ABSOLUTE BIOAVAILABILITY OF LEAD ACETATE AND MINING WASTE LEAD IN RATS

The primary purpose of this study was to generate data that could be u sed to determine the absolute bioavailability of lead using data from a previous study in which soil containing lead from mining waste was m ixed with feed. Young male and female Sprague-Dawley rats (7-8 weeks o f age, five/sex/group) were given either soluble lead acetate mixed in a purified diet (AIN-76(TM)) at three different dose levels (1, 25, a nd 250 ppm Pb for 30 consecutive days) or intravenously at doses of 0. 02, 0.20, and 2.0 mg Pb/kg BW for 29 days. A control group (purified d iet only) was also included. The intravenous groups were used to provi de maximal absorption (lead presumed to be 100% bioavailable) and accu mulation data for lead in blood, bone, and liver. The lead acetate gro ups were used to evaluate the comparability of the present study with a previous study that compared bioavailable lead from ingested soil an d lead acetate. Group mean whole blood, bone and liver lead concentrat ion values increased with increasing dose levels for all treatment gro ups. A linear relationship was observed between blood lead concentrati on and dose following intravenous administration of lead and this prov ided empirical support for using blood lead concentrations at supposed steady state (similar to 30 days) to compute the bioavailability of l ead administered by different routes and from different sources. The a bsolute bioavailability values of mining waste lead in soil were low b ased on the results for all tissue types. Absolute bioavailability val ues for lead acetate in dosed feed for blood, bone, and liver were app roximately 6-, 19-, and 20-fold greater, respectively, than mining was te lead. Based on the current design and test system used, the absolut e bioavailability of mining waste lead in soil administered in feed wa s approximately 3% based on blood data and less than 1% based on bone and liver data. These data are consistent with the low solubility of t he constituent lead mineral phases in Butte soils.