In Vivo X-Ray Fluorescence of Bone Lead in the Study of Human Lead Metabolism

Abstract

It is well known that lead is toxic. Since the full effects, particularly of long term, low level exposure are not well understood, further knowledge of lead metabolism has significant public health implications. Traditionally, clinical studies of lead's effect on health have relied heavily on blood lead levels as an indicator of lead exposure. However, this is unsatisfactory, because blood lead levels principally reflect only recent exposure and lead in serum is more readily bioavailable than whole blood. Over 90% of the lead body burden is in bone, where it has a long residence time. Therefore, bone lead measurements are reflective of cumulative exposure. The bone lead detection system at McMaster University uses a ¹⁰⁹Cd source, which is positioned at the centre of the detector face (HPGE). This arrangement allows great flexibility, since one can sample lead in a range of different bone sites due to a robust normalization technique that eliminates the need to correct for bone geometry, thickness of overlying tissue, and other related factors. Lead in both the tibia and the calcaneus, whole blood lead, and serum lead have been measured in a group of 49 active lead workers (Nova Pb bone lead survey). Before studying the interrelationships between the above measurements, work was done to improve the programs which fit the bone lead spectra. That is, work was done to link the amplitudes of the alpha and beta peaks and to investigate the sensitivity of the analysis on the channel ranges and start parameters. The main goal of this project was to carefully study the interrelationships between the major components of any human lead metabolism model, bone, whole blood, and serum, in order to establish a solid basis for computer modelling of lead metabolism.