Date post: | 20-Mar-2018 |
Category: |
Documents |
Upload: | trinhquynh |
View: | 213 times |
Download: | 1 times |
Chapter One: Introduction
1
Chapter One
Introduction
1.1 Introduction
Due to high and rapid development in the oil industry at the last
century, many different problems had occurred, one of them is the
environmental pollution in all elements of the environment, such as water,
soil and air, which began to raise serious questions that need a rapid
solutions. Soil pollution is one of these environmental pollutions.
In general, there are many sources of soil pollution, man-made sources
including automobiles, power generation and the industrial activities. They
represent the main source of air pollution and thus causes soil pollution by
precipitation; especially, oil industry activities using huge amount of
consumable fuel, like power plants and oil refinery; due to the high rate
emission of fume, solid particulates and toxic gases more than other
industry in quantity (Afaj and Al-Khashab, 2007).
These industries are more hazardous to the environment upon its
existence within the limits of the cities, or its existence within urban area,
and or near the agricultural terrines such as Al-Daura power plant, south
Baghdad power plant and Al-Daura oil refinery.
1.2 Aim of Study
Due to higher increase in oil industry activities in Iraq, since there are a
little information of the environmental status of the areas around the
refinery locations, and the concerns of a possible environmental pollution
Chapter One: Introduction
2
that will cause health and life threats to living organisms, this study was
carried out.
The results of this study, therefore, will be helpful to decision-makers,
planners, scientists, and the local communities. The study will also be
useful as a base for decision making to protect the environment in areas
surrounding various oil refineries in the country.
1.3 Study Objectives
1.3.1 Overall Objective
The overall objective of the study is to assess the risk level of heavy
metals pollution in soils and plants in areas surrounding Al-Daura refinery
sites in Baghdad.
1.3.2 Specific Objectives
1. Determine the concentration of the heavy metals, such as zinc,
nickel, lead and cadmium in the soil and plants (seasonal vegetable),
and illustrate the distribution of these pollutants within the
production units of the refinery and in the area around the refinery by
using ArcGIS software; and to indicate the areas of high
concentration for the selected pollutants after comparison with the
standards values.
2. To study the environmental impact of these pollutants on the areas
near and around the refinery.
3. Study the relation between the pollutants and type of soil within the
depth of sample.
4. Set the appropriate environmental solutions and recommendations.
Chapter One: Introduction
3
1.3.3 Hypotheses
The study was conducted based on the hypotheses that: -
1. The area around Al-Daura refinery is significantly and highly polluted
with heavy metals.
2. There are many levels of heavy metals and chemicals in soil and plants
species growing around the oil refining areas.
1.4 Study Area
The study area is located at the south-west of Baghdad governorate,
specifically at Al-Daura region, just 4 Km from the city centre of Baghdad,
close to the western bank of Tigers River. Seventeen locations of sample,
soil and plants, distributed as seven inside the refinery and ten outside it,
Figs.(1-1) and (1-2) show the study area and sample locations.
Chapter One: Introduction
4
Fig.(1-1) Study Area Location in Baghdad.
Chapter One: Introduction
5
Fig.(1-2) Location of Samples.
Chapter One: Introduction
6
1.5 Thesis Layout
The present work is divided into five chapters:
Chapter One includes the present brief introduction and the objectives
of the present study.
Chapter Two contains a brief theoretical background and also
introduces the essential literature available about the soil polluted by heavy
metals.
Chapter Three is concerned with the oil refinery technology,
experimental and field works for detecting heavy metals concentration in
soil and plants, and soil characteristics measurements.
Chapter Four involves with the results obtained from field and
laboratory experimental work and the discussion of these results.
Chapter Five contains conclusions and recommendations for future
works.
Chapter Two: Theoretical Background and Literatures Review
7
Chapter Two
Theoretical Background and Literatures Review
2.1 Introduction
Heavy metals have been differently defined by many sectors of
academia. Many different definitions have been proposed – some based on
density, some on atomic weight, and some on chemical properties or
toxicity (Duffus, 2002). Heavy metals are natural components of the earth
crust which cannot be degraded or destroyed [EPA (SA), 2009].
Many industries, such as refining, mining and smelting give rise to
release of heavy metals into the environment, and also because the adverse
effects of these metals on the environment, many researchers, studies and
legislations have been introduced all over the world to explain the effects
of heavy metals on the environment generally.
2.2 Heavy Metals
The metals are classified as “heavy metals” if, in their standard state,
they have a specific gravity of more than 5 (Issa, 2008). There are sixty
known heavy metals. Heavy metals can accumulate over time in soils and
plants and could have a negative influence on physiological activities of
plants (e.g., photosynthesis, gaseous exchange, and nutrient absorption),
causing reductions in plant growth, dry matter accumulation and yield
(Devkota and Schmidt, 2000). There are many terms used to describe and
categorize metals, including trace metals, transition metals, micronutrients,
toxic metals and heavy metals. Many of these definitions are arbitrary, and
these terms have been loosely used in the literature to include elements that
do not strictly meet the definition of the term. Metals are defined as any
Chapter Two: Theoretical Background and Literatures Review
8
element that has a silvery luster and is a good conductor of heat and
electricity (McLean and Bledsoe, 1992).
2.2.1 Fate of Heavy Metals in Soil and Environment
The incidence of heavy metal contamination from both natural and
anthropogenic sources has increased concern about possible health effects.
Natural and anthropogenic sources of soil contamination are widespread
and variable (Tahir et al., 2007). According to Ross (1994), the
anthropogenic sources of metal contamination can be divided into five
main groups:
(1) metalliferous mining and smelting (arsenic, cadmium, lead and
mercury); (2) industry (arsenic, cadmium, chromium, cobalt, copper,
mercury, nickel, zinc); (3) atmospheric deposition (arsenic, cadmium,
chromium, copper, lead, mercury, uranium); (4) agriculture (arsenic,
cadmium, copper, lead, selenium, uranium, zinc); and (5) waste disposal
(arsenic, cadmium, chromium, copper, lead, mercury, zinc). Heavy metal
contamination of soil results from anthropogenic processes, such as
refining (Conservation Current, 2005), mining (Navarro et al., 2008),
smelting procedures (Brumelis et al., 1999) and agriculture (Vaalgamaa
and Conley, 2008) as well as natural activities.
Chemical and metallurgical industries are the most important sources of
heavy metals in the environment (Cortes et al., 2003). Industries, such as
plating, ceramics, glass, mining, refining and battery manufacture are
considered the main sources of heavy metals in local water systems,
causing the contamination of groundwater with heavy metals.
Heavy metals which are commonly found in high concentrations in
landfill leachate, are also a potential source of pollution for groundwater
(Aziz et al., 2004). Large areas of agricultural land are contaminated by
heavy metals that mainly originate from former or current mining activities,
Chapter Two: Theoretical Background and Literatures Review
9
industrial emissions or the application of sewage sludge. Metals exist in
one of four forms in the soil: mineral, organic, sorbed (bound to soil), or
dissolved. Sorbed metals represent the third largest pool and are generally
very tightly bound to soil surfaces. Although mineral, organic and sorbed
metals are not immediately absorbed by plants, they can slowly release
metals into solution (Jones and Jacobsen, 2003). The inability to determine
metal species in soils hampers efforts to understand the mobility,
bioavailability and fate of contaminant metals in environmental systems
together with the assessment of the health risks posed by them and the
development of methods to remediate metal contaminated sites (D‟Amore
et al., 2005). However, in some natural soils developed from metal rich
parent materials as well as in contaminated soils, up to 30 to 60% of heavy
metals can occur in easily unstable forms (Karczewska et al., 1998). In soil,
metals are found in one or more of several "pools" of the soil, as described
by Shuman (1991):
1. dissolved in the soil solution;
2. occupying exchange sites in inorganic soil constituents;
3. specifically adsorbed in inorganic soil constituents;
4. associated with insoluble soil organic matter;
5. precipitated as pure or mixed solids;
6. present in the structure of secondary minerals; and/or
7. present in the structure of primary minerals
In situations where metals have been introduced into the environment
through human activities, metals are associated with the first five pools.
Native metals may be associated with any of the pools depending on the
geological history of the area. The aqueous fraction and those fractions in
equilibrium with this fraction, i.e., the exchange fraction, are of primary
importance when considering the migration potential of metals associated
with soils (McLean and Bledsoe, 1992).
Chapter Two: Theoretical Background and Literatures Review
10
Heavy metals occur naturally in the environment, but may also be
introduced as a result of land use activities. Natural and anthropogenically
introduced concentrations of metals in near-surface soil can significantly
vary due to the different physical and chemical processes operating within
soils across geographic regions (Murray et al., 2004). Migration of metals
in the soil is influenced by physical and chemical characteristics of each
specific metal and by several environmental factors. The most significant
environmental factors appear to be (1) soil type, (2) total organic content,
(3) redox potential and (4) pH (Murray et al., 1999). Although heavy
metals are generally considered to be relatively immobile in most soils,
their mobility in certain contaminated soils may exceed ordinary rates and
pose a significant threat to water quality (Bunzl et al., 2001). Organic
manure, municipal waste and some fungicides often contain fairly high
concentrations of heavy metals.
Soils receiving repeated applications of organic manures, fungicides and
pesticides have exhibited high concentrations of extractable heavy metals
(Han et al., 2000) and increased concentrations of heavy metals in runoff
(Moore et al., 1998). Previous studies indicate that metal constituents of
surface soil directly influence the movement of metals, especially in sandy
soils (Moore et al., 1998; Cezary and Singh, 2001).
2.2.2 Behavior of Heavy Metals in Soil
Monitoring the endangerment of soil by heavy metals is of interest
due to their influence on ground and surface water (Clemente et al., 2008;
Boukhalfa, 2007) and also on flora (Pandey and Pandey 2008; Stobrawa
and Lorenc-Plucińska, 2008), animals and humans (De Vries et al., 2007).
The overall behavior of heavy metals in soil is said to be governed largely
by their sorption and desorption reactions with different soil constituents,
especially clay components (Appel and Ma, 2002).
Chapter Two: Theoretical Background and Literatures Review
11
The chemical behavior of heavy metals in soils is controlled by a
number of processes, including metal cation release from contamination
source materials (e.g., fertilizer, sludge, smelter dust, ammunition, slag),
cation exchange and specific adsorption onto surfaces of minerals and soil
organic matter, and precipitation of secondary minerals (Manceau et al.,
2000). The relative importance of these processes depends on soil
composition and pH. In general, cation exchange reactions and
complexation to organic matter are most important in acidic soils, while
specific adsorption and precipitation become more important at near-
neutral to alkaline pH values (Voegelin et al., 2003). El-Ghawi et al. (2007)
studied the trace metal concentrations in some Libyan soils and found that
the concentrations in clay surface soil are higher than in sandy soil. The
multiple regression analyses performed confirmed the importance of pH as
well as other soil properties, such as composition, electrical conductivity
and organic matter or carbonates on the behavior of nutrients and heavy
metals (Soriano-Disla et al., 2008). Increased anthropogenic inputs of Cu
and Zn in soils have caused a considerable concern relative to their effect
on water contamination (Zhang et al., 2003).
Oxidizing conditions generally increase the retention capacity of
metals in soil, while reducing conditions will generally reduce the retention
capacity of metals (McLean and Bledsoe, 1992). Filep (1998) stated that
contaminants reaching the soil can be divided into two groups, namely
micropollutants and macropollutants. Micropollutants are natural or
anthropogenic molecules, which are toxic at very low concentration.
Macropollutants are present in the environment locally and/or temporarily
to a much higher degree than normal level. The main micropollutants of
soils are inorganic or organic compounds.
(1) Inorganic micropollutants are mainly the toxic and potentially toxic
heavy metals (Pb, Cd, Ni, Zn, Cr, Hg, Cu, etc.), (2) Organic
Chapter Two: Theoretical Background and Literatures Review
12
micropollutants include pesticides and certain non-pesticide organic
molecules: e.g., aliphatic solvents, monocyclic aromatics, halogenated
aromatics, polychlorinated biphenyls (PCBs) and polycyclic aromatic
hydrocarbons (PAHs), surfactants, plastifiers. Frequent macropollutants
are:
Inorganic (nitrogenous fertilizers).
Organic (crude oil and products of oil industry).
In liquid phase, they exist as hydrated ions, soluble organic and
inorganic complexes and as a component of fine disperse floating colloids.
In the solid, phase they occur as insoluble precipitates and minerals on the
surface of organic and inorganic colloids in exchangeable and non-
exchangeable (specific adsorbed) forms (Filep, 1998).
2.2.2.1 Accumulation
Atanassov et al. (1999) stated that heavy metals are of interest due to
their abundance in the environment, which has increased considerably as a
result of human activities. Their fate in polluted soils is a subject of study
because of the direct potential toxicity to biota and the indirect threat to
human health via the contamination of groundwater and accumulation in
food crops (Martinez and Motto, 2000). Heavy metals are dangerous,
because they tend to bioaccumulate. This means that the concentration of a
chemical in a biological organism becomes higher relative to the
environmental concentration (Kampa and Castanas, 2008). Heavy metal
pollution of soil enhances plant uptake, causing accumulation in plant
tissues, eventual phytotoxicity and change of plant community (Gimmler et
al., 2002). In environments with high nutrient levels, metal uptake can be
inhibited because of complex formation between nutrient and metal ions
(Gothberg et al., 2004). Therefore, a better understanding of heavy metal
sources, their accumulation in the soil and the effect of their presence in
Chapter Two: Theoretical Background and Literatures Review
13
water and soil on plant systems seems to be a particularly important issue
(Sharma et al., 2004). Accumulation of heavy metals can also cause a
considerable detrimental effect on soil ecosystems, environment and human
health due to their nobilities and solubilities which determine their
speciation (Kabata-Pendias and Pendias, 1992).
