Mercury alert

By Debora MacKenzie EXPOSURE to mercury in the womb raises children’s blood pressure in later life, according to a study in the Faeroe Islands. The data—which indicate an effect at one-third of the current limit for mercury in food—are being examined by UN advisers meeting in Rome this week to review these limits. Philippe Grandjean of Odense University in Denmark measured mercury in the umbilical cord blood of 917 babies born during 1986 and 1987 in the Faeroe Islands, where some mothers ate whalemeat containing mercury. An examination of the children seven years later revealed subtle impairments of their cognitive and motor skills, proportional to the level of mercury in cord blood (This Week, 22 November 1997, p 4). Further analysis of the data has now shown that the children exposed to higher levels of mercury in the womb also had significantly higher blood pressure. Grandjean’s study is the first to show a cardiovascular effect from prenatal mercury exposure. Blood pressure in the seven-year-olds averaged 100/60—within the normal range—but both systolic and diastolic pressures were 14 points higher in children who received 10 micrograms of mercury per litre of umbilical cord blood, compared with those exposed to 1 microgram per litre. Higher prenatal doses had no further effect. Grandjean, who is publishing his results in the July issue of Epidemiology, points out that raised blood pressure during childhood predisposes people to cardiovascular disease. Grandjean is confident that prenatal exposure is responsible, rather than exposure in childhood, as the amount of mercury in the hair of the seven-year-olds did not correlate with their blood pressure. He suggests that damage to the nerves that control the heart may be behind the effect, as there was less variability in the time between successive heartbeats in the children with higher blood pressure. “The shocking thing was that we saw all of this increase within the levels of mercury that are now permitted,” says Grandjean. The maximum weekly dose of mercury currently recommended by the Codex Alimentarius, the UN’s food safety body, is 0.3 milligrams per kilogram of body weight. According to Grandjean, this is enough to yield maternal blood levels of mercury three times as high as those that produced the blood pressure effects in his study. “This is potentially an extremely important new area of mercury toxicity,” says Ellen Silbergeld, a toxicologist at the University of Maryland in Baltimore. The US Environmental Protection Agency wants lower limits for mercury in fish—the main source of the metal for most people—but the US Food and Drug Administration opposes the cuts, fearing that too much food will become unusable. As the FDA represents the US at the meeting of Codex advisers, the country is unlikely to back any plan to lower mercury limits,
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