ABSTRACT
The levels of Pb, Cr, Ni Zn, Fe,Cu, Co, Mn, Cd and Hg were determined in
water, Sediment and Fish Samples taken monthly for six months from march 2002 –
August 2002, from the Southern basin of Kainji Lake and below the dam (Jebba
Lake), in order to determine the pollution status of the Lake and the impact of the
hydro-power plant as per heavy metal discharge. Flame AAS and EDXRFS
techniques were used for the analysis and both techniques indicate the order of
relative abundance as Fe > Mn > Cr > Pb > Co > Ni > Cu > Zn > Cd > Hg > in water;
Fe > Mn > Zn > Ni > Co > Cr > Cu > Pb > Cd > Hg in sediments; and Fe, Zn > Mn >
Cu > Ni > Co > Cr > Pb > Cd > Hg in fish.
The level of these metals in all the samples were within the tolerable and
internationally acceptable limits. This implies that the Lake is safe. The results also
do not show the hydro-power plant as a major source of these metals in the Lakes.
TABLE OF CONTENTS
Declaration ………………………………………………………………….. ii
Certification ……………………………………………………………………… iii
Dedication …………………………………………………………………….. iv
Acknowledgement …………………………………………………………… v
Abstract. …………………………………………………………………… vi
Table of Contents …………………………………………………………… vii
List of Tables ………………………………………………………………….. x
List of Figures ………………………………………………………….. xi
List of Plates …………………………………………………………………. xvi
CHAPTER ONE
INTRODUCTION
1.1 Background Study ………………………………………………………. 1
1.2 History and Description of the Kainji Lake…..………………….. …….. 5
1.3 The Niger River, it’s Discharge and Sediment Transport……………. 7
1.4 Objectives of the Research………………………………………………. 8
CHAPTER TWO
LITERATURE REVIEW
2.1 Heavy Metals and Their Sources………………………………………… 12
2.1.1 Geo-chemical Sources……………………………………………………. 12
2.1.2 Anthropogenic Sources …………………………………………….. 13
2.2 Distribution of Heavy Metals in the Aquatic Environment……………. 14
viii
2.2.1 Heavy Metals in Lake Waters……………………………………………. 14
2.2.2 Heavy Metals in Sediments………………………………………………. 15
2.2.3 Heavy Metals Accumulation in Fishes………………………………….. 16
2.3 Hydro-electric Power Generation………………………………………. 17
2.3.1 Environmental Impact of Hydro-Power Generation…………………… 17
CHAPTER THREE
MATERIALS AND METHODS
3.1 Preamble………………………………………………………………… 19
3.2 Description of Sampling Area…………………………………………. 19
3.3 Sample Treatment …………………………………………………… 21
3.3.1 Water Samples………………………………………………………… 21
3.3.2 Sediment Samples……………………………………………………. 22
3.3.3 Fish Samples………………………………………………………….. 22
3.4 Sample Preparation …………….……………………………………. 23
3.4.1 Wet Digestion of Sediments …………..……………………………….. 23
3.4.2 Wet Digestion of Fish. ………………………………………………… 23
3.5 Sample Analysis. ……………………………………………………. 23
3.5.1 Preparation of Standard Solutions for AAS……………………….. 23
3.5.2 Preamble ………………………………..………………………. 23
3.5.3 Water and Fish ………………………………………………….. 27
3.5.4 Sediments…………………………………………………………….. 27
3.6 Statistical Analysis…………………………………………………… 28
ix
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 Preamble………………………………………………………………… 29
4.1.1 Water…………………………………………………………………. 29
4.2 Preamble….…………………………………………………………….. 40
4.2.1. Sediments……………………………………………………………….. 40
4.3 Preamble……………………………………………………………… 50
4.3.1 Fish……………………………………………………………………. 50
4.4 Summary of Metal Levels in the Samples………………………… 56
4.5 Comparison of Mean Levels of Heavy Metals in Water,
Sediments and Fish………………………………………………… 57
4.6 Comparison of mean levels of heavy metals in Tilapia
(Oreochromis. niloticus) and Chrysicthys (Chrysicthys. auratus)…… 60
4.7 Comparison of Mean Heavy Metal Levels between
Kainji Lake and Jebba Lake……………………………………….. 61
4.8 Comparison of Results from AAS and EDXRFS………………. 62
CHAPTER FIVE
CONCLUSION
5.1 Summary of Findings……………………….…………………….. 64
References……………………………………………………………….. 66
Appendices …………………………………………………… 78
x
LIST OF TABLES
Table I: Operating Condition of the Atomic Absorption
Spectrophoto-meter…………………………………………………. 26
xi
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND STUDY
Problems such as the destruction of environments, soil erosion and the
extinction of species are important for the future of mankind, yet it is pollution which
arouses interests because of its direct impact on health, food supply, degradation of
items of cultural heritage, overt effects on forests, rivers, coastlines and ecosystems
(Alloway and Ayres, 1993).