Several studies have indicated that the crops grown on soils
contaminated with heavy metals have higher concentrations of heavy
metals than those grown on uncontaminated soil (Nabulo, 2006). Heavy
metals accumulating in soil directly (or through plants indirectly) enter
food chains, thus endangering herbivores, indirectly carnivores and not
least the top consumer humans (Kadar, 1995). Plant cells have mechanisms
for bioaccumulation, selective absorption and storage of a great variety of
molecules. This allows them to accumulate nutrients and essential minerals
(Cunningham, 2001). Compounds accumulate in living organisms any
time, they are taken up faster than they are broken down (metabolized) or
excreted (O‟Brien, 2008). Total levels of heavy metals have shown a trend
relationship between metal concentration in soil and long term irrigation
(Abdelazeem et al, 2007).
Metals such as lead, arsenic, cadmium, copper, zinc, nickel, and
mercury are continuously being added to our soils through various
agricultural activities; such as agrochemical usage and long-term
application of urban sewage sludge in agricultural soils; industrial
activities, such as waste disposal, waste incineration and vehicle exhausts
together with anthropogenic sources. All these sources cause accumulation
of metals and metalloids in our agricultural soils and pose threat to food
safety issues and potential health risks due to soil to plant transfer of metals
(Khan, 2005). Investigations of heavy metal migration and accumulation in
natural conditions are very laborious as it is difficult to control all
Chapter Two: Theoretical Background and Literatures Review
14
numerous factors influencing metal behavior in the field (Ermakov et al.,
2007).
2.2.2.2 Solubility and Mobility
Among the negative impacts related to human activities, the
mobilization of heavy metals from their naturals reservoirs to the aquatic
and terrestrial ecosystems has become a generalized problem almost
worldwide (Han et al., 2002; Koptsik et al., 2003; Salemaa et al., 2001).
Heavy metal solubility and mobility in soils are of environmental
significance due to their potential toxicity to both humans and animals
(Chirenje et al., 2003).
The transfer and the chemical stability of metal contaminants in soils
and sediments are controlled by a complex series of biogeochemical
processes, depending on variables like pH, clay content and redox potential
(Vanbroekhoven, 2006).
Trace metal mobility is closely related to metal solubility, which is
further regulated by adsorption, precipitation and ion exchange reactions in
soils (Ma and Dong, 2004). Pb is reported to be the least mobile among the
other heavy metals, but the Cd is known to be the most mobile under
conditions of different soils (Kabata-Pendias and Pendias, 1992).
The transfer of heavy metals from soils to plants is dependent on
three factors: (1) the total amount of potentially available elements
(quantity factor), (2) the activity as well as the ionic ratios of elements in
the soil solution (intensity factor), and (3) the rate of element transfer from
solid to liquid phases and to plant roots (reaction kinetics) (Brummer et al.,
1986). However, changes in soil solution chemistry, such as pH, redox
potential and ionic strength, may also significantly shift the retention
processes of trace metals by soils (Gerringa et al., 2001).
Chapter Two: Theoretical Background and Literatures Review
15
These effects may be further complicated by ligand competition from
other cations (Norrstrom and Jacks, 1998). Soil redox status varies
temporally and spatially. In a surface soil, it is influenced by the rainfall,
bioactivity, and changes in the land use, whereas it varies mainly with the
fluctuation of water table (Boul et al., 1997). Reduction in the redox
potential may cause changes in metal oxidation state, formation of new
low-soluble minerals and reduction of Fe, resulting in release of associated
metals (Baumann et al., 2002; Chuan et al., 1996). Metal solubility
increases usually as the pH decreases, with the notable exception of metals
present in the form of oxyanions or amphoteric species. Since soil solution
properties might change with time (for example following sludge
application), the solubility and speciation of metals might also be time-
dependent (Mo et al., 1999). As the soil pH increases, the solubility and
availability of these trace nutrients decrease (Mellbye and Hart, 2003). The
solubility of most metals becomes limited around pH values of 5.5 to 6.0.
Immobilization of metals by the mechanisms of adsorption and
precipitation will prevent movement of the metals to the ground water.
Metal-soil interaction is such that when metals are introduced at the soil
surface, the downward transportation does not occur to any great extent
unless the metal retention capacity of the soil is overloaded or metal
interaction with the associated waste matrix enhances mobility. Changes in
soil environmental conditions over time, such as the degradation of the
organic waste matrix, changes in pH, redox potential, or soil solution
composition, due to various remediation schemes or to natural weathering
processes may also enhance the metal mobility (McLean and Bledsoe,
1992).
Chapter Two: Theoretical Background and Literatures Review
16
2.2.2.3 Bioavailability
Bioavailability depends on biological parameters and on the
physicochemical properties of metals, their ions and their compounds.
These parameters in turn depend upon the atomic structure of the metals,
which is systematically described by the periodic table (VanLoon and
Duffy, 2000). The bioavailability and mobility of metals in soil depend
strongly on the extent of their sorption with solid phases. Partitioning of
heavy metals between solid and aqueous phases is controlled by properties,
such as surface area, surface charge (induced by the formation of organic
coatings on the surface), pH, ionic strength and concentration of
complexing ligands (Petrovic et al., 1999).
The pH and redox potential affect the bioavailability of metals in
solution; at high pH, the elements are present as anions, while at low pH
the bioavailability of metals ions is enhanced (Peterson et al., 1984). In
natural systems, the bioavailability of trace metals is primarily controlled
by adsorption-desorption reactions at the particle-solution interface (Backes
et al., 1995). The availability of metals also decreases in the calcareous soil
horizons because of the enhanced buffering capacity of these horizons
(Sipos, 2004). The soil pH will influence both the availability of soil
nutrients to plants and how the nutrients react with each other. Hollier and
Reid (2005) stated that at a low pH, many elements become less available
to plants, while others such as iron, aluminum and manganese become
toxic to plants and in addition, aluminum, iron and phosphorus combine to
form insoluble compounds. In contrast, at high pH levels, calcium ties up
phosphorus, making it unavailable to plants, and molybdenum becomes
toxic in some soils. Generally, heavy metals become increasingly mobile
and available as the pH decreases (Tyler and Olsson, 2001) depending on
the actual combination of physical and chemical properties of soil
(Shuman, 1985).
Chapter Two: Theoretical Background and Literatures Review
17
2.2.2.4 Toxicity
Recently, pollution of the general environment has gathered an
increased global interest. In this respect, the contamination of agricultural
soils with heavy metals has always been considered a critical challenge in
the scientific community (Faruk et al., 2006). Heavy metals are generally
present in agricultural soils at low levels. Due to their cumulative behavior
and toxicity, however, they have a potentially hazardous effect not only on
crop plants but also on human health (Das et al., 1997). Even metals,
essential to plant growth, like copper (Cu), manganese (Mn), molybdenum
(Mo), and zinc (Zn) but can be toxic to the plants at high concentrations in
the soil. Some elements, not known to be essential to plant growth, such as
arsenic (As), barium (Ba), cadmium (Cd), chromium (Cr), lead (Pb), nickel
(Ni) and selenium (Se) are also toxic at high concentrations or under
certain environmental conditions in the soil (Slagle et al., 2004).
Both pH and redox potential affect the toxicity of heavy metals by
limiting their availability (Peterson et al., 1984). At low pH, metals
generally exist as free cations; at alkaline pH, however, they tend to
precipitate as insoluble hydroxides, oxides, carbonates, or phosphates
(Mamboya, 2007). Chemical hazards include chemical agents like heavy
metals, nutrients, such as nitrogenous compounds, phosphorus compounds,
minerals, insecticides, pesticides, fertilizers, fungicides, herbicides and
organic hazards (Nabulo et al., 2008).
Metals, unlike the hazardous organics, cannot be degraded. Some
metals, such as Cr, As, Se and Hg can be transformed to other oxidation
states in soil, thus influencing their mobility and toxicity (McLean and
Bledsoe, 1992). Many of them (Hg, Cd, Ni, Pb, Cu, Zn, Cr, Co) are highly
toxic both in elemental and soluble salt forms. The high concentration of
heavy metals in soils is toxic for soil organisms: bacteria, fungi and higher
organisms (Woolhouse, 1993). Short-term and long-term effects of
Chapter Two: Theoretical Background and Literatures Review
18
pollution differ, depending on metal and soil characters (Kadar, 1995;
Nemeth and Kadar, 2005). In the after-effect of heavy metal pollutions, the
role of pollutant bounding or leaching increases, which determines their
bioavailability and toxicity (Mathe-Gaspar et al., 2005). When the soil is
acidified it increases the concentration of free aluminum ions in the water
that is in the soil, and these are potentially toxic to the root systems of
plants.
The mobility of many heavy metals also increases when the soil
becomes more acidic. Perhaps, the most serious consequence of the higher
metal concentrations is their negative effect on many of the decomposers
that live in the soil (Elvingson and Agren, 2004). The U.S. Environmental
Protection Agency (U.S. EPA, 1993) regulates nine trace elements for the
land-applied sewage sludge: As, Cd, Cu, Pb, Hg, Mo, Ni, Se and Zn. Only
six of these elements (Cu, Ni, Zn, Cd, Pb, Se) are considered to be
phytotoxic (Schmidt, 1997). Accounting for element speciation,
complexation and the dynamic interaction of solid surfaces (soils, organic
matter and live plants) and water with trace elements, it is difficult to
determine the maximum allowable total trace element concentrations that
can exist in soils without becoming potentially toxic to plants or harming
the environment (Slagle et al., 2004).
2.2.3 General Features of the Investigated Heavy Metals
2.2.3.1 Zinc
Zinc is a very common substance that occurs naturally. It is the 23rd
most abundant element in the Earth's crust. Many foodstuffs contain certain
concentrations of zinc. Drinking water also contains certain amounts of
zinc, which may be higher when it is stored in metal tanks. Industrial
sources or toxic waste sites may cause the zinc amounts in drinking water
to reach levels that can cause health problems.
Chapter Two: Theoretical Background and Literatures Review
19
(http://www.lenntech.com/periodic/elements/zn.htm)
Zinc occurs naturally in air, water and soil, but zinc concentrations
are rising unnaturally due to the addition of zinc through human activities.
Most zinc is added during industrial activities, such as mining, coal and
waste combustion and steel processing. Some soils are heavily
contaminated with zinc, and these are because the use of sewage and
composted materials in agricultural and the use of agrochemicals, such as
fertilizers and pesticides (Alloway, 1995). Some of the studies have also
linked high Zn levels to accumulation from traffic, industry input (Imperato
et al., 2003) vehicle emissions and tyre and brake abrasion (Garty et al.,
1985; Ward, 1990).
Zinc is strongly adsorbed onto organic matter and clay particles in
the soil and this adsorption is related to the Cation Exchange Capacity of
the system in acidic media and is influenced by organic ligands in alkaline
media (Antoniadis, 1998).
Health Effects of Zinc: Zinc is a trace element that is essential for
human health. When people absorb too little zinc, they can experience a
loss of appetite, decreased sense of taste and smell, slow wound healing
and skin sores. Zinc-shortages can even cause birth defects.
Although humans can proportionally handle large concentrations of
zinc, too much zinc can still cause eminent health problems, such as
stomach cramps, skin irritations, vomiting, nausea and anemia. Very high
levels of zinc can damage the pancreas and disturb the protein metabolism
and cause arteriosclerosis. Extensive exposure to zinc chloride can cause
respiratory disorders.
Chapter Two: Theoretical Background and Literatures Review
20
In the work place environment, zinc contagion can lead to a flu-like
condition known as metal fever. This condition will pass after two days and
is caused by over sensitivity.
Zinc can be a danger to unborn and newborn children. When their
mothers have absorbed large concentrations of zinc, the children may be
exposed to it through blood or milk of their mothers.
(http://www.lenntech.com/periodic/elements/zn.htm)
Effects of Zinc on the Environment: The world's zinc production is
still rising. This basically means that more and more zinc ends up in the
environment.
Water is polluted with zinc due to the presence of large quantities of
zinc in the wastewater of industrial plants. This wastewater is not purified
satisfactory. One of the consequences is that rivers are depositing zinc-
polluted sludge on their banks. Zinc may also increase the acidity of
waters.
Some fish can accumulate zinc in their bodies, when they live in
zinc-contaminated waterways. When zinc enters the bodies of these fish, it
is able to bio magnify up the food chain.
Large quantities of zinc can be found in soils. When the soils of
farmland are polluted with zinc, animals will absorb concentrations that are
damaging to their health. Water-soluble zinc that is located in soils, can
contaminate the groundwater.
Zinc cannot only be a threat to cattle, but also to plant species. Plants
often have a zinc uptake that their systems cannot handle due to the
accumulation of zinc in soils. On zinc-rich soils, only a limited number of
plants have a chance of survival. That is why there is not much plant
Chapter Two: Theoretical Background and Literatures Review
21
diversity near zinc-disposing factories. Due to the effects upon plants, zinc
is a serious threat to the productions of farmlands. Despite of this zinc-
containing, manures are still applied.
Finally, zinc can interrupt the activity in soils, as it negatively
influences the activity of microorganisms and earthworms. The breakdown
of organic matter may seriously slow down because of this.
(http://www.lenntech.com/periodic/elements/zn.htm)
2.2.3.2 Nickel
Most nickel on Earth is inaccessible, because it is locked away in the
planet's iron-nickel molten core, which is 10 % nickel. The total amount of
nickel dissolved in the sea has been calculated to be around 8 billion tons.
Organic matter has a strong ability to absorb the metal which is why coal
and oil contain considerable amounts. The nickel content in soil can be as
low as 0.2 ppm or as high as 450 ppm in some clay and loamy soils. The
average is around 20 ppm. Nickel occurs in some beans where it is an
essential component of some enzymes. Another relatively rich source of
nickel is tea which has 7.6 mg/kg of dried leaves.
(http://www.lenntech.com/periodic/elements/ni.htm)
Health Effects of Nickel: Nickel is a compound that occurs in the
environment only at very low levels. Humans use nickel for many different
applications. The most common application of nickel is the use as an
ingredient of steel and other metal products. It can be found in common
metal products, such as jewellery.
Foodstuffs naturally contain small amounts of nickel. Chocolate and
fats are known to contain severely high quantities. Nickel uptake will boost
when people eat large quantities of vegetables from polluted soils. Plants
are known to accumulate nickel, and as a result, the nickel uptake from
Chapter Two: Theoretical Background and Literatures Review
22
vegetables will be eminent. Smokers have a higher nickel uptake through
their lungs. Finally, nickel can be found in detergents.
