CHAPTER ONE

1.0 INTRODUCTION TO THE STUDY.

The dramatic increase in public awareness and concern about the state of the global

and local environments which has occurred in recent decades has been accompanied and

partly prompted by an ever growing body of evidence on the extent to which pollution has

caused severe environmental degradation. The introduction of harmful substances into the

environment has been shown to have many adverse effects on human health, agricultural

productivity and natural ecosystems. (Garbarino et al.,1995).

Heavy metals is a general collective term which applies to the group of metals and metalloids

with atomic density greater than 4 g/cm3 or 5 times or more, greater than water (Nriagu and

Pacyna,1988; Hawkes, 1997). Their pollution of the environment, even at low levels and the

resulting long – term cumulative health effects are among the leading health concerns all over

the world. (Huton and Symon, 1986; Mc. Cluggage, 1991).

Metals constitute the largest class of elements in the periodic table. As a group, metals share

some common physical, chemical and electrical properties (D’Amore et al., 2005). Metals are

hard and strong, capable of being shaped mechanically (malleable and ductile), are good

conductors of heat and electricity and they have lustrous surfaces when clean. They tend to

lose electrons and form cations.

Metals, a major category of globally distributed pollutants, are natural elements that have

been extracted from the earth and harnessed for human use. Metals are notable for their wide

environmental dispersion from various activities; their tendency to accumulate in select

tissues of the human body; and their overall potential to be toxic even at relatively minor

levels of exposure.

1

Soils along highways typically contain high amount of heavy metals such as Fe, Mn, Zn, Pb,

and Cd, most commonly from vehicle exhaust and wear of vehicle parts. Since these heavy

metals do not degrade naturally, accumulation of high concentration in soils can be toxic to

organisms living in surrounding environment (Purves, 1985). Metals are natural parts of the

eco-system occurring in soil, rock, water, air and organism. A few metals including Cu, Mn,

and Zn are essential to plant metabolism in trace amounts. It is only when metals are present

at excessive levels in bioavailable forms, that they become potentially toxic.

Heavy metal contamination of roadside soil has been of major concern regarding their

toxicity, persistence and non-degradability in the environment. Heavy metal contamination of

roadside soil usually derives from anthropogenic sources such as emissions from automobile

exhaust, waste incineration, land disposal of wastes, use of agricultural inputs, emissions

from industrial processes, and wet and/or dry atmospheric deposits (Alloway, 1995).

1.1 AIMS AND OBJECTIVES.

1.1.1 General aims.

The aims of this study is to investigate the chemical fractionation and distribution of

heavy metals in roadside soil samples obtained within the Iwo area and to establish the heavy

metal concentration levels within the study area.

1.1.2 Specific objectives.

● To determine total Mn, Fe, Cd, Zn and Pb in street dusts and roadside soils samples,

● To identify and quantify different Mn, Fe, Cd, Zn and Pb species in the samples using

modified Tessier’s nine stage sequential extraction method,

2

● To establish the spatial distribution of heavy metals around major roads within Iwo area of

Osun State, Nigeria.

1.2 JUSTIFICATION OF THE STUDY.

The town of Iwo is on the rise, the increase in banking system, higher institutions, and

generally the influx of different tribes of people into the small town has caused a sharp

increase in the amount of vehicles that goes into the town on a daily basis and therefore

leading to increased amount of heavy metals that pollute the environment and since they do

not degrade naturally, high concentration in the soils can become harmful to living organisms

in the environment.

The modified Tessier’s method was used to determine the chemical fractionations of heavy

metals in roadside soil (Tessier et al., 1979). It is the best known and most widely used

sequential extraction procedure, hence its popularity. The method provides comprehensive

information on the interaction between different species of the metal and environmental

media such as road side soil, in order to be able to predict their environmental impact. It is

most likely that the chemical properties of soil and sediment play an important role in heavy

metal retention or removal from road side soil. The impact of these properties may vary

according to the nature of the roads. There was, therefore, a need to investigate the behaviour

of the heavy metals distribution from roads with different characteristics.

3

1.3 SCOPE OF THE STUDY.

The present study was aimed at assessing the heavy metal fractions and distribution of

roadside soil of some selected roads in Iwo. Spatial distribution would only be investigated;

traffic counts, temporal study and physico-chemical analysis would be considered in further

study.

4

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 ENVIRONMENTAL POLLUTION

Pollution is defined as the release of waste material or energy into land, water or air

that may cause detriment or lower the quality of life. Moreover, pollution can be defined as

the act of polluting or polluted state i.e. the state or condition of being polluted, meaning the

presence of pollutants in the environment (Encarta, 2009).

