ASSESSMENT OF HEAVY METALS IN WILD AND FARMED AFRICAN CATFISH CLARIAS GARIEPINUS (BURCHELL, 1822) IN SELECTED RIVERS AND FISH FARMS

Thesis Overview

<p> </p><div><p><strong>1.0</strong>&nbsp; &nbsp; &nbsp; &nbsp;<strong>INTRODUCTION</strong></p><p><strong>1.1</strong>&nbsp; &nbsp; &nbsp; &nbsp;<strong>Background</strong>&nbsp;<strong>of</strong>&nbsp;<strong>the</strong>&nbsp;<strong>Study</strong></p><p>In recent years the concentrations of toxic metals in many ecosystems are reaching</p><p>unprecedented levels. The increasing use of metals in industry and mining activities have led</p><p>to serious environmental pollution through effluents and emanations (Güven <em>et</em>&nbsp;<em>al.,</em>&nbsp;1999).</p><p>Under certain environmental conditions, heavy metals may accumulate and cause serious</p><p>ecological damage. The aquatic ecosystem is often seen as the ultimate recipient of almost</p><p>everything including heavy metals (Ogoyi <em>et</em>&nbsp;<em>al.,</em>&nbsp;2011). Pollution of heavy metals in aquatic</p><p>environment is a growing problem worldwide and currently it has reached an alarming rate.</p><p>There are various sources of heavy metals; some originates from anthropogenic activities like</p><p>draining of sewage, dumping of hospital wastes and recreational activities. Conversely,</p><p>metals also occur in small amounts naturally and may enter into aquatic system through</p><p>leaching of rocks, airborne dust, forest fires and vegetation (Fernandez and Olalla, 2000). As</p><p>heavy metals cannot be degraded, they are continuously being deposited and incorporated in</p><p>water, sediment and aquatic organisms (Linnik and Zubenko, 2000), thus causing heavy</p><p>metal pollution in water bodies.</p><p>Heavy metal is any metallic chemical element that has a relatively high density and is toxic or</p><p>poisonous at low concentrations (Ngumbu, 2014). Examples of heavy metal include mercury,</p><p>cadmium, arsenic chromium, thallium and lead. As trace elements, some heavy metals (e.g.</p><p>copper, iron, zinc, manganese and selenium) are essential to maintain the metabolism of the</p><p>human body. However, at higher concentrations they can lead to poisoning (Lenntech, 2014).</p><p>Heavy metals can enter the human food through water, air, soil, plants and animals. The</p><p>pollution of the environment by heavy metals is viewed as an international problem because</p><p>1</p></div><p><br></p><div><p>of its effects. In recent years, the pollution of aquatic environment with heavy metals has</p><p>become a worldwide problem because of their potential toxic effect and also most of them</p><p>accumulate in tissues and organs of aquatic organism (Goldstein and Hewitt,</p><p>1990andGledhill <em>et</em>&nbsp;<em>al.,</em>&nbsp;1997).</p></div> <br><p></p>