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Mercury & Neurodevelopment

Over the past several years, increasing attention has focused on the health risks associated with consumption of mercury-contaminated seafood and freshwater fish. NIEHS-supported investigators have found evidence of developmental delays in children of mothers whose diets exposed them to methylmercury during pregnancy. These findings have led to the lowering of permissible emissions of mercury into the environment, along with health advisories about the dangers of eating mercury-contaminated fish.

Mercury & Neurodevelopment: Developmental Delay in Cognitive Functions for Each 10-Fold Increase in Prenatal Exposure to Mercury

Mercury is a naturally occurring metallic element that is extremely toxic to the brain, kidneys, and developing fetus. Mercury is released into the environment from mining ore deposits, emissions from coal-burning power plants, automobile emissions, and disposal of industrial wastes. Once it enters water supplies, mercury is converted to an organic toxin called methylmercury that accumulates in the tissues of larger fish. People are exposed to methylmercury primarily through the consumption of contaminated fish.

Numerous studies have shown that methylmercury is a developmental neurotoxin that readily passes through the placenta and damages the fetal nervous system. In the early 1990s, NIEHS-funded researchers at the University of Rochester conducted a nine-year study on children in the Republic of the Seychelles to assess the developmental effects of low-dose exposure to methylmercury. The researchers tested 779 children at intervals of 6, 19, 29, and 66 months of age, whose mothers ate an average of 12 fish meals per week while pregnant.. The test results revealed no ill effects from the high-fish diet.

However, results of studies funded jointly by the NIEHS and the European Commission’s Climate Research Programme have shown some evidence of a link between mercury and developmental deficits. Cognitive tests performed on seven-year-old Faroe Islands children, whose mothers’ diets of fish and whale blubber exposed them to high levels of methylmercury during her pregnancy, revealed significant impairments in language, attention, and memory. The researchers also noted similar cognitive deficits in these children when tested at 14 years of age.

The NIEHS is funding additional studies to determine whether nutritional factors associated with fish consumption might protect the fetal brain from the adverse effects of environmental toxicants. Researchers are also conducting studies on the possible interaction between methylmercury and polychlorinated biphenyls, toxic pollutants that were also present in the whale meat and blubber consumed by the Faroe Island subjects.

These studies have provided regulatory agencies with evidence of the developmental effects of mercury at environmentally relevant doses. This has resulted in the establishment of national fish consumption advisories for at-risk groups including women who are pregnant, those who might become pregnant, and nursing mothers.

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Last Reviewed: November 09, 2007