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The distribution and occurrence of heavy metals in water column of the
Anambra River were investigated in the dry season adopting standard chemical
methods. Following the establishment of the presence and appreciable
concentration of heavy metals in various stations (P<0.05) in the water column,
biological effects of two heavy metals (copper and zinc) were investigated in
laboratory bioassays against prevalent fish species of the river (Oreochromis
niloticus and Clarias gariepinus) based on the toxicity scale of 96hLC50 to
evaluate possible risk effect of the metals on the aquatic species and human
population depending on the river. Toxicity ranking for zinc and copper in the
water revealed copper to be consistently more toxic to the test species with
Oreochromis niloticus being more sensitive. The binary mixtures in
predetermined ratios (1:1 and 1:2) of zinc and copper acting against the test
animals showed significant departures when compared to levels of toxicity
attained by the individual constituent metals when acting alone against the same
species. In a majority of cases, the resultant interactions (Zn-Cu against fish
species) were in conformity to the model of synergism while fewer instances
portrayed antagonism and additive action. There is high risk of heavy metal
poisoning among the human population depending on the river and heavy metal
related public health effects observed in a survey are circumstantial evidence.
The work recommends setting more realistic and effective safe limits and
standards to minimize and properly manage heavy metal polluted water bodies.
1.1 Background of the Study
Amongst the several heavy metals that pose some risk to our
environment, thirty- five of them have been listed or known to have
significant occupational problems in man.
Interestingly, small amounts of these elements are common in our
environment and diet. Moreover these elements are actually necessary for
good health but large amounts of any of them may cause acute or chronic
toxicity (Glanze, 1996).
Heavy metal toxicity can result in damaged or reduced mental and
nervous functions, ATP depletion and damage to blood composition,
lungs, kidneys, liver and other vital organs (Wright, Welbourn and
Martin, 1991). Long term exposure may result in slowly progressing
physical, muscular, and neurological degenerative processes that mimic
Alzheimer’s disease, Parkinson’s disease, muscular dystrophy and
multiple sclerosis (Wright et al., 1991). Repeated long term contact with
some metals or their compounds may even cause cancer (International
Occupational Safety and Health Information Centre, 1999).
For some heavy metals, toxic levels can be just above the
background concentrations naturally found in nature (Dupler, 2001).
Therefore, it is important for us to inform ourselves about these metals
and to take protective measures against excessive exposure. Based on the
above background, most widely used/encountered heavy metals are the
focus of this work and these are mercury, arsenic, cadmium, iron,
manganese, chromium, zinc, copper, lead, sodium and potassium. In
most parts of the world, heavy metal toxicity is an uncommon medical
condition (International Safety and Health Information Centre, 1999).
When these metals are found in our immediate environmental media
unrecognized or inappropriately treated, toxicity can result in significant
illness and reduced quality of life (Ferner, 2001).
Industrial activities worldwide are characterized by the production
of a wide variety of end products that are useful to mankind; however all
production pathways are accompanied by emission of waste products that
enter the environment (Adetoro, 2004). Industrial wastes have been
shown to be a complex admixture of several classes of pollutants such as
synthetic chemicals of various types, hydrocarbons and heavy metals
(Oyewo, 1998; Otitoloju, 2003). Among the pollutants which find their
way into the Anambra River, heavy metals are important (Igwilo, Afonne,
Maduabuchi, and Orisakwe, 2006). Also important to mention is that they
are non-biodegradable and remain in the environment long after the
elimination of source (Otitoloju, 2002). Although most of these metal
pollutions are anthropogenic, there are a few examples of localized ones
resulting from natural weathering of ore bodies (Hager and Abrahamsen,
1990) mining and smelting (Walker, Hopkin, Sibly and Peakau, 2001).
They are considered priority pollutants because they easily bioaccumulate
in the food chain (Chukwu, 1991). Heavy metals, although usually
considered pollutants, are natural substances with the exceptions of
radioisotopes produced in man-made nuclear reactions (Walker et al.,
2001). Heavy metal contents of Anambra River have been earlier reported
by Igwilo et al. (2006) and Obodo (2004) attributing the loading to
various anthropogenic activities in and around the river.
