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ODILINYE IFEADIKANWA OZIOMA HAVILAH

PG/MSC/09/51141

POLLUTION LEVELS OF SOME HEAVY METALS AND TOTAL PETROLEUM

HYDROCARBONS (TPH) IN SOIL SAMPLES FROM UMUORIE OIL SPILL SITE, UKWA WEST

LOCAL GOVERNMENT OF ABIA STATE

Faculty of Physical Sciences

Department of Industrial Chemistry

Nwamarah Uche

Digitally Signed by: Content manager’s Name

DN : CN = Weabmaster’s name

O= University of Nigeria, Nsukka

OU = Innovation Centre

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POLLUTION LEVELS OF SOME HEAVY METALS AND TOTAL PETROLEUM

HYDROCARBONS (TPH) IN SOIL SAMPLES FROM UMUORIE OIL SPILL SITE,

UKWA WEST LOCAL GOVERNMENT AREA OF ABIA STATE.

BY

ODILINYE, IFEADIKANWA OZIOMA HAVILAH

PG/M.Sc/09/51141

A RESEARCH PROJECT SUBMITTED IN PARTIAL FUFILMENT OF THE

REQUIREMENTS FOR THE AWARD OF THE DEGREE OF MASTER OF

SCIENCE IN FOSSIL FUEL CHEMISTRY IN THE DEPARTMENT OF PURE AND

INDUSTRIAL CHEMISTRY, FACULTY OF PHYSICAL SCENCES,

UNIVERSITY OF NIGERIA, NSUKKA

FEBRUARY, 2012.

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CHAPTER ONE

1.0 INTRODUCTION

The discovery of Crude-Oil exploration and exploitation in the crude-oil producing zones has

made Nigeria to experience eruptive and rare changes in her economic growth, particularly in

the past fifty years when crude oil export replaced agriculture as the basis of the Nigeria

economy. This has caused the oil industry to rise to an unassailable loftiness in the Nigerian

economy, contributing the lion share to Gross Domestic Product and accounting for the bulk

of federal government revenue and foreign exchange earnings since early 1970 1. The history

of crude oil exploration in the Niger Delta area of Nigeria dates back to 1956 when Shell

British Petroleum (now Royal Dutch Shell) discovered crude oil at Oloibiri, a village in the

Niger Delta, and commercial production began in 1958. Today, there are 606 oil fields in the

Niger Delta, of which 360 are on-shore and 246 off-shores, 2. Nigeria is now the largest oil

producer in Africa and the sixth largest in the world, averaging 2.7 million barrels per day

(bbl/d) in 2006. Central Intelligent Agency (CIA), 3, stated that Nigeria’s economy is heavily

dependent on earnings from the oil sector, which provides 20% of GDP, 95% of foreign

exchange earnings, and about 65% of budgetary revenues.

However, the activities of crude oil exploration, exploitation and drilling in Nigeria which

has been on the increase since its inception in 1908 has birthed serious cases of

environmental pollution at an alarming rate. The growth of the country's oil industry,

combined with a population increase and lack of enforcement of environmental regulations

has led to substantial damage to Nigeria's environment, especially in the Niger Delta region.

4.

Nigeria as a major producer and exporter of crude petroleum oil has continued to experience

oil spills which have exposed its environment to hazards and its attendant effects on

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agricultural lands as well as on plant growth and development, 5. Increasing petroleum

exploration, refining and the operation of petroleum companies in the Niger Delta region of

Nigeria have led to the wide scale contamination of most of its creeks, swamps Rivers and

streams. Onifade et al. 6 and Asonye et al 7, reported the concentrations of lead [Pb],

chromium [Cr], cadmium [Cd], iron [Fe], zinc [Zn], manganese [Mn] and copper [Cu] in

water samples of rivers, streams and waterways in southern Nigeria, exceeding the guidelines

of world health organisation (WHO). In 1998 alone, a total of 390 cases of oil spills were

reported in the Niger Delta Region of Nigeria 8. An estimated 9 to 13 million barrels (1.5

million tons) of oil has spilled in the Niger Delta ecosystem over the past 53 years,

representing about 50 times the estimated volume spilled in the Exxon Valdez oil Spill in

Alaska in 1989 9. The consequences of this has been enormous financial loss, extensive

habitat degradation, and poverty leading to the continuous crises in the Niger Delta area, this

situation has recently culminated into kidnapping of oil workers, and even children. 10, 11.

1.1 Definition of crude oil

Crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of

hydrocarbons of various molecular weights and other liquid organic compounds, which are

found in geologic formations beneath the earth’s surface, 12. It is also referred to as petroleum

that is removed from the Earth in liquid state or is capable of being so removed, 13. Or a

naturally occurring liquid that can be distilled or refined to make fuels, lubricating oils,

asphalt, and other valuable products, 14. Crude oil also refers to natural gas, asphalt or tar

(obtained from tar sands - a mixture of tar and thick viscous heavy oils). Crude oil undergoes

refining to yield fuels, including petrol, kerosene, jet fuel, diesel fuel and furnace oil. It is

also the source of greases and waxes 14. Crude oil and natural gas are used to make a variety

of compounds such as (ethylene, propylene, butadiene, benzene, toluene, xylene, ammonia

and methane) - for the manufacturing of hundreds of petrochemical products, including

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paints, plastics, synthetic rubbers and fibres, fertilizers, drugs, lubricants, waxes, bitumen and

explosives such as trinitroluenes (TNT) - by nitration of toluene obtained from coal tar and

dynamite (nitro-glycerine mixed with some absorbent substance to reduce danger of

explosion by shock) 15. TNT mixed with other chemicals such as ammonium nitrate,

powdered aluminium and charcoal produces Amonal which is a more powerful explosive

than TNT 16. Crude oil is recovered mostly through drilling. This usually comes after the

structural geology studies (at the reservoir scale), sedimentary basin analysis and reservoir

characterization (mainly in terms of porosity and permeable structures) have been carried

out,17.

1.2 Processes of crude oil formation

Crude oil is formed from the remains of plants and animals (algae, zooplankton,

phytoplankton, shrubs and trees) which died in great numbers about 300 million years ago.

These dead plant remains settled downwards through the water and thus gradually

accumulated in the depth of the seas and rivers in a process known as the ‘organic rain’.

This accumulated organic matter is covered by gradually thickening layers of inorganic

sediments (silt, mud, sand etc) brought by periodic flooding of the swamp. As the thickness

of the covering sediments increases with time, the accumulated organic matter experiences

deeper and deeper burial. This cover minimizes rotting by reducing the availability of

oxygen. The conversion of organic matter into fuel takes place in two stages:

1.2.1. Diagenesis :

This is the biochemical stage of fuel formation. Most of the processes in this stage are

catalysed by bacteria. The main products of diagenesis are methane, carbon dioxide, water

and kerogen. The processes which occur during diagenesis include; Rotting, mouldering and

putrefaction.

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1.2.2. Catagenesis:

This is also known as the geochemical stage of fuel formation. It involves the conversion of

the kerogen to fuels which takes millions of years. At this stage, the organic matter is buried

so deeply that all the reactions are completely anaerobic. The important factors affecting the

reactions during catagenesis are; Temperature, pressure, time, and composition of the organic

matter

1.3. Characteristics of crude oil

The different varieties of crude oils range from very fluid volatile liquids to viscous and

semi-solid materials. Crude oil is mainly either black or green, but it can also be light yellow

or transparent 18. Crude oil varies considerably in density and is described as heavy, average

and light. The densities of different crude oils are usually measured using the American

Petroleum Institute degrees--gravity scale (API) as devised by the American Petroleum

Institute. Crude oils with 10˚ API gravity or less are considered to be heavy oils. Heavy oils

have 5˚-20˚ API gravities 19. Average crude oils have 20˚-25˚ API gravities. Light crude oils

have 25˚-55˚ API gravities, 20. Light crude oils are very fluid and can be produced from

surface reservoirs faster and in greater quantities than the heavy crude oils. Light crude oils

are more valuable because of its high petrol content. Petrol is the most valuable product

refined from petroleum 21.

1.4. Crude oil compositions

Crude oils and natural gas are called hydrocarbons because they are made up of entirely

carbon and hydrogen, along with some minor impurities - Sulphur, Nitrogen and Oxygen, 22.

The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic

hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulphur, and

trace amounts of metals such as iron, nickel, copper and vanadium. According to Hyne, 23,

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the exact molecular composition varies widely from formation to formation but the

proportion of chemical elements varies over narrow limits as follows:

Table 1.1: Crude oil composition by weight

Element Percent range

Carbon 83 to 87%

Hydrogen 10 to 14%

Nitrogen 0.1 to 2%

Oxygen 0.05 to 1.5%

Sulphur 0.05 to 6.0%

Metals < 0.1%

Four types of hydrocarbon molecules appear in crude oil. The relative percentage of each

varies from oil to oil and this determines the properties of each crude oil 24.

Table 1.2: Hydrocarbon composition of crude oil by weight

Hydrocarbon Average Range

Paraffins 30% 15 to 60%

Naphthenes 49% 30 to 60%

Aromatics 15% 3 to 30%

Asphaltics 6% Remainder

The main difference between crude oil and natural gas is the size of the hydrocarbon

molecules. The hydrocarbon molecules in natural gas have one to four carbons each and they

exist as gas at the earth’s surface. Natural gas is a colourless, odourless and composed mostly

of methane 25. Crude oil is composed of many different hydrocarbon molecules, each with

five to sixty carbon atoms. These hydrocarbon molecules exist as straight chains, circles, and

branched chains. Liquid hydrocarbons exist in deep reservoirs, where it is very hot, and are

trapped by overlying rock formations with lower permeability 26. At very high temperatures,

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some hydrocarbons that are normally liquid occur as gas and natural gas mixtures. When the

natural gas is brought to the surface, the gas cools and the liquid molecules condense,

forming a condensate. Sulphur exists to varying extent as an impurity in some crude oils.

When the crude oil contains less than 10% Sulphur it is called “sweet” crude. When it

contains more than 10% Sulphur it is called “sour” crude. Sulphur is removed before refining

in natural gas processing plants before the gas is distributed to consumers 27. The hydrogen

sulphide removed during the refining and processing of crude oil and natural gas is

subsequently converted into by-product elemental sulphur. The vast majority of the

64,000,000 metric tons of sulphur produced worldwide in 2005 was by-product sulphur from

refineries and natural gas processing plants 28. And because it requires this extra processing,

sour crude is worth less than sweet crude.

Crude oils are often classified according to their content. The classification of crude is based

on whether it is paraffinic, asphaltic, or mixed based crude 29:

(i) Asphalt-based crude - usually black in colour and when refined produces high quality

petrol and asphalt.

(ii) Paraffin-based crude - usually greenish in colour and when refined they produce

more paraffin wax and high quality motor lubricating oils.

(iii) Mixed-based crude - are a combination of the other two.

1.5. Processes of crude oil refining

The refining process depends on the chemical processes of distillation (separating liquids by

their different boiling points) and catalysis (which speeds up reaction rates), and uses the

principles of chemical equilibria. Chemical equilibrium exists when the reactants in a

reaction are producing products, but those products are being recombined again into

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reactants. By altering the reaction conditions the amount of either products or reactants can

be increased. Refining is carried out in three main steps:

1.5.1. Step 1 – Separation

The crude oil is separated by boiling points into six main grades of hydrocarbons: refinery

gas (used for refinery fuel), gasoline (naphthas), kerosene, light and heavy gas oils and long

residue. This initial separation is done by distillation. The long residue is further separated

in the butane desaphalting unit, and the refinery gas is separated into hydrogen sulphide in the

Shell ADIP process. The ADIP process is a regenerative process developed to selectively

reduce H2S in gas to very low concentrations, while a good selectivity for H2S in the presence

of CO2 can be achieved. The ADIP process uses an aqueous solution of di-isopropanol amine

(DIPA) and an aqueous solution of methyldiethanol amine (MDEA). The ADIP process can

also be used for enrichment of acid gas feed to a sulfur recovery plant, to achieve a higher

H2S content.

Distillation: The first step in the refining of crude oil, whether in a simple or a complex

refinery, is the separation of the crude oil into fractions (fractionation or distillation). These

fractions are mixtures containing hydrocarbon compounds whose boiling points lie within a

specified range. A continuous flow of crude oil passes from the storage tanks through a

heating coil inside a furnace, where it is heated to a predetermined temperature. The heated

oil then enters the fractionating column, which is a tall cylindrical tower containing trays

suitably spaced and fitted with vapour inlets and liquid outlets.

Upon entering the column, the liquid/vapour mixture separates - the vapour passing upwards

through the column, the liquid portion flowing to the bottom from where it is drawn off as

"long residue". The vapours rise through the tray inlets, become cooler as they rise, and

partially condense to a liquid which collect on each tray. Excess liquid overflows and passes

through the liquid outlets onto the next lower tray. The bottom of the column is kept very hot

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but temperatures gradually reduce towards the top so that each tray is a little cooler than the

one below it.

Ascending hot vapours and descending cooler liquids mix on each tray and establish a

temperature gradient throughout the length of the column. When a fraction reaches a tray

where the temperature corresponds to its own particular boiling range, it condenses and

changes into liquid. In this way the different fractions are separated from each other on the

trays of the fractionating column and are drawn off for further treatment and blending.

The fractions that rise highest in the column before condensing are called light fractions, and

those that condense on the lowest trays are called heavy fractions. The very lightest fraction

is refinery gas, which is used as a fuel in the refinery furnaces. Next in order of volatility are

gasoline (used for making petrol), kerosene, light and heavy gas oils and finally long residue.

1.5.2. Step 2 - Conversion

Among the oils separated out from the original crude (refinery gas, gasoline, kerosene, light

and heavy gas oils and asphalt), only refinery gas can be used as it is, and even this is usually

ADIP treated. All the others require some further treatment before they can be made into the

final Crude Oil products. This firstly involves the removal of sulphur (as it interferes with the

success of some later processes) and then the chemical conversion of the oils into more

desirable compounds.

Desulphurisation: The oil products all naturally contain some sulphur compounds. These

must be removed from gasoline, kerosene and diesel oils before catalytic reforming (the next

conversion process) as otherwise the sulphur poisons the catalyst used. The sulphur is

removed by reacting the sulphur compounds with hydrogen, forming hydrogen sulphide,

which can be removed as a gas from the cooled liquid oil. The process is carried out over a

catalyst at a pressure of about 20 atmospheres and a temperature of about 3500C. Under these

conditions the oils are gaseous.

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1.5.3. Step 3 - Purification

The crude oil has now been separated into refinery gas, hydrogen sulphide, naphtha,

kerosene, gas oil, asphalt and bitumen. Two more processes have to be carried out, on the

naphtha and the hydrogen sulphide respectively, before the hydrocarbons are ready for

blending into saleable products.

Sulphur recovery: Crude oil as received for refining contains sulphur in levels up to a few

tenths of a percent weight. It is removed from oil products mainly by the desulphurisation

process described above which results in the formation of hydrogen sulphide, and further H2S

is separated out of the refinery gas. This H2S is converted to sulphur in a two step process.

Firstly, the "Claus" process of partial combustion of H2S is used to form SO2 and this SO2 is

then reacted with the remaining H2S to produce sulphur. This sulphur recovery process takes

place in one thermal and two catalytic stages and recovers 95% of the sulphur. The final 1 or

2 % volume of H2S in the "tail gas" from the last catalytic reactor is burnt in a separate

incinerator so that the effluent gas finally discharged to the atmosphere has an

environmentally acceptable H2S content of less than 5 ppm by volume.

The overall reaction occurring is as follows:

H2S + ½ O2 → S + H2O (l)

This overall reaction (1) is the sum of two exothermic reactions, the oxidation of H2S to SO2

(2) and the subsequent reaction between H2S and SO2 to form sulphur and water (3):

H2S + 1½ O2 → SO2 + H2O (2)

2H2S + SO2 → 3S + 2H2O (3)

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In the first stage of the process (the 'thermal stage'), enough air is supplied to convert one

third of the H2S in the acid feed gases to SO2 and H2O according to equation (2). In addition

to this, any hydrocarbons and NH3 in the feed gases are completely combusted:

C3H8 + 5O2 → 3CO2 + 4H2O (4)

NH3 + ¾ O2 → ½N2 + 1½ H2O (5)

In the second and the third stage of the "Claus" process more H2S is converted to sulphur

according to equation (3). To shift the equilibrium of this reaction as far as possible to the

right side lower reaction temperatures are applied to these stages. To assure sufficient high

reaction rates, the reactions take place in the presence of a catalyst.

