IN-VIVO MEASUREMENTS OF LEAD IN BONE IN LONG-TERM EXPOSED LEAD SMELTER WORKERS

In-vivo measurements of lead concentrations in calcaneus (mainly trabe cular bone) and tibia (mainly cortical bone) were performed by x-ray f luorescence (XRF) in 70 active and 30 retired lead smelter workers who had long-term exposure to lead. Comparison was made with 31 active an d 10 retired truck assembly workers who had no known occupational expo sure to lead. After physical examination, all participants provided bl ood and urine samples and answered a computerized questionnaire. Since 1950, blood lead has been determined repeatedly in lead workers at th e smelter, which made it possible to calculate a time-integrated blood lead index for each worker. Lead concentrations in blood, urine, calc aneus, and tibia in active and retired lead workers were significantly higher than in the corresponding control groups (p < .001). The highe st bone lead concentrations were found among retired lead workers (p < .001), which was the result of considerably higher lead exposure duri ng 1940 to 1960. Lead concentrations in calcaneus in active lead worke rs were significantly higher than in tibia when expressed in ug of lea d per gram of bone mineral, which suggests a quicker absorption over t ime in this mainly trabecular bone. The estimated biological half-time s were 16 y in calcaneus (95% confidence interval [95% Cl] = 11-29 y) and 27 y in tibia (95% Cl = 16-98 y). A strong positive correlation wa s found between lead concentrations in calcaneus and tibia for all lea d workers (r = 0.54; p < .001). A strong positive correlation was also found between the bone lead concentrations and the cumulative blood l ead index. Blood lead, at the time of study, correlated well with bone lead concentrations in retired-but not in active-workers, reflecting the importance of the endogenous (skeletal) lead exposure. The finding s in this study indicate that bone lead measurements by XRF can give a good index of long-term lead exposure. Tibia measurements offer a hig her precision than calcaneus measurements. The method is of particular interest in epidemiologic studies of adverse health effects caused by long-term lead exposure.