Metals and other pollutants such as sewage, sawdust, hydrocarbons
and organic wastes, when introduced into water bodies, can bring about
alteration of physicochemical characteristics of such a water body and
hence would affect species diversity (Akpata, 1987, Oyewo 1998, Saliu
and Ekpo 2006).
In many instances, heavy metals occur in natural bodies of water at
levels below their toxic thresholds. However due to their non-degradable
nature, such sublethal concentrations may still pose risk of damage via
uptake and subsequent bioaccumulation by organisms which cannot
effectively metabolise and excrete the absorbed metals.
The main route by which heavy metals enter the aquatic
environment is through the discharge of metal-laden municipal and
industrial effluents, directly into the water bodies or indirectly via
drainages and canals (Angino, Magnuson, Wangh, Galke, and Bredfeldt,
1970; Oyewo, 1998). The discharge of these metals into the environment
also occurs during industrial processes and incineration of waste products
containing metallic compounds.
Environmental research in any country conventionally should
concentrate among other things on the pollutants that are considered as
priority in terms of frequency and intensity of occurrence. Typically, the
Anambra River acts as a sink or reservoir that receives waste water
effluent from different parts of the locality and hinterland (Igwilo et al.,
In response to this, there have been a few investigations on the
occurrence and distribution of heavy metals in the Anambra River. Such
authors have found measurable quantities of heavy metals although they
failed to relate such levels of occurrence to biological action such as acute
toxicity and sub lethal chronic action. Anambra River is the natural
habitat of several fish species such as Clarias and Tilapia species. These
fish species particularly the pelagic species are useful in assessing water
quality in the field and laboratory because they are ubiquitous, sedentary
in nature and have long life cycles; hence they act as continuous monitors
of the water bodies they inhabit. Earlier works (Okonkwo and Obiakor,
2008; 2009; Odo, Didigwu, and Eyo, 2009) have provided information on
the biology and ecology of these species. What was lacking in their
report is detailed empirical data on the interaction of these locally
important species with this important pollutant heavy metal detected in
the water column of Anambra River.
1.2 Statement of the Problem
Surface water use has been of tremendous application across the globe for
various purposes: domestic, industrial, agricultural etc. But studies by
different people in both developing and developed countries of the world
show that pollutants from various sources get to the surface water and
pollute it. (Obodo 2004, Igwilo et al. 2006, Clark 1992, Matti 2001,
Oyewo 1998 and Don-Pedro 1996). Otitoloju (2002) explained that
industrial effluents released into the environment get to the surface water
and pollute it with priority heavy metals; hence the author recommended
the toxicity testing of the most sensitive species in the field to assess
possible ecological damage that could result from these toxicants.
Consequently, Igwilo et al. (2006) supported the above fact and
advocated for a means to avert possible imbalance in the fish population
structure and the residents around the river feeding on toxic metals.
In Nigeria, and indeed many other developing countries, there are
host of unplanned and unorganized uses of river for various purposes,
including solid waste dumping, effluents disposal, siting of wide scale
toilet facilities, disposal of chemical wastes and wrong and frequent
application of artificial fertilizers. These are done without putting the
water quality of the river into consideration.
A casual inspection of Anambra River shows that there are
unhealthy, unplanned and unorganized uses of the river for various
purposes like solid waste dumping, effluents disposal, siting of wide scale
toilet facilities, disposal of chemical wastes, use of poisonous chemicals
in fishing, and indiscriminate application of fertilizers for farming
activities around the banks of the river at various locations. These
activities have negatively affected the quality and activities of the river in
a number of ways.
Firstly, the aesthetic value of the river has long disappeared. In
addition, the river is heavily silted, especially at the lower course.
Consequently, the depth and width of the river have greatly reduced.
Moreover, some activities which greatly depend on the quality of the
river like swimming have been greatly affected. Furthermore, fishing in
the river which used to be one of the means of sustaining livelihood for
the inhabitants of the area has drastically reduced.
