The Port Pirie cohort study which began in 1979 at the Department of Community Medicine, University of Adelaide, Australia, has been followed into the primary school age range and examines intelligence at the age of 7 years in relation to lifetime exposure to lead. In 494 children from a lead smelting community, the IQ was inversely related to both antenatal and postnatal blood level concentrations. An increase in blood lead concentration from 10 to 30 mcg/dL was associated with a deficit in verbal IQ that varied according to age from 5.5 to 6.4 points. In full scale IQ, the estimated deficit was 4.4 - 5.3 points. [1]

COMMENT. Mahaffey KR from the National Institute of Environmental Health Sciences, North Carolina, comments in an editorial that the results of 3 longitudinal studies (Australia, Boston and Cincinnati) demonstrate that the lead associated decrements in intelligence are persistent across cultures, racial and ethnic groups, and social and economic classes. They are not limited to socially and economically disadvantaged children [2]. Meta-analysis of 7 studies showed an average decrease of 0.25 IQ points for each 1 mcg/dL increase in blood lead levels (BPb). This inverse relationship between IQ and BPb continued well below 10 mcg/dL. [3]

Lead encephalopathy was diagnosed in 10 Saudi Arabian children, ages 8-48 months during 1984-1988. The mean BPb was 6.1 umol/L (range, 2.5-13 umol/L) [4]. In Washington, D.C. 590 (20.8%) of children aged 9 months to 3 years examined showed blood lead concentrations of 0.5 umol/L or more, which exceeded the acceptable CDC limits. At levels between 0.5 and 1.2 umol/L, the free erythrocyte protoporphyrin (FEP) screening test was a very poor predictor of toxic blood lead values. [5]