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Acute metal and metalloid toxicity is uncommon but 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 term heavy metal has a historical tradition in clinical medicine, but has been criticized by chemists as lacking in a precise definition or scientific merit. An alternative term, toxic metal, which also lacks firm definition, is sometimes used instead. In clinical toxicology, the following metals, noted in ascending atomic weight, are usually considered under the concept of "heavy" or "toxic" metal poisoning: beryllium, vanadium, cadmium, barium, osmium, mercury, thallium, and lead, with lead and mercury being the metals most clinically significant concerning human 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 elements are generally considered metalloids: boron, silicon, germanium, arsenic, antimony, tellurium, and polonium; arsenic is the most clinically significant 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, the metals and metalloids 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 poisoned when the metal source is environmental or industrial (Table 203-1).
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