Perfluorooctanesulfonic acid

Perfluorooctanesulfonic acid (PFOS) (conjugate base perfluorooctanesulfonate) is a chemical compound having an eight-carbon fluorocarbon chain and a sulfonic acid functional group, and thus it is a perfluorosulfonic acid and a perfluoroalkyl substance (PFAS). It is an anthropogenic (man-made) fluorosurfactant, now regarded as a global pollutant. PFOS was the key ingredient in Scotchgard, a fabric protector made by 3M, and related stain repellents. The acronym "PFOS" refers to the parent sulfonic acid and to various salts of perfluorooctanesulfonate. These are all colorless or white, water-soluble solids. Although of low acute toxicity, PFOS has attracted much attention for its pervasiveness and environmental impact. It was added to Annex B of the Stockholm Convention on Persistent Organic Pollutants in May 2009.<ref name="PR09May">Template:Cite book</ref>

History

In 1949, 3M began producing PFOS-based compounds by electrochemical fluorination.<ref name=Paul>Template:Cite journal</ref> In 1968, organofluorine compounds were detected in the blood serum of consumers, and in 1976, perfluorooctanoic acid (PFOA) or a related compound such as PFOS were suggested as components.<ref name=Kennedy2004>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref name=Lau04>Template:Cite journal</ref> In 1997, 3M detected PFOS in blood from global blood banks,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> although the company's internal documents indicate knowledge of this decades earlier, dating from the 1970s.<ref name="Fellner">Template:Cite news</ref> In 1999, the U.S. Environmental Protection Agency began investigating perfluorinated compounds after receiving data on the global distribution and toxicity of PFOS, the key ingredient in Scotchgard.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> For these reasons, and USEPA pressure,<ref>Template:Cite news</ref> the primary American producer of PFOS, 3M, announced, in May 2000, the phaseout of the production of PFOS, PFOA, and PFOS-related products.<ref name="3M08">3M: "PFOS-PFOA Information: What is 3M Doing?" Template:Webarchive Accessed October 25, 2008.</ref><ref name="Fellner" /> Most other manufacturers (particularly, those in Europe) phased out the production of PFOS and perfluorooctanoic acid (PFOA) in 2000 and 2006, respectively. A shorter-chain PFOS (perfluorohexanesulfonic acid, PFHxS), was included in Annex A to the Stockholm Convention in 2022.<ref>Template:Cite journal</ref>

Currently, most of PFOS and PFOS-related chemicals are produced in China.<ref>Template:Cite journal</ref>

Chemistry

Template:More citations needed The main method used for the industrial scale production of PFOS is electrochemical fluorination (ECF).<ref>Template:Cite book</ref> ECF is an electrolysis method whereby the precursor of octanesulfonyl fluoride is electrolyzed in a solution of hydrogen fluoride to give perfluorooctanesulfonyl fluoride. This production method also results in shorter chain perfluoroalkyl substances being formed.Template:Cn PFOS predominates in the resultant mixture. A distinct isomer ratio has been observed in PFOS produced by ECF, in the order of 70% linear PFOS, 25% branched and 5% terminal; this is not a function of the production process but rather that the precursor also exhibits this isomer ratio. ECF was the means by which 3M produced PFOS up until May 2000 when the company announced a phaseout of fluorosurfactants.

Although 89 constitutional isomers of PFOS are possible,<ref>Template:Cite journal</ref> environmental samples usually consist of a mixture of the linear isomer and 10 branched isomers.<ref>Template:Cite journal</ref>

Telomerisation involves constructing the PFOS molecule using short chain (often 2-carbon) precursors and adding a sulfonate group as a final step. This production process results in 100% linear PFOS. This production method, whilst cleaner and resulting in a much purer product than ECF, is not known to have been widely used except for the production of reagent grade PFOS and analytical standards.Template:Cn