A preliminary survey conducted prior to the main eco-survey
showed that various wastes are discharged into the river. Sewage
dislodgers and various industries were seen discharging their wastewater/
effluents into the river.
1.3 Research Questions
1. What are the levels of physicochemical parameters detected in
Anambra River?
2. What are the levels of occurrence and distribution of heavy metals
in Anambra River?
3. What is the acute toxicity (LC50) of heavy metals found to be the
most abundant in the Anambra River acting singly against selected
fish species?
4. What is the joint toxicity of mixtures of priority heavy metals
recorded in the river?
5. What are the prevalent heavy metal health related effects among
the resident population using the river?
6. How do the parameters detected comply with the recommended
standard of compliance?
7. What are the environmental implications and recommendations on
the findings?
1.4 Aim and Objectives
The aim of this work is to evaluate the possible risk effects of
heavy metals in Anambra River.
The following objectives were used to achieve the above aim.
(1) to investigate the physicochemical parameters of the river, that
enhances the availability and mobility of heavy metals,
(2) to identify the levels of occurrence and distribution of heavy metals
in Anambra River.
(3) to investigate the differential toxicity (LC50) of selected heavy
metals found to be most abundant in the Anambra River acting
singly against selected fish species, Oreochromis nuloticus and
Clarias gariepinus, which are prevalent as reported by Odo et al.
(2009) and confirmed in field survey.
(4) to investigate the joint action toxicity of the simple binary mixtures
of priority heavy metal pollutants recorded in the Anambra River
against the test animals mentioned above.
(5) to investigate the prevalent heavy metal related health effects
among the susceptible human population using the river.
(6) to compare the levels of parameters detected against recommended
standard of compliance and
(7) to examine the environmental implications and make relevant
recommendations based on the findings.
1.5 Research Hypotheses
The study tested the following hypotheses;
Research Hypothesis One
H0- there is no significant difference between the heavy metal
concentrations in the Anambra River water and WHO Effluent Standards.
Research Hypothesis Two
H0- the mean concentration of the different metals and samples
obtained from the stations of the Anambra River are not equal.
1.6 Justification of the Work
This present work is not just due but of great importance
considering that;
(1) When the concentration of effect of these heavy metals through
simulation study of acute toxicity (LC50) that can lead to 50%
mortality of fish population is established, it will help the
regulatory bodies to establish criteria for a workable environmental
safe limit for these metals in Anambra River and other similar
water bodies in the sub-region.
(2) It will aid in maintaining and sustaining the fish population
structure of Anambra River.
(3) The choice to study heavy metals and the physicochemical
parameters in this present study is because according to Chukwu
(1991) these metals are considered priority pollutant because they
easily bio-accumulate in the food chain and Otitoloju (2002) stated
that they are non-biodegradable and remain in the environment
long after elimination of source. The mobility and availability of
these metals in the aquatic environment are enhanced by these
physicochemical parameters studied.
(4) The choice of dry season for this study is because during the dry
season as the water level decreases due to high evapo-transpiration,
there is high concentration of these metals (Ezeonyejiaku, 2009).
(5) The toxicity data that will be obtained by the testing procedures
described in this study are eventually going to be used to make
assessments of hazard and risk. Where hazard is the potential to
cause harm and risk is the probability that harm will be caused.
Risk assessments depends on making a comparison between two
(a) The toxicity of a compound expressed as a concentration LC50.
(b)The anticipated exposure of an organism to the same chemical,
expressed in the same unit as one (a concentration in water to
which the organism is exposed). In hazard assessment, a toxicity
test can give a plot which relates the frequency of a toxic effect
(e.g. mortality) to the dose that is given. From this, an LC50 can be
estimated. This can be compared with a putative high
environmental concentration to decide whether a hazard exists. A
ranking of compounds according to their toxicity is important at
this stage. If toxicity is very low, then a compound is not regarded
as being hazardous and vice versa.