In the past, pollution used to be regarded as a local problem, close to where sources are

located. However, the industrialization of society, the explosion of the human population,

massive urbanization and the introduction and use of cars has caused growth in all spheres of

life. This growth has been coupled with an increase in waste by-products. Pollution has now

become a pandemic issue because pollutants can cross borders with the help of wind, water

and all other agents of pollution. Recently, results have shown that the harmful effects of

pollution only become apparent after long periods of exposure to it and so monitoring

pollution has suddenly become important as well as where it occurs (Alloway& Ayres, 1997).

Natural organic matter, that is, the remains of dead plants and animals are

biodegradable. These materials are broken down by microorganisms in water and soil. In this

way, nature takes care of its own waste. Synthetic organic products such as dichlorodiphenyl-

trichloroethane(DDT) are persistent and are not biodegradable due to their affinity for non-

aqueous lipid tissues. Inorganic pollutants are usually man-made and are common in the areas

of domestic or industrial wastes.

Common forms of pollution that affect human life are air, water and soil pollutions.

Air pollution is a process that involves the release of gaseous chemicals and particulates into

5

the atmosphere. Common examples include carbon monoxide (CO), sulphur dioxide (SO2),

chlorofluorocarbons (CFCs), nitrogen oxides (NOx) and heavy metals in form of particulates

produced by industry and motor vehicles. Water pollution affects oceans and inland water

bodies. Examples include organic and inorganic chemicals, heavy metals, petrochemicals and

microorganisms. Water pollution may also occur in the form of thermal pollution and the

depletion of dissolved oxygen. Soil contamination often occurs when chemicals are released

by spillages or underground storage tank leakage.

Environmental pollution can also result from natural disasters. For example, hurricanes often

cause water contamination from sewage and petrochemical leaks from ruptured storage tanks

contaminating ground water. Some sources of pollution, such as nuclear power plants or oil

tankers, can produce widespread and potentially hazardous releases when accidents occur.

2.1.1 SUGGESTIONS TO CONTROL ENVIRONMENTAL POLLUTION:

It is clear that fossil fuels are among the biggest sources of pollution. The need to find

alternative renewable sources of energy which can replace fossil fuels in the future has

become a major issue which has to addressed as soon as possible.

Building solar panels and using dry solar energy systems to meet at least part of home

electricity needs is another emerging opportunity for dry enthusiasts. This can really make a

positive difference to the environment and reduce current pollution levels.

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2.2 HEAVY METALS

A heavy metal is a member of a loosely-defined subset of elements that exhibit

metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and

actinides.

Heavy metals constitute the largest class of elements in the periodic table. Heavy metals

occur naturally at levels that are not considered to have any toxic effects to plants, animals

and humans. Metals comprise 75% of the known elements and can form alloys with each

other and with non metals (Sparks, 2005). They have useful properties such as strength,

malleability and conductivity of heat and electricity. Some metals exhibit magnetic properties

and others are excellent conductors of electricity.

Heavy metals such as manganese, zinc, copper, chromium and iron are essential elements

when present in small amounts, heavy metals such as Pb and Hg are toxic at all levels.

The behaviour and toxicity of heavy metals or their compounds in the environment depends

largely on their concentrations and their chemical forms (Kot & Namiesnik, 2000; Tokalioglu

et al., 2003). For example, Cr (III) in food is an essential element, its stable; whereas Cr(VI)

is mobile and harmful. Also, the organic form of mercury is more toxic than its inorganic

derivative. While, the inorganic form of arsenic is more toxic than its organic form. Cases of

human poisoning by heavy metals have been reported. Cadmium (Cd) and its compounds are

extremely toxic at all levels but many metals are essential to life, although they occur only in

trace amounts in the body tissues.

7

2.3 HEALTH HAZARDS ASSOCIATED WITH HEAVY METALS.

Humans are always exposed to the natural levels of trace elements. Under normal

circumstances, the body is able to control some of these amounts. Increased exposure may

occur through inhalation of airborne particles or through ingestion of contaminated soil by

children or by absorption through the skin.

Metals can cross the placenta and harm an unborn child in pregnant women. Children are the

most susceptible to health problems caused by heavy metals, because their bodies are smaller

and still developing (Thomson, 2007). High levels of toxic metals deposited in body tissues

and subsequently in the brain may cause significant developmental and neurological damage,

including depression, increased irritability, anxiety, insomnia, hallucinations, memory loss,

aggression and many other disorders. Chronic effects of prolonged low level exposure to

arsenic poisoning causes skin pigmentation, keratoses, skin cancers and death if exposed to

high levels. Mercury poisoning symptoms include blindness, deafness, brain damage,

digestive problems, kidney damage, lack of coordination and mental retardation. Cadmium

poisoning causes softening of the bones and kidney failures and was responsible for the “itai-

itai” disease (a name derived from the painful screams in Japanese language) due to the

severe pain in the joints and the spine (Wikipedia, 2007). Cadmium was released in the rivers

by mining companies in the mountains in Japan in the late 1940’s. The disease arose from

increased uptake of cadmium in locally consumed rice grown in paddy fields irrigated with

cadmium-contaminated river water.

