Neurodevelopmental effects of postnatal lead exposure at very low levels.

This study is among the first to examine specific neurobehavioral deficits in children exposed at very low lead levels. A systematic analysis for the presence of a threshold of lead exposure was conducted. The sample consisted of 246 African American, inner-city children from whom blood lead concentrations were assessed at 7.5 years of age. The results consistently show neurobehavioral deficits in relation to low levels of lead in the areas of intelligence, reaction time, visual-motor integration, fine motor skills, attention, including executive function, off-task behaviors, and teacher-reported withdrawn behaviors. Effects were identified in the specific domains of attention, executive function, visual-motor integration, social behavior, and motor skills, which have been previously suggested as part of lead's "behavioral signature". Visual inspection of nonparametric regression plots suggested a gradual linear dose-response relation for most endpoints. No threshold discontinuity was evident. Regression analyses in which lead exposure was dichotomized at 10 microg/dl were no more likely to be significant than analyses dichotomizing exposure at 5 microg/dl. Given that associations were found between lead levels as low as 3 microg/dl for multiple outcomes, these data provide additional evidence that there is no apparent lower bound threshold for postnatal lead exposure.