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Perfluorooctanoic acid

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Template:Chembox new Perfluorooctanoic acid (PFOA), also known as C8, is a man-made surfactant. PFOA can designate the acid itself or its principal salts (like ammonium perfluorooctanoate, also known as APFO).

Manufacture and uses

PFOA is used as an industrial surfactant. Its ammonium salt is an emulsifier for the processing of fluoropolymers especially polytetrafluoroethylene (PTFE, or Teflon). In aqueous solution, ammonium perfluorooctanoate forms micelles that contain tetrafluoroethylene and the growing polymer.[1]

PFOA has four main synthesis routes: electrochemical fluorination of octanoic acid, oxidation of perfluoroiodooctane, carboxylation of perfluoroiodooctane, and fluorotelomer olefin oxidation.[2]

Properties

See also: perfluorocarbons

As with related perfluorinated compounds, the properties of PFOA arise from the nature of the carbon-fluorine (C-F) bond in tandem with the properties associated with the polar "head group." The C-F bond is one of the strongest in organic chemistry and is rarely the result of natural processes.[3] Polyfluorinated molecules exhibit high chemical and thermal stability. (While throwing hydrocarbons on a fire will only fuel it, fluorocarbons are used in fire-fighting foams). C-F bonds also strengthen the underlying backbone carbon-carbon bonds. Because of its stability, PFOA is not metabolized.[4] Like other fluorocarbons, the perfluorinated chain of PFOA engages in only weak van der Waals interactions, making fluorinated surfactants like PFOA lipophobic,[5] despite the perfluorinated chain being non-polar. PFOA, therefore, does not accumulate in fat tissue, unlike other organohalogens.

The acid form of PFOA has a water solubility of only ~26 μg/L.[6] However, PFOA has a pKa of about 0.[7] So PFOA is found in environmental and biological fluids as the anion perfluorooctanoate, fully dissociated from its salts.[8] The conjugate base perfluorooctanoate has a water solubility of 3.4 g/L, ~ 105 times more solublity than the acid form of PFOA.[6] The oxygens on PFOA are the means by which it binds proteins with fatty acid or hormone substrates such as serum albumin,[9] liver fatty acid-binding protein,[10] and the nuclear receptor PPARα.[11] Therefore, PFOA is mainly found in the blood serum and liver of humans and other animals. In a study with retired fluorochemical production workers, PFOA had an elimination half-life of 3.8 years (arithmetic mean) and 3.5 years (geometric mean).[12] Because of this long half-life, PFOA has the to potential to bioaccumulate.

The eight-carbon chain length of PFOA and PFOS make their salts highly effective surfactants. For this reason, the two have found wide production and are thus typically found in the highest concentrations in the environment. Thus, they are the most studied and most subject to health, environmental, and regulatory concerns. Ironically, the very properties that make PFOA useful - its stability and bipolar character - also contribute to its toxicological and environmental impacts.

Sources

Sources of PFOA vary widely. PFOA can be emitted from fluorochemical plants. For example, the Dupont Washington Works facility in Washington, WV estimated total PFOA emissions of 80,000 lbs in 2000 and 1,700 lbs in 2004.[8]

PFOA is also formed as an unintended byproduct in the production of fluorotelomers.[13] Fluorotelomers containing residual PFOA are in turn used in consumer products. Of interest due to the potential for human exposure are fluorotelomer-based paper coatings used in direct food contact.[14] These coatings give papers resistance to oil soaking in from fatty foods. In an U.S. Food and Drug Administration (FDA) study, fluorotelomer-based paper coatings were found to contain 88,000-160,000 ppb PFOA, while microwave popcorn bags contained 6-290 ppb PFOA, and residual PFOA was also detected in finished PTFE products including PTFE/Teflon cookware.[14] Separately, PFOA byproduct is also found in aqueous film forming foam (AFFF), a component of fire-fighting foams.