8

2.4 HEAVY METALS IN THE ENVIRONMENT.

The main source for metal input to plants and soils is atmospheric deposition. Volatile

metalloids such as As, Hg, Se, and Sb can be transported over long distances in gaseous

forms or enriched in particles, while trace metals such as Cu, Pb, and Zn are transported in

particulate phases (Adriano, 2001; Adriano et al. 2005). Microorganisms can transform

metals such as Hg, Se, Sn, As, and Cr by means of oxidation– reduction and methylation (the

process of replacing an atom, usually a H atom, with a methyl group) and dimethylation

reactions. These processes affect transport or mobility and solubility or toxicity of metals

(Adriano 2001; Sparks 2005). Methylation is favoured in environments characterized by low

oxygen levels, low pH, and high soil organic matter (SOM) contents.

Heavy metal contamination of soils is a far more serious problem than air or water pollution

because heavy metals are usually tightly bound by the organic components in the surface

layers of the soil. Heavy metals can also be very quickly translocated through the

environment by erosion of the soil particles to which they are adsorbed or bound and re-

deposited elsewhere. The transport, cycling, fate, bioavailability and toxicity of heavy metals

are markedly influenced by their physico-chemical forms in water, sediments and soils.

Whenever a heavy metal or its compound is introduced into an aquatic environment, it is

subjected to a wide variety of physical, chemical and biological processes. These include

hydrolysis, chelation, complexation, redox, biomethylation, precipitation and adsorption

reactions.

2.4.1 ANTHROPOGENIC SOURCES OF HEAVY METALS;

Anthropogenic sources of heavy metals include agriculture (fertilizers, animal

manures and pesticides), metallurgy (mining, smelting and metal finishing), sewage sludge,

9

scrap disposal and energy production (power plants, leaded and unleaded petrol). (Adriano

2001).

2.5 METAL ADDITIVE IN PETROL.

Petrol in high compression internal combustion engines, has a tendency to ignite

early, causing a damaging ‘engine knocking’ noise (Wikipedia, 2006). To obtain the

maximum energy from the petrol, the compressed fuel-air mixture inside the combustion

chamber needs to burn evenly, propagating out from the spark plug until all the fuel is

consumed (Hamilton, 1995). “Knocking” occurs when these reactions form products that can

auto ignite before the flame front arrives.

Lead and recently manganese are commonly used as metallic additives in petrol. They are

added as petrol soluble chemicals that can produce the desired effect at the parts-per-million

concentration range. These additives prevent premature ‘knocking’, protect engine valves

against wear and increase the efficiency and power of engines (Chevron, 2002).

10

CHAPTER THREE

3.0 MATERIALS AND METHODS

3.1 STUDY AREA

The study was conducted within the town of Iwo, the second largest town in Osun

State. The samples were collected with a cutlass and put into a air-tight polythene bag. The

samples were taken at 0cm – 5cm into the soil.

3.1.1 SAMPLING SITES

The sampling sites were at the following road junctions: Odo Ori Roundabout; Ibadan

Express Road; Bowen Road; Ejigbo Road; Hospital Road; Adeeke Road; Osogbo Road;

Agbowo Estate, Waterworks Road.

3.1.2 PRE-TREATMENT

All the glass wears, were washed with non-ionic detergents, rinsed with tap water

then with distilled water and soaked in 10% Nitric acid for 48 hours to avoid trace metals

contamination.

3.2 METHODS.

3.2.1 SELECTIVE SEQUENTIAL EXTRACTION.

The modified procedure of Tessier et al (1979, 1985) was used for this study except

for the introduction of two important fractions (water soluble and plant available). In this

scheme, heavy metals were separated into nine operationally defined fractions: water soluble

(S1), exchangeable (S2), bound to carbonate (S3), plant available (S4), bound to Mn oxide (S5),

bound to amorphous Fe oxide (S6), bound to crystalline Fe oxide (S7), bound to organic

matter (S8), and residual fraction (S9).

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Principle: Sequential extraction to fractionate metals or other elements in solid

materials (soils, sediments, sludge, solid waste, etc.) into several groups of different

leachability is widely employed to determine the distribution of metals in different phases.

Although the procedures used are generally tedious and time consuming, the results furnish

detailed information about the origin, mode of occurrence, bioavailability, potential mobility,

and transport of the metals in natural environments. The technique is therefore, widely used

as a tool for the study of the origin and fate of metals in the environment.

