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.

Thesis Overview

<p> INTRODUCTION<br>1.1 BACKGROUND TO THE STUDY<br>Water pollution is any form of damage to the physical, chemical and biological characteristics of<br>water which then affect the quality and suitability for any designated use or purpose1, 2. Hence, it is<br>an issue of great importance to protect the water sources from faecal, agricultural and industrial<br>contamination or pollution which is continually threatening terrestrial and aquatic ecosystem due to<br>increasing exposure of untreated wastes and chemical agents that are capable of causing damage to<br>the environment3-5. For example, it has been reported that storm water runoff from urban areas<br>contains numerous pollutants like polycyclic aromatic hydrocarbons (PAHs), heavy metals (HMs),<br>biocides and suspended solids which are toxic or harmful to the aquatic environment and also have<br>potential negative ecological impacts on receiving waters6. The negative impacts include<br>eutrophication, oxygen depletion and chronic toxic effect towards aquatic flora and Fauna. The<br>contamination of the environment, particularly the aquatic ecosystems by harmful waste indicators<br>such as heavy metals and polycyclic aromatic hydrocarbons is a serious problem in the society<br>because the environment is a direct receptacle for waste products generated in the space within the<br>environment7, 8.<br>Here, however, heavy metals and polycyclic aromatic hydrocarbons are of particular concern due to<br>their prevalent toxicity to aquatic organisms and are persistent in the environment9, 10. The toxicity of<br>the aquatic environment poses threat to man for the fact that safe and suitable potable water supply<br>for drinking and other uses are lacking especially in the rural settlement in Nigeria which makes<br>rural dwellers to depend on rivers, streams, natural ponds, Lakes, shallow hand dug wells and<br>1 7<br>collection of rainfalls to meet their water needs as well as depending on aquatic animals which are<br>capable of bio-accumulating pollutants like Heavy metals (HMs) and polycyclic aromatic<br>hydrocarbons (PAHs) as sources of food11-13.<br>Polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) have been reported to have very<br>carcinogenic, mutagenic and teratogenic effect on aquatic animals and humans who consume them<br>or have direct encounter with the pollutants, especially with occupational exposure8, 14-19, therefore it<br>is consequential to take the environmental study of Heavy metals and polycyclic aromatic<br>hydrocarbons very seriously to avert their possible effect and costly consequence of their<br>contamination effects if not checked.<br>By definition, heavy metals (HMs) are loosely defined as members of a subset of elements that have<br>density above 5.0 gcm-3, exhibiting metallic properties and are chemically toxic to plants and<br>animals20-22. Examples of heavy metals include Mercury (Hg), lead (Pb), Iron (Fe), Cadmium (Cd),<br>Copper (Cu), Arsenic (As), Thallium (TI), Manganese (Mn), Nickel (Ni), Vanadium (V) and<br>Selenium (Se). The most important metals with regards to potential toxic effects are As, Cd, Cr, Hg,<br>Pb and Zn; and Metals which in small quantities are essential for healthy growth but when in excess<br>become hazardous include Co, Cu, Mn, Ni and Se respectively23. Whereas, Polycyclic aromatic<br>hydrocarbons (PAHs) on the other hand are large group of compounds containing two or more fused<br>aromatic rings in linear, angular or clustered arrangement which sixteen of them are classified by the<br>U.S environmental protection agency as pollutant of high priority having characteristics of<br>persistence in the environment24,25. The sixteen (16) priority polycyclic aromatic hydrocarbons<br>(PAHs) include Naphthalene (NA), Acenaphthylene (ACY), Acenaphthene (ACE), fluorene (FL),<br>phenanthrene (PH), Anthracene (AN), Fluoranthene (Flu), Pyrene (PY), Benzo[a] anthracene (BaA),<br>Chrysene (CH), Benzo[b] fluoranthene (BbF), Benzo[K] fluoranthene (BKF), Benzo[a] pyrene<br>1 8<br>(BaP), Indeno[1,2,3 – Cd] pyrene (IP), Dibenzo[ah] anthracene (DA) and Benzo [g,h,i] Perylene<br>(BP)25, 26.<br>Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in nature and are<br>daily being leached into rivers, lakes and oceans from natural and anthropogenic sources like rock<br>weathering, waste water, industrial effluents, and incomplete combustion of organic materials, fossil<br>fuel and petroleum. The pollutants are distributed in the rivers water, sediments and are bioaccumulated<br>by the fishes and other aquatic animals in the water and this leads to bio-magnification<br>of these pollutants in the food chain 7, 12, 26-29.<br>The toxicity of heavy metals depends on the physical and chemical conditions which also affect the<br>mobility and bioavailability. These conditions include pH, temperature, water hardness salinity,<br>organic matter, redox, complexing ligands and ion strength. Polycyclic aromatic hydrocarbons<br>(PAHs) toxicity is also enhanced by dissolved oxygen, hardness and are often found attracted to<br>stable particles in the water which settles in the sediment and not in the water phase because PAHs is<br>hydrophobic and lipophilic in character. Because of the above mentioned characteristics of these<br>pollutants, several studies have shown that the sediment is usually highly toxic than the water<br>component of aquatic environment hence, sediments are seen to be repository for these pollutants<br>(PAHs and HMs) 6, 29-31.<br>Therefore, this research work is focused on the determination or assessment of heavy metals and<br>polycyclic aromatic hydrocarbons (PAHs) in water, fish and sediments of the confluence of rivers<br>Niger and Benue, in Lokoja, Kogi state, Nigeria.<br>1 9<br>1.2 Statement of the Problem<br>The main sources of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in the rivers<br>and lakes are precipitation and urban runoff which leached these pollutants from both natural and<br>anthropogenic sources into the water environment32. Five countries in the west-African region<br>including Guinea, Mali, Niger, Benin and Nigeria have River Niger passed through their landmark<br>and share in the usage of river Niger which originated from the Guinea highland in southern Guinea<br>with Nigeria being the last country before the outpouring of the river into the Atlantic Ocean33-34.