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The concentration of six heavy metals and six of sixteen (16) US EPA priority polycyclic aromatic
hydrocarbons (PAHs) in water, fish and sediment samples of the confluence of rivers Niger and
Benue were investigated in triplicates using atomic absorption spectrophotometer (AAS) for the
heavy metals determination and gas chromatography coupled with mass spectrometer detector for
the PAHs after acid digestion of the samples for heavy metals,liquid-liquid and solid-liquid
extraction for the PAHs samples. The heavy metals were profiled for dry and rainy seasons whereas,
the PAHs concentration in the samples were profiled for only rainy season in five sample locations.
The concentration of the metals in water across the locations ranged from Cd (0.038 to 0.089),
Cr(0.106 to 0.240), Cu(0.092 to 0.0164), Fe(0.682 to 0.878), Pb(0.058 to 0.309) mg/L with
distribution pattern of Zn>Fe>Pb>Cr>Cu>Cd for the dry season water samples and Cd(ND to
0.027), Cr(ND), Cu(ND to 0.021), Fe(2.236 to 13.634), Pb(0.119 to 0.205) and Zn(0.121to 0.216)
mg/L with distribution patter of Fe>Zn>Pb>Cd>Cu>Cr during the rainy season.The sediments’
metals concentration across locations ranged from Cd(2.189 to 2.893), Cr(4.367 to 9.927),
Cu(3.433 to 6.780), Fe(233.210 to 254.160), Pb(8.967 to 17.420) and Zn(6.027 to 20.380) mg/kg
with distribution pattern of Fe>Zn>Pb>Cr>Cu>Cd during the dry season and Cd (0.321 to 1.024),
Cr(0.456 to2.662), Cu(ND to 8.599), Fe(1.234 to 2.062), Pb(8.721 to 17.737) and Zn(12.350 to
66.343)mg/kg with distribution pattern of Zn>Pb>Cu>Cr>Fe>Cd for the rainy season samples.The
mean concentration of the metals in Catfishduringthe dry and rainy seasons were Cd(3.367 and
0.666) Cr(- and 0.293), Cu(7.050 and 4.952), Fe(44.775 and 1.230), Pb(3.842 and 8.683) and
Zn(63.625 and 85.266)mg/kg and the Tilapia mean concentration values for dry and rainy seasons
were as follows Cd(4.850 and 0.453), Cr(- and 0.164), Cu(8.042 and 1.658), Fe(44.108 and 0.198),
Pb(4.717 and 6.704), Zn(63.742 and 40.680) mg/kg.The concentrations of the PAHs in water across
locations ranged from Nap(ND to 0.543), Ph(ND to 0.083) Ant (ND to 0.083), BbF(0.080 to 0.093),
BkF(0,083 to 0.093) and BaP(0.083 to 0.113) mg/L with distribution pattern of
Nap>BaP>BbF=BkF>Ant=Ph.The concentration of PAHs in sediment across the locations ranged
as follows Nap(ND to 2.210), Ph(ND to 0.053), Ant(ND to 0.053), BbF(0.053 to 0.383), BkF(0.053
to 0.110) and BaP(ND to 0.053)mg/kg with distribution pattern of
Nap>BbF>BkF>Ph=Ant=Bap.The mean concentration value of PAHs in Catfish and Tilapia were
Nap(2.383 and 1.947), Ph(0.050 and 0.057), Ant(0.057 and 0.057), BbF(0.043 and ND), BkF(0.043
and ND) and BaP(0.050 and ND).The result of the heavy metals in water and fish samples were
tested for non-carcinogenic and carcinogenic health risk using health risk assessment models such
as hazard quotient (HQ), Total hazard index(THI) cancer risk(CR) and cancer risk index(CRI). The
health risk assessment showed that Cd andPb are of great concern.The ecological risk factors for
the concentration of heavy metal and PAHs in sediment were estimated using ecological risk models
such as geo-accumulation index (I-geo), contamination factor (CF), single ecological risk factor(ER),
ecological risk index (RI), pollution load index (PLI) and polycyclic aromatic hydrocarbons
pollution index (PPI).The results showed that sediment pollution ranged from no heavy metals
pollution, low risk and very high risk pollution.The heavy metals and PAHs data were subjected to
ANOVA at probability values less than 0.05 (P<0.05) level of significance.The heavy metals
concentration in sediment were significantly different but, HMsand PAHs were all not different
significantly in the water and fish respectively. The data generated for HMS and PAHs were
correlated for source identification and the correlation showed that the majority of the pollutants
were from the same source.