Finally, the SRU tail gas (which contains less than 5% sulphur) is oxidised in a catalytic

incinerator at a temperature of approximately 400oC. At this temperature, achieved by

burning fuel gas in addition to the process gases, the H2S and sulphur vapour/mist are

practically completely oxidised in the presence of a catalyst according to the reactions:

H2S + 1½ O2 → H2O + SO2

S + O2 → SO2

The sulphur is produced in liquid form and heated handling/loading facilities provide sulphur

storage before loading into road tankers for delivery to fertiliser works.

1.6. Uses of crude oil

Crude oil was known in the ancient world and had several uses. Usually found bubbling up

to Earth’s surface at what are called oil seeps, crude oil was used essentially for lighting, as a

lubricant, for caulking ships (making them watertight), and for jointing masonry (for

building), 20. Crude oil and its by-products (natural gas, gasoline, kerosene, asphalt, and fuel

oil, among others) did not have any real economic value until the middle of the nineteenth

century when drilling was first used as a method to obtain it. Today, oil is produced on every

continent including Nigeria. Crude oil in its various forms, has been used since ancient times,

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and is now important across societies, including in economy, politics and technology.

Modern industrialised societies use crude oil primarily to achieve a degree of mobility on

land, sea and in the air, which was barely unimaginable less than hundred years, 30. The rise

in importance was mostly due to the invention of the internal combustion engine, the rise in

commercial aviation and the increasing use of plastic 31. Presently, crude oil is found to be

very useful in the following areas;

1.6.1. Fuel production

The most common distillation fractions of petroleum are fuels. These include;

Liquefied petroleum gases: (LPGs) are gases refined from crude oil or natural gas, liquefied

under pressure for easy transportation. The term includes ethane, ethylene, propane,

propylene, butane, butylenes, isobutane and isobutylene. LPGs account for 4 percent of

refinery products.

Still gas: also known as refinery gas is a generic term for any gas produced by refining crude

oil. Still gases include methane, ethane, butane and propane. Although containing the same

constituent elements as LPGs, still gas is used to fuel refineries and as a chemical feedstock.

Gasoline: accounts for roughly 44 percent of all refinery products. Gasoline is not a single

hydrocarbon, but may be a blend of several. In areas with air quality problems, ethanol or

other additives may be added to gasoline to reduce emissions. (Ethanol is a bio-fuel that adds

oxygen to gasoline making it an “oxygenate”, so that it burns with fewer emissions; Gasoline

also can occur naturally within crude oil, although this product is more unstable and volatile

than refined gasoline. 32.

Jet fuel: also called aviation gasoline, is kerosene blended to specifications for general and

military aircraft. These specifications include a low freezing point (to keep fuel fl owing at

high altitudes), low combustibility (to help make handling safer and airplane crashes more

survivable) and high energy content with low weight (to allow planes to gain and hold

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altitude). Jet fuel accounts for 9 percent of refinery products, 32. Diesel fuel and heating oil:

are “distillates” fuels distilled in refineries and blended with light oils. They are similar,

although diesel has lower sulphur content. Both fuels are available in three grades depending

on the intended use. The highest grade of diesel (with the lightest hydrocarbons) fuels buses;

the middle grade fuels railroad locomotives, trucks and automobiles; and the lowest grade

fuels off –road vehicles such as agricultural and construction equipment. Diesel and heating

oil account for about 23 percent of refinery products. Diesel has more energy per gallon than

gasoline and is less volatile, but it also produces more emissions than gasoline.

Speight, 33 listed the following fuels in the order of increasing boiling range:

Table 1.3: Petroleum fractions with their boiling ranges

Fraction

Boiling Range (0C)

Liquefied petroleum gas -40

Butane -12 to -1

Gasoline (Petrol) -1 to 180

Jet fuel 150 to 205

Kerosene 205 to 260

Fuel oil 205 to 290

Diesel fuel 260 to 315

1.6.2. Manufacture of Other derivatives

Some of the resultant hydrocarbons obtained from crude oil distillation may be mixed with

other non-hydrocarbons, to create other end products as enumerated by the National Energy

Technology Laboratory 34.

i. Alkenes (olefins) which can be manufactured into plastics or other compounds.

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ii. Lubricants (produces light machine oils, motor oils, and greases, adding viscosity

stabilizers as required).

iii. Sulphur or Sulphuric acid. These are useful industrial materials. Sulphuric acid is

usually prepared as the acid precursor oleum, a by-product of sulphur removal from

fuels.

iv. Bulk tar.

v. Asphalt

vi. Petroleum coke, used in speciality carbon products or as solid fuel.

vii. Paraffin wax.

viii. Aromatic petrochemicals to be used as precursors in other chemical production.

1.6.3. Agriculture

Since the 1940s, agricultural productivity has increased geometrically, largely due to the

increased use of energy-intensive mechanization, fertilizers and pesticides. Nearly all

pesticides and some fertilizers are made from crude oil, 35.

1.7. Statement of problem

Despite the numerous economic value of crude oil, the ravaging impact of crude oil spills on

the environment has been one of the major concerns among oil producing states globally. The

Department of Petroleum Resources estimated that from 1976 to 1996, 1.89 million barrels of

petroleum were spilled into the Niger Delta out of a total of 2.4 million barrels, spilled in

4,835 incidents, 36. According to The daily independent news paper of 19th July, 2010, 35,

approximately 220 thousand cubic metres of petroleum were reported to have been spilled.

Another major concern is the inability of the oil producing companies to completely recover

the spilled oil. According to a report from united Nation Development programme (UNDP)

37, there have been a total of 6,817 incidents of oil spills between 1976 and 2001, which

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account for a loss of three million barrels of oil, which more than 70% was not recovered. It

was reported that most of these spills occurred off-shore (69%), a quarter was in swamps and

6% spilled on land. These Oil spill incidents have led to the massive release of heavy metals

and polycyclic aromatic hydrocarbons into the environment which in turn has resulted in the

destruction of the coastal vegetation and Pollution of drinkable water in oil producing

regions. Agricultural production cannot sustain people’s livelihood while at the same time the

natural resources that agricultural production depends on is destroyed or polluted 38.

According to a report by Asonye et al. 39 ; the concentrations of lead (Pb), chromium (Cr),

cadmium (Cd), iron (Fe), zinc (Zn), manganese (Mn) and copper (Cu) in water samples of

rivers, streams and waterways in southern Nigeria, exceed the guidelines of World Health

Organisation,(WHO).

Bioaccumulation of heavy metals by aquatic life poses a dangerous threat to human lives

because they could be transferred directly to human beings upon consumption 40. Also

polycyclic aromatic hydrocarbons can be persistent potential carcinogens particularly in

sediments and solid matrices, 41. All these substantiate the fact that humans which are at the

receiving end stand at risk 42. If the issue of oil spills is neglected, it could be estimated that

in the future both arable farmlands and drinking water would be completely unsafe for

farming and domestic use respectively.

The present study which is aimed at ascertaining the extent of crude oil pollution of the

Umuorie oil spill site can therefore be expressed thus: ‘‘Pollution levels of some heavy

metals and Total petroleum hydrocarbons (TPH) in soil samples from Umuorie oil spill site,

Ukwa west Local Government Area of Abia state’’.

1.8. Study Area

Umuorie is a small town located in Ukwa west is a local Government area of Abia State,

Nigeria. Ukwa west local government area which has its head quarters in the town of Oke

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Ikpe; has an area of 271 km2 and a population of 88,555 at the 2006 census. The local

Government is the only oil producing area in Abia State. Its oil producing communities

include: Umuorie, Owaza, Uzoaku, Umuokwor, amongst others. The Oil Well at Umuorie

was opened in 1962 227, after which Shell Petroleum Development Commission, (SPDC) had

continued its operation in the community. The region enjoys the humid tropical climate

characterized by the hot and wet conditions and experiences slightly high temperature; about

34°C, all year round, 228. The implication is that there is a prolonged rainy season in the

region. The indigenes of Umuorie are majorly farmers and fisher men.

Umuorie village was used as the study area because of the spill which occurred on the 25th of

August 2011 as a result of pipeline burst. The spill was reported to cause the destruction of

perennial crops around the oil spill site 43. The crops affected included plantain plantation,

cassava farms, and vegetable garden, orange and banana trees. The environment was also

reported to be filled with odour of crude oil.

1.9. Objectives of the study

The objectives of the present study include the following;

i. To determine the level of pollution by some heavy metals in Umuorie oil spill site,

located in Ukwa west L.G.A of Abia State.

ii. To determine the level of pollution by Total petroleum hydrocarbons in Umuorie oil

spill site, located in Ukwa west L.G.A of Abia State.

iii. To provide baseline information about the heavy metals and Total Petroleum

Hydrocarbon pollution levels of the study area.

iv. To compare the results obtained to internationally accepted limits as specified by the

Department for petroleum resources (DPR).

v. To highlight the negative impacts of crude oil spillage on the environment.

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1.10. Scope of work

This work covered the quantitative determination of the following heavy metals; Arsenic,

Nickel, Mercury, Cadmium, Vanadium and Lead; It also covered the quantitative

determination of Total Petroleum Hydrocarbons in an oil spill site located in Umuorie village

of Ukwa west Local Government.

1.11. Aim of Study

The present study is aimed at ascertaining the extent of crude oil pollution of the Umuorie oil

spill site and can therefore be expressed thus: ‘Pollution Levels of Some Heavy Metals And

Total Petroleum Hydrocarbon (TPH) of Soil Samples in Umuorie Oil Spill Site, Ukwa West

Local Government Area of Abia State’.

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CHAPTER TWO

2.0. LITERATURE REVIEW

Crude oil pollution can be defined as the release of contaminants or pollutants associated with

the extraction of crude oil into the environment. Crude oil pollution is also said to occur when

there is man-made or man aided alterations of chemical, physical or biological quality of the

environment to an extent which is detrimental to that environment or beyond acceptable limit

as a result of the extraction, storage or transportation of petroleum oil, 44.Crude oil pollutants

are generated from three major sources, these are:

2.1 Oil spills

Oil spills involve the release of dangerous hydrocarbons such as benzene and poly nuclear

aromatic hydrocarbons [PAHs] and heavy metals into the soil and water sources. These

spillages affect vast stretches of land and waterways thus polluting not only crops but also

marine life and the sources of water for domestic uses: In Ogoni, between 1993 and mid-

2007, there has been a recorded 35 incidences of oil spills. This is aside from the unnoticed

slicks and unreported cases of oil spills, 44. Some of the major global marine oil spills

include;

(a) Argo Merchant - On December 15, 1976, the Argo Merchant ran aground on Fishing Rip

(Nantucket Shoals), 29 nautical miles southeast of Nantucket Island, Massachusetts in high

winds and ten foot seas. Later, the vessel broke apart and spilled its entire cargo of 7.7

million gallons of fuel oil.

(b) Amoco Cadiz - The Amoco Cadiz encountered stormy weather and ran aground off the

coast of Brittany, France on March 16, 1978. Its entire cargo of 68.7 million gallons of oil

spilled into the sea.

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(c) Burmah Agate – On November 1, 1979, the Burmah Agate collided with the freighter

Mimosa southeast of Galveston Entrance in the Gulf of Mexico, resulting in explosion and a

fire that affected an estimated 2.6 million gallons of oil causing it to be released into the

environment, and another 7.8 million gallons to which was consumed by the fire.

(d) Ixtoc I - The 2-mile-deep exploratory well, Ixtoc I, blew out on June 3, 1979 in the Bay of

Campeche off Ciudad del Carmen, Mexico. By the time the well was brought under control

in March, 1980, an estimated 140 million gallons of oil had spilled into the bay. The oil spill

from the Ixtoc 1 blowout threatened a rare nesting site of the Kemp’s Ridley sea turtle, an

endangered species. Field and laboratory data on the nests of turtle eggs found a significant

decrease in survival of hatchlings, and some hatchlings had developmental deformities, 45.

(e) Exxon Valdez - On March 24, 1989, the Exxon Valdez ran aground on Bligh Reef in

Prince William Sound, Alaska. It spilled 10.8 million gallons of oil into the marine

environment, and impacted more than 1,100 miles of non-continuous Alaskan coastline. This

was the largest oil spill in the U.S. history.

(f) Barge Cibro Savannah – On March 6, 1990, the Cibro Savannah exploded and caught fire

while departing the pier at the Citgo facility in Linden, New Jersey. About 127,000 gallons of

oil remained unaccounted for after the incident.

(g) Megaborg - The Megaborg released 5.1 million gallons of oil as the result of a lightening

accident and subsequent fire. The incident occurred 60 nautical miles south-southeast of

Galveston, Texas on June 8, 1990.

(h) Jupiter - On September 16, 1990, the tank vessel Jupiter was offloading gasoline at a

refinery on the Saginaw River near Bay City, Michigan, when a fire started on board and the

vessel exploded.

21

(i) Arabian Gulf Spills – In January of the 1991 Gulf War, the Iraqi Army destroyed tankers,

oil terminals, and oil wells in Kuwait, causing the release of about 900,000,000 barrels of oil.

This was the largest oil spill in history.

(j) Barge Bouchard 155 – On August 10, 1993, three ships collided in Tampa Bay, Florida:

the barge Bouchard 155, the freighter Balsa 37, and the barge Ocean 255. The Bouchard 155

spilled an estimated 336,000 gallons of fuel oil into Tampa Bay.

(k) Prestige - On 13th November 2002, the tanker ‘PRESTIGE (81,564 DWT)’, carrying a

cargo of 77,000 tonnes of heavy fuel oil, suffered hull damage in heavy seas off northern

Spain. In all, it is estimated that some 63,000 tonnes were lost from the Prestige.

(l) BP oil spill in the Gulf of Mexico; this is presently the world’s largest oil spill. The spill

has caused extensive damage to marine and wildlife habitats, and the fishing and tourism

industries. The Deepwater Horizon, owned by Transocean and leased to BP, caught fire April

20, 2010, after an explosion and sank. The rig, with a platform bigger than a football

field was one of the most modern and was drilling in 5,000 feet of water.

Fig 2.1: Oil slick in the Gulf of Mexico

2.2 Gas Flares;

Gas flaring is the unscientific burning of excess hydrocarbons gathered in an oil/gas

production flow station/site, 46. It is an elevated vertical conveyance found accompanying the

presence of oil wells, gas wells, rigs, refineries, chemical plants, natural gas plants, and

Barge

Oil films floating on water

22

landfills. They are used to eliminate waste gas which is otherwise not feasible to use or

transport. They also act as safety systems for non-waste gas and are released via pressure

relief valve when needed to ease the strain on equipment. They protect gas processing

equipment from being over pressured. Also in case of an emergency situation, the flare

system helps burn out the total reserve gas, 47. The primary purpose of gas flaring is to act as

a safety device to protect vessels or pipes from over-pressuring due to unplanned upsets.

Pressure control valves are set at predetermined pressures to release excess gas, thus allowing

continued operation during upset conditions. Whenever plant equipment items are over-

pressured, the pressure relief valves on the equipment automatically release gases (and

sometimes liquids as well) which are routed through piping runs called flare headers to the

flare stacks. The gases and/or liquids are separated in a flare knock out drum with the gas

piped to the flare stacks for burning or for lighter gases venting. The size and brightness of

the resulting flame depends upon how much flammable material was released. Typically

there may be more than one flare system handling high pressure gas, low pressure gas, sour

or corrosive gas, cold gas and wet gas. Vents (unignited flares) are used typically on gas

plants for emergency gas disposal and are designed to operate in an emergency at sonic

velocity. Flare gas recovery systems are occasionally used to collect low flows of waste gas

and return it to the Process Plant as opposed to burning the gas. Steam can be injected into

the flame to reduce the formation of black smoke. The injected steam does however make the

burning of gas sound louder, which can cause complaints from nearby residents. Compared to

the emission of black smoke, it can be seen as a valid trade off. In order to keep the flare

system functional, a small amount of purge gas flows continuously, whilst there are

continuously burning pilots, so that the system is always ready for its primary purpose of

burning as an over-pressure safety system. Enclosed ground flares are engineered to eliminate

topic and corrosive components, reduce smoke, and contain the flame within the enclosure.

