Population growth and industrialization of the world has dramatically increased the
overall environmental load of heavy metals. The effects of pollution by heavy metals are
not only an environmental problem but also a public health matter. In this study, raw
water samples were collected from two sites (A and B) along river Kubanni, two sites (C
and D) along river Galma and also at Zaria Dam (site E) all in Zaria, Nigeria. Vegetable
samples (lettuce and tomato) were also collected from farmlands located along the banks
of the rivers at sites where raw water samples were collected. Treated water samples were
also collected from the public water supply in Zaria. For this purpose Zaria metropolis
was divided into 8 zones (TA-TH). Sampling was done during the dry season (February to
April 2006) and rainy season (August to October 2006). All the samples were analysed
for lead, manganese and copper using the Atomic Absorption spectrophotometer (AAS).
Lead and copper were not detected in any of the raw water samples analysed. However,
manganese was detected in all the raw water sample analysed. In the dry season,
manganese concentrations ranged from 0.58 ± 0.28 mg/l to 2.52 ± 1.65 mg/l while in the
rainy season, the concentrations ranged from 0.12 ± 0.05 mg/l to 5.36 ± 0.26 mg/l.
Lead and manganese were detected in all the vegetable samples analysed. The mean lead
concentrations in the dry season ranged from 0.40 ± 0.01 mg/l to 0.80 ± 0.003 mg/l while
in the rainy season the concentrations ranged from 0.38 ± 0.01 mg/l to 22.6 ± 0.07 mg/l.
The mean manganese concentration in vegetable samples ranged from 0.1 ± 0.003 mg/l to
0.3 ± 0.006 mg/l in the dry season and 0.13 ± 0.007 mg/l to 0.21 ± 0.003 mg/l in the rainy
season. Copper on the other hand, was only detected in samples contacted from just one
site (site D) in the rainy season with concentration ranging from 9.5 ± 0.12 mg/l to 9.7 ±
For the analysis of treated water samples, lead and copper were not detected. However,
manganess was detected in all the samples analysed with the dry season recording
concentrations ranging from 0.02 ± 0.02 mg/l to 3.53 ± 0.85 mg/l while the rainy season
recorded 0.00 ± 0.00 mg/l to 2.81 ± 0.31 mg/l.
TABLE OF CONTENTS
Title page i
Table of contents vi
List of Appendices ix
List of Figures x
List of Maps xi
List of Tables xii
Chapter 1: Introduction 1
1.1 Causes of pollution 1
1.2 Water pollution 3
1.2.1 Types of water pollution 4
1.2.2 Water pollutants 4
1.2.3 Effects of water pollutants 6
1.3 Statement of problem 6
1.4 Justification for the study 7
1.5 Objectives of the study 7
Chapter 2: Literature review 9
2.1 Heavy metals and pollution 9
2.2 Toxicity and adverse health effect of heavy metals 11
2.3 Lead 13
2.3.1 Sources of exposure to lead 13
2.3.2 Target tissues for lead 13
2.3.3 Signs and symptoms of lead toxicity 14
2.4 Manganese 15
2.4.1 Sources of exposure to manganese 15
2.4.2 Target tissue for manganese 16
2.4.3 Signs and symptoms of manganese toxicity 17
2.5 Copper 17
2.5.1 Sources of exposure to copper 18
2.5.2 Target tissues for copper 18
2.5.3 Signs and symbols of copper toxicity 18
2.6 Theory of atomic absorption spectrophotometry 19
Chapter 3: Materials and Methods 21
3.1 Materials 21
3.1.1 Chemicals and Reagents 21
3.1.2 Equipment and Glassware 21
3.1.3 Instrumentation 22
3.2 Methods 23
3.2.1 Description of study area 23
3.2.2 Sampling points for treated water 25
3.2.3 Sampling points for raw water 25
3.2.4 Sample collection and preservation 27
3.2.5 Collection of raw water samples 27
3.2.6 Collection of treated water samples 28
3.2.7 Collection of vegetable crop samples 28
3.3 Analysis of samples 28
3.3.1 Preparation of stock solution 28
3.3.2 Preparation of calibration curve 29
3.3.3 Pretreatment and analysis of lead, manganese and copper in water 29
3.3.4 Pretreatment and analysis of lead, manganese and copper in
vegetable samples 29
Chapter 4: Results 31
4.1 Concentration of lead, manganese, and copper in raw water sample 31
4.2 Concentration of lead, manganese, and copper in treated water sample 31
4.3 Concentration of lead, manganese and copper in vegetable samples 31
4.4 Seasonal variation in the mean levels of lead, manganese and copper
in samples analysed 37
4.5 Mean pH values in raw and treated water 38
Chapter 5: Discussion and Conclusion 41