Fluorotelomer alcohols themselves, such as 8:2 fluorotelomer alcohol, H(CF2)8CH2CH2OH, can degrade into PFOA. This process requires oxidation of the last CF2 carbon adjacent to the ethyl alcohol group.[15] This process has been observed to via the metabolism of male rats.[16] Flurotelomer alcohols are a known contaminant of coating products such as Zonyl FSE (Dupont), which contains 3% residual fluorotelomer alcohol.[17]

Additionally, larger fluorotelomer compounds, called polyfloroalkyl phosphate surfactants (PAPS), can be metabolized by rats to form PFOA.[18] These compounds are also present in fluorotelomer paper coatings; one of the structures given in the 2005 U.S. Food and Drug Administration study incorporates two individual 8:2 fluorotelomer alcohol monomers into a single molecule via a phosphate group using two phospho-ester (P-O-C) linkages.[14] According to a USA Today article, fluorotelomer coatings are used in fast food wrappers, candy wrappers, and pizza box liners [1]. Fluorotelomer coatings can be applied to food contact paper in the concentration range of 0.4%.[14] Microwave popcorn bags are of particular interest because the high cooking temperatures increase the migration of fluorotelomers; the amount estimated to migrate into food is around 3000-4000 ppb.[14] 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.[19] Therefore, fluorotelomers are thought of as potential source of PFOA to humans from direct ingestion and potential metabolism.

However, two exposure estimates do not consider the direct ingestion of PFOA and PFOA precursors from food packaging as the major source of human exposure; the major exposure route for humans to PFOA is considered the diet itself, including food and drinking water, but excluding the contributions from PFOA precursors and food contact materials.[20][21] Water contamination of PFOA is increased by some waste water treatment plants (WWTP), which can output more PFOA than is input, indicative of biodegradation of PFOA precursors rinsed down domestic, commercial, and industrial drains.[22] German researchers also observed this effect, with a 20 fold increase in WWTP PFOA outflow vs. inflow, and identified WWTPs as the major source of local river contamination.[23]

In a New York State Department of Health study, PFOA was detected in the gas phase coming from new nonstick cookware and microwave popcorn bags.[24]

Health concerns

PFOA induced liver tumors, Leydig cell tumors, and pancreatic acinar tumors in rats fed 300 ppm PFOA for 2 years.[25] PFOA is also a developmental toxicant. Studies with pregnant mice fed PFOA in the low ppm range resulted in litters of pups with developmental delays and lower birth weight.[26][27]

For humans, blood serum levels of PFOA have been linked to lower fetal growth factors such as birth weight, birth length, abdominal circumference, and head circumference.[28][29][30] The study within the Danish National Birth Cohort used a sample size of 1400 and maternal serum while the Baltimore, MD study used a sample size of 293 and umbilical cord serum. Taken together, these studies suggest PFOA lowers human fetal growth factors; however, findings between the two studies regarding birth length were not replicated. These findings have prompted scientific discussion.[31][32][33][34] A Canadian study with a sample size of 101 pregnant mothers used maternal serum and umbilical cord blood in their analysis but they did not find any inverse relationship between PFOA levels and birth weight.[35]

Low ppb levels of PFOA and related compounds (PFOS, PFNA, and PFHxS) have been detected in the blood serum of nearly all Americans; in a Centers for Disease Control and Prevention (CDC) paper, PFOA was detected in 99.7% of National Health and Nutrition Examination Survey (NHANES) 2003-2004 samples, with a geometric mean of 3.9 ng/mL (≈ppb) and a LOD of 0.1 ng/mL (≈ppb).[36] In the years between 1999-2000 and 2003-2004, PFOA concentrations decreased by about 25% in the blood serum of Americans.[36] PFOA also appears in the environment worldwide including oceans,[37] rivers,[38] arctic snow,[39] and surface and drinking waters.[40] The durability of PFOA can lead to bioaccumulation in food chains, especially in Atlantic marine animals. In light of concerns about its pervasiveness, its major U.S. manufacturer, 3M, announced in May 2000 that it would cease producing the PFOA. DuPont, one of the largest U.S. users of PFOA, then built its own plant in Fayetteville, North Carolina to manufacture PFOA.

