The study assessed the physicochemical parameters of the water and concentrations of Cd, Co, Cr, Cu, Pb and Zn in the water, sediments and organs (bones, brain and flesh) of Clarias gariepinus, Oreochromis niloticus and Synodontis nigrita obtained from River Niger, River Benue (close to their confluence) and after the confluence point at Lokoja, Nigeria during the months of March, June, September and December 2013. By using standard procedures, the chemical oxygen demand, dissolved oxygen, turbidity, biological oxygen demand, total dissolved solids, total hardness, conductivity and pH of the water were determined. The ranges of these parameters were 98.25 – 141.73 mg/L, 2.26 – 14.39 mg/L, 5.33 – 23.13 NTU, 5.56 – 15.59 mg/L, 457.91 – 781 mg/L, 48.85 – 245.83 mg/L, 65.61 – 233.39 μs/cm and 6.77 – 8.07 respectively. All the parameters were above the acceptable limits set by World Health Organisation (WHO), except pH. The concentrations (mg/L) of Cd, Co, Cr, Cu, Pb and Zn in the water samples were in the range of 0.0082 – 0.0276, 0.0042 – 0.0279, 0.0480 – 0.1391, 0.0979 – 1.8037, 0.0003 – 0.0047 and 0.7671 – 2.8510 respectively. Only Pb and Zn were in levels within the permissible limit set by WHO and the concentrations recorded between the rivers and across sampling periods were significantly different. The concentrations of Cd, Co, Cr, Cu, Pb and Zn in the sediments were in the range of 0.2026 – 2.0203, 2.1567 – 20.5421, 13.1767 – 33.0976, 7.0832 – 23.4040, 0.1054 – 2.5593 and 12.9263 – 32.8418 mg/kg respectively. The mean concentration of Cd in the sediment was above the ISQG (Interim Freshwater Standard Quality Guidelines) limit of 0.6000 mg/kg. The pollution load index for the heavy metals indicates low to moderate pollution state of the sediments while the geoaccumulation index for Cd, Co, Cr, Cu, Pb and Zn also suggest low to moderate
pollution of the sediments by Cd, Co and Cr. The organs of the three fish species bio-accumulate Cd, Co, Cr, Cu and Pb above their respective permissible limit. The bone accumulated the metals more than the brain and the level was least in the flesh for all the metals. However, Zn was below the acceptable limit in all the species and organs. Cd and Pb accumulate more in O. niloticus followed by C. gariepinus and least in S. nigrita. Generally, the parameters for the water samples obtained in March 2013 were the highest. The results indicate pollution of the rivers, so enforcement of environmental laws that will minimize anthropogenic activities is imperative.
TABLE OF CONTENTS
Title Page Title Page i Declaration ii Certification iii Dedication iv Acknowledgement v Abstract vi Table of Contents viii List of Tables xv List of Figures xvi Plates xviii List of Appendices xix Abbreviations xxi CHAPTER ONE 1.0 INTRODUCTION 1 1.1 Statement of Problem 4 1.2 Justification of the Study 5
1.3 Aims and Objectives 5 CHAPTER TWO 2.0 LITERATURE REVIEW 7 2.1 Physicochemical Parameters of Water 7 2.1.1 Temperature 7 2.1.2 pH 7 2.1.3 Dissolved oxygen 8 2.1.4 Biochemical oxygen demand 9 2.1.5 Chemical oxygen demand 9 2.1.6 Hardness and alkalinity 9 2.1.7 Turbidity 10 2.1.8 Total dissolved solids and electrical conductivity 11 2.2 Heavy Metals and their Health Implications 11 2.2.1 Cadmium 11 2.2.2 Cobalt 13 2.2.3 Chromium 14 2.2.4 Copper 14 2.2.5 Lead 15
2.2.6 Zinc 16
2.3 Fish Species 17 2.4 Pollution of River Water 18 2.5 Pollution of River Sediments 26 2.6 Heavy Metal Accumulation in Fish 28 2.7 Limits for Heavy Metals in Rivers 30 CHAPTER THREE 3.0 MATERIALS AND METHODS 32 3.1 Materials 32 3.2 Reagents 32 3.3 Preparation of Reagents 32 3.4 Study Area 35 3.5 Sampling 36 3.5.1 Water sampling and pretreatment 40 3.5.2 Sediment sampling and pre-treatment 40 3.5.3 Fish sampling and pre-treatment 40 3.6 Determination of Physicochemical Parameters of Water 41 3.6.1 Turbidity 41 3.6.2 Total dissolved solids 41
3.6.3 pH 41
3.6.4 Electrical conductivity 42 3.6.5 Hardness 42 3.6.6 Dissolve oxygen 43 3.6.7 Chemical oxygen demand 43 3.6.8 Biological oxygen demand 44 3.8 Preparation of Calibration Curves 44 3.9 Digestion of Samples 45 3.9.1 Digestion of water sample 45 3.9.2 Digestion of sediment samples 45 3.9.3 Digestion of fish sample 46 3.10 Wavelength, Current, Burner Height and Slit width of Measurement 46 3.11 Statistical Analysis of Results 46 CHAPTER FOUR 4.0 RESULTS 51 4.1 Physicochemical parameters of water 51 4.2 Heavy metals concentrations in water 52 4.3 Pearson’s correlation matrices 61 4.4 Heavy metals concentrations in sediment 61
