SELECTED ASPECTS OF THE SPATIAL-DISTRIBUTION OF LEAD IN BONE

The macrodistribution of lead within the skeletal system is not uniform, and is clearly dependent on bone type (compact or trabecular), age and (to a lesser extent) gender During active growth, lead deposition favors trabecular bones sites but in adulthood lead accumulates more actively in compact bone. The extent and patterns of the higher variability in trabecular bone sites require better definition through further study. Lead tends to be deposited in bone at sites of most active calcification at the time it is absorbed. During the first 15 years of life the bone growth centers dominate the process of calcification. In adulthood osteon remodelling and trabecular plate mineral exchanges are the principal calcifying sites. Both patterns probably deteriorate in old age. Microdeposition patterns of lead could be expected to conform to these changes. However, it is difficult to integrate the reported information into a clearly defined chronological sequence, because many of the studies did not control for age and other variables with sufficient precision. Furthermore, kinetic studies suggest lead is deposited in multiple sites not only among soft tissues but also within bone in molecular forms possessing varying affinities. Current efforts to design instrumentation for in vivo diagnostic lead measurements as we# as therapeutic methods to mobilize and remove lead in bone require more precise knowledge than is now available concerning lead macrodistribution, microdistribution and anatomic sites of kinetic compartments. Appropriately designed studies employing contemporary, sensitive techniques involving isotopes, microradiographs, autoradiographs, histology, tomography, and high energy x-ray fluorescence (synchrotron radiation-induced x-ray emission - SRIXE) are now capable of generating the needed data.