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Correspondence

Uncertainties in the Relationship between Tibia Lead and Cumulative Blood Lead Index

Norm Healey, David R. Chettle, Fiona E. McNeill, David E. B. Fleming

Health Canada, Sidney, British Columbia, Canada, E-mail:norm_healey@hc-sc.gc.ca, McMaster University, Hamilton, Ontario, Canada, Mount Allison University, Sackville, New Brunswick, Canada

Citation: Healey N, Chettle DR, McNeill FE, Fleming DEB 2008. Uncertainties in the Relationship between Tibia Lead and Cumulative Blood Lead Index. Environ Health Perspect 116:A109-A109. http://dx.doi.org/10.1289/ehp.10778

Online: 1 March 2008

D.R.C. has occasionally been retained by private and public sector interests as a consultant for his expertise on in vivo X-ray fluorescence (XRF) bone Pb measurement; a portion of his previous and current research efforts has been funded by industry. D.E.B.F. has twice been retained as a consultant by private and public sector interests for his expertise on lead exposure and XRF bone lead analysis; a portion of his research program has been partially funded by industry. The remaining authors declare they have no competing financial interests.

Uncertainties in the relationship between bone Pb and cumulative blood lead index (CBLI), including evidence of nonlinearity and differences between the sexes, should be appropriately recognized when setting workplace blood Pb limits to achieve target bone Pb concentrations.

Schwartz and Hu (2007) recommended a maximum occupational tibia Pb concentration of 15 μg/g. They stated that, based on the slope of the relationship between tibia Pb and CBLI calculated by Hu et al. (2007), a tibia Pb of 15 μg/g can be avoided by limiting the CBLI to < 200–400 μg-years/dL.

Hu et al. (2007) acknowledged the uncertainty in the slope of the relationship between tibia Pb and CBLI. However, over the range of cumulative Pb exposures that would produce a tibia Pb concentration of 15 μg/g, the slope of the relationship between tibia Pb and CBLI may be less than the slope of 0.05 [95% confidence interval (CI), 0.046–0.055] μg/g per μg-years/dL calculated by Hu et al. (2007).

Table 1 presents slopes and mean tibia Pb concentrations among subjects of eight published studies. Gerhardsson et al. (1993) reported a slope of 0.022 μg/g per μg-years/dL (no uncertainty reported) and Armstrong et al. (1992) reported a slope of 0.10 (± 0.02) μg/g per μg-years/dL. These represent a greater range of slopes than reported by Hu et al. (2007).

These data also suggest that the tibia Pb versus CBLI slope may not be constant, with lower slopes evident for lower tibia Pb and CBLI levels. This trend has been noted previously (Chettle 2005;Fleming et al. 1997). For tibia Pb concentrations of approximately 15 μg/g, a slope of approximately 0.025 μg/g per μg-years/dL seems equally plausible as the slope calculated by Hu et al. (2007).

A slope of 0.025 μg/g per μg-years/dL yields an allowable CBLI of 600 μg-years/dL, or an average annual blood Pb concentration of 15 μg/dL for 40 working years. This compares to 5–10 μg/dL for 40 working years associated with Schwartz and Hu’s (2007) recommended CBLI of 200–400 μg-years/dL.

These slopes are also based on studies of predominantly male subjects and may not account for differences in Pb toxicokinetics between the sexes (McNeill et al. 2000;Popovic et al. 2005).

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Table 1.

Various slopes of the relationship between tibia Pb and CBLI, and related mean tibia Pb concentration among study subjects.

References Top

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  2. Cake KM 1994. In Vivo X-Ray Fluorescence of Bone Lead in the Study of Human Lead Metabolism [Master’s Thesis]. Hamilton, Ontario, Canada: McMaster University.
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