ABSTRACT
In the geological and social environments, trace elements are those present in very small amounts. In the biological environment a further consideration is important, because it appears that some trace elements have an essential role in living systems, while the presence of others is merely fortuitous. Progress in trace element research has been decisively influenced by advances in analytical chemistry. The main reason for the extraordinary potency of the essential trace elements is that most of their work is done as components of enzymes or hormones. Iron acts both as a structural element and as a trace element. Iron is essential for the life of all organisms, except some bacteria. The maintenance of life in any organism depends on a multitude of chemical processes. Iodine is unique also in the extent to which it is concentrated in one tissue.
