Methylmercury Fact Sheet

Overview: There are no confirmed cases of methylmercury toxicity in the United States from consumption of commercial seafood. The amount of mercury equated with serious illness has only been seen in international industrial accidents and poisonings several decades ago. The levels present in those instances are on a scale dramatically different than the levels seen in commercial seafood. Meanwhile, it is estimated that low omega-3 (seafood) consumption is responsible for 84,000 deaths each year in the U.S.

What is methylmercury toxicity?

Mercury toxicity is not defined by a specific lab test score. Toxicity is dependent on the type of mercury (organic, inorganic and vapor) and the type of test that is administered. Organic mercury, specifically methylmercury, is the type that exists in trace amounts in fish. Methylmercury levels in humans are usually detected through blood or hair analysis. Lab tests often measure total (inorganic plus organic) mercury, which is not an accurate gauge of methylmercury from eating fish. Methylmercury lab test results and seafood consumption data alone demonstrate the relationship between eating fish and methylmercury exposure -- not the relationship between methylmercury and health effects.

What are the federal mercury markers?

Committee on the Toxicological Effects of Methylmercury of the National Research Council (NRC) Benchmark Dose Level (BMDL) = 58 micrograms (µg)/L

In 2000, the NRC determined a BMDL of 58 micrograms per liter through an analysis of umbilical cord blood. The committee defined the benchmark dose level as “the lowest dose, estimated from the modeled data, which is expected to be associated with a small increase in the incidence of adverse outcome (typically in the range of 1% to 10%).”

U.S.Environmental Protection Agency’s (EPA) Reference Dose (RfD) for methylmercury = 5.8 micrograms (µg)/L blood

The EPA RfD is not a lab reference. It is defined as the level of daily exposure over the course of a lifetime that is not likely to cause harmful health effects in humans, including those in sensitive subpopulations. The RfDincludes a ten-fold safety factor.

U.S.Food and Drug Administration’s (FDA) Action Level =1 part per million (ppm) methylmercury in edible portion of seafood.

The FDA Action Level for methylmercury represents limits at or above which FDA will consider if legal action to remove fishfrom the market is warranted. An average commercial fish in the U.S. marketplace, weighted for consumption, contains 0.086 ppm methylmercury, far below the rigorous FDA standard.

How do American women compare to the federal mercury markers?

In 2003, the National Health and Nutrition Examination Survey found the following:

  • “Measures of mercury exposure in women of childbearing age and young children generally fall below levels of concern.”
  • Mean concentration of total blood mercury in children = 0.34 µg/L

Mean concentration of total blood mercury in women = 1.20 µg/L

  • No women had blood mercury concentrations at the benchmark dose level (58 µg/L) or higher.
  • Approximately 6% of child-bearing aged women had concentrations higher than the U.S. EPA RfD (5.8 µg/L). The RfD includes a ten-fold safety factor.
  • On average, U.S. women of childbearing age and children are exposed to methylmercury at levels well below cultures with diets rich in fish. U.S. women’s levels compared as follows:

-1/15th those of the women in the SeychellesIslands

-1/10th those of the women in the Faroe Islands

-1/8th those of women in Japan

-1/3rd those of women in Hong Kong

-1/9th those of pregnant women in Taiwan

U.S. children’s (ages 1-5) levels compare to said cultures as follows:

-1/25th those of children in the Faroe Islands

References

Methylmercury toxicity

U.S. Environmental Protection Agency Reference Dose (RfD) for methylmercury

U.S. Food and Drug Administration Action Level for methylmercury

Committee on the Toxicological Effects of Methylmercury of the National Research Council (NRC) Benchmark Dose Level (BMDL)

1999-2002 National Health and Nutrition Examination Survey (NHANES) data

U.S. Agency for Toxic Substances & Disease Registry (ATSDR) Minimal Risk Level (MRL) for Hazardous Substances for methylmercury

Additional resources

  • Program on Agriculture and Animal Health Policy (PAAHP) of the Center for Food, Nutrition, and Agriculture Policy (CFNAP) at the University of Maryland Real Mercury Facts Glossary of Terms

National Fisheries Institute, July 2009