Perfluorooctanoic acid (PFOA), also known as C8 and perfluorooctanoate, is a synthetic, stable perfluorinated carboxylic acid and fluorosurfactant. One industrial application is as a surfactant in the emulsion polymerization of fluoropolymers. PFOA has been manufactured since the 1940s in industrial quantities. It is also formed by the degradation of precursors such as some fluorotelomers.
PFOA persists indefinitely in the environment. It is a toxicant and carcinogen in animals. In people, it is detected in the blood of general populations in the low and sub-parts per billion range. Chemical plant employees and surrounding subpopulations have been identified with higher blood levels. Exposure is most consistently associated with increased cholesterol and uric acid levels, but there is insufficient evidence to conclude that PFOA exposure results in adverse health effects in people.
As a result of a class-action lawsuit and community settlement with DuPont, three epidemiologists are conducting studies on the population surrounding a chemical plant that was exposed to PFOA at levels greater than in the general population. If PFOA exposure is found to be likely to lead to an increased risk of disease, future liabilities for DuPont will be triggered. Full results from the study are expected in 2011.
How general populations are exposed to PFOA is not completely understood. PFOA has been detected in industrial waste, stain resistant carpets, carpet cleaning liquids, house dust, microwave popcorn bags, water, food, and PTFE. Although some cookware is marketed as PFOA-free, PTFE non-stick cookware is considered an insignificant exposure pathway.
In 1999, the United States Environmental Protection Agency (USEPA) began investigating perfluorinated chemicals after receiving data on the global distribution and toxicity of PFOS.[12] For these reasons, and USEPA pressure,[13] in May 2000, 3M announced the phaseout of the production of PFOA, PFOS, and PFOS-related products.[14] 3M stated that they would have made the same decision regardless of USEPA pressure.[15]
Because of the 3M phaseout, in 2002 DuPont built its own plant in Fayetteville, NC to manufacture the chemical.[16] The chemical has received attention due to litigation from the PFOA-contaminated community around DuPont's Washington Works Washington, WV facility, along with USEPA focus. Research on PFOA has demonstrated ubiquity, animal-based toxicity, and some associations with human health parameters and potential health effects. Additionally, advances in analytical chemistry in recent years have allowed the routine detection of low- and sub-parts per billion levels of PFOA in a variety of substances.[11]
PFOA is also synthesized by the telomerization represented below, where the telogen is the organoiodine compound and the taxogen is the unsaturated tetrafluoroethylene.[17][19]
ADONA, ammonium 4,8-dioxa-3H-perfluorononanoate, is 3M's PFOA replacement in the emulsion polymerization of fluoropolymers.[26]As a salt, the dominant use is as an emulsifier for the emulsion polymerization of fluoropolymers such as polytetrafluoroethylene (PTFE, or Teflon), polyvinylidene fluoride, and fluoroelastomers.[27][28] For this use, 3M subsidiary Dyneon has a replacement emulsifer[29] despite DuPont stating PFOA is an "essential processing aid".[30] PFOA is used in the production of Gore-Tex[31] as it is PTFE-based. In PTFE processing, PFOA is in aqueous solution and forms micelles that contain tetrafluoroethylene and the growing polymer.[32] PFOA can be used to stabilize fluoropolymer and fluoroelastomer suspensions prior to further industrial processing and in ion-pair reversed-phase liquid chromatography it can act as an extraction agent.[33] PFOA also finds uses in electronic products and as an industrial fluorosurfactant.[31][34]
In a 2009 USEPA study of 116 products—purchased between March 2007 and May 2008 and found to contain at least 0.01% fluorine by weight—the concentrations of PFOA were determined.[35] Concentrations shown below range from not detected, or ND, (with the detection limit in parenthesis) to 6750 with concentrations in nanograms of PFOA per gram of sample—or parts per billion—unless stated otherwise.
Strong polarized carbon–fluorine bonds make PFOA environmentally persistent.The carboxylate "head" of PFOA is hydrophilic while the fluorocarbon tail is hydrophobic and lipophobic. The "tail" is hydrophobic due to being non-polar and lipophobic because fluorocarbons are less susceptible to the London dispersion force than hydrocarbons.[36] PFOA is an ideal surfactant because it can lower the surface tension of water more than hydrocarbon surfactants while possessing exceptional stability due to the presence of multiple carbon–fluorine bonds.[34][36] The stability of PFOA is desired industrially, but a cause of concern environmentally. PFOA is resistant to degradation by natural processes such as metabolism, hydrolysis, photolysis, or biodegradation[24] making it persist indefinitely[37] in the environment.
