CHAPTER ONE
1.0       INTRODUCTION
Increasing industrialization has been accompanied throughout the world by the extraction and distribution of mineral substances from their natural deposits.
Following concentration, many of these undergone chemical changes through technical processes and finally pass by way of effluent, sewage dumps and dust into the water, the earth and the air and thus into the food chain.
The term heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at high concentrations. Examples of heavy metals include Mercury (Hg), Cadmium (Cd), Arsenic (As), Lead (Pb), Chromium (Cr), Thallium (Ti). Heavy metals are natural components of the earth’s crust.  They cannot be degraded or destroyed.  To a small extent they enter bodies via food, drinking water and air.  For food analyst they are termed contaminants which are undesirable materials, which have been added to advertently before, during or after processing of foods.  Heavy metals are dangerous because they tend to bioaccumulate.  Bioaccumulation means an increase in the concentration of the chemical in biological organism overtime compared to the chemical concentration in the environment, compounds accumulate in living things anytime they are take up and stored faster than they are broken down or excreted.
During the early life most substances that people were likely to encounter in their daily lives were derived with little modification from the earth, the animals, vegetables, crops or the mineral sources. Today, there is an extensive existence of synthetic chemical in the environment a class, which was not present until their creation by human scientific and industrial effort.  The domination of chemicals is increasing in our lives, can we imagine life without Agrochemicals, pharmaceuticals, preservatives, colourants, plastics, etc. (Envis Newsletter, 2002).  Heavy metals can enter a waste or even from acidic rain breaking down soils and many heavy metals into streams, lakes, rivers and ground water.