4.5 Pollution load and Geoaccumulation indices 72 4.6 Heavy metals concentrations in organs of Fishes 79 CHAPTER FIVE 5.0 DISCUSSION 89 5.1 Physicochemical Properties of Water Samples 89 5.1.1 Biochemical oxygen demand 89 5.1.2 Chemical oxygen demand 90 5.1.3 Conductivity 92 5.1.4 Dissolved oxygen 93 5.1.5 Hardness 94 5.1.6 pH 95 5.1.7 Total dissolved solids 96 5.1.8 Turbidity 97 5.2 Heavy Metals in Water Samples 98 5.2.1 Cadmium 98 5.2.2 Cobalt 99 5.2.3 Chromium 101
5.2.4 Copper 102 5.2.5 Lead 103 5.2.6 Zinc 104 5.3 Correlation Analysis of Water Parameters 105 5.4 Heavy Metal Content in Sediment Samples 108 5.4.1 Cadmium 108 5.4.2 Cobalt 110 5.4.3 Chromium 111 5.4.4 Copper 112 5.4.5 Lead 113 5.4.6 Zinc 114 5.5. Pollution Load Index of Heavy Metals in Sediment 115 5.6 Geoaccumulation Index of Heavy Metals in Sediment 116 5.7 Heavy Metal Concentrations in Organs of Fishes 116 5.7.1 Cadmium 116 5.7.2 Cobalt 117 5.7.3 Chromium 118
5.7.4 Copper 119 5.7.5 Lead 119 5.7.6 Zinc 120 CHAPTER SIX 6.0 SUMMARY AND CONCLUSION 122 6.1 Summary 122 6.2 Conclusion 123 6.3 Recommendation 124 References 125 Appendices
1.0 INTRODUCTION The most often polluted of part of the environmental is the aquatic systems, which include the water, sediments, fishes and other faunas. This is because contaminants in the air, soil or on land ultimately end up in the aquatic systems via local precipitation, water runoff and leaching of rocks and solid wastes (Osibanjo et al., 1998). Sewage, industrial wastes, and agricultural chemicals such as fertilizers and pesticides, mineral and petroleum exploration and exploitation are however, the main causes of pollution in aquatic system (Apina, 1999). The aquatic environment with its water quality is considered the main factor controlling the state of health and disease in both cultured and wild fishes. Pollution of the aquatic environment by inorganic and organic chemicals is a major factor posing serious threat to the survival and quality of aquatic organism such as fish (Samir and Shaker, 2008). Water pollution occurs when a body of water is adversely affected due to addition of large amounts of materials to the water thereby making it unfit for intended use. Two forms of water pollution exist; point sources (anthropogenic) and non-point source (natural processes). Point sources of pollution occur when harmful substances are emitted directly into a body of water. This includes effluent sewage treatment works, or waste from factories. While non-point source delivers pollutants indirectly through environmental conditions, for example fertilizer or herbicide application is carried into streams by rain in form of run-off which in turn affects aquatic life (Maitera et al., 2011). Pollution arising from non-point sources account for majority of contaminants in streams and lakes.
Water quality plays a role in the distribution of fish. The importance of measuring physical, chemical and biological variables was considered at the technical consultation on enhancement of fisheries of small water bodies in Harare (Aweke and Taddes, 2004). The physicochemical characteristics of water are important parameters as they may directly or indirectly affect its quality and consequently its suitability for the distribution and production of fish and other aquatic animals (George et al., 2010). Water pollution in Nigeria has been attributed to the following sources: municipal and agricultural waste, urban run-off, organic pollutants and sediment pollutants. Environmental contaminants such as hydrocarbons, heavy metals and pesticides have been known to have direct toxic effects when released into the aquatic environment (Forstner et al., 1998). Over the last few decades, there has been growing interest in determining the levels of heavy metals in the marine environment; and attention was drawn to the measurement of contamination levels in public food supply, particularly fish, which serves as a major source of protein with low health implications (Kalay et al., 1999; Rose et al., 1999; Tariq et al., 1993). Heavy metals are non-biodegradable and once discharged into water bodies, can either be adsorbed on sediment particles or accumulated in aquatic organisms. Fish may absorb dissolved elements and heavy metals from surrounding water and food, which may accumulate in various tissues in significant amounts (Opaluwa and Umar, 2010) and elicit toxicological effects at critical targets. Also, fish may accumulate significant concentrations of metals in water even if those metals are below detection limit in routine water samples (Atolaye et al., 2006). Therefore, fish might prove a better indicator for detecting metals in freshwater contamination.
