Biomedical aspects of trace element speciation

Speciation affects the bioavailability and toxicity of elements and so is i mportant in toxicology and nutrition. Exploitation of speciation profiles i n medical management is widely unexplored. Isotopic speciation in the body can also offer clues to sources of exposure. The redox state of some elemen ts determines toxicity and affects transport across biological barriers. Di stinguishing inorganic from organometallic forms of Hg, Pb, and Sn is impor tant to assess exposure to the more toxic organometallic species, whereas t he organic forms of the metalloids As and Se reflect metabolism and detoxif ication. Special questions of speciation arise in therapeutic metal chelati on and the use of metal-based drugs, contrast, and imaging agents. Essentia l elements in blood plasma are distributed among one or more macromolecular species, with generally a small low molecular mass fraction that is diffic ult to define because of the complex composition of the biological fluid, i ncluding amino and other organic acids, and thiols. Albumin and/or transfer rin dominate the macromolecular species of many essential and non-essential elements.