Bisphenol A

Bisphenol A (BPA) is an organic synthetic compound with the chemical formula (CH3)2C(C6H4OH)2 belonging to the group of diphenylmethane derivatives and bisphenols, with two hydroxyphenyl groups. It is a colorless solid that is soluble in organic solvents, but poorly soluble in water (0.344 wt % at 83 °C).
BPA is a precursor to important plastics, primarily certain polycarbonates and epoxy resins, as well as some polysulfones and certain niche materials. BPA-based plastic is clear and tough, and is made into a variety of common consumer goods, such as plastic bottles (including water bottles), food storage containers, baby bottles, sports equipment, CDs, and DVDs. Epoxy resins derived from BPA are used to line water pipes, as coatings on the inside of many food and beverage cans, and in making thermal paper such as that used in sales receipts. In 2015, an estimated 4 million tonnes of BPA-derived chemical were produced, making it one of the highest volume of chemicals produced worldwide.
BPA is a xenoestrogen, exhibiting estrogen-mimicking, hormone-like properties. Although the effect is very weak, the pervasiveness of BPA-containing materials raises concerns. Since 2008, several governments have investigated its safety, which prompted some retailers to withdraw polycarbonate products. Since then, BPA-free plastics have been manufactured using alternative bisphenols such as bisphenol S and bisphenol F, but there is controversy around whether these are actually safer.
History.
Bisphenol A was prepared in 1891 by Russian chemist Aleksandr Dianin.
In 1934 workers at I.G. Farbenindustrie reported the coupling of BPA and epichlorohydrin. Over the following decade, coatings and resins derived from similar materials were described by workers at the companies of DeTrey Freres in Switzerland and DeVoe and Raynolds in the US. This early work underpinned the development of epoxy resins, which in turn motivated production of BPA. The utilization of BPA further expanded with discoveries at Bayer and General Electric on polycarbonate plastics. These plastics first appeared in 1958, being produced by Mobay and General Electric, and Bayer.
In terms of the endocrine disruption controversy, the British biochemist Edward Charles Dodds tested BPA as an artificial estrogen in the early 1930s. He found BPA to be 1 / 37,000 as effective as estradiol. Dodds eventually developed a structurally similar compound, diethylstilbestrol (DES), which was used as a synthetic estrogen drug in women and animals until it was banned due to its risk of causing cancer; the ban on use of DES in humans came in 1971 and in animals, in 1979. BPA was never used as a drug.
Uses.
In 2003, U.S. consumption was 856,000 tons, of which 75% was used to make polycarbonate plastic and 21% for epoxy resins. In the U.S., less than 5% of the BPA produced is used in food contact applications, but remains in the canned food industry and printing applications, such as sales receipts.
Polycarbonates.
Bisphenol A is a precursor to polycarbonate plastics. Its reaction with phosgene is conducted under biphasic conditions; the hydrochloric acid is scavenged with aqueous base:
3.6 million tonnes (8 billion pounds) of BPA are consumed for this purpose yearly. These polymers do not contain BPA, but esters derived from it.
Epoxy and vinyl ester resins.
BPA is a precursor in production of major classes of resins, specifically the vinyl ester resins. This application usually begins with alkylation of BPA with epichlorohydrin.
Specialized derivatives.
BPA is a versatile building block from which many derivatives have been prepared. Nitration gives dinitrobisphenol A. Bromination gives tetrabromobisphenol A (TBBPA), which exhibits fire retardant properties.
Several drug candidates have been developed from bisphenol A, including Ralaniten, Ralaniten acetate, and EPI-001.
Health effects.
BPA's ability to mimic the effects of natural estrogen derive from the similarity of phenol groups on both BPA and estradiol, which enable this synthetic molecule to trigger estrogenic pathways in the body. Typically phenol-containing molecules similar to BPA are known to exert weak estrogenic activities, thus it is also considered an endocrine disruptor (ED) and estrogenic chemical. Xenoestrogens is another category the chemical BPA fits under because of its capability to interrupt the network that regulates the signals which control the reproductive development in humans and animals.
