Assessment Of Heavy Metals And Polycyclic Aromatic Hydrocarbons In Water, Fish And Sediments Of Rivers Niger And Benue Confluence, In Lokoja, Kogi State, Central Nigeria

CHAPTER ONE

INTRODUCTION 

1.1 BACKGROUND TO THE STUDY    

Water pollution is any form of damage to the physical, chemical and biological characteristics of water which then affect the quality and suitability for any designated use or purpose^{1, 2}. Hence, it is an issue of great importance to protect the water sources from faecal, agricultural and industrial contamination or pollution which is continually threatening terrestrial and aquatic ecosystem due to increasing exposure of untreated wastes and chemical agents that are capable of causing damage to the environment^3-5. For example, it has been reported that storm water runoff from urban areas contains numerous pollutants like polycyclic aromatic hydrocarbons (PAHs), heavy metals (HMs), biocides and suspended solids which are toxic or harmful to the aquatic environment and also have potential negative ecological impacts on receiving waters⁶. The negative impacts include eutrophication, oxygen depletion and chronic toxic effect towards aquatic flora and Fauna. The contamination of the environment, particularly the aquatic ecosystems by harmful waste indicators such as heavy metals and polycyclic aromatic hydrocarbons is a serious problem in the society because the environment is a direct receptacle for waste products generated in the space within the environment^{7, 8}.

Here, however, heavy metals and polycyclic aromatic hydrocarbons are of particular concern due to their prevalent toxicity to aquatic organisms and are persistent in the environment^{9, 10}. The toxicity of the aquatic environment poses threat to man for the fact that safe and suitable potable water supply for drinking and other uses are lacking especially in the rural settlement in Nigeria which makes rural dwellers to depend on rivers, streams, natural ponds, Lakes, shallow hand dug wells and collection of rainfalls to meet their water needs as well as depending on aquatic animals which are capable of bio-accumulating pollutants like Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) as sources of food^11-13.

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) have been reported to have very carcinogenic, mutagenic and teratogenic effect on aquatic animals and humans who consume them or have direct encounter with the pollutants, especially with occupational exposure^{8, 14-19}, therefore it is consequential to take the environmental study of Heavy metals and polycyclic aromatic hydrocarbons very seriously to avert their possible effect and costly consequence of their contamination effects if not checked.

By definition, heavy metals (HMs) are loosely defined as members of a subset of elements that have density above 5.0 gcm^-3, exhibiting metallic properties and are chemically toxic to plants and animals^20-22. Examples of heavy metals include Mercury (Hg), lead (Pb), Iron (Fe), Cadmium (Cd), Copper (Cu), Arsenic (As), Thallium (TI), Manganese (Mn), Nickel (Ni), Vanadium (V) and Selenium (Se). The most important metals with regards to potential toxic effects are As, Cd, Cr, Hg, Pb and Zn; and Metals which in small quantities are essential for healthy growth but when in excess become hazardous include Co, Cu, Mn, Ni and Se respectively²³. Whereas, Polycyclic aromatic hydrocarbons (PAHs) on the other hand are large group of compounds containing two or more fused aromatic rings in linear, angular or clustered arrangement which sixteen of them are classified by the U.S environmental protection agency as pollutant of high priority having characteristics of persistence in the environment^24,25. The sixteen (16) priority polycyclic aromatic hydrocarbons (PAHs) include Naphthalene (NA), Acenaphthylene (ACY), Acenaphthene (ACE), fluorene (FL), phenanthrene (PH), Anthracene (AN), Fluoranthene (Flu), Pyrene (PY), Benzo[a] anthracene (BaA), Chrysene (CH), Benzo[b] fluoranthene (BbF), Benzo[K] fluoranthene (BKF), Benzo[a] pyrene (BaP), Indeno[1,2,3 – Cd] pyrene (IP), Dibenzo[ah] anthracene (DA) and Benzo [g,h,i] Perylene (BP)^{25, 26}.

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in nature and are daily being leached into rivers, lakes and oceans from natural and anthropogenic sources like rock weathering, waste water, industrial effluents, and incomplete combustion of organic materials, fossil fuel and petroleum. The pollutants are distributed in the rivers water, sediments and are bio-accumulated by the fishes and other aquatic animals in the water and this leads to bio-magnification of these pollutants in the food chain ^{7, 12, 26-29}.

The toxicity of heavy metals depends on the physical and chemical conditions which also affect the mobility and bioavailability. These conditions include pH, temperature, water hardness salinity, organic matter, redox, complexing ligands and ion strength. Polycyclic aromatic hydrocarbons (PAHs) toxicity is also enhanced by dissolved oxygen, hardness and are often found attracted to stable particles in the water which settles in the sediment and not in the water phase because PAHs is hydrophobic and lipophilic in character. Because of the above mentioned characteristics of these pollutants, several studies have shown that the sediment is usually highly toxic than the water component of aquatic environment hence, sediments are seen to be repository for these pollutants (PAHs and HMs) ^{6, 29-31}.

Therefore, this research work is focused on the determination or assessment of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in water, fish and sediments of the confluence of rivers Niger and Benue, in Lokoja, Kogi state, Nigeria.