Humans may be exposed to nickel by breathing air, drinking water,
eating food or smoking cigarettes. Skin contact with nickel-contaminated
soil or water may also result in nickel exposure. In small quantities, nickel
is essential, but when the uptake is too high, it can be a danger to human
health.
An uptake of too large quantities of nickel has the following
consequences:
Higher chances of development of lung cancer, nose cancer,
larynx cancer and prostate cancer.
Sickness and dizziness after exposure to nickel gas.
Lung embolism.
Respiratory failure.
Birth defects.
Asthma and chronic bronchitis.
Allergic reactions, such as skin rashes, mainly from jewellery.
Heart disorders.
Nickel fumes are respiratory irritants and may cause pneumonitis.
Exposure to nickel and its compounds may result in the development of a
dermatitis known as “nickel itch” in sensitized individuals.
(http://www.lenntech.com/periodic/elements/ni.htm)
Effects of Nickel on the Environment: Nickel is widely used in
industry, as it is a metal which does not corrode as much as Fe. It is,
therefore, used in the production of alloys, on which it confers them stain
and corrosion protection (Bunce, 1993).
Nickel is released into the air by power plants and trash incinerators.
It will than settle to the ground or fall down after reactions with raindrops.
Chapter Two: Theoretical Background and Literatures Review
23
It takes usually a long time for nickel to be removed from air. Nickel can
also end up in surface water when it is a part of wastewater streams.
The larger part of all nickel compounds that are released to the
environment, will adsorb to sediment or soil particles and become
immobile as a result. In acidic ground, however, nickel is bound to become
more mobile and it will often rinse out to the groundwater. It is evident that
the local solid waste litter and anthropogenic activities, such as burning of
fuel and residual oil contribute to the increase in Ni content in the soil
(Alloway, 1995), and the organic matter has a great influence on this
element as Ni can be strongly adsorbed by it (Leeper, 1978).
There is not much information available on the effects of nickel upon
organisms other than humans. It is known that high nickel concentrations
on sandy soils can clearly damage plants, and high nickel concentrations in
surface waters can diminish the growth rates of algae. Microorganisms can
also suffer from growth decline due to the presence of nickel, but they
usually develop resistance to nickel after a while.
For animals, nickel is an essential foodstuff in small amounts. But,
nickel is not only favorable as an essential element; it can also be
dangerous, when the maximum tolerable amounts are exceeded. This can
cause various kinds of cancer on different sites within the bodies of
animals, mainly of those that live near refineries.
(http://www.lenntech.com/periodic/elements/ni.htm)
2.2.3.3 Lead
Native lead is rare in nature. Currently, lead is usually found in ore
with zinc, silver and copper, and it is extracted together with these metals.
The main lead mineral is in Galena (PbS), and there are also deposits of
cerrussite and anglesite which are mined.
Chapter Two: Theoretical Background and Literatures Review
24
Lead occurs naturally in the environment. However, most lead
concentrations that are found in the environment, are a result of human
activities. Due to the application of lead in gasoline, an unnatural lead-
cycle has consisted. Deposition related to automobile emissions and
transportations sector, in general (considering the long residence time of
Pb), may be the major source of increase in Pb content (Chatterjee and
Banerjee, 1999; Madrid et al., 2002; Imperato et al., 2003). The greatest
and most commonly known use of Pb is as fuel additives (Pb(CH3)4 and
Pb(C2H5)4) which are „anti knocking‟ agents (Baird, 1995). Lead is also
used as a absorber of high energy X and γ rays and in roofing, while PbO is
used in crystal glass, because it dispenses light spectrally (Bunce, 1993).
The larger particles will drop immediately to the ground and pollute
soils or surface waters, the smaller particles will travel long distances
through air and remain in the atmosphere. Part of this lead will fall back on
earth when it is raining. This lead-cycle caused by human production is
much more extended than the natural lead-cycle. It has caused lead
pollution to be a worldwide issue.
(http://www.lenntech.com/periodic/elements/pb.htm)
Health Effects of Lead: Lead is a soft metal that has known many
applications over the years. It has been widely used since 5000 BC for
application in metal products, cables, pipelines, in paints and pesticides.
Lead is one out of four metals that have the most damaging effects on
human health. It can enter the human body through uptake of food (65%),
water (20%) and air (15%).
Foods, such as fruit, vegetables, meats, grains, seafood, soft drinks
and wine may contain significant amounts of lead. Cigarette smoke also
contains small amounts of lead.
Chapter Two: Theoretical Background and Literatures Review
25
Lead can enter drinking water through corrosion of pipes. This is
more likely to happen when the water is slightly acidic. That is why public
water treatment systems are now required to carry out pH-adjustments in
water that will serve drinking purposes.
For as far as known, lead fulfils no essential function in the human
body, it can merely do harm after uptake from food, air or water.
Lead can cause several unwanted effects, such as:
Disruption of the biosynthesis of hemoglobin and anemia.
A rise in blood pressure.
Kidney damage.
Miscarriages and subtle abortions.
Disruption of nervous systems.
Brain damage.
Declined fertility of men through sperm damage.
Diminished learning abilities of children.
Behavioral disruptions of children, such as aggression,
impulsive behavior and hyperactivity.
Lead can enter a foetus through the placenta of the mother. Because
of this, it can cause a serious damage to the nervous system and the brains
of unborn children.
(http://www.lenntech.com/periodic/elements/pb.htm)
Environmental Effects of Lead: Not only leaded gasoline causes
lead concentrations in the environment to rise, but also other human
activities, such as fuel combustion, industrial processes and solid waste
combustion, also contribute.
Chapter Two: Theoretical Background and Literatures Review
26
Lead can end up in water and soils through corrosion of leaded
pipelines in a water transporting system and through corrosion of leaded
paints. It cannot be broken down and can only convert to other forms.
Lead accumulates in the bodies of water organisms and soil
organisms. These will experience health effects from lead poisoning.
Health effects on shellfish can take place even when only very small
concentrations of lead are present. Body functions of phytoplankton can be
disturbed when lead interferes. Phytoplankton is an important source of
oxygen production in seas and many larger sea-animals eat it.
(http://www.lenntech.com/periodic/elements/pb.htm)
Soil functions are disturbed by lead intervention, especially near
highways and farmlands, where extreme concentrations may be present.
Soil organisms suffer from lead poisoning, too. Lead is strongly adsorbed
to organic matter in soils, more than any other heavy metal, and therefore,
organic matter is a very important sink for Pb in polluted soils. (Kabata-
Pendias and Pendias, 1992).
Lead is one of the hazardous metals that can transport to the humans
and animals through the chain food and can accumulate in the body,
causing a physiological damage.
2.2.3.4 Cadmium
Cadmium can mainly be found in the earth's crust. It occurs always
in combination with zinc. Cadmium also consists in the industries as an
inevitable by-product of zinc, lead and copper extraction. After being
applied, it enters the environment mainly through the ground, because it is
found in soils is phosphate fertilizers and manures (Kabata-Pendias and
Pendias, 1992).
Chapter Two: Theoretical Background and Literatures Review
27
Naturally, a very large amount of cadmium is released into the
environment, about 25,000 tons a year. About half of this cadmium is
released into rivers through weathering of rocks, and some cadmium is
released into air through forest fires and volcanoes. The rest of the
cadmium is released through human activities, such as manufacturing.
No cadmium ore is mined for the metal, because more than enough is
produced as a byproduct of the smelting of zinc from its ore, sphelerite
(ZnS), in which CdS is a significant impurity, making up as much as 3%.
Consequently, the main mining areas are those associated with zinc.
(http://www.lenntech.com/periodic/elements/cd.htm)
Health Effect of Cadmium: Human uptake of cadmium takes place
mainly through food. Foodstuffs that are rich in cadmium can greatly
increase the cadmium concentration in human bodies. Examples are liver,
mushrooms, shellfish, mussels, cocoa powder and dried seaweed.
An exposure to significantly higher cadmium levels occurs when
people smoke. Tobacco smoke transports cadmium into the lungs. Blood
will transport it through the rest of the body where it can increase effects by
potentiating cadmium that is already present in the cadmium-rich food.
Other high exposures can occur to people who live near hazardous
waste sites or factories that release cadmium into the air and to people who
work in the metal refinery industry. When people breathe in cadmium it
can severely damage the lungs. This may even cause death.
Cadmium first transports to the liver through the blood. There, it is
bond to proteins to form complexes that transport to the kidneys. Cadmium
accumulates in kidneys, where it damages filtering mechanisms. This
causes the excretion of essential proteins and sugars from the body and
further kidney damage.
Chapter Two: Theoretical Background and Literatures Review
28
Other health effects that can be caused by cadmium are:
Diarrhea, stomach pains and severe vomiting.
Bone fracture.
Reproductive failure and possibly even infertility.
Damage to the central nervous system.
Damage to the immune system.
Psychological disorders.
Possibly DNA damage or cancer development.
(http://www.lenntech.com/periodic/elements/cd.htm)
Environmental Effects of Cadmium: Cadmium has a wide range of
uses in the industry (Volensky, 1990). Cadmium waste streams from the
industries end mainly up in soils. The causes of these waste streams are for
instance, zinc production, phosphate ore implication and bio industrial
manure. Cadmium waste streams may also enter the air through
(household) waste combustion and burning of fossil fuels. Because of the
regulations, only little cadmium now enters the water through disposal of
wastewater from households or industries.
Another important source of cadmium emission is the production of
artificial phosphate fertilizers. Part of the cadmium ends up in the soil after
the fertilizer is applied on farmland, and the rest of the cadmium ends up in
the surface water when the waste from fertilizer productions is dumped by
production companies.
Cadmium can be transported over great distances when it is absorbed
by sludge. This cadmium-rich sludge can pollute the surface water as well
as soils.
Chapter Two: Theoretical Background and Literatures Review
29
Cadmium strongly adsorbs to organic matter in soils. When
cadmium is present in soils, it can be extremely dangerous as the uptake
through food will increase. Soils that are acidified, enhance the cadmium
uptake by plants. This is a potential danger to the animals that are
dependent upon the plants for survival. Cadmium can accumulate in their
bodies, especially when they eat multiple plants. Cows may have large
amounts of cadmium in their kidneys due to this.
Earthworms and other essential soil organisms are extremely
susceptive to cadmium poisoning. They can die at very low concentrations,
and this has consequences for the soil structure. When cadmium
concentrations in soils are high, they can influence the soil processes of
microorganisms and threat the whole soil ecosystem.
In aquatic ecosystems, cadmium can bio accumulates in mussels,
oysters, shrimps, lobsters and fish. The susceptibility to cadmium can vary
greatly between aquatic organisms. Salt-water organisms are known to be
more resistant to cadmium poisoning than freshwater organisms.
Animals eating or drinking cadmium sometimes get high blood-
pressures, liver disease and nerve or brain damage.
(http://www.lenntech.com/periodic/elements/cd.htm)
2.3 Soil Properties and Heavy Metals
2.3.1 Soil pH
The link between soil pH and heavy metal threshold values reflects
the complex interaction between the heavy metals and the various soil
properties (Gawlik and Bidoglio, 2006). pH is a measure of the hydrogen
ion concentration acidity or alkalinity of the soil. Measured on a
logarithmic scale, a soil at pH 4 is 10 times more acidic than a soil at pH 5
Chapter Two: Theoretical Background and Literatures Review
30
and 100 times more acidic than a soil at pH 6. Increasing and decreasing
the soil pH influence the chemical reactions in the soil (Thien and Graveed,
1997).
Alkalinity is usually an inherent characteristic of soils, although
irrigation can increase the alkalinity of saline soils. Soils made alkaline by
calcium carbonate alone have rarely pH values above 8.5 and are termed
„calcareous‟. Under normal conditions, the most desirable pH range for
mineral soil is 6.0 to 7.0 and 5.0 to 5.5 for organic soil.
At the neutral values of pH, Zn, Ni and Pb have a strong relation
with soil solids, and hence its movement towards the deeper layers will be
limited or very slowly (Kabata-Pendias and Pendias, 1992).
The buffer pH is a value used for determining the amount of lime to
apply on acidic soils with a pH less than 6.6. Increases in soil pH can occur
as the result of organic matter decomposition, because mineralization and
ammonification processes release OH- ions and consume H
+ ions (Ritchie
and Dolling, 1985). Colloid and metal mobility were enhanced by
decreases in solution pH and colloid size and increases in organic matter,
which resulted in higher elution of sorbed and soluble metal loads through
a metal–organic complex formation (Karathanasis et al., 2005). Soil
weathering often involves soil acidification, and most chemical
immobilization reactions are pH dependent. Alkaline amendments reduce
the concentration of heavy metals in soil solution by raising the soil pH,
thereby allowing the formation of insoluble metal precipitates, complexes
and secondary minerals (Mench et al., 1994).
2.3.2 Organic Matter
Soil organic matter is the most important indicator of soil quality and
productivity and consists of a complex and varied mixture of organic
substances. Commonly, soil organic matter is defined as the percentage of
Chapter Two: Theoretical Background and Literatures Review
31
humus in the soil. Humus is the unidentifiable residue of plant soil
microorganisms and fauna that becomes fairly resistant to further decay.
Organic matter is very important in the functioning of soil systems
for many reasons (Jankauskas et al., 2007). Soil organic matter increases
soil porosity, thereby increasing infiltration and water-holding capacity of
the soil, providing more water availability for plants and less potentially
erosive runoff and agro-chemical contamination (Lal et al., 1998). Clay
minerals and organic matter have a contrary effect on heavy metal retention
in soils. There are factors dependent (e.g., clay minerals) on and
independent (e.g., organic matter) of bedrock, of which a common effect
forms the actual distribution of heavy metals in soils (Sipos, 2003).
Chemical elements in the soil are more adsorbed on the finest soil particles
(colloids) which are clay and humus. Although they are small in size,
colloids play a major influence in soil properties (Thien and Graveed,
1997). The organic matters are important factor in adsorption and
accumulation of heavy metals in soil (Alloway, 1995; Kabata-Pendias and
Pendias, 1992).