BPA has been found to bind to both of the nuclear estrogen receptors (ERs), ERα and ERβ. It is 1000- to 2000-fold less potent than estradiol. BPA can both mimic the action of estrogen and antagonize estrogen, indicating that it is a selective estrogen receptor modulator (SERM) or partial agonist of the ER. At high concentrations, BPA also binds to and acts as an antagonist of the androgen receptor (AR). In addition to receptor binding, the compound has been found to affect Leydig cell steroidogenesis, including affecting 17α-hydroxylase/17,20 lyase and aromatase expression and interfering with LH receptor-ligand binding.
In 1997, adverse effects of low-dose BPA exposure in laboratory animals were first proposed. Some studies have found that BPA increases anxiety in rats. Modern studies began finding possible connections to health issues caused by exposure to BPA during pregnancy and during development. As of 2014, research and debates are ongoing as to whether BPA should be banned or not.
A 2007 study investigated the interaction between bisphenol A's and estrogen-related receptor γ (ERR-γ). This orphan receptor (endogenous ligand unknown) behaves as a constitutive activator of transcription. BPA seems to bind strongly to ERR-γ (dissociation constant = 5.5 nM), but only weakly to the ER. BPA binding to ERR-γ preserves its basal constitutive activity. It can also protect it from deactivation from the SERM 4-hydroxytamoxifen (afimoxifene). This may be the mechanism by which BPA acts as a xenoestrogen. Different expression of ERR-γ in different parts of the body may account for variations in bisphenol A effects. BPA has also been found to act as an agonist of the GPER (GPR30).
According to the European Food Safety Authority "BPA poses no health risk to consumers of any age group (including unborn children, infants and adolescents) at current exposure levels". But in 2017 the European Chemicals Agency concluded that BPA should be listed as a substance of very high concern due to its properties as an endocrine disruptor.
In 2012, the United States' Food and Drug Administration (FDA) banned the use of BPA in baby bottles.
The U.S. Environmental Protection Agency (EPA) holds the position that BPA is not a health concern. In 2011, Andrew Wadge, the chief scientist of the United Kingdom's Food Standards Agency, commented on a 2011 U.S. study on dietary exposure of adult humans to BPA, saying, "This corroborates other independent studies and adds to the evidence that BPA is rapidly absorbed, detoxified, and eliminated from humans – therefore is not a health concern."
The Endocrine Society said in 2015 that the results of ongoing laboratory research gave grounds for concern about the potential hazards of endocrine-disrupting chemicals – including BPA – in the environment, and that on the basis of the precautionary principle these substances should continue to be assessed and tightly regulated. A 2016 review of the literature said that the potential harms caused by BPA were a topic of scientific debate and that further investigation was a priority because of the association between BPA exposure and adverse human health effects including reproductive and developmental effects and metabolic disease.
In July 2019, the European Union upheld a decision by the European Chemicals Agency to list BPA as a substance of very high concern, the first step in the procedure for restrictions of its use. The decision is based on concerns about BPA's toxicity for human reproduction.
Environmental effects.
In 2010, the U.S. Environmental Protection Agency reported that over one million pounds of BPA are released into the environment annually. BPA can be released into the environment by both pre-consumer and post-consumer leaching. Common routes of introduction from the pre-consumer perspective into the environment are directly from plastics, coat and staining manufacturers, foundries who use BPA in casting sand, or transport of BPA and BPA-containing products. Post-consumer BPA waste comes from effluent discharge from municipal wastewater treatment plants, irrigation pipes used in agriculture, ocean-borne plastic trash, indirect leaching from plastic, paper, and metal waste in landfills, and paper or material recycling companies. Despite a rapid soil and water half-life of 4.5 days, and an air half-life of less than one day, BPA's ubiquity makes it an important pollutant. BPA has a low rate of evaporation from water and soil, which presents issues, despite its biodegradability and low concern for bio-accumulation. BPA has low volatility in the atmosphere and a low vapor pressure between 5.00 and 5.32 Pascals. Aqueous solutions of BPA absorbs at wavelengths greater than 250 nm.
