ABSTRACT
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1.1 INTRODUCTION The composition of the various elements which make up the human body resembles that found in the earth surface and in the surrounding oceans. In the course of evolution, humans, like other forms of life, have had to adapt themselves to changing environmental conditions by acquiring a variety of mechanisms through which the uptake, transport, and storage of the chemical components essential to biological function are regulated by the body. At least eight trace elements have been found to be essential for man. These are iron, copper, zinc, manganese, cobalt, selenium, chromium, and molybdenum. In addition, some six other trace metals are essential for other mammals. Disease can occur as a result of a deficiency or excess of these essential metals. Several other minerals and metals whose presence is not essential for normal biologic function can act as toxins and induce disease in humans as a result of acute or chronic exposure. Currently, the most important environmental metallic toxins are lead, mercury, arsenic, and thallium.
