Early dentine lead levels and subsequent cognitive and behavioural development.

While a number of studies have reported associations between lead levels and cognitive development and behaviour in cross-sectionally studied child samples, there have been relatively few studies of the long term effects of early lead exposure. This issue was studied in a birth cohort of 1265 New Zealand children who were assessed with respect to: (a) dentine lead levels at ages 6-8 years; (b) cognitive and behavioural outcomes at 12, 13 years; (c) various confounding factors. The results of the analysis show: (a) the presence of small but consistent bivariate associations (ranging in absolute size from r = .08 to .20) between early lead levels and later school performance and behaviour; (b) after adjustment for both errors of measurement in test scores and lead levels and adjustment for confounding factors these correlations reduced to between .07 and .14. Nonetheless these correlations remained statistically significant. The evidence is consistent with the view that early mildly elevated lead levels are associated with small but relatively long term deficits in cognitive ability and attentional behaviours.