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==Identification in plastics==
==Identification in plastics==
There are [[Plastic_identification_code#Plastic_Identification_Code|seven classes]] of plastics used in packaging applications. Type 7 is the catch-all "other" class, and some type 7 plastics, such as polycarbonate (sometimes identified with the letters "PC" near the [[recycling symbol]]) and epoxy resins, are made from bisphenol A monomer.<ref name=Fiege/> When such plastics are exposed to hot liquids, bisphenol A leaches out 55 times faster than it does under normal conditions, at up to 32&nbsp;[[nanogram|ng]]/hour.<ref name="sciam2008">{{cite journal|author=Biello D | title=Plastic (not) fantastic: Food containers leach a potentially harmful chemical | journal=Scientific American | volume=2 | date=2008-02-19 | url=http://www.sciam.com/article.cfm?id=plastic-not-fantastic-with-bisphenol-a | accessdate=2008-04-09}}</ref> Type 3 ([[PVC]]) can also contain bisphenol A as antioxidant in plasticizers.<ref name=Fiege/> Types 1 ([[PET]]), 2 ([[HDPE]]), 4 ([[LDPE]]), 5 ([[Polypropylene]]), and 6 ([[polystyrene]]) do not use bisphenol A during polymerization or package forming,<ref> ''http://www.ehponline.org/docs/2006/8804/letter.html'' Environmental Health Perspectives Volume 114, Number 2, February 2006 </ref> and thus will not leach bisphenol A into food or beverages.
There are [[Plastic_identification_code#Plastic_Identification_Code|seven classes]] of plastics used in packaging applications. Type 7 is the catch-all "other" class, and some type 7 plastics, such as ([[polycarbonate]]) (sometimes identified with the letters "PC" near the [[recycling symbol]]) and epoxy resins, are made from bisphenol A monomer.<ref name=Fiege/> When such plastics are exposed to hot liquids, bisphenol A leaches out 55 times faster than it does under normal conditions, at up to 32&nbsp;[[nanogram|ng]]/hour.<ref name="sciam2008">{{cite journal|author=Biello D | title=Plastic (not) fantastic: Food containers leach a potentially harmful chemical | journal=Scientific American | volume=2 | date=2008-02-19 | url=http://www.sciam.com/article.cfm?id=plastic-not-fantastic-with-bisphenol-a | accessdate=2008-04-09}}</ref> Type 3 ([[PVC]]) can also contain bisphenol A as antioxidant in plasticizers.<ref name=Fiege/> Types 1 ([[PET]]), 2 ([[HDPE]]), 4 ([[LDPE]]), 5 ([[Polypropylene]]), and 6 ([[polystyrene]]) do not use bisphenol A during polymerization or package forming,<ref> ''http://www.ehponline.org/docs/2006/8804/letter.html'' Environmental Health Perspectives Volume 114, Number 2, February 2006 </ref> and thus will not leach bisphenol A into food or beverages.


==References==
==References==

Revision as of 02:27, 30 April 2008

Template:Chembox new

Bisphenol A (abbreviated BPA) is an organic compound with the formula (CH3)2C(C6H4OH)2. Containing two phenol functional groups, it is a difunctional building block to several important polymers and polymer additives.[1] Bisphenol A has become controversial because it mimics estrogen and thus could induce hormonal responses.[2][3]

Synthesis

Bisphenol A is prepared by the reaction of acetone with two equivalents of phenol. The reaction is catalyzed by an acid, such as hydrochloric acid (HCl) or a sulfonated polystyrene resin. Typically, a large excess of phenol is used to ensure full condensation:

(CH3)2CO + 2 C6H5OH → (CH3)2C(C6H4OH)2 + H2O

A large number of ketones undergo analogous condensation reactions. The method is efficient and the only by-product is water.[1]

History and use

Further information: [[:Polycarbonate]]

Bisphenol A was first reported by A.P. Dianin in 1891.[4][5] Bisphenol A's current uses are numerous. It is used in the synthesis of polyesters, polysulfones, and polyether ketones, as an antioxidant in some plasticizers, and as a polymerization inhibitor in PVC. It is a key monomer in production of polycarbonate plastic and epoxy resins.[1] Polycarbonate plastic, which is clear and nearly shatter-proof, is used to make a variety of common products including baby and water bottles, sports equipment, medical devices, CDs, and household electronics.[6] Epoxy resins are used as coatings on the inside of some food and beverage cans.

