ACCUMULATED BODY BURDEN AND ENDOGENOUS RELEASE OF LEAD IN EMPLOYEES OF A LEAD SMELTER

Bone lead levels for 367 active and 14 retired lead smelter workers we re measured in vivo by X-ray fluorescence in May-June 1994. The bone s ites of study were the tibia and calcaneus; magnitudes of concentratio n were used to gauge lead body burden. Whole blood lead readings from the workers generated a cumulative blood lead index (CBLI) that approx imated the level of lead exposure over time. Blood lead values for 204 of the 381 workers were gathered from workers returning from a 10-mon th work interruption that ended in 1991; their blood level values were compared to their tibia and calcaneus lead levels. The resulting rela tions allowed constraints to be placed on the endogenous release of le ad from bone in smelter workers. Calcaneus lead levels were found to c orrelate strongly with those for tibia lead, and in a manner consisten t with observations from other lead industry workers. Relations betwee n bone lead concentration and CBLI demonstrated a distinctly nonlinear appearance. When the active population was divided by date of hire, a significant difference in the bone lead-CBLI slope emerged. After a c orrection to include the component of CBLI existing before the workers ' employment at the smelter was made, this difference persisted. This implies that the transfer of lead from blood to bone in the workers ha s changed over time, possibly as a consequence of varying exposure con ditions.