Bisphenol A (BPA) is a
chemical compound primarily used in the manufacturing of various
plastics. It is a colourless solid which is
soluble in most common organic
solvents, but has very poor solubility in water.[2][7] BPA is produced on an industrial scale by the
condensation reaction of
phenol and
acetone. Global production in 2022 was estimated to be in the region of 10 million tonnes.[8]
The health effects of BPA have been the subject of prolonged public and scientific debate.[12][13][14] BPA is a
xenoestrogen, exhibiting hormone-like properties that mimic the effects of
estrogen in the body.[15] Although the effect is very weak,[16] the pervasiveness of BPA-containing materials raises concerns, as exposure is effectively lifelong. Many BPA-containing materials are non-obvious but commonly encountered,[17] and include coatings for the inside of
food cans,[18] clothing designs,[19] shop receipts,[20] and dental fillings.[21] BPA has been investigated by public health agencies in many countries, as well as by the
World Health Organization.[12] 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.[22] BPA-free plastics have also been introduced, which are manufactured using alternative bisphenols such as
bisphenol S and
bisphenol F, but there is also controversy around whether these are actually safer.[23][24][25]
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.[27] The utilization of BPA further expanded with discoveries at
Bayer and
General Electric on
polycarbonateplastics. These plastics first appeared in 1958, being produced by
Mobay, General Electric, and Bayer.[28]
The British biochemist Edward
Charles Dodds tested BPA as an artificial
estrogen in the early 1930s.[29][30][31] Subsequent work found that it bound to
estrogen receptors tens of thousands of times more weakly than
estradiol, the major natural female sex hormone.[32][16] 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.[29] BPA was never used as a drug.[29]
Production
The synthesis of BPA still follows Dianin's general method, with the fundamentals changing little in 130 years. The
condensation of
acetone (hence the suffix 'A' in the name)[33] 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 the
sulfonic acid form of
polystyrene sulfonate.[34] An excess of phenol is used to ensure full condensation and to limit the formation of byproducts, such as
Dianin's compound. BPA is fairly cheap to produce, as the synthesis benefits from a high
atom economy and large amounts of both starting materials are available from the
cumene process.[7] As the only
by-product is water, it may be considered an industrial example of
green chemistry. Global production in 2022 was estimated to be in the region of 10 million tonnes.[8]
Usually, the addition of acetone takes place at the
para position on both phenols, however minor amounts of the ortho-para (up to 3%) and ortho-ortho isomers are also produced, along with several other minor by‑products.[35] These are not always removed and are known impurities in commercial samples of BPA.[36][35]
About 65–70% of all bisphenol A is used to make
polycarbonate plastics,[9][10] which can consist 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.[43] This process converts the individual molecules of BPA into large polymer chains, effectively trapping them.
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 di
acrylate and di
methacrylate derivatives (bis-EMA, or EBPADMA). These may be incorporated at low levels in vinyl ester resins to change their physical properties[46] and see common use in
dental composites and
sealants.[47][48]
Minor uses
The remaining 5% of BPA is used in a wide range of applications, many of which involve plastic.[49] BPA is a main 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 low.
Polyetherimides such as Ultem can be produced from BPA via a nitro-displacement of appropriate bisnitroimides.[51][52] These
thermoplasticpolyimide plastics have exceptional resistance to mechanical, thermal and chemical damage. They are used in medical devices and other high performance instrumentation.
PVC can contain BPA and its derivatives through multiple routes. BPA is sometimes used as an antioxidant in
phthalates,[58] which are extensively used as
plasticizers for PVC. BPA has also been used as an antioxidant to protect sensitive PVC
heat stabilizers. Historically 5–10% by weight of BPA was included in barium-cadmium types, although these have largely been phased out due health concerns surrounding the
cadmium. BPA diglycidyl ether (BADGE) is used as an acid scavenger, particularly in PVC
dispersions, such as organosols or
plastisols,[59][60] which are used as coatings for the inside of food cans, as well as embossed clothes designs produced using
heat transfer vinyl or
screen printing machines.[19]
BPA is used to form a number of
flame retardants used in plastics.[61] Bromination of BPA forms
tetrabromobisphenol A (TBBPA), which is mainly used as a reactive component of polymers, meaning that it is incorporated into the polymer backbone. It is used to prepare fire-resistant
polycarbonates by replacing some bisphenol A. A lower grade of TBBPA is used to prepare
epoxy resins, used in
printed circuit boards. TBBPA is also converted to tetrabromobisphenol-A-bis(2,3,-dibromopropyl ether) (TBBPA-BDBPE) which can be used as a flame retardant in
polypropylene. TBBPA-BDBPE is not chemically bonded to the polymer and can leach out into the environment.[62] The use of these compounds is diminishing due to restrictions on
brominated flame retardants. The reaction of BPA with
phosphorus oxychloride and
phenol forms
bisphenol-A bis(diphenyl phosphate) (BADP), which is used as a liquid flame retarder in some high performance
polymer blends such as polycarbonate/
ABS mixtures.[63]
Other applications
BPA is used as an antioxidant in several fields, particularly in
brake fluids.[64]
BPA is used as a developing agent in
thermal paper (shop receipts).[20] Recycled paper products can also contain BPA,[65] although this can depend strongly on how it is recycled.