It is also a precursor to the flame retardant tetrabromobisphenol A, and was formerly used as a fungicide.[7]

Global production of bisphenol A in 2003 was estimated to be about 3 million metric tonnes (t).[8] In the U.S., it is manufactured by Bayer MaterialScience, Dow Chemical Company, General Electric, Hexion Specialty Chemicals, and Sunoco Chemicals. In 2004, these companies produced just over 1 million t of bisphenol A, up from just 7,260 t in 1991. In 2003, annual U.S. consumption was 856,000 t, 72% of which was used to make polycarbonate plastic and 21% going into epoxy resins.[6]

Health effects

Bisphenol A has a low acute toxicity, with an oral LD50 of 3250 mg/kg in rats.[9] However, bisphenol A is an endocrine disruptor, and there is concern that long term low dose exposure to bisphenol A may induce chronic toxicity in humans.[10]

Early studies of bisphenol A's hormonal activity

Bisphenol A was investigated in the 1930s during the search for estrogen mimics. From this study the synthetic compound diethylstilbestrol was shown to be a better competitor with estrogen.[citation needed] Bisphenol A, like many other compounds, is known to be an estrogen receptor agonist.[11] Such agonists can activate estrogen receptors, leading to similar physiological effects as the body's own estrogens.[12] The first evidence of the estrogenicity of bisphenol A came from experiments in the 1930s in which it was fed to ovariectomized rats.[13][14]

Recent studies and risk assessments

A consensus statement by 38 BPA experts concluded that average levels in people are above those that cause harm to animals in laboratory experiments,[15] and a panel sponsored by the U.S. National Institutes of Health determined that there was 'some concern' about BPA's effect on fetal and infant brain and behavior.[6] A 2008 draft report by the U.S. National Toxicology Program (NPT) agreed with the panel, concluding that "there is some concern for neural and behavioral effects in fetuses, infants, and children at current human exposures," and that there is "some concern for bisphenol A exposure in these populations based on effects in the prostate gland, mammary gland, and an earlier age for puberty in females." The NPT also concluded that there is negligible concern that "exposure of pregnant women to bisphenol A will result in fetal or neonatal mortality, birth defects or reduced birth weight and growth in their offspring" or that it causes adverse effects in exposed adults.[16]

In April 2008, the Canadian government released its Draft Screening Assessment for bisphenol A, which concluded that the chemical may pose some risk to infants[17] and proposed classifying the chemical as "'toxic' to human health and the environment."[18] This action follows Canadian regulators decision in 2006 to select bisphenol A as one of 200 substances deserving of thorough safety assessments after preliminary studies had found it to be 'inherently toxic'; the chemical had not previously been studied by them in depth, having been accepted under grandfather clauses when stricter regulations were passed in the 1980s.[19]

In January 2006, the German Federal Institute for Risk Assessment announced that polycarbonate baby bottles are safe, stating that published research is "difficult to interpret and [is] occasionally contradictory".[20] An assessment released later that year by the European Union’s Food Safety Authority reached a similar conclusion, expressing "considerable reservations" about the biological significance and robustness of the low-dose exposure studies on rodents.[21] In 2007 Japan has also concluded that "the current exposure levels of BPA will not pose any unacceptable risk to human health that a ban is not needed."[22]

Some hormone disrupting effects in studies on animals and human cancer cells have been shown to occur at levels as low as 2–5 ppb (parts per billion). It has been claimed that these effects lead to health problems such as, in men, lowered sperm count and infertile sperm. Recent studies have confirmed that bisphenol A exposure during development has carcinogenic effects and produce precursors of breast cancer.[23][24] However, neither the U.S. Environmental Protection Agency[25] nor the International Agency for Research on Cancer[26] have evaluated Bisphenol A for possible carcinogenic activity. Bisphenol A has been shown to have developmental toxicity, carcinogenic effects, and possible neurotoxicity.[27][28] Recent studies suggest it may also be linked to obesity by triggering fat-cell activity.[29] Schizophrenia research indicates endocrine disruptors like BPA may be involved in schizophrenia pathogenesis.[30]

