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Bisphenol A

Possible health risks

Bisphenol A is known to be an estrogen receptor agonist which can activate estrogen receptors leading to similar physiological effects as the body's own estrogens. The first evidence of the estrogenicity of bisphenol A came from experiments in the 1930s in which it was fed to ovariectomized rats. 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. Bisphenol A has been shown to have developmental toxicity, carcinogenic effects, and possible neurotoxicity. Recent studies suggest it may also be linked to obesity by triggering fat-cell activity.

Various environmental groups have claimed that exposure to bisphenol A from polycarbonate-containing consumer products poses a potential human health risk. However, government regulatory agencies in Europe, Japan, and the United States have all concluded that normal use of these products is harmless. The independence of United States scientific panels from industry influence has been questioned however. Furthermore, peer reviewed publications have appeared pointing out flaws within the chemical industry funded studies that report bisphenol A safety. In 2006, Canadian regulators selected bisphenol A as one of 200 substances deserving of thorough safety assessments after preliminary studies found it to be 'inherently toxic'; the chemical has not previously been studied by them in depth, having been accepted under grandfather clauses when stricter regulations were passed in the 1980's. The research will begin in May 2007, and take some time to complete. The city of San Francisco, California, banned the sale of baby bottles and other products for young children containing bisphenol A in June 2006, effective December 2006, and was at the time the only jurisdiction in the world to outright forbid the substance. The ban was never enforced, and in May 2007 the city repealed the ban.

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". A subsequent study by the European Union’s Food Safety Authority reached a similar conclusion, and sharply criticized the methodology used in many of the low-dose exposure studies on rodents.

Bisphenol A has been known to leach from the plastic lining of canned foods and to a lesser degree plastics which are cleaned with harsh detergents or used to contain acidic or high temperature liquids. Infants fed with concentrated (canned) infant formula have among the highest exposures of anyone eating canned foods. Infants fed canned formula with polycarbonate bottles can consume quantities of bisphenol A up to 13 µg/kg/day. The chemical is found in most people who live in developed countries at low 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) is considered safe - satisfying a thousand-fold margin of safety - by the United States Environmental Protection Agency.

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.

Polycarbonate & Bisphenol A – Potential hazards in food contact applications

Polycarbonate may be appealing to manufacturers and purchasers of food storage containers due to its clarity and toughness, being described as lightweight and highly break resistant particularly when compared to silica glass. Polycarbonate may be seen in the form of single use and refillable plastic water bottles.

More than 100 studies have explored the bioactivity of bisphenol A leachates from polycarbonates. Bisphenol A appeared to be released from polycarbonate animal cages into water at room temperature and that it may have been responsible for enlargement of the reproductive organs of female mice.

An analysis of the literature on bisphenol A leachate low-dose effects by vom Saal and Hughes published in August 2005 seems to have found a suggestive correlation between the source of funding and the conclusion drawn. Industry funded studies tend to find no significant effects while government funded studies tend to find significant effects.

Research by Ana M. Soto, professor of anatomy and cellular biology at Tufts University School of Medicine, Boston, published Dec. 6 in the online edition of Reproductive Toxicology (DOI: 10.1016/j.reprotox.2006.10.002) describes exposure of pregnant rats to bisphenol A at 2.5 to 1,000 µg per kg of body weight per day. At the equivalent of puberty for the pups (50 days old), about 25% of their mammary ducts had precancerous lesions, some three to four times higher than unexposed controls. The study is cited as evidence for the hypothesis that environmental exposure to bisphenol A as a fetus can cause breast cancer in adult women.

One point of agreement among those studying polycarbonate water and food storage containers may be that using sodium hypochlorite bleach and other alkali cleaners to clean polycarbonate is not recommended, as they catalyze the release of the Bisphenol-A. The tendency of polycarbonate to release bisphenol A was discovered after a lab tech used strong cleaners on polycarbonate lab containers. Endocrine disruption later observed on lab rats was traced to exposure from the cleaned containers.

A chemical compatibility chart shows reactivity between chemicals such as polycarbonate and a cleaning agent. Alcohol is one recommended organic solvent for cleaning grease and oils from polycarbonate. For treating mold, Borax:H₂O 1:96 to 1:8 may be effective.

Synthesis

Polycarbonate can be synthesized from bisphenol A and phosgene (carbonyl dichloride, COCl₂). The first step in the synthesis of polycarbonate from bisphenol A is treatment of bisphenol A with sodium hydroxide. This deprotonates the hydroxyl groups of the bisphenol A molecule.

The deprotonated oxygen reacts with phosgene through carbonyl addition to create a tetrahedral intermediate (not shown here), after which the negatively charged oxygen kicks off a chloride ion (Cl^-) to form a chloroformate.

The chloroformate is then attacked by another deprotonated bisphenol A, eliminating the remaining chloride ion and forming a dimer of bisphenol A with a carbonate linkage in between.

Repetition of this process yields polycarbonate, a polymer with alternating carbonate groups and groups from bisphenol A.

Interaction with other chemicals

(1) At room temperature. At temperatures above 60°C hydrolysis is more present, degrading the plastic. Degradation depends on time and temperature.

Using sodium hypochlorite (bleach) and other alkali cleaners on polycarbonate is not recommended as they cause the release of bisphenol A, a known endocrine disrupter.

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