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A study of 917 seven-year-old children in the Faeroe Islands has shown subtle delays in neurological development if the mothers had high intakes of methylmercury from eating frequent seafood dinners during pregnancy. The study was reported this week by an international team of scientists in the November-December issue of the journal, Neurotoxicology and Teratology. The higher the mercury exposure in the mother’s womb, the greater the risk that slight delays in the development of attention span, memory, language, and other brain functions may occur. The project was carried out in the Faeroe Islands, in the North Atlantic north of Shetland, where dietary mercury exposure mainly originates from eating pilot whale meat. Coal burning is the major source of mercury pollution, which causes contamination of seafood and fresh-water fish worldwide. The project was supported by the European Commission under its Environment and Climate Research Programme and by the US National Institute of Environmental Health, part of the National Institutes of Health.
This is the first large study of children to show effects resulting from relatively low maternal exposures. The researchers interviewed mothers who gave birth at the three Faeroese hospitals in 1986-1987. Under the leadership of Dr. Pal Weihe, Medical Director of the Faeroese Hospitals, a blood sample from the umbilical cord was collected for mercury analysis, and the mother's hair was also analysed. The overall average maternal hair-mercury concentration was 4.3 micrograms per gram of hair. A detailed examination of the children had to wait until the children were old enough to participate in detailed neurological tests.
"The reason that scientists have may underestimated this problem in the past is that mercury affects the development of the nervous system, and these effects may not be apparent right away," explained Professor Philippe Grandjean of Odense University in Denmark, who led the international research team. "The brain is extremely susceptible to toxic chemicals during foetal development, but we waited until the children were seven years old so that we could examine the effects in sufficient detail," he added.
The study utilised sophisticated neuropsychological and neurophysiological techniques, and the Danish-Faeroese 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 Faeroes.
"Several domains of brain function may be affected by prenatal methylmercury exposure," explained Professor Roberta F. White of Boston University, USA, who evaluated the neuropsychological results. “Most of the results remained within normal ranges, and neurophysiological and other clinical tests did not show any association with mercury exposure. However, the neuropsychological tests showed that a doubling in mercury exposure on the average is associated with a developmental delay of about two months”.
According to Prof. Grandjean, "Although most European and American diets do not include whale meat, the study is relevant to general concerns about mercury pollution, because the developmental delays appeared at relatively low levels of maternal mercury intake." Mercury in fish mostly occurs in the form of methylmercury. Tragic episodes from Japan have documented that the mercury in the mother's fish diet can pass into the foetus and cause irreversible brain damage, but little has been known about effects at lower exposures. In the 1950s, an outbreak of methylmercury poisoning took place in Minamata, Japan, from consumption of fish heavily contaminated by mercury in waters polluted by industrial waste. Many children were reported to have psychomotor retardation resulting from their mothers' consumption, during pregnancy, of these heavily mercury-contaminated fish. Concern about mercury from industrial pollution has led to “health advisories” that now restrict fishing - or advise limited consumption of the fish caught - in some waters in the United States. Taking into account these uncertainties, in 1995 the US Environmental Protection Agency considerably lowered its estimate of methylmercury exposures considered to be without harm. "The study from the Faeroe Islands suggests that increased vigilance is needed regarding pollution involving this neurotoxicant," concludes Grandjean.
Research in the area of environment and health has been supported and funded by the Commission since 1973 and is one of the “key actions” proposed by the Commission for the forthcoming Fifth Framework Programme (1998-2002).
For further information, please contact:
Prof. Philippe Grandjean, M.D.
Institute of Community Health, Odense University
Dr Canice Nolan
Mr Stephen Gosden
Press and Information Officer
PRESS RELEASES | PRESS RELEASES OF 1997 | 15.02.2000