CHAPTER ONE

1.0 INTRODUCTION

The 20th century has witnessed a lot of concern over the relationship between man and his

environment. The escalating contamination of the environment by toxic substances is of

growing concern in Nigeria and worldwide (Ezemonye and Enuneku, 2005). The

accumulation of toxic metals to hazardous levels in aquatic biota has become a problem of

increasing concern (Idodo-Umeh, 2002). Rivers are used as a source of drinking water for

humans and considered as a sink for waste. Undoubtedly, a riverine aquatic environment

suffers the consequences of domestic and industrial activities occurring in its watershed

(Taweel et al., 2013). In Nigeria, environmental management practices are inefficient due to

poor infrastructure and lack of environmental protection awareness (Ihedioha and Okoye,

2012). As a result of the ineffectiveness of purification systems, waste water may become

seriously dangerous, leading to the accumulation of toxic products in the receiving waster

bodies with potentially serious consequences on the ecosystem (Aghalino and Eyinla, 2009).

A wide range of contaminants are continuously introduced into the aquatic environment

mainly due to increased industrialization, technological development, growing human

population, oil exploration and exploitation, agricultural and domestic wastes run-off (Lima

et al., 2008). Chief among such contaminants are heavy metals. When released into the

environment, heavy metals find their way into the aquatic systems where they are deposited.

In aquatic environment, organisms like fishes concentrate them in their tissues through the

effects of bio-concentration, bioaccumulation and the food chain process (Enuneku et al.,

2013). Heavy metals contamination may have devastating effects on the ecological balance

of the environment and the diversity of aquatic organisms (Farombi et al., 2007). The

discharge of industrial wastes containing toxic heavy metals into water bodies may have

1

significant effects on fish and other aquatic organisms, which may endanger public health

through consumption of contaminated seafood and irrigated food crops (Eneji et al., 2011).

1.1 Sources of Heavy Metals Pollution in the Aquatic Environment

There are two major sources of heavy metals in the aquatic environment: natural sources

and anthropogenic sources. Heavy metals occur naturally in the environment at very low

concentrations, mainly due to weathering of soils and their associated bedrocks (Idodo-

Umeh, 2002). They may also result from acidic rain resulting in the breakdown of soils and

the release of heavy metals into streams, lakes, rivers, and groundwater (Lenntech, 2011).

In recent times however, there has been an unprecedented increase in the level of these

metals due to human activities (Sabo et al., 2013). The major sources of heavy metal

pollution in urban areas of Africa are anthropogenic (Lenntech, 2011). Heavy metals may

enter a water supply from industrial and household wastes. High levels of heavy metals in

soil, water and atmosphere and the biota are often related to industrial activities, burning of

fossil fuels, chemical dumping, application of agro-allied chemicals such as fertilizer and

certain pesticides (Oyekunle et al., 2012). Trace elements and heavy metals introduced into

aquatic environments as a result of the activities of man come through: agriculture,

industrialization and generated pollutants through mining and urbanization are ultimately

absorbed by deposits and incorporated into the sediments (Olajire et al., 2003).

1.2 Occurrence and Forms of Selected Heavy Metals

1.2.1 Lead

Lead is the commonest heavy metal and accounts for 13 mg/kg of the Earth’s crust. Lead

compounds can be found in all parts of our environment as a result of human activities, such

2

as the burning of fossil fuel burning, mining, and manufacturing (World Health

Organization [WHO], 2011). The most common sources of lead exposure are lead-based

paint and possibly water pipes in older homes, contaminated soil, household dust, drinking

water, lead crystal, lead in certain cosmetics and toys, and lead-glazed pottery (Martin and

Griswold, 2009). Lead exists in various oxidation states (O, I, II and IV), which are of

environmental importance. The divalent form Pb (II) is reported to be the form in which

most Pb is bio-accumulated by aquatic organisms (Department of Water Affairs and

Forestry [DWAF], 1996).

1.2.2 Aluminium

Aluminium is the most abundant metallic element and constitutes about 8% of the Earth's

crust. Aluminium is released to the environment mainly by natural processes. It occurs

naturally in the environment as silicates, oxides, and hydroxides, combined with other

elements, such as sodium and fluoride, and as complexes with organic matter. Dissolved

aluminium concentrations in waters with near-neutral pH values usually range from 0.001 to

0.05 mg/litre but rise to 0.5–1 mg/litre in more acidic waters or water rich in organic matter

(WHO, 2003). Aluminium metal is used as a structural material in the construction,

automotive, and aircraft industries, in the production of metal alloys, in the electric industry,

in cooking utensils, and in food packaging. Aluminium compounds are used as antacids,

antiperspirants, and food additives. Aluminium salts are also widely used in water treatment

as coagulants to reduce organic matter, colour, turbidity, and microorganism levels (Agency

for Toxic Substance and Disease Registry [ATSDR], 1992).

3

1.2.3 Nickel

Nickel is a lustrous white, hard, ferromagnetic metal. Several nickel salts, such as the

acetate, chloride, nitrate, and sulfate, are soluble in water, whereas carbonates and

hydroxides are far less soluble and sulfides, disulfides, subsulfides, and oxides are

practically insoluble in water (Morgan and Flint, 1989). Nickel may be present in some

ground waters as a consequence of dissolution from nickel ore-bearing rocks. Nickel occurs

predominantly as the ion Ni(H2O)62+ in natural waters at pH 5-9 (International Programme

on Chemical Safety [IPCS], 1991). The natural background levels of nickel in water are

relatively low in open ocean water, the values range from 0.228 to 0.693μg/L, while in fresh

water systems, the value is generally less than 2μg/L (Air Quality Guidelines, 2000). Nickel

is used mainly in the production of stainless steels, non-ferrous alloys, and super alloys.

Other uses of nickel and nickel salts are in electroplating, as catalysts, in nickel–cadmium

batteries, in coins, in welding products, and in certain pigments and electronic products

(International Agency for Research on Cancer [IARC], 1990). It is estimated that 8% of

nickel is used for household appliances (IPCS, 1991). Nickel is also incorporated in some

food supplements, which can contain several micrograms of nickel per tablet (European

Union, 2004).

1.2.4 Chromium

Chromium is an industrially important metal, which has the potential to contaminate

drinking water sources. Chromium can exist in water as either Cr III or Cr VI. Cr VI in

water will eventually be reduced to Cr III by organic matter. The rate at which this occurs

depends on the amount of organic matter present in the water, and on the pH and redox

potential of the water (Clifford and Man-Chau, 1988). Chromium is presently common in

most of the effluent streams when compared to other heavy metals. Hexavalent chromium,

4

Cr VI is considered as the major environmental concern as it is more water soluble, more

easily enters living cells, and is much more toxic than Cr III (Carol et al., 2012). Chromium

enters environmental waters from anthropogenic sources such as electroplating factories,

leather tanneries and textile manufacturing facilities. Chromium also enters groundwater by

leaching from soil (Martin and Griswold, 2009).