Sediments act as a sink and constant source of supply of pollutants that enter water bodies depending on physical, biological and chemical factors like temperature, pH, redox potential, ionic strength, anthropogenic input, type and concentration of organic and inorganic ligands and available surface area of adsorption (Jenneth et al., 1980; Davies et al. 1991). According to Haan et al. (1994), sediment is composed of many materials including individual primary particles, aggregates, organic materials and associated chemicals and is considered to be fully characterized when its shape, size, density, composition, texture, mineralogy and stability are known. There is a direct link between surface water and sediment contamination. Accumulated heavy metals or organic pollutants in sediment could be released back into the water with deleterious effects on human health. Sediments consist of sand, clay and silt components and since most anthropogenic contaminants (those associated with human activity) are also associated with clay and silt components, elevated concentrations of heavy metal in sediments can be a good indicator of man-induced pollution and the sources of pollution in aquatic systems (Forstner, et al., 1998). Metal ions can be incorporated into the sediment as flood occurs. This can form a food chain with higher concentration in aquatic organisms to a level that affects their physiological state. Trace metals such as Zn, Cu and Fe play a biochemical role in the health conditions of all aquatic plants and animals; therefore, they are essential in the aquatic environment in trace amounts. However, the consequent high concentration of heavy metals that may accumulate in the aquatic phase is a threat to humanity (Mason, 2002). The term “heavy metal” was in use as far back as 1817, when Gmelin divided the elements into non-metals, light metals and heavy metals. Heavy metals are those metals
whose densities fall within 5.308–22.000 g/cm3 (Hawkes, 1997). Heavy metals are found naturally in the earth, and become concentrated as a result of human activities and are known to be non-biodegradable. Common sources are from mining and industrial wastes; vehicle emissions; lead-acid batteries; fertilizers, paints and treated woods. Lead is the most prevalent heavy metal contaminant. As a component of tetra-ethyl, it was used extensively in gasoline during the 1930s-1970s. Lead levels in the aquatic environments of industrialised societies have been estimated to be two to three times those of pre-industrial levels. Heavy metals “can bind to vital cellular components, such as proteins, enzymes, and nucleic acids, and interfere with their functioning. Symptoms and effects can vary according to the metal or metal-compound, and the dose involved. Generally, long-term exposure to heavy metals can lead to carcinogenic, central and peripheral nervous system and circulatory effects (Neilen and Marvin, 2008). 1.1 Statement of Problem Lokoja town generally is faced with poor disposal system in that, the bank of the confluence is used as dumping ground for waste. It was also reported by marketers that quantity of fish in Lokoja market has drop drastically as compared to past years due to reduced amount of fish in the confluence. Visibility study then led to oral interview of fishermen at the confluence in which they attested that fishes were dying in the water leading to shortfall in quantity. This then led to the presumption that the fishes were dying possibly due to poor water quality which could either results in mortality or reduced their reproductive viability.
1.2 Justification of the Study As part of good environmental management, a periodical assessment of the environment is necessary considering the global warming of the world. Man‟s activities such as the use of chemicals in farm lands, discharge of sewage, use of chemicals for fishing etc, introduce pollutants to the aquatic system. Pollutants of high risk are heavy metals which are not biodegradable as such pose serious health implication when eventually consumed to a particular level. More so, the recent flood in the study area could also introduce some of these pollutants. In view of the above, this works is considered to be timely and relevant in investigating the pollution status of the rivers to enable policy makers come up with new management strategies of the rivers, and to also enlighten the public on the safety or otherwise of the water and fish from the study area within the time frame. 1.3 Aim and Objectives This research work is aimed at determining the physicochemical parameter and some heavy metals in water, sediments and three species of fish from River Niger, River Benue in the vicinity of their confluence point at Lokoja, Nigeria in order to establish the pollution status and the safety or otherwise of the fishes for human consumption. This aim will be achieved through the following set of objectives: 1) To examine the levels of the following physicochemical parameters in the water: pH, hardness, conductivity, turbidity, dissolved oxygen, biochemical oxygen demand, total dissolved solids and chemical oxygen demand in each of the river for one year on a quarterly basis;
2) To determine the concentrations of Cd, Co, Cr, Cu, Pb and Zn in the water of each river for a period of one year on a quarterly basis;
3) To determine the concentrations of Cd, Co, Cr, Cu, Pb and Zn in the sediment of each river for a period of one year on a quarterly basis; 4) To determine the concentrations of Cd, Co, Cr, Cu, Pb and Zn in the bones, brain and flesh of Clarias gariepinus (Catfish), Oreochromis niloticus (Tilapia) and Synodontis nigrita collected at the study area for a period of one year in each of the sampling period; 5) To assess the pollution indices of the water, sediment and fish with respect to the river and seasonal variation.
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