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KEY POINTS
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Persons at either end of the life span, young children or elderly people, are more susceptible to toxicity from exposure to a particular level of metal than most adults.
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Metals that provoke immune reactions include mercury, gold, platinum, beryllium, chromium, and nickel.
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Complexation is the formation of a metal ion complex in which the metal ion is associated with a charged or uncharged electron donor, referred to as a ligand.
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Chelation occurs when bidentate ligands form ring structures that include the metal ion and the two ligand atoms attached to the metal.
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Metal–protein interactions include binding to numerous enzymes, the metallothioneins, nonspecific binding to proteins such as serum albumin or hemoglobin, and specific metal carrier proteins involved in the membrane transport of metals.
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Metals are typically defined by physical properties of the element in the solid state. General metal properties include high reflectivity (luster), high electrical conductivity, high thermal conductivity, and mechanical ductility and strength. A characteristic of toxicological importance is that metals exhibit variable oxidation states and may react in biological systems by losing one or more electrons to form cations. An overview of toxic effects of metals is shown in Fig. 23–1.
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Unique among pollutant toxicants, metals are all naturally occurring and are ubiquitous to some level within the human environment. Regardless of how safely metals are used in industrial processes or consumer products, some level of human exposure is inevitable. Metals are elements that are neither created nor destroyed by human endeavors. Human use of metals can alter its chemical form or speciation and thereby impact toxic potential. Production of metal nanoparticles has created many novel metal properties including unique toxicities. Metals are persistent and potentially more toxic in the human environment. Metal exposures contribute to the etiology of diseases of essentially all organ systems (Table 23–1). Several metals are known or probable carcinogens promoting a range of cancer types.
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Movement of Metals in the Environment
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