Bisphenol A
Bisphenol A (BPA) is a chemical compound primarily used in the manufacture of various plastics. It is a colourless solid which is soluble in organic solvents, but is only poorly soluble in water. It is produced on an industrial scale by the condensation of phenol and acetone, with global production in 2022 expected to reach 10 million tonnes. Its largest single application is as a co-monomer in the production of polycarbonates, which accounts for 65-70% of all BPA production. 25-30% is used in the manufacture of epoxy resins and vinyl ester resins. The remaining 5 % is used as a major component of several high-performance plastics and as a minor additive in PVC, polyurethane, thermal paper and several other materials. It is not a plasticizer, although it is often wrongly labelled as such. The heath effects of BPA have been the subject of prolonged public and scientific debate. BPA is a xenoestrogen, exhibiting estrogen-mimicking, hormone-like properties. Although the effect is very weak, the pervasiveness of BPA-containing materials raises concerns, as exposure is effectively lifelong. Many BPA-containing materials are non-obvious but commonly encountered, and include coatings for the inside of food  cans, clothing, shop receipts and dental fillings. BPA has been investigated by public health agencies in many countries, as well as by the World Health Organization. While normal exposure is below the level currently associated with risk, several jurisdictions have taken steps to reduce exposure on a precautionary basis, in particular by banning BPA from baby bottles. There is some evidence that BPA exposure in infants has decreased as a result of this. BPA-free plastics have also been introduced, which are 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 reported in 1891 by the 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. Production. The synthesis of BPA  still follows Dianin's general method, with the fundamentals having changed little in 130 years. The condensation of acetone (hence the suffix 'A' in the name) with two equivalents of phenol is catalyzed by a strong acid, such as concentrated hydrochloric acid, sulfuric acid, or a solid acid resin such as polystyrene sulfonate. An excess of phenol is used to ensure full condensation and to limit the formation of by-products, such as Dianin's compound. Large amounts of both starting materials are available from the cumene process, making it fairly cheap to produce. Global production in 2022 is expected  to reach 10 million tonnes. The reaction is strongly para selective but minor amounts of the ortho-para (up 3%) and ortho-ortho isomers are also produced, along with several other minor by-products. These are not always removed and are known impurities in commercial samples of BPA. Uses and applications. Polycarbonates. Between about 65-70% of all bisphenol A is used to make polycarbonate plastics, which can consists of nearly 90% BPA by mass. Polymerisation is achieved by a reaction with phosgene, conducted under biphasic conditions; the hydrochloric acid is scavenged with aqueous base. This process converts the individual  molecules of BPA into large polymer chains, effectively trapping them. Epoxy and vinyl ester resins. About 25-30% of all BPA is used in the manufacture of epoxy resins and vinyl ester resins. For epoxy resin it is first converted to its diglycide ether (usually abbreviated BADGE or DGEBA). This is achieved by a reaction with epichlorohydrin under basic conditions. Some of this is further reacted with methacrylic acid to form bis-GMA, which is used to make vinyl ester resins. Alternatively, and to a much lesser extent, BPA may be ethoxylated and then converted to its diacrylate and dimethacrylate  derivatives. These may be incorporated at low levels in vinyl ester resins to change their physical properties. Minor uses. The remaining 5% of BPA is used in a wide range of applications, many of which are also to do with plastic. BPA is a major component of several high-performance plastics, the production of these is low compared to other plastics but still equals several thousand tons a year. Comparatively minor amounts of BPA are also used as additives or modifiers in some commodity plastics. These materials are much more common but their BPA content will be minimal. BPA substitutes . Concerns about the health effects of BPA have led many manufacturers to replace BPA with substitutes, particularly bisphenol S and bisphenol F. However, health concerns have been raised about these substitutes as well. In the similar compound Bisphenol F, the F signifies formaldehyde Numerous ketones undergo analogous condensation reactions. Human safety. Exposure. The presence of BPA in plastics and other commonplace materials means that most people are frequently exposed to trace levels of this compound. The primary source of human exposure is via food, as epoxy and PVC are used