Some toxicologists and regulatory agencies have criticized low-dose toxicity studies, especially those that involved injecting bisphenol A directly into animals, since human exposures typically involve ingestion and subsequent metabolization in the liver; the experimental design of some of these studies has also been questioned.[31][32] Studies have also appeared pointing out flaws in chemical industry funded studies that report bisphenol A is safe.[33] The U.S. Congress is currently investigating the Weinberg Group, a chemical industry consulting group, for its role in downplaying the health effects of bisphenol A and other chemicals.[34]

Dose (µg/kg/day) Effects (measured in studies of mice or rats,
descriptions are from Environmental Working Group)[35][19] 		Study Year
0.025 Permanent changes to genital tract 2005[36]
0.025 Changes in breast tissue that predispose cells to hormones and carcinogens 2005 [37]
2 increased prostate weight 30% 1997[38]
2 lower bodyweight, increase of anogenital distance in both genders, signs of early puberty and longer estrus. 2002[39]
2.4 Decline in testicular testosterone 2004[40]
2.5 Breast cells predisposed to cancer 2007[41]
10 Prostate cells more sensitive to hormones and cancer 2006[42]
10 insulin resistance develops in 2 days, chronic hyperinsulinemia at day 4 2006[43]
10 Decreased maternal behaviors 2002[44]
20 Damage to eggs and chromosomes 2003[45]
25 Health Canada provisional human exposure limit 1999
30 Reversed the normal sex differences in brain structure and behavior 2003[46]
50 U.S. human exposure limit 1998[47]
50 European Food Safety Authority tolerable daily intake level 2007[48]

Human exposure to bisphenol A

Bisphenol A has been known to leach from the plastic lining of canned foods and, to a lesser degree, polycarbonate plastics that are cleaned with harsh detergents or used to contain acidic or high-temperature liquids.[49] Studies by the CDC found bisphenol A in the urine of 95% of adults sampled in 1988-1994[50] and in 93% of children and adults tested in 2003-04.[51] Almost all exposure is through diet, and infants fed with liquid formula are among the most exposed. Infants fed canned formula with polycarbonate bottles can consume quantities of bisphenol A up to 13 µg/kg/day (see table below),[52] while the most sensitive animal studies show effects at much lower concentrations. Debate continues on what is the safe limit of this compound. Within the United States, an exposure of up to 50 µg/kg/day (50 ppb/day) is considered safe[19] by the United States Environmental Protection Agency.[53]

Dr. Maida Galvez, a pediatrician studying BPA, recommends parents stay away from bottles containing the chemical and says, "We know the animal studies raise concerns, but there aren't human studies showing effects yet ... so, when we don't have the evidence, what we recommend is that parents try to err on the side of caution."[54]

Population Estimated daily bisphenol A intake, μg/kg/day.
Table adapted from the National Toxicology Program Expert Panel Report.[6]
Infant (0-6 months)
formula-fed
1-11
Infant (0-6 months)
breast-fed
0.2-1
Infant (6-12 months)
1.65-13
Child (1.5-6 years)
0.043-14.7
Adult
0.008-1.5

Restrictions and discontinuance

On April 18, 2008 Canadian Health Minister Tony Clement announced that Canada intends to ban the import, sale, and advertising of polycarbonate baby bottles containing bisphenol A over concerns of the safety of bisphenol A. While Health Canada concluded that human exposures are less than the levels deemed to be potentially unsafe, the margin of safety was considered too low for formula-fed infants.[55][56] Around the same time, Wal-Mart announced that it was immediately ceasing sales in all its Canadian stores of food containers, water and baby bottles, sippy cups, and pacifiers containing bisphenol A, and that it would phase out baby bottles made with it in U.S. stores by early 2009.[57] Nalgene also announced it will stop using the chemical in its products,[58] and Toys-R-Us said it will cease selling baby bottles made from it.[59]

As of the release of NTP and Health Canada reports, 10 U.S. states,[60] including Connecticut[61] and New Jersey,[62] already had legislation pending that would affect the use of BPA in containers. In the wake of the new reports and the ensuing media attention, U.S. Senator Charles Schumer (D–N.Y.) announced that he plans to introduce legislation banning bisphenol A. The Energy and Commerce Committee in the House of Representatives is also investigating the FDA's approval of the chemical.[17]

