Toxicological Significance of Metals

If one considers the toxicity of a metal ion with regard to its location in the periodic table, a pattern can be seen [67] Toxicity increases with a decrease in the stability of the electron configuration. Consequently, the heavy metals of the sixth period and their compounds are potentially the most toxic elements. This increase in toxicity can be explained by the increasing affinity of these metals for amino, imino, and sulfhydryl groups, which form the active centers of a number of enzymes. 

Plot of the charge/radius ratio (z/r) against ionization energy (/j) to the divalent state of a metal atom. The relationship between hard and soft metal ions is clearly seen. (From Ref. lOb by permission of Oxford University Press.) 

There are different mechanisms by which metals can cause toxic effects, as discussed below. 7.2.7. Electrolytes 

There are also different mechanisms for the toxic action of heavy metals [66]  

One metal may substitute for another, essential metal, e.g., in an enzyme, resulting in toxic effects. 

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The ubiquitous nature of metals from both natural and anthropogenic sources combined with their necessity in biological processes produce a complex system for study. Metal distributions in abiotic and biotic systems must be examined to accurately assess impact on ecosystems. Wildlife studies of exposure and effect can be challenging, but the results are more complete than evaluation of only metal concentrations. Birds are good sentinel species because they visible, sensitive to toxins, and occupy different trophic positions. Therefore, studies to assess avian population status, reproductive success, and toxicological significance of metal exposures can be extrapolated to other wildlife and possibly humans. 

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