Title page i
Certification ii
Dedication iii
Acknowledgement iv
Abstract v
Table of Contents vi
List of Tables x
List of Figure xiii
List of Abbreviation xiv
1.0 Background to the Study 1
1.2 Statement of the Problem 4
1.3 Aim and Objectives of the Research 5
1.4 Purpose of the Study 6
1.5 Significance of the Study 6
1.6 Scope of the Study 7
2.1 General Over View 8
2.2 Heavy Metals 9
2.3 Review on Heavy Metals in Water, Sediments and Fish 10
2.4 Sources of Heavy Metals in Aquatic Ecosystem 12
2.4.1 Point Sources of Pollution 12
2.4.2 Nonpoint Sources of Pollution 12
2.5 Factors Affecting Mobility, Bioavailability and Bio-toxicity of Heavy Metals 15
2.5.1 Temperature 16
2.5.2 pH 16
2.5.3 Cation Exchange Capacity (CEC) 17
2.5.4 Moistune 17
2.5.5 Redox Potential 18
2.5.6 Partition Coefficient 18
2.5.7 Organic Matter 18
2.6 Environmental Health Impact of Heavy Metals 19
2.6.1 Arsenic (AS) 19
2.6.2 Copper (Cu) 20
2.6.3 Cadmium (Cd) 20
2.6.4 Lead (Pb) 21
2.6.5 Mercury (Hg) 21
2.6.6 Iron (Fe) 23
2.6.7 Vanadium (V) 23
2.6.8 Zinc (Zn) 23
2.6.9 Nickel (Ni) 24
2.7 Techniques for Heavy Metals Determination 24
2.7.1 Atomic Absorption Spectrometry (AAS) 24
2.7.2 Inductively Coupled Plasma Atomic Emission Spectrometry 25
2.7.3 Inductively Coupled Plasma Spectrometry (ICP-MS) 26
2.8 Polycyclic Aromatic Hydrocabons (PAHs) 26
2.8.1 Nomenclatune of Polycyclic Aromatic Hydrocarbons 28
2.8.2 Review of Works on PAHs in Water Sediment and Fish 30
2.8.3 Sources of PAHs in the Environment 35
2.8.4 Environmental Health Impact of PAHs 36
2.9 Technique for PAHs Determination: Gas CHroatograp 37
2.9.1 Gas Chromatograph Coupled with Mass Spectrometer GC-MS 38
3.1 Materials 40
3.2 Description of Study Area 40
3.3 Samples and Sampling Technique 42
3.4 Physicochemical Parameters 43
3.5 Sample Preparation for Heavy Metals Determination 43
3.5.1 Water Samples Preparation for Heavy Metals Determination 43
3.5.2 Fish Samples Processing and Digestion for Heavy Metals Determination 44
3.5.3 Sediment Samples Preparation for Heavy Metals Determination 45
3.5.4 Atomic Absorption Spectrometer Conditions for Analysis 45
3.6 Sample Preparaton for PAHs Quantification 46
3.6.1 Water Samples Preparation for PAHs Quantification 46
3.6.2 Fish Samples Preparation for PAHs Quantification 47
3.6.3 Sediment Samples Preparation for PAHs Quantification 47
3.6.4 Gas Chromatography – Mass Spectrometry Conditions 47
3.7 Statistical Data Analysis and Quality Control Studies 48
3.7.1 Statistical Data Analysis and Precision 48
3.7.2 Quality Control Studies /Spike and Recovery 48
3.7.3 The limit of detection (LOD) and Quantitation (LOQ) 49
3.8 Risk Assessment Models for Carcinogenic and Non-Carcinogenic Risk Factors 49
3.8.1 The non-carcinogenic risk: Hazard Quotient (HQ) 50
3.8.2 Total Hazard Index (THI) 52
3.8.3 Carcinogenic Health Effect 52
3.8.4 Bioaccumulation Factor and Transfer Factor 54
3.9 Ecological Risk Assessment of HMs in the rivers’ Sediments 55
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3.9.1 PAHs Pollution Index (PPI) 55
3.9.2 Potential Ecological Risk Index (RI) 55
3.9.3 Geo-accumulation Index (I-geo) 57
3.9.4 Pollution Load Index (PLI) and Contamination Factor (CF) 58
3.9.5 Contamination Factor (CF) 58
4.1 Results of Physicochemical Parameters 60
4.2 Results of quality control Studies/Recovery Analysis 61
4.3 Results of the Concentration of heavy Metals in Water Sediment and Fish 62
4.4 Results of the Concentration of PAHs in Water, Fish and Sediment 71
4.5 Results of Estimated daily intake (EDI) of Heavy Metals and Polycyclin Aromatic
Hydrocarbons through Ingestion of water and Fish and cancer risk (CR) for adult
and a child during the dry and rainy season 76
4.6 The results of the Ecological risk Assessment of Heavy Metals in Sediment. 82
4.7 Statistical Correlation and Source Identification of HMs and PAHs 85
4.8 Discussion 94
4.8.1 Data analysis: Analysis of variance (ANOVA) 94
4.8.2 Correlation Analysis and Source Identification 94
4.8.3 Concentration of Heavy Metals in Water and Fish Samples vis-à-vis Human Health
Risk Assessment
4.8.4 Concentration of Heavy Metals in Sediment Samples vis-à-vis Ecological Risk Assessment
4.8.5 Polycyclic aromatic Hydrocarbons in Water Fish and Sediments Samples vis-à-vis
Health and Ecological Risk Assessment 103
5.0 Conclusion and Recommendation 105




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 purpose1, 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 environment3-5. 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
environment7, 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 environment9, 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
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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 food11-13.
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 exposure8, 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
animals20-22. 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 environment24,25. 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
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(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 bioaccumulated
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.
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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 Ocean33-34.
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
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reduced fish catches and reduced fish catches is reported to be a result of pollution from various
discharge of municipal wastes/sewage and other pollution37-39. 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
a) Evaluate the levels of PAHs in water, fish and sediments samples from the rivers confluence.
b) Assess the total levels of Heavy Metals in the water, sediments and fish samples selected.
c) Determine Transfer factor (TF) of HMs from sediment to fish and therefore determine the
bioaccumulation of the pollutants.
d) Assess the possible health hazard posed by ingestion of fish and use of the river waters
e) 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
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f) 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:
a) for the first time, provide baseline data on heavy metals (HM) and polycyclic aromatic
hydrocarbons (PAHs) for this area of study.
b) 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.
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c) therefore, the result could be used by the Kogi State and Nigerian governments in Legislation
as regards to waste disposal and waste management.
d) 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 (GCMS)
techniques for the determination of the polycyclic aromatic hydrocarbons (PAHs)
respectively41, 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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