to line the inside of food cans to prevent corrosion  of the metal by acidic foodstuffs. Polycarbonate drinks containers are also a source of exposure, although most disposable drinks bottles are actually made of PET, which contains no BPA. Among the non-food sources, exposures routes include through dust, thermal paper, clothing, dental materials, and medical devices. Although BPA exposure is common it does not accumulate within the body, with toxicokinetic studies show the biological half-life of BPA in adult humans to be around 2 hours. The body first converts it into more water soluble compounds via glucuronidation or sulfation, which are then removed in urine. This allows for  total exposure to be easily motioned by urine testing. Health effects and regulation. The heath effects of BPA have been the subject of prolonged public and scientific debate. Concern is mostly related to its estrogen-like activity, although it can interact with other receptor systems as an endocrine-disrupting chemical. These interactions are all very weak, but exposure to BPA is effectively lifelong, leading to concern over possible cumulative effects. Studying this sort of long-term, low-dose interaction is difficult, and although there have been numerous studies, there are considerable discrepancies in their conclusions regarding the nature of the  effects observed as well as the levels at which they occur. A common criticism is that industry-sponsored trials tend to show BPA as being safer than studies performed by academic or government laboratories, although this has also been explained in terms of industry studies being better designed. Public health agencies in the EU, US, Canada, Australia and Japan as well as the WHO have all reviewed the health risks of BPA, and found normal exposure to be below the level currently associated with risk. Regardless, due to the scientific uncertainty, many jurisdictions have taken steps to reduce exposure on  a precautionary basis. In particular, infants are considered to be at greater risk, leading to bans on the use of BPA in baby bottles and related products by the US, Canada, and EU amongst others. Bottle producers have largely switch from polycarbonate to polypropylene and there is some evidence that BPA exposure in infants has decreased as a result of this. The European Chemicals Agency has added BPA to the Candidate List of substances of very high concern (SVHC), which would make it easier to restrict or ban its use in future. In the United States, there are 12 states , in addition to Washington, D.C., that have restrictions in place against BPA in some way. 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, although less so than phenol. Pharmacology. 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). Environmental safety. Prevalence and persistence. BPA has been detectable in the natural environment since the 1990s and is now widely distributed. It is primarily a river pollutant, but has also been observed in the marine environment, and in soils. Lower levels can also been detected in air. The solubility of BPA in water is low (~300 g/ton of water ) but this is still sufficient to make it a significant means of distribution into the environment. Many of the largest sources of BPA pollution are water-based, particularly wastewater from industrial facilities using BPA. Paper recycling can be a major source of release when this includes thermal paper, leaching from PVC items may also be a significant source, as can landfill leachate. In all cases wastewater treatment can be highly effective at removing BPA, with reductions of 91–98%. Regardless, the remaining 2-9% of BPA will continue through to the environment, with low levels of BPA commonly observed in surface  water and sediment in the U.S. and Europe. Once in the environment BPA is aerobically biodegraded by a wide a variety of organisms. It's half life in water has been estimated at between 4.5 - 15 days, degradation in the air is faster than this, while soil samples degrade more slowly. BPA in sediment degrades most slowly of all, particularly where this is anaerobic. Environmental effects. BPA is environmental contaminant of emerging concern. Despite its short half-life and non-bioaccumulating character, the continuous release of BPA into the environment causes continuous exposure to both animal and plant life. Although  many studies have been performed, these often focus on a limited range of model organisms and can use BPA concentrations well beyond environmental levels. As such, the precise effects of BPA on the growth, reproduction, and development of aquatic organism is not fully understood. Regardless, the existing data shows the effects of BPA on wildlife to be generally negative. Certain species, such as invertebrates and amphibians seem to be particularly affected BPA also appears to effect development and reproduction in a wide range of wildlife species.