Examines the relationships between low-level exposure to lead and children’s performance on intelligence tests. Study participants were 172 children whose blood lead concentrations had been measured at 6-month intervals starting at 6 months of age and who were assessed on the Stanford-Binet Intelligence Scale at 3 and 5 years of age. Results were adjusted for such variables as maternal IQ and use of tobacco during pregnancy as well as quality of the home environment. Key findings reveal that: (1) children’s intellectual functioning at 3 and 5 years of age was inversely associated with blood lead concentrations, even when their peak concentrations fell below Centers for Disease Control and World Health Organization levels; and (2) the effects of lead on IQ were proportionately greater at lower lead concentrations. These findings suggest that children with blood lead concentrations below 10 g per deciliter merit more intensive investigation, and that there may be no threshold for adverse consequences of lead exposure. More children in the United States may be adversely affected by environmental lead exposure than had been previously estimated. Because there is no effective treatment for children with moderately elevated blood lead levels, primary prevention of lead exposure is necessary.