1.3 Justification of the Study

The Benin River is of great importance to inhabitants in the many villages through which it

flows. The inhabitants of surrounding villages rely mainly on the river for their domestic

water supply, fishing, sand mining and inter-village transportation. The river also receives

effluents from many industries such as ASCA oil, Optima, Total Asphalt blending plant,

sawmills and abattoirs along the river bank. Although several studies have previously been

carried out on the Benin River to determine the level of heavy metal contamination, very

scarce information is available on the level of heavy metals at Koko which is a major fishing

community along the stretch of the river.

The dearth of information on the level of heavy metals in the river as a result of human

activities in the area has necessitated this study. This study is justified by the need to assess

and ascertain the levels of Pb, Al, Ni and Cr in catfish, Synodontis clarias which is the

dominant fish species in the river, in order to ascertain its suitability for human

consumption. The catfish is a common and important fish species of bio-economic value to

the inhabitants of the area. Also, its benthic feeding habit makes it a valid representative of

the state of the sediment which acts as a sink for heavy metals in the river.

5

1.4 Objectives of the Study

The objectives of the study are as follows:

1. To determine the occurrence and ascertain the levels of heavy metals (lead,

aluminium, nickel and chromium) in the water of Benin River at Koko.

2. To determine the concentrations of the heavy metals in catfish (Synodontis clarias)

found in the river.

3. To compare the concentration of heavy metals in the water and fish ascertain

whether they fall within the safe limits/standards for potable drinking water and fish

and fishery products as recommended by the Food and Agriculture Organization

(FAO), World Health Organization (WHO), and Standard Organization of Nigeria

(SON).

6

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 Water and Pollution

Water is one of the earth’s natural resources and three quarters of the earth’s surface is

covered by it (Akpofure et al., 2007). It is a most valuable resource to man and living things

and is essential for the sustenance of life on earth as exemplified by its diversified uses

which include drinking, cooking, washing, irrigation, and farming. Water is indeed life and

thus is the most important natural resource, without which life would be non-existent.

Availability of safe and reliable source of water is an essential prerequisite for sustained

development (Asonye et al., 2007). Clean water is essential to life but water in its natural

state may not be pure because it is a universal solvent possessing the ability to dissolve

numerous substances and so contains a lot of impurities either in solution or suspension that

can be injurious to human health, if it exceeds tolerable limits. It is therefore important that

water for drinking and domestic use must be free from significant concentration of toxic and

stray substances (WHO, 1999).

Adverse changes to the water quality of one stream can impact all the bodies of water

downstream – rivers, lakes, or even the ocean. When water quality degrades, changes to

plant, invertebrate, and fish communities may occur and affect the entire food chain

(Wakawa et al., 2008). Urbanization and industrial activities in developing countries,

including Nigeria, has gradually led to the deterioration of the quality of the natural

environment in recent years (Oguzie, 2002). Pollution from human and industrial wastes

dumped directly into rivers in and around major urban centres has led to various metal

contamination and loss of the natural ecosystems (Ihenyen and Aghimien, 2002).

7

According to Atubi (2009), the uncontrolled disposal of waste into water renders water

unsafe for economic use and recreational purposes and poses a threat to human life through

the spread of water borne diseases and water caused health problems. There are four main

sources of aquatic pollution: industrial waste, municipal wastes, agricultural run-offs and

accidental spillage. The toxic metals from various industrial and domestic sources are

usually discharged at dumpsites and are more often than not discharged into water bodies

(Eddy et al., 2006; Davies et al., 2008).

2.2 Heavy Metals in the Aquatic Environment

Ada et al. (2012) defined heavy elements as those metallic elements with high atomic

weight that is at least five times greater than that of water. They are also known as trace

metals because they exist in minute quantities in biological systems (Duruibe et al., 2007).

Of the 92 naturally occurring elements, approximately 30 metals and metalloids are

potentially toxic to humans (Ming-Ho, 2005). Metals occur naturally in the earth's crust, and

their contents in the environment can vary between different regions resulting in spatial

variations of background concentrations. The distribution of metals in the environment is

governed by the properties of the metal and influences of environmental factors (Khlifi and

Hamza-Chaffai, 2010). High levels of some essential trace elements (copper, zinc and iron)

in aquatic organisms may not be unconnected to the biological importance of such metals

(Omoigberale and Ikponmwosa-Eweka, 2010).

The concern about heavy metals stems from their persistence in the environment as they are

not easily degraded either through biological or chemical means unlike most organic

pollutants (Sabo et al., 2013). Sediment acts as both carrier and potential sources of

contaminants in an aquatic environment and can serve as a pool that can retain or release

contaminants to the water column by various processes of remobilization (Davies and

8

Abowei, 2009). However, total metal concentration in sediment is not a good estimation of

bioavailability. Contamination of the sediment matrix by heavy metal may accumulate in

fishes and other aquatic resources which may eventually get into human food chains

(Iwegbue et al., 2007).

2.3 Importance of Fish to Man

The growing human population has increased the need for food supply. Fish, a living

resident of the aquatic environment, is a common table food which is usually consumed by

humans for protein nourishment. Worldwide, people obtain about 25% of their animal

protein from fish and shellfish (Bahnasawy et al., 2009). In 2004, about 75% (105.6 million

tonnes) of estimated world fish production was used for direct human consumption (FAO,

2006). It has been predicted that fish consumption in developing countries will increase by

57 percent, from 62.7 million tons in 1997 to 98.6 million in 2020 (Retnam and Zakaria,

2010).

Compared to other meats such as beef and pork, fish is more easily digestible and

inexpensive. Fish like other food aquatic animals contain essential amino acids, fatty acids,

protein, carbohydrates, vitamins and minerals (Sen et al., 2011). The real importance of fish

in human diet is not only in its content of high-quality protein, but also to the two kinds of

omega-3 polyunsaturated fatty acids: eicosapentenoic acid (EPA) and docosahexenoic acid

(DHA). Omega-3 (n-3) fatty acids are very important for normal growth where they reduce

cholesterol levels and the incidence of heart disease, stroke, and preterm delivery. Fish also

contain vitamins and minerals which play essential role in human health (Burger and

Gochfeld, 2005; Al-bader, 2008).