El-Ghawi et al. (2005) showed that the trace metals concentrations in
clay surface soils are higher than in the sandy soils, humic and folic acid
(organic matter) that capture the elements. Heavy metal cations sorb to the
soil organic matter and other forms of humified natural organic matter. The
type of sorption by the natural organic matter affects the environmental fate
of the heavy metal.
Heavy metal cations form sparingly soluble phosphate, carbonates,
sulfides and hydroxides. Sorption and many metal precipitation processes
are highly pH dependent with increased sorption with pH. The pH of the
soil-residual system is often the most important chemical property
governing sorption and precipitation of heavy metals (Basta et al., 2005).
Chapter Two: Theoretical Background and Literatures Review
32
2.3.3 Microbiological Effect
Microbes are arguably the most important consideration in managing
the living soil. Soil microbes are responsible for the greatest percentage of
nutrient recycling within the soil (Fenchel et al., 1998).
Metals play an integral role in the life processes of microorganisms.
The and metals, such as calcium, cobalt, chromium, copper, iron,
potassium, magnesium, manganese, sodium, nickel and zinc are an
essential source of micronutrients and are used for redox processes.
Microbial transformations of metals serve various functions. Generally,
microbial transformations of metals can be divided into two main
categories: redox conversions of inorganic forms and conversions from
inorganic to organic form and vice versa (Turpeinen, 2002). Through
oxidation of iron, sulfur, manganese and arsenic, microbes can obtain
energy (Santini et al., 2000). On the other hand, reduction of metals can
occur through dissimilatory reduction, where microorganisms utilize metals
as a terminal electron acceptor for anaerobic respiration (Turpeinen, 2002).
For example, oxyanions of chromium (Quilntana et al., 2001) can be used
in a microbial anaerobic respiration as terminal electron acceptors.
Microorganisms may possess reduction mechanisms that are not coupled to
respiration, but instead, are thought to impart metal resistance (Turpeinen,
2002); for example, aerobic and anaerobic reduction of Cr(VI) to Cr(III)
(Quilntana et al., 2001).
Microbiological processes can either dissolve metals, thereby
increasing their bioavailability and potential toxicity, or immobilize them
and thereby reducing the bioavailability of metals (Turpeinen, 2002). In
microbial systems, the term redox conditions refer to the microbial terminal
electron accepting processes taking place. If oxygen is present, aerobic
conditions will dominate and microbial metabolism takes place with
oxygen as the terminal electron acceptor.
Chapter Two: Theoretical Background and Literatures Review
33
Nitrate, oxides and hydroxides of manganese (IV) and iron (III),
sulfate and carbon dioxide can be used as electron acceptors in order to
gain energy for microbial maintenance and growth (Stumm and Morgan,
1996). Heavy metals are often mixed with organic pollutants in
contaminated sites.
In anaerobic soils, the redox potential was shown to be negatively
correlated with microbial activity (Kralova et al., 1992). Low redox
potential developed with increased soil moisture content because of the
partial or complete displacement of oxygen from soil and rapid
consumption of oxygen by soil microbes (Savant and Ellis, 1964). The
redox potential was also found to be affected by the microbial activity in
aerobic soils. Volk (1993) showed that in arable, the soils moisture
indirectly decreased the redox potential by increasing the bacterial activity.
As in other studies (Faulkner et al., 1989), a relationship between the
moisture content and redox status was observed.
2.4 Oil Refinery Technology
2.4.1 Oil Refinery Process
An oil refinery is an industrial process plant where crude oil is
processed and refined into more useful petroleum products, such as
gasoline, diesel fuel, asphalt base, heating oil, kerosene and liquefied
petroleum gas (Gary and Handwerk, 1984; Leffler, 1985). Oil refineries are
typically large sprawling industrial complexes with extensive piping
running throughout, carrying streams of fluids between large chemical
processing units.
2.4.1.1 Operation
Crude oil is separated into fractions by the fractional distillation. The
fractions at the top of the fractionating column have lower boiling points
Chapter Two: Theoretical Background and Literatures Review
34
than the fractions at the bottom. The heavy bottom fractions are often
cracked into lighter, more useful products. All of the fractions are further
processed in other refining units.
Raw or unprocessed ("crude") oil is not useful in the form it comes
in out of the ground. Although "light, sweet" (low viscosity, low sulfur) oil
has been used directly as a burner fuel for the steam vessel propulsion, the
lighter elements form explosive vapors in the fuel tanks, and so it is quite
dangerous, especially in warships. For this and many other uses, the oil
needs to be separated into parts and refined before use in fuels and
lubricants, and before some of the byproducts could be used in
petrochemical processes to form materials, such as plastics, detergents,
solvents, elastomers and fibers, such as nylon and polyesters. Petroleum
fossil fuels are used in ship, automobile and aircraft engines. These
different hydrocarbons have a different boiling point, which means they
can be separated by distillation. Since the lighter liquid elements are in
great demand for use in internal combustion engines, a modern refinery
will convert heavy hydrocarbons and lighter gaseous elements into these
higher value products using complex and energy intensive processes.
Oil can be used in so many various ways, because it contains
hydrocarbons of varying molecular masses, forms and lengths, such as
paraffins, aromatics, naphthenes (or cycloalkanes), alkenes, dienes and
alkynes. Hydrocarbons are molecules of varying length and complexity,
made of only hydrogen and carbon atoms. Their various structures give
them their differing properties and thereby uses. The trick in the oil
refinement process is separating and purifying these.
Once separated and purified of any contaminants and impurities, the
fuel or lubricant can be sold without any further processing. Smaller
molecules, such as isobutene and propylene or butylenes can be
recombined to meet specific octane requirements of fuels by processes,
Chapter Two: Theoretical Background and Literatures Review
35
such as alkylation or less commonly, dimerization. The octane grade of
gasoline can also be improved by a catalytic reforming which strips the
hydrogen out of hydrocarbons to produce aromatics which have much
higher octane ratings. Intermediate products, such as gas oils can even be
reprocessed to break heavy, long-chained oil into a lighter short-chained
one by various forms of cracking, such as fluid catalytic cracking, thermal
cracking and hydrocracking. The final step in gasoline production is the
blending of fuels with different octane ratings, vapor pressures and other
properties to meet the product specifications.
Oil refineries are large scale plants, processing from about a hundred
thousand to several hundred thousand barrels of crude oil per day. Because
of the high capacity, many of the units are continuously operated (as
opposed to processing in batches) at steady state or approximately steady
state for long periods of time (months to years). This high capacity also
makes the process optimization and advanced process control very
desirable (Alfredo, 2008).
2.4.1.2 Major Products of Oil Refineries
Most products of oil processing are usually grouped into three
categories: light distillates (LPG, gasoline and naphtha), middle distillates
(kerosene, diesel), heavy distillates and residuum (fuel oil, lubricating oils,
wax and tar).
This classification is based on the way crude oil is distilled and
separated into fractions (called distillates and residuum). (Leffler, 1985)
• Liquid petroleum gas (LPG)
• Gasoline (also known as petrol)
• Naphtha
• Kerosene and related jet aircraft fuels
• Diesel fuel
Chapter Two: Theoretical Background and Literatures Review
36
• Fuel oils
• Lubricating oils
• Paraffin wax
• Asphalt and Tar
• Petroleum coke
2.4.1.3 Common Process Units Found in a Refinery
The number and nature of the process units in a refinery determine
its complexity index.
• Desalter unit washes out the salt from the crude oil before it enters
the atmospheric distillation unit.
• Atmospheric Distillation unit distills the crude oil into fractions.
• Vacuum Distillation unit further distills the residual bottoms after
the atmospheric distillation.
• Naphtha Hydrotreater unit uses the hydrogen to desulfurize naphtha
from the atmospheric distillation. The naphtha must be hydreotreated
before sending to a Catalytic Reformer unit.
• Catalytic Reformer unit is used to convert the naphtha-boiling
range molecules into a higher octane reformate (reformer product). The
reformate has a higher content of aromatics, olefins and cyclic
hydrocarbons. An important byproduct of a reformer is the hydrogen
released during the catalyst reaction.
The hydrogen is used either in the hydrotreaters or the hydrocracker.
• Distillate Hydrotreater unit desulfurizes the distillates (such as
diesel) after the atmospheric distillation.
• Fluid Catalytic Cracker (FCC) unit upgrades the heavier fractions
into lighter, more valuable products.
• Hydrocracker unit uses the hydrogen to upgrade the heavier
fractions into lighter, more valuable products.
Chapter Two: Theoretical Background and Literatures Review
37
• Visbreaking unit upgrades the heavy residual oils by thermally
cracking them into lighter, more valuable reduced viscosity products.
• Merox unit treats the LPG, kerosene or jet fuel by oxidizing
mercaptans to organic disulfides.
• Coking units (delayed coking, fluid coker, and flexicoker) process
the very heavy residual oils into gasoline and diesel fuel, leaving petroleum
coke as a residual product.
• Alkylation unit produces a high-octane component for gasoline
blending.
• Dimerization unit converts the olefins into higher-octane gasoline
blending components. For example, butenes can be dimerized into
isooctene which may subsequently be hydrogenated to form isooctane.
There are also other uses for dimerization.
• Isomerization unit converts the linear molecules to higher-octane
branched molecules for blending into gasoline or feeding to alkylation
units.
• Steam reforming unit produces the hydrogen for the hydrotreaters
or hydrocracker.
• Liquefied gas storage units for propane and similar gaseous fuels at
a pressure sufficient to maintain in liquid form. These are usually spherical
vessels or bullets (horizontal vessels with rounded ends).
• Storage tanks for crude oil and finished products, usually
cylindrical, with some sort of vapor emission control and surrounded by an
earthen berm to contain spills.
• Amine gas treater, Claus unit and tail gas treatment for converting
hydrogen sulfide from hydrodesulfurization into elemental sulfur.
• Utility units, such as cooling towers for circulating cooling water,
boiler plants for steam generation, instrument air systems for pneumatically
operated control valves and an electrical substation.
Chapter Two: Theoretical Background and Literatures Review
38
• Wastewater collection and treating systems consisting of API
separators, dissolved air flotation (DAF) units and some types of further
treatment (such as an activated sludge biotreater) to make such water
suitable for reuse or for disposal.(Beychok, 1967)
• Solvent refining units use the solvent, such as cresol or furfural to
remove the unwanted, mainly the asphaltenic materials, from the
lubricating oil stock (or diesel stock).
• Solvent dewaxing units remove the heavy waxy constituents
petrolatum from the vacuum distillation products (Alfredo, 2008).
2.4.1.4 Flow Diagram of Typical Refinery
The figure (2-1) is a schematic flow diagram of a typical oil refinery
that depicts the various unit processes and the flow of intermediate product
streams that occurs between the inlet crude oil feedstock and the final end
products. The diagram depicts only one of the literally hundreds of
different oil refinery configurations. The diagram also does not include any
of the usual refinery facilities providing utilities such as steam, cooling
water, and electric power as well as storage tanks for crude oil feedstock
and for intermediate products and end products.
There are many process configurations other than that depicted in
Fig.(2-1). For example, the vacuum distillation unit may also produce
fractions that can be refined into end products such as: spindle oil used in
the textile industry, light machinery oil, motor oil, and steam cylinder oil.
As another example, the vacuum residue may be processed in a coker unit
to produce petroleum coke.
Chapter Two: Theoretical Background and Literatures Review
39
Fig.(2-1) Flow Diagram of a Typical Oil Refinery (Alfredo, 2008).
Chapter Two: Theoretical Background and Literatures Review
40
2.4.1.5 Specialty End Products
These will blend various feedstocks, mix appropriate additives,
provide short term storage and prepare for bulk loading to trucks, barges,
product ships and railcars.
• Gaseous fuels, such as propane stored and shipped in liquid form
under pressure in specialized railcars to the distributors.
• Liquid fuels blending (producing automotive and aviation grades of
gasoline, kerosene, various aviation turbine fuels and diesel fuels, adding
dyes, detergents, antiknock additives, oxygenates and anti-fungal
compounds as required). They may be shipped by barge, rail, tanker ship
and regionally in dedicated pipelines to point consumers, particularly
aviation jet fuel to major airports, or piped to distributors in multi-product
pipelines using product separators called pipeline inspection gauges
("pigs").
• Lubricants (light machine oils, motor oils and greases, adding
viscosity stabilizers as required) usually shipped in bulk to an offsite
packaging plant.
• Wax (paraffin) used in the packaging of frozen foods, among
others. may be shipped in bulk to a site to prepare as packaged blocks.
• Sulfur (or sulfuric acid), byproducts of sulfur removal from the
petroleum which may have up to a couple percent sulfur as organic sulfur-
containing compounds. Sulfur and sulfuric acid are useful industrial
materials. Sulfuric acid is usually prepared and shipped as the acid
precursor oleum.
• Bulk tar shipping for offsite unit packaging for use in tar-and-
gravel roofing.
• Asphalt unit, prepares the bulk asphalt for shipment.
• Petroleum coke, used in specialty carbon products or as a solid fuel.
Chapter Two: Theoretical Background and Literatures Review
41
• Petrochemicals or petrochemical feedstocks which are often sent to
the petrochemical plants for further processing in a variety of ways. The
petrochemicals may be olefins or their precursors, or various types of
aromatic petrochemicals (Alfredo, 2008).
2.4.1.6 Siting/Locating of Petroleum Refineries
The principles of finding a construction site for refineries are similar
to those for other chemical plants:
• The site has to be reasonably far from residential areas.
• Facilities for raw materials access and products delivery to markets
should be easily available.
• Processing energy requirements should be easily available.
• Waste product disposal should not cause difficulties.
For refineries which use large amounts of process steam and cooling
water, an abundant source of water is important. Because of this, oil
refineries are often located (associated to a port) near navigable rivers or
even better on a sea shore. Either is of dual purpose, making also available
cheap transport by river or by sea. Although the advantages of crude oil
transport by the pipeline are evident, and the method is also often used by
oil companies to deliver large output products, such as fuels to their bulk
distribution terminals, the pipeline delivery is not practical for small output
products. For these, rail cars, road tankers or barges may be used.
It is useful to site refineries in areas where there is abundant space to
be used by the same company or others, for the construction of
petrochemical plants, solvent manufacturing (fine fractionating) plants
and/or similar plants.
