Normal Blood Mercury Levels
The normal level of mercury in the blood is less than 5 μg/L (micrograms per liter) or 5 ppb (parts per billion), which is the reference value recommended by the U.S. Environmental Protection Agency and the National Academy of Sciences. 1, 2
Reference Ranges for Blood Mercury
- The geometric mean concentration of total blood mercury in the general U.S. population is approximately 1.02 μg/L for women of childbearing age and 0.34 μg/L for children 2
- Blood mercury levels above 5.8 μg/L are considered to exceed the EPA's recommended reference dose, below which exposures are considered to be without adverse effects 2
- In high-end fish consumers, blood mercury levels can range significantly higher, with means of 13-15 μg/L observed in some populations 1
Factors Affecting Blood Mercury Levels
- Fish consumption is the primary determinant of blood mercury levels, with levels approximately 4 times higher in people who eat 3 or more servings of fish in a 30-day period compared to non-fish eaters 2
- Different fish species contain varying levels of mercury, with predatory fish like swordfish typically containing higher concentrations 1
- Blood mercury concentrations are generally higher in adults compared to children (approximately 3-fold difference) 2
- Racial/ethnic differences exist in blood mercury levels, with higher concentrations observed in certain populations including Asians, Native Americans, and Pacific Islanders 3
- Age is a factor, with blood mercury concentrations approximately 1.5 times higher among women 30-49 years of age compared to women 16-29 years of age 3
Monitoring and Clinical Significance
- Blood mercury follows first-order elimination kinetics with a half-life of approximately 60 days after exposure cessation 4
- For individuals with blood lead concentrations between 10 and 19 μg/dL, quarterly blood measurements are recommended 5
- For those with sustained blood lead concentrations below 10 μg/dL, semiannual measurements are recommended 5
- Pregnant women should avoid lead exposure that would result in blood lead concentrations above 5 μg/dL 5
Interpretation of Blood Mercury Results
- Interpretation becomes more challenging as concentrations approach population norms (blood mercury < 10-20 μg/L) 6
- When blood mercury levels exceed 5 μg/L, it is advisable to identify and reduce sources of exposure, particularly fish consumption 2
- Massively elevated levels (which can reach as high as 16,000 μg/L in severe cases) indicate significant mercury toxicity requiring immediate medical attention 6
Special Considerations
- Children are more vulnerable to the neurodevelopmental effects of mercury exposure 2
- Based on U.S. birth rates and blood mercury distribution, over 300,000 newborns each year may be exposed in utero to methyl mercury concentrations higher than those considered safe 3
- Individuals who consume large amounts of certain fish species should be particularly vigilant about monitoring their blood mercury levels 1, 4