Bisphenol A

Bisphenol A is a organic compound with the formula (CH₃)₂C(C₆H₄OH)₂. Containing two phenol functional groups, it is an difunctional building block to several important polymers and polymer additives.^[1] Bisphenol A has become controversial because it mimics estrogen and thus can induce hormonal responses.

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Synthesis

Bisphenol A is prepared by the reaction of two equivalents of phenol with one equivalent of acetone. Hydrogen chloride (HCl) and or sulfonated polystyrene is used as a catalyst. Typically, a large excess of phenol is used to ensure full condensation:

2 (CH₃)₂CO + 2 C₆H₅OH → (CH₃)₂C(C₆H₄OH)₂ + H₂O

The methodology is an example of a "green chemical reaction" in the sense that the process is efficient and the only by-product is water.^[1]

History and use

Bisphenol A was first synthesized by A.P. Dianin in 1891.^[2][3] Bisphenol A current uses are numerous. It is a key monomer in production of polycarbonate plastic and epoxy resins. Otherwise it is used in the following polymer types: polyesters, polysulfones, and polyether ketones. Bisphenol A is also used as an antioxidant in plasticizers and as a polymerization inhibitor in PVC.^[1]

It is a precursor to the flame retardants tetrabromobisphenol A.

Safety aspects

See http://ptcl.chem.ox.ac.uk/MSDS/BI/bisphenol_A.html With a low toxicity and negligible skin permeability, bisphenols are sufficiently safe that they are used as antioxidants in cosmetics and foods.^[1]

Estrogen receptor controversy

Bisphenol A was investigated in the 1930s during the search for estrogen mimics. From this study the synthetic compound diethylstilbestrol was shown to be a competent competitor with estrogen.^{[citation needed]} Bisphenol A, like many other compounds, is known to be an estrogen receptor agonist. Such agonists can activate estrogen receptors, leading to similar physiological effects as the body's own estrogens.^[4] The first evidence of the estrogenicity of bisphenol A came from experiments in the 1930s in which it was fed to ovariectomized rats.^[5][6] 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.^[7] Bisphenol A has been shown to have developmental toxicity, carcinogenic effects, and possible neurotoxicity.^[8][9] Recent studies suggest it may also be linked to obesity by triggering fat-cell activity.^[10]

A consensus statement by 38 BPA experts concluded that average levels in people are above those that cause harm to animals in laboratory experiments.^[11]. However, government regulatory agencies in Germany and Japan have concluded that normal use of these products is safe.^[12] A NIH-sponsored panel in the U.S. determined that there was 'some concern' about BPA's effect on fetal and infant brain and behavior. ^[13] Peer reviewed publications have appeared pointing out flaws within the chemical industry funded studies that report bisphenol A safety.^[14] 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 had not previously been studied by them in depth, having been accepted under grandfather clauses when stricter regulations were passed in the 1980s. The research will begin in May 2007, and take some time to complete.^[15] 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.^[16] 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".^[17] 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.^[18]

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.^[19] The chemical is found in almost everyone that lives in developed countries at low concentrations. Infants fed with liquid 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,^[20] 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^[15] by the United States Environmental Protection Agency^[21] - well above the levels found to have caused negative health effects in studies (see table below).

Growing awareness of health concerns in the U.S. retail sector, particularly in chains promoting healthy food and lifestyles, has led to a number of classes of products containing Bisphenol A to be withdrawn. In 2005, Patagonia Inc., a retailer of outdoor gear, ceased selling polycarbonate bottles. In 2006, Whole Foods Markets ceased selling baby bottles. In 2007, Mountain Equipment Co-op ceased selling bottles containing BPA.^[22]

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.^[24]

Identification in Plastics

Highlighted types in the table below are believed to not leach chemicals in any significant amount. Type 7 is the highest risk for BPA (Biphenol A) leaching.^[25]

There are seven groups of plastic polymers^[26], each with specific properties that are used worldwide for many packaging applications (see table below). Each group of plastic polymer can be identified by its Plastic Identification code (PIC) - usually a number or a letter abbreviation. For instance, Low-Density Polyethylene can be identified by the number "4" and/or the letters "LDPE". The PIC appears inside a three-chasing arrow recycling symbol. The symbol is used to indicate whether the plastic can be recycled into new products.

The PIC was introduced by the Society of Plastics Industry, Inc. which provides a uniform system for the identification of different polymer types and helps recycling companies to separate different plastics for reprocessing. Manufacturers of plastic food packaging and containers can voluntarily mark their products with the PIC. Consumers can identify the plastic types based on the codes usually found at the base or at the side of the plastic food packaging and containers. The PIC is usually not present on packaging films, as it is not practical to collect and recycle most of this type of waste.

References