What's BPA, and do I really need a new water bottle?

If it weren't for a laboratory mishap roughly 10 years ago, it's possible you wouldn't be reading this article. But in August 1998, the geneticist Dr. Patricia Hunt was studying the ovaries of mice and noticed her data behaving strangely. For some reason, chromosomal errors leaped from 2 percent to 40 percent in the mice making up her control group. These abnormalities eventually would lead to miscarriage and birth defects. The determined cause: BPA [source: Neimark].

After running more tests, Hunt learned that all of the mice cages and water bottles were contaminated with BPA that had leached out of the polycarbonate plastic. When she replaced the plastics, the mice cells returned to normal. Her work revealed that exposure to BPA disrupts fetal development, as well as the eggs of the fetus that will be responsible for the next generation.

Since her discovery, Hunt and other researchers have become convinced that BPA is a cause for concern in humans, as well as mice. Critics of the studies linking BPA to cell damage, however, argue that the research isn't conclusive. Some point to a 2002 study showing that humans process BPA differently than mice, so we won't necessarily experience the same health effects. Others say that the BPA that finds its way into the food supply is safely below the limits set by the U.S. Environmental Protection Agency.

A plastics industry Web site called Bisphenol-A.org says BPA is completely safe unless you regularly eat 1,300 pounds (590 kilograms) of canned or bottled food a day [source: Zandonella]. The American Chemistry Council and the U.S. Food and Drug Administration seem to agree. Although the agency is reviewing its stance, it continues to downplay concerns about using products made with BPA [source: Dunham].

Other government bodies, such as the U.S. Department of Health and Human Services and the U.S. Centers for Disease Control and Prevention say that there is some concern about risks to humans who consume BPA. The differences of opinion among these factions arise partly because the ill effects of BPA are linked primarily with mice and partly because of the nature of the chemical itself.

BPA is a difficult substance to nail down; it doesn't behave like a typical toxin. While other chemicals labeled as toxic have clear-cut impacts (asbestos exposure leads to cancer, lead poisoning causes reduced mental capacity), BPA is sneakier. Rather than harm the body outright, BPA is an endocrine disruptor. It changes the way our body's hormones function, mimicking our own natural hormones -- in this case, estrogen.

Estrogen can alter the behavior of more than 200 genes, which control the growth and repair of nearly every organ and tissue in the body [source: Environmental Working Group]. Among other things, estrogen affects fetal development, cell structure and the onset of puberty, and your body's cells are highly sensitive to even tiny changes in estrogen levels.

Studies show that doses of BPA between 2 and 20 micrograms per kilogram of body weight alter the reproductive system of male mice. Babies fed canned formula heated in a polycarbonate bottle may consume that amount in just one day [source: Neimark]. So while some early toxicity studies done on BPA determined that high doses were safe, it's important to remember that BPA doesn't behave like your average toxin. Scientists aren't sure why, but high amounts of BPA don't always seem to affect genes the same way low doses do. It sounds counterintuitive, but with BPA, it turns out that less is actually more [source: Zandonella].

Should you, the consumer, swear off all plastics? Probably not. Learn some more sensible recommendations next.

Depending on who you listen to, BPA may or may not be a cause for concern, but there's no doubt that you're exposed. A 2004 study by the U.S. Centers for Disease Control and Prevention detected BPA in almost 93 percent of Americans [source: CDC]. A separate study by the Environmental Working Group, a U.S. nonprofit, found BPA in more than 50 percent of 97 commonly consumed canned goods at levels that caused adverse health effects in animal experiments [source: Environmental Working Group].

Mice seem to be harmed when they're exposed to BPA in those kinds of amounts, but does that mean people are too? Conclusive findings could take decades because the effects of estrogens may not show up until later in an individual's life. Thorough studies must follow a line of cells for many decades, and many people aren't willing to wait. Canada, for one, became the first country to officially declare BPA a toxic chemical, a decision that could lead to a partial or complete ban of its food-related use within two years. The European Union is also taking a more proactive approach, requiring companies to prove that a chemical is safe before it's cleared for the market. The U.S., on the other hand, requires proof that a chemical is not safe.

For countries where the government is taking a "wait and see" approach, never underestimate the power of you, the consumer. It was consumer demand that forced companies like Nalgene and Playtex to alter their products. Until other companies follow suit or the FDA changes its stance, there are several steps you can take to limit your exposure. And yes, one of those steps is to replace your beat-up polycarbonate water bottle and to stop using polycarbonate containers to hold food and beverages. If you'd rather not buy new containers, at least make sure yours aren't scratched and that you wash them by hand -- extreme heat and degradation increase the likelihood of BPA leaching out.

Here are some other steps you can take, courtesy of the Green Guide Institute:

If BPA turns out to be harmless to humans, at least you can say you're doing your part for the Earth.

For more information on our plastic world, try some of the links on the following page.