EPA's Report on the Environment: External Review Draft
Blood Mercury Level
Note to reviewers of this draft revised ROE: This indicator reflects data through 2010. EPA anticipates updating this indicator in 2014.
Mercury is a naturally occurring metal. However, through many industrial processes (e.g., chemical manufacturing operations, coal combustion), mercury is widespread and persistent in the environment. It is found in elemental form and in various organic compounds and complexes. Organic methylmercury—the form of mercury that is of primary public health significance—can accumulate in the food chain in aquatic systems and lead to high concentrations in predatory fish. The major source of human exposure to methylmercury in the U.S. is consumption of contaminated fish (mostly predatory and larger species) and shellfish (Caldwell et al, 2009; NRC, 2000).
The human health effects of mercury are diverse and depend on the forms of mercury encountered and the severity and length of exposure. Fetuses and children may be more susceptible to mercury than adults, with concern for the occurrence of developmental and neurological health effects (NRC, 2000). Prenatal exposures interfere with the growth and migration of neurons and have the potential to cause irreversible damage to the developing central nervous system.
This indicator reports the total blood mercury levels (includes organic and inorganic) among U.S. women age 16 to 49 and children age 1 to 5, using data from the 1999-2010 continuous National Health and Nutrition Examination Survey (NHANES). NHANES began reporting blood mercury data for all eligible participants age 1 and over in 2003. The findings of the expanded data set will be reported in future updates. NHANES is a series of surveys conducted by the Centers for Disease Control and Prevention’s (CDC’s) National Center for Health Statistics that is designed to collect data on the health and nutritional status of the civilian, non-institutionalized U.S. population using a complex, stratified, multistage, probability-cluster design. CDC’s National Center for Environmental Health conducted the laboratory analyses for the biomonitoring samples. Beginning in 1999, NHANES became a continuous and annual national survey. The data presented here cover six different survey periods: 1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008, and 2009-2010.
What the Data Show
Exhibit 1 presents the geometric mean and four percentiles (50th, 75th, 90th, and 95th) of blood mercury for women age 16 to 49, by race and ethnicity, sampled during each of the continuous NHANES survey periods. Among women age 16 to 49 years geometric mean blood mercury levels fluctuated throughout the survey period, ranging from 0.789 micrograms per liter (µg/L) (2007-2008) to 1.02 µg/L (1999-2000). Decreases from 1999-2000 to 2009-2010 occurred for all four percentiles, but were most pronounced at the 90th (35.7 percent) and 95th (40.0 percent) percentiles.
Among the three racial/ethnic groups reported in Exhibit 1, black non-Hispanic women age 16 to 49 consistently had the highest geometric mean blood mercury levels over time, followed by white non-Hispanics and then Mexican Americans.
Exhibits 2 and 3 display geometric mean and four percentiles for children age 1 to 5, by sex and race and ethnicity, respectively. The geometric mean remained largely the same during the first three survey periods: 0.343 µg/L in 1999-2000, 0.318 µg/L in 2001-2002, and 0.326 µg/L in 2003-2004. The geometric mean for females was consistently higher than for males during the first three survey periods, with a range of 0.329-0.377 µg/L for females compared to 0.302-0.317 µg/L for males (Exhibit 2). For each of the first three survey periods, non-Hispanic blacks had a higher geometric mean than Mexican Americans and non-Hispanic whites (Exhibit 3). The geometric means for total, sex, and race/ethnicity for Mexican Americans and non-Hispanic whites during 2005-2010, and for non-Hispanic blacks from 2005-2008, were not reported because the proportion of results below the limit of detection was too high to provide a valid result.
The relatively small number of samples collected in a two-year cycle (e.g., 1999-2000 or 2001-2002) may, in some cases, result in measures of central tendency that are unstable from one survey period to the next.
Health-based benchmarks for blood levels of mercury have not been established.
Data used for this indicator were generated with Stata statistical software utilizing the NHANES laboratory files available online in SAS® transport file format (CDC, 2012).
For More Information
- CDC National Health and Nutrition Examination Survey
- CDC National Report on Human Exposure to Environmental Chemicals
- CDC Mercury Biomonitoring Summary
- Learn how this indicator fits into a conceptual diagram for: Fish Mercury Contamination
- This indicator relates to: Exposure to Environmental Contaminants
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