BPA interferes with nitrogen fixation at the roots of leguminous plants associated with the bacterial symbiont "Sinorhizobium meliloti." BPA affects soybean seedlings with respect to root growth, nitrate production, ammonium production, and the activities of nitrate reductase and nitrite reductase. At low doses of BPA, the growth of roots were improved, the amount of nitrate in roots increased, the amount of ammonium in roots decreased, and the nitrate and nitrite reductase activities remained unchanged. However, at considerably higher concentrations of BPA, the opposite effects were seen for all but an increase in nitrate concentration and a decrease in nitrite and nitrate reductase activities. Nitrogen is both a plant nutritional substance, but also the basis of growth and development in plants.
A 2005 study conducted in the United States had found that 91–98% of BPA may be removed from water during treatment at municipal water treatment plants. A more detailed explanation of aqueous reactions of BPA can be observed in the Degradation of BPA section below. Nevertheless, a 2009 meta-analysis of BPA in the surface water system showed BPA present in surface water and sediment in the U.S. and Europe. According to Environment Canada in 2011, "BPA can currently be found in municipal wastewater. […]initial assessment shows that at low levels, bisphenol A can harm fish and organisms over time."
BPA affects growth, reproduction, and development in aquatic organisms. Among freshwater organisms, fish appear to be the most sensitive species. Evidence of endocrine-related effects in fish, aquatic invertebrates, amphibians, and reptiles has been reported at environmentally relevant exposure levels lower than those required for acute toxicity. There is a widespread variation in reported values for endocrine-related effects, but many fall in the range of 1μg/L to 1 mg/L.
A 2009 review of the biological impacts of plasticizers on wildlife published by the Royal Society with a focus on aquatic and terrestrial annelids, molluscs, crustaceans, insects, fish and amphibians concluded that BPA affects reproduction in all studied animal groups, impairs development in crustaceans and amphibians and induces genetic aberrations.
Toxicity.
BPA exhibits very low acute toxicity as indicated by its LD50 of 4 g/kg (mouse). In those mice, weight gain was reduced and exhibited estrogen-like properties. Reports indicate that it is a minor skin irritator as well, though less so than phenol.
The FDA's National Center for Toxicology Research conducted its own research studies. In rodent studies, the amount of BPA passed from the mother to the unborn offspring after oral administration was found to be insignificant. The BPA administration dose for the rodents was 100-1000 times higher than human exposure.
Production.
World production capacity of BPA was 1 million tons in the 1980s, and more than 2.2 million tons in 2009. It is a high production volume chemical. This compound is synthesized by the condensation of acetone (hence the suffix A in the name) with two equivalents of phenol. The reaction is catalyzed by a strong acid, such as hydrochloric acid (HCl) or a sulfonated polystyrene resin. Industrially, a large excess of phenol is used to ensure full condensation; the product mixture of the cumene process (acetone and phenol) may also be used as starting material:
Numerous ketones undergo analogous condensation reactions.
BPA substitutes.
Concerns about the health effects of BPA have led many manufacturers to replace BPA with substitutes such as bisphenol S (BPS) and diphenyl sulfone. However, health concerns have been raised about these substitutes as well.
Reactions.
Nitration yields Dinitrobisphenol A. Bromination yields Tetrabromobisphenol A that has been used in flame retardant epoxy materials but is becoming more generally avoided due to restrictions on using halogenated species in general.
Identification in plastics.
In the U.S., plastic packaging is split into seven broad classes for identification purposes by a Resin identification code. As of 2014 there are no BPA labeling requirements for plastics in the U.S. "In general, plastics that are marked with Resin Identification Codes 1, 2, 4, 5, and 6 are very unlikely to contain BPA. Some, but not all, plastics that are marked with the Resin Identification Code 7 may be made with BPA." 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. Type 3 (PVC) may contain bisphenol A as an antioxidant (not a plasticizer) in "flexible PVC" softened by plasticizers, but not rigid PVC such as pipe, window frames, and siding.
Legislation.
The U.S. Food and Drug Administration (FDA) has ended its authorization of the use of BPA in baby bottles and infant formula packaging, based on market abandonment, not safety. The European Union and Canada have banned BPA use in baby bottles.
Currently in the United States, there are 12 states, in addition to Washington D.C. that have restrictions in place against BPA. These states include California, Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, Nevada, New York, Vermont, Washington, and Wisconsin. Each state's restrictions differ slightly, but all restrict the use of BPA in some way.
The following are some examples of legislation in place in these states: 