Actions

Industry and Legal Actions

DuPont has used PFOA for over 50 years at its Washington Works plant near Parkersburg, WV. Area residents sued DuPont in 2001, claiming that the chemical contaminated area drinking water. As part of the settlement, DuPont is paying for blood tests and health surveys of residents believed to be affected. Up to 60,000 people are expected to participate in the study, which will be reviewed by epidemiologists to determine any long-term health effects.

On December 13, 2005 DuPont announced a settlement with the EPA in which DuPont will pay US$10.25 million in fines and an additional US$6.25 million for two supplemental environmental projects without any admission of liability.

U.S. Federal Government Actions

In 2004, DuPont was investigated by the Environmental Protection Agency (EPA) for allegedly covering up knowledge of possible health effects of PFOA exposure in a study of pregnant employees, including evidence of PFOA in umbilical cord blood.[citation needed] The EPA pursued charges against DuPont for failure to report violations filed under the Toxic Substances Control Act and the Resource Conservation and Recovery Act.

In October 2005, a U.S. Food and Drug Administration (FDA) study was published revealing PFOA and PFOA precursor chemicals in food contact and PTFE/Teflon products[14].

On January 25, 2006, the EPA announced a long-term, voluntary program to reduce PFOA emissions and to eliminate PFOA use in products by the year 2015. While a New York Times article the next day claimed that companies would "stop using" PFOA, the EPA described its objective as "elimination of PFOA...from emissions and products" but not as a chemical intermediate to produce other substances.

On February 15, 2006, the EPA's Science Advisory Board recommended that PFOA should be considered a likely carcinogen.[citation needed]

On May 26, 2006, an EPA Science Advisory Board letter was addressed to EPA Administrator Stephen L. Johnson, which included an Executive Summary of EPA Science Advisory Board positions regarding the carcinogenic potential of PFOA to humans. Only about 1/4 of the advisers agreed with the EPA's own PFOA hazard descriptor of “suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential" while about 3/4 of the advisers thought the stronger designation of PFOA as "likely to be carcinogenic" was warranted.[41]

On November 21, 2006, EPA ordered DuPont company to offer alternative drinking water or treatment for public or private water users living near DuPont's Washington Works plant in West Virginia (and in Ohio), if the level of PFOA detected in drinking water is equal to or greater than 0.50 parts per billion (ppb). This measure lowered action level and replaced the previous 150 ppb threshold that had been established in March 2002.[42]

According to a May 23, 2007, Environmental Science & Technology Online article, U.S. Food and Drug Administration research regarding food contact papers as a potential source of PFOA to humans is ongoing.[17]

In November 2007, the Centers for Disease Control and Prevention (CDC) published data on PFOA concentrations comparing 1999-2000 vs. 2003-2004 NHANES samples.[36]

U.S. State Government Actions

On February 13, 2007, the New Jersey Department of Environmental Protection issued a "preliminary health-based guidance" level of 0.04 ppb in drinking water,[43] due to PFOA being found at "elevated levels in the system's drinking water near DuPont's massive Chambers Works chemical plant."[44]

On March 1, 2007, the Minnesota Department of Health lowered its Health Based Value for PFOA in drinking water from 1.0 ppb to 0.5 ppb,[45] where "the sources are landfilled industrial wastes from a 3M manufacturing plant."[46]

European action

Recently, PFOA was found in German drinking water samples in concentrations of up to 0.60 ppb.[47]

See also

External links

References

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  • Lau C, Thibodeaux JR, Hanson RG; et al. (2006). "Effects of perfluorooctanoic acid exposure during pregnancy in the mouse". Toxicology Science. 90: 510–518. doi:10.1093/toxsci/kfj105. PMID 16415327. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
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