Frederick vom Saal is a respected American biology professor who keeps a running tally of the scientific literature investigating the health effects of bisphenol A, a chemical used in one of the world's most widely used plastics. By his count, 130 papers have been published on the effects of low-dose exposures to the chemical. Dr. vom Saal, a professor at the University of Missouri, found that more than 90 per cent of the government-financed studies noted adverse effects from the chemical, but not one of the 11 industry-backed ones.
The subject is of more than just passing academic interest because practically everyone is exposed to bisphenol A — or BPA, for short — on a daily basis. It is used to make a range of things, from tinted Nalgene bottles, to dental sealants for children's teeth, to coatings on compact discs and the sealants on the inside of most tin cans.
The widespread use of BPA wouldn't be a problem, except that the chemical doesn't stay put in products. It leaches out and gets into people, and trace amounts are now found in almost everyone. This worries many researchers because BPA, besides being good for making plastic, is a chemical that mimics the female estrogen hormone.
Experiments on lab animals exposed to small doses of BPA have linked it to low sperm counts, the earlier onset of puberty, insulin resistance and diabetes, prostate abnormalities and skewed mammary gland development, among other effects. Some researchers, such as Dr. vom Saal, worry that these sorts of adverse effects, if they occur in people, seem to mirror recent human disease and health trends.
This view is not shared by the chemical industry. “BPA is not a risk to human health at the extremely low levels at which people might be exposed from use of, for example, polycarbonate plastic,” said Steven Hentges, a spokesman on BPA at the American Plastics Council, based in Arlington, Va.
Dr. vom Saal, one of the world's leading authorities on hormones and synthetic chemicals that act like them, begs to differ. “The chemical companies think they can lie with impunity about the published scientific literature,” he said.
For academe, those are fighting words and they reflect the controversy enveloping BPA. Although humans carry trace amounts of many industrial chemicals in their tissues, there is intense scientific interest in contaminants such as BPA because they have an unusual property: When absorbed by living things, they act like hormones.
Because BPA has a shape similar to the estrogen hormone, it is able to fit into the same receptors that estrogen uses to signal cells to turn biological functions on and off. For Dr. vom Saal, the idea that the entire population is being given a dose of a synthetic estrogen through plastic “is supported by hundreds of published articles” and is “an extremely critical public health issue.”At the heart of safety disputes over BPA are the results of the low-dose experiments with animals and test-tube cell cultures.
The general public is most familiar with high-dose research, the traditional and rather crude tests in which lab animals are stuffed with large amounts of compounds to see how much it takes to kill them outright, to produce effects such as weight loss, or to induce cancer in them. Based on the results of high-dose U.S. experiments in 1982, BPA was not found to be excessively dangerous. At the time, researchers noted that the chemical caused weight loss in rodents at the lowest dose used; based on this observation, an exposure standard was established by the U.S. Environmental Protection Agency.
It set a safe daily exposure standard of 50 micrograms per kilogram of weight — which would be about the size of two grains of sand consumed by an average-sized man.
