Bisphenol A (Environmental & Earth Science)
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.
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.
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.
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.
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