KNOY: Just ahead, how human activity on the Galapagos could leave the islands a paradise plundered. First, this Environmental Health Note from Diane Toomey.

TOOMEY: In recent years there has been growing concern that disorders such as autism may be linked to the cumulative effect of childhood vaccinations. That's because many vaccines use a mercury-based preservative known as thimerosal, and mercury is a known neurotoxin. Now, for the first time, researchers have completed a detailed analysis of blood mercury levels in infants immunized with vaccines containing thimerosal. In this small study, University of Rochester researchers took blood samples from about three dozen infants about a week to three weeks after vaccination. Researchers found that most children had blood mercury levels of one or two nanograms per milliliter. That's well below the EPA's safety limit of 5.8 nanograms, a threshold regulators believe that itself is a small fraction of the mercury concentration that would actually cause harm. In this study, the highest level of mercury found in an infant was 4.1 nanograms, still below the EPA limit.

Researchers also say it appears that mercury is excreted from infant's bodies much quicker than previously thought. Thimerosal has recently been phased out of U.S. vaccines, but it is still widely used in vaccines administered overseas. And that's this week's Environmental Health Note. I'm Diane Toomey.

KNOY: And you're listening to Living on Earth.