5.1 Concentration of lead, manganese, and copper in raw water samples 41
5.2 Concentrations of lead, manganese and copper in treated water samples 43
5.3 Concentrations of lead, manganese and copper in vegetable samples 46
5.3.1 Concentration of lead in vegetable samples 46
5.3.2 Concentration of manganese in vegetable sample 47
5.3.3 Concentration of copper in vegetable samples 49
5.4 Mean pH values of raw and treated water sample 50
5.5 Conclusion 51
5.6 Recommendations 52
LIST OF APPENDICES
I: AAS calibration of concentration vs absorbance for lead 57
II: AAS calibration of concentration vs absorbance for manganese 58
III: AAS calibration of concentration vs absorbance for copper 59
IV: Mean concentrations of lead, manganese and copper
(mg/l + s.e.m) in raw water samples 60
V: Mean concentrations of lead, manganese and copper
(mg/l + s.e.m) in treated water samples 61
VI: Concentrations of lead in vegetable samples 62
VII: Concentrations of manganese in vegetable samples 63
VIII: Concentrations of copper in vegetable samples 64
LIST OF FIGURES
1. Mean concentrations of lead, manganese and copper in raw water
2. Mean concentrations of lead, manganese and copper in treated
water samples 33
3. Mean concentrations of lead in the vegetable samples 34
4. Mean concentrations of manganese in the vegetable samples 35
5. Mean concentrations of copper in the vegetable samples 36
LIST OF MAPS
1 Zaria and Environs 24
2 Sampling sites for raw water 26
An essentially accurate definition of pollution is “too much of something in the wrong
place”. Thus any chemical can become a “pollutant” if it is present at high concentration.
Nonetheless some chemicals can be selected as being of high priority for control in the
environment because, they are frequently found there, are capable of exerting adverse
effects at low concentrations, they remain unchanged in the aquatic environment for long
periods or because they biomagnify in food chains. Often the priority chemicals selected
display more then one of these characteristics (Harrison, 1993).
Pollutants are numerous and includes; gases, such as sulphur dioxide and nitrogen oxides,
particulate matter such as smoke particles, pesticides and radioactive isotopes in the
atmosphere and water ways, sewage, organic chemicals, and phosphates in water, solid
waste on land, excessive heating (thermal pollution) of rivers and lakes and many other
toxic metals such as zinc, copper, lead, mercury etc.
In some cases, the environmental levels of most of the pollutant are largely due to natural
sources while in others the levels are largely produced by man’s activities. Even when
natural sources are more important on a global scale, man generated pollutants may be
more important in urban and industrial areas where the adverse effects of pollution are
1.1 Causes of Pollution
One of the factors that affect the degradation of the environment is population growth.
The development of thousands of chemical compounds to restore and enhance the soil
fertility and to protect many of the domesticated species, has enabled man to expand his
food producing capacity significantly. These activities together with the birth of modern
medicine have resulted in an explosive growth of population with inevitable
consequences. A study conducted by the SCEP (Study of Critical Environmental
Problems) group points out that the demand for minerals, energy and space are
exponentially increasing at a rate of 5 to 6 percent per year and if this trend continues, the
next doubling of population will increase the environmental impact six fold.
The increased demand for energy has resulted in the extensive burning of coal and other
fossil fuels. When coal and other fossil fuels are burnt or processed, a variety of
pollutants are emitted in to the atmosphere. These include, particulates, trace elements, a
variety of hydrocarbons, and sulphur and nitrogen compounds. Probably the most
important pollutant emitted by coal combustion is sulphur (IV) oxide (SO2). Sulphur (IV)
oxide is oxidized to H2SO4 and some of the H2SO4 in turn reacts with trace elements
emitted alongside SO2 or other substances present in the atmosphere to form submicronsize
sulphate compounds. Recent studies indicate that it is the ‘mist’ containing H2SO4
and metallic, and not SO2 gas itself that is the major ingredient in sulphur pollution.