Indirect routes

Perfluorooctylsulfonyl compounds degrade to PFOS.<ref>Template:Cite book</ref> Examples include Template:Ill (N-MeFOSE), a carpet stain repellent, and Template:Ill (N-EtFOSE), a paper treatment.<ref>Template:Cite journal</ref> Also perfluorooctanesulfonamide is a precursor.<ref name=Leh>Template:Cite journal</ref> About 50 precursors were named in the 2004 proposed Canadian ban on PFOS.<ref>Template:Cite journal</ref>

Degradation

PFOS virtually does not degrade under environmental conditions and is thus highly persistent. Waste water treatment plants are also unable to degrade PFOS.<ref>Template:Cite journal</ref> On the other hand, precursors are transformed to PFOS in waste water treatment plants.<ref>Template:Cite journal</ref>

Properties

The C₈F₁₇ subunit of PFOS is hydrophobic and lipophobic, like other fluorocarbons, while the sulfonic acid/sulfonate group adds polarity. PFOS is an exceptionally stable compound in industrial applications and in the environment because of the effect of aggregate carbon–fluorine bonds. PFOS is a fluorosurfactant that lowers the surface tension of water more than that of hydrocarbon surfactants.

Uses

Perfluorooctanesulfonic acid was usually used as the sodium or potassium salts.

• PFOS was the key ingredient in Scotchgard, a fabric protector made by 3M, and numerous stain repellents.
• PFOS, together with PFOA, has also been used to make aqueous film forming foam (AFFF), a component of fire-fighting foams, and alcohol-type concentrate foams.
• PFOS compounds can also be found in some impregnation agents for textiles, paper, and leather; in wax, polishes, paints, varnishes, and cleaning products for general use; in metal surfaces, and carpets.
• In the semiconductor industry, PFOS is used in multiple photolithographic chemicals including: photoacid generators (PAGs) and anti-reflective coatings (ARCs). It has been phased out in the European Union semiconductor industry due to health concerns.
• PFOS is the key ingredient in Skydrol, a fire-resistant hydraulic fluid used in commercial aviation.

The most important emission sources of PFOS have been metal plating and fire-fighting foams.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Because of concerns about PFOS, F-53B has been used as a replacement for mist suppression in metal plating.<ref>Template:Cite journal</ref>

Levels in humans

Because of its chemical properties, PFOS will remain in the body for several years. It is estimated that it takes 4 years for half of this substance to be eliminated from the body.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

PFOS is detected in the blood serum of almost all people in the U.S., but concentrations have been decreasing over time. In contrast, PFOS blood levels appear to be rising in China<ref>Template:Cite journal</ref> where PFOS production continues. A study of ca. 2000 teenagers from 9 European countries with most samples collected in years 2016-2018 found higher blood concentrations of several PFOS’s in those, who consumed more seafood, eggs or offal, as well as in those from North and West (versus the South and East) Europe. Within the same country, boys had a higher PFOS concentrations than girls. A typical PFOS blood concentration range in this study was 1,500–2,500 ppb. <ref>PFAS levels and determinants of variability in exposure in European teenagers – Results from the HBM4EU aligned studies (2014–2021). 2023. Int J Hyg Environ Health. 247/. D. Richterová, E. Govarts, L. Fábelová, K. Rausová, L. Rodriguez Martin, L. Gilles, et al. doi: 10.1016/j.ijheh.2022.114057.</ref>

Much higher levels of blood PFOS (12,830 ppb) have been reported in people with occupational exposure <ref>Template:Cite journal</ref>—or possibly 1,656 parts per billion<ref>Template:Cite journal</ref>—in a consumer. Occupationally exposed individuals may have an average level of PFOS over 1000 parts per billion, and a small segment of individuals in the upper range of the general population may be over the 91.5 parts per billion level.<ref name="pmid18629339">Template:Cite journal</ref>

PFOS exposure has been demonstrated as early as fetal development during pregnancy since PFOS can easily pass through the placenta.<ref name="Sunderland 131–147">Template:Cite journal</ref> It has been shown that fetal exposure to PFOS is quite prevalent and has been shown to be detected in greater than 99% of umbilical cord serum samples.<ref name="Tarapore 3794">Template:Cite journal</ref>

PFOS has been detected in U.S. freshwater fish,<ref>Template:Cite news</ref><ref>Template:Cite journal</ref> as well as in municipal wastewater<ref>Template:Cite journal</ref> and drinking water samples,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> worldwide, at concentrations ranging between few ng/L and some μg/L.

