Question 2c: How many teeth per child are required?

Preliminary results from the initial four teeth indicated that consistent lead ratios at the same age interval were found in primary dentine, although this pattern was less consistent closer to the pulp cavity where lead ratios increased rapidly. Based on these trends, only one transect was ablated in the 16 remaining teeth in order to further explore the value of lead ratios in dentine as a biomarker of the history of lead exposure. Although I collected two teeth for each child, it was not possible to measure the age of ablation pits for child HT8 tooth 84 (HT8-84) due to poor section quality.

For the 15 remaining teeth with histological data, the age ranges for dentine formation at the sampled points ranged from 98 days (~3 months) before birth to 1,102 days (~3 years) after birth. The average measurement error was low except in the two teeth from child HT3, discussed further below.

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Age interval

Lead ratios

HT2-54 HT2-64

The pattern of lead ratio distribution and lead ratios in primary dentine in the two teeth from each child (8 children) are shown in Figures 4.12-4.27. Most of the teeth show the same pattern observed in the initial two teeth each child, with lower lead ratios in enamel, higher ratios in dentine, and the highest ratios near the pulp cavity, with the exception of child HT14 (Teeth 74 and 84). For this child at the same age interval, average lead ratios in primary dentine of tooth 84 were 4-5 times higher than those in tooth 74. Although child HT3 had the highest lead ratios but two teeth from this child also show consistent lead ratios at the same age interval.

Figure 4.12 Lead ratio distribution for the two teeth from child HT2

Figure 4.13 Lead ratios in primary dentine for two teeth from child HT2

HT2-54-Mes HT2-64-Mes

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Age interval

Lead ratios

HT3-55 HT3-65

Figure 4.14 Lead ratio distribution for the two teeth from child HT3

Figure 4.15 Lead ratios in primary dentine for two teeth from child HT3

HT3-55-Dist HT3-65-Mes

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Age interval

Lead ratios

HT5-54 HT5-65

Figure 4.16 Lead ratio distribution for the two teeth from child HT5

Figure 4.17 Lead ratios in primary dentine for two teeth from child HT5 HT5-65-Dist HT5-54-Mes

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

Age interval

Lead ratios

Figure 4.18 Lead ratio distribution for the two teeth from child HT8

Figure 4.19 Lead ratios in primary dentine for child HT8 tooth 85

HT8-85-Dist HT8-84-Dist

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Age interval

Lead ratios

HT9-55 HT9-65

Figure 4.20 Lead ratio distribution for the two teeth from child HT9

Figure 4.21 Lead ratios in primary dentine for two teeth from child HT9 HT9-55-Dist

HT9-65-Dist

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Age interval

Lead ratios

HT12-84 HT12-85

Figure 4.22 Lead ratio distribution for the two teeth from child HT12

Figure 4.23 Lead ratios in primary dentine for two teeth from child HT12

HT12-84-Mes HT12-85-Mes

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Age interval

Lead ratios

HT13-75 HT13-84

Figure 4.24 Lead ratio distribution for the two teeth from child HT13

Figure 4.25 Lead ratios in primary dentine for two teeth from child HT13 HT13-84-Mes HT13-75-Mes

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Age interval

Lead ratios

HT14-74 HT14-84

Figure 4.26 Lead ratio distribution for the two teeth from child HT14

Figure 4.27 Lead ratios in primary dentine for the two teeth from child HT14 HT14-84-Mes HT14-74-Mes

146 As shown in Figure 4.28 with the X axis scaled to the same values for all teeth pairs, little difference was seen between lead ratios sampled in the primary dentine at the same age interval for the two teeth from the same child with exception of child HT3 and HT14, indicating that one transect in one tooth is probably sufficient to recreate patterns of lead incorporation over the child’s early years, although pairs showed continue to be studied until we know more about this inter-tooth variability.

With respect to inter-child variability, we found that the majority of the transects from each child showed a consistent pattern in dentine of low lead ratios that slightly increased by age interval, with the highest lead ratios being found in the dentine near the pulp cavity. However, the two teeth from child HT3 did not follow this pattern (Figure 4.15).

Lead ratios in primary dentine for this child increased until interval 304-346 days (8 months) after birth, then they slightly decreased around one year after birth, and afterwards significantly increased moving towards the pulp cavity. These reproducible changes in lead ratios can be traced in both deciduous molars (HT3-55, 65) from birth to dentine pulp cavity. This lead distribution seems likely to be due to lead exposure experienced by this child during their early life, and therefore suggests that dentine analysed using this technique may be useful in identifying the history of lead exposure.

Summary

Question 2c: How many teeth per child are required?

Answer: The results showed that differences in lead ratios between good sections in two teeth from the same child were small although we do not provide sufficient evidence that one tooth is sufficient. We recommend an expansion of this study with a larger number of samples and the collection of multiple teeth from each of the participants to allow

refinement and confirmation of the histological technique proposed in the present study.

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Lead ratios

HT5-54 HT5-65

Lead ratios in child HT8 (HT8- 85)

0

0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233 Age interval

0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233 Age interval

0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233 Age interval

Lead ratios

HT14-74 HT14-84

Figure 4.28 Comparison of primary dentine lead ratios of all samples from two teeth each child

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