Another environmental problem of great concern, which is related to sulphur in fossil
fuels, is acid rain. The environmental effect of acid rain probably include increased
leaching of nutrients such as calcium from soil, changes in metabolic rates of organisms
which depend on acid or base catalysts, and corrosion of basic materials such as
limestone and marble (Okeniyi, 2000).
Coupled with rapid population growth, other factors such as urbanization, rapid industrial
development, mining, agricultural activities etc have resulted in huge accumulation of
wastes and pollutants. These pollutants, which in most cases contain heavy metals, may
end up in water bodies such as river, lakes, streams etc, thereby polluting them. These
water bodies which are used extensively for irrigation of crops could lead to the
introduction of these heavy metals in to the food chain if they are taken up by the crops.
N.I. Dike and co-workers in a study conducted between January and April 2003 observed
very high levels of Pb, Cu, Fe and Cd in River Jakara in Kano. On the other hand, high
levels of the same metals were reported in vegetable crops cultivated along the banks of
River Kaduna (Ojeka and Achi, 2004).
The industrialization of the world has dramatically increased the overall environmental
load of heavy metals to the point that our societies are dependent upon them for proper
functioning. Industry and commercial processes have actively mined, refined,
manufactured, burned and manipulated heavy metal compounds, for a number of reasons.
Today heavy metals are abundant in our drinking water, air and soil due to our increased
use of these compounds.
Other causes of pollution include sewage and fertilizers which contains nutrients such as
nitrates and phosphates. In excess level, nutrients stimulate growth of aquatic plants and
algae. Excessive growth of these types of organisms clogs our waterways, use up
dissolved oxygen as they decompose, and this in turn affects the respiratory ability of fish
and other invertebrates in the water.
1.2 Water Pollution
Comprising over 70 % of the earth’s surface, water is undoubtedly the most precious
natural resource on our planet. Its many uses include drinking and other domestic uses,
industrial cooling, power generation, irrigation, transportation and water disposal. In the
chemical process industry water is used as a reaction medium, a solvent, a scrubbing
medium, and a heat transfer agent.
Although humans recognize that water is essential for life, we disregard it by polluting
our rivers, lakes and oceans. Subsequently, we are slowly but surely harming our planet
to the point where organisms are dying at a very alarming rate.
1.2.1 Types of Water Pollution
Water pollution occurs when a body of water is adversely affected due to the addition of
large amounts of materials to the water. When it is unfit for its intended use, water is
considered polluted. Two types of water pollution exist, point source and non-point
Point source pollution: point sources of pollution occur when harmful substances are
emitted directly in to the water body. This is best illustrated by the oil spillage into the
sea that occurs as a result of oil drilling activities.
Non point source pollution: A non point sources delivers pollutants indirectly through
environmental changes. An example of these types of water pollution is when fertilizer
from a cultivated field is carried in to a stream by rain, in the form of run-off which in
turn affects aquatic life.
The technology exists for point source pollution to be monitored and regulated, although
political factors many complicate matters. Non point sources account for a majority of the
contaminants in streams and lakes.
1.2.2 Water Pollutants
The problem of water pollution due to discharge of domestic and industrial waste into
aquatic system has already become a serious problem in the country. The rivers and lakes
near urban centers emit disgusting odours and fish are being killed in millions along sea
coasts in the Niger Delta. The origin of these problems must be attributed to many
sources and types of pollutants. Some of these pollutants may have indirect effects whilst
substances normally not considered as pollutants may become so under special
circumstances. These water pollutants may be classified into eight categories as described
Oxygen Demanding Wastes: Dissolved oxygen is consumed in their breakdown by
microorganism, thus exerting a demand on the availability of dissolved oxygen.
Disease Causing Agent: Water is a potential carrier pathogenic microorganisms from
sewage and municipal wastes.
Synthetic Organic Compound: An example is the pesticides. These compounds are not
biodegradable, are accumulative toxic poisons and may reach objectionable levels in
Plant Nutrients: Nitrogen and phosphorus are essential for plant and animals’ growth
and metabolism. When present in water bodies in large concentrations, an excess algal
growth, known as “algal broom” appears over the water. This reduces light penetration
and restricts atmospheric reoxygenating of the water.