Levels in wildlife

A variety of wildlife species have had PFOS levels measured in egg, liver, kidney, serum, and plasma samples and some of the highest recorded values as of January 2006 are listed below.<ref name=hou>Template:Cite journal Supporting Information (PDF).</ref>

Species	Geography	Year	Sample	PFOS (ppb)
Bald eagle	Midwestern United States	1990–93	plasma	2,200
Brandt's cormorant	California, US	1997	liver	970
Guillemot	Baltic Sea, Sweden	1997	egg	614
Carrion crow	Tokyo Bay, Japan	2000	liver	464
Red-throated loon	North Carolina, US	1998	liver	861
Polar bear	Sanikiluaq, Nunavut, Canada	2002	liver	3,100
Harbor seal	Wadden Sea, the Netherlands	2002	muscle	2,725
Bottlenose dolphin	Charleston, South Carolina, US	2003	plasma	1,315
Common dolphin	Mediterranean Sea, Italy	1998	liver	940
Mink	Michigan, US	2000–01	liver	59,500
Common shiner	Ontario, Canada	2001	liver	72,900
Great tit	near 3M, Port of Antwerp, Belgium	2007	liver	553–11,359<ref>Template:Cite journal</ref>

Despite the global wide-ranging restriction, PFOS concentrations in air continued to increase at many monitoring stations between 2009 and 2017.<ref>Template:Cite journal</ref>

Health effects in humans and wildlife

There is a growing body of research investigating the health effects of PFOS in humans and animals, including the reproductive, developmental, liver, kidney, thyroid, and immunological effects.<ref name="Blake 152565">Template:Cite journal</ref> According to a 2002 report by the Environmental Directorate of the OECD, "PFOS is persistent, bioaccumulative, and toxic to mammalian species."<ref name="OECD02">Template:Cite journal</ref>

Pregnancy outcomes

Several studies have focused on pregnancy outcomes in infants and mothers who are exposed to PFOS during pregnancy. For developing offspring, exposure to PFOS occurs through the placenta.<ref name="Sunderland 131–147"/> While the impact of PFOS compounds on fetal development continues to be an ongoing investigation, findings have demonstrated a relationship between PFOS exposure in pregnant mothers and negative birth outcomes.<ref>Template:Cite journal</ref>

There has been some evidence to suggest that PFOS levels in pregnant women have been associated with preeclampsia, preterm labor, low birth weight and gestational diabetes.<ref>Template:Cite journal</ref><ref name=":0">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Although, the strongest association is between PFOS levels with preterm birth and preeclampsia.<ref name=":0" /><ref>Template:Cite journal</ref> There has been some evidence to suggest that PFOS impairs fetal growth during pregnancy, although findings have been inconsistent.<ref name=":0" />

The specific physiological mechanisms behind adverse pregnancy outcomes with PFOS exposure remain unclear. One proposed cause has to do with PFOS impairment on placental blood flow.<ref name="Blake 152565"/> This mechanism could help explain several of the pregnancy-related outcomes from PFOS exposure including such as intrauterine growth development, low birth weight, preterm birth labor, and preeclampsia. Additional physiological mechanisms may include disruption in inflammatory signals during pregnancy, decreased trophoblast signaling and trophoblast migration.<ref>Template:Cite journal</ref> Additionally, PFOS exposure has been shown to be related to the downregulation genes corresponding to growth factors, pregnancy-related signal transducers, and maternal hormones.<ref>Template:Cite journal</ref> PFOS impact on thyroid hormone regulation also has the potential to impact several birth outcomes.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Breastfeeding and lactation