Deinking can remove 95% of BPA,[9] with the pulp produced used to make newsprint, toilet paper and facial tissues. If deinking is not performed then the BPA remains in the fibers, paper recycled this way is usually made into
corrugated fiberboard.[9]
Concerns about the health effects of BPA have led some manufacturers replacing it with other bisphenols, such as
bisphenol S and
bisphenol F. These are produced in a similar manner to BPA, by replacing acetone with other
ketones, which undergo analogous condensation reactions.[7] Thus, in
bisphenol F, the F signifies
formaldehyde.
Health concerns have also been raised about these substitutes.[66][24] Alternative polymers, such as
tritan copolyester have been developed to give the same properties as polycarbonate (durable, clear) without using BPA or its analogues.
As a result of the presence of BPA in plastics and other commonplace materials, most people are frequently exposed to trace levels of BPA.[67][68][69] 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,[10] thermal paper,[20] clothing,[19] dental materials,[70] and medical devices.[17] Although BPA exposure is common it does not accumulate within the body, with
toxicokinetic studies showing the
biological half-life of BPA in adult humans to be around two hours.[71][72] The body first converts it into more water-soluble compounds via
glucuronidation or
sulfation, which are then removed from the body through the urine. This allows exposure to be easily determined by urine testing, facilitating convenient
biomonitoring of populations.[22][17][73] Food and drink containers made from Bisphenol A-containing plastics do not contaminate the content to cause any increased cancer risk.[74]
The health effects of BPA have been the subject of prolonged public and scientific debate,[12][13][14] with
PubMed listing more than 18,000 scientific papers as of 2024.[75] Concern is mostly related to its
estrogen-like activity, although it can interact with other receptor systems as an
endocrine-disrupting chemical.[76] 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.[12] A common criticism is that industry-sponsored trials tend to show BPA as being safer than studies performed by academic or government laboratories,[14][77] although this has also been explained in terms of industry studies being better designed.[13][78]
Public health agencies in the EU,[79][80][81] US,[82][83] Canada,[84] Australia[85] and Japan as well as the
WHO[12] 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,[86] leading to bans on the use of BPA in
baby bottles and related products by the US,[87] Canada,[88] and EU[89] amongst others. Bottle producers have largely switched from polycarbonate to
polypropylene and there is some evidence that BPA exposure in infants has decreased as a result of this.[22] 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.[90][91] In June 2023 after the EFSA reported about the toxicity of BPA the European Union has passed the resolution in early 2024 to ban BPA in all the food contact material including plastic and coated packaging and it said it would also address other bisphenols to avoid replacing with other harmful substances.
BPA exhibits very low
acute toxicity (i.e. from a single large dose) as indicated by its
LD50 of 4 g/kg (mouse). Reports indicate that it is a minor skin irritant as well, although less so than
phenol.[7]
Bisphenol A's interacts with the
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.[93] BPA binding to ERR-γ preserves its basal constitutive activity.[93] It can also protect it from deactivation from the SERM
4-hydroxytamoxifen (afimoxifene).[93] This may be the mechanism by which BPA acts as a
xenoestrogen.[93] 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).[94]
Environmental safety
Distribution and degradation
BPA has been detectable in the natural environment since the 1990s and is now widely distributed.[95] It is primarily a river pollutant,[96] but has also been observed in the marine environment,[97] in soils,[98] and lower levels can also be detected in air.[99] The solubility of BPA in water is low (~300 g per ton of water)[2] but this is still sufficient to make it a significant means of distribution into the environment.[98] 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,[9][100]leaching from PVC items may also be a significant source,[96] as can landfill
leachate.[101]
In all cases,
wastewater treatment can be highly effective at removing BPA, giving reductions of 91–98%.[102] 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.[103]
Once in the environment BPA is aerobically biodegraded by a wide a variety of organisms.[95][104][105] Its
half life in water has been estimated at between 4.5 and 15 days, degradation in the air is faster than this, while soil samples degrade more slowly.[98] BPA in sediment degrades most slowly of all, particularly where this is anaerobic.
Abiotic degradation has been reported, but is generally slower than biodegradation. Pathways include
photo-oxidation, or reactions with minerals such as
goethite which may be present in soils and sediments.[106]
Environmental effects
BPA is an environmental
contaminant of emerging concern.[101] Despite its short half-life and non-
bioaccumulating character, the continuous release of BPA into the environment causes continuous exposure to both plant[107] and animal 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.[108] As such, the precise effects of BPA on the growth, reproduction, and development of aquatic organism are not fully understood.[108] Regardless, the existing data shows the effects of BPA on wildlife to be generally negative.[109][110] BPA appears able to affect development and reproduction in a wide range of wildlife,[110][111] with certain species being particularly sensitive, such as
invertebrates and
amphibians.[109]
4-tert-Butylphenol - used as a chain-length regulator in the production of polycarbonates and epoxy resins, it has also been studied as a potential endocrine disruptor
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