Declining blood lead levels and changes in cognitive function during childhood - The Port Pirie Cohort Study

Context.-Many studies have found a significant inverse association between early exposure to environmental lead and cognitive function in childhood. W hether these effects are reversible when exposure is reduced is not clear. Objective.-To assess the reversibility of the apparent effects of lead on c ognitive abilities in early childhood by testing whether declines in blood lead concentrations beyond the age of 2 years are associated with improveme nts in cognition. Setting.-Urban and rural communities surrounding a large lead smelter in Po rt Pirie, South Australia. Participants.-A total of 375 children followed up from birth to the age of 11 to 13 years. Design.-Long-term prospective cohort study. Main Outcome Measures.-The Bayley Mental Development Index at age 2 years, the McCarthy General Cognitive Index at age 4 years, and IQs from the Wechs ler Intelligence Scale (revised version) at ages 7 and 11 to 13 years. Results.-Mean blood lead concentrations in the children decreased from 1.02 mu mol/L (21.2 mu g/dL) at age 2 years to 0.38 mu mol/L (7.9 mu g/dl) at a ge 11 to 13 years, but cognitive scores in children whose blood lead concen tration declined most were generally not improved relative to the scores of children whose blood lead levels declined least. Changes in IQ and decline s in blood lead levels that occurred between the ages of 7 and 11 to 13 yea rs (r = 0.12, P = .09) suggested slightly better cognition among children w hose blood lead levels declined most. Conclusion.-The cognitive deficits associated with exposure to environmenta l lead in early childhood appear to be only partially reversed by a subsequ ent decline in blood lead level.