23

Gas flaring in Nigeria began in 1956 with an output of 2,014 million cubic feet; after Shell

D’archy and British Petroleum discovered the first oil in Oloibiri; presently Bayelsa State in

1950. Today as petroleum exploration and exploitation intensify, gas flaring is now

associated with every oil producing community in the Niger-Delta region, 48. It is estimated

that about 60 percent of the over 2 billion standard cubic feet of natural gas produced in

Nigeria is flared, 49,50. Gas flaring is most commonly identified by the glaring sight created

by the ten-meter-high flame that burns continuously from vertical pipes at the many facilities

owned by the oil companies and it is the most significant source of air emission from offshore

oil and gas installations. The burning of these gases releases huge volumes of greenhouse

gases into the atmosphere, while emitted sulphur dioxide returns to the soil as acid rain, 51.

The acid rain, when it falls to the earth’s surface, is corrosive in nature, and causes

widespread damage to the environment, 52. The acid rain problem is evidenced by the fact

that the corrugated iron roofs of the people of the oil-bearing enclave now last less than five

years whereas before now they last for well over 20 years, 53. These gases also cause

increased temperatures, low agricultural productivity, and changes in the aquatic ecosystem

48, 54. Gas flare sites, which often times are situated close to villages, produce “soot”, which is

deposited on building roofs of nearby villages. When it rains, this soot runs off the roofs of

building and pollutes the soil and water aquifers of the people. The presence of soot in the

gas that is flared is a tacit violation of the Department of Petroleum Resources’

Environmental Guidelines and Standards, 55, for the petroleum industry. It specified that

during gas flaring, pre-treated ‘clean’ gas shall be burnt and flare shall be luminous and

bright. Ikelegbe [56], has shown that flaring sites around Isoko area of Delta State generates

tremendous heat. One of such production flow stations is located at Ebocha in Egbema in the

Niger-Delta. These gases which are mostly emitted in the Niger-Delta area of Nigeria cause

serious health problems for the Inhabitants of the region; mainly respiratory tract diseases as

24

well as damage to wild life and vegetations 51, 57. A study of the surface and groundwater

samples from gas flared region of Warri and a neighboring town, Abraka, where minimal gas

flaring activity takes place revealed that that waters in a gas flared environment contain

higher concentrations of harmful heavy metals such as barium, selenium, cadmium,

chromium, iron, manganese and copper. There is also an increase in conductivity, colour, as

well as a change in taste of water in the gas flaring environment when compared to areas

having minimal gas flaring activities 52.

Expert reports of oil exploration in Iko Community in Ikot Abasi Local Government Area of

Akwa Ibom State revealed that gas flaring has caused most of the buildings in the

community, especially those structures with corrugated iron sheet roofs, to experience

massive damage resulting in frequent changes and leakages. Apart from the burning and “die-

back” effect of gas flaring, which were visible in plantain and cocoyam leaves, the dry humid

mornings in Ikot Abasi harboured photochemical smog in the lower atmosphere which causes

irritation of the eye and the body 58.

The flaring of gas in Nigeria is considered a national problem because the cost of continued

flaring of gas cannot be quantified. For example, flaring of gas implies that a potential source

of energy is being wasted. Besides, a huge source of revenue has been going up in flames. It

has been estimated that about five hundred million Naira (N500, 000.000) is lost to gas

flaring daily in Nigeria, 59. The economic constraints measures to manage the environment

are considered luxury more fit for the rich and developed countries 60. Current statistics

indicates that Nigeria accounts for about 28% of the total amount of gas flared globally, 61.

Ojeifo, 62 stated that Over 170 trillion cubic feet of gas is produced in Nigeria, of which more

than 70% is burnt off, with Shell Petroleum Development Company of Nigeria taking the

lead. The World Bank estimates that over 134 billion cubic metres of natural gas are flared or

vented annually, an amount equivalent to more than 20 percent of the United States’ gas

25

consumption or 33 percent of the European Union’s gas consumption per year, 63. This

flaring which is highly concentrated has 10 countries accounting for 70% of its emissions,

and twenty for 85%. Nigeria was named among the top ten leading contributors to world gas

flaring in 2010, (in declining order): Russia (26%), Nigeria (11%), Iran (8%), Iraq (7%),

Algeria (4%), Angola (3%), Kazakhstan (3%), Libya (3%), Saudi Arabia (3%) and Venezuela

(2%),63. In addition to the gas flaring, an estimated annual average of about 2,300 m3 of

refined and unrefined petroleum products is jettisoned into the environment through spillage,

62.

In recent years, efforts have been made by the Federal Government and the oil industry to cut

back on gas flaring or end the practice altogether and eventually enhance natural gas

utilization in Nigeria due to pressure from oil bearing communities and global environmental

movements. A major event in this regard was the start of natural gas exports in 1999 from

plants at Bonny Island in the Atlantic Coast. The NLNG Company, formed in the early

1990’s, is a joint venture involving Nigeria, Shell, Total-Elf, and Agip. The government also

has put in place some initiatives to abate gas flaring. These include: the establishment of the

National Fertilizer Company of Nigeria (NAFCON), Aluminum Smelter Company of Nigeria

(ALSCON) and the Liquefied Natural Gas Project (NLNG), which perhaps is the most

ambitious gas project in the country. There is also the proposed West African Gas Project.

Natural gas is also used to fire most of the National power holding Authority’s thermal

stations 63. The $3.8bn Nigeria Liquefied Natural Gas (NLNG) facility on Bonny Island,

which was completed in September 1999, is also expected to process 252.4 billion cubic feet

of LNG annually. The third LNG production train, with an annual capacity of 130.6 Billion

Cubic Feet (BCF), began operations in November 2002. The third train will increase NLNG’s

overall LNG processing capacity to 383 billion cubic feet per year. Apart from the motion

26

toward increasing gas utilization, Aghalino 50 stated that the following existing legislations

were aimed at reducing gas flaring in Nigeria. They include:

The Petroleum (Drilling and Production) Regulation Decree No. 51 of 1969 which provides

that licensee or leasee must submit feasibility study, program or proposal for gas utilization

not later than five years after the commencement of production

The Associated Gas Re-injection Decree 99 of 1979 which mandates producing companies to

submit proposals for utilization of natural gas. They were expected to stop gas flaring from

1st of January 1984. The Decree empowered the Minister of Petroleum Resources to grant

permission to the oil companies to flare gas based on certain conditions. Consequence for

violation is forfeiture of the acreage concerned.

The Associated Gas Re-injection Amendment Decree 7 of 1985, introduced a penalty charge

of two kobo/1000 standard cubic feet, (standard cubic feet) of gas flared at the fields where

authority to flare was not granted. In 1990, the penalty was increased to fifty kobo / 10000

standard cubic feet. This was further raised to ten Naira / 1000 standard cubic feet in 1998.

The Fiscal Incentive Guarantee and Assurance Decree (FIGAD) 30 of 1990 were meant to

hasten the development of the NLNG project rather than gas flaring. It exempts companies

involved in the NLNG project from import duties and export charges. It also grants them tax

holidays.

The government has also established the following institutions to aid and co-ordinate gas

development in the country. These include the Nigerian Gas Company – a subsidiary of the

NNPC with responsibility for gas gathering and transmission in the country. Also involved is

the gas division in NNPC with responsibility for coordinating gas investment and

management of government interest in joint venture arrangement 64.

27

2.3. Effluent and waste discharges.

Another source of oil related pollution is the discharge of effluents into the surrounding

environment, sometimes into the water, by the oil companies. This is a common occurrence

during exploration or seismic surveys by oil companies. Effluents and Wastes include

produced water, drilling fluids (mud), drill cuttings (crushed rock), diesel emissions, pipe

washings and chemicals associated with operating mechanical, hydraulic, and electrical

equipment, such as biocides, solvents, and corrosion inhibitors,65. There is also the use of

chemicals during seismic activities.

About 98% of the waste from crude oil exploration and production (E&P) is produced water,

with estimates at 480,000 barrels per day 66. Produced water is a water mixture consisting of

hydrocarbons (e.g., PAH, organic acids, phenols, and volatiles), naturally occurring

radioactive materials, dissolved solids, and chemical additives used during drilling. It is

however concluded that “hydrocarbons are likely contributors to produced water toxicity, and

their toxicities are additive, so that although individually the toxicities may be insignificant,

when combined, aquatic toxicity can occur, 66, 67.

Drilling mud and cuttings are of environmental concern because of their potential toxicity

and the large volume that are discharged during drilling. The major constituents of drill

cuttings such as baryotes and bentonitic clays when dumped on the ground prevent local plant

growth until natural processes develop new topsoil, 44. There are Three types of drilling

fluid, they include; oil-based mud (OBM; diesel or mineral oil serves as base fluid), water-

based mud (WBM), and synthetic-based mud (SBM). WBM and SBM typically contain

arsenic, barium, cadmium, chromium, copper, iron, lead, mercury, and zinc, 68.

A study carried out by the Continental Shelf Associates, Inc. 68 on the impact of synthetic-

based drilling fluids (SBF: mixtures of organic isomers) collected from near and far distances

28

from four E&P drilling sites in the Gulf of Mexico indicated that near-field sediments were

toxic to amphipods (crustaceans). It was also found that Chemicals associated with both

WBM and SBM waste solids in near-field sediments contributed to sediment toxicity.

Significantly higher mercury and lead concentrations were found in near-field sediments than

in far-field sediments for some sites. Red crabs found in the near-field sediments had high

concentrations of toxins, such as arsenic, barium, chromium, and mercury.

2.4 Causes of crude oil pollution in Nigeria

The main cause of oil spill in Nigeria 69 includes: Sabotage- Some of the citizens of this

country in collaboration with people from other countries engage in oil bunkering. They

damage and destroy oil pipelines in their effort to steal oil from them. SPDC claimed in 1996

that sabotage accounted for more than 60 percent of all oil spilled at its facilities in Nigeria,

stating that the percentage has increased over the years both because the number of sabotage

incidents has increased and because spills due to corrosion have decreased with programs to

replace oil pipelines70. crude theft and bunkering ; Pirates are stealing Nigeria's crude oil at a

phenomenal rate, stealing nearly 300,000 barrels per day from our oil and selling it illegally

on the international trade market. Nigeria lost about N7.7 billion in 2002 as a result of

vandalisation of pipelines carrying petroleum products. The amount, according to the PPMC,

a subsidiary of NNPC, represents the estimated value of the products lost in the process.

Illegal fuel siphoning as a result of the thriving black market for fuel products has increased

the number of oil pipeline explosions in recent years. In July 2000, a pipeline explosion

outside the city of Warri caused the death of 250 people. An explosion in Lagos in December

2000 killed at least 60 people. The NNPC reported 800 cases of pipeline vandalization from

January through October 2000. In January 2001, Nigeria lost about $4 billion in oil revenues

in 2000 due to the activities of vandals on our oil installations. The government estimates that

as much as 300,000 bbl/d of Nigerian crude is illegally bunkered (freighted) out of the

29

country, 71. Equipment failure: These include (wellhead blow out, valves and flanges failure,

corrosion either through chemical or biological agent, Human error or technical failure). As a

result of the small size of the oil fields in the Niger Delta, there is an extensive network of

pipelines between the fields which carry oil from the well heads to the flow stations- allowing

many opportunities for leaks. Thousands of barrels of oil have been spilled into the

environment through our oil pipelines and tanks in the country. This spillage is as a result of

our lack of regular maintenance of the pipelines and storage tanks. Some of these facilities

have been in use for decades without replacement. About 40,000 barrels of oil spilled into the

environment through the offshore pipeline in Idoho. 72

2.5 Impacts of crude oil pollution on the Environment.

Crude oil exploration is a major economic venture in Nigeria which Aiyesanmi 73 noted has

resulted to the release of polycyclic aromatic hydrocarbons and heavy metals into soils and

water bodies through oil spillage. In soils, petroleum hydrocarbon creates conditions which

lead to unavailability of essential nutrients to plants, 74. It implies that the soil remains

unsuitable until the crude oil is degraded to a tolerable level, 75. The amount of natural crude

oil seepage was estimated to be 600,000 metric tons per year with a range of uncertainty of

200,000 metric tons per year 76. The discharge of crude oil whether accidentally or due to

human activities is a main cause of water and soil pollution and they constitutes a serious

environmental problem which can threaten human health and that of beneficial organisms in

the environment 77, 78. Report revealed that thirteen years after the Exxon Valdez oil spill in

Prince William Sound, the toxic effects were still being felt due to the remaining bulk of the

less-weathered subsurface oil, 79. Crude oil spills may cause damage to the environment in

many ways; in water oil film floating on the water surface could prevent natural aeration, thus

leading to the death of fresh water or marine life. Fish may ingest spilled oil or food

impregnated with oil, such fish has been observed to be unpalatable, 14. Oil spill on land may

30

lead to retardation of vegetation growth, and cause soil infertility for a long period of time

until natural processes re-establish stability 80, 81, 82,. Kyung-Hwa Baek et al, 22 observed that

the growth of corn, especially in root development was acutely reduced in soil contaminated

with as little as 1% (w/w) crude oil. And that corn was entirely unable to germinate in 5%

(w/w) crude oil-contaminated soil. Idodo-ume and Ogbeibu, 83, investigated The values of

Total Petroleum Hydrocarbons (TPH) and heavy metals in soils, plantain fruits and cassava

tubers harvested from farms impacted with petroleum and non-petroleum activities at

Olomoro, Isoko south local government area, Delta state, Nigeria and observed that The

values of heavy metals and TPH were higher in cassava tubers and plantain fruits harvested

from petroleum impacted soil than those harvested from non-petroleum impacted soil. This

indicated hyper accumulation and soil pollution 84. The low oxygen that characterise

mangrove ecosystems makes the oil that penetrates root systems to persist for long periods 85,

86, 87 .This has led to the damage of Vegetation on cultivated land, many forests and

agricultural land. Common food crops like Musa spp (plantain) Discorea spp (yam), Manihot

esculenta (cassava), and Saccharum officinarum (sugar cane) have also been reported to be

affected by oil spills 88. Marine oil pollution in coastal areas is a subject of global interest,

due to the large number of toxic substances transported from human activities 89, 90, 91. Crude

oil spills have also been known to cause damage of aesthetic values due to unsightly slicks or

oiled beaches. It has also been known to cause damage to wild life such as sea birds and

marine mammals and Modification of marine ecosystems and habitats.

2.6 Total petroleum hydrocarbon

Total Petroleum Hydrocarbon (TPH) refers to the measurable amount of petroleum based

hydrocarbons in an environmental matrix. Petroleum hydrocarbons are commonly found

environmental contaminants, though they are not usually classified as hazardous wastes. The

31

main hydrocarbons found in crude oil are aliphatics (paraffins), alicyclics (naphthenes), and

polycyclic aromatic hydrocarbons (PAHs) with the following general characteristics;

2.6.1 Aliphatics and Alicyclics

(i) Quickly broken down by natural processes

(ii) Residence time in environment is less than a day

(iii) Straight chain or ring carbon structures with weak bonds

(iv) Low fluorescence characteristic

2.6.2 Polycyclic Aromatic Hydrocarbons (PAH):

(i) Most abundant of the main hydrocarbons found in crude oils

(ii) Many are toxic

(iii) Can be carcinogenic to plants and animals

(iv) Difficult to separate from water using regular filtering techniques making them

a potential human health hazard

(v) 6-sided carbon rings which contain strong bonds

(vi) Prolonged breakdown by natural processes

2.7. Polycyclic aromatic Hydrocarbons in crude oil

Polycyclic aromatic hydrocarbons [PAHs] are fused-ring compounds that enter soil systems

and natural waters via wastewater effluents from coke and petroleum refining industries,

accidental spills and leakages, rainwater runoff from highways and roadways, or from

intentional disposal in the past [92].

