Lead in Deciduous Teeth - A Comment

by Brian Gulson, Macquarie University,
Graduate School of environment and CSIRO, North Ryde

The article by Anne Winner in LEAD Action News Volume 2, Number 3 Early Lead Poisoned Child in the Classroom contains excellent information for those .dealing with school children, especially in view of the most recent research in the U.S. which reinforces the earlier work of Needleman et al., correlating tooth and blood leads with behaviour and attention deficits in the classroom.

However, the section on lead concentrations may be slightly misleading. I have been analysing teeth from children (and adults) from different communities including Broken Hill, Sydney and recently-arrived migrants from Eastern Europe for both lead concentration and lead isotope ratios; the latter give information about the source of lead.

I have found that even though analysis of a whole tooth is simpler than other methods, it can camouflage important information about the earlier lead exposure of the child.

To gain this information, the crown of the tooth is sliced into sections; the crown is all that is generally available for analysis in children as the root is resorbed (and thus the tooth falls out as it loses its "anchor"). The incisural section, which is mainly enamel and a small amount of primary coronal dentine (Figure 1) provides information about the lead burden of the mother during gestation and earliest childhood. The cervical section (section closest to the gums), consists mainly of secondary dentine and provides information about the integrated lead exposure of the child from birth to the time of exfoliation of the tooth (when it falls out). It provides information during the critical time of maximum blood lead (-12 to 30 months) when mouthing activity is greatest.

These data and some from the literature show that the enamel generally contains less lead than the dentine, especially in a child who had intensive mouthing activity and/or lived in a lead environment (mining, smelting, old home renovations).

Hence analysis of a whole tooth may underestimate the lead exposure of the child. In fact even the sectioning approach may underestimate the lead exposure in some children as analysis of rare roots of teeth have shown even higher amounts of lead than in the coronal dentine (Figure 2).

In light of these results, I would like to suggest that the "normal" values of Graeme Waller's analyses noted in the article, should be lower. Graeme's mean value was 5.2 ppm Pb, but the data were skewed, as one might anticipate in biological samples. The majority of his data were < 5 ppm Pb. hence, the majority of unexposed children i.e. BPb <10 µg/dL, should have lead concentrations in whole teeth of <5 ppm, given that the lead concentrations in the enamel are generally <2 ppm.