PFOS has been measured in breastmilk and is estimated to contribute the greatest level of PFOS exposure in infants. Specifically, the duration of breastfeeding has been shown to be associated with increases in PFOS in infants.<ref>Template:Cite journal</ref> Some evidence has shown that breastmilk accounts for more than 94% of the PFOS exposure in infants up to six months old.<ref>Template:Cite journal</ref> The Agency for Toxic Substances and Disease Registry (ATSDR) concluded that breastfeeding benefits continue to outweigh potential risks associated with PFOS in breastmilk.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Thyroid disease

Increased levels of PFOS have been shown to accumulate in thyroid gland cells and have been associated with altered thyroid hormone levels in adults.<ref name=":1">Template:Cite journal</ref><ref>Template:Cite journal</ref> Appropriate levels of thyroid hormone during pregnancy are critical for a developing fetus as this hormone is involved with brain development and body growth.<ref>Template:Citation</ref> Studies have demonstrated a relationship between PFOS exposure and thyroid dysfunction during pregnancy resulting in altered thyroid hormone levels in both the mother and the fetus.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Hypercholesterolemia

PFOS has been associated with increased risk of abnormal levels of cholesterol.<ref name="Steenland">Template:Cite journal</ref><ref name="Nelson">Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Specifically, epidemiological studies in humans have reported an association between increased PFOS levels and the total cholesterol and low density lipoprotein (LDL) cholesterol.<ref>Template:Cite journal</ref>

Chronic kidney disease

Serum levels of PFOS were found to be associated with increased risk of chronic kidney disease in the general US population.<ref name="Shankar et al, 2011">Template:Cite journal</ref> "This association was independent of confounders such as age, sex, race/ethnicity, body mass index, diabetes, hypertension, and serum cholesterol level."<ref name="Shankar et al, 2011" />

Cancer

Research demonstrating the association between PFOS and cancer is still ongoing. A few studies have demonstrated an elevated risk for prostate and bladder cancer, however, there were notable limitations in the design and analysis of these studies.<ref name=":0" /> As of November 2023, the International Agency for Research on Cancer (IARC) has classified PFOS as possibly carcinogenic to humans (Group 2b) based on “strong” mechanistic evidence.<ref>Template:Cite journal</ref> The Division of Cancer Epidemiology & Genetics (DCEG) is currently investigating the association of several PFAS compounds and cancers including kidney cancer, testicular cancer, prostate cancer, ovarian and endometrial cancer, thyroid cancer, non-hodgkins lymphoma, and childhood leukemia.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In wildlife

The levels observed in wild animals are considered sufficient to "alter health parameters".<ref>Template:Cite journal</ref><ref>Peden-Adams et al. (June 2008). In PFAA Days II Template:Webarchive (PDF). p. 28.</ref>

PFOS affects the immune system of male mice at a blood serum concentration of 91.5 parts per billion, raising the possibility that highly exposed people and wildlife are immunocompromised.<ref name="pmid18629339" /> Chicken eggs dosed at 1 milligram per kilogram (or 1 part per million) of egg weight developed into juvenile chickens with an average of ~150 parts per billion in blood serum—and showed brain asymmetry and decreased immunoglobulin levels.<ref>Template:Cite journal</ref>

Regulation

Globally

It was added to Annex B of the Stockholm Convention on Persistent Organic Pollutants in May 2009.<ref name="PR09May"/> Originally, parties agreed on acceptable proposes (time-unlimited exemptions) for the following uses—in addition to a range of specific exemptions (time-limited):<ref>SC-4/17: Listing of perfluorooctane sulfonic acid, its salts and perfluorooctane sulfonyl fluoride</ref>

• Photo-imaging
• Photo-resist and anti-reflective coatings for semi-conductors
• Etching agent for compound semi-conductors and ceramic filters
• Aviation hydraulic fluids
• Metal plating (hard metal plating) only in closed-loop systems
• Certain medical devices (such as ethylene tetrafluoroethylene copolymer (ETFE) layers and radio-opaque ETFE production, in-vitro diagnostic medical devices, and CCD colour filters)
• Fire-fighting foam
• Insect baits for control of leaf-cutting ants from Atta spp. and Acromyrmex spp.

