Introduction

Bisphenol A (BPA) is used in the production of polycarbonate plastic products including baby bottles, plastic water bottles and the lining of food cans. Additionally BPA is present in a variety of other consumer products such as electronic goods, CDs, DVDs, adhesives, vehicle dashboards, pipes, thermal fax papers, plastic food wraps and some types of dental fillings.

Although recent concerns relate to the estrogenic activity of BPA, the estrogenic attributes of the chemical have been known since 1936.

Production of BPA

BPA is a synthetic chemical compound (monomer) manufactured by combining two phenol molecules with a single acetone through undergoing condensation reaction. 

Figure 1. Structural formula of Bisphenol A. (Source: Wikipedia)

Polymers of BPA are linked by ester bonds that can be hydrolyzed easily with increasing temperature and at high or low pH.

6.4 billion pounds of BPA are produced worldwide annually and demand for BPA is expected to increase by six to ten percent.

Detection of BPA in Humans

BPA has been detected in human blood and urine. CDC (Center for Disease Control) has found BPA concentration of up to eight parts per billion (ppb) in urine samples that were collected for testing within the U.S. from 2003 through 2004. Urine samples were obtained from 2517 people ranging in age from 6 years old and above. Nearly 90% of the people tested had BPA in their urine ranging from 0.1 to 10.0 ppb. Additionally, BPA has been detected in the blood and placenta of pregnant women, and in the blood and amniotic fluid of the human fetus. 

Figure 2. Food can linings like these may contain Bisphenol A. (Source: Wikipedia)

BPA is known to be present in the liquid contents of tinned food cans. BPA polymers may hydrolyze and leach out from these containers even under normal room temperature conditions.

Hot contents like boiling water increases the amount of BPA leached from plastic bottles as well as baby bottles into the contents of the bottle as more leaching occurs under higher temperatures. Some studies have shown that BPA also leaches from baby bottles from actions like brushing, dishwashing and sterilizing. 

Figure 3. Some baby bottles like this may contain Bisphenol A. (Source: Wikipedia)

Effects of BPA on laboratory animals

Animal research studies reveal a range of adverse effects caused by exposure to BPA at various life-stages, ranging from negative effects on reproductive endpoints to behavioral changes. For example, offspring of female mice exposed to BPA through lactation have shown behavioral changes by exhibiting more aggressive behaviors, while, high doses of BPA (in adult female mice) have resulted in decreased fertility, reducing the number of offspring.

BPA causes changes in prostate weight of rodents like mice, and has been reported to cause malformations in the urethra, and recent studies suggest that BPA may interact with the androgen receptor (AR), resulting in inappropriate expression of AR-mediated genes. BPA exposure to female rat offspring during gestation and lactation delays the onset of puberty.

Animal studies have also shown that BPA causes precancerous changes in mammary and prostate glands of rodents depending on which life stage they are exposed, and chromosomal abnormalities in the oocytes of adult female mice.

Metabolism of Bisphenol A

BPA is metabolized mainly into monoglucuronides but smaller amounts of other conjugates (complex of two or more molecules covalently linked) may be present as well. There is evidence suggesting that some metabolites of BPA are 250 fold more potent than BPA itself.

References

• Toxic Nation.Ban Bisphenol A Fact Sheet
• Josephson, J. 2003.[http://www.jstor.org/stable/3455631 Bisphenol Aggression: Effects Shown in Mice.] Environmental Health Perspectives. February 2003.
• Centre for Disease Control (CDC). 2007. Spotlight on Bisphenol A and 4-tertiary-Octylphenol. National Report on Human Exposure to Environmental Chemicals.
• Hileman, Bette. Chemical and Engineering News: Government & Policy- Bisphenol A On Trial. April 16, 2007.
• Matsumoto, A., Kunugita, N., Kitagawa, K., Isse, T., Oyama, T., Foureman, G.L., Morita, M., Kawamoto, T. 2003. Bisphenol A Levels in Human Urine. Environmental Health Perspectives. 111: 101-104.
• National Toxicology Program. 2008. NTP Brief on Bisphenol A.

• Saal, F.S., Hughes, C. 2005. An Extensive New Literature Concerning Low-Dose Effects of Bisphenol A Shows the Need for a New Risk Assessment. Environmental Health Perspectives. 113: 926-933.
• University of Cincinnati. 2008. Plastic Bottles Release Harmful Chemicals (Bisphenol A) After Contact with Hot Liquids. Science Daily. Feburary 4, 2008.
• California Pacific Medical Center. 2008. Common Organic Compound Found In Many Household Products May Pose Health Risk to Breast Cells. Science Daily. April 3, 2008.
  
• Timms, B.G., Howdeshell, K.L., Barton, L., Bradley, S., Richter, C.A., Saal, F.S., Bern, H.A. 2005. Estrogenic Chemicals in Plastic and Oral Contraceptives Disrupt Development of the Fetal Mouse Prostrate and Urethra. Proceedings of the National Academy of Sciences of the United States of America. 102: 7014-7019.
• Welshons, W.V.,Nagel, S.C., Saal, F.S. 2006. Large Effects From Small Exposures. III. Endocrine Mechanism Mediating Effects Of Bisphenol A At Levels of Human Exposure. Endocrinology. 147: 56-69.
• WWF- UK. 2000. Toxic chemicals threatens children’s health.
• Yan, H., Takamoto, M., Sugane, K. Exposure to Bisphenol A Prenatally or in Adulthood Promotes TH2 Cytokine Production Associated with Reduction of CD4+CD25+ Regulatory T Cells. Environmental Health Perspectives. 116: 514-518.