Polycyclic aromatic hydrocarbons or polynuclear aromatic hydrocarbons (PAHs) are

compounds produced through incomplete combustion and pyrolysis of organic matter. Both

natural and anthropogenic sources such as forest fires, volcanic eruptions, vehicular

32

emissions, residential wood burning, petroleum catalytic cracking, and industrial combustion

of fossil fuels contribute to the release of PAHs to the environment, 93. The introduction of

PAHs in the marine environment is performed via processes such as the combustion of

organic matter (pyrolytic origin), the slow transformation of organic matter in geothermal

scale (petroleum hydrocarbons), and degradation of biogenic material (diagenesis). The

naturally formed PAHs are biosynthesis products from oil upwelling and occur in the marine

sediments at very low levels ranging from 0.01 - 1 µg/g dry weight (background

concentrations). On the contrary, human activities are sources of a number of PAHs in the

aqueous environment with the highest values being recorded in estuaries and coastal areas, as

well as in areas with intense vessels transport and oil treatment. 94 polycyclic aromatic

hydrocarbons (PAHs) are pollutants of concern due to their persistent nature in the marine

ecosystem, thus they can cause long-term adverse effect to the marine life 95. PAH toxicity

can also be attributed to the fact that they are widely distributed in the environment and many

of them have carcinogenic properties 96. A lot of PAHs have been detected in the air, soil,

marine sediments, reservoir water, and in some type of food products. Among a long list of

various contaminants, polycyclic aromatic hydrocarbons (PAHs) constitute a major

environmental concern on marine ecosystems because of their adverse health effects on

organisms, including endocrine disrupting activity, 97, 98, 99. PAHs have been reported to cause

toxicity in aqueous plants depending on the kind of the plant and the environmental

conditions. Some of them which are carcinogenic are on the USEPA list of priority

pollutants. These substances are considered as priority substances due to their environmental

behaviour and their harmful effects 100. They are characterized by high toxicity, high stability

in the environment and high lipophilicity, resulting in their transport through the trophic

chain with final destination being the human organism 101,102. In 2008, 17 PAHs were

identified as priority pollutants by the national waste minimization programme, a project

33

which is funded by US Environment Protection Agency, 103. The identified pollutants are

listed as follows; acenaphthene, acenaphthylene, anthracene, benz[a]anthracene,

benzo[a]pyrene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[ghi]perylene,

benzo[j]fluoranthene, benzo[k]fluoranthene, chrysene, coronene, dibenzo(a,h)anthracene,

fluoranthene, fluorene, indeno(1,2,3-cd)pyrene, phenanthrene, pyrene

PAHs are considered to be common organic contaminants and generally generated from the

natural and anthropogenic processes. They can be introduced into the marine environment by

various ways such as oil spill, urban runoff, domestic and industrial wastewater discharges

104. Anthropogenic PAHs can be classified as pyrolytic and petrogenic. Pyrolytic PAHs are

formed as a consequence of incomplete fuel combustion whereas petrogenic PAHs are

mainly derived from the crude oil or unburned fuel and its refined products, 105. PAHs are

globally distributed; with the highest concentrations generally occurring close to urban

centres. Oil spills have also been reported to influence PAH concentrations in local areas, 106.

Polycyclic aromatic hydrocarbons (PAHs) typically coexist in very complex mixtures, such

as coal tar, creosote, and diesel fuel 107. Such mixtures can occur as distinct organic phases,

often called nonaqueous-phase liquids, as dissolved or colloid-associated solutes in

groundwater or as sorbed species associated with soils and sediments. , Products such as

creosote and asphalt also contribute to PAH occurrence in the environment, 108.

Polycyclic aromatic hydrocarbons (PAHs) which are the major hazardous components of oil

spills 109 have been shown to exhibit toxicity in fishes which have been exposed to high

concentrations for long time intervals. Long-term exposure to high concentrations of PAHs

can result in decrease of growth and of reproduction capability of various species in the

marine. In the biennial ranking comprised of chemicals deemed to pose the greatest possible

risk to human health, PAHs placed tenth in 1999 before moving to fifth in 2001 and settling

in at seventh in 2005 110. Both the Agency for toxic substances and disease registry (ATSDR)

34

and US environmental protection agency (USEPA) recognize the potential importance of

PAHs due to their ubiquity in many urban and rural environments, [111]. Moreover,

abnormalities such as liver tumours, kidney problems have been reported to occur as a result

of long term exposure to PAHs, 97.

35

Fig 2.2: Structure of selected PAHs

Naphthalene Acenaphthene Acenaphthylene

Fluorene

Anthracene Phenanthrene Fluoranthrene

Pyrene

Chrysene Cholanthrene Perylene

Benzo[a]pyrene

Coronene

36

2.8. Physical and chemical properties of polycyclic aromatic hydrocarbons

The physical and chemical properties of PAHs are affected by the number and position of the

aromatic rings as well as the number, position and nature of the atoms that can be present in

the molecule, these parameters also affect their environmental behaviour and their

interactions with biota and human, 112. ΡAΗs have high melting and boiling points and low

water solubilities. Their solubility in water decreases, while correspondingly their boiling and

melting point increases, with increasing molecular weight, 113. For example naphthalene

(MW=128) has a water solubility value of 31 µg l-1, melting point 80.5°C and boiling point

218° C, while chrysene (ΜW=228) has water solubility 0.006 µg.l-1 melting point 255°C and

boiling point of 448 °C. Table 4 presents the basic physical and chemical characteristics for

the PAHs most frequently detected in environmental matrices, 114.

37

Table 2.1: Physical and chemical characteristics of selected PAHs (Adopted from

ATDSR, 114

)

* at 20°C ; ** at 25°C

Chacteristics Formula Molecular Weight

Melting point (0C)

Boiling point (0C)

Water solubility (g 100 ml-1)

Log Kow Vapour pressure (mm Hg)

Phenantrene C14H10 178.233 99.5 340 1.18 x 10-4

4.45

Fluoranthene C6H12 202.255 110.8 375 2.65 x 10-5

4.90 5.6 x 10-6**

Pyrene C6H10 202.255 156 404 1.3 x 10-6 4.88 2.5 x 10-6**

Benzo [a]anthracene

C18H12 228.2928 159.8 437.6 1.4 x 10-6 5.61 2.2 x 10-8*

Benzo [b] fluroanthene

C20H12 252.3148 167 357 1.2 x 10-7 6.04 5.0 x 10-7*

Benzo [k] fluroanthene

C20H12 252.3148 215.7 480 5.5 x 10-8 6.06 9.59 x 10-11*

Benzo [e] pyrene

C20H12 252.3148 178 472 ˂0.1 5.6 x 10-9**

Indeno [1,2,3] cd pyrene

C22H12 276.3368 162.5 536 6.2 x 10-6 6.58 10-11x10-6*

Benzo [g,h,i] perylene

C22H12 276.3368 278.3 500 2.6 x 10-8 6.50 1.03 x 10-10**

Dibenzo [a,h] anthracene

C22H14 278.3526 266 524 5 x 10-8 6.84 1.0 x 10-16*

38

PAHs possess very characteristic UV absorbance spectra. These often possess many

absorbance bands and are unique for each ring structure. Thus, for a set of isomers, each

isomer has a different UV absorbance spectrum than the others. This is particularly useful in

the identification of PAHs. Most PAHs are also fluorescent, emitting characteristic

wavelengths of light when they are excited (i.e. when the molecules absorb light). The

extended pi-electron electronic structures of PAHs lead to these spectra, as well as to certain

large PAHs also exhibiting semi-conducting and other behaviours. 115. Polycyclic aromatic

hydrocarbons are lipophilic, meaning they mix more easily with oil than water. The larger

compounds are less water-soluble and less volatile (i.e., less prone to evaporate). Because of

these properties, PAHs in the environment are found primarily in soil, sediment and oily

substances, as opposed to in water or air, 116. However, they are also a component of concern

in particulate matter suspended in air. Natural crude oil and coal deposits contain significant

amounts of PAHs, arising from chemical conversion of natural product molecules, such as

steroids, to aromatic hydrocarbons. They are also found in processed fossil fuels, tar and

various edible oils, 117.

2.9. Health implications of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons are important widespread environmental pollutants, which

are formed and released into environment through natural and anthropogenic sources. They

are toxic; some of them carcinogenic, persistent and bioaccumulative compounds, 118. The

effects on human health will depend mainly on the length and route of exposure, the amount

or concentration of PAHs one is exposed to, and of course the innate toxicity of the PAHs. A

variety of other factors can also affect health impacts including subjective factors such as pre-

existing health status and age. The ability of PAHs to induce short-term health effects in

humans is not clear, 119. Occupational exposures to high levels of pollutant mixtures

containing PAHs have resulted in symptoms such as eye irritation, nausea, vomiting,

39

diarrhoea and confusion. Since the end of the 18th century, many ΡΑΗs were recognized as

carcinogens and mutagens. It has been proven that some of them induce skin cancer and there

are suspicions that some PAHs may induce lung cancer. However, carcinogenic activity is

observed only after exposure to high concentrations for a long time. 120.

Like many other environmental chemicals that are associated with breast cancer risk, PAHs

are lipophilic and are stored in the fat tissue of the breast. PAHs have been shown to increase

risk for breast cancer through a variety of mechanisms. The most common PAHs are weakly

estrogenic (estrogen mimicking), due to interactions with the cellular estrogen receptor 121

PAHs can also be directly genotoxic, meaning that the chemicals themselves or their

breakdown products can directly interact with genes and cause damage to the de-oxy

ribonucleic acid (DNA), 122. Several epidemiological studies have implicated PAH exposure

in increased risk for breast cancer. One of the studies from the Long Island breast cancer

study project found that women with the highest level of PAH-DNA adducts had a 50 percent

increased risk of breast cancer. PAH-DNA adducts are indicators of problems in DNA repair

in cells, one of the early hallmarks of tumour development, 123. The Centre for Children's

environmental health reports that exposure to PAH pollution during pregnancy is related to

adverse birth outcomes including low birth weight, premature delivery, and heart

malformations,124. Detrimental long-term, high-level exposure may lead to consequences

including cataracts, kidney and liver damage, jaundice, and skin irritation and redness,

specifically for naphthalene contact,119. The immune system also is vulnerable and

benzo[a]pyrene (B(a)P) in large doses suppresses the system and damages erythrocytes,114.

Laboratory research on female rats, as summarized by the Cornell university program on

breast cancer and environmental risk factors (BCERF) 125, indicated that breast tissue

injection and consistent high dose ingestion of B(a)P and dibenzo(a,l)pyrene caused a

40

significant increase in the development of breast cancer 125. However these results have not

been proven with any consistency in human studies.

2.10. Heavy metals in crude oil

The term heavy metal refers to any metallic chemical element that has a density of more than

5g/cm3 and is toxic or poisonous at low concentrations. Heavy metal includes most metals

with an atomic number greater than 20, but excludes alkali metals, alkaline earths,

lanthanides and actinides. Heavy metals are natural components of the Earth's crust. They

cannot be degraded or destroyed, 126. They exist in water in colloidal, particulate and

dissolved phases, 127. Their occurrence in water bodies is either of natural origin, 128,129 (e.g.

eroded minerals within sediments, leaching of ore deposits and volcanism extruded products)

or of anthropogenic origin e.g accidental oil spillages from tankers, 130,131, solid waste

disposal 132, refining and manufacturing processes 133, as well as from fertilizers for

agricultural purposes, 134, 135. Heavy metals are dangerous because they tend to

bioaccumulate, 136,137 (i.e. they increase in concentration in a biological organism over time,

compared to the actual concentration in the environment). They are also stored faster than

they are broken down (metabolized) or excreted.

Heavy metal contamination of soil and water is one of the most serious environmental

problems across the world due to their toxicity to human, animals, plants and microbes

138,139,140. For this reason, the investigation of heavy metals in soil is essential since even

slight changes in their concentration above the acceptable levels, whether due to natural or

anthropogenic factors, can result in serious environmental and subsequent health problems,

141,128,137. In order to protect human health, guidelines for the presence of heavy metals in

water have been set by different International Organisations such as USEPA, WHO, EPA,

European Union Commission142, The most common heavy metals that humans are exposed to

41

are aluminium, chromium, nickel, copper, arsenic, cadmium, lead and mercury. aluminium

has been associated with alzheimer’s and parkinson’s disease, senility and presenile

dementia. Arsenic exposure can cause among other illness or symptoms cancer, abdominal

pain and skin lesions. Cadmium exposure produces kidney damage and hypertension. Lead is

a commutative poison and a possible human carcinogen 143, while for mercury, toxicity

results in mental disturbance and impairment of speech, hearing, vision and movement, 144. In

addition, lead and mercury may cause the development of autoimmunity in which a person’s

immune system attacks its own cells. This can lead to joint diseases and ailment of the

kidneys, circulatory system and neurons.

2.11. Environmental and health impacts of heavy metals

Heavy metal can cause serious health effects with varied symptoms depending on the nature

and quantity of the metal ingested, 127. They produce their toxicity in plants by forming

complexes with proteins, in which carboxylic acid (–COOH), amine (–NH2), and thiol (–SH)

groups are involved, 145. Moreover, metals cannot be broken down and when concentrations

inside the plant cells accumulate above threshold or optimal levels, it can cause direct toxicity

by damaging cell structure (due to oxidative stress caused by reactive oxygen species) and it

can also cause indirect toxic effects by replacing essential nutrients at cation exchange sites in

plants 146. Food items that constitute human diet (including animals) are contaminated when

they get in contact with heavy metal polluted environmental media-air, soil and water 147. In

the evaluation of cadmium (Cd) and zinc (Zn) in atmospheric deposit, soil, wheat and milk;

Vidovic et al 148 observed that decreased Cd levels of 93% in atmospheric deposits resulted in

decreased Cd concentrations of 17% in cattle feeds and 13% in milk and decreased Zn levels

of 58% in atmospheric deposits resulted in decreased Zn concentrations of 30% in soil, 17%

in cattle feeds and 17% in milk concluding that heavy metals from atmospheric deposits

directly influence the level of heavy metals in other studied media.

42

2.12. Mercury (Hg)

Mercury was known to the ancient Chinese and Hindus, and has been found in Egyptian

tombs dating from 1500 B.C. The element owes its name to the planet Mercury; the symbol is

derived from the latin hydrargyrum meanng liquid silver. In the middle ages the element was

called argentums vivum. Mercury is a mixture of 7 isotopes with atomic number between 196

and 204, the most abundant being 202 Hg (29.80 %). The tendency to form covalent bonds is

found in a considerable number of compounds of Hg with S, N, and C. The organometallic

derivatives of mercury are remarkably stable. Mercurial compounds are insoluble, with the

exception of the nitrate, chlorate, and perchlorate. However, mercury is very slightly soluble

in water (0.3 µ mol/L) and organic solvents.

Release of mercury from coal combustion is a major source of mercury contamination.

Releases from manometers at pressure measuring stations along gas/oil pipelines also

contribute to mercury contamination. After release to the environment, mercury usually exists

in mercuric (Hg2+), mercurous (Hg22+), elemental (HgO), or alkylated form (methyl/ethyl

mercury), 149. Mercury is a hazardous environmental contaminant. In Japan, 2,252 people

have been affected and 1,043 have died due to minamata disease for the past two decades,

caused by elevated mercury pollution from a chemical plant 150,151.

Mercury naturally enters the environment through the breakdown of minerals into soil,

which is then dispersed through the movement of air and water. Since the start of the

industrial revolution in the 18th century, the release of mercury into the environment has

been heavily amplified. Currently, the anthropogenic release of mercury accounts for up to

two-thirds of the total mercury in the environment, 152. Other common sources of mercury

pollution in these countries include industrial mining, chemical manufacturing, solid waste

disposal, and metals smelting. Mercury is naturally present in soils at concentrations ranging

between 0.003 and 4.6mg/kg 153; In most cases below 0.5mg /kg 154,155, whereas in

43

contaminated sites, concentrations of up to 11,500 and 14,000 mg /kg have been reported

156,157,158,. In these contaminated areas where Hg entrance to the system is mainly via surface

spills, wastewater discharge, and/or by condensation of atmospheric Hg, the element tends to

accumulate in the soil surface horizons, and is mainly retained by sorption onto organic

compounds and, to a lesser extent, clays 159,160. Mercury and its compounds play an important

part in electrochemistry. The metal itself is used as a coolant in certain types of reactors, in

the metallurgy of gold and silver, as a catalyst in organic chemistry, and in the manufacture

of lamps, relays, and switches. Both mercury and its compounds are highly toxic. Out of the

10 000 tones of mercury produced worldwide yearly, it has been estimated that 25 % is

consumed by the chlor-alkali industry, 20 % in electric equipment, 15 % in paints, 10 % in

control and measurement system, 5 % in agriculture, 3 % in dental practice, 2 % in laboratory

and 20 % in others which include detonators, catalysts, preservatives and cosmetics161.

