Ultratrace elements biological roles

Environmental and agricultural studies involve a number of different materials that need to be analysed. The principal test materials encountered by the analyst in this sector are soils, sediments, air, dusts, water, plant material and animal tissue. For completely practical reasons, we need to know the composition of these media over wide concentration ranges, from major constituents to elements at ultratrace levels. One is especially interested in the way elements are transferred between media, their biological role and metabolic pathways, and their ultimate fate. 

The quality of the experimental evidence for nutritional essentiality varies widely for the ultratrace elements. The evidence for the essentiality of three elements, iodine, molybdenum and selenium, is substantial and noncontroversial specific biochemical functions have been defined for these elements. The nutritional importance of iodine and selenium are such that they have separate entries in this encyclopedia. Molybdenum, however, is given very little nutritional attention, apparently because a deficiency of this element has not been unequivocally identified in humans other than individuals nourished by total parenteral nutrition or with genetic defects causing disturbances in metabolic pathways involving this element. Specific biochemical functions have not been defined for the other 15 ultratrace elements listed above. Thus, their essentiality is based on circumstantial evidence, which most often is that a dietary deprivation in an animal model results in a suboptimal biological function that is preventable or reversible by an intake of physiological amounts of the element in question. Often the circumstantial evidence includes an identified essential function in a lower form of life, and biochemical actions consistent with a biological role or beneficial action in humans. The circumstantial evidence for essentiality is substantial for arsenic, boron, chromium, nickel, silicon, and vanadium. The evidence for essentiality for the... 

Table 2 Excretion, retention, and possible biological roles of the ultratrace elements ...

None of the suggested biological functions or roles of any of the ultratrace elements have been conclusively or unequivocally identified in higher forms of life except for those of molybdenum. 

The role of metals and other elements in the health of humans, animals, and plants continues to be of great interest both on a routine basis and in research. Two recent reviews described the important impact of ICP-MS in biomedical research [227, 228]. ICP-MS provides the ability to measure multiple elements at ultratrace levels rapidly and to measure isotope ratios at low enough concentrations so that stable isotope tracers can be used for biomedical research [229]. Much remains unknown about the role of metals and their speciation on biological activity, in large part as a result of inadequate measurement techniques. 

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