The Neurodevelopmental Toxicity of Lead: History, Epidemiology, and Public Health Implications

Despite great successes in reducing children's exposure to lead, it remains the most important environmental contaminant in terms of impact on children's cognitive and behavioral development. In this chapter, we discuss what is known about the relationships linking greater lead exposure and neurodevelopmental impairment. Among most salient conclusions are that a “safe” level of lead exposure has not been identified, and that the inverse relationship between blood lead concentration and children's IQ scores is non-linear such that the rate of decline in IQ per μg/dL is greater for concentrations < 10 μg/dL than for concentrations > 10 μg/dL. Greater blood lead concentrations are also associated with reduced academic achievement, greater risk of ADHD, and greater propensity to engage in anti-social behaviors. Although data are limited, neuroimaging studies reveal persistent relationships between childhood blood lead concentration and alterations in brain structure and function in young adulthood. Although lead's effects on neurodevelopment are often described as “irreversible,” it is more appropriate to describe them as “persistent,” as few studies have evaluated whether interventions, such as the provision of increased neurodevelopmental supports, alters the time course of the deficits. Which genetic factors alter lead neurotoxicity is at present largely unknown but is a topic of much current work. It seems likely that the critical window of vulnerability to lead neurotoxicity is endpoint-specific. It is hoped that lessons learned over the course of the long history of research on lead can be applied proactively to other neurotoxic environmental contaminants so that the risks to children can be reduced more expeditiously.