This is to say that work on physicochemical characteristics and
heavy metal evaluations of any surface water gives credence (and is of
great importance) in the management of the surface water which is an
indispensable aspect of the environment of that place.
1.7 Significance of the Study
This study has the following significance:
1) Study of this type will invariably aid in maintaining the fish
population of the river and sustain the employment status of the
local fishermen by portraying the heavy metal concentrations of the
water that could lead to the death/ reduction of biodiversity.
2) The toxicity testing will also help regulatory bodies to establish or
modify the existing effluents limitation standard and water quality
criteria for the protection of resident aquatic lives in Anambra
River and other similar bodies of water in the sub-region
3) Since heavy metal pollution has always been associated with fish
diversity decline, the control of this pollution in Anambra River
will guarantee abundant and readily available fish necessary for the
essential protein needs of the local population and beyond.
1.8 Limitations of the Study
The limitations of this study are listed below;
(1) A study of this type is supposed to cover both the rainy season, but
here only dry season was covered because conjectural explanations
from literature reports revealed the concentration of these
pollutants to increase due to evaporation.
(2) The investigator was evidently seen as a threat/Government official
working to stop some activities in and around the river and this
affected the response rate on the use of chemicals item in the
1.9 Scope of the Study
Due to the nature of the study, data were generated using two
methodologies – survey and experimental methods.
Use of chemicals in fishing and farming in the Anambra River as
well as water related health effects were obtained using well structured
questionnaire. It is obvious that there are many chemical pollutants that
exist in nature, which could be found in a river. However, this study
covered only the priority pollutants, heavy metals, which are of
environmental concern because they are important constituents of
industrial, municipal and domestic effluents and wastes. The metals
evaluated were Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper
(Cu), Iron (Fe), Mercury (Hg), Potassium (K), Manganese (Mn), Lead
(Pb), Zinc (Zn) and Sodium (Na). The physicochemical parameters of the
river of which some enhance the availability and mobility of these heavy
metals were also evaluated. These parameters included; pH,
conductivity, colour, odour, turbidity, total suspended solid (TSS), total
dissolved solid (TDS), dissolved oxygen (DO), total hardness (TH),
alkalinity, chloride, nitrate, nitrite, phosphate, biological oxygen demand
(BOD), chemical oxygen demand (COD), and temperature. The study
covered only the dry season.
In response to the above, a simulation study of the acute toxicity
(LC50) of the most abundant heavy metals in the river were tested in
single and binary mixtures against prevalent fish species (Oreochromis
niloticus and Clarias gariepinus) of the river in laboratory assay to
extrapolate the heavy metal concentration of effect that can lead to 50%
mortality of the fish diversity. According to Walker et al. (2001), the
essence of toxicity testing is to assess the possible risk of ecological
damage from a given toxicant/pollutant.
1.10 Conceptual Framework: Dose Response Relationships
This work is conceptualized on the Dose-response relationships. Of
central importance in both toxicology and ecotoxicology is the
relationship between the quantity of chemical to which an organism is
exposed and the nature and degree of consequent harmful (toxic) effects.
Dose-response relationships provide the basis for assessment of hazards
and risks presented by environmental chemicals. This simple basic
concept immediately raises questions about the definition of poisons
because everything depends on dose. Paracelsus (1493-1541) recognized
the dilemma and stated: “All substances are poisons; there is none that is
not a poison. The right dose differentiates a poison and a remedy-or in
other words, “the dose makes the poison”.
There are many different ways by which toxicity can be measured.
Most commonly, the measure (end point) is death. Many toxicity tests
provide an estimate of the dose (or the concentration in food, or water)
which will cause a toxic response at the 50% level, e.g. the median lethal
dose is the dose that will kill 50% of a population. In lethal toxicity
testing, LC50 represents the median lethal concentration.
