On its own, of course, biomonitoring proves just about nothing; it simply spits out long lists of parts per billion and parts per trillion. If researchers already know how much of a certain chemical will harm our health, those numbers can be immediately put to use by regulators and activists. "We suddenly have a very direct measure of exposure," says Jane Houlihan, vice president for research of the Environmental Working Group. "We no longer have to make sloppy corrections."

Much of the time, the path from data to action is not so clear. So there are a few parts per trillion of Nasty-Sounding Chemical X in your bloodstream. Will it hurt you? "The response from the chemical industry is always 'Show me the link,'" says Theo Colborn, an authority on hormone-disrupting chemicals and the author of the 1996 book "Our Stolen Future."

It's extremely difficult for scientists -- and politicians -- to blame particular pollutants for health problems. Congress didn't ban PCBs until almost 40 years of research had established their disastrous effects, and it took us about 20 years to decide that smoking caused disease.

But when biomonitoring data is paired with detailed health studies, such links can emerge more quickly: If Chemicals X and Y coincide with curiously high rates of Disease A, researchers have good reason to dig deeper.

Biomonitoring has already helped lawmakers take precautionary steps. In the late 1990s, for instance, Swedish scientists studied archived breast-milk samples and found that their levels of PDBEs -- a group of flame retardants widely used in the plastic components of computers -- had been doubling every five years for the past 25 years. Researchers in California followed up with a study of human breast tissue, finding that women in the San Francisco Bay area exhibited the world's highest recorded PDBE levels.

PDBEs are related to the notorious PCBs, but their health effects are not as well understood. Yet news of their rapid accumulation in human bodies led the European Union to reduce its use of PDBEs in the late 1990s; this year, it approved a ban on PDBEs that will take effect in mid-2006. The California Legislature recently prohibited the use of certain types of PDBEs beginning in 2008.

This better-safe-than-sorry approach is controversial, but some say precautionary regulations are based in medical tradition. "If we have reason to believe that an agent causes disease, we can invoke the old public-health principle of prevention," says Michael McCally, the president-elect of Physicians for Social Responsibility. "We simply need to revisit it."

For the test subjects themselves, these knotty political issues have become painfully personal. Brody might never be sure if the traces of Dursban in her body are eroding her health, but she's certain they've added a new urgency to her daily work: She's the founder and executive director of the nonprofit Health Care Without Harm, a group that promotes environmentally safe medical practices.

"It made me understand more deeply how we're all in this together," she says. "If there's Dursban in me, this can't just be about being a smarter shopper. It has to be about having the kind of government that protects us from the problems we can't protect ourselves from."

Recent Stories