The reason is to allow easy access to large output refinery products
for further processing, or plants that produce chemical additives that the
Chapter Two: Theoretical Background and Literatures Review
42
refinery may need to blend into a product at source rather than at blending
terminals (Alfredo, 2008).
2.4.1.7 Safety and Environmental Concerns
The refining process releases numerous different chemicals into the
atmosphere. Consequently, there are substantial air pollution emissions,
and a notable odor normally accompanies the presence of a refinery. Aside
from air pollution impacts, there are also wastewater concerns, (Beychok,
1967) risks of industrial accidents, such as fire and explosion, and noise
health effects due to industrial noise.
The public has demanded from many governments to place restrictions on
the contaminants that refineries release, and most refineries have installed
the equipment needed to comply with the requirements of the pertinent
environmental protection regulatory agencies.
2.5 Previous Studies Concerning of Heavy Metals
A brief review of works published about soil contamination is
presented below:
Hana and Al-Hilali, (1986) analyzed (720) soil samples to
determine the contents of (Cr, Ni, Zn, Pb, Cu and V) elements in the soil of
Mesopotamian plain, Iraq. The authors concluded that the Mesopotamian
plain sediments are relatively free from pollution of time being. The results
have also shown that a geochemical differentiation between various
sedimentary soil units within the Mesopotamian plain is possible.
Al-Kendy, (2005) measured the lead concentration in the soil at (0, 8
and 15 m) from both the eastern and western sides of Mohammed Al-
Kasim highway road in the east of Baghdad city. The results ranged
between (20-4550 µg/g) for (48) samples. The study proves the fact that the
concentrations of lead decrease with distance from the edge of the
Chapter Two: Theoretical Background and Literatures Review
43
highway, and this agrees with previous studies. The pH results of the study
area were ranged between (6.9-8.2), and the organic content ranged
between (11.6-38.8 %). For the same study, lead measured at four sites in
Baghdad as an environmental background, the arithmetic mean was (19.75
µg/g) and the results were (20.5 µg/g in Al-Husseinyah, eastern north of
Baghdad; 19.5 µg/g in Al-Taji, western north of Baghdad; 21 µg/g in Al-
Kamaliyah, eastern south of Baghdad; 18 µg/g in Al-Sweeb, western south
of Baghdad).
UNEP, (2005) studied a selective hot spots region in Iraq, such as
Al-Qadissiya, Al-Suwaira, Khan Dhari, Al-Mishraq, Ouireej to determine
the qualitative and quantitative pollution of air, water and soil and their
effects on the environment. The results of laboratory and field tests have
shown that the soil and water are contaminated with heavy metals,
hydrocarbons and other parameters. The study also specifies the
approximate concentrations of each contaminant.
Al-Maliky, (2005) constructed maps to explain the zones of
distributions and concentrations of pollutants in air, water and soil of
Baghdad city. These maps were constructed depending on an integrated
measured and collected data base utilizing a GIS and Arcview software.
The concentrations of air pollutants, such as TSP, Pb, Co, SO2 and HC
were measured, and the obtained results have shown that TSP levels
exceede the standard level of pollution. The water quality of Tigris River
was also studied by testing the physical and chemical properties (electrical
conductivity, TDS, TSS and total hardness) of 13 water samples. In
addition to air and water, Al-Maliky tested the concentration of heavy
metals (Zn, Cu, Co, Ni and Cd) in trace elements of Baghdad soil and
concluded that Baghdad city soil is contaminated with low percentages of
Co, Cd, Ni and Cu.
Chapter Two: Theoretical Background and Literatures Review
44
Kaur and Rani, (2006) presented detailed spatial information on
bio-available heavy metal concentrations in the soil and surface/sub surface
water by testing of 144 randomly selected samples in the study area of
(Delhi). This information was based on the actual soil/water surveys,
standard laboratory methods and GIS techniques. The ESP values together
with EC and pH values were then used for assessing the quality of the
tested soil samples. In addition, Cu, Fe, Mn, Zn, Cd, Cr, Ni and Pb
concentrations were also estimated. Then, the map of the tested area was
digitalized in an Arc-View spatial Analyst-GIS software to characterize the
regional distribution of physico-chemical characteristics of the soil/waters.
They concluded that the generated maps for each trace metal can be used
for understanding the spatial distribution, type and extent of heavy metal
pollution in the soils and surface/sub surface waters.
Neupane, (2006) examined the concentration of As, Cr, Cu, Ni, Pb
and Zn in arable and forest soils near Pemberville, Ohio in (60) soil
samples obtained from (10) sites. The soil samples contain a large
proportion of fines (32% clay and 37% silt). The soil samples were
digested according to EPA 3050B method and analyzed for heavy metals
with ICP-AES. The results of tests prove that the variations of heavy metal
contents in the layer from the surface to 50 cm depth are as follows: As
increased from (4.6 to 11) mg/kg, Cr increased from (19 to 23) mg/kg and
Ni increased from (21 to 25) mg/kg. While, the content of Cu decreased
from (27 to 17) mg/kg, and Pb content decreased from (16 to 10) mg/kg
respectively
Sahib, (2007) measured the lead concentrations in (16) testing
locations in different districts of Baghdad city, and the soil samples were
taken from the gardens of school which lies the chosen districts to represent
the environment of these districts and their conditions. The samples were
taken at four depths (0, 10, 20 and 30 cm from the soil surface) for each
Chapter Two: Theoretical Background and Literatures Review
45
district. The results ranged between (28-1865 µg/g) for all soil samples.
The pH values in this study ranged between (6.8- 8.2), the organic content
results ranged between from (4.5-19.8 %) and the organic matter was
noticed to accumulate at the top layers of the soil and decreased with depth.
Salman, (2007) measured the concentrations of heavy metals (Pb,
Ni, Co, Cd, Cu, Fe and Cr) in several ecological components, (soil, surface
water, palm fronds ash, dust and molluscan Shells) in Al-Basra Province.
Salman also indicated the probable sources of pollution and proposed the
proper remediation methods as well as comparing the concentrations of
heavy metals in the studied ecological components with the local and
international standards. The obtained results have shown increasing in the
concentrations of some heavy metals (Pb, Co, Cd and Cr) in the studied
ecological components and decreasing in others (Ni, Cu, Fe) as compared
with the local and world standards. The main reason for increasing the
concentrations of heavy metals in several ecological components in Al-
Basra province is the anthropogenic activities, like the disposal of sewage
water and domestic wastes, and the industrial wastes, especially from the
oil industries in the west of Al-Basra.
Barbooti et al., (2008) intended to assess the environmental effects
of the operations of Al-Daura refinery on the land and water environment.
An overview of the site was first performed using a specially designed
Environmental Site Assessment (ESA) checklist. Soil samples were
collected at various depths from almost all locations inside the refinery.
The performance of the wastewater treatment system was evaluated.
Samples of rain water accumulated in ponds were collected and analyzed.
For evaluation of the ground water quality and the nature of soil layers, a
monitoring well drilled in the vicinity of a wide dumping area of heavy
untreatable materials. Water samples were taken from this well for several
weeks period. Some field tests were carried out to evaluate the hydrocarbon
Chapter Two: Theoretical Background and Literatures Review
46
in soil, dissolved oxygen (DO), pH and electrical conductivity (EC) for
water. Laboratory analysis on water and soil included heavy metal
determination in soil extracts, such as (V, Ni and Pb) and types of
hydrocarbon pollutants in water and soil samples. Oil content
determinations as well as other routine analysis were carried out on water
samples to indicate any possible hydrocarbon pollution of the ground
water. The assessment of heavy metals concentration is that the danger
from these metals is limited due to their insolubility in water.
Zhang et al., (2009) studied the effect of the land use and soil
properties on the total and available concentration of Cu by using a
correlation and analysis of variance (ANOVA) in China. A total of 276
surface soil samples were collected from seven land uses. For each soil
sample, the total and available concentration of Cu, pH, organic matter,
total nitrogen and cation exchangeable capacity were measured. This study
also included drawing a probability map for the grains Cu that exceed 10
mg/kg by using ArcGIS software. The analyses have shown that the land
use has significant effects on Cu concentration and soil properties,
especially the total nitrogen and pH.
Chapter Three: Field and Experimental Work
47
Chapter Three
Field and Experimental Work
3.1 Introduction
This chapter includes the description of the field and experimental
work that took place and a description of the location, at which this work
was applied. The experimental work of this study consisted of measuring of
some characteristics of soil samples as well as the measurement of heavy
metals level in these samples. While the field works consist of collecting
soil samples from representative areas inside and outside the refinery.
Finally, a brief description for the instruments and chemical
materials used in the experimental work has been also reviewed.
3.2 Al-Daura Refinery
Al-Daura refinery which is one of the refineries operated by the
Midland Refineries Company (MRC), is located to the south east, just 4
Km from the city centre of Baghdad, close to the western bank of Tigers
river (Fig.(1-1) (p.4) shows Al-Daura refinery location in Baghdad).
It occupies an area with nearly (1,011,714 m2). Al-Daura refinery is the
oldest and largest one in Iraq and marks the true beginning of the modern
oil refinery industry (Afaj and Al-Khashab., 2007). It was constructed at
1953 by major oil companies, like Fortes Wheeler, M. W. Kellog and
Exxon research and engineering. The refinery was developed and expanded
from 1956 to 2004 by many companies, such as the Italian, Japanese,
Yugoslavian, Germany and American companies to include different new
Chapter Three: Field and Experimental Work
48
units and plants. About more than 5000 workers work in different
departments of the refinery.
Al-Daura refinery consists of three main processes departments which
are:
1. Light oil department.
2. Lube oil department.
3. Power and utilities department.
In addition to ten services department, such as Maintenance and
Mechanical, Safety and Fire Fighting, Studies and Engineering, Research
and Quality Control, Training and Development, Environment,
Accounting, Stores and Purchasing, Personal and Administration.
Al-Daura refinery receives an average amount of 100,000 m3/day or 36
million m3/year, which is equal to 12.6 million ton/year of crude oil from
different oil fields in Basra, Naft Khana, Kirkuk in addition to oil fields of
East Baghdad to produce in different separation techniques, such as
physical, thermal and chemical. Their several components include fuel and
nonfuel products, such as liquid petroleum gas LPG, Gasoline, Kerosene,
Jet Fuel, Gas Oil, Diesel Oil, Lubricating Oils and Asphalt of different
grades. Approximately more than 95% of the petroleum products of Al-
Daura oil refinery are fuel products.
About 100,000 m3 of crude oil from different origins will be blended as
a mixture, this blended crude oil produces some products, like Liquid
petroleum gas LPG, Kerosene, Jet Fuel, Gas Oil, Gasoline and Heavy Fuel
Oil.
The Reduced Crude (R.C.) of the refining possesses in Light Oil
department will be provided and sent out to the Lube Oil department. Its
amount ranges to about 2,100 m3/d, where the other amount of R.C. can be
Chapter Three: Field and Experimental Work
49
supplied to the power station out the refinery, like Al-Daura Power Plant
and South Baghdad Power Plant. Also, about 350 m3/d of R.C. will be
supplied to the Power and Utilities department. The main products in the
Lube Oil department are Lubricating Oil, Greases, Waxes and Asphalt of
different grades.
3.3 Location of Samples
The selected locations of samples were as follows: (1) ten locations
outside the refinery, and (2) seven locations inside it, as shown in the
Fig.(1-2) (p.5), those locations were chosen according to security
conditions during samples collection and determinants of site.
These sample locations might reflect the heavy metals pollution arising
from the oil refinery activities in all directions. Other one location was
chosen in a rural (control) area, in the University of Baghdad, to compare
between the heavy metals concentration in the study area and a sample
from the rural area not affected by the pollution.
3.4 Sampling Process
The soil samples were taken from a 5 cm depth from the top surface
of the soil used for chemical tests and physical properties for the soil, and
at 60 cm depth by using auger (maximum depth can auger be reached about
60 cm). Three samples were taken from each depth for each location to
take an average of results.
The plant samples were taken from all location in Fig.(1-2) (p.6).
Chapter Three: Field and Experimental Work
50
All the samples were taken during the period from Dec/2010 to
Feb/2011, and collected in labeled sacks and transported directly to the
laboratory.
The coordinates of all locations for samples were also taken by using
a geographic position system (GPS) instrument type GARMIN.
3.5 Laboratory Tests
3.5.1 Physical Tests of Soil
The following soil characteristics were measured for each sample from
each testing location:
1. Organic Content.
2. pH Value Measurement.
3. Soil Classification:
Specific Gravity.
Grain Size Analysis.
Atterberg Limits (Liquid Limit & Plastic Limit).
All physical tests were conducted in the Soil laboratory at the University
of Technology.
3.5.1.1 Organic Content Measurement
The objective of the organic content measuring is to calculate the
amount of organic matters in soil samples according to (Rcsp, 1988).
The procedure of measuring organic content was executed by taking (5 gm)
of dried ground soil and placed in a burning furnace to 550 oC for 2 hours.
Chapter Three: Field and Experimental Work
51
The organic content percentage can be then calculated by applying
the following equation:
………. (3-1)
Where:
OC %: organic content percentage.
Ww: wet weight of soil sample before burning (gm).
Wd: dry weight of soil sample after burning (gm).
W: weight of dried ground soil = 5 gm.
3.5.1.2 pH Value Measurement
The approach of this measurement was performed according to
(Rayment and Higginson, 1992).
The procedure of measuring the (pH) value is as follows:
1. The pH value was determined as 1:5 soil: distilled water suspension,
by taking 20 gm of dry ground soil: 100 ml of distilled water.
2. The suspension was shaken using a mechanical stirrer for one hour at
15 rpm.
3. The suspension was filtered with filtering papers.
4. The electrode of pH meter was immersed into the filtered sample,
and the pH value was recorded.
Chapter Three: Field and Experimental Work
52
3.5.1.3 Soil Classification
Specific Gravity (Gs): The Specific gravity for all soil samples were
tested according to (BS: 1377, 1975, Test 6B).
Grain Size Analysis: The soil samples were tested according to
ASTM (D422).
Atterberg Limits: The soil samples were tested according to (BS:
1377, 1975, Test 2B) for liquid limit and (BS: 1377, 1975, Test 3)
for plastic limit.