The fundamental principle underlying this scheme is based on a careful selection of

reagents and detailed operating conditions to give satisfactory results for the targeted phases

or fractions of the metals. Since heavy metals exist in different forms and are bound to

different sites and components in the soil, appropriate solvents or reagents are equilibrated at

specific pH, concentration and temperatures to ensure timely dissolution of these metals in

solution. The metals are released into solution on solubility basis, exchange reactions

between exchange sites in the clay and organic matter matrix, reducing conditions which

favour the release of the metals held in the occluded fractions and also oxidizing conditions

of the organic, sulphide and all oxidizable matter in the soil. The metals are determined using

the appropriate spectrophotometric techniques. It is important to emphasise that this

operationally defined extraction procedure provides knowledge on metal affinity to soil

components and the strength with which they are bound to the matrix (Narwal et al., 1999).

Procedure: One gram of each soil sample was weighed and extractions were made

through steps (S) by centrifugation and filtration at 10,000 rpm placing the sample in

polyethylene centrifuge tubes. Distilled/deionised water was used to wash the residues

following subsequent extractions in order to ensure selective dissolution and avoid possible

inter-phase mixing between the extractants. All samples were run in duplicates.

12

S1 Water soluble metals: Water-soluble metals were extracted with a solution of

50ml distilled deionised water at pH 7.0 and at 280C for 2 hours.

S2 Exchangeable metals: The residue from (a) was extracted with 25ml of 1.0M

NH4COOCH3 (pH = 7.0). The suspension was shaken for 30 min at 280C.

S3 Metals bound to carbonate: The residue from (b) was extracted with 1M sodium

acetate (CH3COONa) adjusted to pH 5.0 with acetic acid (CH3COOH). The suspension was

shaken for 5 hours.

S4 Plant Available Metals: The residue from (c) was extracted by shaking with a

solution mixture of 50ml of 0.025M HCl + 0.05M H2SO4 for 30 mins at 280C.

S5 Bound to Mn-Oxide: The residue from (d) was shaken for 30 minutes at 28 0C with

a solution of 25ml 0.1M NH2OH.HCl in 25% CH3COOH (pH 2 – 3).

S6 Bound to Amorphous Fe-oxide: The residue from (e) was extracted with 25ml of

0.2M (NH4)2C2O4 (pH 3.0) for 30 minutes at 500C using a water bath with occasional stirring.

S7 Bound to Crystalline Fe-oxide: The residue from (f) was extracted using 25ml of

0.04M NH2OH.HCl in 25% acetic acid (pH 2) and heated in a water bath with occasional

stirring at 1000C for 6 hours.

S8 Bound to organic matter: The residue from (g) was extracted with 10ml of 0.02M

HNO3 and 15ml of 30% H2O2 (adjusted to pH 2 with HNO3). The mixture was then heated to

850C for 5 hours with occasional agitation. A second 15ml liquot of 30% (pH 2 with HNO3)

was added and the mixture heated again to 850C for 3 hours with intermittent agitation. After

cooling, 5ml of 3.2M NH4COOCH3 in 20% (v/v) HNO3 was added and the samples diluted to

20ml and agitated continuously for 30 min.

13

S9 Residual metals: The residue from (h) was digested with a mixture of concentrated

HNO3 and HClO4 for 8 hours.

The metal content of all the extracts in the centrifuged solutions were determined by atomic

absorption spectrophotometer (Unicam Solar 1969 Series). Standard solutions for the metals

were prepared for each extraction step in a background solution of the extracting reagents.

The following metals were determined , Pb, Cd, Cr, Ni, Cu, Zn, Mn, Fe, and V. All the

analysis were done in duplicates.

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CHAPTER FOUR.

4.0 RESULTS AND DISCUSSION.

The following tables represent the concentrations of heavy metals of the roadside soil

samples that were extracted with the selective sequential extraction methods.

Tables 4.1 to 4.9 presents the results of the selective sequential extraction methods which

showed that Fe is more predominant in the roadside soils in Iwo with the highest average

mean value of 21.24±3.74µg/g (Table 4.5) and Cd is the lowest occurring heavy metal in the

soils with an average mean value of 0.04±0.01µg/g (Table 4.3) which is well expected

because it has been reported that iron (Fe) occurs at high concentration in Nigeria soil

(Asaolu et al., 1997; Asaolu and Olaofe, 2004; Nwajei and Gagophien, 2000), and it will seen

that in all the roadside soils in Iwo, Fe is the most occurring heavy metal.

TABLE 4.1: Concentration of water soluble metals of roadside soil in Iwo (µg/g).

