Estimation of cumulative lead releases (lead flux) from the maternal skeleton during pregnancy and lactation

Recent longitudinal studies with human subjects and nonhuman primates using high-precision stable lead isotopes show that lead is mobilized from the m aternal skeleton during pregnancy and the postpartum period. We have now ca lculated the cumulative lead release (lead flux in micrograms) mobilized fr om the skeleton during these periods by means of analysis of monthly PbB sa mples from recent immigrants to Australia. Results included a statistically significant inverse relationship (P = .006) between the lead flux and the time of conception after the arrival of the subjects in Australia. By using an area-under-the-curve approach to determine the added lead inputs to blo od during pregnancy and nursing versus a baseline value, the net lead relea se to blood varied from 0.9 to 10.1 mu g/d, which is equivalent to 0.3 to 4 .03 mg of lead. With group PbB concentrations usually less than 3 mu g/dL, the observed releases imply a high skeletal turnover of greater than 10% an d possibly greater than 30% in some subjects during pregnancy and the postp artum period. These elevated rates in some subjects may partly arise from l ow daily calcium intakes, being one half to two thirds of that of recommend ed daily requirements. The lead flux calculated from a cumulative approach was compared with other approaches: first-order kinetics, bone turnover, bo ne x-ray fluorescence measurements, and the International Commission for Ra diological Protection lead pharmacokinetic model. Calculated lead releases and remaining bone lead concentrations would likely not be detectable by cu rrent x-ray fluorescence methods.