Researchers have found disturbing new evidence suggesting that environmental exposure to a ubiquitous substance may cause chromosomally abnormal pregnancies. They have learned that low levels of a compound used in the manufacture of some plastic food and beverage containers and some baby bottles interfere with cell division in the eggs of female mice. The disruption of cell division can result in an abnormal number of chromosomes in the eggs, a condition known as aneuploidy, which is the leading cause of mental retardation and birth defects in humans. Down syndrome is an example of a disorder caused by the addition of an extra chromosome.

Patricia Hunt, Ph.D., lead author of the study appearing in the April issue of the journal Current Biology, is concerned because the compound, called Bisphenol A (BPA), which shows hormone-like properties and mimics the effects of naturally produced estrogens, produces a significant increase in genetic abnormalities at extremely low levels.

"Our studies provide the first direct evidence that environmental exposure to BPA acts to disrupt the maturation of the egg and demonstrate a dose-related increase in abnormalities," says Hunt, an associate professor of genetics at the Case Western Reserve University School of Medicine and an expert in the causes of genetic abnormalities in egg cells. "In addition, they show that, at least in the mouse, exposure to very low doses of BPA within the human exposure range produces detectable effects."

"These studies raise important questions about the potential impact on human reproduction of BPA and other man-made substances that mimic the actions of hormones," she says.

The scientists say the beverage bottles that contain BPA are the ones with the number 7 in the recycling symbol. The baby bottles with BPA are the clear type. They say that colored baby bottles do not contain BPA, and they recommend handwashing baby bottles rather than cleaning in a dishwasher.

Hunt's laboratory began studying the effects of BPA after control (or normal) mice in research projects began showing genetic abnormalities. In mice, the rate of these abnormalities usually is low. The defects were traced to plastic cages and plastic water bottles that had been inadvertently cleaned with a harsh detergent. The detergent caused BPA to leach from the polycarbonate material used to make the cages and bottles. Over several years, Hunt and her team proceeded to determine how much BPA the mice had been inadvertently exposed to, which was a relatively large amount. Then, they scaled back to see how small a dose would produce effects. This amounted to daily doses of 20 parts/billion over five to seven days, an extremely low level.

"We can't say anything about the effects of BPA on humans," says Hunt. "Nevertheless, the cell division program for eggs is extraordinarily similar in mice and humans, and the results of our studies in mice are disturbing because brief exposure during the final stages of egg growth were sufficient to cause significant increases in meiotic abnormalities."

Other authors on the study from Case Western Reserve University are K.E. Koehler, C.A. Hodges, A. Ilagan, R.C. Voigt, T. J. Hassold; from Thoren Caging Systems, Inc., S. Thomas, and from RTI International Research Triangle, B.F. Thomas.

The studies are supported by the National Institutes of Health, an ACS postdoctoral fellowship, and a Culpepper Foundation Pilot Initiative Grant.