The presence and bioaccumulation pattern of some heavy metal concentrations in wild and farmed African catfish, Clarias gariepinus (Burchell, 1822) muscles collected from selected rivers and fish farms in Kaduna State, Nigeria, were assessed. Fish and water samples used for the assessment were collected during the wet and dry seasons from River Kaduna, River Galma in Zaria; and from two fish farms in Sabon Tasha, Kaduna and Dakace, Zaria. Physico-chemical parameters, such as Puissance Hydrogen (pH), temperature, Turbidity etc., were also analysed. The analyses of heavy metals, Iron (Fe), Lead (Pb), Nickel (Ni), Cadmium (Cd) and Mercury (Hg), in all water and Clarias gariepinus muscle samples was carried out in the Multi-User Science Research Laboratory, Department of Chemistry, Ahmadu Bello University, Zaria, using Thermo-element Solar S4 Atomic Absorption Spectrophotometer (AAS), while the Varian Generation Accessory (VGA 77) with closed end cell was used for Hg determination. The results obtained were subjected to t-test analysis to determine the level of significance (p < 0.05) between the means, while Pearson correlation coefficient was employed to determine the relationships. pH was highest in River Kaduna during the wet season, in the upstream (7.04), while there was a dip in the downstream (6.67) during the dry season. Seasonal variations in temperature were evident, as the ranges obtained in the rivers were from 27.03°C – 30.68°C and the farms ranged from 23.76°C – 27.42°C, which were within World Health Organization (WHO) recommended threshold (30°C – 36°C). Dissolved Oxygen (DO) varied widely in the rivers (5.11mg/l – 7.04mg/l) as well as in the farms (9.29mg/l – 10.74mg/l). Total dissolved solids (TDS)obtained in this study were all very high (Rivers: 54.91mg/l – 82.09mg/l, Farms: 28.43mg/l – 42.03mg/l), but were all lower than the WHO standardindicativeofportability (1000 – 1600mg/l). Heavy metal concentrations in water samples and heavy metal bio-accumulation in both wild and farmed C. gariepinus muscles showed irregular distributions with descending order of:Fe >Pb>Hg>Ni > Cd. Fe levels were the highest in both rivers water samples (3.23mg/l), closely followed by Pb (0.78) and Hg (0.69mg/l), while the farms also had Fe as the dominant element (1.31mg/l), with Pb (0.26mg/l) and Hg (0.09mg/l), respectively. Both water bodies had Ni concentration (0.2mg/l) higher than the WHO limits of 0.02mg/l, while the farms? concentration (0.03mg/l) was slightly higher than WHO threshold limit. In the muscle of C. gariepinus, Fe concentrations were also high in rivers (3.53mg/kg), while the Farms was 1.44mg/kg, all above the FAO recommended limit (0.5mg/kg) in fish. Generally, only Cd didnot exceed the maximum permissible limits in the tissues ofC. gariepinus. However, with Fe, Hg, Pb and Ni all higher than the acceptable limits, most especially in the rivers, this could pose a serious health risk to consumers. Thus, a close periodical and regular monitoring of heavy metal pollution in the water bodies is strongly advocated.

