Doctors had long known that exposure to high doses of lead caused mental lapses, even permanent brain damage and death. But what about the low-level exposure that many children, like the ones playing in the yard, absorbed every day â merely by living in older urban neighborhoods thick with lead paint and industrial contamination?
No one knew. No one could study the effects carefully, because the available tests for lead exposure were of hair, blood, or fingernails â each flawed in its own way. Bone is the most accurate long-term repository: Once absorbed into the body, lead circulates in the blood and accumulates in the skeleton. But taking bone samples â biopsies â is painful and hardly justifiable for the sake of a hypothesis, especially in young children.
Yet Dr. Needleman had seen an earlier study of lead poisoning, a small one, which measured accumulated lead exposure in teeth. Teeth are a part of the human skeleton. And young children shed them.
âThat was the insight that changed everything,â said Dr. Bernard Goldstein, former dean of the University of Pittsburghâs graduate school of public health. âHerb became the Tooth Fairy.â
In a series of studies â small ones in Philadelphia and a much larger project in the Boston area â Dr. Needleman offered children aged 6 and 7 small rewards for their loose teeth, once they had fallen out. Those teeth told a story: Children living in poor urban neighborhoods had lead levels five times higher, on average, than those of their peers in the suburbs.
In a landmark 1979 paper in The New England Journal of Medicine, which included more than 2,000 children, he and his co-authors â he was then at Harvard â explained the associated consequences in devastating detail. Children whose accumulated exposure to lead was highest in the group scored four points lower on an I.Q. test than youngsters whose exposure was at the…