The study was reported today by an international team of scientists in the November-December issue of the journal Neurotoxicology and Teratology.
The project was carried out in the Faroe Islands, in the North Atlantic north of Shetland, where dietary mercury exposure mainly originates from eating pilot whale meat. Although whale concentrates PCBs as well as mercury, the scientists said they had compensated for the effects of this additional pollutant, which is also a potential neurotoxin. Worldwide, mercury causes contamination of seafood and fresh-water fish. Coal burning is a major source of environmental mercury.
The study was supported by the U.S. National Institute of Environmental Health Sciences, a part of the National Institutes of Health, and by the European Commission under its Environment and Climate Research Programme.
The study is the only one to date to report these associations at these exposure levels.
The researchers interviewed mothers who were giving birth at the three Faroes hospitals in 1986-1987. Under the leadership of Dr. Pal Weihe, Medical Director of the Faroes Hospitals, a blood sample from the umbilical cord was collected for mercury analysis, and the mother's hair was also analyzed. A detailed examination of the children had to wait until the children were old enough to participate in detailed neurological tests.
Professor Philippe Grandjean of Odense University in Denmark, who led the international research team, said, "The brain is extremely susceptible to toxic chemicals during fetal development, but we waited until the children were seven years old so that we could examine the effects in sufficient detail."
The study utilized sophisticated neuropsychological and neurophysiological techniques, and the Danish-Faroe research team was helped by colleagues from the USA and Japan. In one of the largest and most intensive studies ever in this field, each child went through five hours of detailed examinations, and the clinical team spent almost six months in the Faroes.
Professor Roberta F. White of Boston University, who evaluated the neuropsychological results, said, "Several domains of brain function may be affected by prenatal methylmercury exposure.
"Most of the results remained within normal ranges," she continued, "but any developmental delay in young school children may be a concern."
Professor Grandjean said, "Although most European and American diets do not include whale meat, the study is relevant to general concerns about mercury pollution. The study from the Faroe Islands suggests that increased vigilance is needed regarding pollution with this neurotoxicant."
NIEHS Director Kenneth Olden, Ph.D., said, "The study was carried out with apparent care and with very sophisticated testing, and its long-anticipated publication will permit others to review its methodology and the strength and persuasiveness of its data. The significance of effects identified in this study will need to be evaluated in the context of other studies of fish-eating populations including another large NIEHS-sponsored study in the Seychelles Islands." The latter study found no evidence of developmental problems but has not followed children as long as has the Faroe Islands study.
An interagency working group, Olden noted, is currently reviewing a Congressionally-mandated report on the effects of mercury. The group is looking at a number of peer-reviewed scientific studies.
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For Further Comment: Philippe Grandjean, M.D., in Denmark, 011-45-6557.3769. Roberta F. White, Ph.D., Professor of Neurology at BU School of Medicine, 617-278-4517.
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Journal
Neurotoxicology and Teratology