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2.4 Uptake of Heavy Metals by Fish

Among animal species, fishes are the inhabitants that cannot escape from the detrimental

effects of these pollutants. Fishes are at the apex of the aquatic food chain and can

bioaccumulate some of these substances into their tissues (Olaifa et al., 2004). Fish

accumulates heavy metals directly from water and diet and contaminant residues may

ultimately reach concentration levels hundreds or thousands of times above those measured

in the water, sediment and food (Goodwin et al., 2003). Pollutants enter fish through a

number of routes (skin, gills, oral consumption of water, food and non-food particles). On

absorption, pollutants are transported in the blood stream to either a storage point (i.e. bone)

or to the liver for transformation and/or storage (Nussey et al., 2006). Fish has been reported

to accumulate metals from water by diffusion through the skin and gills as well as oral

consumption/drinking of water (Oguzie, 2003). The toxicity of a substance is a function of

concentration and duration of exposure of an organism to the toxicant (Ogundele et al.,

2004).

Transport of metals in fish occurs through the blood where the ions are usually bound to

proteins. The metals are brought into contact with the organs and tissue of the fish and

consequently accumulated to a different extent in different organs or tissues of the fish.

Once heavy metals are accumulated by an aquatic organism, they can be transported through

the upper class of the food chain (Ayandiran et al., 2009). As a consequence, fish are often

used as indicators of heavy metals contamination in the aquatic ecosystem because they

occupy high trophic levels and are important food source (Agah et al., 2009). The

concentration of heavy metals in fish is related to several factors such as the food habits and

foraging behaviours of the organism (Obasohan and Oronsaye, 2004); trophic status, source

of a particular metal, distance of the organism from the contamination source (Obasohan

10

and Eguavoen, 2008); the physico-chemical properties of the contaminants, its distributions

in the aquatic system, the feeding behaviours and metabolism of the aquatic organism

(Lawrence et al., 2009); bio-magnification and/or bio-diminishing of a particular metal

(Barlas, 1999); food availability, metallothioneins and other metal detoxifying proteins in

the body of the animal (Deb and Fukushima, 1999); temperature, transport of metal across

the membrane and the metabolic rate of the animal (Oronsaye, 1989); physical and chemical

properties of the water and the seasonal changes in the taxonomic composition of the

different trophic levels affecting the concentration and accumulation of heavy metals in the

body of the fish (Chen and Folt, 2000; Ada et al., 2012); and the adaptation capacity of the

fish to heavy metal loads (Shah and Altindag, 2005). Metal bioaccumulation is largely

attributed to differences in uptake and depuration period for various metals in different fish

species (Tawari-Fufeyin and Ekaye, 2007).

2.5 Human Health Concerns

Concern about heavy metal contamination of fish has been largely motivated by the adverse

effects on humans, given that consumption of fish is the primary route of heavy metal

exposure (Nsikak et al., 2007). ATSDR (2008) discovered that the contamination chain of

heavy metals almost always follows a cyclic order: industry, atmosphere, soil, water, foods

and human. Since diet is the main route of exposure to heavy metals, and fish represent a

part of human diet, it is not surprising that polluted fish could be a dangerous dietary source

of certain toxic heavy metals (Bogut, 1997). The frequent presence of Pd, Cr, Zn and Cd in

industrial wastes and the associated high toxicity along with considerable bioaccumulation

in freshwater fishes make them toxicant that should be given due consideration in aquatic

toxicology (Flessas et al., 2000).

11

Human consumption of contaminated fish with the potential for adverse health effects has

been identified in Great Lakes region of the United States (Schwartz et al., 1983). A pair-

matched study from Canada reported that fish eaters from this environment had relatively

higher blood lead levels than non-fish eaters (Mergler et al., 1998). Heavy metals can cause

serious health effects with varied symptoms depending on the nature and the quantity of the

metal ingested (Adepoju-Bello and Alabi, 2005). Studies suggest that aluminium might have

a possible connection with developing Alzheimer’s and Parkinson’s disease as researchers

found what they considered to be significant concentration of aluminium in the brain tissue

of Alzheimer’s patients. Aluminium also causes senility and presenile dementia (Bakare-

Odunola, 2005). Low level exposure to chromium can irritate the skin and cause ulceration

while long term exposure can cause kidney and liver damage, and damage to circulatory and

nerve tissue (ATSDR, 2000). The carcinogenicity of hexavalent Cr to man and other

mammals and the prevalence of the use of this metal in the leather and textile industries

provide sufficient motivation for the continued monitoring of fish for this metal (Carol et

al., 2012).

2.6 Cases of Aquatic Pollution in Nigeria

Nigeria’s inland water bodies have been subjected to various forms of degradation due to

pollution (Sabo et al., 2013). The situation is exacerbated in coastal areas by activities such

as the unloading of fertilizers, oil and fuel transportation which create spillages that directly

pollute the waters, industrial effluents, mining and dredging activities (Chukwu, 2006). Oil

spills in Nigeria occur due to a number of causes that include corrosion of pipelines and

storage tanks, sabotage, accidents in oil production operations and pipeline vandalism

(Atubi, 2011).

12

In the Niger Delta there is high shipping traffic and seawater is visibly contaminated by

waste including crude oil. Oil in the aquatic environment may be damaging in a variety of

ways. These may involve changes in the composition of aquatic communities that affect

their ability to survive, permanent damage and, in some cases, massive mortalities (Nwilo

and Badejo, 2005). Oil pollution of water also constitute a potential health risk to humans

who use water for domestic and drinking purposes and consume fish found therein (Atubi,

2009). Owamah (2013) showed that the concentration of heavy metals in petroleum-

impacted rivers was significantly greater than the concentration in non-impacted rivers.

Like in many other countries of the world, several studies have been carried out on water

bodies in Nigeria in order to determine the concentrations of heavy metals in fish and fish

organs, water, effluents and sediment (Oguzie, 2003; Obasohan and Oronsaye, 2004;

Iwegbue et al., 2007; Obasohan, 2007; Ada et al., 2012; Osakwe and Peretiemo-Clarke,

2013; Jeje and Oladepo, 2014). High concentrations of heavy metals have been reported by

some researchers (Obasohan and Eguavoen, 2008; Nwajei et al., 2012; Owamah, 2013) in

the oil prospecting Niger Delta region of Nigeria. Egborge (2000) and Otukunefor and

Biukwu (2005) reported that the pollution levels of aquatic ecosystems observed in the

Niger Delta region are a result of unregulated effluent discharges and unsustainable methods

of petroleum extraction. Nwajei et al. (2012) attributed the high concentrations of heavy

metals (manganese, lead, cadmium, chromium, nickel and copper) in River Niger to the

industrial and anthropogenic wastes which are continuously discharged into the river.