Pollution is the introduction by man into the environment of substances or
energy liable to cause hazards to human health, harm living resources and
ecological systems, damage to structures, amenity or interference with legitimate
uses of the environment (Holdgate, 1979). Substances that cause pollution are
termed pollutants. Environmental pollution is insidious and its harmful effects
become apparent after long periods of exposure. Many toxic chemicals are used in
our daily lives because their particular use is not thought to constitute a hazard to
health and the advantage of using them out weigh their possible risks. Sometimes
materials which are considered as harmless may constitute pollutants if they are
present in excess or in the wrong place at the wrong time (BMA, 1991). Certain
substances may also be present in the environment not causing any obvious harm
but their careful analysis and diagnosis will reveal their harmful effect.
Pollutants are responsible for many illnesses such as cancer, neurological
conditions, chronic bronchitis, asthma and so on (IAEA, 1976). For these reasons
pollutants have been classified into primary which exert harmful effects in the form in
2
which they enter the environment, and secondary pollutants which are synthesized
as a result of chemical processes, from less harmful precursors in the environment.
Most pollutants enter the environment as emissions or as discharges (to water
bodies) either from discrete point (e.g. factory) or diffuse sources e.g. run-off from
agricultural land. The effect of any pollutant discharged into the environment
depends on its toxicity, persistence, dispersion properties, chemical reactions
including decomposition that the compound undergoes, tendency to be bioaccumulated
in food chains and ease of control. Every pollution has a pathway which
involves the pollutant, the source, the medium of transport (air, water, land) and the
target (organisms, ecosystem) ( Holdgate, 1979).
Most industrial and municipal wastes end up in rivers, Lakes and seas. Lakes
and reservoirs are natural sinks for nutrients, metals, salts and organic matter which
enter through storm run-off, controlled waste discharges and feeder streams.
Significant concentration of these pollutants can accumulate in bottom sediment over
the years. A number of complex biological and chemical processes occur between
the contaminants, the bottom sediments and overlying waters. These processes and
associated reactions exert a significant oxygen demand satisfied primarily by
dissolved oxygen (DO) in overlying waters. (Hayes et al., 1998).
Lakes and surface water reservoirs are important freshwater resource. They
provide water for domestic and for irrigation. They provide an essential resource for
industry and a source of renewable energy in the form of hydro-power. Lakes are a
source of essential protein in the form of fish and a home to significant elements of
the world’s biological diversity. They are important source for tourism and recreation,
3
and are culturally and aesthetically important for people throughout the world. They
play important role in flood control (UNEP, 1994).
Lakes attract human settlement hence pollution from agriculture run-off and
toxic chemicals are common. Unlike the rapidly flowing water in rivers, water remains
in Lakes for months or years is easily polluted. Water quality in Lakes is degraded
when human activities are intensified and there is population increase in the
drainage basin around them. The level of deterioration of the environment in any
community depends on the effect of population, affluence and technology (Meadows
et al., 1992).