Fraction 1 Mn Fe Zn Pb Cd

Adeke 8.03±0.06 13.03±020 5.11±0.15 0.09±0.00 0.04±0.01

Agbowo 10.10±0.25 19.93±0.10 6.09±0.15 0.10±0.00 0.05±0.00

Bowen 11.20±0.24 20.03±0.07 5.17±0.28 0.10±0.00 0.05±0.00

Ejigbo 10.10±0.12 16.10±0.16 4.87±0.19 0.11±0.00 0.06±0.00

Exp 9.81±0.08 17.08±0.33 4.00±0.04 0.10±0.00 0.05±0.00

Hosp 10.40±0.09 17.43±0.14 5.12±0.16 0.09±0.01 0.03±0.00

Odoori 10.56±0.14 21.06±0.11 4.31±0.10 0.10±0.00 0.05±0.00

Osogbo 12.25±0.20 19.02±0.33 5.14±0.10 0.12±0.00 0.05±0.00

Waterworks 11.0±0.21 21.04±0.42 6.62±0.13 0.09±0.00 0.04±0.00

Mean±SD 10.36±1.12 18.30±2.58 5.16±0.79 0.10±0.01 0.05±0.01

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TABLE 4.2: Concentration of exchangeable metals of roadside soil in Iwo (µg/g).

Fraction 2 Mn Fe Zn Pb Cd

Adeke 11.87±0.19 20.09±0.32 5.95±0.09 0.09±0.00 0.04±0.00

Agbowo 11.35±0.19 21.29±0.51 5.65±0.19 0.09±0.00 0.05±0.01

Bowen 9.93±0.26 20.95±0.15 6.32±0.15 0.11±0.00 0.04±0.00

Ejigbo 8.68±0.52 17.32±0.16 6.89±0.16 0.11±0.01 0.05±0.00

Exp 11.10±0.16 23.07±0.07 8.04±0.08 0.12±0.00 0.04±0.01

Hosp 13.08±0.14 21.06±0.17 6.32±0.10 0.09±0.00 0.04±0.00

Odoori 10.48±0.14 20.06±0.11 4.49±0.10 0.10±0.00 0.05±0.00

Osogbo 11.01±0.04 18.07±0.11 6.08±0.12 0.10±0.00 0.05±0.00

Waterworks 10.44±0.13 19.69±0.45 4.99±0.02 0.11±0.00 0.04±0.01

Mean±SD 10.71±1.36 19.62±2.36 6.25±0.82 0.11±0.01 0.04±0.01

TABLE 4.3: Concentration of metals bound to carbonate of roadside soil in Iwo (µg/g).

Fraction 3 Mn Fe Zn Pb Cd

Adeke 13.00±0.16 21.98±0.10 6.33±0.15 0.08±0.00 0.04±0.00

Agbowo 12.01±0.05 17.14±0.25 4.99±0.02 0.10±0.00 0.05±0.00

Bowen 7.05±0.10 15.19±0.27 4.68±0.16 0.10±0.00 0.05±0.01

Ejigbo 9.44±0.13 18.15±0.24 5.22±0.19 0.09±0.00 0.04±0.00

Exp 10.10±0.30 17.03±0.12 4.94±0.11 0.09±0.00 0.05±0.00

Hosp 12.09±0.14 19.50±2.48 6.09±0.13 0.08±0.00 0.03±0.00

Odoori 14.09±0.15 22.97±0.15 6.21±0.16 0.11±0.00 0.05±0.00

Osogbo 8.90±0.25 16.02±0.07 5.26±0.09 0.10±0.00 0.04±0.00

Waterworks 13.10±0.15 20.89±0.20 5.72±0.15 0.09±0.00 0.04±0.00

Mean±SD 11.09±2.26 18.77±2.71 5.50±0.60 0.10±0.01 0.04±0.01

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TABLE 4.4: Concentration of plant available metals of roadside soil in Iwo (µg/g).

Fraction 4 Mn Fe Zn Pb Cd

Adeke 15.15±0.25 24.87±0.20 6.99±0.03 0.09±0.00 0.04±0.00

Agbowo 11.37±0.20 24.01±0.48 6.45±0.10 0.10±0.01 0.04±0.00

Bowen 14.07±0.17 21.94±0.10 6.29±0.15 0.10±0.01 0.04±0.00

Ejigbo 10.01±0.18 20.09±0.16 6.00±0.03 0.10±0.00 0.05±0.00

Exp 9.54±0.26 15.96±0.33 5.20±0.09 0.09±0.00 0.04±0.00

Hosp 11.03±0.08 22.22±0.21 6.08±0.13 0.09±0.00 0.04±0.00

Odoori 8.06±0.11 12.95±0.13 4.43±0.08 0.08±0.00 0.04±0.00

Osogbo 13.09±0.14 21.24±0.54 7.03±0.18 0.11±0.00 0.05±0.00

Waterworks 9.93±0.27 20.99±0.02 6.32±0.02 0.10±0.00 0.05±0.00

Mean±SD 11.36±2.25 20.48±3.68 6.09±0.81 0.10±0.01 0.04±0.01

TABLE 4.5: Concentration of metals bound to manganese oxide of roadside soil in Iwo (µg/g).