<br>There is this belief around Lokoja that river Niger is more polluted than the river Benue because<br>river Benue is only share in usage between Cameroon where it originates from and Nigeria where it<br>joins the river Niger in Lokoja, Kogi State35. But, it has beenreported that the high rate of untreated<br>effluent discharged into River Benue at Makurdi is alarming and that the rural dwellers uses this<br>river as toilet as well as means of getting rid of their solid waste, and this water is the main source of<br>drinking water to some of them as well as source of the fish they eat and export for their income36<br>and the degradation of water quality is a significant problem for the River Niger because of the<br>growth of large cities along the river’s banks which has not been accompanied by development of<br>wastewater collection and treatment plants, whether for domestic or industrial<br>wastewater33.Therefore, it becomes pertinent to check the effect of pollution on the river body and<br>the aquatic lives in the river respectively to avoid the effect of the pollution in man who depends on<br>the fishes of this river for food.<br>Lokoja is a community located at the bank of river Niger at the confluence of rivers Niger and Benue<br>in Kogi state central Nigeria. The native people of Lokoja are predominantly farmers and fishermen.<br>In recent times, the city is experiencing unusually high temperatures, problems of desertification and<br>change in local vegetation, excessive deforestation, erosion and siltation of the river leading to<br>2 0<br>reduced fish catches and reduced fish catches is reported to be a result of pollution from various<br>discharge of municipal wastes/sewage and other pollution37-39. It was also established that toxic<br>effects are also experienced due to detergents, petroleum products and domestic factories40. River<br>Niger at the Lokoja axis, upstream from the confluence do experience inflow of pollutants from solid<br>wastes from the two major markets opposite the river bank and domestic wastes from the residents<br>of the community. Also contributing chemical pollutants are agrochemicals from the agricultural<br>activities taking place on the river bank especially the agricultural scheme launched by the Kogi<br>state government. Similarly, pollutants are added to the waters by all other countries and states that<br>share in the usage of the rivers Niger and Benue before getting to Lokoja, Kogi State.<br>1.3 Aim and Objectives of the Research<br>The aim of this research study is to ascertain the level of pollution of the confluence of rivers, Niger<br>and Benue, and the objectives are as follows: to<br>a) Evaluate the levels of PAHs in water, fish and sediments samples from the rivers confluence.<br>b) Assess the total levels of Heavy Metals in the water, sediments and fish samples selected.<br>c) Determine Transfer factor (TF) of HMs from sediment to fish and therefore determine the<br>bioaccumulation of the pollutants.<br>d) Assess the possible health hazard posed by ingestion of fish and use of the river waters<br>studied<br>e) Determine the ecological risk index (ERI), Index of geo-accumulation, Contamination factor<br>and Pollution load index posed by the heavy metals in the sediments and<br>2 1<br>f) Compare the results with the set standards for water and fish by regulatory agencies.<br>1.4 Purpose of the study<br>The purpose of this research study is to understand and ascertain the different level or quantity of<br>polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) that goes into the different rivers<br>from the natural and anthropogenic sources and the contribution of the pollutants by the two rivers<br>(Niger and Benue) to the downstream of the confluence in addition to the aim of the study, in order<br>to ascertain the level of danger posed by these rivers based on the level of pollutants contributed by<br>the rivers. Also, the level of the pollutants in the different rivers is of significance to the<br>determination of the river that contributes more pollutants to the fish and other aquatic animals in the<br>river, downstream of the confluence.<br>1.5 Significance of the Study<br>Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution studies have been<br>conducted in other areas downstream of River Niger but none is yet conducted at the confluence of<br>rivers, Niger and Benue even though large numbers of fishes are caught from this axis and sold to<br>the Nigerian people for consumption and export. Hence, the work will:<br>a) for the first time, provide baseline data on heavy metals (HM) and polycyclic aromatic<br>hydrocarbons (PAHs) for this area of study.<br>b) generate data to be used to assess the impact of these heavy metals (HM) and polycyclic<br>aromatic hydrocarbons (PAHs) in water and fish consuming populace in the area of study.<br>2 2<br>c) therefore, the result could be used by the Kogi State and Nigerian governments in Legislation<br>as regards to waste disposal and waste management.<br>d) the result will be of use to Health management practitioners in the diagnoses of certain<br>diseases prevalent in the area of study which could be caused by heavy metals.<br>1.6 Scope of the Study<br>The study was designed to assess and evaluate the level of Heavy Metals (HMs) and polycyclic<br>aromatic hydrocarbons (PAHs) contamination in the water, fish and sediments of rivers Niger and<br>Benue confluence in Lokoja, Kogi State, central Nigeria using atomic absorption spectrophotometer<br>for the heavy metals determination and gas chromatography coupled with mass spectrometry (GCMS)<br>techniques for the determination of the polycyclic aromatic hydrocarbons (PAHs)<br>respectively41, 42. The physico-chemical characteristics of the media were also measured using<br>appropriate probes since they are the factors responsible for the environmental mobility and<br>bioavailability of the pollutants. The work was limited to a dry and rainy season for HMs analysis<br>and a rainy season for PAHs analysis and to the confluence of rivers Niger and Benue and three<br>kilometers (3 km) upstream and downstream of the confluence respectively.<br>2 3 <br></p>