On Feb. 8, the Environmental Quality Institute (EQI) at the University of North Carolina-Asheville released the largest ever biomonitoring study of mercury levels in the U.S. population. Based on hair samples from more than 6,600 women, researchers found that 20 percent of women of childbearing age exceed the EPA's recommended mercury limit.

In support of the study, Sierra Club and Greenpeace sponsored mercury-testing events. Individuals were also able to order testing kits online. "We found the greatest single factor influencing mercury exposure was the frequency of fish consumption," says Dr. Steve Patch, EQI's co-director. Coal-fired power plants produce 42 percent of industrial mercury pollution in the U.S., and airborne mercury emissions from these plants often settle into lakes, streams, and oceans, contaminating fish and shellfish. Polluted fish along with the mercury they contain then winds up on dinner tables. Mercury is a persistent bioaccumulative toxin, which means it collects as it moves up the food chain and concentrates at the top, slots occupied by people and a few other "high-order" consumers.

The Centers for Disease Control and Prevention (CDC) conducted a similar study in 1999 as part of its National Health and Nutrition Examination Survey. The project tested hair mercury levels in 838 children one to five years of age, and 1,726 women between 16 and 49 years old. The study found mercury exposure similar to those of the EQI study. In addition, CDC estimated from its study that between 300,000 and 630,000 newborns each year may be exposed before birth to mercury concentrations above the EPA limit, above which the risk increases that neurological development will be adversely affected.

Biomonitoring studies, such as the CDC and EQI study, can help improve public health policy by indicating trends in chemical exposures, identifying communities that are disproportionately affected or particularly vulnerable, assessing the effectiveness of current regulations, and setting priorities for legislative and regulatory action. The biomonitoring studies point to a need for improved policies, environmental and health advocates argue, because after years of progress in pollution prevention and reduction of toxic releases, these studies' results still show dangerously high levels of toxic substances in peoples' bodies.

Unfortunately, thus far biomonitoring's usefulness as a public health tool has been constrained by the limited number and scope of studies performed. For instance, while July 2005 marked the release of CDC's Third National Report on Human Exposure to Environmental Chemicals, a nation-wide biomonitoring study released every two years, many critics continue to describe the study as too small and limited for use on a national scale. The study only examines exposure levels in 2,500 people across the country. Many scientists have called for more extensive national research and more focused biomonitoring studies, such as state-specific programs, that would help make the connection between sources of toxics, at-risk populations, and pollution-prevention measures. Sadly, efforts thus far to establish state biomonitoring programs have been blocked. Last year, the California legislature passed what would have been the country's first state-wide biomonitoring program; however, the bill (SB 600) was vetoed by Governor Arnold Schwarzenegger.