Fraction 5 Mn Fe Zn Pb Cd

Adeke 19.0±0.18 24.52±0.28 5.99±0.02 0.10±0.00 0.04±0.00

Agbowo 15.44±0.12 24.15±0.25 5.89±0.20 0.11±0.01 0.05±0.00

Bowen 10.93±0.17 21.07±0.13 5.96±0.25 0.11±0.01 0.04±0.00

Ejigbo 21.07±0.13 27.99±0.23 6.98±0.04 0.10±0.01 0.05±0.00

Exp 7.88±0.21 16.04±0.09 5.00±0.01 0.10±0.00 0.04±0.00

Hosp 17.13±0.27 21.77±0.30 5.87±0.20 0.09±0.00 0.04±0.00

Odoori 8.44±0.09 16.97±0.24 5.25±0.07 0.10±0.00 0.04±0.00

Osogbo 13.03±0.08 19.84±0.39 4.28±0.12 0.10±0.00 0.04±0.00

Waterworks 10.89±0.22 18.80±0.41 4.01±0.01 0.10±0.00 0.05±0.00

Mean±SD 13.76±4.53 21.24±3.74 5.47±0.91 0.10±0.01 0.04±0.01

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TABLE 4.6: Concentration of metals bound to amorphous iron oxide of roadside soil in Iwo (µg/g).

Fraction 6 Mn Fe Zn Pb Cd

Adeke 12.29±0.13 20.05±0.09 5.83±0.15 0.09±0.00 0.04±0.00

Agbowo 9.91±0.19 17.96±0.14 5.16±0.13 0.09±0.00 0.04±0.00

Bowen 15.59±0.55 24.04±0.21 6.25±0.16 0.10±0.01 0.05±0.00

Ejigbo 13.88±0.20 16.87±0.20 4.99±0.05 0.09±0.00 0.04±0.00

Exp 7.49±0.15 13.40±0.15 4.27±0.16 0.11±0.01 0.05±0.00

Hosp 10.96±0.19 21.99±0.01 5.33±0.20 0.11±0.01 0.05±0.00

Odoori 10.02±0.05 17.07±0.17 4.93±0.27 0.10±0.01 0.05±0.00

Osogbo 14.16±0.24 21.97±0.16 6.08±0.13 0.10±0.01 0.05±0.00

Waterworks 9.94±0.13 17.16±0.25 5.41±0.11 0.11±0.00 0.05±0.00

Mean±SD 11.58±2.52 18.95±3.23 5.36±0.61 0.10±0.01 0.05±0.01

TABLE 4.7: Concentration of metals bound to crystalline iron oxide of roadside soil in Iwo (µg/g).

Fraction 7 Mn Fe Zn Pb Cd

Adeke 17.43±0.15 22.66±0.12 6.01±0.03 0.09±0.00 0.04±0.00

Agbowo 9.12±0.19 16.15±0.54 5.22±0.14 0.10±0.00 0.05±0.00

Bowen 10.06±0.27 14.07±0.21 5.88±0.20 0.11±0.01 0.05±0.00

Ejigbo 8.37±0.54 12.90±0.15 5.44±0.17 0.09±0.00 0.03±0.00

Exp 15.03±0.14 29.67±0.16 6.83±0.17 0.10±0.00 0.05±0.00

Hosp 10.82±0.33 12.52±11.92 6.26±0.09 0.09±0.00 0.04±0.00

Odoori 11.41±0.15 21.13±0.37 6.00±0.03 0.11±0.01 0.05±0.00

Osogbo 14.97±0.34 21.99±0.03 5.99±0.12 0.08±0.01 0.04±0.00

Waterworks 14.49±0.16 20.00±0.02 5.00±0.19 0.09±0.00 0.05±0.00

Mean±SD 12.41±3.06 18.90±6.15 5.85±0.55 0.10±0.01 0.05±0.01

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TABLE 4.8: Concentration of metals bound to organic matter of roadside soil in Iwo (µg/g).

