53B); and that alternative turned out to be just as persistent, bioaccumulative and biomagnifying, thyroid-disrupting in mammals, and — on the half-life measure — worse. Inferred framing; the underlying persistence, bioaccumulation and toxicity findings are peer-reviewed The lesson generalises directly to how you should read "PFAS-free," "next-generation," and "safer chemistry" claims on the products that are in your bedroom: a swap to a chemically similar cousin is not the same as removing the hazard.

What does NOT help

Trusting "PFOS-free" as a proxy for "PFAS-free." F-53B is the definitive counterexample — a PFOS-free product built on a compound that shares PFOS's worst properties.
Assuming a "next-generation" or "alternative" fluorochemical is safer. The alternative here proved more biopersistent in humans than the chemical it replaced.
Reading the near-zero US water detection as reassurance about PFAS generally. It reflects only that this particular Chinese industrial compound has no North American source — the PFAS that are found in US water (PFOA, PFOS and others) are covered on their own Atlas pages.

Open research questions

Human health effects at real-world exposure levels — the toxicology is largely animal and in-vitro; population dose-response for 9Cl-PF3ONS specifically is still emerging. Speculation re: pace and direction of human epidemiology
Whether F-53B use, and therefore environmental loading, is rising or falling as Chinese PFAS policy evolves. Speculation — no current production-trend data located
Whether any measurable global transport (e.g. via seafood trade or atmosphere) produces detectable Western exposure over time, given the compound's persistence. Inferred open question from documented atmospheric and seafood detections in China

Where you meet 9Cl Pf3Ons across your home

The same compound turns up in more than one place you live. Here's where it shows up in Embr — each links to the full breakdown for that part of your home.

Your tap water

Citations

Wang S, Huang J, Yang Y, Hui Y, Ge Y, Larssen T, Yu G, Deng S, Wang B, Harman C (2013). First report of a Chinese PFOS alternative overlooked for 30 years: its toxicity, persistence, and presence in the environment. Environmental Science & Technology, 47(18):10163-10170. DOI 10.1021/es401525n Peer-reviewed — foundational report; F-53B "as resistant to degradation as PFOS"
Shi Y, Vestergren R, Xu L, Zhou Z, Li C, Liang Y, Cai Y (2016). Human exposure and elimination kinetics of chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs). Environmental Science & Technology, 50(5):2396-2404. DOI 10.1021/acs.est.5b05849 Peer-reviewed — median human half-life 15.3 years; most biopersistent PFAS reported to date
Liu Y, Ruan T, Lin Y, Liu A, Yu M, Liu R, Meng M, Wang Y, Liu J, Jiang G (2017). Chlorinated polyfluoroalkyl ether sulfonic acids in marine organisms from Bohai Sea, China: occurrence, temporal variations, and trophic transfer behavior. Environmental Science & Technology, 51(8):4407-4414. DOI 10.1021/acs.est.6b06593 Peer-reviewed — 6:2 Cl-PFESA dominant and biomagnifying up the marine food chain
Wu Y, Deng M, Jin Y, Mu X, He X, Luu NT, Yang J, Chen R, Zhang C (2019). Toxicokinetics and toxic effects of a Chinese PFOS alternative F-53B in adult zebrafish. Ecotoxicology and Environmental Safety, 171:460-466. DOI 10.1016/j.ecoenv.2019.01.010 Peer-reviewed — bioaccumulation (log BCF 2.36-3.65), liver damage, oxidative stress
Hong SH, Lee SH, Yang JY, et al. (2020). Orally administered 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) causes thyroid dysfunction in rats. Toxics, 8(3):54. DOI 10.3390/toxics8030054 Peer-reviewed — ~2x decrease in serum T3/T4, thyroid follicular hyperplasia at ≥5 mg/kg/day
US Environmental Protection Agency. Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) — monitors 29 PFAS including 9Cl-PF3ONS via EPA Method 533, sampling 2023-2025; occurrence source for this page. epa.gov/dwucmr Regulatory — occurrence data (1 of 10,289 systems; max 3.4 ng/L)
US Environmental Protection Agency. Per- and Polyfluoroalkyl Substances (PFAS) — the April 2024 National Primary Drinking Water Regulation sets MCLs for six PFAS; 9Cl-PF3ONS is not among them. epa.gov/sdwa/pfas Regulatory
Stockholm Convention on Persistent Organic Pollutants. PFAS Overview — PFOS, its salts and PFOSF listed in Annex B (2009; exemptions tightened 2019). The metal-plating PFOS exemption drove F-53B adoption; 6:2 Cl-PFESA is not itself individually listed. pops.int Regulatory
National Center for Biotechnology Information. PubChem Compound Summary CID 22568738 — 9-chlorohexadecafluoro-3-oxanonane-1-sulfonic acid (9Cl-PF3ONS / 6:2 Cl-PFESA), CAS 756426-58-1, formula C₈HClF₁₆O₄S. pubchem.ncbi.nlm.nih.gov Regulatory / database — identity and CAS

