1.1 Background to the Study

Heavy metals are elements with specific gravity greater than 5.0. They are metals which can be toxic even in small concentrations. Heavy metals are introduced into the environment through many sources such as weathering of rocks and soils; volcanic eruptions and various forms of other human activities involving mining, processing or use of metals and other substances containing contaminants (Lincoln et al., 2007; Ewuim and Akime, 2012). According to Biney et al. (2005), heavy metals are partitioned between water sediments, suspended solids and aquatic biota in water bodies and tend to accumulate more in sediments than in aquatic organisms and water as such sediments acts as sinks and supply of heavy metals to overlying water columns (Brooks et al., 2010, Gbem et al., 2001). When heavy metals enter water bodies, they change water quality, bind to sediments and accumulate in aquatic biota causing anemia, disturbance of physiological functions and mortalities of fish (Baeyans et al., 2001; Eichler et al., 2006). Specifically, aquatic organisms experience histo- logical and morphological changes in circulatory systems, biochemistry, physical behaviour and organism’s reproduction (Kedebe and Wondimu, 2004; Olaifa et al., 2003).


The introductions of toxicants into an environment where fishes are found stun them and or acts as a stressor on the fish and other organisms found in that environment (Capar and Yess, 1996, Kakulu et al., 1987). The toxicants in water bodies may dissolve the oxygen concentration which eventually impairs aquatic organism respiration thus leading to asphyxiation. Reproduction is also impaired during bioaccumulation of toxicants (Mayer, 2001). As water temperature increases, rate of biological processes increases and may result in increase in metal uptake by fish and gram (g) hydrogen Ion concentration (pH). As pH decreases, more dissolved metals ions are produced. Ionic forms of heavy metals induce acute poisoning in aquatic animals leading to immediate fish kills while complex forms lead to chronic poisoning and bioaccumulation in fish tissues over a longer period (Ellis et al., 1989; Baeyans et al., 2005).

Toxicology testing is conducted to determine the degree to which a substance can damage a living or nonliving organisms by analyzing the actual chemical in the samples or the used laboratory animals in studies. It has been in use for a long time in detecting potential hazards effects chemicals can have on living organisms via bioaccumulation of level of toxicants. The measure of a chemical’s toxicity is its Median Lethat Dosage (LD50) value which is the concentration that can cause average kills of 50 percent of a test population of animals on trial. This is usually reported in milligrams of the chemical per kilogram of a test animal’s life weight. The smaller the values, the more toxic the chemical referred. Chemicals with LD50 values greater than 500mg/kg in rats or mice are generally considered safe in agriculture (Mayer,  2001; Cunningham et al., 2011; Hadioui et al., 2005). Heavy metal pollution of water has become a major environmental problem since the advent of agricultural and industrial revolution and today most water bodies are contaminated with heavy metals released from domestic, industrial and other man-made activities. In modern times, one of the main threats to the health  of ecosystems is the exposure to a myriad of toxic substances and compounds such as mercury, cadmium, lead, copper, arsenic, air pollutants, pesticides, plastics, cigarette smoke, diesel fumes and nano-particles found  in products like perfumes and sunscreens. Their introduction into aquatic environment is caused by direct or indirect agricultural and industrial discharges (Zhang et al., 2009; Von Linden et al., 2003).

Heavy metals contamination could be detrimental to ecological balance of the recipient environment and to a diversity of aquatic organisms. Lead is a heavy metal which can seriously harm the human central nervous system, especially in children. It damages the kidneys and the immune system very easily. Exposure to lead causes premature births, diminished mental ability, mental retardation in infants and children making learning difficult and reduced rates of growth (Hu, 2000). Lead has been identified in at least 1,272 of the 1,684 hazardous waste sites that have been proposed for inclusion on the Environmental Protective Agency (EPA) National Priorities List (NPL) (Schmitt and Brumbaugh, 1990; Herbert, 2004; WHO, 2006). The majority of cases  of lead poisoning are due to oral ingestion and absorption through the gut. Lead poisoning in adults occurs more frequently during exposure in the workplace and primarily involves the central nervous system. Symptoms of hemopoietic system involvement include hypo chromic anaemia with basophilic stippling of the erythrocytes, hyperactivity, anorexia, decreased play activity; low intelligence quotient and poor school performance have been observed in children with high lead levels (USEPA, 1998, USEPA, 2002). Lead crosses the placenta during pregnancy and has been associated with intrauterine death, prematurity and low birth weight (Leighton et al., 2003; Kris-Ether ton et al., 2003; Nriagu et al., 1996).

