Study of the relationships between bone lead levels and its variation withtime and the cumulative blood lead index, in a repeated bone lead survey

The study aims were to: (i) investigate long term human lead metabolism by measuring the change of lead concentration in the tibia and calcaneus; and (ii) assess whether improved industrial hygiene was resulting in a slow acc umulation of lead in an exposed workforce. Cd-109 excited K X-ray fluoresce nce was used to measure tibia lead and calcaneus lead concentrations in 101 workers in a secondary lead smelter. 51 subjects had had similar bone lead measurements 5 years previously. Most of the other subjects had been hired since the first survey. Measurements of whole blood lead were available fo r the large majority of subjects. Tibia lead concentrations fell significan tly (p < 0.001) in the 51 subjects with repeated bone lead measurements, fr om a mean of 39 mu g Pb (g bone mineral)(-1) to 33 mu g Pb (g bone mineral) (-1). The change correlated negatively with the initial tibia lead concentr ation, producing an estimate for an overall half-life of 15 years, with a 9 5% confidence interval of 9 to 55 years. Adding continuing lead exposure an d recirculation of bone lead stores to the regression models produced half- life estimates of 12 and 9 years, respectively, for release of lead from th e tibia. The repeat subjects showed no net change in calcaneus lead (64 mu g Pb (g bone mineral)(-1) initially, 65 mu g Pb (g bone mineral)(-1) 5 year s later). Subjects not measured previously had average lead concentrations of 15 mu g Pb (g bone mineral)(-1) in the tibia and 13 mu g Pb (g bone mine ral)(-1) in the calcaneus. The rate of clearance of lead from the tibia (9 to 15 years) is towards the more rapid end of previous estimates. The lack of a significant fall in the calcaneus lead was surprising. Attempts should be made to repeat this observation. If confirmed, it would have implicatio ns for models of lead metabolism. The relatively low lead concentrations in the non-repeat subjects are reassuring. However, observation after a longe r period of employment would be desirable.