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Acute metal and metalloid toxicity is an uncommon clinical entity
that can be a cause of 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
use of the term heavy metal has an historical tradition
in clinical medicine, but the term 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 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 either (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.1 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 197-1).
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