THE BIOACCESSIBILITY OF METAL AND METALLOID TOXICANTS IN COMPOUNDS USED HISTORICALLY IN MEDICINES, TOILETRIES, AND MURDERS

Many minerals and manufactured compounds containing potentially toxic heavy metals and metalloids (MMC's) were used historically for medicinal purposes (i.e., laxatives; emetics; microbicides; treatments for stomach upset, ulcers, ringworms). Examples include cinnabar, mercury chloride salts, mercury(II) cyanide, white arsenic (arsenic oxide), red arsenic (realgar), yellow arsenic (orpiment), stibnite, potassium or sodium antimony tartrate, and thallium salts. Some MMC's were also used in personal care products (i.e., white lead and white arsenic used in makeup). Diverse MMC's have been used for centuries in paints, wood preservatives, pesticides, and many other commercial applications. History is replete with murder cases known or speculated to have resulted from poisoning by various MMC's, many of which were readily available to prospective murderers due to their common societal usage. Many more poisoning cases arose from accidental exposures. Due to toxicity concerns, most medicinal and personal uses and many commercial uses of MMC's have ceased; however, medicinal uses of MMC's persist for some specialized treatments, and in some cultures.

In part, the difference between a medicine and a poison is one of dose. However, toxicities of MMC's also depend strongly on the bioaccessibility of their contained toxicants in water-based body fluids encountered along the various exposure pathways. Different compounds of the same toxicant differ in solubility and dissolution kinetics, and therefore bioaccessibility; e.g., lead acetate is highly water-soluble, lead carbonate is highly bioaccessible in stomach acid, and lead sulfide has relatively low bioaccessibility in stomach acid. Once a bioaccessible toxicant is released into the body, chemical reactions with body fluids or other materials (such as ingested food) can influence the extent to which it is subsequently absorbed, distributed, and metabolized in the body, through changes in speciation or oxidation state, or by precipitation as or sorption onto solid phases. This talk will use results of in vitro physiologically based extraction tests, where substances are reacted with various simulated body fluids, to provide insights into potential chemical reactions that MMC's may undergo in vivo, and resulting implications for toxicity.