PFOA is found in environmental and biological fluids as the anion perfluorooctanoate.[38] PFOA is absorbed from ingestion and can penetrate skin.[9] The oxygens on PFOA are how it binds proteins with fatty acid or hormone substrates such as serum albumin, liver fatty acid-binding protein, and the nuclear receptors PPARĪ±[28] and possibly CAR.[39] In animals, PFOA is mainly present in the liver, blood, and kidneys.[9] PFOA does not accumulate in fat tissue, unlike traditional organohalogen persistent organic pollutants.[40] In humans, PFOA has an average elimination half-life of about 3 years.[41][42][43] Because of this long half-life,[44] PFOA has the potential to bioaccumulate.
Most industrialized nations have average PFOA blood serum levels ranging from 2–8 parts per billion;[50] the highest consumer sub-population identified was in Korea—with about 60 parts per billion.[48] In Peru,[51] Vietnam,[52] and Afghanistan[53] blood serum levels have been recorded to be below one part per billion. In 2003–2004 99.7% of Americans had detectable PFOA in their serum with an average of about 4 parts per billion,[54] and concentrations of PFOA in US serum have declined by 25% in recent years.[55] Despite a decrease in PFOA, the longer perfluorinated carboxylic acid PFNA is increasing in the blood of US consumers.[54]
8:2 fluorotelomer alcohol, (8:2 FTOH), degrades environmentally to PFOAPFOA can form as a breakdown product from a variety of precursor molecules. PFOA precursors can be transformed to PFOA by metabolism, biodegradation, or atmospheric processes. Examples include 8:2 fluorotelomer alcohol (F(CF2)8CH2CH2OH), polyfluoroalkyl phosphate surfactants (PAPS),[60] and possibly N-EtFOSE alcohol (F(CF2)8SO2N(Et)CH2CH2OH).[45][61] When PTFE is degraded by heat (pyrolysis) it can form PFOA as a minor product.[62][63] The Organisation for Economic Co-operation and Development (OECD) has compiled a list of 615 chemicals that have the potential to break down into perfluorocarboxylic acids (PFCA) including PFOA.[64] However, not all 615 have the potential to break down to form PFOA.
A majority of waste water treatment plants (WWTPs) that have been tested output more PFOA than is input, and this increased output has been attributed to the biodegradation of fluorotelomer alcohols.[65] A current PFOA precursor concern are fluorotelomer-based polymers; fluorotelomer alcohols attached to hydrocarbon backbones via ester linkages may detach and be free to biodegrade to PFOA.[66]
Citizens that lived in the PFOA contaminated area around DuPont's Washington Works Washington, WV facility were found to have higher levels of PFOA in their blood from drinking water. The highest PFOA levels in drinking water were found in the Little Hocking water system, with an average concentration of 3.55 parts per billion during 2002–2005.[6] Individuals who drank more tap water, ate locally grown fruits and vegetables, or ate local meat, were all associated with having higher PFOA levels. Residents who used water carbon filter systems had lower PFOA levels.
Microwave popcorn bags can contain residual PFOA from fluorotelomersPFOA is also formed as an unintended byproduct in the production of fluorotelomers[72] and is present in finished goods treated with fluorotelomers, including those intended for food contact. Fluorotelomers are applied to food contact papers because they are lipophobic: they prevent oil from soaking into the paper from fatty foods. Also, fluorotelomers can be metabolized into PFOA.[73] In an U.S. Food and Drug Administration (USFDA) study, lipophobic fluorotelomer-based paper coatings (which can be applied to food contact paper in the concentration range of 0.4%) were found to contain 88,000–160,000 parts per billion PFOA, while microwave popcorn bags contained 6–290 parts per billion PFOA.[74] Toxicologists estimate that microwave popcorn could account for about 20% of the PFOA levels measured in an individual consuming 10 bags a year if 1% of the fluorotelomers are metabolized to PFOA.[73] Fluorotelomer coatings are used in fast food wrappers, candy wrappers, and pizza box liners.[75] PAPS, a type of paper fluorotelomer coating, and PFOA precursor, is also used in food contact papers.[60]
Despite DuPont's asserting that "cookware coated with DuPont Teflon non-stick coatings does not contain PFOA,"[76] residual PFOA was also detected in finished PTFE products including PTFE cookware (4–75 parts per billion).[74] However, PFOA levels ranged from undetectable (<1.5) to 4.3 parts per billion in a more recent study.[35] Also, non-stick cookware is heated—which should volatilize PFOA; PTFE products that are not heated, such as PTFE sealant tape, had higher (1800 parts per billion) levels detected.[77] Overall, PTFE cookware is considered an insignificant exposure pathway to PFOA.[78][79]
PFOA persists indefinitely in the environment. It is a toxicant and carcinogen in animals. In people, it is detected in the blood of general populations in the low and sub-parts per billion range. Chemical plant employees and surrounding subpopulations have been identified with higher blood levels. Exposure is most consistently associated with increased cholesterol and uric acid levels, but there is insufficient evidence to conclude that PFOA exposure results in adverse health effects in people.
