USE OF ENDOGENOUS, STABLE LEAD ISOTOPES TO DETERMINE RELEASE OF LEAD FROM THE SKELETON

The stable lead isotope methodology can be used to study the release o f lead from bone into the circulation because of its potential to dist inguish circulatory lead from ''older'' and isotopically different ske letal lead that may have been accumulated years or decades earlier. He re we report the initial results from a larger ongoing study that eval uates the skeleton as a source of lead to the circulation in environme ntally exposed human subjects. Lead concentrations and stable lead iso topic compositions were measured in blood and trabecular bone samples obtained from five patients who underwent total hip or knee joint repl acement. All subjects contained low blood (1-6 mu g/dl) and bone (0.6- 7 mu g/g dry weight) lead concentrations typical of environmentally ex posed individuals. There were relatively large differences in the lead isotopic compositions between the paired blood and bone samples from each subject. These isotropic differences are attributed to difference s in the lead isotopic compositions of past versus current lead exposu res and to the long elimination half-life of lead in the skeleton comp ared to lead in the circulation. Based on these data, we determined th at the skeleton contributed 40-70% of the lead in the blood of these s ubjects. This initial study demonstrates the utility of the stable lea d isotope methodology for investigating the release of lead from the s keleton. It also shows that the skeleton can be an important endogenou s source of lead exposure in environmentally exposed humans.