Methylmercury Exposure from Ocean Fish Consumption and Neurodevelopment

Thomas Clarkson and Christopher Cox
University of Rochester
R01ES10219, R01ES08442, P30ES01247, and T32ES07371

Background: Exposure to methylmercury before birth 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 products, but there have been conflicting reports on whether this level of exposure is harmful. NIEHS has funded to long-term studies on distinct populations of children in the Faeroe Islands and the Republic of Seychelles with distinctly different dietary exposures. The Faeroe Islanders consume whale meat while the Seychelle populations consumes only fish. The overriding question addressed by these studies is whether seafood consumption by pregnant and nursing women results in mercury exposures in their children at levels high enough to cause harm.

Advance: The study highlighted here was carried out in a population cohort, which consisted 779 mother-infant pairs residing in the Republic of Seychelles. The mothers reported consuming 12 meals of fish per week. These fish contained about the same concentrations of methylmercury as commercial ocean fish found elsewhere. Only two endpoints were associated with prenatal methylmercury exposure. Increased exposure was associated with decreased performance in a standardized motor control test and improved scores in the hyperactivity index of the Conner's teacher rating scale.

Implication: These data do not support the hypothesis that there is a neurodevelopmental risk from prenatal methylmercury exposure resulting solely from maternal ocean fish consumption. An accompanying editorial by Dr. Constantine G Lyketsos of the Division of Geriatric Psychiatry and Neuropsychiatry at Johns Hopkins Hospital reaches the same conclusion. "On balance, the existing evidence suggests that methylmercury exposure from fish consumption during pregnancy, of the level seen in most parts of the world, does not have measurable cognitive or behavioral effects in later childhood." The editorial goes on to state that "the positive findings from the Faeroe Islands and New Zealand studies may be related to the fact that pilotwhale blubber and shark muscle contain 5-7 times the concentrations of methylmercury than the fish consumed in the Seychelles." Dr. Lyketsos final conclusion is that "there is no reason for pregnant women to reduce fish consumption below current levels, which are probably safe."

Citation: Myers GJ, Davidson PW, Cox C, Shamlaye CF, Palumbo D, Cernichiari E, Sloane-Reeves J, Wilding GE, Kost J, Huang LS, Clarkson TW. Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study. Lancet. 2003 May 17;361(9370):1686-92.