In response to the recent events, an American Chemistry Council (ACC)/BPA Global Group spokesman said, “The weight of scientific evidence, as assessed by Health Canada and other agencies around the world, provides reassurance that consumers can continue to safely use products made from bisphenol A."[63] The ACC says that bisphenol A does not pose a risk to consumers and has called on the Food and Drug Administration to review the chemical. The ACC also called the media coverage of the controversy "unnecessarily confusing and frightening the public."[61] The Grocery Manufacturers Association also insists that bisphenol A is safe, and argues that "Data purporting to demonstrate 'low' dose effects on the male reproductive system by BPA have not been successfully replicated and, therefore, are not credible to estimate human health risks and safety in light of the weight of a large body of evidence to the contrary."[64]

In the U.S. retail sector, growing concern over bisphenol A exposure had already led a number of retailers to stop using bisphenol A, particularly chains promoting healthy food and lifestyles. In 2005, Patagonia Inc. ceased selling polycarbonate bottles, and in 2006, Whole Foods Markets ceased selling baby bottles as did Mountain Equipment Co-op in 2007.[65]

The city of San Francisco, California, banned the sale of baby bottles and other products for young children containing bisphenol A effective December 2006, and was, at the time, the only jurisdiction in the world to outright forbid the substance.[66] The ban was never enforced, and in May 2007 the city repealed the ban.

Environmental risk

As an environmental contaminant this compound interferes with nitrogen fixation at the roots of leguminous plants associated with the bacterial symbiont Sinorhizobium meliloti. Despite a half-life in the soil of only 1–10 days, its ubiquity makes it an important pollutant.[67] According to Health Canada, "initial assessment shows that at low levels, bisphenol A can harm fish and organisms over time. Studies also indicate that it can currently be found in municipal wastewater."[68]

Identification in plastics

There are seven classes of plastics used in packaging applications. Type 7 is the catch-all "other" class, and some type 7 plastics, such as (polycarbonate) (sometimes identified with the letters "PC" near the recycling symbol) and epoxy resins, are made from bisphenol A monomer.[1] When such plastics are exposed to hot liquids, bisphenol A leaches out 55 times faster than it does under normal conditions, at up to 32 ng/hour.[69] Type 3 (PVC) can also contain bisphenol A as antioxidant in plasticizers.[1] Types 1 (PET), 2 (HDPE), 4 (LDPE), 5 (Polypropylene), and 6 (polystyrene) do not use bisphenol A during polymerization or package forming,[70] and thus will not leach bisphenol A into food or beverages.

References

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  54. ^ Parents Concerned Over Potentially Toxic Baby Bottles ABC News, Feb. 7, 2008.
  55. ^ [http://www.ec.gc.ca/substances/ese/eng/challenge/batch2/batch2_80-05-7.cfm Government of Canada. 2008. Draft Screening Assessment for The Challenge Phenol, 4,4' -(1-methylethylidene)bis- (Bisphenol A)Chemical Abstracts Service Registry Number 80-05-7.
  56. ^ The government has given the public 60 days to comment on the proposed ban starting April 19, 2008 and will evaluate whether the ban will become law in October 2008. "Government of Canada Takes Action on Another Chemical of Concern: Bisphenol A". Retrieved 2008-04-18.
  57. ^ Wal-Mart to pull baby bottles made with chemical BPA: Washington Post, Market Watch, April 18, 2008.
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  64. ^ "Canada Could Ban Baby Bottles Containing Bisphenol A". Environment News Service. April 22, 2008. Retrieved April 24, 2008.
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  66. ^ "Anxieties about toxics". San Francisco Chronicle. 2006-11-22. {{cite news}}: Check date values in: |date= (help)
  67. ^ Fox, J.E., J. Gulledge, E. Engelhaupt, M.E. Burrow & J.A. McLachlan (2007). "Pesticides reduce symbiotic efficiency of nitrogen-fixing rhizobia and host plants". Proc. Nat. Acad. Sci. 104: 10282–7.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  68. ^ Bisphenol A Fact Sheet, Health Canada. Assessed April 19, 2008.
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  70. ^ http://www.ehponline.org/docs/2006/8804/letter.html Environmental Health Perspectives Volume 114, Number 2, February 2006

External links

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