Copper antagonisms

Data concerning the toxicity of the four discussed toxic minerals are presented in Tables 4.5 and 4.6. The uptake of elements is not entirely independent of one another. Elements of similar chemical properties tend to be taken up together. Sometimes one element has an inhibiting effect on another, or there can be a synergistic effect, e.g., enhancement of absorption of calcium in the presence of adequate amounts of phosphorus, or cadmium and lead hindering calcium and iron absorption, or zinc and copper antagonism and their influence on the ratio of Zn/Cu on copper deficiency. 

Synthetic aspects of Cu—Mo—S systems and their possible relevance to copper-molybdenum antagonism. S. Sarker and S. B. S. Mishra, Coord. Chem. Rev., 1984,59, 239-264 (80). 

Cationic antagonisms induced by trace elements excesses have been demonstrated in plants as well as animals. Excesses of either manganese or iron in soil have resulted in deficiencies of the other in soybeans (152). Likewise, excess soil concentration of copper has resulted in manganese deficiency in crops (153). Plants, like animals, also demonstrate chromosomal aberrations (particularly to aluminum and cadmium) (15) as well as enzymatic alterations in response to excess exposure (16). 

Copper was recognized as nutritionally essential by 1924 and has since been found to function in many cellular proteins.470-474 Copper is so broadly distributed in foods that a deficiency has only rarely been observed in humans.4743 However, animals may sometimes receive inadequate amounts because absorption of Cu2+ is antagonized by Zn2+ and because copper may be tied up by molybdate as an inert complex. There are copper-deficient desert areas of Australia where neither plants nor animals survive. Copper-deficient animals have bone defects, hair color is lacking, and hemoglobin synthesis is impaired. Cytochrome oxidase activity is low. The protein elastin of arterial walls is poorly crosslinked and the arteries are weak. Genetic defects in copper metabolism can have similar effects. 

A second example of cluster formation involves the antagonism between molybdenum and copper. The presence of high concentrations of molybdenum in pasture soils is known to lead to symptoms of copper deficiency in animals. This has been attributed to the formation of thiomolyb-dates in the rumen of grazing animals, which then interfere with the metabolism of copper through the formation of cluster compounds of molybdenum and copper. It has been shown that thiomolyb-date, MoS42, readily forms such clusters on reaction with phosphines and copper(II) salts under appropriate conditions. Structures are shown in Figure 38.992,993 Reaction between thiomolybdate and copper compounds in aqueous solution have also been reported.994... 

Interactions Overabundance of one trace element can interfere with the metabolic use of another element available at normal levels. For example, addition of large amounts of zinc to a diet interferes with (antagonizes) intestinal copper absorption, resulting in copper deficiency from a diet with adequate copper content. Copper deficiency can provoke iron deficiency and anaemia. Molybdenum deficiency in animals can be induced by co-administration of large amounts of the similar element tungsten. Iron deficiency can also increase retention of cadmium and lead, and selenium has been proposed to protect against cadmium and mercury toxicity. 

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