Emoyan et al. (2006) also confirmed high levels of heavy metal contamination of River

Ijana - an effluent receiving stream that flows by the Warri refinery.

Obasohan (2008) indicated that the amount of municipal wastes discharged into the Ogba

River was responsible for the high levels of Cr, Ni and Mn in the cichlid fish, Hemichromis

13

fasciatus from the river. Higher levels of Fe, Cu, Pb, Cd and Zn recorded in Clarias

anguillaris than in Oreochromis niloticus by Yehia and Sebaee (2012) was attributed to

differences in metabolic rates, feeding habits and fish species. Aluyi et al. (2003) recorded

relatively high counts of bacteria resulting from high incidence of human activities

including defecation, washing and bathing in the surrounding communities in the River

Ethiope – a connecting water body to the Benin River. A recent study by Osakwe and

Peretiemo-Clarke (2013) revealed the heavy metals profile of River Ethiope sediment to

include Zn, Pb, Fe, Ni, Mn, Cu, Cr, Cd and V. Ogbeibu et al. (2014) gave the heavy metals

profile of the sediment of Benin River to include contaminants such Cr, Zn, Mn, Cu, Ni and

Pb.

Heavy metals deserve special attention as they represent a group of highly toxic substances

accumulating in the tissues of aquatic organisms and being conveyed through the food chain

to human (Enuneku et al., 2014). According to Christopher et al. (2011), as long as human-

induced generation of heavy metals continues in industrial and domestic activities, sustained

measurement will be needed to assess the effectiveness of the set limitation standards and

facilitate the identification and quantification of the state of environmental degradation

attributable to the discharged heavy metals.

14

CHAPTER THREE

3.0 MATERIALS AND METHODS

3.1 Description of the Study Area

The Benin River (Figure 1) is located in the coastal belt of Southern Nigeria at the western

boundary of the upper Delta and the lowlands. This River drains the major rivers Ethiope,

Ossiamo, Osse and Siluko into the Atlantic Ocean. It is approximately 93 km long with

average width of 3.0 and 1.4 km in its downstream and upstream section, respectively. Koko

town is the local government headquarters of Warri North Local Government Area. It is a

riverine cosmopolitan town and a sea port located on latitude 6°00’N and longitude 5°28’E.

The major occupations of the inhabitants include fishing, carving of canoes, net making,

hunting, clothes dyeing and farming. The climate is equatorial and is marked by two distinct

seasons: the dry season and the rainy season. The dry season lasts from November to April

and is significantly marked by the cool “harmarttan” dusty haze from the north-east winds.

The rainy season spans May to October with a brief dry spell in August, but it frequently

rains even in the dry season. The area is characterized by tropical equatorial climate with

mean annual temperature of 32.8°C and annual rainfall of 2673.8mm. There are high

temperatures of between 36°C and 37°C. Relative humidity is high all year round, and

varies between 50% and 80%. The natural vegetation is of rainforest with swamp forest in

some areas. The forest is rich in timber trees, palm trees, as well as fruit trees.

The town is located along the stretch of the Benin River and the inhabitants rely on the river

for their domestic water supply, fishing, sand-mining and inter-village transportation. Many

human activities within and around this river include dredging, logging, fishing, boating,

watercraft maintenance, discharging of petroleum products, saw milling, transportation,

15

laundering, bathing and swimming. Coupled with these are other forms of activities that can

cause pollution, such as oil spillage and industrial wastes discharge. Although petroleum

prospecting does not take place in its immediate vicinity, Koko town falls within the

petroleum prospecting and processing region of western Niger Delta. While there has been

no recent incident of oil spillage or environmental pollution in the town, it once attracted the

attention of the Federal Government and the international community in 1988 when

hazardous wastes from a European country was reportedly dumped in a certain location at

the port after access was granted to some Italian frauds by a native of the town. It was this

occurrence that spurred the Nigeria government into developing a constitution on

environmental pollution and waste management (Kocasoy, 2003).

16

17

Figu

re 1: Map

of the B

enin

River at K

oko sh

owin

g samp

led station

s.S

ource: Enuneku et al. (2014)

3.2 Duration of the Study

The study spanned three months during the rainy season (July - September, 2014). Water

and fish (Synodontis clarias) samples were collected from two sampling stations along the

stretch of the river twice every month for the analysis of heavy metal concentrations.

3.3 Sampling Stations

Two sampling stations were established along the stretch of the river. The stations are

subjected to activities including dredging, logging, fishing, watercraft maintenance,

discharging of petroleum products, saw-milling, water transportation, laundering, bathing

and swimming, waste dumping and defecation. The different kinds of pollutants include

organic and inorganic compounds such as crude oil and refinery products through normal

operations as effluents, operational failures and sabotage. The river also receives effluents

from industries such as ASCA oil, Optima, Total Asphalt blending plant, fish landing sites

and sales points along the river bank.

3.4 Collection of Samples

3.4.1 Collection of fish samples

Fresh fish (Synodontis clarias) samples were procured from fishermen at the landing site.

The fish were caught using cast nets and hooks. The samples were collected in polythene

bags and immediately transported to the laboratory.

3.4.2 Collection of water samples

Plastic water bottles with screw cork were used in collection of water samples from each

sampling point at a depth of 30cm below water surface. The bottles were pre-cleaned with

18

detergent and rinsed with distilled water. At the point of collection, the previously washed

bottles were first rinsed with water from the river before collecting the water.

3.5 Preparation of Samples

3.5.1 Preparation of fish samples

In the laboratory, the fish samples were identified using identification keys according to

Idodo-Umeh (2003). Routine body measurements such as body lengths (total, fork and

standard) were determined with a measuring board and recorded to the nearest 0.1cm while

weight was determined using a top loader (Mettler, P. E. 230) and recorded to the nearest

0.1g respectively. The fish samples were oven-dried to constant weight at 90°C for 48

hours. The dried samples were ground into powder using a porcelain mortar and pestle.

They were kept in foil papers, labelled and stored at a temperature of -10°C prior to

digestion.

3.5.2 Preparation of water samples

The collected water samples were taken to the laboratory and immediately acidified to pH

1.5 using 10% HNO3 to arrest microbial activities and prevent the mineralization and

adsorption of the heavy metals to the walls of the bottles. All the samples were properly

labelled and stored in a refrigerator at a temperature of about -4°C.

3.6 Digestion of Samples

3.6.1 Digestion of fish samples

A method described by Oyekunle et al. (2011) was employed in digesting the fish samples.

