Lead and the Philadelphia Tooth Fairy Project

For much of the 20th century, America was plagued by a terrible lead poisoning epidemic that sent children into comas, convulsions, and even death. Lead paint covered the walls of homes throughout the nation, especially in the old, industrial cities, and poisoned hundreds of thousands of children. Philadelphia, it turns out, was the birthplace of a revolution in thinking about the impact of lead on children's development.

In the 1960s, as Civil Rights organizations, community groups and political activists turned the country's attention to poverty, lead poisoning became a symbol of the terrible price that children paid for absentee landlords who crowded families into poorly maintained and crumbling tenements.

But as health departments  began assessing and addressing the worst conditions, they uncovered ever-more troubling facts. Huge numbers of children had blood lead levels above 40 micrograms per deciliter (µg/dL), then the amount that was considered dangerous in children, but did not show overt clinical symptoms.(Today, blood-lead levels above 5 µg/dL are considered the "reference level" above which the Centers for Disease Control and Prevention recommends action be taken.)

In a 1974 paper in the New England Journal of Medicine, pediatrician and psychiatrist Herbert Needleman and a group from the University of Pennsylvania raised the question of whether transitory blood lead levels alone were an adequate measure of safety or harm  and whether children with low levels of lead in their bodies suffered subtler neurological and intellectual damage. Needleman and his colleagues knew that calcified tissue, such as that found in baby teeth, stored lead—and they hit upon the idea of using that as a means of measuring long-term exposure and its effects on children.

In a research effort whimsically called the Philadelphia Tooth Fairy Project, Needleman's team allied with dentists in the city's "lead belt"—a "J"-shaped swath of North Philadelphia that largely follows lines of poverty— to collect 69 baby teeth. They also collected 40 teeth from suburban dentists for comparison. The results of their analysis were startling: children living in poor, urban neighborhoods had nearly five times the levels of lead in their teeth compared to those living in the suburbs. They also uncovered the troubling fact that those children, who with more lead in their bodies performed worse on I.Q. tests, had behavioral problems and generally did worse in school than the children with lower levels .

Researchers had always known that lead in the blood was only a snapshot of a child's recent exposures to the toxic metal. They also knew that some of the lead  children ingested accumulated in their bones and remained there for years, even decades. But there was little consensus about—and there had been no way of accurately measuring—the impact of lead that had accumulated over time. In the wake of Needleman's research, no longer would scientists, physicians, and the public health community be able to take comfort in focusing only on the acute impacts of lead as measured by elevated blood lead levels.

Needleman's continuing work would eventually set off a firestorm of opposition from the lead industry, for it confirmed what the public health community had been observing for a decade. In 1971, lead was banned in paint used in public housing, and in 1978 the Consumer Product Safety Commission prohibited its use in all household paints. In the 1980s, the EPA began to restrict the amount of lead in gasoline; by the mid-1990s, leaded gasoline was banned in the United States automobiles. What would befall Needleman in the 1980s, after his second and most important article on the effects of low level exposures appeared in the New England Journal, was foreshadowed by the industry's reaction to this early 1970s observation.

In October 1972, Needleman traveled to Amsterdam to present a paper at a symposium on environmental health aspects of lead that was sponsored by the Commission of European Communities and the recently established U.S. Environmental Protection Agency. This meeting, Needleman later told journalist Lydia Denworth, was where he realized that powerful interests were going to oppose his scientific findings: "I woke up to the fact that it wasn't just that the truth will come out." The meeting brought together hundreds of representatives from 21 countries, including government, industry, and independent research scientists. Forty-two came from the United States; 18 of them were industry representatives, some of whom took a very dim view of Needleman's work.

The professor began his talk by discussing the difficult problem that relatively low-level lead exposure presented for researchers and clinicians alike. Lead poisoning challenged the older paradigm of what constituted health and disease. It was unlike acute infectious diseases that ultimately resolved themselves or resulted in observable, permanent damage. Unlike polio, for example, which left many of its young victims  visibly disabled, children who were poisoned by lead looked normal. In all but extreme cases, initial neurological, emotional, cognitive, and behavioral problems might be easily overlooked. While IQ loss, dyslexia, hyperactivity, and behavioral issues were certainly known to change a child's future, these symptoms of lead poisoning were not commonly ascribed to lead.

Needleman was among the first to suggest that the effects of lead poisoning could be thought of as "a family of curves," starting with subtle biological change "at the lowest levels"; continuing with irritability, awkward gait, and fevers at the middle levels;  comas and convulsions near the top, "and ending with death at the highest end of the scale." He reminded the audience that between 250,000 and 400,000 American children had blood lead levels in excess of 40 µg/dL and asked: "How many of these children have behavior disorders, disturbances of cognitive function, or emotional disorders related to this body burden?" He reminded them of what they already knew: that children living "in the urban American ghetto, and whose blood levels are consistently higher than their middle-class counterparts, are known to have an increased prevalence of mental retardation, learning disabilities, and behavior disorders."

Needleman challenged the scientific community to take the next step, to find out whether or not relatively low-level exposure to lead would produce damage. "If a means could be found to identify older children considered asymptomatic with elevated body burdens of lead," he said, measuring their cognitive performance while controlling for other factors known to retard development would allow researchers to more accurately determine "the effects on their brains of sub-clinical exposure."

Using statistical methods and the evolving tools of epidemiology,  a field that  developed in the search for sources of infectious disease outbreaks, Needleman probed further into the effects of childhood lead poisoning. His work proposed to use the tools of epidemiology to uncover diseases among populations that no clinician could diagnose by examining any single individual.

Certainly, epidemiology had been used before in the investigation of disease, and it had been particularly important in uncovering the statistical relationship between lung cancer and smoking, and between heart disease and diet. But Needleman, who trained and practiced at Children's Hospital of Philadelphia, Pennsylvania Hospital and Temple University before moving to the University of Pittsburgh in 1980, opened up a whole new realm of medicine and public health. His approach to looking at the impact on children of low-level lead exposures would challenge our thinking, not only about what constitutes an environmental disease, but also about how society can protect its citizens from subtle, unseen, and even undefined danger from toxins.

Gerald Markowitz is a professor of history at City University of New York's John Jay College. David Rosner is a professor of sociomedical sciences and history at Columbia University. Their book Lead Wars: The Politics of Science and the Fate of America's Children was published this year by the University of California Press.

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