CHAPTER ONE: INTRODUCTION

1.1    Background of the Study
In recent years the concentrations of toxic metals in many ecosystems are reaching unprecedented levels. The increasing use of metals in industry and mining activities have led to serious environmental pollution through effluents and emanations (Güven et al., 1999). Under certain environmental conditions, heavy metals may accumulate and cause serious ecological damage. The aquatic ecosystem is often seen as the ultimate recipient of almost everything including heavy metals (Ogoyi et al., 2011). Pollution of heavy metals in aquatic environment is a growing problem worldwide and currently it has reached an alarming rate. There are various sources of heavy metals; some originates from anthropogenic activities like draining of sewage, dumping of hospital wastes and recreational activities. Conversely, metals also occur in small amounts naturally and may enter into aquatic system through leaching of rocks, airborne dust, forest fires and vegetation (Fernandez and Olalla, 2000). As heavy metals cannot be degraded, they are continuously being deposited and incorporated in water, sediment and aquatic organisms (Linnik and Zubenko, 2000), thus causing heavy metal pollution in water bodies.
Heavy metal is any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations (Ngumbu, 2014). Examples of heavy metal include mercury, cadmium, arsenic chromium, thallium and lead. As trace elements, some heavy metals (e.g. copper, iron, zinc, manganese and selenium) are essential to maintain the metabolism of the human body. However, at higher concentrations they can lead to poisoning (Lenntech, 2014). Heavy metals can enter the human food through water, air, soil, plants and animals. The pollution of the environment by heavy metals is viewed as an international problem because of its effects. In recent years, the pollution of aquatic environment with heavy metals has become a worldwide problem because of their potential toxic effect and also most of them accumulate in tissues and organs of aquatic organism (Goldstein and Hewitt, 1990andGledhill et al., 1997). However, the amount of absorption and bioaccumulation of the heavy metals depends on ecological, physical, chemical and biological condition and the kind of element and physiology of organisms (Jaffer et al., 1988). Heavy metals are considered the most important form of pollution of the aquatic environment because of their toxicity and accumulation by marine organisms (Eletta et al., 2003; Malik, 2004; Obasohan et al., 2006 and Igwemmar et al., 2013). There is increasing concern about the quality of foodsin several parts of the world. The determination of toxic elements in food has prompted studies on toxicological effect of these elements in food. Fish as an important component of the human diet, is generally appreciated as one of the healthiest and often times referred to as the “cheapest” source of protein, as its amino acid compositions are richer in Cysteine than most of the other sources of protein (Eletta et al., 2003).
In Nigeria, limited surveys on heavy metals in fish have been reported. Tawari-Fufeyin (1998) working on whole body tissues of fishes from Ikpoba reservoir in Benin-City reported the concentration of vast amounts of Cadmium (Cd), Chromium (Cr), Copper (Cu), Lead (Pb), Manganese (Mn), Nickel (Ni) and Zinc (Zn). Also Nwaedozie (1998) noted that heavy metals such as Hg, Cd, Pb, Cr, Zn and Fe were identified in appreciable quantities in the fish samples from Kaduna River. Obasohan et al. (2006) examined the concentrations of Cu, Mn, Zn, Pb, Cr, Ni and Cd in fish tissues of two tropical fish species from Ogba River, Nigeria.While Alinnor and Obiji (2010) investigated the level of heavy metals – Pb, Fe, Cd, Mn, Hg, Cu and Zn in fish samples from Nworie River in Imo State.
Specifically, aquatic systems are more sensitive to heavy metal pollutants and the gradual increase in the levels of such metals in the aquatic environment, mainly due to anthropogenic sources have now become a problem of primary concern (Oluyemi and Olabanji, 2011). This is due to their persistence as they are not usually eliminated either by biodegradation or by chemical means, in contrast to most organic pollutants. Moreover, the decay of organic materials in aquatic systems together with detritus formed by natural weathering processes and uncontrolled mining activities provides a rich source of nutrients in both the bottom sediments and overlaying water body (Jafari and Gunale, 2006and Wade et al., 2008), with microorganisms, microflora and algae capable of incorporating and accumulating these metal species into their living cells from the various supply sources (Jaffar et al., 1988).
Consequently, fishes become enriched with the accumulated substances, and eventually man, consuming these fishes inevitably suffers from the results of an enrichment process which have taken place at different trophic levels (Zhuang et al., 2013). However, it has been noted that heavy metal concentrations vary according to demographic climates. Heavy metals concentration are reported in industrialized nations such as China, United States of America (USA), Germany, Russia and Japan, where most imported fishes are cultured before sold to Nigeria(Huang, 2003; USEPA, 2009; Molina, 2011; FAO, 2012; WHO, 2012;Zhuang et al., 2013 and Abubakar et al., 2015). For instance, Huang (2003) reports that heavy metals entering the aquatic ecosystems in the coastal waters of Eastern Taiwan, are deposited in aquatic organisms continually, which through the effects of bioaccumulation via the food chain becomes potentially toxic to humans as the accumulation can reach substantially high levels, with resultant lethal effects such as renal failure, autism in children, premature births, heart failures etc.