 

 

 

 

1.2 Statement of the Problem

The main sources of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in the rivers and lakes are precipitation and urban runoff which leached these pollutants from both natural and anthropogenic sources into the water environment³². Five countries in the west-African region including Guinea, Mali, Niger, Benin and Nigeria have River Niger passed through their landmark and share in the usage of river Niger which originated from the Guinea highland in southern Guinea with Nigeria being the last country before the outpouring of the river into the Atlantic Ocean^33-34. There is this belief around Lokoja that river Niger is more polluted than the river Benue because river Benue is only share in usage between Cameroon where it originates from and Nigeria where it joins the river Niger in Lokoja, Kogi State³⁵. But, it has beenreported that the high rate of untreated effluent discharged into River Benue at Makurdi is alarming and that the rural dwellers uses this river as toilet as well as means of getting rid of their solid waste, and this water is the main source of drinking water to some of them as well as source of the fish they eat and export for their income³⁶ and the degradation of water quality is a significant problem for the River Niger because of the growth of large cities along the river’s banks which has not been accompanied by development of wastewater collection and treatment plants, whether for domestic or industrial wastewater³³.Therefore, it becomes pertinent to check the effect of pollution on the river body and the aquatic lives in the river respectively to avoid the effect of the pollution in man who depends on the fishes of this river for food.

Lokoja is a community located at the bank of river Niger at the confluence of rivers Niger and Benue in Kogi state central Nigeria. The native people of Lokoja are predominantly farmers and fishermen. In recent times, the city is experiencing unusually high temperatures, problems of desertification and change in local vegetation, excessive deforestation, erosion and siltation of the river leading to reduced fish catches and reduced fish catches is reported to be a result of pollution from various discharge of municipal wastes/sewage and other pollution^37-39. It was also established that toxic effects are also experienced due to detergents, petroleum products and domestic factories⁴⁰. River Niger at the Lokoja axis, upstream from the confluence do experience inflow of pollutants from solid wastes from the two major markets opposite the river bank and domestic wastes from the residents of the community. Also contributing chemical pollutants are agrochemicals from the agricultural activities taking place on the river bank especially the agricultural scheme launched by the Kogi state government. Similarly, pollutants are added to the waters by all other countries and states that share in the usage of the rivers Niger and Benue before getting to Lokoja, Kogi State.

1.3 Aim and Objectives of the Research

The aim of this research study is to ascertain the level of pollution of the confluence of rivers, Niger and Benue, and the objectives are as follows: to

1. Evaluate the levels of PAHs in water, fish and sediments samples from the rivers confluence.
2. Assess the total levels of Heavy Metals in the water, sediments and fish samples selected.
3. Determine Transfer factor (TF) of HMs from sediment to fish and therefore determine the bioaccumulation of the pollutants.
4. Assess the possible health hazard posed by ingestion of fish and use of the river waters studied
5. Determine the ecological risk index (ERI), Index of geo-accumulation, Contamination factor and Pollution load index posed by the heavy metals in the sediments and
6. Compare the results with the set standards for water and fish by regulatory agencies.

 

1.4 Purpose of the study

The purpose of this research study is to understand and ascertain the different level or quantity of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) that goes into the different rivers from the natural and anthropogenic sources and the contribution of the pollutants by the two rivers (Niger and Benue) to the downstream of the confluence in addition to the aim of the study, in order to ascertain the level of danger posed by these rivers based on the level of pollutants contributed by the rivers. Also, the level of the pollutants in the different rivers is of significance to the determination of the ^river that contributes more pollutants to the fish and other aquatic animals in the river, downstream of the confluence.

1.5 Significance of the Study

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution studies have been conducted in other areas downstream of River Niger but none is yet conducted at the confluence of rivers, Niger and Benue even though large numbers of fishes are caught from this axis and sold to the Nigerian people for consumption and export.  Hence, the work will:

1. for the first time, provide baseline data on heavy metals (HM) and polycyclic aromatic hydrocarbons (PAHs) for this area of study.
2. generate data to be used to assess the impact of these heavy metals (HM) and polycyclic aromatic hydrocarbons (PAHs) in water and fish consuming populace in the area of study.
3. therefore, the result could be used by the Kogi State and Nigerian governments in Legislation as regards to waste disposal and waste management.
4. the result will be of use to Health management practitioners in the diagnoses of certain diseases prevalent in the area of study which could be caused by heavy metals.

1.6 Scope of the Study

The study was designed to assess and evaluate the level of Heavy Metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) contamination in the water, fish and sediments of rivers Niger and Benue confluence in Lokoja, Kogi State, central Nigeria using atomic absorption spectrophotometer for the heavy metals determination and gas chromatography coupled with mass spectrometry (GC-MS) techniques for the determination of the polycyclic aromatic hydrocarbons (PAHs) respectively^{41, 42}. The physico-chemical characteristics of the media were also measured using appropriate probes since they are the factors responsible for the environmental mobility and bioavailability of the pollutants. The work was limited to a dry and rainy season for HMs analysis and a rainy season for PAHs analysis and to the confluence of rivers Niger and Benue and three kilometers (3 km) upstream and downstream of the confluence respectively.

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