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Acute metal and metalloid toxicity can cause significant morbidity and mortality if unrecognized and inappropriately treated. Metals are chemical elements that possess three general properties: (1) they are a good conductor of heat and electricity, (2) they are able to form cations, and (3) they can combine with nonmetals through ionic bonds. The terms heavy metal and toxic metals have a historical tradition in clinical medicine, but lack precise definition and scientific merit. In order of ascending atomic weight, the following metals are toxic to humans: beryllium, vanadium, cadmium, barium, osmium, mercury, thallium, and lead. Lead and mercury produce the most clinically significant cases of human metal poisoning.
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Metalloids are chemical elements with properties intermediate to those of metals and nonmetals. Although there is no precise definition, metalloids tend to have these two general properties: (1) they are semiconductors of electricity, and (2) they form amphoteric oxides. In order of ascending atomic weight, the following metalloids are considered toxic to humans: boron, silicon, germanium, arsenic, antimony, tellurium, and polonium, with arsenic being the most clinically significant toxic metalloid.
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Exposure to either metals or nonmetals can be from (1) the pure element, (2) an organic compound containing the toxic element (defined as those compounds that contain carbon), or (3) an inorganic compound containing the element (defined as those that do not contain carbon). Depending on the metal or metalloid, potential toxicity is affected by which chemical form is responsible for the exposure.
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Because of their effects on numerous enzymatic systems in the body, patients with metal or metalloid poisoning often present with protean manifestations primarily affecting five systems: neurologic, cardiovascular, GI, hematologic, and renal. Effects on the endocrine and reproductive systems are less clinically apparent. It is important to recognize an initial “index case” of metal poisoning to prevent others from being exposed or poisoned (Table 203-1).
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