LEAD ISOTOPES: A USEFUL TOOL IN BIOMEDICAL STUDIES

Biomedical/environmental studies with lead isotopes may be divided into five types: (1) clinical studies using artificially enriched isotopes; (2) clinical studies using anthropogenic lead of unusual composition; (3) longitudinal studies using a source of anthropogenic lead that changes in isotope ratio; (4) studies using natural leads of unusual composition; and (5) studies using lead as a marker of bone mineral turnover. Clinical studies with human or animal subjects require special facilities and can only be performed at medical schools or government laboratories. Nonetheless, useful work has been done regarding the dietary uptake of lead, dissolution of retained bullets, and the behavior of the skeleton during pregnancy. Longitudinal studies, in which subjects are followed for an extended period while exposed to sources of anthropogenic lead, are suited to measuring the uptake of environmental lead in adults and children. Natural leads that are somewhat thorogenic may occur in soils developed on old granitic terrains and highly uranogenic leads are found in Phanerozoic limestones. The surprisingly high amounts of lead found in cocoa tend to be thorogenic, indicating that it is natural in origin, while dietary lead may have a large uranogenic component derived from the limestone used to manufacture calcium supplements. The skeleton has two compartments, trabecular and cortical bone, that turn over at different rates, the trabecular being the more rapid. If a woman has grown up in an environment characterized by lead of one isotopic composition and then moves in early adulthood to another environment, her two bone compartments will have different lead isotope ratios. It is then possible to see how each behaves during pregnancy and lactation. The same argument can be applied to examining how each behaves when menopause occurs.