Mercury is used as a catalyst in a variety of industrial and laboratory reactions, some of great

economic value. Its physical property of high conductivity makes the liquid metal valuable in

the electrical industry.

People also are commonly exposed to mercury through the inhalation of vapours produced

through the burning of mercury through various industrial activities; however, many are also

exposed to methyl mercury through the consumption of contaminated food products such as

fish. In 1965, the consumption of fish from regions of the sea contaminated by effluent led to

the appearance of the so-called Minamata sickness in Japan 161. In 1972, Bread cereals

contaminated with fungicides containing mercury led to epidemic poisoning in Iraq. Mercury

in the form of its methyl compounds is specifically the most toxic of the heavy metals. The

salts of bivalent mercury, in the case of chronic consumption, first cause tiredness, loss of

appetite, weight loss and In the end the kidneys fail.. Once mercury enters the human body, it

can permanently damage the brain, kidneys 162, and the development of a foetus. Exposure to

44

methyl mercury can cause arthritis, miscarriages, respiratory failure, neurological damage,

Muscular weakness paralysis and even death. Children are most at risk of mercury exposure,

163.

2.13. Lead (Pb)

Lead is a naturally occurring, bluish-gray metal usually found as a mineral combined with

other elements, such as sulphur (i.e. PbS, PbSO4) or oxygen (PbCO3), and ranges from 10 –

30mg kg-1 in the earth‟s crust 152. Lead belongs to the fourth column of the periodic table

(Group IVB); its maximum valency is therefore IV, but II is far more stable.

Ionic lead, lead (II), lead oxides and hydroxides and lead-metal oxyanion complexes are the

general forms of lead that are released into the soil, groundwater and surface waters. The

most stable forms of lead are Pb (II) and lead-hydroxy complexes. Lead (II) is the most

common and reactive form of lead; forming mononuclear and polynuclear oxides and

hydroxides 149. Lead (II) compounds are predominantly ionic (for example, Pb2+ SO42-),

whereas lead (IV) compounds tend to be covalent (for example, tetraethyl lead, Pb(C2H5)4.

Some lead (IV) compounds, such as PbO2, are strong oxidants. Lead forms several basic

salts, such as Pb(OH)2.2PbCO3, and Pb(SO4) 2, which are very powerful oxidizing agents.

Often, lead is most widely used in industries for manufacturing pipes, conducting materials,

accumulators, lead chambers, printing characters, soldering and coloured pigments 164. Lead,

though not a normal component of the crude oils can be accidentally introduced in heavy oils

in the form of TEL or TML (tetra-ethyl and tetra-methyl lead) that are conventional anti-

knock additives of the gasoline. In storage battery industry, lead - antimony alloys is used as

grids and lugs; litharge (PbO), red lead (Pb3O4) and grey lead (PbO2) as active material

pasted on the plates. Red lead and yellow lead chromate are used as pigments in paints 164.

The toxicities and environmental effects of organo-lead compounds are particularly

noteworthy because of the former widespread use and distribution of tetraethyl-lead as a

45

gasoline additive. The symptoms of acute lead poisoning are headache, irritability, abdominal

pain and Lead encephalopathy which is characterized by sleeplessness and restlessness.

Children may be affected by behavioural disturbances, learning and concentration difficulties.

In severe cases of lead encephalopathy, the affected person may suffer from acute psychosis,

confusion and reduced consciousness. People who have been exposed to lead for a long time

may suffer from memory deterioration, prolonged reaction time and reduced ability to

understand. Individuals with average blood lead levels under 3 µmol/l may show signs of

peripheral nerve symptoms with reduced nerve conduction velocity and reduced dermal

sensibility. If the neuropathy is severe, the lesion may be permanent. In less serious cases, the

most obvious sign of lead poisoning is disturbance of haemoglobin synthesis, and long-term

lead exposure may lead to anaemia. Acute exposure to lead is known to cause proximal renal

tubular damage and Long-term lead exposure may also give rise to kidney damage 165

Furthermore, lead is also known to accumulate in the body more rapidly than it is excreted.

Lead is known to retard haemoglobin production; the cause of anaemia. Other effects are

damages to the nervous systems, the kidneys and the brain. Lead is also known to cause

precipitation of protein, through the interaction of lead ions with the sulphydryl (-SH) groups

of proteins. Studies on human skeletons prove that lead tends to be accumulated in bones, and

its excretion out of the human body is rather slow 166. Maximum lead levels allowed in fish

for consumption in Malaysia is 2µg/g 164.

2.14. Nickel (Ni)

The name nickel is derived from the German word nickel, meaning Satan or Old Nick’s, and

from kupfernickel for Old Nick’s copper. Nickel is one of the transition elements in Group

VIIIB of the periodic table and has chemical similarities to iron and cobalt. It has atomic

number; 28 and atomic weight; 58.6934 respectively. Nickel was first used as an alloy,

mainly in coinage. The ancient Chinese produced “white copper” (paktong), essentially the

46

same as the modern alloy nickel-silver, by smelting ores containing copper, nickel and zinc.

Nickel was first isolated in 1751 when the Swedish chemist Baron Axel Frederic Cronstedt

prepared an impure sample of the metal from an ore containing niccolite. It was first prepared

in relatively pure form in 1804 by H.T. Richter 261

.

The accumulation of Ni in most of agriculture fields are mainly due to sewage sludge

application and use of industrially polluted river water 167,168,169, Nickel occurs naturally in

the environment although rarely in its elemental form 170. Nickel has a strong affinity for iron

and sulphur, forming nickel-iron sulphides such as pentlandite [(Ni, Fe)9S8] within basic

igneous rocks and sulphides such as millerite (NiS) and ullmanite (NiSbS) in mineralised

areas 170,171. Nickel also substitutes for iron in other rock forming minerals such as pyrite, and

occurs as oxides and silicates within laterite deposits as a result of the prolonged weathering

of parent rocks in tropical climates 170,171.

In its elemental form, nickel is a hard, lustrous, silvery-white transition metal, 172. However,

its powder is reactive in air and may spontaneously ignite It is moderately hard and is a

fairly good conductor of heat and electricity. The melting point of nickel is 1453°C, boiling

point is 2732°C, specific gravity is 8.902 (25°C), with a valence of 0, 1, 2, or 3. Nickel is

resistant to corrosion by air and water under ambient conditions and combines readily with

other metals including iron, copper, chromium and zinc to form alloys. Nickel forms

compounds in various oxidation states although the most important is +2, 172, It forms

divalent salts with virtually every anion and it also forms organo metallic complexes

including nickel carbonyl [Ni(CO)4], which is a colourless volatile and highly reactive

liquid173. In general, nickel organometallic compounds are not very stable, often only

intermediate complexes in the synthesis of other organic compounds 173. The primary uses of

nickel metal are in the production of alloys including stainless steel, in nickel plating, in the

47

manufacture of nickel containing products such as batteries and welding electrodes, and in

the production of chemicals containing nickel including nickel sulphate, nickel chloride, and

in catalysts 174. Nickel salts are used mainly in the production of catalysts, in nickel plating,

in batteries, and in the manufacture of pigments and other nickel containing chemicals, 174

Nickel metal alloys and nickel plated items have been used extensively in the transport,

consumer, industrial and construction sectors including the production of motor vehicles,

consumer white goods and bathroom fittings, kitchen and tableware, electronics, food

processing, textiles, fasteners, wires, and cables 174. Nickel is a potent skin sensitizer (that is,

able to cause allergic reaction in humans) and has been reported to be one of the most

common causes of allergic contact dermatitis, 175,176,177,178. Ingestion of nickel can cause skin

reactions in previously sensitised individuals. Nickel dermatitis produces erythema, eczema

and lichenification of the hands. The other main concern for oral exposure to nickel is its

developmental toxicity potential, which has been observed in experimental animal studies. In

most of these experimental studies, the exposure dose of nickel used has been considerably

higher than the nickel content in the normal daily diet 179. Soluble nickel salts and the mixture

of nickel sulphides and oxides present in refinery dust are carcinogenic to the lung and nasal

tissues in humans. Nickel hypersensitivity also causes asthma and conjunctivitis.

2.15. Vanadium (V)

Vanadium is an element with an atomic weight of 50.94 g.mol−1 and the atomic number is 23.

It has a density of 6.11 g.cm-3, with a melting point of 1890 0C and boiling point of 3380 0C.

Metallic vanadium is a shiny, silvery metal with a metallic body-centered cubic structure and

it has a few naturally occurring isotopes, i.e. V-50 (0.25%) and V-51 (99.75%), respectively,

seven other radioisotopes of the element have been synthesized. Pure vanadium is

comparatively soft and ductile, but impurities have a hardening and embrittling effect 180.

Vanadium is widely distributed in the earth’s crust but in small quantities, with an average

48

concentration of 76 x 10-4% 181,182. Vanadium is found in many petroleum products.

Vanadium occurs naturally in fuel oils and coal 183,184. It is also a by-product of petroleum

refining 185. The extraction of vanadium from petroleum ash is a possible future source of the

element 186. Increases in human-induced vanadium emissions, due to the combustion of fossil

fuels, now equal natural emissions from continental dust, marine aerosols, and volcanic

activity 187.

Vanadium is a natural element in the earth. It has no particular odour. In the environment it

is usually combined with other elements such as oxygen, sodium, sulphur, or chloride, 188.

One manmade form, vanadium oxide (vanadium bound to oxygen), is most often used by

industry in making steel. Vanadium oxide can be a yellow-orange powder, dark-grey flakes,

or yellow crystals. Much smaller amounts are used in making rubber, plastics, ceramics, and

certain other chemicals 183. About 80% of the production of vanadium is used to make

ferrovanadium or as a steel additive 188.

Vanadium and its compounds are toxic, though this toxicity is variable 187, 185. Toxicity

depends on the valence; it increases with increasing valence, with pentavalent vanadium

being most toxic. In addition, vanadium is toxic as a cation & as an anion 189.

Small amounts of vanadium in the environment tend to stimulate plants but large amounts are

toxic 190. It is considered to be one of the 14 most noxious heavy metals 191. Vanadium

toxicity is attributed to its ability to inhibit enzyme systems such as monoamine oxidase,

atpase, tyrosinase, choline esterase, & cholesterol synthetase 192.

2.16. Cadmium (Cd)

Cadmium is a relatively rare soft metal that occurs in the natural environment typically in

association with zinc ores and, to a lesser extent, with lead and copper ores. Some inorganic

cadmium compounds are soluble in water, while cadmium oxide and cadmium sulphide are

49

almost insoluble, Cadmium as a non-essential element negatively affects plant growth and

development. It is released into the environment by power stations, heating systems, metal-

working industries or urban traffic. 192

Cadmium occurs naturally in the environment from the slow process of erosion and abrasion

of rocks and soil 193 as well as anthropoegenically through various urban/industrial wastes

such as; mining and metal refining 194,195,196, cadmium rich phosphate fertilizers 197 and waste

water irrigation 140. The largest contributors to the cadmium contamination of water are mines

(mine water, concentrate processing water, and leakages from mine tailings); process water

from smelters; phosphate mining and related fertilizer production; and electroplating wastes.

Cadmium (Cd) is a soft, ductile, silver-white metal that belongs together with zinc and

mercury to group IIb in the Periodic Table. It has relatively low melting (320.9 °C) and

boiling (765 °C) points and a relatively high vapour pressure. In the air cadmium is rapidly

oxidized into cadmium oxide. However, when reactive gases or vapour such as carbon

dioxide, water vapour, sulphur dioxide, sulphur trioxide or hydrogen chloride are present,

cadmium vapour reacts to produce cadmium carbonate, hydroxide, sulphite, sulphate or

chloride, respectively. These compounds may be formed in chimney stacks and emitted to the

environment. Several inorganic cadmium compounds are quite soluble in water e.g. acetate,

chloride and sulphate, whereas cadmium oxide, carbonate and sulphide are almost insoluble

198 Cadmium is mainly used as an anticorrosion coating in electroplating, as an alloying metal

in solders, as a stabilizer in plastics (organic cadmium), as a pigment, and as a component of

nickel-cadmium batteries. .

Like other toxic metals, Cadmium is also taken up by the plants and gets accumulated in

various plant parts as free metal which may adversely affect the plant growth and metabolism

199,200,201. Even at low concentration, Cd may adversely affect the plant reproduction by

50

inhibiting pollen germination and tube growth, 202. A cytogenetic and biochemical study on

the response of Vigna radiata to cadmium stress showed that Cd exhibited inhibitory effect

on mitotic index and chromosome number considerably in a dose and time dependent manner

203. A study was carried out on the toxicity effects of cadmium on seed growth and

germinaton , using soil amended with various levels of cadmium (viz, 10, 30, and 50 mg/ kg).

The results of the study showed that cadmium treatment was inhibitory to seed germination,

plant growth and biochemical constituents of cowpea plants, when compared to control

plants, 204.

The WHO Ambient water quality guidelines for drinking water and other water resources

intended for drinking, to protect human health is 3mg/L

2.17. Arsenic (As)

Arsenic is a metalloid having three allotropic forms; yellow, black, and gray, which are

distributed widely in the earth’s crust. It is located in Groups 13, 14, 15, 16 and 17 of the

Periodic Table. Arsenic has an atomic number of 33 and atomic mass of 74.9241.It also has

melting and boiling point of 817.0˚c and 1090.15˚k respectively. Pure arsenic is rarely found

in the environment. More commonly, it bonds with various elements such as oxygen, sulphur,

and chlorine to form inorganic arsenic compounds and with carbon and hydrogen to form

organic arsenic compounds.

Arsenic occurs as a major constituent in more than 200 minerals, including elemental

Arsenic, arsenide, sulphides, oxides, arsenates and arsenites; most of which are ore minerals

or their alteration products. The most abundant As ore mineral is arsenopyrite (FeAsS),

followed by realgar (AsS) and orpiment (As2S3) 205, Arsenic can be released into the

environment through natural processes such as volcanic action, weathering and water-rock

interactions, upwelling of geothermal water, and forest fires can release As into the

51

environment. Extreme As concentrations in natural water are rare, but are most frequently

observed in ground waste 206,207. The natural occurrence of arsenic in groundwater is directly

related to the arsenic complexes present in soils. Arsenic can liberate from these complexes

under some circumstances. Since arsenic in soils is highly mobile, once it is liberated, it

results in possible groundwater contamination, 208. It is also released through anthropogenic

sources such as industrial products (wood preservatives, paints, dyes, metals,

pharmaceuticals, pesticides, soaps and semiconductors), burning of coal, agricultural

activities, waste disposal of As-containing products and mining and smelting operations, 209.

The highest mineral concentrations can be found as arsenides of copper, lead, silver, and

gold, but high levels may also be found in some coal.

Arsenic occurs in two allotropic forms. The more common form of arsenic is a shiny, gray,

brittle, metallic-looking solid. The less common form is a yellow crystalline solid. It is

produced when vapours of arsenic are cooled suddenly. When heated, arsenic does not melt,

as most solids do. Instead, it changes directly into a vapour (gas). This process is known as

sublimation. However, under high pressure, arsenic can be forced to melt at about 814°C

(1,500°F). Arsenic has a density of 5.72 grams per cubic centimetre.

Arsenic as a metalloid or inorganic semiconductor occurs most commonly with valence states

of +3 (arsenite, As [III]) and +5 (arsenate, As [V]) 210. Arsenic forms both inorganic and

organic compounds including hydrides (e.g., arsine), halides, oxides, acids, and sulphides.

The toxicity and mobility of As varies with its valence state and chemical form. As (III) is

generally more toxic to humans and four to ten times more soluble in water than As (V).

However, different As-containing chemical compounds exhibit varying degrees of toxicity

and solubility 209. Arsenic is used as a timber preservative in a copper-chromium-arsenic

(CCA) cocktail. Consequently many sites associated with the timber industry or where

treated timber is used, are contaminated with arsenic. 211. Several studies show that CCA

52

leaches out of treated timber into surrounding soil 212,213,214,215 or water 216,217. Arsenic was

also used in various agricultural insecticides, termination and poisons. For example, lead

hydrogen arsenate was a common insecticide on fruit trees, but contact with the compound

sometimes resulted in brain damage among those working the sprayers.218 These form of

insecticides have been replaced by monosodium methyl arsenate (MSMA) and disodium

methyl arsenate (DSMA) –which are less toxic organic forms of arsenic. . These applications

are however declining, as many of these compounds are being phased out, 219.