3.5.2 Chemical Laboratory Test of Soil
The chemical laboratory test includes finding the concentrations of
heavy metals, such as Zinc (Zn), Nickel (Ni), Lead (Pb) and Cadmium (Cd)
by using Atomic Absorption Spectrometry (AAS) device. This device was
adopted in this work, and the chemical extraction was prepared in the
laboratories of the Central Agency for Standardization and Quality Control
in the Ministry of Planning.
The procedure of chemical extract preparation was as follows:
(Jardoa and Nickless, 1989).
1. All samples were dried in a drying oven to 105 oC for 24 hours.
2. All samples were ground and sieved with 105 mesh sizes.
3. A (1 gm) from the sieved soil was extracted with 10 ml of
concentrated HNO3 acid (Analar nitric acid) on a hot plate for
heating till the volume reached 2 ml, then the sample (extracted
sample) was left to stand 2 hours.
4. After that, the sample was first diluted with distilled water twice, and
then, the sample was filtered on Whatman 541 papers, and finaly, a
Chapter Three: Field and Experimental Work
53
second dilution was made for the sample with distilled water for 25
ml volume.
Then the sample placed in the Atomic Absorption Spectrophotometer
(AAS) to measure the heavy metals concentrations.
The results obtained from the AAS were in (mg/L) and to convert these
results to (µg/g), the following formula has been applied: (Karnoob, 1986)
………. (3-2)
Where:
Y: heavy metals concentration in soil sample (µg/g).
X: heavy metals concentration obtained from AAS instrument (mg/L).
V: sample volume used in the AAS = 25 ml.
I: dilution factor.
W: weight of soil extracted = 1 gm.
3.5.3 Chemical Laboratory Tests of plants
The chemical laboratory test for plants (seasonal vegetable) includes
finding the concentrations of Zn, Ni, Pb and Cd by using the Atomic
Absorption Spectrometry (AAS) method. The chemical extraction was
prepared in the same laboratories of the Central Agency for Standardization
and Quality Control in the Ministry of Planning.
Chapter Three: Field and Experimental Work
54
The plants samples were taken from the field (the whole plant with
its roots) and placed in plastic sacks and then transported to the lab to run
the tests on them.
The procedure of chemical extract preparation was as follows:
(Haswel, 1990)
1. The plant samples were first washed with distilled water and
then dried completely.
2. Cutting the sample into small pieces and taking 2 gm from it.
3. Adding 40 mL from nitric acid (HNO3) and covering the
sample for one night to soak.
4. Heating the sample until appearance of steam and left to cool.
5. Adding 3 mL from berchloric acid (HClO4) and heating the
sample with opening cover until dried.
6. Leaving the residual for cooling, then adding 2 mL from
hydrochloric acid (HCl) with 2-3 mL distilled water and
heating the sample until the residual dissolved.
7. Cooling and filtering the sample, rinsing the filtered one with
distilled water to 50 mL, and then the sample was ready to
analysis by Atomic Absorption Spectrometry (AAS).
3.6 Apparatuses Used in All Experiments
The apparatuses used were:
1. Atomic Absorption Spectrophotometer.
Type: SHIMADSU AA6300
Use: Detection for the heavy metals concentration levels in soil and
plants extracts.
Chapter Three: Field and Experimental Work
55
2. Geographic Position System (GPS).
Type: GARMIN
Model: rino 120
Use: Determination for the coordinate of the samples location.
3. Digital indicator balance with a range of (0.0001-220.0000 gm).
4. Digital indicator balance with a range of (0.01- gm).
5. Drying oven with a maximum temperature degree of 200 oC.
6. Burning furnace for burning soil to 550 oC.
7. Casagrande device.
8. Hydrometer H-152.
9. Pycnometer.
10. Set of sieves.
11. Auger and shovel.
Chapter Four: Results and Discussion
56
Chapter Four
Results and Discussion
4.1 Introduction
This chapter includes the results of the experimental work for both
heavy metals and soil characteristics, beside the statistical analysis for these
results. The relationship between the heavy metals concentrations and the
soil characteristics has been also introduced, analyzed and discussed.
4.2 Heavy Metals Concentration Results in Soil
Heavy metals concentrations levels were measured in soil samples
which were taken from the testing locations at different depths (5 and 60
cm from soil surface).
The total results of heavy metals concentration are listed in tables
(4-1) to (4-8).
Chapter Four: Results and Discussion
57
Table (4-1) The Results of Zinc Concentrations and Soil Characteristics
Outside the Refinery Location. S
am
ple
No.
Position Depth
(cm)
Av. Zn con.
(µg/g)
[Mean
Allow. Val.
(50 µg/g)]
Ratio
Ratio
OC% pH Clay
% East North
1 447921.8 3681095
5 71.1 1.422 5.182 13.45 7.6 20.5
60 52.7 1.054 3.841 8.62 7.3
2 447640.5 3681216
5 40.2 0.804 2.930 12.2 7.3 12.3
60 47.6 0.952 3.469 9 6.9
3 448271.5 3682971
5 35.2 0.704 2.566 6 7.8 2.15
60 62.6 1.252 4.563 6.04 7.5
4 447674.1 3683174
5 62.5 1.25 4.555 7.54 8.1 15.5
60 58.8 1.176 4.286 5.87 7.8
5 446309.7 3682524
5 54.2 1.084 3.950 5.91 6.9 13
60 29.7 0.594 2.165 3.36 7
6 446695.6 3682706
5 59 1.18 4.300 11.87 7.2 18
60 52.1 1.042 3.797 7 7.1
7 444986.0 3682242
5 15 0.3 1.093 1.48 7.6 1.7
60 16.5 0.33 1.203 1.35 7.7
8 445361.1 3681741
5 33.8 0.676 2.464 8.29 7 1.85
60 60 1.2 4.373 4.49 7.2
9 445429.1 3680757
5 42 0.84 3.061 9.34 7.2 14.3
60 41.5 0.83 3.025 4.5 7
10 445146.1 3680584
5 43.3 0.866 3.156 8.31 7.3 9
60 56.6 1.132 4.125 8.43 6.9
Note: All bold numbers in tables means that this value exceeded the mean allowable
value.
Chapter Four: Results and Discussion
58
Table (4-2) The Results of Zinc Concentrations and Soil Characteristics
Inside the Refinery Location. S
am
ple
No.
Position Depth
(cm)
Av. Zn con.
(µg/g)
[Mean
Allow. Val.
(50 µg/g)]
Ratio
Ratio
OC% pH Clay
% East North
11 446569.8
3682261
5 101.8 2.036 7.420 6.65 7.4 43
60 51.2 1.024 3.732 4.1 7.1
12
447027.4
3682652
5 77.5 1.55 5.649 5.13 7.6 20
60 101.3 2.026 7.383 4.35 7.6
13
447144.6
3682469
5 60.9 1.218 4.439 4.2 7.8 8
60 48.7 0.974 3.550 4.54 7.7
14
447567.7
3681528
5 52.6 1.052 3.834 3.83 7.4 2.2
60 44.2 0.884 3.222 3.8 7.2
15
447075.4
3681779
5 66.8 1.336 4.869 6.68 8.1 22
60 50.2 1.004 3.659 5 7.8
16
447048.9
3682156
5 115.1 2.302 8.389 8.67 7.5 33
60 86.2 1.724 6.283 3.94 7.4
17
446751.8
3681911
5 128.9 2.578 9.400 9.26 7.8 35
60 76.2 1.524 5.554 4.68 7.4
Chapter Four: Results and Discussion
59
Table (4-3) The Results of Nickel Concentrations and Soil Characteristics
Outside the Refinery Location. S
am
ple
No.
Position Depth
(cm)
Av. Ni con.
(µg/g)
[Mean
Allow. Val.
(20 µg/g)]
Ratio
Ratio
OC% pH Clay
% East North
1 447921.8 3681095
5 117.4 5.870 4.278 13.45 7.6 20.5
60 94.8 4.740 3.455 8.62 7.3
2 447640.5 3681216
5 104.1 5.205 3.794 12.2 7.3 12.3
60 113.4 5.670 4.133 9 6.9
3 448271.5 3682971
5 89.2 4.460 3.251 6 7.8 2.15
60 136 6.800 4.956 6.04 7.5
4 447674.1 3683174
5 100.6 5.030 3.666 7.54 8.1 15.5
60 128.5 6.425 4.683 5.87 7.8
5 446309.7 3682524
5 95 4.750 3.462 5.91 6.9 13
60 54.5 2.725 1.986 3.36 7
6 446695.6 3682706
5 118.3 5.915 4.311 11.87 7.2 18
60 105 5.250 3.827 7 7.1
7 444986.0 3682242
5 30.6 1.530 1.115 1.48 7.6 1.7
60 37.3 1.865 1.359 1.35 7.7
8 445361.1 3681741
5 84.5 4.225 3.079 8.29 7 1.85
60 127.8 6.390 4.657 4.49 7.2
9 445429.1 3680757
5 107.4 5.370 3.914 9.34 7.2 14.3
60 91.3 4.565 3.327 4.5 7
10 445146.1 3680584
5 103.9 5.195 3.786 8.31 7.3 9
60 117.8 5.890 4.293 8.43 6.9
Chapter Four: Results and Discussion
60
Table (4-4) The Results of Nickel Concentrations and Soil Characteristics
Inside the Refinery Location. S
am
ple
No. Position
Depth
(cm)
Av. Ni
con.
(µg/g)
[Mean
Allow.
Val.
(20 µg/g)]
Ratio
Ratio
OC% pH Clay
% East North
11 446569.8 3682261
5 110.1 5.505 4.012 6.65 7.4 43
60 90 4.500 3.280 4.1 7.1
12 447027.4 3682652
5 106.1 5.305 3.867 5.13 7.6 20
60 145.5 7.275 5.302 4.35 7.6
13 447144.6 3682469
5 89 4.450 3.243 4.2 7.8 8
60 79.6 3.980 2.901 4.54 7.7
14 447567.7 3681528
5 90.8 4.540 3.309 3.83 7.4 2.2
60 85.6 4.280 3.120 3.8 7.2
15 447075.4 3681779
5 120.9 6.045 4.406 6.68 8.1 22
60 103.9 5.195 3.786 5 7.8
16 447048.9 3682156
5 124.4 6.220 4.534 8.67 7.5 33
60 97 4.850 3.535 3.94 7.4
17 446751.8 3681911
5 116.2 5.810 4.235 9.26 7.8 35
60 104.3 5.215 3.801 4.68 7.4
Chapter Four: Results and Discussion
61
Table (4-5) The Results of Lead Concentrations and Soil Characteristics
Outside the Refinery Location. S
am
ple
No.
Position Depth
(cm)
Av. Pb con.
(µg/g)
[Mean
Allow. Val.
(28 µg/g)]
Ratio
Ratio
OC% pH Clay
% East North
1 447921.8 3681095
5 13 0.464 26.0 13.45 7.6 20.5
60 10.8 0.386 21.6 8.62 7.3
2 447640.5 3681216
5 9.9 0.354 19.8 12.2 7.3 12.3
60 7.3 0.261 14.6 9 6.9
3 448271.5 3682971
5 7.5 0.268 15.0 6 7.8 2.15
60 8 0.286 16.0 6.04 7.5
4 447674.1 3683174
5 6 0.214 12.0 7.54 8.1 15.5
60 14 0.500 28.0 5.87 7.8
5 446309.7 3682524
5 6 0.214 12.0 5.91 6.9 13
60 3.5 0.125 7.0 3.36 7
6 446695.6 3682706
5 9.5 0.339 19.0 11.87 7.2 18
60 8.3 0.296 16.6 7 7.1
7 444986.0 3682242
5 2.8 0.1 5.6 1.48 7.6 1.7
60 5 0.179 10.0 1.35 7.7
8 445361.1 3681741
5 9.7 0.346 19.4 8.29 7 1.85
60 5.7 0.204 11.4 4.49 7.2
9 445429.1 3680757
5 8.4 0.300 16.8 9.34 7.2 14.3
60 4.9 0.175 9.8 4.5 7
10 445146.1 3680584
5 4.3 0.154 8.6 8.31 7.3 9
60 3.8 0.136 7.6 8.43 6.9
Chapter Four: Results and Discussion
62
Table (4-6) The Results of Lead Concentrations and Soil Characteristics
Inside the Refinery Location. S
am
ple
No.
Position Depth
(cm)
Av. Pb con.
(µg/g)
[Mean
Allow. Val.
(28 µg/g)]
Ratio
Ratio
OC% pH Clay
% East North
11 446569.8 3682261
5 64.4 2.300 128.8 6.65 7.4 43
60 7.9 0.282 15.8 4.1 7.1
12 447027.4 3682652
5 5.1 0.182 10.2 5.13 7.6 20
60 7.2 0.257 14.4 4.35 7.6
13 447144.6 3682469
5 1.45 0.052 2.9 4.2 7.8 8
60 0.5 0.018 1.0 4.54 7.7
14 447567.7 3681528
5 1.4 0.050 2.8 3.83 7.4 2.2
60 0.7 0.025 1.4 3.8 7.2
15 447075.4 3681779
5 48.4 1.729 96.8 6.68 8.1 22
60 9.4 0.336 18.8 5 7.8
16 447048.9 3682156
5 6.8 0.243 13.6 8.67 7.5 33
60 2.7 0.096 5.4 3.94 7.4
17 446751.8 3681911
5 10 0.357 20.0 9.26 7.8 35
60 5.6 0.200 11.2 4.68 7.4
Chapter Four: Results and Discussion
63
Table (4-7) The Results of Cadmium Concentrations and Soil
Characteristics Outside the Refinery Location. S
am
ple
No. Position
Depth
(cm)
Av. Cd
con.
(µg/g)
[Mean
Allow. Val.
