This is why I think the government and environmental groups sometimes jump the gun when they find out a substance may be harmful.
Toxic-tort lawyers aren't going to like this: Evidence is growing that most hazardous chemicals, as well as radiation, not only are harmless at low doses–but may actually do a body good. Scientists who study this mind-bending effect, called hormesis, have quietly marshaled a wealth of examples showing that it's real. And it appears to be more the rule than the exception–long-ignored signs of the phenomenon have been unearthed in hundreds of studies on everything from toxic heavy metals to dread carcinogens like dioxin.
Here's the standard technique: Lab animals are exposed to megadoses of a toxin, causing pronounced effects that are readily measured. That yields guesstimates of the human effects at megalevels. To estimate the risk at low doses, regulators assume that the toxic effects fall in a straight line with the dose. Tumor incidence in rats vs. doses of saccharin, for instance, would be graphed on X and Y axes as a straight line. The handy line shows the purported risk at doses down to zero.
But scientists who go to the trouble of measuring actual toxic effects at low levels often observe a J-shaped "dose response" curve instead of a straight line. That means the risks many toxins pose at real-world levels have probably been exaggerated. The J-curve also suggests an idea that, at first blush, seems daft: Policies that foster small exposures to toxins might be better for public health than ones aimed at eliminating them.
When Bush took office and decided to investigate the science of arsenic's effects on the body, the environmental groups slammed him for not pushing the limits lower immediately. But this is exactly why he was right to wait and look over the facts and studies. Too bad politics is more concerned with hype than evidence.