Bisphenol A Totally Explained

Everything about Bisphenol-a totally explained

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

Synthesis

Bisphenol A was first reported by A.P. Dianin in 1891. It 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: ť (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. 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.
Global production of bisphenol A in 2003 was estimated to be about 3 million metric tonnes (t). In the U.S., it's 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. However, bisphenol A is an endocrine disruptor: it's an estrogen receptor agonist, and such agonists can act like the body's own hormones, leading to similar physiological effects on the body. There is thus concern that long term low dose exposure to bisphenol A may induce chronic toxicity in humans.

Endocrine disruption

The first evidence of the estrogenicity of bisphenol A came from experiments in the 1930s in which it was fed to ovariectomized rats. Since then, its endocrine disrupting properties have been extensively investigated, and more than 100 studies have been published "rais[ing] health concerns" about the chemical. For example, studies have demonstrated developmental toxicity, carcinogenic effects, and possible neurotoxicity at low doses in animal models (see table below). Recent studies suggest it may also be linked to obesity by triggering fat-cell activity and have confirmed that bisphenol A exposure during development has carcinogenic effects and produce precursors of breast cancer. However, neither the U.S. Environmental Protection Agency nor the International Agency for Research on Cancer have evaluated Bisphenol A for possible carcinogenic activity. In 2007, a consensus statement by 38 experts on bisphenol A concluded that average levels in people are above those that cause harm to animals in laboratory experiments, and a panel convened by the U.S. National Institutes of Health determined that there was "some concern" about BPA's effects on fetal and infant brain development and behavior.
   In April 2008, the Health Canada released its Draft Screening Assessment for bisphenol A, which concluded that the chemical may pose some risk to infants and proposed classifying the chemical as "'toxic' to human health and the environment." This action follows Canadian regulators selection of bisphenol A in 2006 as one of 200 substances deserving of thorough safety assessments after preliminary studies had found it to be "inherently toxic"; the chemical hadn't previously been studied by them in depth, having been accepted under grandfather clauses when stricter regulations were passed in the 1980s.
   In contrast to the recent actions in North America, in January 2006 the German Federal Institute for Risk Assessment announced that polycarbonate baby bottles are safe and stated that published research on the health effects of Bisphenol A is "difficult to interpret and [is] occasionally contradictory". 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. In 2007 Japan also concluded that "the current exposure levels of BPA won't pose any unacceptable risk to human health that a ban isn't needed."
   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, and the experimental design of some of these studies has also been questioned. Studies have also appeared pointing out flaws in chemical industry funded studies that found no evidence of adverse effects from low dose exposure, and a study from 2008 concluded that blood levels of bisphenol A in neonatal mice are the same whether it's injected or ingested.

Selected studies on low dose bisphenol A exposure in animals

Dose (µg/kg/day)	Effects (measured in studies of mice or rats, descriptions are from Environmental Working Group)
0.025	Changes in breast tissue that predispose cells to hormones and carcinogens	2005
2	increased prostate weight 30%	1997
2	lower bodyweight, increase of anogenital distance in both genders, signs of early puberty and longer estrus.	2002
2.4	Decline in testicular testosterone	2004
2.5	Breast cells predisposed to cancer	2007
10	Prostate cells more sensitive to hormones and cancer	2006
10	Decreased maternal behaviors	2002
30	Reversed the normal sex differences in brain structure and behavior	2003
50	U.S. human exposure limit (not a result from an animal study, but a guideline set by EPA)	1998

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. Studies by the CDC found bisphenol A in the urine of 95% of adults sampled in 1988-1994 and in 93% of children and adults tested in 2003-04. 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), 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
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."

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