BPA was thrust into the spotlight by a laboratory mishap. In August 1998, geneticist Patricia Hunt, Ph.D., now at Washington State University in Pullman, noticed that chromosomal errors in the mouse cells she was studying had shot up—from 1 or 2 percent to 40 percent, as published in the April 2003 Current Biology. Hunt traced the effect to polycarbonate cages and water bottles that had been washed with a harsh detergent. When her team replaced all the caging materials with non-polycarbonate plastics, the cell division returned to normal.

But not all scientists think BPA is capable of doing such harm to humans. Some deny that BPA disrupts hormones. A study funded by the Society of the Plastics Industry and published in the July 2002 Toxicological Sciences that explored the effects of low doses on three generations of rats found no effect on reproduction or development. "If you look at all the data together, you don't find a consistent pattern of effects that are characteristic of an estrogenic chemical," says Steven G. Hentges, Ph.D., executive director of the Polycarbonate Business Unit at the American Plastics Council. Others argue that rodent studies such as Hunt's are not relevant to humans. A study published in the October 2002 Chemical Research in Toxicology of human volunteers found that a human body neutralizes and excretes BPA far more rapidly than a rat's body does.

So far, regulatory agencies agree. "Based on all the evidence available at this time, the FDA sees no reason to change its long-held position that current [BPA] uses with food are safe," George Pauli, Ph.D., associate director for science and policy at the FDA's Office of Food Additive Safety, wrote in a November 28, 2005, letter.

Vom Saal counters that the studies showing BPA is safe are "profoundly flawed and in some cases exhibit outright fraud." Last year, he published a paper showing that 100 percent of the industry-funded studies, 11 in all, found no harmful effects from BPA, while 90 percent of government-funded low-dose studies, 104 in number, found harmful effects. "Among people who have actually read this literature there is no debate, just an illusion of controversy," he says.

Meanwhile, new studies continue to reveal the potential for harm. A January 2006 study indicates that BPA may enhance the risk of developing Type II diabetes. Angel Nadal, Ph.D., and his team at the University of Miguel Hernández de Elche in Alicante, Spain, found that BPA altered the function of mouse pancreatic cells, which produce insulin. Unhealthy diet, a lack of exercise and a genetic predisposition are the main factors in triggering diabetes, says Nadal. "However, our feeling is that these factors could be exacerbated by the presence of environmental pollutants such as bisphenol A."

Human studies might settle the controversy over BPA, but so far they have been too limited to prove much. One study linked women with ovarian disfunction to elevated blood levels of BPA, and another found that blood levels of BPA were three times higher in women who'd suffered recurrent miscarriages than in women with successful pregnancies. While intriguing, these studies were from a small sample group. A more definitive result could be gained from a large-scale study to track people's exposures, follow them for years and look for health effects. The National Toxicology Program is planning a future evaulation of BPA.

Some scientists urge that action be taken now, regardless. "Science is not in the business of demonstrating anything beyond a shadow of a doubt," says Ana Soto, M.D., a professor and researcher at Tufts University School of Medicine in Boston, who has found that BPA alters mammary-gland development in mice. "We cannot wait that long to discover whether this chemical is harming human reproduction and development." However, because government agencies remain unconcerned, it is unlikely that BPA will disappear from consumer products anytime soon. A California bill to ban BPA in baby toys and feeding products was defeated in January.