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Monday, March 31, 2003, 12:00 p.m. EDT
A sudden increase in chromosome abnormalities in a mouse colony has raised questions about the safe level of exposure for bisphenol A, a chemical used to make some common plastics and resins.
In a research paper supported by the National Institute of Environmental Health Sciences (http://www.niehs.nih.gov), scientists at a genetics laboratory and an associated animal research center, both at Case Western Reserve University in Cleveland, describe the accident in the April 1 issue of the journal Current Biology :
The scientists found that the colony's semi-rigid plastic cages had deteriorated as the result of a handler's use of the wrong cleaner - a harsh detergent - which damaged the cages and led to the release of small amounts of the plasticizer bisphenol A, which is often abbreviated as BPA.
This low level exposure led to "highly significant" increases in abnormalities in the mice's developing eggs, called oocytes. These results were then confirmed in an experiment in which the animals' eggs were deliberately exposed, the scientists reported.
First author Patricia A. Hunt, Ph.D., of the Department of Genetics at Case Western Reserve said that the sudden increase in abnormalities appeared in a mouse colony used as a control group. "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 that the plastic cages looked kind of the worst for wear. I thought maybe the autoclave" - a system producing pressurized steam to keep conditions sterile - "was causing the deterioration. I asked my co-workers to check on that. On my return, I was told that the autoclave didn't produce that effect on the plastic but that a temporary animal worker had mistakenly used a harsh, alkaline detergent on them.
"We then confirmed that such a detergent could break down the plastic caging and water bottles chemically, exposing the mice to bisphenol A at low levels."
The researchers then deliberately exposed mice to small amounts of bisphenol A. They found that, once again, their eggs showed greatly increased rates of two chromosome abnormalities. In normal mouse or human eggs, the chromosomes line up, ready for the egg to split in two when fertilized. But in many of the eggs of the exposed mice, the chromosomes were not aligned but disorganized. In addition, the egg cells of the exposed mice frequently had too few or too many chromosomes, a condition called aneuploidy.
These kinds of chromosomal abnormalities are the leading cause of miscarriage, congenital defects and mental retardation in humans.
Dr. Hunt said, "We don't know what the effects, if any, may be on humans at these low levels, but a study in Germany indicates pregnant women are exposed to similar levels of BPA, which is used in food and beverage containers. Certainly we should be concerned enough to carry out extensive further study."
Terry J. Hassold, Ph.D., is the head of the second laboratory involved in these studies. Other colleagues on the research are Kara E. Koehler, Ph.D., Marta Susiarjo, Craig A. Hodges, Ph.D., Arlene Ilagan, and Robert Voight. All are with the Department of Genetics or the Animal Resource Center of Case Western.
Sally Thomas of Thoren Caging Systems Inc. of Hazleton, Pa., and Brian F. Thomas, Ph.D., of RTI International of Research Triangle Park, N.C., also participated in the work.
Research on bisphenol A has stirred controversy for years. Generally, traditional testing - such as the 103-week rodent study carried out by the National Toxicology Program in 1982 - has not raised concerns, but several other studies have.
In 1997, research at the University of Missouri-Columbia suggested BPA has an estrogen-like activity. In these experiments, pregnant mice were exposed to low levels of bisphenol A at a time when their male fetuses' prostates were developing. The male offspring subsequently developed enlarged prostates at adulthood, the scientists reported in the NIEHS journal Environmental Health Perspectives.
Recently, the European Commission's Scientific Committee on Food lowered its Tolerable Daily Intake for bisphenol A five-fold.
Several years ago, EPA asked the National Toxicology Program to assemble a panel of academic, government and industry scientists to make recommendations on BPA and other environmental estrogens. In 2001, the panel said, among other things, that BPA might require special types of additional testing to assure that the levels permitted are safe.
Dr. Hunt and her colleagues suggested today that their study of immature mouse eggs might be the basis for such sensitive new testing.
The National Toxicology Program is headquartered at NIEHS in Research Triangle Park, N.C. NIEHS is one of the institutes of the National Institutes of Health, a part of the U.S. Department of Health and Human Services.
Some of the funding for the study came from a pool by the industry-supported American Chemistry Council. The Council, in 2001, agreed to provide $1 million to NIEHS for studies on human reproduction and fetal and childhood development. The Council has no role in selecting the studies, which are approved by the regular, independent peer review used by NIH.
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