The Kainji Lake is important to Nigeria in many respects. It’s establishment
was a dream come true. (Olagunju, 1972) had this to say about the dam:
Men have dreamed, men have planned,
Men have toiled to bring to life,
The vision of those who first saw,
The Potential of the River Niger,
For harnessing its waters,
To provide Power for progress.
The completion of the project represented the foundation stone for the
modernization of Nigeria (Gowon, 1969). The hydro-electricity generated from the
dam provides the energy supply for both industrial and domestic use. It is source of
fish supply. The flood control achieved as a result of the construction of the dam has
led to expansion of irrigation agriculture in areas down stream. Its excellent
panoramic view makes it an attraction for tourism (NEPA, 1977).
4
The expansion of agriculture around the Lake has its attendant
consequences. Addition of chemical substances to soils and crops has become a
general practice in agriculture. The purpose of the chemicals are the improvement of
the nutrient supply in soil (fertilizers) or crop protection and diseases control
(Pesticides). These practices may result in soil degradation as result of
accumulation of the chemical substances at undesirable levels. Fertilizers are
usually not sufficiently purified during the processes of manufacture, for economic
reasons. They usually contain several impurities amongst them heavy metals
(Eugenia et al., 1996). Heavy metals also form part of the active compounds of
pesticides.
Excess of heavy metals in soils is caused by using fertilizers, metallopeslicides
and sewage sludges or by industrial activities and the concentration of
heavy metals in soils can increase by repeated and excessive fertilizer and pesticide
applications. Some countries have set tolerance limits on heavy metal addition to soil
because their long-term effects are unknown (Berth and L’Hermite, 1987). These
limits are usually established for the tillage layer of soil where most crop-root activity
occurs.
The Kainji Lake is formed from river Niger and is located at about 3200 Km
South of its source (NEDECO, 1959) and receives water from the numerous
inflowing rivers that form its tributaries. The Lake receives inflowing water from
Malende, Kpan, Wata, Swashi streams and Teme, Dero streams as well as storm
run-off from Yelwa, Mahuta, Ulaira, Gafara, Wara, Garafini, Monai and Anfani
settlements (Obot, 1984). (Fig 1.1).
5
In this study, water, sediment and fish samples taken from Kainji Lake and
below the dam (Jebba Lake) are examined in order to determine the level of heavy
metals such as Pb, Cr, Cd, Cu, Zn, Hg, Fe, Co, Mn and Ni. The extension of
sampling to below the dam (Jebba Lake) is to gauge relatively the level of
contribution as per heavy metal discharge into the Lake by the hydro-generation
station. Both flame atomic absorption spectrometry (FAAS) and X-ray fluorescence
spectrometry (EDXRFS) have been used in the determination.
1.2 History and Description of the Kainji Lake
Due to rising demand for electricity about 50 years ago the then electricity
corporation of Nigeria (ECN) saw the need for a large and cheap source of power. It
therefore commissioned Balfour Beatty and Company Limited of Britain to
investigate the hydro-electric potential of the Niger in the Vicinity of Jebba. Also a
separate investigation of the hydro-electric potential of the Kaduna river at Shiroro
gorge was carried out by the then Northern Nigeria government in collaboration with
ECN The federal government had commissioned the Netherlands Engineering
Consultants (NEDECO) to carry out a hydrological survey of the rivers Niger and
Benue (Olagunju, 1972).
6
Fig.1. 1: Map of Kainji lake showing the basins. (Source: Obot, 1984)
7
representative of the Federal Government, the Northern Region and ECN)
recommended that initial development be carried out at near Kurwasa (in Kainji area)
to be later followed by developments at Shiroro and Jebba. Further detailed
investigation led to the first dam being built at Kainji (102km upstream of Jebba)
(NEDECO and Balfour Beatty, 1961). (Plate 1 & Fig1.2).