2g of the milled fish sample was measured into a 250ml conical flask. 20ml of nitric acid

19

and perchloric acid (3:1) were added to the sample. The mixture was heated over an electric

plate under a hood until the sample became a clear solution. Digestion was terminated with

the appearance of white fumes of perchloric acid. The solution was allowed to cool before

adding 5ml of 20% hydrochloric acid (HCl). The digest was filtered into a 100ml volumetric

flask using Whatman No.1 filter paper and made up to the 100ml mark with distilled water.

The digest was stored in a 100ml plastic reagent bottle. Blanks were prepared using the

same volume of mixed acids.

3.6.2 Digestion of water samples

Digestion was carried out according to the method described by Galyean (2010). 2ml of

water sample was digested using 15ml concentrated nitric acid (HNO3) in a 250ml conical

flask. The mixture was heated over an electric hot plate at a temperature of between 200°C

and 250°C under a hood until the volume was reduced to 5ml. The digest was allowed to

cool and was transferred into a 100ml volumetric flask and made up to mark by adding

distilled water. The digest was stored in a 100ml plastic reagent bottle awaiting analysis.

Blank samples were prepared using the same quantity of nitric acid.

3.7 Analysis of Heavy Metals

The metals were analyzed at the Martlet Environmental Research Laboratory in Benin-city

using an atomic absorption spectrophotometer (AAS) (Solar 969 Unicam series) with solar

software. Acetylene flame was used as the oxidant and the source of radiation was a hollow

cathode lamp. The AAS (Plate 2) was calibrated for lead, aluminium, nickel and chromium.

The standard solutions of each metal salt and blank samples were run with each set of

experimental digest. The limits of detection for the various metals were: Pb, 0.2μg/g; Al,

1.0μ/g; Ni, 0.2μg/g and Cr, 0.2μg/g.

20

Plate 1: Synodontis clarias (Mochokidae)

Plate 2: UNICAM 969 Atomic Absorption Spectrophotometer

Source: Martlet Environmental Research Laboratory, Benin City.

21

3.8 Experimental Design

The experiment was designed as a factorial experiment in complete randomized design

(CRD) for the metals (Pb, Al, Ni and Cr) involving 2 locations x 3 months x 2 sources

(water and fish) replicated twice.

3.9 Statistical Analysis

Data obtained were analyzed using computer software (Genstat Version 8.1, 2005). One

way analysis of variance (ANOVA) was used in all cases to test for significant differences

between means at 5% probability level. Significant treatment means were separated using

the New Duncan’s Multiple Range Test (Alika, 2006).

22

CHAPTER FOUR

4.0 RESULTS

The results obtained from the analyses of the concentration of heavy metals in the water and

Synodontis clarias of the Benin River at Koko are presented below.

4.1 Heavy Metals Concentration in Synodontis clarias of Benin River at Koko

4.1.1 Lead (Pb)

The total mean Pb value recorded in Synodontis clarias during this study was 1.507mg/kg.

Fish caught at Station 2 recorded a higher Pb value (1.518mg/kg), with the concentration

being highest (1.915mg/kg) in July and lowest (1.115mg/kg) in September (Fig. 2). At

Station 1, the mean Pb concentration recorded was 1.497mg/kg. The highest monthly value

(1.910mg/kg) at Station 1 was recorded in August while the lowest mean concentration

(1.135mg/kg) was recorded in July. The highest mean monthly Pb value (1.717mg/kg) was

recorded in August while the lowest value (1.280mg/kg) was recorded in September.

One-way analysis of variance (ANOVA) based on absolute values indicated that the mean

Pb concentrations recorded in Synodontis clarias did not vary significantly (p>0.05)

between the sampled stations and the months. The monthly mean concentration was

significantly different (p<0.05) between August and September. The monthly rank profile of

Pb in Synodontis clarias of Benin River at Koko in a descending order was: August > July >

September.

23

1 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

July

August

September

Sampling stations

Con

cent

rati

on o

f P

b (m

g/kg

)

Figure 2: Monthly variations in the mean concentration of Pb in Synodontis clarias of Benin River at Koko

24

1 20

1

2

3

4

5

6

JulyAugustSeptember

Sampling stations

Con

cen

trat

ion

of

Al (

mg/

kg)

Figure 3: Monthly variations in the mean concentration of Al in Synodontis clarias

of Benin River at Koko

25

4.1.2 Aluminium (Al)

The total mean Al concentration recorded in Synodontis clarias during the study period was

5.170mg/kg. Fig. 3 shows that a higher Al value (5.278mg/kg) in the fish was recorded at

Station 2, where July had the highest value (5.140mg/kg) and August the lowest value

(4.970mg/kg). The mean Al concentration (5.062mg/kg) recorded at Station 1 was slightly

lower with July again recording the highest monthly value (5.895mg/kg) while September

recorded the least value (4.880mg/kg). The highest monthly Al value (5.518mg/kg) was

recorded in July while the lowest value (4.978mg/kg) was recorded in September.

The mean Al concentration was significantly different (p<0.05) between the sampled

stations and the months. The concentration was however not significantly different (p>0.05)

between August and September. The monthly rank profile of Al concentration recorded in

Synodontis clarias of Benin River at Koko in a descending order was: July > August >

September.

4.1.3 Nickel (Ni)

The total mean Ni concentration recorded in Synodontis clarias during the study was

2.380mg/kg. Station 2 recorded a higher mean Ni concentration (2.408mg/kg) than Station 1

(2.352mg/kg) (Fig. 4). At Station 1, the highest monthly mean value (2.995mg/kg) was

recorded in July while the lowest mean value (1.700mg/kg) was recorded in September. At

Station 2, the highest mean concentration (2.845mg/kg) was recorded in July while the

lowest value (2.020mg/kg) was recorded in September. The highest mean monthly

concentration (2.920mg/kg) was recorded in July while September had the lowest value

(1.860mg/kg).

26

There was no significant difference (p>0.05) in Ni concentration between the sampling

stations. However, Ni concentration varied significantly (p<0.05) between the months

except in August where the concentration 0f Ni recorded was not significantly different

(p>0.05) from September. The monthly rank profile of Ni in Synodontis clarias of Benin

River at Koko in a descending order was: July > August > September.

4.1.4 Chromium (Cr)

The total mean concentration of Cr recorded during the study was 0.075mg/kg. As shown in

Fig. 5, Station 2 recorded a slightly higher Cr value (0.076mg/kg) than Station 1

(0.074mg/kg). At Station 2, July recorded the highest monthly Cr value (0.088mg/kg) while

the lowest value (0.065mg/kg) was recorded in September. At Station 1, the highest mean

Cr concentration (0.085mg/kg) was recorded in July while the lowest monthly Cr value

(0.065mg/kg) was recorded in September. The highest monthly mean Cr value

(0.087mg/kg) was recorded in July while the lowest value (0.065mg/kg) was recorded in

September.