Arsenic is linked with toxic effects from both ingestion and inhalation exposure. Soluble

inorganic arsenicals are generally recognized as more toxic than organic forms, with As(III)

being more toxic than As(V), Blackfoot disease was perhaps the most notorious vascular

disease from As poisoning, which was recognized in Taiwan as early as 1920 and

characterized by coldness and numbness in the feet, followed by ulceration, black

discoloration and dry gangrene of the affected parts 198. Long-term exposure to arsenic in

drinking-water causes increased risks of cancer in the skin, lungs, bladder and kidney. It also

leads to other skin-related problems such hyperkeratosis and changes in pigmentation. The

occurrence of arsenic diseases depends on the ingestion of arsenic compounds and their

excretion from the body. It has been reported that 40% to 60% arsenic can be retained by the

human body. It indicates that the level of hazards will be higher with the greater consumption

of arsenic contaminated water. 220. Arsenic has also been reported to show plant toxicity even

at low concentration, 199.

Arsenic contamination in groundwater used for drinking purposes has been envisaged as a

problem of global concern. As a result, the world health organization (WHO) has set a

provisional guideline value of 10 µg/L or 0.01 mg/L for arsenic in drinking-water and

according to the international agency for research on cancer (IARC) there is enough evidence

to conclude that “arsenic and arsenic compounds” can cause cancer in humans 121.

53

2.18. Methods for analysing heavy metals

Common techniques used for metal analyses include:

(i) Flame Atomic Absorption Spectroscopy (FAAS)

(ii) Graphite Furnace Atomic Absorption Spectroscopy (GFAAS)

(iii) X-ray Fluorescence Spectroscopy (XRF)

(iv) Particle Induced X-ray Emission Spectroscopy (PIXE)

(v) Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES)

(vi) Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)

(vii) Neutron Activation Analysis (NAA)

(viii) Cold Vapour Atomic Fluorescence Spectrometry (CVAFS) for mercury

(ix) Ion chromatography for soluble metals

(x) Electron Microscopy for qualitative analysis

When analysing soil for heavy metals; XRF, Atomic absorption and ICP (Inductive Coupled

Plasma) are the primary accredited methods with proven high precision. Heavy metals

associate themselves with organic compounds within the soil making the metal ion immobile

or partially so within the soil structure. To completely release the metals for liquid analysis an

extraction process has to be applied to the soil sample. Some methods of determination

require the sample to undergo chemical digestion to release the metals so that analysis can be

achieved however the XRF method does not require this procedure to be applied. However

as a general rule, if analyzing 6 elements or less, then AAS is the best method. For analyzing

7 elements or more, ICP is recommended, 249.

2.19. Atomic Absorption Spectroscopy

Atomic Absorption Spectroscopy (AAS) is a spectro analytical procedure for the qualitative

54

and quantitative determination of chemical elements employing the absorption of optical

radiation (light) by free atoms in the gaseous state, 123. In analytical chemistry, the technique

is used for determining the concentration of a particular element (the analyte) in a sample to

be analyzed. AAS can be used to determine over 70 different elements in solution or directly

in solid samples. It is the most widely utilised method today for rapid and quantitative

element analysis. The detection limit in this case lies at up to 0.1 ppt (1 billionth) under

optimum test conditions. Atomic absorption spectrometry was first used as an analytical

technique, and the underlying principles were established in the second half of the 19th

century by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff, both professors at the

University of Heidelberg, Germany. The modern form of AAS was largely developed during

the 1950s by a team of Australian Chemists. They were led by Sir Alan Walsh at the

commonwealth scientific and industrial research organization (CSIRO), division of chemical

physics, in Melbourne, Australia.

The significant advantages of AAS are its high selectivity and detection sensitivity. For this

reason, the process has rapidly achieved a position of importance in the field of scientific

analysis. AAS has many uses in different industries. Many raw materials are examined, and

AAS is widely used to check that the major elements are present and that toxic impurities are

lower than specified. In the mining industry, the amounts of metals, e.g. gold in rocks can be

determined by AAS to see whether it is worth mining the rocks to extract the gold. In the

agricultural industry, animal fodder is analyzed for possible metal impurities. Also within

clinical and environmental analysis, AAS is an important analytical technique.

Principles: The technique makes use of absorption spectrometry to assess the concentration of

an analyte in a sample. It requires standards with known analyte content to establish the

relation between the measured absorbance and the analyte concentration and relies therefore

on Beer-Lambert Law 182 In short, the electrons of the atoms in the atomizer can be promoted

55

to higher orbitals (excited state) for a short period of time (nanoseconds) by absorbing a

defined quantity of energy (radiation of a given wavelength). This amount of energy, i.e.,

wavelength, is specific to a particular electron transition in a particular element. In general,

each wavelength corresponds to only one element, and the width of an absorption line is only

of the order of a few picometers (pm), which gives the technique its elemental selectivity.

The radiation flux without a sample and with a sample in the atomizer is measured using a

detector, and the ratio between the two values (the absorbance) is converted to analyte

concentration or mass using Beer-Lambert Law.

Upon introduction of the metal solution into the instrument, the solution is vapourised by the

flame or a furnace, and the trace metal to be detected is dissociated from its chemical bonds

into its elemental form. A hollow cathode or electrodeless discharge lamp provides

characteristic radiation energy for the metal. The wavelength of this emitted radiation must

match the absorption wavelength of the metal to be determined. The amount of energy

absorbed by the metal atoms is related to their concentration. Since each metal absorbs light

at a characteristic wavelength, analysis for each metal requires a different light source, and

only one element can be determined at a time.

Figure 2.3: Basic Configuration of an AAS

There are two main AAS techniques, flame atomic absorption spectroscopy (FAAS) and

graphite furnace atomic absorption spectroscopy (GFAAS). Both techniques are based on

56

similar principles used for measuring metals in solution. However, they differ in the method

used for sample introduction into the instrument. In FAAS, the sample is atomised with a

nebuliser and introduced into a flame, normally an air/acetylene flame. A graphite furnace

electro thermal atomiser is used in GFAAS.

2.20. Flame Atomic Absorption Spectroscopy (FLAAS)

Flame Atomic Absorption Spectroscopy is a fast and easy technique with an extremely high

sensitivity (especially for elements like Pb, Cd, Cu and Cr), although problems can arise as a

result of chemical (a much worse situation than with ICP-AES) and spectral interferences.

The sample is atomized in the flame, through which radiation of a chosen wavelength (using

a hollow cathode lamp) is sent. The amount of absorbed radiation is a quantitative measure

for the concentration of the element to be analyzed. The most current gas mixtures used are

air/acetylene and nitrous-oxide/acetylene. The latter resulting in higher atomization

efficiencies and thus better detection limits for elements like Si, Al, Sc, Ti, V and Zr. The

air/acetylene flame can be used for easy atomizable elements (e.g. As and Se). Background

correction can be achieved with a deuterium lamp although several disadvantages

subsequently occur.

A disadvantage of the AAS technique is the non linearity of the calibration curves when

absorbance becomes higher than 0.5 to 1. The relative standard deviations are between 0.3

and 1% for absorbances of 0.1 to 0.2. Detection limits for flame AAS vary enormously: from

1 - 5 ppb (e.g. Ca, Cd, Cr, Cu) to more than 1000 ppb (e.g. P). Some elements (e.g. B, C, Br)

cannot be measured at all.

In flame atomic absorption spectroscopy a liquid sample is aspirated and mixed as an aerosol

with combustible gasses (acetylene and air or acetylene and nitrous oxide.) The mixture is

ignited in a flame of temperature ranging from 2100 to 2800 degrees C (depending on the

57

fuel gas used.) During combustion, atoms of the element of interest in the sample are reduced

to the atomic state. A light beam from a lamp whose cathode is made of the element being

determined is passed through the flame into a monochronometer and detector. Free, unexcited

ground state atoms of the element absorb light at characteristic wavelengths; this reduction of

the light energy at the analytical wavelength is a measure of the amount of the element in the

sample.

2.21. Graphite Furnace Atomic Absorption (GFAA)

Graphite furnace atomic absorption spectrometry is a highly sensitive spectroscopic

technique that provides excellent detection limits for measuring concentrations of metals in

aqueous and solid samples. GFAA has been used primarily in the field for the analysis of

metals in water. GFAA could be used to determine metals in soil, but the sample preparation

for metals in soil is extensive and is not practical for field applications. GFAA cannot be

described as a truly field portable instrument. GFAA instruments are extremely sensitive and

therefore, must be operated in a clean, climate controlled environment. This can be difficult

but not impossible to achieve in a field environment. In addition, the 220-volt electrical

power requirement often precludes remote operation. However, GFAA is an example of

“taking the laboratory to the field.” Miniaturization of electronics has significantly reduced

instrument size and weight, making it easier to use the instrument in a field laboratory.

In atomic absorption spectrometry, light of a specific wavelength is passed through the

atomic vapour of an element of interest, and measurement is made of the attenuation of the

intensity of the light as a result of absorption. Quantitative analysis by AAS depends on: (1)

accurate measurement of the intensity of the light and (2) the assumption that the radiation

absorbed is proportional to atomic concentration.

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Samples to be analyzed by GFAA must be vapourized or atomized, typically by using a flame

or graphite furnace. The graphite furnace is an electro thermal atomizer system that can

produce temperatures as high as 3,000°C. The heated graphite furnace provides the thermal

energy to break chemical bonds within the sample and produce free ground-state atoms.

Ground-state atoms then are capable of absorbing energy, in the form of light, and are

elevated to an excited state. The amount of light energy absorbed increases as the

concentration of the selected element increases.

GFAA has been used primarily for analysis of low concentrations of metals in samples of

water. GFAA can be used to determine concentrations of metals in soil, but the sample

preparation for metals in soil is somewhat extensive and may require the use of a mobile

laboratory. The more sophisticated GFAAs have a number of lamps and therefore are capable

of simultaneous and automatic determinations for more than one element.

Logistical needs include reagents for preparation and analysis of samples, matrix modifiers, a

cooling system, and a 220-volt source of electricity. In addition, many analytical components

of the GFAA system require significant space, which typically is provided by a mobile

laboratory.

The advantages of GFAA spectrometry include: Greater sensitivity and detection limits than

other methods, direct analysis of some types of liquid samples, Low spectral interference and

very small sample size.

Atomic absorption spectroscopy measurements are subject to interference from a number of

confounding influences: background, spectral, ionisation, chemical and physical interferences

have all been identified. Appropriate choice of filter media and matrix matching of the

samples to standards tend to minimise interference, 221. Overall, AAS has less interference

than other techniques used for measuring metals in air.

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High-volume samplers are normally used for sampling when FAAS or GFAAS analysis is

planned. Both techniques are destructive and require that the sample be extracted or digested

before introduction into system as a solution. The detection limit of the GFAAS is normally

about two orders of magnitude better than the FAAS.

2.22. X-ray fluorescence spectroscopy

X-ray fluorescence spectroscopy (XRF) is a very powerful and comparatively inexpensive

method for determining elements in airborne particulate matter collected onto filters. The

sample on the filter is irradiated with a beam of X-rays. This primary radiation interacts with

the elements in the sample to produce vacancies in the inner atomic shells, which then de-

excite to produce characteristic secondary X-ray radiation. The wavelengths detected indicate

which types of elements are present, and the quantity is determined from the intensity of the

X-rays at each characteristic wavelength.

X-ray fluorescence spectroscopy can be used to determine all elements with atomic weights

from 11 (sodium) to 92 (uranium). A typical commercial instrument uses up to seven

fluorescences to determine up to 44 chemical elements, and it is normally calibrated with thin

metal foils and salts.

In a modification of the XRF technique, called wavelength dispersive analysis, X-ray are

used to excite the samples and crystal spectrometers are used to disperse and analyse the

characteristic secondary X-rays according to their wavelength. A semiconductor detector

converts the energy of the incident secondary X-ray into a voltage pulse whose amplitude is

proportional to that energy. The resolution of the semiconductor detector is adequate enough

to separate X-ray lines from elements of adjacent atomic numbers. Thus the instrument is

capable of performing simultaneous multiple element analysis for typical aerosol samples.

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The XRF technique is non-destructive and requires minimal sample preparation – the filter

(sample) can be inserted directly into the instrument for analysis. Although it is a relatively

inexpensive technology, the detection limits are normally higher than other analysis

techniques. The detection limits depend upon the filter types used, and concentrations are

corrected for filter blanks. As a result of the higher detection limits of XRF; Partisol or

dichotomous samplers, which sample onto Nylon or Teflon filters, are normally used for

sampling when samples are to be analysed by XRF. High-volume samplers normally use

quartz-filters and these have high background levels of several elements.

For soil analysis two versions of instrument are used for on-site analysis. (1) Portable unit:

where the ‘gun’ is placed in close proximity to the soil and a near instantaneous reading is

provided. (2) Laboratory instruments where samples are presented to the analyser. The hand

held units can also be used in the laboratory with the use of an appropriate stand.

The theory of operation:- When high energy X-Rays from the gun strike a metal atom, some

of the low energy electrons within the atom are literally knocked out of their orbits; this

leaves a ‘hole’ and higher energy electrons from electron shells further away take up the void

but in doing so they have to lose energy to be able to stay in the that orbit this energy is lost

as X-rays these X-rays are known as fluorescent X-rays and each metal has a characteristic

set of emissions which can be used to identify the metal the amplitude of these provide

information regarding the concentration of the element within the target sample.

The advantage of the XRF gun is that it is possible to use safely with the minimum of training

and results are almost instantaneous. The disadvantages are that the penetration depth of the

X-rays within the soil sample is only a few mm and there are attenuation issues with wet soils

or sludge which can be overcome by drying the sample before analysis.

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2.23. Inductively Coupled Plasma

Inductively Coupled Plasma has been commercially available for over 40 years and is used to

measure trace metals in a variety of solutions.

Principle: Sample solutions are introduced into the ICP as an aerosol that is carried into the

center of the plasma (superheated inert gas). The plasma desolvates the aerosol into a solid,

vapourizes the solid into a gas, and then dissociates the individual molecules into atoms. This

high temperature source (plasma) excites the atoms and ions to emit light at particular

wavelengths, which correspond to different elements in the sample solution. The intensity of

the emission corresponds to the concentration of the element detected.

Figure 2.4: Basic Configuration of an ICP

ICP can be performed using various techniques, two of which are inductively coupled

plasma – absorption emission spectroscopy (ICP-AES) and inductively coupled plasma-mass

spectroscopy (ICP-MS)

2.24. Inductively Coupled Plasma-Atomic Emission Spectroscopy

Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) is used to

simultaneously determine the concentration of several trace elements in an acid solution. The

technique is based on the measurement of atomic emission by optical spectroscopy. The

sample is introduced into the instrument in solution form, and the atoms in the sample

solution are excited with an argon plasma 'torch'. When the excited atoms return to their

normal state, each element type emits a characteristic wavelength of light. The intensities of

62

the wavelengths detected indicate the presence and amounts of specific elements. The plasma

is produced by a radio frequency generator, which sends an oscillating current through a coil

placed around a quartz tube. The oscillating current produces an oscillating magnetic field

that interacts with ions formed in a flowing stream of argon gas in the quartz tube. This

results in the formation of plasma in the form of a toroid or doughnut. The emission spectrum

from the plasma is resolved by dispersion with a grating spectrometer, and the relative

intensities and concentrations of the elements present calculated.

Up to sixty-one elements can be analysed simultaneously by ICP-AES, at a rate of one

sample per minute. The technique allows analysis over a large range of concentrations-up to

5 orders of magnitude. As with FAAS and GFAAS, the airborne particulate matter sample

must be extracted and digested before introduction into the instrument as a solution.

Typically, the ICP-AES detection limits for many metals are equal to or just better than those

of FAAS, but GFAAS detection limits are better than ICP-AES for most metals (Appendix

E). High-volume samplers are normally used for sampling when ICP-AES analysis is

planned.

