Chelated lead in relation to lead in bone and ALAD genotype

In order to assess whether lead in bone is available for chelation by 2,3 meso-dimercaptosuccinic acid (DMSA), 21 workers (10 active and 11 retired) from a secondary lead smeltery were studied. A morning urine sample was obtained from all participants, followed by ingestion of 10 mg per kg body weight of the chelating agent DMSA. All urine produced during the following 24 h was collected in consecutive 6- and 18-h portions. Concentrations of lead in blood (B-Pb) and urine were determined by flameless atomic absorption spectrometry (AAS), in plasma (P-Pb) by inductively coupled plasma mass spectrometry (ICP-MS), and in finger bone (Bone-Pb) by K X-ray fluorescence technique (XRF), DMSA-chelatable lead excreted in the 24-h portion correlated well with the excretion in the 6-h portion (U-Pb-6h; r(s) = 0.95; P < 0.001), U-Pb-6h showed a nonlinear relationship to B-Pb (r(s) = 0.84; P < 0.001) and linear relationships to P-Pb (r(s) = 0.91; P < 0.001) and lead in morning urine (r(s) = 0.95; P < 0.001). In active workers, but not in retired ones, P-Pb and U-Pb-6h showed some relationship to Bone-Ph. In alternative multiple regression models B-Pb or P-Pb were both significant predictors of U-Pb-6h, while Bone-Pb did not significantly improve the models. It can, thus, be concluded that DMSA-chelatable lead mainly reflects lead concentrations in blood, soft tissues, and possibly also trabecular bone. It is not a good index of total body burden and long-term exposure. For such estimations cortical Bone-Pb is more valid, as it contains the major fraction of long-term accumulated lead in the body. Further, the mobilization test did not give better information than measurements of lead levels in blood, plasma, or urine without chelation. (C) 1999 Academic Press.