No abstract

The relationship between dentine lead levels and measures of cognitive ability was examined for a birth cohort of New Zealand children studied until the age of 9. There were small, consistent and stable correlations between dentine lead measures and all measures of cognitive ability including intelligence, word recognition and teacher ratings of school performance. After adjustment for the effects of confounding covariates, sample selection factors and possible reverse causal effects, the correlations between intelligence and dentine lead levels became non-significant. However, small but statistically significant correlations persisted between dentine lead values and all measures of school performance after adjustment for sources of confounding. It is concluded that the weight of the evidence from this analysis favours the hypothesis that low level lead exposure may have deleterious effects on levels of achievement in children.

Dentine lead levels were obtained for a sample of 996 children who were participants in a longitudinal study of child development. Mean dentine lead levels were just over 6 micrograms g-1 and had a log normal distribution. The relationship between dentine lead values and a number of variables (social background, residence in old weatherboard housing, residence on busy roads, pica) describing exposure to sources of lead was analysed. This showed that all factors made small but statistically significant contributions to variations in dentine lead values and that collectively these factors explained 10% of the variance in lead values. The implications of these results are discussed.