Fraction 8 Mn Fe Zn Pb Cd

Adeke 14.43±0.15 23.07±0.33 7.92±0.14 0.10±0.00 0.05±0.00

Agbowo 19.57±0.62 29.16±0.27 7.14±0.22 0.09±0.00 0.04±0.00

Bowen 8.93±0.39 14.88±0.21 5.95±0.25 0.12±0.01 0.05±0.00

Ejigbo 9.40±0.12 18.08±0.17 6.03±0.06 0.10±0.00 0.04±0.00

Exp 10.45±0.09 20.97±0.26 6.14±0.09 0.11±0.01 0.05±0.00

Hosp 10.11±0.17 20.97±0.17 6.87±0.20 0.09±0.00 0.04±0.00

Odoori 8.04±0.13 13.08±0.15 5.00±0.02 0.10±0.01 0.05±0.00

Osogbo 20.99±0.14 25.05±0.38 7.09±0.14 0.10±0.00 0.05±0.00

Waterworks 17.03±0.41 22.72±0.18 6.66±0.20 0.11±0.01 0.05±0.00

Mean±SD 13.22±4.78 20.89±4.84 6.53±0.84 0.10±0.01 0.05±0.01

TABLE 4.9: Concentration of residual metals of road sidesoil in Iwo (µg/g).

Fraction 9 Mn Fe Zn Pb Cd

Adeke 11.06±0.13 22.94±0.30 5.98±0.03 0.08±0.00 0.04±0.00

Agbowo 8.59±0.22 16.96±0.23 5.26±0.09 0.09±0.00 0.04±0.00

Bowen 8.06±0.11 14.04±0.42 4.87±0.16 0.09±0.00 0.04±0.00

Ejigbo 8.84±0.47 14.08±0.34 5.36±0.09 0.10±0.00 0.05±0.00

Exp 10.43±0.13 19.25±0.38 5.43±0.15 0.10±0.00 0.04±0.00

Hosp 9.46±0.09 19.93±0.12 5.63±0.15 0.09±0.00 0.04±0.00

Odoori 15.87±0.21 22.60±0.58 6.06±0.18 0.10±0.00 0.04±0.00

Osogbo 9.42±0.14 21.12±0.56 6.20±0.09 0.13±0.01 0.05±0.00

Waterworks 7.84±0.25 16.11±0.30 4.99±0.02 0.11±0.01 0.05±0.00

Mean±SD 9.95±2.38 18.56±3.33 5.53±0.46 0.10±0.01 0.04±0.01

19

The highest concentration of heavy metal recorded was Fe with mean value 29.67±0.16µg/g

(Table 4.7) on the Express Road and the lowest was Cd with mean value 0.03±0.00µg/g

(Table 4.1) on the Hospital Road which might be due to the fact that higher number of

vehicles travel on the Express Road than on the Hospital Road which is a residential area.

This assumption will be backed by Eitminavičius L., Matusevičius K., Antanaitis A., (2001)

who stated that soils along highways tend to be polluted with Fe and other heavy metals such

as Zn, Cd, Pb etc.

On the average, the concentration of iron, manganese, zinc, and all other heavy metals

extracted vary from one location to another. This could be attributed to geological

distribution of minerals that vary from one location to the other. Similar variations were

reported in roadside soils of highways in Egypt (Adriano et al., 2007).

The overall order Fe > Mn > Zn > Pb > Cd will support the values below and can be seen in

Fig 4.1. The overall total mean values are Fe (175.71±32.62µg/g), Mn (104.44±24.26µg/g),

Zn (51.74±6.39µg/g), Pb (0.91±0.09µg/g), Cd (0.40±0.09µg/g).

Mn Fe Zn Pb Cd0

20

40

60

80

100

120

140

160

180

Total mean values

Total mean values

Fig 4.1: Total Mean Values of Mn, Fe, Zn, Pb, Cd

20

The total concentration of heavy metals were found out and Fe was discovered to be

predominant in the roadside soils that were selected from the nine sampling points, it is very

clear that Fe have the highest leading value due to some factors which may include, wear and

tear of tyres on the road, vehicle exhaust and corrosion of metals because in all these nine

sampling locations there is possibility of the mentioned factors to occur frequently or

sparingly, sources of Zn could be associated with human activities such as the use of

chemicals or zinc based fertilizers by farmers (Egila and Nimyel, 2002). Concerning Pb, one

of the heavy metals in the result above showed that it’s level is lowest, this is simply so

because Pb’s major source arises mainly from refineries, TEL(tetra ethyl lead) in vehicle

gasoline “which is not in use in this country”, industries e.t.c which is very rare in above

mentioned areas while the remaining heavy metals which include Mn, Cd, are referred to as

the trace elements, and in small quantities, the above heavy metals are nutritionally essential

for a healthy life.

21

4.1 HEAVY METAL FRACTIONS.

The diagrams below (Fig. 4.2 - 4.6) represent the distribution of heavy metals in the

roadside soils of Iwo. The distribution shows the level of the percentage each heavy metal

occur in each fractions that is in water soluble metals, exchangeable metals, metals bound to

carbonate, plant available metals, metals bound to mn-oxide, metals bound to amorphous fe-

oxide, metals bound to crystalline fe-oxide, metals bound to organic matter and residual

metals.