As a result of a class-action lawsuit and community settlement with DuPont, three epidemiologists are conducting studies on the population surrounding a chemical plant that was exposed to PFOA at levels greater than in the general population. If PFOA exposure is found to be likely to lead to an increased risk of disease, future liabilities for DuPont will be triggered. Full results from the study are expected in 2011.
How general populations are exposed to PFOA is not completely understood. PFOA has been detected in industrial waste, stain resistant carpets, carpet cleaning liquids, house dust, microwave popcorn bags, water, food, and PTFE. Although some cookware is marketed as PFOA-free, PTFE non-stick cookware is considered an insignificant exposure pathway.
Contents[hide] |
[edit] History
In 1947, 3M began producing PFOA by electrochemical fluorination.[2] In 1951, DuPont started using PFOA in the manufacturing of fluoropolymers in Washington, WV.[6] In 1961, DuPont was aware of hepatomegaly in mice fed with PFOA.[7][8] 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.[9][10][11] In the 1980s and 1990s researchers investigated the toxicity of PFOA.[8]In 1999, the United States Environmental Protection Agency (USEPA) began investigating perfluorinated chemicals after receiving data on the global distribution and toxicity of PFOS.[12] For these reasons, and USEPA pressure,[13] in May 2000, 3M announced the phaseout of the production of PFOA, PFOS, and PFOS-related products.[14] 3M stated that they would have made the same decision regardless of USEPA pressure.[15]
Because of the 3M phaseout, in 2002 DuPont built its own plant in Fayetteville, NC to manufacture the chemical.[16] The chemical has received attention due to litigation from the PFOA-contaminated community around DuPont's Washington Works Washington, WV facility, along with USEPA focus. Research on PFOA has demonstrated ubiquity, animal-based toxicity, and some associations with human health parameters and potential health effects. Additionally, advances in analytical chemistry in recent years have allowed the routine detection of low- and sub-parts per billion levels of PFOA in a variety of substances.[11]
[edit] Synthesis
PFOA has two main synthesis routes, electrochemical fluorination (ECF) and telomerization.[2] The equation below represents the ECF route with hydrofluoric acid reacting with octanoic acid chloride.[17]- H(CH2)7COCl + 17 HF → H(CH2)7COF + C7H16 + 2 C8F16O + HCl + H2
PFOA is also synthesized by the telomerization represented below, where the telogen is the organoiodine compound and the taxogen is the unsaturated tetrafluoroethylene.[17][19]
- C2F5I + 3 C2F4 → C2F5(C2F4)3I
[edit] Applications
PFOA has widespread applications. In 1976 PFOA was reported as a water and oil repellant "in fabrics and leather and in the production of floor waxes and waxed papers";[20] however, it is believed that paper is no longer treated with perfluorinated compounds, but with fluorotelomers with less than 0.1% PFOA.[21] The compound is also used in "insulators for electric wires, planar etching of fused silica",[19] fire fighting foam,[2][22] and outdoor clothing.[23] As a protonated species, the acid form of PFOA was the most widely used perfluorocarboxylic acid used as a reactive intermediate in the production of fluoroacrylic esters.[24][25]
In a 2009 USEPA study of 116 products—purchased between March 2007 and May 2008 and found to contain at least 0.01% fluorine by weight—the concentrations of PFOA were determined.[35] Concentrations shown below range from not detected, or ND, (with the detection limit in parenthesis) to 6750 with concentrations in nanograms of PFOA per gram of sample—or parts per billion—unless stated otherwise.