The mean concentration of Cr varied significantly (p<0.05) between the three months except

between August and September where the concentration was not significantly different

(p>0.05). The mean concentration did not vary significantly between the sampling stations

(p>0.05). The monthly rank profile for Cr concentration in Synodontis clarias of Benin

River at Koko in a descending order was: July > August > September.

27

1 20

0.5

1

1.5

2

2.5

3

3.5

July

August

September

Sampling stations

Con

cen

trat

ion

of

Ni (

mg/

kg)

Figure 4: Monthly variations in the mean concentration of Ni in Synodontis clarias of Benin River at Koko

28

1 20

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

July

August

September

Sampling stations

Con

cent

rati

on o

f C

r (m

g/kg

)

Figure 5: Monthly variations in the mean concentration of Cr in Synodontis clarias of Benin River at Koko

29

4.2 Heavy Metals Concentrations in Water of Benin River at Koko

4.2.1 Lead (Pb)

The total mean concentration of Pb recorded in water of Benin River during the study was

0.187mg/l. The mean Pb concentration (0.208mg/l) was higher in Station 1, with the highest

value (0.230mg/l) recorded in July while the lowest value (0.190mg/l) was recorded in

September (Fig. 6). At Station 2, the mean Pb concentration was 0.165mg/l with July having

the highest value (0.170mg/l) and September with the lowest value (0.160mg/l). July

recorded the highest mean concentration (0.200mg/l) of Pb with while September recorded

the lowest value (0.175mg/l).

The concentration of Pb was not significantly different (p>0.05) between the sampling

stations and the months except between August and September. The monthly rank profile of

Pb in water of Benin River at Koko in a descending order was: July > August > September.

30

1 20

0.05

0.1

0.15

0.2

0.25

July

August

September

Sampling stations

Con

cen

trat

ion

of

Pb

(m

l/L)

Fig 6: Monthly variations in the mean concentration of Pb in water of Benin River at Koko

31

1 20

0.5

1

1.5

2

2.5

3

3.5

4

4.5

July

August

September

Sampling stations

Con

cen

trat

ion

of

Al (

ml/L

)

Figure 7: Monthly variations in the concentration of Al in water of Benin River at

Koko

32

4.2.2 Aluminium (Al)

The total mean concentration of Al recorded during the study was 2.863mg/l. The mean

concentration (3.185mg/l) of Al was higher at Station 2, with the highest value (3.900mg/l)

recorded in July and the lowest value (2.680mg/l) recorded in September (Fig. 7). At Station

1, the mean Al concentration was 2.542mg/l; July recorded the highest value (2.910mg/l)

and September with the lowest value (2.210mg/l) at Station 1. The highest monthly mean

concentration (3.405mg/l) of Pb in water was recorded in July while September had the

lowest value (2.445mg/l).

The concentration of Al varied significantly (p<0.05) between the sampling stations and the

months. However, the mean concentration (2.740mg/l) recorded in August was not

significantly different (p>0.05) from the value (2.445mg/l) recorded in September. The

monthly rank profile of Al in water of Benin River at Koko in a descending order was: July

> August > September.

4.2.3 Nickel (Ni)

The total mean Ni concentration recorded during the study was 0.628mg/l. The mean

concentration (0.640mg/l) of Ni was higher in Station 2, with the highest value (0.740mg/l)

recorded in July while the mean Ni concentration (0.590mg/l) was equal in August and

September (Fig. 8). The same pattern was observed at Station 1 where the mean Ni

concentration recorded was 0.615mg/l, with July recording the highest value (0.745mg/l)

while August and September had equal concentration value (0.550mg/l). The highest mean

monthly Ni concentration (0.742mg/l) was recorded in July while September and August

both recorded a concentration value of 0.570mg/l.

33

The concentration of Ni was not significantly different (p>0.05) between the sampling

stations. However, the mean concentration obtained was significantly different (p<0.05)

between the months except in August and September (both 0.570mg/l). The monthly rank

profile of Ni in water of Benin River at Koko in a descending order was: July > August =

September.

4.2.4 Chromium (Cr)

The recorded total mean concentration of Cr in water of Benin River was 0.056mg/l. Station

1 recorded the highest mean Cr concentration (0.058mg/l), with the highest value

(0.060mg/l) recorded in July while the concentration (0.057mg/l) was equal for August and

September (Fig. 9). A similar pattern was observed at Station 2 with a mean Cr

concentration of 0.054mg/l; July again recorded the highest value (0.057mg/l) while an

equal concentration value (0.053mg/l) was recorded in August and September. The highest

monthly mean Cr concentration (0.058mg/l) was recorded in July while September and

August had an equal mean concentration value (0.055mg/l).

The concentration of Cr was not significantly different (p>0.05) between the sampled

stations but was significantly different (p<0.05) between the months. However, the mean

concentration did not vary significantly (p>0.05) August compared to September. The

monthly rank profile of Cr in water of Benin River at Koko in a descending order was: July

> August = September.

34

1 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8July

August

September

Sampling stations

Con

cen

trat

ion

of

Ni (

ml/L

)

Figure 8: Monthly variations in the concentration of Ni in water of Benin River at Koko

35

1 20

0.01

0.02

0.03

0.04

0.05

0.06

0.07July

August

September

Sampling stations

Con

cen

trat

ion

of

Cr

(ml/L

)

Figure 9: Monthly variations in the concentration of Cr in water of Benin River at

Koko

36

CHAPTER FIVE

5.0 DISCUSSION

From the results obtained, the presence of Pb, Al, Ni and Cr were ascertained in the water

and fish (Synodontis clarias) of the Benin River at Koko. Heavy metals are non-

biodegradable natural resources but their levels have increased due to domestic, industrial,

mining and agricultural activities (Kalay and Canli 2000; Yousafzai and Shakoori 2008). If

the concentration levels of these elements increased beyond the level required, they can act

in either acutely or chronically toxic manner (Gulfaraz et al., 2001). Concerned national and

international bodies including WHO (1998, 2006), FAO (1983, 2008) and SON (2007) have

prescribed maximum guideline values for these heavy metals both in potable drinking-water

and food fish.

5.1 Heavy Metals Concentration in Synodontis clarias of Benin River at Koko

Results obtained indicated higher heavy metals concentrations in fish than those recorded in

water. The result agrees with observation of Goodwin et al. (2003) that fish accumulates

heavy metals directly from water and diet and contaminant residues may ultimately reach

concentration levels hundreds or thousands of times above those measured in the water,

sediment and food. The recorded concentrations of the Pb, Al, Ni and Cr varied in the fish.