(0.45 µg/g)]
Ratio
Ratio
OC% pH Clay
% East North
1 447921.8 3681095
5 0.03 0.067 3 13.45 7.6 20.5
60 1.22 2.711 122 8.62 7.3
2 447640.5 3681216
5 0.02 0.044 2 12.2 7.3 12.3
60 0.61 1.356 61 9 6.9
3 448271.5 3682971
5 0.01 0.022 1 6 7.8 2.15
60 0.24 0.533 24 6.04 7.5
4 447674.1 3683174
5 0.01 0.022 1 7.54 8.1 15.5
60 0.01 0.022 1 5.87 7.8
5 446309.7 3682524
5 0.02 0.044 2 5.91 6.9 13
60 0.25 0.556 25 3.36 7
6 446695.6 3682706
5 0.03 0.067 3 11.87 7.2 18
60 0.5 1.111 50 7 7.1
7 444986.0 3682242
5 0.02 0.044 2 1.48 7.6 1.7
60 0.02 0.044 2 1.35 7.7
8 445361.1 3681741
5 0.03 0.067 3 8.29 7 1.85
60 1.7 3.778 170 4.49 7.2
9 445429.1 3680757
5 0.01 0.022 1 9.34 7.2 14.3
60 0.02 0.044 2 4.5 7
10 445146.1 3680584
5 0.02 0.044 2 8.31 7.3 9
60 2.1 4.667 210 8.43 6.9
Chapter Four: Results and Discussion
64
Table (4-8) The Results of Cadmium Concentrations and Soil
Characteristics Inside the Refinery Location. S
am
ple
No.
Position Depth
(cm)
Av. Cd con.
(µg/g)
[Mean
Allow. Val.
(0.45 µg/g)]
Ratio
Ratio
OC% pH Clay
% East North
11 446569.8 3682261
5 0.21 0.467 21 6.65 7.4 43
60 0.06 0.133 6 4.1 7.1
12 447027.4 3682652
5 0.06 0.133 6 5.13 7.6 20
60 2.31 5.133 231 4.35 7.6
13 447144.6 3682469
5 0.01 0.022 1 4.2 7.8 8
60 0.12 0.267 12 4.54 7.7
14 447567.7 3681528
5 0.05 0.111 5 3.83 7.4 2.2
60 0.07 0.156 7 3.8 7.2
15 447075.4 3681779
5 0.03 0.067 3 6.68 8.1 22
60 0.64 1.422 64 5 7.8
16 447048.9 3682156
5 0.04 0.089 4 8.67 7.5 33
60 0.07 0.156 7 3.94 7.4
17 446751.8 3681911
5 0.01 0.022 1 9.26 7.8 35
60 1.3 2.889 130 4.68 7.4
From previous tables, the concentrations results ranged as follows:
Zinc: From (15- 128.9 µg/g) at top soil.
From (16.5- 101.3 µg/g) at 60 cm from soil surface.
Nickel: From (30.6- 124.4 µg/g) at top soil.
From (37.3- 145.5 µg/g) at 60 cm from soil surface.
Lead: From (1.4- 64.4 µg/g) at top soil.
From (0.5- 14 µg/g) at 60 cm from soil surface.
Cadmium: From (0.01- 0.21 µg/g) at top soil.
Chapter Four: Results and Discussion
65
From (0.01- 2.31 µg/g) at 60 cm from soil surface.
Tables (4-1) to (4-6) show that the concentrations of Zn, Ni and Pb,
with some exceptions, accumulate at the top soil and decrease with the
depth. This accumulation of heavy metals in top of soil is due to the
accumulation of organic matters at these layers which act as absorbent; this
fact has been proved before by (El-Ghawi et al., 2005). Also, the neutral
values of pH play an important role to keep the accumulation of heavy
metals at the top layers of soil, because at the neutral values of pH, Zn, Ni
and Pb have a strong relation with the soil solids, and hence its movement
towards the deeper layers will be limited or very slowly. This fact has been
proved by (Kabata-Pendias and Pendias, 1992).
Tables (4-7) and (4-8) indicate that the concentrations of Cd at the
top soil is less than in the 60 cm depth from top soil surface, this is because
the Cd goes readily to solution during the weathering (Kabata-Pendias and
Pendias, 1992).
The surface accumulation of heavy metals on the soil proved that the
atmospheric heavy metals are the main source of heavy metals in the soil.
The atmospheric heavy metals are transported to soil by dry and wet
deposition and are related with soil solids.
4.3 Distribution of Heavy Metals Concentrations in Soil
Zinc: The Zn concentration in the study area at the top soil varies
from (15- 128.9 µg/g) with a mean value of (62.4 µg/g). The observed
values have been reportedly higher than the common world average for
total Zn concentrations in soil (50 µg/g) (Alloway, 1995). It is also higher
than the mean concentrations of trace elements calculated on the world
scale for silty soil (60 µg/g) (Kabata-Pendias and Pendias, 1992).
Chapter Four: Results and Discussion
66
At (60 cm) depth from soil surface, the Zn concentration varies from
(16.5- 101.3 µg/g) with a mean value of (55.1 µg/g). This mean value has
been higher than the common world average illustrated above.
This study indicates that (64.7%) of all soil samples contain zinc
concentration greater than the standard limit of zinc in soil; and (100%) of
all samples contain zinc concentration greater than (13.72 µg/g) which is
the zinc concentration in soil sample from the rural area.
The maximum concentrations of Zn inside the refinery were near the
old storage basins and in the center of refinery, and the maximum value
outside the refinery was near the expressway (Mohammed Al-Kasim),
which is agricultural area, because the main sources of Zn have been
reported as an agricultural use of sewage and composted materials and the
use of agrochemicals, such as fertilizers and pesticides (Alloway, 1995).
Some of the studies have also linked the high Zn levels to accumulation
from the traffic and industry input (Imperato et al., 2003) and also from the
vehicle emissions and tire and brake abrasion (Ward, 1990).
Rainfall was the main reason that makes the fluctuation in the path of
Zn concentration with soil depth, because the solubilization of Zn minerals
during weathering produces mobile Zn+2
, especially in acid, oxidizing
environments (Kabata-Pendias and Pendias, 1992).
The distribution of Zn levels at the top soil and 60 cm depth from
surface in the study area is illustrated in Fig.(4-1) and Fig.(4-2),
respectively.
Chapter Four: Results and Discussion
67
Fig.(4-1) Distribution of Zinc at Top soil
Chapter Four: Results and Discussion
68
Fig.(4-2) Distribution of Zinc at 60 cm Depth from Soil Surface
Chapter Four: Results and Discussion
69
Nickel: The Ni content in the study area at the top soil varies from
(30.6- 124.4 µg/g) with a mean concentration of (100.5 µg/g). The
observed mean value is higher than the world average concentration of Ni
in soil, which is around (20 µg/g) (Alloway, 1995). These results exceed
the calculated world mean for silty soil (26 µg/g) (Kabata-Pendias and
Pendias, 1992).
At (60 cm) depth from soil surface, the Ni concentration varies from
(37.3- 145.5 µg/g) with a mean value of (100.7 µg/g). This value is also
exceeding the above mean values.
This study points out that (100%) of all soil samples contain nickel
concentration greater than the standard limit of nickel in soil; and (100%)
of all samples contain nickel concentration greater than (27.44 µg/g) which
is the nickel concentration in soil sample from the rural area.
Maximum concentrations of Ni inside the refinery were in the center
of refinery and near the flare, and the maximum value outside the refinery
was near the expressway (Mohammed Al-Kasim) and near to the flare. It is
evident that local solid waste litter and anthropogenic activities, such as
burning of fuel and residual oil contribute to the increase in Ni content in
the soil of the study area (Alloway, 1995).
Ni is easily mobilized during weathering. However, unlike Ni+2
is
relatively stable in aqueous solutions and is capable of migration over a
long distance, therefore, the Ni concentration path is with the soil depth are
fluctuated.
Figs.(4-3) and (4-4) show the distribution of Ni levels at the top soil and 60
cm depth from surface in the study area, respectively.
Chapter Four: Results and Discussion
70
Fig.(4-3) Distribution of Nickel at Top soil
Chapter Four: Results and Discussion
71
Fig.(4-4) Distribution of Nickel at 60 cm Depth from Soil Surface
Chapter Four: Results and Discussion
72
Lead: The Pb content in the study area varies from (1.4- 64.4 µg/g)
at top soil with a mean value of (12.6 µg/g). The observed values are less
than the calculated world average of silty soil (28 µg/g) (Kabata-Pendias
and Pendias, 1992).
Also, the Pb contents at 60 cm depth from soil surface (0.5- 14 µg/g)
are less than the calculated world average value.
This study indicates that (6%) of all soil samples contain lead
concentration greater than the standard limit of lead in soil; and (97%) of
all samples contain lead concentration greater than (0.5 µg/g) which is the
lead concentration in soil sample from the rural area
The maximum concentrations of Pb inside the refinery were near the
power former unit, and the maximum values outside the refinery were at
samples near the road sides. Deposition related to the automobile emissions
and transportations sector, in general (considering the long residence time
of Pb), may be the major source of increase in Pb content (Chatterjee and
Banerjee, 1999; Madrid et al., 2002; Imperato et al., 2003).
Pb is reported to be the least mobile among the other heavy metals
(Kabata-Pendias and Pendias, 1992), therefore, the Pb content paths with
the depth of soil were less fluctuated among other heavy metals.
Figs.(4-5) and (4-6) depict the distribution of Pb levels at the top soil and
60 cm depth from surface in the study area, respectively.
Chapter Four: Results and Discussion
73
Fig.(4-5) Distribution of Lead at Top soil
Chapter Four: Results and Discussion
74
Fig.(4-6) Distribution of Lead at 60 cm Depth from Soil Surface
Chapter Four: Results and Discussion
75
Cadmium: The Cd content in the study area varies from (0.01- 0.21
µg/g) at top soil with a mean value of (0.035 µg/g). The observed values
are less than the calculated world mean for silty soil (0.45 µg/g) (Kabata-
Pendias and Pendias, 1992).
At (60 cm) depth from soil surface, the Cd concentration varies from
(0.01- 2.31 µg/g) with a mean value of (0.66 µg/g). This mean value has
been higher than the common world mean illustrated above.
This study shows that is (20.6%) of all soil samples contain cadmium
concentration greater than the standard limit of cadmium in soil; and
(82.35%) of all samples contain cadmium concentration greater than (0.01
µg/g) which is the cadmium concentration in soil sample from the rural
area.
The maximum concentrations of Cd inside the refinery were near the
flare, and the maximum values outside the refinery were at samples near
the roadsides, which were agricultural areas. Cadmium has a wide range of
uses in the industry (Volensky, 1990), and a significant source of Cd in
soils is the phosphate fertilizers (Kabata-Pendias and Pendias, 1992).
Among the other trace metals, Cd is known to be most mobile under
conditions of different soils (Kabata-Pendias and Pendias, 1992), therefore,
the concentration of Cd increases with soil depth.
Figs.(4-7) and (4-8) reveals the distribution of Cd levels at the top soil and
60 cm depth from surface in the study area, respectively.
Chapter Four: Results and Discussion
76
Fig.(4-7) Distribution of Cadmium at Top soil
Chapter Four: Results and Discussion
77
Fig.(4-8) Distribution of Cadmium at 60 cm Depth from Soil Surface
Chapter Four: Results and Discussion
78
The results have shown that the concentrations of heavy metals
inside the refinery were higher than outside it, and they decrease with the
wind direction (Western North), and the areas in this direction were
agricultural areas without any industrial activities, their irrigation is from
the Tigres River. Therefore, the concentration of heavy metals is very low
in the top soil, and there is no clear effect from the refinery activities. In the
other hand, the southern side of the refinery has a high concentration,
which were also agricultural areas, because there are the expressway
(Mohammed Al-Kasim) and station of electrical generation (South
Baghdad) to the Eastern South side from the refinery.
4.4 Soil Characteristics Results and Their Relationship with Heavy
Metals Concentrations
4.4.1 Organic Content Results
The results of organic content (OC %) are listed in Table (4-1), these
ranges are as follows:
From (1.48- 13.45 %) at top soil.
From (1.35- 9 %) at 60 cm from soil surface.
The results of organic contents manifest that the organic content,
with few exceptions, decreases with the depth. That is due to the
accumulation of decomposed plants and hydrocarbons emitted from the
refinery in the top layers of soil.
The relationship between the organic content and heavy metals
concentrations at each depth are shown in Figs.(4-9) to (4-16). These
figures indicate that the heavy metals concentration increases at the high
organic content sites. That is because the organic matters play an important
role in heavy metals adsorption on soil solids and also absorption. That
agrees with the results obtained by (Alloway, 1995; Kabata-Pendias and
Chapter Four: Results and Discussion
79
Pendias, 1992) when they found that the organic matters are an important
factor in adsorption and accumulation of heavy metals in soil.
Chapter Four: Results and Discussion
80
Fig.(4-9) Organic Content Relationship with Zinc Concentration at top soil
for all the Testing Locations
Fig.(4-10) Organic Content Relationship with Zinc Concentration at 60cm
Depth for all the Testing Locations
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14 16
Zn
con
. µ
g/g
Organic cont. %
0
20
40
60
80
100
120
0 1 2 3 4 5 6 7 8 9 10
Zn
Con
. µ
g/g
Organic cont. %
Chapter Four: Results and Discussion
81
Fig.(4-11) Organic Content Relationship with Nickel Concentration at top
soil for all the Testing Locations
Fig.(4-12) Organic Content Relationship with Nickel Concentration at
60cm Depth for all the Testing Locations
0
20
40
60
80
100
120
140
0 2 4 6 8 10 12 14 16
Ni
con
. µ
g/g
Organic cont. %
0
20
40
60
80
100
120
140
160
0 1 2 3 4 5 6 7 8 9 10
Ni
con
. µ
g/g
Organic cont. %
Chapter Four: Results and Discussion
82
Fig.(4-13) Organic Content Relationship with Lead Concentration at top
soil for all the Testing Locations
Fig.(4-14) Organic Content Relationship with Lead Concentration at 60cm
Depth for all the Testing Locations
0
10
20
30
40
50
60
70
0 2 4 6 8 10 12 14 16
Pb
con
. µ
g/g
Organic cont. %
0
2
4
6
8
10
12
14
16
0 1 2 3 4 5 6 7 8 9 10
Pb
con
. µ
g/g
Organic cont. %
Chapter Four: Results and Discussion
83
Fig.(4-15) Organic Content Relationship with Cadmium Concentration at
top soil for all the Testing Locations
Fig.(4-16) Organic Content Relationship with Cadmium Concentration at
60cm Depth for all the Testing Locations
0
0.05
0.1
0.15
0.2
0.25
0 2 4 6 8 10 12 14 16
Cd
con
. µ
g/g
Organic cont. %
0
0.5
1
1.5
2
2.5
0 1 2 3 4 5 6 7 8 9 10
Cd
con
. µ
g/g
Organic cont. %
Chapter Four: Results and Discussion
84
These results showed that there is a weak direct correlation;
therefore, one can’t be estimate the heavy metals concentration in soil
depending on the organic content percentage and at certain depth.