Inorganic Chemicals and Minerals: Example includes inorganic salts, mineral acids
metal, and their compounds. These pollutants enter water bodies from municipal and
industrial wastes and mine run-off. Most of these substances, particularly the heavy
metals are toxic and capable of building up in the food chain
Radioactive Substances: These can enter humans through food and water, and get
accumulated in blood and certain vital organs like thyroid gland, liver, bones and
muscular tissues. Radium (a waste product of Uranium ore mining) is considered to be a
hazard in drinking water.
Thermal Discharge: Used coolant water from power plants and industries is usually
discharged directly in to water bodies. This could result in increase in temperature of the
water bodies with a consequent decrease in oxygen saturation percentage and also
accelerates the lowering of dissolved oxygen levels.
Oil: Oil and oil wastes enter rivers and other water bodies from several sources like
industrial effluents, oil refineries and storage tanks, automobile wastes oil, petrochemical
plants. All these make a significant contribution to the pollution of the aquatic
1.2.3 Effects of Water Pollutants
Drop in the level of Dissolve Oxygen leading to deoxygenating of the aquatic system.
Municipal wastes and sewage introduce pathogenic microorganisms into drinking
water, which can cause diseases such as typhoid fever.
Synthetic organic chemicals e.g. pesticides are not biodegradable and thus accumulate
to toxic levels in the environment.
Heavy metals tend to bioaccumulate and toxic concentrations can build up in the food
Human activities that cause increase in water temperature can result in decreased
oxygen saturation percentage and thus lowering of Dissolved oxygen levels.
Oil slick on the surfaces of water can prevent oxygen transfer from the atmosphere
leading to very low dissolved oxygen levels.
1.3 Statement of Problem
Human beings have been exposed to heavy metals for an immeasurable amount of time.
Rapid increase in populations, coupled with other factors such as urbanization, rapid
industrial development, mining, agriculture etc, result in huge accumulation of wastes
and pollutants which end up in water bodies such as rivers, streams and lakes thereby
polluting them (Dike et al, 2004). Heavy metals are also present in virtually every area of
modern consumerism such as rivers construction materials, cosmetics, medicines,
processed food, fuel sources, personal care products, etc. It is very difficult for anyone to
avoid exposure to any of the many harmful heavy metals that are so prevalent in our
environment. Heavy metals toxicity represents an uncommon, yet clinically significant
medical condition. If unrecognized or inappropriately treated, heavy metal toxicity can
result in significant morbidity and mortality (Ferner, 2005).
1.4 Justification for the Study
Zaria like any other urban area in Nigeria, is experiencing an upsurge in pollution due to
population growth, municipal waste disposal, exhaust emissions, agricultural activities,
industrial and commercial process. The products and effluents from such processes may
end up in the water bodies, thus contributing to the heavy metal contamination of such
water bodies in Zaria. Also, food crops that are irrigated using these water bodies may
also take up some of these metals. Thus, introducing these metals into the food chain
where they tend to bioaccumulate.
Due to the toxicity and health hazards of heavy metals, this study is aimed at
investigating the levels of Lead (Pb), Manganese (Mn) and Copper (Cu) in raw and
treated water samples as well as some vegetable crops.
1.5 Objectives of the Study
This study is aimed at determining the levels of Lead, Manganese and Copper in raw
water samples from rivers Kubanni and Galma, and their respective tributaries as well as
concentration of these elements in some vegetable crops cultivated along the banks of
these rivers. Also raw and treated water samples will be collected from Zaria Dam as well
as from other parts of Zaria metropolis to determine the concentration of the elements in
The objectives of the study are to:
(i) Determine the level of Pb, Mn and Cu in raw water samples from rivers Kubanni
and Galma, and compare with levels in the vegetable crops cultivated along their
(ii) Determine the level of the metals in raw water samples from Zaria Dam and
compare with the levels to be determined from treated water samples around Zaria
(iii) Compare the levels of Pb, Mn and Cu in raw and treated water with W.H.O limits
for safe drinking water and also compare the levels in the vegetable crops with
FAO threshold values for crops.
(iv) Compare the levels of Pb, Mn and Cu obtained in the dry season to that obtained
in the rainy season and determine the seasonal variation if any.
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