Plastics ingredient disrupts fetal-egg development.

A common estrogen-mimicking chemical can damage eggs while an animal is still in the womb, researchers report.

Bisphenol A is found in polycarbonate plastics--those used to make baby bottles and hard-shell water bottles--and in the lining of food cans. The chemical also turns up in human tissues at concentrations of several parts per billion.

Earlier research had linked bisphenol A to reproductive problems in male and female mice. In 2003, molecular geneticist Patricia A. Hunt of Washington State University in Pullman and her colleagues exposed female mice to doses of the chemical typical of environmental concentrations. This increased the likelihood that eggs would have abnormal numbers of chromosomes (SN: 4/5/03, p. 213).

But "the process of making an egg is incredibly long," notes Hunt. Egg development begins in the female fetus, stops before birth, and then resumes just before ovulation. To look for effects of exposure during the earlier developmental phase, Hunt's team implanted bisphenol A pellets in pregnant mice. The pellets released the same dose used in the group's earlier experiment.

The researchers compared eggs from the female offspring of these pregnant mice with eggs from mice whose mothers had carried a placebo pellet. Up to 40 percent of the eggs from females exposed to bisphenol A as fetuses had abnormal numbers of chromosomes, the group reports in the January PLoS Genetics. Only about 3 percent of the placebo group showed that abnormality.

"The mother's exposure is influencing the genetic quality of her grandchildren," says Hunt.--A.C.