THERE may be no safe level of lead for children. Even blood levels below the international safe limit damage children鈥檚 intelligence 鈥� and lead does proportionately more damage at these lower levels than at higher ones.
Researchers studied 172 young children in Rochester, New York state. They regularly monitored lead levels in the children鈥檚 blood and gave them intelligence tests when they were 3 and 5 years old.
After allowing for factors known to affect IQ, such as household income and education, the team found that children with blood lead levels up to the World Health Organization鈥檚 safe limit of 10 micrograms per decilitre had IQs that were 7.4 points lower on average than children with 1 渭g/dl (The New England Journal of Medicine, vol 348, p 1517). But in children with blood lead levels of between 10 and 30 渭g/dl, there was only a small additional decline, by another 2.4 IQ points.
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鈥淚t is an excellent study. I don鈥檛 think we can say there is a safe level of exposure,鈥� says neurologist David Bellinger, a member of the US Centers for Disease Control鈥檚 Advisory Committee on Childhood Lead Poisoning Prevention.
The study is small, but if its conclusions are correct, lead is impairing the intelligence of millions of children worldwide. While only 1 in 50 children under 5 years old in the US have blood lead levels over 10 渭g/dl, for instance, 1 in 10 have levels over 5 渭g/dl. Levels are falling in most developed countries, but many children are still exposed to major sources such as old lead paint and water pipes.