2.25. Inductively Coupled Plasma Mass Spectrometry

The Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) technique involves the use of

an argon plasma torch to generate elemental ions for separation and identification by mass

spectrometry (MS). More than 60 elements can be determined simultaneously, including their

isotopes 221. The sample, in solution, is introduced by nebulisation into a radio frequency

plasma where energy transfer processes take place. The ions are extracted from the plasma

through a differentially pumped interface and separated on the basis of their mass-to-charge

ratio by a quadrupole mass spectrometer. These mass spectrometers normally have a

minimum resolution capability of 1 atomic mass unit peak width at 5% peak height and can

determine the isotopes of the elements.

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The Inductively Coupled Plasma coupled with a mass spectrograph give very high sensitivity

for the determination of elements and even isotopes. This technique has the ability to detect

very low levels (parts per billion) of most elements in a sample. The dynamic range is

typically ten orders of magnitude and data reduction is relatively simple. Rapid data

acquisition and data reduction enable the measurement of large numbers of samples in a short

period of time. ICP-MS is the technique of choice for trace element analysis of natural

waters, minerals, and rocks. High precision is achieved by using multiple internal standards.

As with FAAS, GFAAS and ICP-AES, the sample has to be extracted and digested before

introduction into the instrument in solution form. An ICP-MS instrument has the lowest

detection limit of all the instruments described.

The advantage of ICP is that it can analyze multiple elements at one time and has longer

linear ranges compared to AAS and GFAAS. The linearity for ICP ranges from 4 to 6 orders

of magnitude whereas AAS and GFAAS range from 2 to 3 orders of magnitude. ICP has less

chemical interference than AAS or GFAAS due to the high temperature of the plasma and

also has less matrix interference due to its mode of sample introduction. Furthermore, ICP

has a variety of emission lines to choose from to reduce interference from other elements and

to increase sensitivity

2.26. Cold Vapour Atomic Fluorescence Spectrometry for Mercury

Cold Vapour Atomic Fluorescence Spectrometry (CVAFS) is used to analyse elemental

mercury collected from ambient air. Mercury (Hg) exists in air in the vapour and particulate

phase. Ambient air is drawn through gold-coated bead traps, at a low flow rate of 0.3 L/min,

resulting in the collection of vapour phase Hg by amalgamation. However, as a result of its

very low ambient concentration, particulate mercury is collected by trapping onto a glass-

fibre filter, through which air is drawn at a higher flow rate of 30 L/min, over 12-24 hours.

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Particulate phase mercury, collected on the glass-fibre filter, is extracted with nitric acid then

all forms of mercury in the extract are oxidised to Hg2+ ions using BrCl. The Hg2+ ions are

next reduced to volatile Hgo using SnCl2. The liberated mercury is collected on a gold-coated

bead trap and determined by dual-amalgamation CVAFS. This involves the thermal

desorption of the mercury from the gold-plated bead trap into the CVAFS detector cell where

the mercury absorbs incident ultraviolet radiation and fluoresces. The fluorescence signal is

detected by a photomultiplier tube that converts the signal to a voltage proportional to the

amount of mercury present.

2.27. Methods for analysing total petroleum hydrocarbons (TPH)

There are various methods for determining TPH in environmental samples, these include:

High performance liquid chromatography (HPLC), Gas chromatography-flame ionisation

detector (GC-FID) and Gas chromatography-mass spectrometry (GC-MS). Each has

advantages and disadvantages. HPLC is generally the most sensitive, but is subject to

interferences and not as widely available as other techniques. GC is also subject to

interferences and is not as sensitive, but is relatively inexpensive and a good screening tool.

GCMS is also not as sensitive as HPLC, and is relatively expensive, but the MS gives

positive identification. With the use of selected ion monitoring (SIM), the detection limits can

be reduced by 5-10X, approaching those of HPLC.

Generally, in samples expected to be relatively free of interferences, HPLC is the preferred

technique. For samples with potential problems, such as those known to contain petroleum

products, GCMS may be more suitable with fewer interferences, while for unknown samples,

GC can be used as a screening method to determine the appropriate course of action.

2.28. Gas chromatography

Gas chromatography (GC) is an analytical technique for separating compounds based

primarily on their volatilities. Gas chromatography (GC), is a common type of

65

chromatography used in analytical chemistry for separating and analysing compounds that

can be vapourized without decomposition. Typical uses of GC include testing the purity of a

particular substance, or separating the different components of a mixture (the relative

amounts of such components can also be determined). In some situations, GC may help in

identifying a compound. In preparative chromatography, GC can be used to prepare pure

compounds from a mixture, 222.

In gas chromatography, the mobile phase (or "moving phase") is a carrier gas, usually an

inert gas such as helium or an unreactive gas such as nitrogen. The stationary phase is a

microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or

metal tubing called a column (a homage to the fractionating column used in distillation). The

instrument used to perform gas chromatography is called a gas chromatograph (or

"aerograph", "gas separator"), 223.

The gaseous compounds being analyzed interact with the walls of the column, which is

coated with different stationary phases. This causes each compound to elute at a different

time, known as the retention time of the compound. The comparison of retention times is

what gives GC its analytical usefulness.

Principle: A gas chromatograph uses a flow-through narrow tube known as the column,

through which different chemical constituents of a sample pass in a gas stream (carrier gas,

mobile phase) at different rates depending on their various chemical and physical properties

and their interaction with a specific column filling, called the stationary phase. As the

chemicals exit the end of the column, they are detected and identified electronically. The

function of the stationary phase in the column is to separate different components, causing

each one to exit the column at a different time (retention time). Other parameters that can be

used to alter the order or time of retention are the carrier gas flow rate, column length and the

temperature.

66

In a GC analysis, a known volume of gaseous or liquid analyte is injected into the "entrance"

(head) of the column, usually using a micro syringe (or, solid phase micro extraction fibers,

or a gas source switching system). As the carrier gas sweeps the analyte molecules through

the column, this motion is inhibited by the adsorption of the analyte molecules either onto the

column walls or onto packing materials in the column. The rate at which the molecules

progress along the column depends on the strength of adsorption, which in turn depends on

the type of molecule and on the stationary phase materials. Since each type of molecule has a

different rate of progression, the various components of the analyte mixture are separated as

they progress along the column and reach the end of the column at different times (retention

time). A detector is used to monitor the outlet stream from the column; thus, the time at

which each component reaches the outlet and the amount of that component can be

determined. Generally, substances are identified (qualitatively) by the order in which they

emerge (elute) from the column and by the retention time of the analyte in the column. There

are various components which make up the gas chromatograph, they include:

2.28.1. Supply or Carrier Gas

The carrier gas is usually helium, hydrogen, or nitrogen. This serves as the mobile phase that

moves the sample through the column. The carrier gas flow can be quantified by either linear

velocity, expressed in cm/sec, or volumetric flow rate, expressed in ml/min. The linear

velocity is independent of the column diameter while the flow rate is dependent on the

column diameter

2.28.2. Injector

The injector is a hollow, heated, glass-lined cylinder where the sample is introduced into the

GC. The temperature of the injector is controlled so that all components in the sample will be

vapourized. The glass liner is about 4 inches long and 4mm internal diameter.

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2.28.3. Column

The GC column is the heart of the system. It is coated with a stationary phase which greatly

influences the separation of the compounds. The structure of the stationary phase affects the

amount of time the compounds take to move through the column. Typical stationary phases

are large molecular weight polysiloxane, polyethylene glycol, or polyester polymers of 0.1 to

2.5 micrometer film thickness. Columns are available in many stationary phase sizes. A

typical capillary column is 15 to 60 meters in length and 0.25 to 0.32 mm ID. A typical

packed column is 6 to 12 feet long and 2.2 mm ID.

2.28.4. Oven

The column is placed in an oven where the temperature can be controlled very accurately

over a wide range of temperatures. Typically, GC oven temperatures range from room

temperature to 300˚C, but cryogenic conditions can be used to operate at temperatures from

about -20˚C to 20˚C.

2.28.5. Detector

As compounds come off the column, they enter a detector. The compound and detector

interact to generate a signal. The size of the signal corresponds to the amount the compound

present in the sample. There are several different types of detectors that can be employed,

depending on the compounds to be analyzed. These detectors can measure from 10-15 to 10-6

gram of a single component. Common detectors are flame ionization (FID) for carbon-

containing compounds, electron capture (ECD) for halogenated compounds, flame

photometric Detector (FPD) for compounds containing sulphur or phosphorous and nitrogen-

phosphorous detectors (NPD) for compounds containing nitrogen and phosphorous. Chiral

separation also can be achieved by gas chromatography.

2.28.6. Data recorder

The data recorder plots the signal from the detector over time. This plot is called a

chromatogram. The retention time, which is when the component elutes from the GC system,

is qualitatively indicative of the type of compound. The data recorder also has an integrator

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component to calculate the area under the peaks or the height of the peak. The area or height

is indicative of the amount of each component.

Figure 2.5: Schematic diagram of a Gas Chromatographic System

2.29. Gas chromatography/Flame Ionisation Detector (GC-FID)

GC-FID is similar to gas chromatography (GC), with one important difference: the use of a

flame ionisation detector (FID) for detection. The first flame ionization detector was

developed in 1957 by scientists working for the Commonwealth Scientific and Industrial

Research Organisation (CSIRO) in Melbourne, Australia 224,225,226. The flame ionization

detector (FID) is one of the most used detectors for gas chromatography (GC). The

application area is wide. For example, petrol for airplanes, kerosene, is carefully analyzed

with the FID as a routine control. The composition of the kerosene is of great importance for

the energy conversion. A completely different area is the packaging of food. During the

69

processing of polystyrene, different hydrocarbons are added to create the end-product. When

polystyrene is used within the food industry, it is crucial that the product is analyzed for any

residues of the hydrocarbons, since they can influence the quality of the food and harm

human health.

The FID is well suited for analysis of hydrocarbons, such as methane, ethane, acetylene etc.,

but also for organic substances containing hydrocarbons and for volatile organic compounds

(VOCs). In an FID, the sample undergoes combustion in a hydrogen/synthetic air flame. Ions

and free electrons are formed in the flame. The charged particles produce a measurable

current flow in the gap between two electrodes in the detector. The resulting current flow is

of greater strength than the signal produced by the pure carrier gas and the fuel gas flame

alone. This signal differential provides information about the sample. The current is

proportional to the ion formation which depends on the composition of the separated sample.

The FID is a general detector which, after additional configurations, can be used for more

specific components. For example, by placing a methanizer ahead of the FID, components

containing carbon can undergo transformation to methane and thereby become suitable for

further FID analysis. CO and CO2 are commonly analyzed this way. For the determination of

organic nitrogen/phosphorus compounds, a different FID configuration is needed. The sample

passes a heated alkali source, where charged particles are formed in contact with the alkali

source. This method is normally named alkali flame ionization, but it is also referred to as

thermionic detection. The detector used for this method belongs to the group of detectors in

which thermal energy is used as source for ionization. This method is often also called

nitrogen/phosphorous detection; the acronym for the corresponding detector is NPD.

Flame ionization detectors are extremely sensitive and have a wide range of linearity [254],

their only disadvantage is that they consume the sample. An important facet of the FID is the

use of a carrier gas to transfer the sample from the injector through the column and into the

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FID. The carrier gas must be inert and may not be adsorbed onto the column material. Helium

or nitrogen are normally used as carrier gases for the FID, sometimes hydrogen is also used.

The detector gases, hydrogen and synthetic air, respectively serve as fuel gas and oxidizing

gas during the combustion process. Since hydrocarbon impurities, moisture and oxygen

produce a greater baseline noise which has an adverse effect on the detection limit, these

impurities in the detector gases should be kept as low as possible.

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CHAPTER THREE

3.0 METHODOLOGY

3.1. Field Sampling

Method: Systematic random sampling 229 / composite sampling 230.

Apparatus:

(i) Digger

(ii) Measuring tape

(iii) Hand trowel

(iv) Aluminium foil

(v) Hard paper material

The soil samples were collected along the river near the Isimiri flow station owned by Shell

Petroleum Development Commission (SPDC). A one-season data collection method was

employed while soil samples were collected during the raining season (October) 2011.

Systematic random sampling method 229 was used to collect the soil samples. Five (5)

sampling points at a distance of about 50m from each other were mapped out for soil sample

collection. Each of the sampling points were sub sampled into two sample points thereby

making a total of ten sampling points. The soil samples were collected using a clean stainless

steel trowel at a depth of 0-15cm. The collected samples were thoroughly homogenised 230

and placed in a cleaned new aluminium foils which was labelled and placed in an ice chest

and transported to the laboratory where it was air dried at room temperature for three (3)

days. The sample digestion, pre-treatment and analysis were carried out immediately. The

results obtained were analysed statistically using the SPSS statistical package.

3.2. Sample digestion and pre-treatment for Heavy metal determination.

Method: Wet Acid-Digestion method, 231,232.

Apparatus:

(i) Mortar and pestle

(ii) Mesh (2mm)

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(iii) Beaker (50ml)

(iv) Measuring cylinder (50ml)

(v) Volumetric flask (100ml)

(vi) Hot plate (Seta hot model)

(vii) Stop watch

(viii) Fume cupboard

Reagents:

(i) Conc. Hydrochloric Acid, (HCl).

(ii) Conc. Nitric Acid, (HNO3).

(iii) Deionised Water.

Procedure:

• The soil sample was thoroughly homogenised and pulverised using the mortar and

pestle.

• It was sieved using a mesh of 2mm.

• 2g of the soil sample was weighed into a beaker.

• 20ml of 1:1 hydrochloric acid (HCl) and deionised water mixture (70ml each) was

added to the sample and heated at 40oC. The heating continued until it dried up, after

which another 20ml was added and heated until it dried up.

• 5ml of conc. nitric acid (HNO3) was added, this released fumes until it stopped. (This

was carried out in a fume cupboard).

• 20ml of water was added after which the mixture was refluxed

• The mixture was filtered into a 100ml volumetric flask and made up using deionised

water.

3.3. Preparation of standard solutions for heavy metal analysis

Apparatus:

(i) Micropipette

(ii) 50ml volumetric flask

(iii) 25ml volumetric flask

(iv) Measuring cylinders

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(v) Beakers

(vi) Atomic absorption spectrophotometer-AAS ( Buck Scientific: Acussys 211)

Reagents:

(i) 1000 ppm vanadium stock solution

(ii) 1000 ppm nickel stock solution

(iii) 1000 ppm cadmium stock solution

(iv) 1000 ppm arsenic stock solution

(v) 1000 ppm lead stock solution

(vi) 2% HNO3 acid water solution

(vii) Reducing agent

3.3.1. Preparation of secondary stock solution

• 20ml of conc. Nitric acid (HNO3) was pipetted into 1000ml volumetric flask and

made up to mark with deionised water.

• The volume of the main stock solution to be used was determine using the formular;

C1V1=C2V2

C1= Unknown or Intended concentration (1ppm)

V1= Known volume of the volumetric flask (50ml)

C2= Known concentration of the main or original stock solution (1000ppm)

V2= Unknown or intended volume

V2= C1V1 / C2 = 1ppm x 50ml / 1000ppm

V2 = 0.05mls

• This was then taken from the main stock solution and pippetted into a 50ml flask and

made up to mark with 2% HNO3

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3.3.2. Preparation of 5ppb, 50ppb and 250ppb standard solutions and heavy metal

analysis

• For 5ppb:

C1V1 = C2V2

V2 = C1V1 / C2 = 5ppb x 25ml / 1000ppb

V2 = 0.125ml

• For 50ppb:

C1V1 = C2V2

V2 = C1V1 / C2 = 50ppb x 25ml / 1000ppb

V2 = 1.25ml

• For 250ppb:

C1V1 = C2V2

V2 = C1V1 / C2 = 250ppb x 25ml / 1000ppb

V2 = 6.25ml

• These volumes of the stock solution were then pippetted into three different 25ml

volumetric flask and then made up to mark with acid water (2% HNO3).

• 20 micro litres of the of the standard solution was injected into the Graphite Furnace

Atomic Absorption Spectrophotometer (GFAAS) to obtain the calibration curve, after

which 20 micro litres of the digested soil sample was injected into the GFAAS for the

heavy metal analysis.

• Nickel, cadmium, lead and vanadium metals were determined using the Graphite

Furnace AAS, while arsenic and mercury metals were determined using the Hydride

AAS 233 and Cold Vapour AAS 234 respectively.

