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The heavy metals discussed in this chapter—lead, arsenic, mercury, and iron—frequently cause toxicity in humans. The toxicity profiles of metals differ, but most of their effects appear to result from interaction with sulfhydryl groups of enzymes and regulatory proteins. Chelators are organic compounds with 2 or more electronegative groups that form stable bonds with cationic metal atoms. These stable complexes lack the toxicity of the free metals and often are excreted readily. Chelators, which function as chemical antagonists, are used as antidotes in the treatment of heavy metal poisoning.

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Chelating agentA molecule with 2 or more electronegative groups that can form stable coordinate complexes with multivalent cationic metal atoms
ErethismSyndrome resulting from mercury poisoning characterized by insomnia, memory loss, excitability, and delirium
PlumbismA range of toxic syndromes due to chronic lead poisoning that may vary as a function of blood or tissue levels and patient age
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Lead

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Lead serves no useful purpose in the body and can damage the hematopoietic tissues, liver, nervous system, kidneys, gastrointestinal tract, and reproductive system (Table 57–1). Lead is a major environmental hazard because it is present in the air and water throughout the world.

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Table 57–1 Important Characteristics of the Toxicology of Arsenic, Iron, Lead, and Mercury.
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Acute Lead Poisoning

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Because of the ban on lead over 20 years ago in gasoline, and because of bans on other industrial products that previously contained lead, acute inorganic lead poisoning is no longer common in the United States. It can occur rarely from industrial exposures (usually via the inhalation of dust) and in children who have ingested large quantities of chips or flakes from surfaces in older houses covered with lead-containing paint. The primary signs of this syndrome are acute abdominal colic and central nervous system (CNS) changes, including, particularly in children, acute encephalopathy. The mortality rate is high in those with lead encephalopathy, and prompt chelation therapy is mandatory.

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Chronic Lead Poisoning

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