1.2 Statement of the Problems

Since fish is an animal that is particularly affected by these pollutants, different species have been widely used to evaluate the health of aquatic ecosystems (Hu, 2000; Igbal et al., 2008; Laidlaw et al., 2005; Mohammed et al., 2011). Fish is of paramount importance in many nations’ economics and food proteins. In a few countries in the world, fish consumption contributes up to 180 kcal per capita per day, but reaches such high levels only where there is a lack of alternative protein foods grown locally or where there is a strong preference for fish. Nigeria  current national fish demand is around 1.6 million metric tons and it is supplied from imports about 700,000 MT  per year while domestic production is 640,00MT from both marine and freshwater (FAO, 2006, 2007). Fish proteins are essential in the diet of some densely populated countries where the total protein intake level is low, and are very important in the diets of many other countries in the world. Fish is also a valuable source of essential fatty acids and its protein is highly and easily digestible to man. Even in small  quantities, fish will have a significant positive impact on improving the quality of dietary protein intake by complementing the essential amino acids that are often present in low quantities in the rice and vegetable diets which are typical of nay developing states food. Fish is a rich source of lysine and other essential acids that are often deficient in carbohydrate diets and other plant protein sources (Lovell, 1988).

Fish meal is essential feedstuff rich in the essential proteins and essential amino acids nutrients needed by cultured fishes. In fact, livestock and fish feed without fish meal cannot meet the required nutrients for good performance of any of their culture animal (Lovell, 1988; Falayi, 2009). Recent research shows that fish is much more than just an alternative source of animal protein. Fish oils are the richest source of a type of fat that is vital for brain development in unborn babies and infants and cardiovascular therapy (Kris-Etherton et al., 2003). This makes all fish and especially fatty fish, such as tuna, mackerel and sardine, particularly good components of the diet of pregnant and lactating women. It is therefore apparent that fish makes a valuable contribution to the nutritional quality of the diets of the populations of many developing countries in Asia and the Pacific region (FAO, 2006, 2007). Clarias gariepinus is a hardy fish and highly valued in Nigeria. Catfishes of the family Claridae comprise the most commonly cultivated fishes in Nigeria (Adesulu, 2007). The growth of aquaculture in Nigeria now is largely being boosted by a steady rise in catfish culture. It is therefore very important to guide our environment jealously from been polluted by the uncontrolled  use of contaminated inland waters for aquaculture purposes as well as our territorial waters from oil spillages from petroleum exploration.


1.3 Aims and Objective of the Study

The main thrust of this research is to investigate the Disposition Time Of Cadmium And Lead Within The Tissue Of Medium Sized Clarias Garienpinus


1.4 Scope of the Study

The study is to ascertain the quantity of lead that can be accumulated within medium sized clarias garienpinus tissues and the implication in fish. This would then give an indication of how lead is indirectly consumed by man, the ultimate fish consumer.

1.5 Definition of Terms

Cadmium.: a toxic bluish-white malleable ductile divalent metallic element used especially in batteries, pigments, and protective platings

Disposition : This is the way living thing tend to behave or feel

Clarias gariepinus: This is a species of catfish of the family Clariidae, the airbreathing catfishes.

Lead: This is a chemical element with the symbol Pb (from the Latin plumbum) and atomic number 82. It is a heavy metal that is denser than most common materials.

Tissue: this  are groups of cells that have a similar structure and act together to perform a specific function