Bisphenol-A (BPA) is a chemical present in materials many people use every day, such as polycarbonate plastics and the inner coatings of food and beverage containers. Exposure to BPA is quite pervasive: the chemical has been detected in the urine of more than 92% of those in the US who have been tested, and levels are typically higher in children and adolescents than in adults. In the body, BPA acts like the natural hormone estrogen and hence can have hormone-related effects. Rodents exposed to BPA during fetal and neonatal development had an increased risk of mammary and prostate cancers, altered behavior and obesity.

Because of its ubiquity and potential health effects, BPA has come under increasing scrutiny. In one recent study, a group of scientists at Tufts University School of Medicine (Boston, MA) evaluated the effects of intra-uterine and perinatal exposure to BPA on reproductive capacity of female mouse pups.

The group found that fertility decreased over time in female CD-1 mice that were exposed to BPA during fetal and neonatal development (Environ. Health Perspect. doi:10.1289/ehp.1002559; published online 2 December 2010). These mice had fewer successful pregnancies and delivered fewer pups overall than did mice that were not exposed to BPA. Notably, this effect was not apparent in the mice's first pregnancies, but became obvious with later pregnancies. “This finding is important because standard tests of reproductive toxicology currently consist of assessing the success of a first pregnancy in young animals,” said Beverly S. Rubin, one of the study leaders, in a press release. “If subsequent pregnancies are not examined, relevant effects may be missed.”

The effects of BPA were comparable with those of diethylstilbestrol (DES), a hormonally active chemical known to cause reproductive impairment in women after fetal exposure. Like BPA, DES (when tested at low doses) did not cause obvious reproductive problems during first pregnancies, as assessed by the standard tests used by regulatory agencies to evaluate toxicity.

The researchers tested three different doses of BPA, all of which are within the range to which humans are known to be exposed and are below the maximum acceptable daily dose determined by the Environmental Protection Agency. They found that the effects of BPA were dose-specific: the lowest and highest doses both affected fertility but the intermediate dose did not. Carlos Sonnenschein, also a study leader, pointed out that “chemicals have to be tested at a variety of doses in order to avoid false 'no effect' results.”