Low levels of a key building block of polycarbonate can damage chromosomes in mice, raising questions about whether that exposure could contribute to reproductive problems and mental retardation in people, U.S. government researchers said.
The new study, conducted by Case Western Reserve University in Cleveland, found that low levels of exposure to bisphenol A can cause ``highly significant'' increases in chromosome abnormalities in the developing eggs of mice.
What worries researchers is that those same kinds of abnormalities in humans are the leading cause of miscarriages, congenital defects and retardation, the study said.
But, government scientists stressed, it's not clear whether the study is relevant for people, and a plastics industry official said that more-detailed studies have not found problems.
Still, it's not the first time research has raised questions about low doses of BPA, which is used in applications ranging from PC packaging for water and food to dental sealants.
The chemical attracted attention in 1997 when studies found that low levels of exposure to BPA - well below existing safety thresholds - can enlarge prostates and hasten puberty in mice.
But those results could not be reproduced, and a subsequent U.S. government panel said the evidence was not clear enough to reach a firm conclusion. However, recently a European Commission panel drastically lowered its standard for ``safe'' levels of BPA exposure. American Plastics Council officials point out that the levels to which people are exposed still are far below that standard.
The most recent study was done as part of a joint, $4 million research initiative between the National Institute of Environmental Health Sciences and the American Chemistry Council, and will be published in the April 1 issue of the journal Current Biology.
The study found that the eggs of mice exposed to low levels of BPA were not aligned properly for pregnancy, and it said that egg cells frequently had too few or too many chromosomes, a condition called aneuploidy, according to a news release from NIEHS.
``We don't know what the effects, if any, may be on humans at these low levels, but a study in Germany indicates that pregnant women are exposed to similar levels of BPA,'' said Case Western Professor Patricia Hunt, lead author of the study. She could not be reached but was quoted in the NIEHS statement.
``Certainly we should be concerned enough to carry out extensive further study,'' she said.
Steven Hentges, executive director of the polycarbonate business unit of the APC in Arlington, Va., said that research on BPA continues. But he said the larger body of research on BPA has not found those problems.
Several multigenerational studies done by the industry worldwide and by the Japanese government have not found problems with reproductive performance. Those studies went a step further and examined the offspring of the mice for any problems, which the Case Western study did not do.
Hentges also said other studies of BPA exposure in humans have found only trace amounts of the chemical, well below safe levels. Hentges said he is not sure why Hunt interpreted the German study as she did, because human and animal exposure studies use different metrics that can make direct comparisons very difficult.
A scientist at NIEHS in Research Triangle Park, N.C., said the results are surprising, but said the meaning is unclear.
``The question is that, because a mouse is not a man or a woman, to what extent does this translate into concern for the human condition?'' said Michael McClure, chief of the organs and systems toxicology branch at NIEHS.
The Case Western researchers did not set out to study BPA, but were led to it after a lab mishap.
The lab was doing unrelated research with mice when it discovered a sudden increase in chromosome abnormalities in a control group.
Hunt said researchers searched for the cause for several weeks. They came up empty until Hunt noticed that the mice cages looked worn. A temporary lab worker had used an overly harsh detergent to clean the cages, which were made from PC. Subsequent testing confirmed that the detergent could break down both PC cages and water bottles.
The researchers then conducted a full-blown study deliberately exposing mice to BPA.