Construction works for the Kainji dam began in March 1964 and was
completed in December 1968. This work marked the first engineering intervention on
the river Niger. Hence that portion of the river Niger is now a Lake and has lost some
attributes of a river due to backup effects of the dam.
The reservoir (Kainji Lake) covers an area of ≈ 800 Km2. and is 136 Km long.
It is 24 Km at the widest point (NEPA 1977). The building of Jebba dam (102 Km)
downstream of Kainji dam has created the Jebba Lake which extends to below the
Kainji dam. By implication, river Niger seizes to be a river as from Yelwa.
Downstream Yelwa up to Kainji, it is a Lake (Kainji Lake). Another Lake (Jebba
Lake) terminates at Jebba.
1.3 The Niger River, it’s Discharge and Sediment Transport
The Niger rises in the mountains of Sierra-leone on the Fouta Djallon
Highlands (240 Km from the atlantic Ocean) and runs in north-easterly direction. At
Mopti (Kilometer 2856) the river enters the swamp area around Timbuctu where it
looses 65% of its water by evaporation and infiltration. (NEDECO and Balfour Beatty
1961). It then takes a South-easterly course through a semi-desert with hardly any
rainfall in Niamey and then into Nigeria.
8
Between Niamey and Nigerian frontier the river flows through floodplains of
Yelwa receiving water from the drainage area South and West of Malanville and
from the tributary the Sokoto river. It flows through undulating Guinea Savannah and
to Jebba. At Kainji (102 Km upstream Jebba) (Olagunju, 1972) the Niger river was
dammed and this backed up the river upstream to form a Lake (Lake Kainji) its
surface level hundreds of metres higher than the old river level at the dam. The Lake
is regulated to flow through the dam, producing power by turning turbines.
The reigme of the Niger river is determined by its geographical situation. The
run-off from the rains in the Fouta Djallon Highlands travels 2720Km before reaching
Nigeria, six months later (NEDECO, 1959). On its way it passes the swamp area
around Timbuctu where it looses ≈ 65% of its water by evaporation and infiltration.
The water from the upper catchment area is comparatively clean when it reaches
Nigeria, having deposited its silts in the swampy areas. For this reason it is known as
the Black flood (Fig 1.2). The ‘black flood’ occurs between December and March .
The second drainage area contributing to the run-off starts downstream of
Niamey where tributaries in Benin flow north into the Niger. In Nigeria rivers Sokoto,
Malendo, Kontagora, Oil, Moshi, Awum and others contribute to the local flood. This
local flood is milky due to the silt it carries than the clean black flood and is called the
white flood. The white flood occurs between August and November. The black flood
fills a considerable part of the gap between consecutive wet seasons in Nigeria.
1.4 Objectives of the Research
All aquatic organisms are contaminated with metal compounds discharged
into natural waters by man. These substances may be toxic not only to man and the
9
ecosystem but may render water unsuitable for irrigation and domestic purposes
(Kahraman et al., 1976).
Lakes can become polluted without obvious signs (Biney et al., 1994; Alloway
et al., 1993). As a result, environmental monitoring as a means of detecting insidious
pollutants becomes pertinent. The objectives of this work therefore are:
(i) To ascertain the presence of the heavy metals such as Pb, Cr, Cd, Cu,
Zn, Hg, Fe, Co, Mn and Ni in Kainji Lake.
(ii) To determine the concentrations of these metals in water, sediment
and fish samples from the Lake.
(iii) To determine the impact of the Kainji hydropower generation.
10
Km
0
800
1600
2400
3200
4000
Mopti
Mekro
Sirba
Zamfara
Gulbia
Kaduna
Mariga
Kainji
Jebba
Lokoja
Delta
Bamako
Timbuctu
Fig.1. 2: The Niger and its Main Tributaries (NEDECO, 1959)
11
Plate1. 1: Aerial picture of Kainji dam
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