The total mean concentration of heavy metals in recorded fish in decreasing order was: Al >

Ni > Pb > Cr.

The total mean concentration of Pb recorded in fish was 1.507mg/kg. The mean Pb

concentration was similar in Synodontis clarias obtained at both stations and during the

months (p>0.05). The high Pb concentration recorded in the study area may be attributed to

the wastes generated by the industries (Optima and Total), crude oil spillage, and the

37

activities of motorized water crafts since water is the dominant means of transportation in

the area. According to WHO (2011), lead is used in the production of lead acid batteries,

solder, alloys, cable sheathing, rust inhibitors and plastic stabilizers while the tetraethyl and

tetramethyl compounds of lead are used as antiknock compounds in petrol. Lead poisoning

causes inhibition of the synthesis of haemoglobin; dysfunctions in the kidneys, joints and

reproductive systems, cardiovascular system and acute and chronic damage to the central

nervous system (CNS) and peripheral nervous system (PNS) (Ogwuegbu and Muhanga,

2005). The mean Pb concentration (1.507mg/kg) recorded in this study was higher than

value (1.175mg/kg) recorded by Eletta et al. (2003) in Synodontis membranaceous of Asa

River. The concentration level of Pb was however, lower than the concentration levels

reported by Nwajei et al. (2012) in Clarias anguillaris (4.067mg/kg) and Chrysichthys

nigrodigitatus (2.067mg/kg) from River Niger probably due to the rate by which natural and

anthropogenic wastes are continuously being discharged into the River Niger. The

concentration of Pb in fish was below the 2.0mg/kg guideline level recommended by FAO

(1983) and WHO (1998) for fish and fishery products.

The total mean concentration of Al recorded in fish during this study was 5.170mg/kg. The

mean concentration of Al was significantly different (p<0.05) between the sample stations

and also between the months. The concentration was similar (p>0.05) between August and

September. Industrial waste, erosion, dissolution of minerals and salts, atmospheric dust

pollution and rain are the major activities that promote the presence of Al. The level of Al

recorded may be due to its abundance as it constitutes about 8% of the Earth's crust. Al is

released into the environment mainly by natural processes such as melting of the ores

(WHO, 2003). Aluminium metal is used as a structural material in the construction,

automotive, and aircraft industries, in the production of metal alloys, in the electric industry,

in cooking utensils, and in food packaging (ATSDR, 1992). Several factors influence

38

aluminium mobility and subsequent transport within the aquatic environment. These include

chemical speciation, hydrological flow paths, soil–water interactions, and the composition

of the underlying geological materials. Acid environments caused by acid mine drainage or

acid rain can cause an increase in the dissolved aluminium content of the surrounding waters

(ATSDR, 1992; WHO, 1997). The high level of Al recorded at Station 2 may be attributed

to the presence of structural installations and buildings on water at the station whose

metallic properties gradually leach into the river.

The total mean concentration of Ni recorded in fish during this study was 2.380mg/kg.

There was no significant difference (p>0.05) between the sampling stations. However, the

mean concentration recorded was significantly different (p<0.05) between the months.

Nickel is one of the prominent trace metals in petroleum hence the relatively high level

recorded in this study. Nickel has been reported to cause skin irritation, hypersensitivity and

cancer of the lung or nose (International Committee on Nickel Carcinogenesis in Man

[ICNCM], 1990). The Ni concentration recorded during this study was higher than higher

than the value (0.468mg/kg) recorded by Agbozu et al. (2007) in Synodontis clarias from

Taylor Creek. The Ni concentration however, was lower than values recorded by Nwajei et

al. (2012) in Chrysichthys nigrodigitatus (19.533mg/kg) and Clarias anguillaris

(18.500mg/kg) in River Niger. The mean concentration of Ni recorded during this study was

above the safe limit (0.5–0.6 mg/kg) recommended by FAO (1983) for food fish.

The total mean concentration of Cr recorded in fish during this study was 0.075mg/kg. The

concentration was similar at both sampling stations (p>0.05). The mean concentration of Cr

varied significantly (p<0.05) between the three months except between August and

September. Chromium reaches water bodies primarily from the discharge of industrial

wastes and disposal of products containing the metal (Akan et al., 2010). Cr is an essential

39

trace metal and the biologically usable form of Cr plays an essential role in glucose

metabolism. The deficiency of Cr results in impaired growth and disturbances in glucose,

lipid and protein metabolism (Calabrese et al., 1985). Cr is however, toxic above the natural

levels. Low level exposure to chromium can irritate the skin and cause ulceration while long

term exposure can cause damage to the kidney, liver and circulatory and nerve tissues

(ATSDR, 2000). The recorded total mean concentration of Cr was lower than the value

(0.29mg/kg) recorded by Eletta et al. (2003) for Synodontis membranaceous in Asa River

and the values recorded by Nwajei et al. (2012) in Chrysichthys nigrodigitatus

(1.633mg/kg) and Clarias anguillaris (2.233mg/kg) of River Niger. The Cr concentration

recorded in fish during this study was below the maximum allowable levesl (0.15mg/l and

1.0mg/kg) recommended by WHO (1998) and FAO (1983) respectively, for fish and fishery

products.

5.2 Heavy Metals Concentration in Water of Benin River at Koko

Results of this study indicated high levels of heavy metals in the water of Benin River. The

total mean concentration of heavy metals in water in a descending order of magnitude

followed the same pattern as was observed in fish: Al > Ni > Pb > Cr.

The total mean concentration of Pb recorded in water of Benin River at Koko during this

study was 0.187mg/l. Signs of chronic lead toxicity, including tiredness, sleeplessness,

irritability, headaches, joint pain and gastrointestinal symptoms may appear in adults at

blood lead levels of 50–80 μg/dl (WHO, 2011). The recorded mean Pb concentration

(0.871mg/l) was higher than Pb value (0.012mg/l) reported Oguzie and Achegbulu (2010) in

water of Ovia River but lower than the Pb value (1.656mg/l) recorded by Udoidiong et al.

(2013) in lower Cross River. The recorded mean Pb level exceeded the recommended

40

guideline value (0.01mg/l) for potable drinking-water by WHO (2006), SON (2007) and

FAO (2008).

The total mean concentration of Al recorded during this study was 2.863mg/l. This

concentration value was lower than the Al value (7.79mg/l) recorded by Sunday et al.

(2013) in Bindare stream. Symptoms including nausea, vomiting, diarrhoea, mouth ulcers,

skin ulcers, skin rashes, and arthritic pain were noted in humans with high level of Al intake

(Clayton, 1989). This value was higher than the value (0.2mg/l) recommended by WHO

(2006) and SON (2007) for potable water.

