Low level lead exposure and intelligence in the preschool years

Definitive evidence of neuropsychological effects of low level Pb exposure continues to be sought in prospective studies of child development. The period from mid-infancy to age three years is important because behavioral and physiological characteristics of that age are associated with the intake and retention of environmental Pb. In the Cleveland study, we measured blood Pb (PbB) at ages six months, two years, and three years. At ages six months, one year and two year, the Mental Development Index (MDI) of the Bayley Scales of Infant Development was administered. The Stanford Binet Intelligence Scale IQ was obtained at age three years. Eight multiple regression analyses tested the relationship of each of the three PbB measures with the respective current and each ensuring developmental assessment. Demographic data and measures of the caretaking environment were selected as covariates for the control of confounding factors. Six months PbB was not related significantly to any of five assessments with or without control of confounding variables. The remaining three analyses were significant in the initial analyses, but the effect was completely attenuated with statistical control of confounding variables. These results suggest that obtained correlations between lead exposure and preschool intelligence depend on the caretaking environment.