Geriatric Bone Lead Metabolism in a Female Nonhuman Primate Population

A geriatric rhesus monkey (Macaca mulatta) population, previously exposed to lead, was investigated using 109Cd K X-ray fluorescence (K XRF) to determine whether metabolism of lead in bone was similar to that in human populations. The accumulation rate of lead into the tibia in this group of monkeys was determined to be 0.10-0.13 micrograms Pb (g bone mineral)-1 (microgram dl-1 year)-1, which compares well with human data, where the rate has been found to be 0.05-0.10 microgram Pb (g bone mineral)-1 (microgram dl-1 year)-1. In addition, bone lead changes over a 10-month time period were investigated, but no statistically significant difference was found. A halflife for lead in "bone" was calculated by fitting a single exponential model to serial blood lead data; the mean half-life of lead in bone was found to be 3.0 +/- 1.0 years. Both endogenous and exogenous lead exposure were found to be low at the present time, 10 years after cessation of lead intake. It is concluded that rhesus monkeys are an extremely good animal model of human bone lead metabolism and, in addition, that further research is needed to provide a more complete understanding of lead metabolism in geriatric populations.