07 Feb 1996: Children of Fish Consumers Show No Developmental Damage
A study of the children of heavy, daily fish consumers on islands in the Indian Ocean has thus far demonstrated no developmental damage from concentrations of environmental mercury -- as some had theorized might occur.
The research is discussed in 11 reports in the winter 1995-96 issue of the international journal NeuroToxicology, which is out today.
All fish contain mercury from natural and man-made sources -- and the developing fetal brain has been considered especially susceptible to the metal, even when the unborn infants' mothers show no symptoms. But the researchers said their study of more than 1,500 children of Seychelles Islands women, who average 12 (twelve!) fish meals a week, has thus far demonstrated no impairment in development, though it could possibly show up in later years.
The research was executed in two phases: a pilot study of more than 750 children followed by a carefully controlled, longitudinal main study of more than 700 children. The children have been evaluated for mental and physical development from six months to 5 years of age. Today's reports include pilot study results to 5 and main study results to nearly 2.
In the controlled study, the authors report, "Cognitive developmental outcomes up to 2 years of age appear essentially normal following intrauterine exposure to a maternal hair mercury level of about 6 ppm through maternal fish consumption."
One subjective observation -- when nurses observed the activity level of boys in a test session at a little over two years of age -- was lower as mercury exposure increased. The researchers said this observation, which did not pertain to girls in the study, may have been the result of some other factor or be coincidental.
Overall, the researchers summed up the controlled study to date this way:
The Seychelles Islands children "performed cognitive, perceptual, memory, motor and language tasks as well as U.S. toddlers."
The study, which continues, is a collaboration of the Ministry of Health of the Republic of Seychelles, a string of islands northeast of Madagascar, and the University of Rochester, and is supported by the National Institute of Environmental Health Sciences, one of the National Institutes of Health, with additional support from the Food and Drug Administration, the Swedish Medical Research Council and the Republic of the Seychelles. The study's principal investigator, Thomas W. Clarkson, Ph.D., is the director of the University of Rochester Environmental Health Center, one of 17 such university-based centers supported by NIEHS.
Methylmercury, in high concentrations, has long been recognized as an environmental hazard. In the 1950s an outbreak of methylmercury poisoning took place in Minamata, Japan, from the consumption of fish heavily contaminated by mercury in waters polluted by industrial effluent. Twenty-three children were reported to have psychomotor retardation resulting from their mothers' consumption, during pregnancy, of these heavily mercury-contaminated fish.
With NIEHS funding, the University of Rochester group studied a mass poisoning in Iraq in 1971-2 in which at least 600 persons died as a result of the unintended use of mercury-treated seed grain in bread. At the high mercury levels of this accident, many survivors suffered permanent damage, with loss of vision, numbness in their extremities and lack of coordination. The NIEHS/Rochester group in 1989 published data on 83 children born to women with low level exposure in that disaster, and theorized that low levels of exposure might impair development.
A World Health Organization expert committee report in 1990 said "a prudent interpretation" of the Iraqi data could mean that a 5 percent risk of adverse effects on development, such as delayed walking, could be associated with a peak mercury level of 10-20 ppm in maternal hair, a level which could result from frequent consumption of fish.
But the scientists testing the Seychelles Islands children said today that if the risk was present at that level, their study should have detected it -- and did not. The hair of the Seychelles Islands women averaged under 10 ppm but, of 99 with particularly high levels, concentrations were as high as 36 ppm. (Mercury in strands of women's hair provides a convenient and accurate indicator of mercury absorption.) The Seychelles mothers eat large amounts of ocean fish.
NIEHS also is financing a Danish study on the Faroe Islands where there has been mercury exposure and other substances from whale meat and ocean fish. (Persistent contaminants tend to become more concentrated in animals higher in the food chain, such as whales and large fish, that have consumed many smaller animals.) Examinations have just been completed of about 1,000 children, age 7. An international group of researchers is now evaluating the results. The 18 Faroe Islands are an outlying territory of Denmark in the North Atlantic.
Concern about mercury from industrial pollution has led to health advisories that now restrict fishing -- or the consumption of the fish caught -- in some waters of the United States. The University of Rochester researchers said the Seychelles Islands study "may have implications for environmental health policies concerning mercury in fish or fish consumption during pregnancy." They said that although data at older ages is needed, the results available so far indicate that low-level mercury exposure from eating fish during pregnancy shows no harmful effect.
To contact Dr. Clarkson and other University of Rochester scientists involved, please call the UR Medical Center's office of public relations and communications: (716) 275-3676.
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