DEVELOPMENT OF AN IN-VITRO SCREENING-TEST TO EVALUATE THE IN-VIVO BIOACCESSIBILITY OF INGESTED MINE-WASTE LEAD

A screening-level in vitro test was developed to evaluate the relative solubility of ingested lead (Pb) from different mine wastes in the gastrointestinal (GI) tract. The in vitro method, modeled after assay methods for available iron from food, used a laboratory digestion procedure designed to reproduce GI tract chemistry and function. The in vitro method was independently calibrated against a rabbit feeding study, demonstrating that only 1-6 % of the total Pb in four mine-waste samples with disparate Pb mineralogy was bioaccessible. In vitro method development tests indicated that H+ concentration and Cl- complexation control dissolution of Pb-bearing minerals in the stomach and that both GI tract enzymes and organic acids are necessary to maintain Pb in the soluble form on entering the small intestine. The experimental results indicate that ingestion of Pb-bearing mine wastes results in limited Pb solubility and that the in vitro test provides a screening-level estimate of the maximum available Pb from mine wastes.