Nonlinearity in the relationship between bone lead concentrations and CBLI for lead smelter employees

494 smelter employees from New Brunswick participated in a bone lead survey conducted by McMaster University in 2008, using the four element "clover-leaf" geometry germanium detector system. The employees were measured at two different bone sites, tibia and calcaneus, each measurement lasting 30 minutes. Scattered photons, including Pb X-rays, were collected by the germanium detectors located behind the ¹⁰⁹Cd source. A strong positive correlation was observed between tibia and calcaneus lead concentrations. Having been provided with blood lead levels, a cumulative blood lead index (CBLI) was generated. The employees were classified into four groups based on their date of hire, and their CBLI levels were compared to their tibia and calcaneus lead concentrations in the different groups. The slopes of bone Pb versus CBLI varied amongst groups, with those hired earliest showing the steepest slopes. This could be taken to imply a non-linearity in the uptake of Pb by bone from blood. In this paper, the association of the bone lead concentrations versus CBLI has been expressed by a polynomial function for the whole group of employees.