The Poisons Within Us

What with killer spinach and poisoned Chinese toothpaste and dog food, the risks of environmental chemicals have faded into the background lately. But one group of scientists convened by the government thinks that's a mistake, at least when it comes to  a chemical called bisphenol-A. A building block of certain plastics, it is produced in massive amounts (6 billion pounds per year), and is used in the linings of some food cans, in certain plastic water bottles, baby bottles and other products. Traces of bisphenol-A are found in rivers, oceans and wildlife, in many foods, and in our blood.

Figuring it might be a good idea to know what exactly we're dealing with, given bisphenol-A's ubiquity, the National Institute of Environmental Health Sciences (part of the National Institutes of Health) convened 38 experts from around the world to assess the risks of the chemical. (This was the first time NIEHS has undertaken such a comprehensive review of the potential harm from an environmental contaminant.) The result falls somewhat short of reassuring. After examining over 700 published studies, the scientists concluded that the average level of the chemical in Americans’ blood is very high, far above levels associated with adverse effects in rats and mice, and also well above the government's "safe" level. The trouble with having so much of the chemical sloshing around us is that bisphenol-A acts like estrogen, even minuscule amounts of which can have powerful physiological effects.

Just as you'd expect from a hormone-like compound, very low doses of bisphenol-A can adversely affect the reproductive, nervous, endocrine and immune systems in rodents, especially when exposure occurs during fetal development and infancy. For example, in a study just published in Reproductive Toxicology (where the NIEHS panel's report is also published), the female offspring of rats exposed to bisphenol-A shortly before they gave birth developed uterine fibroids, ovarian cysts, and changes in the uterine lining analogous to endometriosis.

What about people? The same effects have been observed in women exposed to DES, or diethylstilbestrol, a synthetic estrogen, prenatally, when their mothers took it to prevent miscarriages. The similarity between what happens to mice and to humans exposed to DES, and the similarities between bisphenol-A and DES effects in mice, suggest that bisphenol-A can also harm the human reproductive system.

Obviously, human studies are needed to find out whether bisphenol-A is harming people. But those are tough to do. It is essentially impossible to identify adult women who do and do not have problems of the reproductive tract, for example, and then figure out what their bisphenol-A exposure was when they were fetuses or babies. The most practical approach is to take a large group of pregnant women, determine the levels of bisphenol-A in their blood now, then track the health of their children. But that would be enormously expensive and could take a generation or longer.

What to do in the face of scientific uncertainty? A perennial problem, and one without a scientific answer. Instead, what scientists (and others) believe turns on values more than data. For instance, University of Missouri researcher Fred vom Saal points out that some 200 studies of how bisphenol-A works show that mouse cells and human cells metabolize it the same way. "We have no reason to expect that bisphenol-A would not have the same effects in humans that it does in experimental animals,” he says, which to him is enough reason to get it out of circulation--especially when the amount of bisphenol-A in the blood of  the average American is about 1,000 times higher than levels that produce adverse effects in animals. Looking at the exact same evidence, though, industry opts to "wait and see" if the stuff really harms human health.

At a press briefing Thursday, vom Saal stressed that while people’s exposure to bisphenol-A is “significant and continuous,” we don’t know how people are exposed. Certain food and soft-drink can linings, water bottles, baby bottles and other plastic containers, and some dental sealants, can leach bisphenol-A into foods or saliva. But no one knows which of these sources (or others) contribute how much to anyone’s exposure. In this case, ignorance is definitely not bliss.