Facts About Mercury Exposure
- The EPA estimates that 8 percent of U.S. women of childbearing age (16 to 49) have concentrations of at least 5.8 ppb of mercury in their blood, the level at which EPA has identified risks to a fetus (5.8 ppb is known as the RfD or 'reference dose').
- Approximately 25% of children exceed the RfD, and 5% of children have methylmercury exposures from fish/shellfish two-to-three times the RfD.
- It has been argued that RfD should be lowered to 3.5 mcg/L, based on recent observations showing that umbilical cord blood mercury concentrations are approximately 70% higher than maternal concentrations . It is important to note that mercury concentration across the placenta was not considered when the reference dose was established.
- The RfD of 5.8 ppb in the blood is equivalent to 1 ppm in the hair.
- Children with high levels of exposure to mercury in the womb--10 to 20 ppm measured in the mother’s hair during pregnency--were found to have brain damage equivalent to a decline of five or six IQ points--comparable to a seven to eight month developmental delay at age 7--and a slight slowing of the brain’s responses to signals.
- Children with moderate levels of exposure to mercury in the womb--1 to 10 ppm in the mother’s hair during pregnency--were found to have a reduction of about 1.5 IQ points (comparable to a one to two month delay in vocabulary development) for each doubling of mercury.
- A recent random-digit-dial fish consumption survey (with subsequent hair mercury levels in women ages 18-45 from 12 states in the Continental US) found that Asians had methylmercury exposures over the reference dose 83% of the time, compared to 12% for the total survey population. 
RfD (reference dose): The EPA's definition of RfD is as follows: "An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data used. Generally used in EPA's noncancer health assessments." [See EPA's Mercury web site for more information.]
 Centers for Disease Control, November 2004 (http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5343a5.htm).
 1997 US Environmental Protection Agency, Mercury Study Report to Congress c7o032-1-1 Office of Air Quality Planning & Standards and Office of Research and Development Volume IV: An Assessment of Exposure to Mercury in the United States (href="http://www.epa.gov/ttn/oarpg/t3/reports/volume4.pdf)
 Stern AH, Smith AE. 2003. An assessment of the cord blood: maternal blood methylmercury ratio: Implications for risk assessment. Environ Health Perspect 111(12):1465-1470.
 Rice DC, Schoeny R, Mahaffey KR. 2003. Methods and rationale for derivation of a reference dose for methylmercury by U.S. EPA. Risk Anal 23:107-115.
 From the same 1997 US Environmental Protection Agency Report cited above (p. 6-15)
 "Health Effects of Seafood Contamination with Methylmercury in the Faroes", Dr. Philippe Grandjean, University of Southern Denmark and Boston University (http://www.masgc.org/mercury/abs-clapp.html)
Knobeloch L, Anderson HA, Imm P, Peters D, Smith A. 2005. Fish consumption, advisory awareness, and hair mercury levels among women of childbearing age. Environmental Res 97(2):219-226.