The total mean Ni concentration recorded in water was 0.628mg/l. Nickel was reported to be

a vital commodity in every area of industrial activity and has worldwide application in the

manufacture of batteries, fertilizer, welding products, electroplating and household

appliances (Sreedevi et al., 1992). Increased nickel concentrations in groundwater and

municipal tap water (100–2500μg/l) in polluted areas and areas in which natural nickel was

mobilized had been reported by McNeely et al. (1972). The recorded value in this study

(0.628mg/l) was higher than the Ni value (0.06mg/l) recorded by Enuneku et al. (2014) in

water of Benin River but lower than the Ni value (3.15mg/l) in Bindare stream recorded by

Sunday et al. (2013). This value however, exceeded the recommended limit (0.02mg/l) by

SON (2007) and FAO (2008) and the guideline value (0.07mg/l) by WHO (2006).

The recorded total mean concentration of Cr in water during this study was 0.056mg/l. The

presence of Cr in soaps and detergents used for washing and bathing coupled with

petroleum products being discharged into the river could be responsible for the high Cr level

in the water. The Cr level was higher than the value (0.02mg/l) reported by Arise et al.

(2013) for creeks around the Kokori-Erhoike Petroleum Flow Station in Delta State, but was

significantly lower than the Cr value (4.19mg/l) in Bindare stream according to the findings

41

of Sunday et al. (2013). The recorded value was above the guideline level (0.05mg/l) for Cr

in drinking-water recommended by WHO (2006), SON (2007) and FAO (2008).

The heavy metals may have their main source in the effluents from the industries along the

river especially the ones producing lubricating oil and importing refined petroleum products

such as ASCA Oil Company Ltd and Total Ltd whose effluents, although not disposed

directly into the Benin River, finally enters the river system indirectly through swampy

creeks and flood run-off

42

CHAPTER SIX

6.0 CONCLUSION AND RECOMMENDATIONS

6.1 Conclusion

Result of the present study has ascertained the presence and provided the concentration

levels of Pb, Al, Ni and Cr in the Benin River at Koko. The Benin River is the major source

of fish for the local communities and also represents an important route for the

transportation of petroleum and allied products. This study showed that the heavy metal

concentration levels obtained in Synodontis clarias were generally below the safe guideline

limits prescribed by FAO (1983) and WHO (1998) for food fish. The Ni value recorded in

Synodontis clarias however, exceeded the FAO (1983) recommended limit (0.5-0.6mg/kg).

Ni is a hazardous heavy metal with the propensity to cause cancer of the lung and nasal

cavity. Increased urbanization results in more wastes being generated and since the river

system is the main recipient of wastes in the area, this must have aggravated the pollution

effects from industrialization. The concentration of the heavy metals in the water of Benin

River at Koko exceeded the limits recommended by WHO (2006), SON (2007) and FAO

(2008). The concentration levels of heavy metals, particularly Cr and Pb, portend danger to

the inhabitants of the study area, who depend on the surface water in the region for drinking

and domestic uses. The consequence of this is that the ignorant inhabitants make use of this

heavily contaminated water to their detriment. It can therefore be concluded that Benin

River at Koko is highly polluted with respect to heavy metals which makes the water unfit

for drinking. It should also be noted that while a generally low level (i.e. below the

recommended limits) of metals was recorded in the dominant fish species (Synodontis

clarias), the high concentration of Ni necessitates that consumption of fish should be

43

monitored to avoid the adverse effects brought about by the bio-accumulation of the metal

in humans.

6.2 Recommendations

In the light of the results obtained from this study, the following recommendations are

considered necessary:

1. Educational programmes should be undertaken to enlighten the locals of the area on

the social, economic and ecological value of the natural rivers and their resources.

2. Safe disposal of domestic sewage, agricultural and industrial effluents should be

practiced and where possible, recycled to reduce the concentrations of these metals

in the aquatic environment.

3. The location of industries and research institutions should be far away from water

bodies. With respect to existing factories and research institutions, necessary steps

should be taken to remove some of the poisonous and harmful chemicals by treating

the effluents before they are discharged into the river.

4. There should be tighter regulations to control inflow of nutrient and chemical

contaminants into aquatic habitats coupled with enforcement of penalties that will be

imposed for illegal and unsustainable developments that degrade these habitats.

5. There should be a periodical test on this water body to ascertain continually its

pollution index.

44

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APPENDIX I

Mean Concentration (mg/kg) of Heavy Metals in Synodontis clarias of Benin River at

the different Stations

Heavy Metals Months Station A Station B

Lead July 1.135 1.915

August 1.910 1.525

September 1.445 1.115

Aluminium July 5.140 5.895

August 4.970 5.060

September 5.075 4.880

Nickel July 2.995 2.485

August 2.360 2.360

September 1.700 2.020

Chromium July 0.085 0.088

August 0.072 0.074

September 0.065 0.065

55

APPENDIX II

Mean Concentration (mg/l) of Heavy Metals in the water of Benin River at the

different Stations

Heavy Metals Months Station A Station B

Lead July 0.230 0.170

August 0.205 0.165

September 0.190 0.160

Aluminium July 2.910 3.900

August 2.505 2.975

September 2.410 2.680

Nickel July 0.745 0.740

August 0.550 0.590

September 0.550 0.590

Chromium July 0.060 0.057

August 0.057 0.053

September 0.057 0.053

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APPENDIX III

SON Standard for Drinking Water in Nigeria

Heavy metals

Maximum permitted levels

(mg/l)Effects on man

Aluminium 0.2 Potential neuro-degenerative disorders

Cadmium 0.01 Toxic to the kidney

Chromium 0.05 Cancer

Copper 1 Gastrointestinal disorder

Iron 0.3 None

Lead 0.01Cancer; interference with vitamin D metabolism; affects mental development in infants; toxic to the central and

peripheral nervous systems

Mercury 0.001 Affects the kidney and central nervous system

Nickel 0.02 Possibly carcinogenic

Zinc 3 None

Source: Standard Organization of Nigeria (2007).

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APPENDIX IV

WHO Guideline Values for Chemicals that are of Health Significance in Drinking-water

Chemical Guideline value (mg/l)

Aluminium 0.2

Antimony 0.02

Arsenic 0.01

Barium 0.7

Cadmium 0.003

Chromium 0.05

Copper 2

Lead 0.01

Manganese 0.4

Mercury 0.006

Molybdenum 0.07

Nickel 0.07

Selenium 0.01

Source: World Health Organization (2006).

58