Formula C8HF17O3S Boiling point 133 °C | Molar mass 500.13 g/mol Classification Sulfonic acid | |
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Related compounds | ||
Perfluorooctanesulfonic acid (conjugate base perfluorooctanesulfonate) (PFOS) is an anthropogenic 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 be synthesized in industrial production or result from the degradation of precursors. 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. "This association was independent of confounders such as age, sex, race/ethnicity, body mass index, diabetes, hypertension, and serum cholesterol level."
Contents
History
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.
Advances in analytical chemistry in recent years have allowed the routine detection of low- and sub-ppb levels of PFOS in food, wildlife, and humans.
Synthesis
Two primary methods are used for the industrial scale production of PFOS: electrophilic (or electrochemical) fluorination (ECF) and telomerisation. ECF is an electrolysis production method where a precursor of perfluoroctanesulfonyl fluoride is dispersed in a solution of hydrofluoric acid and electrified. This production method, whilst economic and mainly results in PFOS, also results in shorter chain perfluoroalkyl substances being formed. PFOS predominates in the resultant mixture, however if the reaction is allowed to continue this begins to favour the production of shorter chain PFAS. 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 production along with other PFOS related products.
Telomerisation involves constructing the PFOS molecule using short chain (often 2-carbon) moieties 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 more pure product than ECF, is not known to have been widely used except for production of reagent grade PFOS and analytical standards.
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. 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.
Uses
Perfluorooctanesulfonic acid is usually used as the sodium or potassium salts.
The most important emission sources of PFOS are metal plating and fire-fighting foams.
Health effects in humans and wildlife
According to a 2002 study by the Environmental Directorate of the OECD "PFOS is persistent, bioaccumulative and toxic to mammalian species."
In 2008, it was shown to affect 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. 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 brain asymmetry and decreased immunoglobulin levels. 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. 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.
The levels observed in wild animals are considered sufficient to "alter health parameters". In people, the highest exposures to PFOS in blood have been 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 can cause cancer, delays in physical development, stunted 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 at 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 U.S., and concentrations have been decreasing over time. In contrast, PFOS blood levels appear to be rising in China. PFOS levels in pregnant women have been associated with preeclampsia. Increased levels have been associated with altered thyroid hormone levels in adults and an increased risk of elevated 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).
Precursors
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. Later, the OECD came up with a document containing a list of 20 pages with potential precursors to PFOS.
Regulation
In May 2009, PFOS was included in Annex B of the Stockholm Convention on persistent organic pollutants by the Fourth Conference of Parties. In 2008 Canada proposed a 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). 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. 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).