Theoretical Model of Gastrointestinal Absorption of Lead

Abstract

SUMMARY A theoretical model is presented which is used to explain gastrointestinal absorption of ingested lead from use of traditional medicines. Dissolution processes are discussed and the relative contributions of pore and passive diffusion through the intestinal epithelium for the resulting species examined. The determination of the rate of absorption is described in terms of a mathematical three‐compartment system and effects of particle size are considered by reference to the Noyes‐Whitney dissolution rate law.

Mass Balance on Surface-Bound, Mineralogic, and Total Lead Concentrations as Related to Industrial Aggregate Bioaccessibility

“…These data demonstrate that the majority of the mineralbound Pb in the slag is distributed homogeneously throughout the slag grains, is refractory and insoluble, and from a geochemical perspective, is unlikely to be bioaccessible over the residence time in the GI tract (2 h in the stomach where Pb may be solubilized and 4 h in the small intestine, the segment of the GI tract where Pb is absorbed; 23,24). The encapsulation of Pb in a siliceous matrix has been demonstrated to reduce bioavailability and leachability (25).…”

The Bioavailability of Lead in Mining Wastes: Physical/Chemical Considerations

“…The ingestion and subsequent decomposition of food substances in the gastro-intestinal tract will release organic ligands, including organic acids, e.g., acetate, ascorbate, citrate, lactate, and amino acids from protein degradation (Tortora, 1980, Marty andRaynaud, 1966). The dissolution of lead from a lead-bearing mineral in the stomach results primarily in PbCl+ due to the high concentration of chloride and the common-ion effect (Healy, 1984). However, as the digestate enters the duodenum, the pH is raised to approximately 6.5.…”

“…For example, histidine, lysine, and cysteine have been shown to enhance iron uptake in the duodenum of Sprague-Dewley rats, due to the formation of complexes sufficiently stable to maintain the solubility of ferric iron. In addition, passive diffusion of neutral lead species across the intestinal epithelium is enhanced by the absorption of water (Blair et al, 1979, Healy, 1984, and Karmakar and Jayaraman, 1988. Thus the formation of stable, soluble Ph-organic ligand complexes may enhance absorption of lead, due to passive diffusion or reduced interaction between ionized lead and tissue phosphate ions (Blair et al, 1979).…”

“…For example, dissolution of PbS has been shown to be dependent on both solubility and particle size (Healy et al, 1982). These two factors are combined in the Noyes-Whitney dissolution rate law (Healy, 1984) i.e.,…”

Oral Absorption, Intestinal Metabolism and Human Oral Bioavailability

“…A drug is defined as being poorly soluble when its dissolution rate is so slow that dissolution takes longer than the transit time past its absorptive sites, resulting in incomplete oral absorption. Based on the Noyes-Whitney equation, many factors can affect a drug's dissolution rate (Healy 1984;Frenning and Stromme 2003):…”