Study Suggests U.S. Mercury Levels Are No Threat to Adult Brains

Megan Weil, MHS
Johns Hopkins Bloomberg School of Public Health
T32ES07141

Background: Elemental mercury is found everywhere in the environment. The major man-made sources in air are the burning of coal for electric power production, mining, smelting of metal ores, and solid-waste incineration. Rainfall deposits mercury into lakes and oceans where it is converted to methylmercury by microorganisms. It enters the aquatic food chain and bioaccumulates in large, long-lived fish such as shark, swordfish, king mackerel and some species of tuna. Fetal exposure to methylmercury has been shown to cause disruptions in neurobehavioral and cognitive development in children. The most common route of exposure is through maternal consumption of mercury-contaminated seafood, but there have been conflicting reports on whether this level of exposure is harmful.

Fish consumption is recommended for older adults due to its high levels of omega-3 fatty acids which are known to have cardiovascular health benefits. Recent scientific findings suggest that fish consumption may also be protective for Alzheimer’s disease. However, since the aging nervous system is more sensitive to neurotoxicants, investigation of mercury exposure in aging populations is considered of great public health importance.

Advance: NIH-supported researchers at the Johns Hopkins Bloomberg School of Public Health have shown that mercury exposure is not linked to neurobehavioral damage or deficits in cognitive function in a group of 474 Americans over 50 years of age. The mean blood mercury level for the study participants (<3 micrograms/liter) is within the range for the general population. In a battery of twelve neurological tests, the researchers found no definitive evidence that blood mercury levels are adversely associated with neurobehavioral test scores in this sample of older adults.

Implications: The current blood-mercury standard established by the EPA for children and women of childbearing age is 5.8 micrograms/liter, which is higher than the average level for this study’s participants. The researchers are quick to point out that this study should not change standards of mercury exposure and consumption, which are currently under debate. Current standards are meant to protect infants and children whose brains are still developing and possibly susceptible to low levels of mercury. However, these findings do suggest that a threshold level of mercury exposure may exist. Further research will be necessary to confirm these results and to determine in any change in current standards is warranted.

Citation: Weil M, Bressler J, Parsons P, Bolla K, Glass T, Schwartz B. Blood mercury levels and neurobehavioral function. JAMA. 2005 Apr 20;293.