MANGANESE: in manganese, it was noted that metals bound to Mn-oxide and metals

bound to organic matter has highest percentage with 13% respectively with residual metals as

lowest in Fig 4.2 and this conclusion is in agreement with the research work of Shadung John

Moja, (2007) who worked on manganese in roadside soils extensively in Tshwane, South

Africa.

IRON: in iron, it was noted that plant available metals, metals bound to Mn-oxide and metals

bound to organic matter are highest with 12% respectively and water soluble metals and

residual metals are lowest with 10% respectively in Fig 4.3.

ZINC: in zinc, metals bound to organic matter was highest with 13% and water soluble

metals, metals bound to Mn-oxide, metals bound to amorphous Fe-oxide are lowest with 10%

respectively in Fig 4.4.

LEAD: in lead, exchangeable metals was highest with 12% and the rest had 11% each in Fig

4.5.

CADMIUM: in cadmium, it was noted that only metals bound to organic matter was highest

with 12% and the remaining fractions have 11% respectively in Fig 4.6.

22

10%

10%

11%

11%

13%

11%

12%

13%

10%

MnWater soluble metal Exchangeable metalsMetal bound to carbonate Plant available metalsMetals bound to Mn-oxide Metal bound to armorphous Fe-oxideMetals bound to crystalline Fe-oxide Organic matterResidual metal

Fig. 4.2: Distribution of Mn in Roadside Soils of Iwo

10%

11%

11%

12%

12%

11%

11%

12%

11%

FeWater soluble metal Exchangeable metalsMetal bound to carbonate Plant available metalsMetals bound to Mn-oxide Metal bound to armorphous Fe-oxideMetals bound to crystalline Fe-oxide Organic matterResidual metal

Fig. 4.3: Distribution of Fe in Roadside Soils of Iwo

23

10%

12%

11%

12%

11%10%

11%

13%

11%

ZnWater soluble metal Exchangeable metalsMetal bound to carbonate Plant available metalsMetals bound to Mn-oxide Metal bound to armorphous Fe-oxideMetals bound to crystalline Fe-oxide Organic matterResidual metal

Fig. 4.4: Distribution of Zn in Roadside Soils of Iwo

11%

12%

11%

11%

11%

11%

11%

11%

11%

PbWater soluble metal Exchangeable metalsMetal bound to carbonate Plant available metalsMetals bound to Mn-oxide Metal bound to armorphous Fe-oxideMetals bound to crystalline Fe-oxide Organic matterResidual metal

Fig. 4.5: Distribution of Pb in Roadside Soils of Iwo

24

11%

11%

11%

11%

11%

11%

11%

12%

11%

CdWater soluble metal Exchangeable metalsMetal bound to carbonate Plant available metalsMetals bound to Mn-oxide Metal bound to armorphous Fe-oxideMetals bound to crystalline Fe-oxide Organic matterResidual metal

Fig. 4.6: Distribution of Cd in Roadside Soils of Iwo

25

CHAPTER FIVE.

CONCLUSION.

The aim of this research was to determine the fractions and levels of heavy metals in

Iwo and to determine their relevance to the environment.

In summarizing the obtained results, it has emerged that in the total amounts of the heavy

metals (Mn, Fe, Zn, Pb, Cd), Fe is predominant. The results presented indicate that the

roadside soil samples collected from the Iwo area contained high level of Fe, 50% followed

by manganese, 35% followed by zinc, 13% and then trace amounts of lead and cadmium with

concentrations not more than 1% respectively. The sequential extraction analysis indicated

that Fe is more concentrated in the roadside soils of Iwo than any other heavy metal because

it has been reported that iron (Fe) occurs at high concentration in Nigeria soil (Asaolu et al.,

1997; Asaolu and Olaofe, 2004; Nwajei and Gagophien, 2000).

In conclusion, small quantities of certain heavy metals are nutritionally essential for a healthy

life. They become toxic when they are not metabolized by the body and accumulate in soft

tissues. It is therefore very important that we take protective measures against excessive

exposure to some of these heavy metals that occur naturally.

RECOMMENDATION.

In further studies, traffic counts, temporal studies, physico-chemical analysis should

be carried out extensively to be able to ascertain heavy metals pollution in soils.

These heavy metals (Mn, Fe, Zn, Pb, Cd) are essential for a healthy life in small

quantities, they become toxic when they are not metabolized by the body and accumulate in

26

soft tissues. It is therefore very important that we take protective measures against excessive

exposure to some of these heavy metals that occur naturally.

27