In 2019, it was decided to only keep one acceptable purpose:<ref>SC-9/4: Perfluorooctane sulfonic acid, its salts and perfluorooctane sulfonyl fluoride</ref>

• Insect baits with sulfluramid (CAS No. 4151-50-2) as an active ingredient for control of leaf-cutting ants from Atta spp. and Acromyrmex spp. for agricultural use only

Canada

In 2023, the Government of Canada is considering addressing PFAS as a class rather than as individual substances or in smaller groups. A report to conclude that PFAS as a class are harmful to human health and the environment, and to define risk management aspects and alternatives to PFAs, is under development."Per-and polyfluoroalkyl substances (PFAS)"

Europe

Based on an OECD study on PFOS<ref name="OECD02" /> and a risk assessment by Europe's Scientific Committee on Health and Environmental Risks<ref name=Scher04>Template:Cite journal</ref> the European Union practically banned the use of PFOS in finished and semi-finished products in 2006 (maximum content of PFOS: 0.005% by weight).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, PFOS use for industrial applications (e.g. photolithography, mist suppressants for hard chromium plating, hydraulic fluids for aviation) was exempted. In 2009 this directive was incorporated into the REACH regulation.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In the summer of 2010 PFOS was added to the regulation on persistent organic pollutants and the threshold was lowered to max. 0.001% by weight (10 mg/kg).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

United States

In 2018 the State of Michigan established a legally enforceable groundwater cleanup level of 70 ppt for both PFOA and PFOS.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In 2020 the Michigan Department of Environment, Great Lakes, and Energy (EGLE) adopted stricter drinking water standards in the form of maximum contaminant levels (MCLs), lowering acceptable levels from the 2018 enforceable groundwater cleanup levels of 70 ppt to 8 ppt for PFOA and 16 ppt for PFOS and adding MCLs for 5 previously unregulated PFAS compounds PFNA, PFHxA, PFHxS, PFBS, and HFPO-DA.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In 2020, a California bill was passed banning PFOS and the following salts as an intentionally added ingredient from cosmetics: ammonium perfluorooctane sulfonate, diethanolamine perfluorooctane sulfonate, lithium perfluorooctane sulfonate and potassium perfluorooctane sulfonate.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In March 2021 the U.S. EPA announced that it will develop national drinking water standards for PFOA and PFOS.<ref>EPA (2021-03-03). "Announcement of Final Regulatory Determinations for Contaminants on the Fourth Drinking Water Contaminant Candidate List." Federal Register, Template:Usfr</ref>

In October 2021 the EPA proposed to designate PFOA and PFOS as hazardous substances in its PFAS Strategic Roadmap.<ref>RIN 2050-AH09</ref><ref>Docket EPA-HQ-OLEM-2019-0341</ref> In September 2022 the EPA proposed to designate as hazardous substances under the Superfund Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA).

See also

• 2005 Hertfordshire Oil Storage Terminal fire
• Fluorocarbons
• Per- and polyfluoroalkyl substances
• Timeline of events related to per- and polyfluoroalkyl substances

External links

• Template:Commons category-inline
• Mason Chemical Company, Fluorosurfactant Structure/Function page
• PFOS risk assessment report
• Centers for Disease Control and Prevention, Polyfluorochemicals fact sheet
• Perfluorinated substances and their uses in Sweden
• Chain of Contamination: The Food Link, Perfluorinated Chemicals (PFCs) Incl. PFOS & PFOA
• Provisional evaluation of PFT in drinking water with the guide substances perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) as examples