| Product | Range |
|---|---|
| Pre-treated carpeting | ND (<1.5) to 462 |
| Carpet-care liquids | 19 to 6750 |
| Treated apparel | 5.4 to 161 |
| Treated upholstery | 0.6 to 293 |
| Treated home textiles | 3.8 to 438 |
| Treated non-woven medical garments | 46 to 369 |
| Industrial floor wax and wax removers | 7.5 to 44.8 |
| Stone, tile, and wood sealants | 477 to 3720 |
| Membranes for apparel | 0.1 to 2.5 ng/cm2 |
| Food contact paper | ND (<1.5) to 4640 |
| Dental floss/tape | ND (<1.5) to 96.7 |
| Thread sealant tape | ND (<1.5) to 3490 |
| PTFE cookware | ND (<1.5) to 4.3 |
[edit] Properties
PFOA is found in environmental and biological fluids as the anion perfluorooctanoate.[38] PFOA is absorbed from ingestion and can penetrate skin.[9] The oxygens on PFOA are how it binds proteins with fatty acid or hormone substrates such as serum albumin, liver fatty acid-binding protein, and the nuclear receptors PPARĪ±[28] and possibly CAR.[39] In animals, PFOA is mainly present in the liver, blood, and kidneys.[9] PFOA does not accumulate in fat tissue, unlike traditional organohalogen persistent organic pollutants.[40] In humans, PFOA has an average elimination half-life of about 3 years.[41][42][43] Because of this long half-life,[44] PFOA has the potential to bioaccumulate.
[edit] Global occurrence and sources
PFOA contaminates every continent.[45] PFOA has been detected in the central Pacific Ocean at low parts per quadrillion ranges, and at low parts per trillion levels in coastal waters.[46] Due to the surfactant nature of PFOA, it has been found to concentrate in the top layers of ocean water.[47] PFOA is detected widely in surface waters, and is present in numerous mammals, fish, and bird species.[45] However, wildlife has much less PFOA than humans, unlike PFOS[48] and other longer perfluorinated carboxylic acids;[49] in wildlife, PFOA is not as bioaccumulative as longer perfluorinated carboxylic acids.[40]Most industrialized nations have average PFOA blood serum levels ranging from 2–8 parts per billion;[50] the highest consumer sub-population identified was in Korea—with about 60 parts per billion.[48] In Peru,[51] Vietnam,[52] and Afghanistan[53] blood serum levels have been recorded to be below one part per billion. In 2003–2004 99.7% of Americans had detectable PFOA in their serum with an average of about 4 parts per billion,[54] and concentrations of PFOA in US serum have declined by 25% in recent years.[55] Despite a decrease in PFOA, the longer perfluorinated carboxylic acid PFNA is increasing in the blood of US consumers.[54]
[edit] Industrial sources
PFOA is released directly from industrial sites. For example, the DuPont Washington Works facility in Washington, WV estimated total PFOA emissions of 80,000 pounds (lbs) in 2000 and 1,700 pounds in 2004.[6] A 2006 study, with two of four authors DuPont employees, estimated about 80% of historical perfluorocarboxylate emissions were released to the environment from fluoropolymer manufacture and use.[2] PFOA can be measured in water from industrial sites other than fluorochemical plants. PFOA has also been detected in emissions from the carpet,[56] paper[57] and electronics industries.[58] The most important emission sources are carpet and textile protection as well as fire-fighting foams.[59][edit] Precursors
A majority of waste water treatment plants (WWTPs) that have been tested output more PFOA than is input, and this increased output has been attributed to the biodegradation of fluorotelomer alcohols.[65] A current PFOA precursor concern are fluorotelomer-based polymers; fluorotelomer alcohols attached to hydrocarbon backbones via ester linkages may detach and be free to biodegrade to PFOA.[66]
[edit] Sources to people
Food,[67] drinking water, outdoor air, indoor air,[68] dust, and food packagings[69] are all implicated as sources of PFOA to people.[60] However, it is unclear which exposure routes dominate[37] because of data gaps. When water is a source, blood levels are approximately 100 times higher than drinking water levels.[70][71]Citizens that lived in the PFOA contaminated area around DuPont's Washington Works Washington, WV facility were found to have higher levels of PFOA in their blood from drinking water. The highest PFOA levels in drinking water were found in the Little Hocking water system, with an average concentration of 3.55 parts per billion during 2002–2005.[6] Individuals who drank more tap water, ate locally grown fruits and vegetables, or ate local meat, were all associated with having higher PFOA levels. Residents who used water carbon filter systems had lower PFOA levels.
[edit] Food contact surfaces
Despite DuPont's asserting that "cookware coated with DuPont Teflon non-stick coatings does not contain PFOA,"[76] residual PFOA was also detected in finished PTFE products including PTFE cookware (4–75 parts per billion).[74] However, PFOA levels ranged from undetectable (<1.5) to 4.3 parts per billion in a more recent study.[35] Also, non-stick cookware is heated—which should volatilize PFOA; PTFE products that are not heated, such as PTFE sealant tape, had higher (1800 parts per billion) levels detected.[77] Overall, PTFE cookware is considered an insignificant exposure pathway to PFOA.[78][79]
No comments:
Post a Comment