A longitudinal study of dentine lead levels and intelligence, school performance and behaviour: the measurement of dentine lead.

Shed deciduous teeth were obtained from a sample of 996 New Zealand children who were participants in a longitudinal study. For each child, estimates of dentine lead were obtained from two samples of dentine. The information was used to estimate the magnitude of random errors of measurement in dentine lead values and it was estimated that between 15 and 20% of the variance in dentine lead values was attributable to random errors of measurement. In addition, dentine lead levels were influenced by small systematic errors of measurement arising from the age at which the tooth was collected and the type of tooth analysed. These sampling factors, however, accounted for less that 3% of the variance in dentine lead values. The implications of these findings for the interpretation of correlations between dentine lead levels and other variables are discussed.

A longitudinal study of dentine lead levels, intelligence, school performance and behaviour. Part I. Dentine lead levels and exposure to environmental risk factors.

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.

A longitudinal study of dentine lead levels, intelligence, school performance and behaviour. Part III. Dentine lead levels and attention/activity.

The relationship between dentine lead levels and maternal/teacher ratings of inattentive/restless behaviour in children was examined for a birth cohort of New Zealand children. There were small but relatively consistent and stable correlations between dentine lead values and behaviour ratings. After correction for errors of measurement in dentine lead values and behaviour ratings it was estimated that the correlation between lead levels and inattentive/restless behaviour was in the region of +0.18. However, after control for various sources of confounding there was only a small, but statistically significant, correlation of +0.08 between lead levels and inattention/restless in children. It is concluded that the weight of the evidence favours the view that there is a very weak causal association between lead levels and attention and activity levels in children.

A longitudinal study of dentine lead levels, intelligence, school performance and behaviour. Part II. Dentine lead and cognitive ability.

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.