An environmental chemical can enter a living organism by one or
more routes of uptake. Depending on the chemical, the species and the
environmental conditions, one route of uptake may be dominant or more
than one may be significant. Both the efficiency of uptake and the degree
of toxic effect differ between these routes. When tests are performed on
aquatic organisms, direct uptake from water is predominantly water or
food, and toxicity testing usually involves continuous exposure to defined
There can be very large differences between groups of organisms
and between species in their susceptibility to the toxic action of
chemicals; there can also be large differences between different strains of
the same species. The selective toxicity ratio (SER) is expressed in terms
of the median lethal dose (MLD) in the following way:
SER = MLD (or concentration) for species A
MLD (or concentration) for species B
Thus, toxicity tests are very rarely carried out on those species
thought to be at risk in the field. When regulatory authorities take
decisions about the release of chemicals into the environment, they base
their decisions on toxicity data obtained with surrogate species, which
may be very different from field species in their susceptibility to
particular chemicals.
From the foregoing, therefore, a study involving toxicity testing
with most abundant and widespread pollutant, heavy metal against
sensitive prevalent test organism (Oreochromis niloticus and Clarias
gariepinus) will be suitable in extrapolating heavy metal concentrations
that would result to 50% mortality of fish population in a given
freshwater habitat such as Anambra River. Consequently, the overlap in
the LC50 toxicity scales of the two fish species would portray their
susceptibility difference and the best predictor of the aquatic heavy metal
1.11 Plan of the Study
The study was organized into five chapters for the sake of clarity
and understanding.
Chapter one gives the introduction, which covers among other
things, statement of problem, the aim and objectives, the research
questions and hypotheses, the conceptual framework, the study area,
scope of study, limitations of study and significance of the study; Chapter
two shows the review of related Literatures; Chapter three conveys the
methodology that was adopted in the research; Chapter four shows the
data presentation, analysis and discussion of findings; and finally in
Chapter five summary, conclusions and recommendations are shown.
1.12 Area of the Study
In discussing the area of study, the location of the river, climate of
the area and economic activities of the area were discussed. This was due
to the nature of the study.
Anambra River is located in Anambra State. The State is located
between latitudes 05o
401N and 07o 10N1
and longitudes 06o
E and 07o
E. It is made up of 21 local government areas and located in the
South-eastern Nigeria. Anambra River runs across Anambra East, and
Onitsha North Local Government Areas.
Two climatic seasons exist in Anambra State, namely rainy season
(March-October) and dry season (November-March). The rainy season is
characterized by heavy down pours accompanied by thunder storms,
heavy flooding, soil leaching, extensive sheet outwash, ground infiltration
and percolation (Egboka and Okpoko, 1984). The annual rainfall of the
area is over 2000m.
On the other hand, the dry season begins when the dry continental
North-Eastern Wind blows from the Mediterranean Sea across the Sahara
Desert down to Southern Nigeria. It is characterized by extensive aridity
and a lot of particulates generation. Again, there is marked lowering of
water table and intense leaf fall (Egboka and Okpoko, 1984). The dry
season is characterized by high temperatures and low humidity, while wet
months have lower temperatures and lower relative humidity. The area
lies within the zone characterized by relative warm temperatures.
Although the temperatures vary slightly, depending on the period of the
year, the dry season has high temperatures and lower humidity. The
temperature is generally between 20oC and 30oC, while the wet months
with higher relative humidity has lower temperatures of between 22oC
and 26oC.
Anambra River lies between Longitudes 6
and 7o
Latitudes 6o
and 6o
. It is a tributary of River Niger which is the third
largest river in Africa.
The sanitary condition of the area surrounding Anambra River is
generally poor as wastes are dumped on a daily basis at the bank of the
river and faeces discharged directly into and around the river. Fertilizer
and pesticides are normally used in agricultural activities around the river
and, these agricultural activities are carried out along the fringes of the
river. These activities: sewage disposal, waste disposal and agricultural
activities through the use of fertilizer and pesticides around the river are
washed out as run-off into the river and this increases the pollution level
of the river.
The inhabitants around the localities of Anambra River mainly
engage in fishing and farming. There is a couple of industries located
around Anambra River, for instance rice mill industries are located in
Otuocha axis of the river.
Figure 1.1: Map showing Anambra River and sampled points
Source: Author’s field survey (2009)


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