|Systematic IUPAC name
|Molar mass||500.13 g/mol|
|Boiling point||133 °C (271 °F; 406 K) at 6 torr|
|EU classification||Toxic (T)
Dangerous for the environment (N)
|R-phrases||R61, R20/22, R40, R48/25, R64, R51/53|
|S-phrases||S53, S45, S61|
|Perfluorooctanoic acid (PFOA), Perfluorobutanesulfonic acid (PFBS), Perfluorooctanesulfonamide (PFOSA), Perfluorononanoic acid (PFNA)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Perfluorooctanesulfonic acid or perfluorooctane sulfonate (PFOS) is a man-made fluorosurfactant and global pollutant. PFOS was the key ingredient in Scotchgard, a fabric protector made by 3M, and numerous stain repellents. It was added to Annex B of the Stockholm Convention on Persistent Organic Pollutants in May 2009. PFOS can form from the degradation of precursors in addition to industrial production. The PFOS levels that have been detected in wildlife are considered high enough to affect health parameters, and recently higher serum levels of PFOS were found to be associated with increased risk of chronic kidney disease in the general US population, consistent with earlier animal studies. "This association was independent of confounders such as age, sex, race/ethnicity, body mass index, diabetes, hypertension, and serum cholesterol level."
In 1949, 3M began producing PFOS-based compounds by electrochemical fluorination resulting in the synthetic precursor perfluorooctane sulfonyl fluoride. In 1968, organofluorine content was detected in the blood serum of consumers, and in 1976 it was suggested to be PFOA or a related compound such as PFOS. In 1997, 3M detected PFOS in blood from global blood banks. 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. For these reasons, and USEPA pressure, the primary American producer of PFOS, 3M, announced, in May 2000, the phaseout of the production of PFOS, PFOA, and PFOS-related products. PFOS and PFOS-related chemicals are currently produced in China.
The synthesis of PFOS uses perfluorooctanesulfonyl fluoride (POSF) as feedstock.
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. Although attention is typically focused on the straight-chain isomer (n-PFOS), which is dominant in commercial mixtures and environmental samples, there are 89 linear and branched congeners that are expected to have different physical, chemical, and toxicological properties.
Perfluorooctanesulfonic acid is 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.
- In Skydrol, a hydraulic fluid used in commercial aviation.
The most important emission sources of PFOS are metal plating and fire-fighting foams.
Threat to people and wildlife
According to a study by the Environmental Directorate of the OECD "PFOS is persistent, bioaccumulative and toxic to mammalian species."
It has been shown to affect the immune system of male mice at a blood serum concentration of ~90 parts per billion, raising the possibility that highly exposed people and wildlife are immunocompromised. Chicken eggs dosed at 1 milligram per kilogram (or 1000 parts per billion) of egg weight developed into juvenile chickens with an average of ~150 parts per billion in blood serum—and showed effects such as brain asymmetry and decreased immunoglobulin levels. Occupationally exposed individuals 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 are also over the 91.5 parts per billion level. 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.
|Bald eagle||Midwestern USA||1990–93||plasma||2,200|
|Brandt's cormorant||California, USA||1997||liver||970|
|Carrion crow||Tokyo Bay, Japan||2000||liver||464|
|Red-throated loon||North Carolina, USA||1998||liver||861|
|Polar bear||Sanikiluaq, Nunavut||2002||liver||3,100|
|Harbor seal||Dutch Wadden Sea, Denmark||2002||muscle||2,725|
|Bottlenose dolphin||Charleston, South Carolina, USA||2003||plasma||1,315|
|Common dolphin||Mediterranean Sea, Italy||1998||liver||940|
The levels observed in wild animals are considered sufficient to "alter health parameters". In people, the highest exposures to PFOS in blood are 12,830 parts per billion for occupational exposure and 656 parts per billion—or possibly 1,656 parts per billion—in a consumer.
In animal studies PFOS also causes cancer, physical development delays, stunts in animal growth, endocrine disruption, and neonatal mortality; neonatal mortality might be the most dramatic result of laboratory animal tests with PFOS. Female mice with blood levels of PFOS within ranges found in wildlife and humans demonstrated higher mortality when infected with influenza A. PFOS reduces the birth size of animals; in humans, correlations between PFOS levels and reduced fetal growth are inconsistent.
PFOS is detected in the blood serum of almost all people in the US, where concentrations are decreasing. By contrast, blood levels of PFOS appear to be rising in China. PFOS levels in pregnant women have been associated with preeclampsia. Levels have also been associated with altered thyroid hormone values and an increased risk of high cholesterol. Levels in US children aged 12–15 were associated with an increased risk (60% over the interquartile range) of attention deficit hyperactivity disorder (ADHD).
Volatile sulfonamide PFOS precursors include N-methyl perfluorooctane sulfonamidoethanol (N-MeFOSE), a carpet stain repellent, and N-ethyl perfluorooctane sulfonamidoethanol (N-EtFOSE), a paper treatment. Perfluorooctanesulfonamide is a precursor. About 50 precursors were named in the 2004 proposed Canadian ban on PFOS.
In May 2009 PFOS was included in Annex B of the Stockholm Convention on persistent organic pollutants by the Fourth Conference of Parties. Canada has a proposed ban on PFOS, only the second chemical proposed for a complete ban under the Canadian Environmental Protection Act.
Based on an OECD study on PFOS and a risk assessment by Europe's Scientific Committee on Health and Environmental Risks 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). Use of PFOS 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. In summer 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).
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