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3.3.3. Preparation of reducing agent for mercury analysis

Apparatus:

(i) Weighing balance

(ii) Wash glass

(iii) Spatula

(iv) Measuring cylinder

(v) Beaker

(vi) 50ml volumetric flask

Reagents:

(i) Hydrochloric acid (HCl)

(ii) Stannous chloride (Tin II chloride / Sncl2)

(iii) Tin metal

(iv) Deionised water

Procedure:

• 5g of fresh stannous chloride was placed into an empty acid- cleaned 50ml plastic

bottle.

• 15ml of conc. HCl and 0.5g Tin metal was added.

• The mixture was swirled and stirred to dissolve the stannous chloride (Sncl2).

• 35ml of deionised water was added and swirled gently to mix.

• This 10% solution was stable and viable for thirty (30) days.

3.4. Determination of soil pH

Method: Electrode method, 235.

Apparatus:

(i) pH meter

(ii) 100ml beaker

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Reagents:

(i) Buffer solutions (4.01, 7.00, 10.01)

Procedure:

• 1gram of the soil sample was weighed into a 100ml beaker.

• 80ml of deionised water was used to dissolve the sample during which it was

stirred continuously for 1h.

• The pH probe was rinsed with deionised water and was blotted with hint free

tissue.

• The pH probe was calibrated with 4.01, 7.00, 10.01 buffer solutions.

• After calibration, the pH probe was rinsed with deionised water and blotted; this

was followed by placing the probe in the beaker containing the soil sample

solution and the pH value taken.

• The pH probe was rinsed again, shaken off excess water and then replaced in the

water solution.

• The pH was determined at a temperature of 31.10C.

3.5. Determination of percentage (%) Total Organic Matter

Method: Oven drying and weighing method, 236.

Apparatus:

(ii) Spatula

(iii) Wash glass

(iv) Oven (Thermo scientific)

(v) Weighing balance

Procedure:

• Wash glass was weighed and the mass recorded.

• 2g of the soil sample was weighed out.

• The mass of the wash glass and the soil sample was also noted.

77

• The wash glass containing the soil sample was heated in an oven for 6h at 2300C.

• It was allowed to cool in a dessicator after which the oven heated soil sample was re-

weighed.

Calculation and results:

I. Wt of wash glass + soil sample before drying = 15.5580

II. Wt of wash glass + soil sample after drying = 15.5205

(I) - (II) = 15.5580 – 15.5205 = 0.0275

% Organic matter = 0.0275g / 2g x 100 = 1.375%

3.6. Determination of Total Petroleum Hydrocarbon (TPH)

Method: Gas Chromatography with flame ionisation detector (GC – FID), 237.

Apparatus:

(i) GC – FID

(ii) Satarious weighing balance

(iii) Funnel

(iv) Filter paper

(v) Rotary evapourator

(vi) Vials bottle

Reagents:

(i) Dichloro methane

(ii) N-Hexane

(iii) Alkane mix (C10 –C40 standard)

Procedure:

• The soil sample was air dried, crushed and sieved using a 2mm mesh.

• 5g of the sieved soil sample was placed in a thimble and extracted with 20ml of

Dichloromethane in a soxhlet extractor for 6h. The extract was concentrated with a

rota evapourator to 2ml and stored in a glass vial.

78

• Another 5g of the sieved soil sample was placed in a thimble and extracted with

20mls of Hexane in a soxhlet extractor for 6h. The extract was concentrated with a

rota evapourator to 2ml and stored in a glass vial.

3.6.1 Column Chromatographic Separation:

• Silica gel (200-400) mesh was heated at 1050C overnight and packed into a glass

column (600mm x 30mm) with i.d (10mm). 5g of the soil sample was introduced into

the glass colum, followed by the solvents. The aliphatic hydrocarbons were eluted

with 60ml of Hexane, while the aromatic hydrocarbon was eluted with 40ml of

Dichloromethane. The eluants were concentrated to 2ml and transferred to a glass

sample vial for gas chromatography.

3.6.2 Gas Chromatography:

• The Gas Chromatography was carried out with a Buck Scientific GC (model 910)

fitted with split / splitless injector. The column used for the separation was a fused-

silica capillary column, (30mm x 0.25mm). The GC was equipped with a flame

ionisation detector. The gas carrier was helium. The oven temperature was

programmed from 500C-3000C at 50C / min. The hold time was 5min at 500C and

30min at 3000C

• 1 micro litre of the Alkane mix was injected into the GC to obtain the standard

chromatograph.

• 1 micro litre of the concentrated DCM and N- Hexane extract was then injected into

the GC for the TPH analysis.

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CHAPTER FOUR

4.0. RESULTS AND DISCUSSION

The assessment of heavy metals and TPHs in the Umuorie oil spill site reflected the degree of

pollution in the soil. This is because soil pollution is considered by many regulatory agencies

to be one of the largest risks to man and many of these heavy metals and hydrocarbons are

bio accumulative in edible plants 238,239k.

The results of the heavy metals and TPH concentrations obtained in the current study are

presented in Table 4.1 and figure 4.1 respectively. The results were compared with the

regulatory standards set by the department of petroleum resources (DPR) 240. The pH of the

soil in the oil spill site was slightly acidic (6.88 ± 0.01). The organic matter content was

(1.375 % ± 0.01).

Table 4.1: Mean concentrations of Heavy metals

Metals Concentration (mg/kg) DPR standards (mg/kg)

(1991)

Vanadium 0.06 ± 0.02 250

Nickel 0.01 ± 0.01 210

Cadmium BDL 10

Lead BDL 530

Arsenic 0.01 ± 0.01 28.2

Mercury BDL 10

BDL: Below detectable limits, DPR: Department of petroleum resources

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Figure 4.1: Graphical representation of heavy metal concentration.

Among all the heavy metals analysed, Vanadium had a concentration of (0.06 ± 0.02

mg/kg), this result agreed with the work of Inengite et al 241, who detected low level of

Vanadium (˂ 0.001 mg/kg) in kolo creek in Niger-Delta . It also agreed with the works of

Osuji and Achugasim 242 in which Vanadium was below detectable limit in Ukpeliede oil

spill site located in Niger-Delta.

Nickel had a concentration of (0.01 ± 0.01 mg/kg), this value agreed with Emoyan et al 243

who detected low level of Nickel (0.030 ± 0.004mg/L) in river Ijana in Ekpan- Warri, but in

variance with the works of Oguntimehin & Ipinmoroti 244 and Okafor & Opuene 245 who

detected high concentrations of nickel in automobile workshops soils in Akure (62.1mg/kg)

and Taylor creek sediments (37.4 ± 2.1 mg/kg) respectively.

The primary sources of the observed heavy metals were drilling fluids and pipe dope. Pipe

dope is used to make up the drill string. Its purpose is to prevent damage to the threads of the

drill pipe and it is almost always used in excess. The excess pipe dope is then washed into the

drilling fluid as the well is drilled. Pipe dope generally has high concentrations of lead. Other

81

sources of heavy metals in oil spills include: produced water, waste oils, air pollutants from

combustion engines, completion fluids, drilling mud and drill cuttings. The drill cuttings

produced from the formation are also covered with the drilling fluid containing heavy metals.

Drilling mud contains a number of metals, including arsenic, cadmium, and lead. These

heavy metals are also contained in paints used to protect equipment and in lube oil in the

engines to run drilling and production equipment.

Crude oil was another major source of the observed heavy metals in the spill. Crude oils

naturally contain variable concentrations of heavy metals, including vanadium and nickel.

These metals are complexed in the petroporphyrin compounds. Porphyrins are a class of

compounds consisting of four pyrrole rings connected by four methene bridges. Vanadium

and nickel porphyrin complexes are formed by metal exchange reactions with animal and

plant metabolic pigments such as hemoglobin and chlorophyll which were present during the

early stages of petroleum formation.

The analysis results showed that the concentration of vanadium was higher than that of

nickel. The observed vanadium/nickel concentration ratio agreed with Hunt (1996) who

stated that oils generally have higher concentration of Vanadium than Nickel. This also

agreed with the works of Nwadinigwe and Nworgu 246, Oderinde 247 and Odebunmi 20 who

reported high Vanadium/Nickel ratios in their various characterisations of crude oil products.

The observed concentrations of the vanadium/nickel ratio also confirmed the spill source to

be of crude oil origin.

Arsenic concentration was (0.01 ± 0.01 mg/kg), this result agreed with the works of Osuji and

Achugasim; 242 who also detected low concentrations of Arsenic (0.601 ± 0.12 mg/kg &

0.560 ± 0.15 mg/kg) in Ukpeliede-I oil spill site. Compounds of arsenic, lead, and cadmium

often occur as trace contaminants from crude oil formation or from other materials used in

the drilling process such as pipe dope.

82

Cadmium, lead and mercury were below detectable limits. The results agreed with Emoyan et

al 243 who reported the concentrations of cadmium and lead to be (0.010 ± 0.004 mg/L) and

(0.025 ± 0.006 mg/L), respectively in river Ijana in Ekpan- Warri. It also agreed with Osuji

and Achugasim 242 who reported Lead to be below detectable limit in Ukpeliede-I oil spill

site. Okafor & Opuene 245 also recorded low concentration of cadmium (0.770 ± 0.13 mg/kg)

in Taylor creek sediments.

The concentrations of cadmium, lead and mercury which was observed to fall below

detectable limit could be attributed to the immobilisation of the heavy metals in the soil. Soil

has the ability to immobilise introduced chemicals like heavy metal ions. The immobilisation

of the heavy metals was mainly due to sorption properties which are determined by

physicochemical properties of the soil such as: amount of clay and organic matter, soil pH,

water content, temperature of the soil and properties of the particular metal ion 255. Soil pH is

one of the most important factors in most sorption processes. Soil pH ultimately determines

the amount of negatively-charged adsorption sites in many soil constituents, including Fe and

Mn oxides, organic matter, carbonates, and the edges of clay minerals 256,257. Thus, as pH

increases (more alkaline), so does the amount of negatively charged sites, which in turn

attracts the cationic metals. Over a relatively short range of pH from intermediate to alkaline,

heavy metal adsorption increases from near zero to near complete adsorption 258. Soil pH also

strongly controls precipitation of heavy metals, which occurs under alkaline conditions 257.

Precipitation also effectively immobilizes heavy metals within a soil profile. This process

was further explained by USDA 253 which reported that alkaline soil pH (6.5 and above)

decreases the mobility and bioavailability of cationic heavy metals such cadmium, mercury

and lead in soils.

The absence of cadmium, mercury and lead from the soil sample can also be said to have

occurred as a result of leaching of the heavy metals down into deeper soil horizons where it

83

became inaccessible. The absence of the analysed heavy metals could also have been as a

result of soil surface run-off. This process involves the removal of soil particles or sediment

by flowing water, wind or raindrop splash.

The presence of phyto-extractive and phyto-volatalising plants around the oil spill site could

also have accounted for the absence of cadmium, mercury and lead. These species of plants

posses the ability to take up or absorb heavy metals and other inorganic contaminants and

accumulate them within their shoots and leaves at concentrations higher than those at which

most other plants would tolerate. These plants absorb contaminants through the root system

and store them in the root biomass or transport them up into the stem and leaves. In phyto-

volatilisation process, the plant takes up the heavy metal in its liquid or solid form and

transforms it to an air-borne vapour. In the case of mercury which volatilizes at room

temperature and lead, they become metabolised by the plants before vaporization.

The low concentration of the heavy metals could have also been attributed to the fact that the

spilled oil contained fewer amounts of heavy metals, 242. The results of all the heavy metals

analysed also confirmed that the component of the spill suspected to be crude oil was

actually pipeline washings as stated by sweet crude reports 254; hence the reason for its low

content of heavy metals.

Generally, the results showed a very low concentration of all the heavy metals analysed. The

results obtained were also below the acceptable limits set by DPR. This generally indicated

that; as at the time of study, the Umuorie oil spill site was not polluted in terms of heavy

metal contamination.

84

Table 4.2: Concentration of Total Petroleum Hydrocarbon

Compound Hydrocarbon range Concentration

(mg/kg)

DPR standard

(1991) (mg/kg)

Total Petroleum

Hydrocarbon

C20- C31 0.003 50

BDL: Below detectable limits, DPR: Department of petroleum resources

Figure 4.2: Graphical illustration of the distribution Frequency of the n-alkanes.

The Total Petroleum Hydrocarbon analysis result showed hydrocarbons within the ranges of

C10-C31. This TPH profile was an indication of the presence of lubricating oil generally

known as Diesel Range Organics (DRO). Manilla and Adeboye 250 detected similar ranges of

hydrocarbons in the sediments of some flood plain lakes in Bayelsa state. The n-alkanes in

the Umuorie oil spill site showed an odd over even preference and the peak of the

hydrocarbon was at C17, C26, and C27. It was observed that the most predominant n-alkane

was C27.

85

C11-C16, C18, C22-C25, C28 & C30 alkanes were not detected in the chromatogram. The absence

of hydrocarbons in oil spill sites is as a result of biodegradation by hydrocarbon-degrading

bacteria and fungi present in the soil. These microorganisms Pseudomonos, Arthrobacter,

Trichodermo, Penicillium, etc feed on and use the organic contaminants for their growth 262.

n-Alkanes of intermediate chain length (CIO – C40.) are degraded most rapidly by soil

microorganisms. The most common pathway of alkane biodegradation is oxidation at the

terminal methyl group. The alkane is oxidised first to alcohol and then to the corresponding

fatty acid. After formation of a carboxyl group the oxidation proceeds by successive removal

of two carbon units through ß-oxidation which is universal to most living systems. Under ß –

oxidation, the beta methylene group is oxidised to a ketone group followed by the removal of

a two-carbon fragment from the compound 259. The end by-products of these reactions are

fatty acids, carbon dioxide and water.

Polycyclic Aromatic Hydrocarbons were observed to be visibly absent from the TPH profile.

The absence of PAHs from the TPH profile could be connected to the fact that PAHs which

fall within the Gasoline range organics (GROs) i.e.C4 –C10 have low molecular weights and

as a result are highly volatile and biodegradable. This suggests that any PAH present at the

time of spill may have been volatilised or degraded by Hydrocarbon degrading bacteria prior

to the time of sample collection. Microbial degradation of gasoline range organics can occur

by aerobic respiration, anaerobic respiration or fermentation. Aerobic microorganisms utilise

oxygen in the process of decomposing hydrocarbons; anaerobes utilise inorganic compounds

such as sulphate. Nitrate or carbon dioxide as terminal electron acceptors; and under

fermenting conditions organic compounds serve as both electron donors and acceptors during

microbe activity. Major gasoline components such as the aromatics and alkanes, as well as

some minor constituents such as ethylene dibromide (EDD) and ethylene dichloride (EDC),

86

have been shown to be more readily degradable under aerobic than under either anaerobic or

fermenting conditions 260.

The TPH analysis result was in consonance with the works of Manilla and Adeboye 250 who

reported that hydrocarbons from the sediments of some flood plain lakes in Bayelsa were

mainly aliphatic. It also agreed with Irwin et al 186 and Potter & Simmons 251 who reported

that typical crude oil contains high concentrations of aliphatic hydrocarbons and lower

concentrations of aromatic hydrocarbons.

The TPH analysis generally showed that the Total Petroleum Hydrocarbon concentration

(0.003 mg/kg) detected in the Umuorie oil spill site was very low compared to the standard

set by the Department of Petroleum Resources (DPR). This is also an indication that the oil

spill site is not polluted in terms of petroleum hydrocarbons.

4.1. Conclusions

The assessment of heavy metals and TPHs in the soil of Umuorie oil spill site reflected that

the site was not polluted at the time of study. The levels of the total petroleum hydrocarbon

(TPH) and heavy metals; vanadium, nickel, cadmium, lead arsenic and mercury were

observed to be very low and also below DPR standards recommended for soils. These facts

suggests that at the time of study, the farm lands were not yet at risk of being adversely

affected and that arable farmers could go on with crop production as minimal phytotoxicity

was expected in these study soils. It is also a pointer that given to subsequent oil spills, there

would be a build up of these compounds because of their bioaccumulative nature.

4.2 Suggestions for Further Work

The study is not conclusive as further investigations needs to be conducted on surrounding

water sources to ascertain the pollution levels by crude oil spills. It is however strongly

recommended that the flow pipes be adequately monitored to ensure that no further spillage

occurs in future.

87

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