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If you are like many readers of The Green Guide, you try and choose foods that are as free as possible of harmful chemicals such as pesticides. But if you consume canned soups, beans and soft drinks, organic or not, you also may be swallowing residues of a controversial chemical called bisphenol A (BPA) that can leak out of the can linings into your food. Nearly all can liners contain BPA, says Geoff Cullen, director of government relations at the Can Manufacturers Institute. BPA has also been found to migrate, under some conditions, from polycarbonate plastic water bottles.

Depending on whom you talk to, BPA is either perfectly safe or a dangerous health risk. The plastics industry says it is harmless, but a growing number of scientists are concluding, from some animal tests, that exposure to BPA in the womb raises the risk of certain cancers, hampers fertility and could contribute to childhood behavioral problems such as hyperactivity.

According to its critics, BPA mimics naturally occurring estrogen, a hormone that is part of the endocrine system, the body's finely tuned messaging service. "These hormones control the development of the brain, the reproductive system and many other systems in the developing fetus," says Frederick vom Saal, Ph.D., a developmental biologist at the University of Missouri. Endocrine-disrupting chemicals can duplicate, block or exaggerate hormonal responses. "The most harm is to the unborn or newborn child," vom Saal says.

Plastic water and baby bottles, food and beverage can linings and dental sealants are the most commonly encountered uses of this chemical. Unfortunately, it doesn't stay put. BPA has been found to leach from bottles into babies' milk or formula; it migrates from can liners into foods and soda and from epoxy resin-lined vats into wine; and it is found in the mouths of people who've recently had their teeth sealed. Ninety-five percent of Americans were found to have the chemical in their urine in a 2004 biomonitoring study by the Centers for Disease Control and Prevention (CDC).

Plastics manufacturers do not deny that BPA is found widely in canned foods and beverages and is routinely ingested. They part ways with vom Saal and other scientists over the human health risks. The levels that leach into food are well below the safety thresholds set by the Environmental Protection Agency (EPA), and the plastics industry website, Bisphenol-A.org, says the chemical is completely safe unless you ingest 1,300 pounds of canned and bottled food daily. In other words, even a canned-food addict will likely ingest 500 times less BPA than the danger level set by the EPA and 100 times less than the standard set by the European Commission Scientific Committee on Food. And common sense tells us that if higher doses are safe, then lower doses must be too, right?

Not necessarily, says vom Saal, who notes that these safety levels are based on 1980s toxicity studies in rats. In those studies, conducted at relatively high doses, the only sign of toxicity was reduced body weight. However, when it comes to hormone disruption, different doses can activate or suppress different genes, vom Saal explains. "That's why early toxicity studies found that the high doses were safe. The studies didn't look at the low doses that are now proving to cause a myriad of harmful effects in animals, including chromosomal damage in female egg cells and an increase in embryonic death in mice. A follow-up to this is a study indicating a relationship of BPA blood levels to miscarriages in Japanese women," he says.