1.2    Statement of Research Problem
Although, Kaduna State is not a heavily industrialized city (Nnaji et al., 2011), it still has its fair share of pollutants within her surrounding, due to the presence of several cottage industries and activities of the Nigerian Bottling Company, Nigeria Breweries, Sunseed Oil Mill, Zaria Industries Limited and the Kaduna Refinery, whose effluents, containing heavy and trace metals are continually being discharged into River Kaduna, River Kubanni, River Galma and other surrounding water bodies (Nwaedozie, 1998; Uzairu et al., 2009; Nnaji et al., 2011; Abubakar et al., 2012). Thus, it is pertinent to examine the levels of heavy metalsconcentrations in wild fish species in river bodies used for aquaculture in Kaduna state, in order to determine the contamination levels.
Also because of the growing aquaculture practice in Nigeria, Kaduna inclusive,farmers are constantly seeking ways to improve and manage fish farms despite water shortages, especially in the northern part of Nigeria (FAO, 2007; Galadima et al., 2011; WHO, 2012) there?s is a growing concern that the water sourced from hand dug wells and boreholes contain heavy metals as a result of sustained practice of illegal mining of solid minerals, urban sewage runoff and inadequate waste management practices (Sakai et al., 1996; Dimuna, 2004; Dan-Azumi and Bichi, 2010; Galadima et al., 2011; Galadima and Garba, 2012; Agwu, 2012). These locally cultured fish speciesmay often contain contaminants, including heavy metals, above acceptable levels. Thus, there is a need to analyse heavy metal concentrations in both wild and locally farmed fishes in Kaduna State, to establish their suitability for human consumption.

1.3    Justification of the Study
Although many studies have been done on the levels of heavy metals in fish samples along theWest African Sub-region (Sodomou et al., 2005; Voegborlo et al., 2006; Christopher et al.,2009; Voegborlo and Adimado, 2010and Kwaansa-Ansah, 2012), very little work hasbeenconducted in Kaduna, Nigeria, especially in relation to an analysis of heavy metals in wild and locally farmed fish species.
Heavy metals are persistent environmental contaminants, and are at least five times denser than water, and as such they cannot be metabolized by the body and thus becomes bio-accumulative (Es?haghi, 2011), thus heavy metal contamination of water bodies has been of major concern regarding their toxicity, persistence and non-degradability in the environment (Onianwa, 2001; Butu, 2013; Iguisiet al., 2001; Udiba et al., 2014).
Also, the role of aquaculture and fisheries to the Nigerian economy is significant but consumers? safety must not be toyed with, but for now it has not reached any appreciable level, primarily due to improper management, inadequate quality control measures and inadequate waste management systems. These have been highlighted as some of the major problems of fish consumption in Nigeria(Kudiet al., 2008; Adewuyi et al., 2010; Galadima and Garba, 2012 and Oforka et al, 2012).

1.4    Aim and Objectives of the Study
This study is aimed at investigating the presence andbioaccumulation pattern of heavy metals in wild and farmed Clarias gariepinus inKaduna to establish theirsuitability for human consumption.
The specific objectives of this study are as follows:

1. To analyse the water quality parameters of the selected rivers and fish farms.
2. To determine the concentration levels of heavy metals in the selected rivers and fish farms.
3. To determine the concentration levels of heavy metals in wild and farmed C. gariepinus in the selected rivers and fish farms.

1.5    Hypotheses
The following null hypotheses would be used in this study:

1. There is no significant difference in water quality parameters of the selected rivers and fish farms.
2. There is no significant difference in heavy metals concentrations in the selected rivers and fish farms.
3. There is no significant difference in heavy metal concentrations in wild and farmed C. gariepinus in the selected rivers and fish farms.