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research on the monomer published on April 1 in Current Biology [13, 546 (2003); C&EN, April 7, page 7]. The American Plastics Council tends to discount the new findings, which have alarmed many scientists. In the article, Patricia A. Hunt, an associate professor of genetics at Case Western Reserve University, reports that when mice are exposed to very low levels of bisphenol A--commonly known as BPA--it induces highly significant increases in two types of chromosomal aberrations in developing mouse eggs. In human eggs, such abnormalities are the leading cause of miscarriage, mental retardation, and congenital defects, such as Down's syndrome. If a mouse egg with a chromosomal aberration were fertilized, the resulting fetus would probably be resorbed in the womb, Hunt says. This would be the equivalent of a miscarriage in a mouse. The levels of BPA the female mice were exposed to in Hunt's research--about 20 ppb--were only slightly higher than what people commonly encounter. Recently, a German group found BPA levels of 2 to 12 ppb in human mothers' and fetal blood. A group of Japanese scientists found concentrations of 0.2 to 19 ppb in the urine of female students. So Hunt's research raises the question of whether BPA in women's blood is affecting the maturation of their eggs. The discovery of chromosomal abnormalities in mouse eggs stemmed from an accident. Hunt was studying how changing hormone levels in the mice led to chromosomal aberrations in their eggs. Suddenly, her control group's eggs showed a sudden increase in the number of abnormalities. She puzzled over what could be affecting the controls. "We suspected it might be caused by something environmental, and so for several weeks we looked for an explanation--especially for any recent changes in the lab. Nothing turned up. But as I was heading out the door for some time off, I noticed the plastic cages looked kind of the worse for wear," Hunt says. She then learned that a technician had accidentally applied an alkaline detergent to the polycarbonate cages housing the lab mice serving as a control group. The detergent leached excessive amounts of BPA from the plastic. Next, Hunt deliberately exposed mice to low doses of BPA, which is weakly estrogenic. Their eggs developed the same two kinds of chromosomal abnormalities as had developed from the lab accident. In normal mouse or human eggs, the chromosomes line up, ready to divide when the egg is fertilized. But in many of the eggs of the exposed mice, the chromosomes were misaligned. This behavior of the chromosomes has been correlated with an increase in aneuploidy, a condition in which the egg cells have too few or too many chromosomes. Even pure water leaches significant amounts of BPA from polycarbonate plastic cages and bottles, other researchers have recently found. A study published on Feb. 5 in the online edition of Environmental Health Perspectives shows that the amount of BPA leached with water is sufficient to cause human breast cancer cells in petri dishes to respond as if they have been exposed to an estrogenic substance. As a consequence of Hunt's research and the EHP paper, manufacturers have started to make lab cages out of alternative plastics such as polypropylene. BPA is important to industry and consumers; about 2 billion lb is produced each year in the U.S. Polycarbonate plastic made from BPA is used for clear plastic baby bottles and many types of food and drink containers. Resins made with BPA line most metal food and beverage cans and are used as dental sealants |
| UPDATE | 05.03 |
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