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PROJECT TOPIC: HEAVY METAL CONCENTRATIONS IN AFRICAN RIVER PRAWN (Macrobrachium vollenhovenii) OF ETHIOPE RIVER

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CHAPTER ONEINTRODUCTION

1.1 BACKGROUND OF THE STUDYThe contamination of freshwaters with a wide range of pollutants has become a matter of great concern over the last few decades. Heavy metals are natural trace components of the aquatic environment, but their levels have increased due to domestic, industrial, mining and agricultural activities (Kalay and Canli, 2000). Trace metals in natural waters and their corresponding sediments have become a significant topic of concern for scientists and engineers in various fields associated with water quality, as well as a concern of the general public. Direct toxicity to man and aquatic life and indirect toxicity through accumulations of metals in the aquatic food chain are the focus of this concern (Odu et al., 2011). At low levels, some heavy metals such as copper, cobalt, zinc, iron and manganese are essential for enzymatic activity and many biological processes. Other metals such as cadmium, mercury, and lead have no known essential role in living organisms, and are toxic at even low concentrations (Al-Weher, 2008). Organic substances from oil spillage and petroleum products disposed into water bodies significantly contaminate and degrade them and could possibly elevate the concentration levels of heavy metals. Heavy metals are persistent and can easily enter food chain and accumulate until they reach toxic levels (Medjor et al., 2012).Aquatic organisms including fish and shellfish accumulate metals to concentration levels many times higher than present in water (Olaifa et al., 2004). Hence, estimation of heavy metal accumulation is of utmost importance in this sector of biotic community. Increased circulation of hazardous heavy metals in soil, water and air has raised considerable concern for environmental protection and human health (Mitra et al., 2012). Heavy metals are one of the more serious pollutants in our natural environment due to their toxicity, persistence and bio-accumulation problems (Tam and Wong, 2000). According to Adedeji and Okocha (2011) the term heavy metal refers to any metallic chemical that has a relatively high density and is toxic or poisonous at low concentrations. Examples include: mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl) and lead (Pb). Heavy metals are natural components of the Earth’s crust. Fish and shellfish can take up metals concentrated at different levels in their different body organs (Khaled, 2004). It has been widely reported in literature that gastropods accumulate metals in their tissues in proportion to the degree of environmental contamination and that they can be used as bio-monitors of marine metallic pollution (Goldberg et al., 1978).


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