Mercury is present in the bodies of most Americans, suggest the US Centers for Disease Control and Prevention (CDC), who recently reported that scientists found measureable levels of mercury in most of the participants taking part in a nationally representative health and nutrition survey. This finding comes from the CDC's "Fourth National Report on Human Exposure to Environmental Chemicals", which, according to the federal agency, is "the most comprehensive assessment to date of the exposure of the US population to chemicals in our environment". For the report, CD scientists analyzed blood and urine samples from participants taking part in the CDC's National Health and Nutrition Examination Survey (NHANES), an ongoing survey that every two years samples members of the US population. The Fourth Report includes results from surveys covering 1999 - 2000, 2001 - 2002, and 2003 - 2004.