From the 1980s many well-designed epidemiological studies have confirmed that low-level, subclinical lead exposure in early life is associated with decrements in children's intelligence. Neurodevelopmental deficits from exposure to a low level of lead have been held to be not only an American problem, but also a worldwide issue in the past decade. Good epidemiological studies were reported from England, Scotland, Germany, Greece, Australia and New Zealand.
Well-designed cross-sectional and prospective studies were carried out to quantify the magnitude of the relation between full scale IQ in children aged five years or more and the burden of lead (PbB or PbT) in early life of children. Of five cross-sectional studies of blood lead, two demonstrated a significant inverse association between lead and IQ even after adjustment for confounders. Two other studies, however, showed no firm evidence of inverse association after adjustment for confounders, and the remaining study demonstrated no significant inverse association of five cross-sectional studies of tooth lead, two indicated an inverse association. between tooth lead and IQ, two others showed no significant inverse association after adjustment for confounders, and the remaining one manifested no association. Of four prospective studies, two revealed strong evidence of an inverse association between blood lead at the age of around two years and IQ. Another one, however, revealed an inverse association between mean postnatal blood level and IQ, while the remaining one demonstrated no significant inverse association between IQ and postnatal blood lead level after adjustment for confounders. In a comprehensive review of 26 epidemiological studies since 1979, including a metaanalysis, Pococok et al. indicated that doubling of the body lead burden (from 10 to 20μg/dl) blood lead or (from 5 to 10μg/g) tooth lead is typically associated with a mean deficit in full-seale IQ of around 1-2 IQ points.
Lead in interior household dust, exterior surface soil, and old residential lead paint, which is deteriorated or removed, constitute the major sources of lead poisoning in children in the United States. Infants and children, who typically engage in hand to mouth activities, frequently come into contact with lead dust in soil and on the floor. Marked declines both in air lead and blood lead concentrations are evident parallel to the phase-down of lead in gasoline and soldered cans by U. S. food processors. The major source of lead in drinking water is from lead pipes used in household plumbing. The CDC revised its guidelines concerning childhood lead poisoning, stating that community prevention activities should be triggered when a large percentage of children in a community have blood lead levels of 10μg/dl, the lowest level at which neurodevelopmental effects were believed to occur. For children with blood lead level concentrations between 10 and 14μg/dl, more frequent rescreening may be needed. For concentrations between 15 and 19μg/dl, in addition to more frequent screening, nutritional and educational advice should be given. In cases where these levels persist, there should be environmental investigation and intervention. All children with blood levels of 20μg/dl or greater should receive environmental evaluation and medical examination. Such children may need pharmacological treatment.