Frequently asked questions

What is 9Cl-PF3ONS?
9Cl-PF3ONS (6:2 chlorinated polyfluoroalkyl ether sulfonate, or 6:2 Cl-PFESA; CAS 756426-58-1) is the major component of the commercial mixture F-53B, a chromium-electroplating mist suppressant used almost exclusively in China. F-53B was adopted around the 1970s as a replacement for PFOS in metal plating. Despite being marketed as an alternative, peer-reviewed research found it is as resistant to degradation as PFOS, bioaccumulative, and has the longest human elimination half-life yet measured for any PFAS — roughly 15 years. The commercial product is the potassium salt; a minor congener, 8:2 Cl-PFESA, is also present.
Is 9Cl-PF3ONS in US drinking water?
Almost never. In EPA's fifth Unregulated Contaminant Monitoring Rule (UCMR 5, sampling 2023-2025), 9Cl-PF3ONS was detected in just 1 of 10,289 US public water systems — about 0.01% — at a maximum of 3.4 ng/L. It is a serious contaminant in China, where it originates from the chrome-plating industry, but it is essentially absent from US tap water. For a North American household the direct relevance is minimal.
Is F-53B regulated in the United States?
9Cl-PF3ONS is NOT one of the six PFAS with maximum contaminant levels in EPA's April 2024 National Primary Drinking Water Regulation. It IS one of the 29 PFAS monitored under UCMR 5, using EPA Method 533, so there is federal occurrence data but no enforceable limit. Internationally, PFOS, its salts, and PFOSF are listed under the Stockholm Convention (Annex B, 2009); F-53B itself is not individually listed. IARC has not evaluated F-53B or 9Cl-PF3ONS.
Where does 9Cl-PF3ONS come from?
The dominant source is the Chinese chromium-electroplating industry, where F-53B is used as a mist suppressant. The first environmental report measured it in plating wastewater at 65-112 micrograms per litre in influent and 43-78 micrograms per litre in effluent — concentrations that were not removed by treatment and passed to rivers at PFOS-comparable levels. It has since been detected biomagnifying in Bohai Sea marine organisms, in Beijing-market seafood, in the Dalian atmosphere, and in over 98% of sampled Chinese people, with the highest levels in plating workers and high fish consumers.
Is F-53B a safer alternative to PFOS?
No — it is close to the opposite, and it is often cited as a textbook example of a regrettable substitution. F-53B was adopted as a PFOS replacement, but peer-reviewed research shows it is as resistant to degradation as PFOS, clearly bioaccumulative and biomagnifying up marine food chains, thyroid-disrupting in rodents, and carries the longest human half-life measured for any PFAS to date at a median of about 15 years. Swapping one long-chain PFAS for a structurally similar alternative reproduced, and in the half-life dimension worsened, the original problem.
How long does 9Cl-PF3ONS stay in the body?
Longer than any other PFAS characterised to date. A 2016 study of exposed Chinese populations estimated a median total elimination half-life of 15.3 years, with a range of 10.1 to 56.4 years, and detected the compound in more than 98% of subjects. For comparison, PFOA and PFOS have human half-lives on the order of a few years. This extreme biopersistence is the single most striking property of the compound.
Should I worry about 9Cl-PF3ONS in my bedroom?
For a North American bedroom, the direct relevance is minimal — it was found in only 1 of 10,289 US water systems and there is no established consumer-product or indoor-dust pathway for it in North America. Its value in this Atlas is as a cautionary tale rather than a bedroom exposure: it shows that replacing one persistent long-chain PFAS with a similar alternative can reproduce or worsen the very problem the swap was meant to solve. The broader lesson applies directly to how you should read PFAS-free and safer-alternative marketing claims.

Related compounds

Embr is a sleep environment company researching the chemistry of the bedroom. See the methodology page for how this Atlas tags claims by evidence strength. For broader context on PFAS in drinking water, see water.

Last reviewed 2026-07-13. If you find a factual error, contact us.