4.4.2 Soil pH Results
The results of pH values of the study area are listed in tables (4-1)
and (4-2). Generally, these results range from (6.9-8.1), and are close to
those measured by (Al-Zubaidy, 1978) when he found that pH values for
Iraqi soil ranged from (7-8) because of the high percent of CaCO3 and
CaSO4.H2O existing in Iraqi soil. Also, the measured pH values are close to
those measured by (Al-Kindy, 2005; Mohammed, 2006; Sahib, 2007),
which ranged from (6.9-8.2), (7.31-7.56) and (6.8-8.2), respectively.
Figs.(4-17) to (4-24) depict the relationship between the heavy
metals level and pH. It’s obvious that the accumulation of heavy metals on
soil solids increases with pH increasing except Cd.
Chapter Four: Results and Discussion
85
Fig.(4-17) pH Values Relationship with Zinc Concentration at Top soil for
all the Testing Locations
Fig.(4-18) pH Values Relationship with Zinc Concentration at 60 cm depth
for all the Testing Locations
0
20
40
60
80
100
120
140
6.8 7 7.2 7.4 7.6 7.8 8 8.2
Zn
con
. µ
g/g
pH
0
20
40
60
80
100
120
6.8 6.9 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9
Zn
con
. µ
g/g
pH
Chapter Four: Results and Discussion
86
Fig.(4-19) pH Values Relationship with Nickel Concentration at Top soil
for all the Testing Locations
Fig.(4-20) pH Values Relationship with Nickel Concentration at 60 cm
depth for all the Testing Locations
0
20
40
60
80
100
120
140
6.8 7 7.2 7.4 7.6 7.8 8 8.2
Ni
con
. µ
g/g
pH
0
20
40
60
80
100
120
140
160
6.8 6.9 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9
Ni
con
. µ
g/g
pH
Chapter Four: Results and Discussion
87
Fig.(4-21) pH Values Relationship with Lead Concentration at Top soil for
all the Testing Locations
Fig.(4-22) pH Values Relationship with Lead Concentration at 60 cm depth
for all the Testing Locations
0
10
20
30
40
50
60
70
6.8 7 7.2 7.4 7.6 7.8 8 8.2
Pb
con
. µ
g/g
pH
0
2
4
6
8
10
12
14
16
6.8 6.9 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9
Pb
con
. µ
g/g
pH
Chapter Four: Results and Discussion
88
Fig.(4-23) pH Values Relationship with Cadmium Concentration at Top
soil for all the Testing Locations
Fig.(4-24) pH Values Relationship with Cadmium Concentration at 60 cm
depth for all the Testing Locations
0
0.05
0.1
0.15
0.2
0.25
6.8 7 7.2 7.4 7.6 7.8 8 8.2
Cd
con
. µ
g/g
pH
0
0.5
1
1.5
2
2.5
6.8 6.9 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9
Cd
con
. µ
g/g
pH
Chapter Four: Results and Discussion
89
These results manifested that there is a weak direct correlation
between Zn, Ni and Pb, and pH value; but there is a weak inverse
correlation between the Cd and pH, and this fact agrees with (Kabata-
Pendias and Pendias, 1992).
4.4.3 Clay Percent Results
All the results of soil properties are given in table (4-9) for each
testing location.
The relationship between the heavy metals concentrations in the
study area and soil type showed that most of the highly polluted location
soils contain a high percent of clay in their compositions. The overall
behavior of heavy metals in soil is said to be governed largely by their
sorption and desorption reactions with different soil constituents, especially
clay components (Appel and Ma, 2002).
Figs.(4-25) to (4-28) illustrate the relationship between the heavy metals
level and clay percent.
Chapter Four: Results and Discussion
90
Table (4-9) Characteristics of Soil Sample.
Sample
no. G% S% M% C% Organic% Gs L.L% P.L%
Unified
class.
1 0 2 77.5 20.5 9.76 2.52 44.65 24.19 Cl
2 0 0.5 87.2 12.3 7.22 2.63 45.61 23.15 Cl
3 0.4 4.8 92.65 2.15 6.62 2.52 42.12 23.13 Cl
4 2.9 9.6 72 15.5 5.52 2.75 33.3 20.1 Cl
5 0.4 11 75.6 13 5.9 2.66 40.1 19.87 Cl
6 22.75 8.25 51 18 5.06 2.67 37.3 22.1 Cl
7 0.24 81.76 16.3 1.7 1.52 2.63 Np. Np. SP.
8 1.56 17.44 79.15 1.85 5.98 2.67 32.14 21.13 Cl
9 13 13.5 59.2 14.3 6.08 2.52 35.95 20.84 Cl
10 23.35 16.8 50.85 9 4.12 2.67 32.9 19.3 Cl
11 0.02 5.98 50 43 4.94 2.74 31.8 19.8 Cl
12 0.32 7.68 72 20 5.86 2.74 34.1 20.1 Cl
13 0.88 25.12 66 8 8.84 2.75 31.6 19.27 Cl
14 0.22 2.78 94.8 2.2 9.16 2.54 45.2 23 Cl
15 1.3 29.7 47 22 4.26 2.65 31.68 16.62 Cl
16 2.34 8.9 55.76 33 4.64 2.71 35.3 21.1 Cl
17 2 14.15 48.85 35 3.96 2.70 31.8 18.8 Cl
Chapter Four: Results and Discussion
91
Fig.(4-25) Clay Percent Relationship with Zinc Concentration
Fig.(4-26) Clay Percent Relationship with Nickel Concentration
0
20
40
60
80
100
120
140
0 5 10 15 20 25 30 35 40 45 50
Zn
con
. µ
g/g
Clay %
0
20
40
60
80
100
120
140
0 5 10 15 20 25 30 35 40 45 50
Ni
con
. µ
g/g
Clay %
Chapter Four: Results and Discussion
92
Fig.(4-27) Clay Percent Relationship with Lead Concentration
Fig.(4-28) Clay Percent Relationship with Cadmium Concentration
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30 35 40 45 50
Pb
con
. µ
g/g
Clay %
0
0.05
0.1
0.15
0.2
0.25
0 5 10 15 20 25 30 35 40 45 50
Cd
con
. µ
g/g
Clay %
Chapter Four: Results and Discussion
93
These previous figures showed that there is a weak direct correlation;
therefore, one can’t estimate the heavy metals concentration in soil
depending on the clay percentage in the soil.
4.5 Heavy Metals Concentration Results in Plants
The concentrations of plants heavy metals suggest that the plant
factors, differences in metal characteristics and differences in soil physical
and chemical properties can influence the variations of metals in plants.
The results of heavy metals concentration of the plants (seasonal
vegetable) in the study area are listed in table (4-10). Generally, these
results show a high concentration of Pb in the study area for many samples.
The permissible value of heavy metals in the plant for the WHO standards
is (Zn=100; Ni=67; Pb=0.3; Cd=0.1 µg/g). The mean value of Pb is (8.12
µg/g), the increases in the Pb concentrations might be resulted from the
growth of the plants in the polluted soil with Pb even when the
concentration in the soil is within permissible limits; these facts show a
high ability for the plants to absorb the Pb from soil, and there is a danger
when the agriculture in the area is polluted with Pb.
Lead is one of the hazardous metals that can transport to the humans
and animals through the chain food and accumulate in the body, causing a
physiological damage.
The mean value of Zn is (44.4 µg/g), and this value is less than the
WHO standards value. Zn is needed by plants as principle micro essential
elements. This may be the reason for their high level of accumulation by
plant species. According to Cunningham and Saigo (2001), plant cells have
mechanisms for bioaccumulation, selective absorption and storage of a
Chapter Four: Results and Discussion
94
great variety of molecules. This allows them to accumulate nutrients and
essential minerals. Apart from being a cytochrome constituent, Zn is
associated with the auxin which is a plant growth hormone (Humphreys,
1987).
Table (4-10) The Results of Heavy Metals Concentration in the Plants at
Study Area Locations.
Sa
mp
le
No
.
Position Zn con.
(µg/g) [Permis. Val.
(100 µg/g)]
Ni con.
(µg/g) [Permis. Val.
(67 µg/g)]
Pb con.
(µg/g) [Permis. Val.
(0.3 µg/g)]
Cd con.
(µg/g) [Permis. Val.
(0.1 µg/g)] East North
1 447921.8 3681095 8.6 0.85 15 0.008
2 447640.5 3681216 10.71 0.8 0.23 0.003
3 448271.5 3682971 38.2 0.5 14.1 0.005
4 447674.1 3683174 35.8 0.62 0.15 0.001
5 446309.7 3682524 2.57 0.52 0.05 0.004
6 446695.6 3682706 32.16 0.58 0.07 0.003
7 444986 3682242 26.75 0.1 0.1 0.001
8 445361.1 3681741 13.11 0.34 0.3 0.008
9 445429.1 3680757 24.37 0.45 5.254 0.001
10 445146.1 3680584 29.5 0.64 4.955 0.01
11 446569.8 3682261 29.2 0.93 24.01 0.04
12 447027.4 3682652 50.6 0.86 0.2 0.01
13 447144.6 3682469 47.7 0.15 9.7 0.008
14 447567.7 3681528 99.9 0.21 0.03 0.006
15 447075.4 3681779 99.9 0.9 29.6 0.009
16 447048.9 3682156 77.9 0.78 19.5 0.007
17 446751.8 3681911 127.9 0.87 14.8 0.002
Chapter Four: Results and Discussion
95
4.6 Summary of the Results Analysis
In general, most of the heavy metals in soil accumulate from the
deposition of atmospheric heavy metals on top soil, and its mobility inside
the soil will depend upon the characteristics of soil itself.
From the results obtained in this research, most concentrations of
heavy metals are decreased with the depth of sampling point (except
cadmium). That means the heavy metals accumulates at the top layers of
soil, and this accumulation is due to the heavy metals in its immobile phase
at the measured value of pH (6.9-8.1). These are the values, at which the
soil particles act as adsorbents for heavy metals; because of the heavy rain
during the last winter, the Cd goes readily into solution and, although
known to occur Cd+2
during the weathering.
The organic content has a significant effect on the heavy metals
accumulation in soil. The complexation and chelating reactions occur
between the organic matters and heavy metals in neutral values of pH due
to the formation of bonds between the heavy metals and organic matters,
and hence the heavy metals movement will be very slow in soil.
Increasing and decreasing soil pH influence the chemical reactions in
the soil. Chemical elements in the soil are more adsorbed on the finest soil
particles (colloids) which are clay and humus. Although they are small in
size, colloids play a major influence in soil properties. They are
electronegative and have a large surface area. These two properties make
them highly reactive and adsorptive, and therefore, greatly influence the
cation exchange capacity of the soil. Soil acidification tends to increase the
desorption of basic cations (calcium, magnesium, potassium, sodium and
heavy metals) from the colloids, as they are replaced by hydrogen ions.
From table (4-9), the hydrometer test shows a high percent of silt in
the soil composition, but the results obtained from the Unified
classification, that depended on liquid limits (L.L) and plasticity index
Chapter Four: Results and Discussion
96
(P.I), indecate a high percent of clay; these differences are because the
heavy metals bond with clay particles and make them coarser particles that
precipitate faster than clay particles.
In the plants, the heavy metals concentration reveals a trace concentration
of Ni and Cd; high concentrations of Pb with moderate levels of Zn. The
high levels of Pb mean the study area is not suitable for agriculture food
crops because the adverse effect of lead to the human and animals.
Chapter Five: Conclusions and Recommendations
97
Chapter Five
Conclusions and Recommendations
5.1 Conclusions
Based on the results, the conclusions from this work can be
summarized in the following items:
1. Zn, Ni and Pb concentrations are accumulated in the top soil
and decreased with the depth inside the soil (except Cd).
2. This study indicates that (64.7%), (100%), (6%) and (20.6%)
of all soil samples contain zinc, nickel, lead and Cadmium
concentration (respectively) greater than the standard limit of
their concentrations in soil.
3. This study, also indicates that (100%), (100%), (97%) and
(82.35%) of all soil samples contain zinc, nickel, lead and
Cadmium concentration (respectively) greater than their
concentrations in soil sample from the rural area.
4. The highest concentrations value of zinc and nickel were in
the center of the refinery; and the highest lead concentration
were near the power former unit; and the cadmium highest
value was near the flare.
5. The pH values are neutral in general, and hence the mobility
of the heavy metals will be limited at these values of pH.
6. The heavy metals make the clay particles coarser because of
the bonding between them.
7. The seriousness of food crops, including seasonal vegetables
because of lead pollution.
Chapter Five: Conclusions and Recommendations
98
5.2 Recommendations
Results of the study are useful to the Ministry of Environment, Al-
Daura refinery and researchers and recommended that:
1. Carrying out further researches on the pollutant identification and
quantification and bio remediation of polluted lands, such as the use
of bacterial transformations of polluted.
2. Soil amendment programs by emphasizing on the increased use of
plant nutrients, like the organic manure, should be established in Al-
Daura, especially in areas around the refinery. The use of manure is
known for correction of soil acidity and firmly binding of metals
within the soil colloids, barring them from being readily available to
the plants and water pollution through a leaching process. Lime
application is useful in raising the soil pH which reduces the metal
availability and hence toxicity.
3. Immediate medical intervention measures should be thought in order
to determine the extent and effects of human diseases associated with
refining pollution in all over the areas surrounding the refining
activities.
4. Maintenance of all the refinery units that cause emissions.
5. Add treatment materials to refining operations for the purpose of
reducing the emissions of heavy metals from the refinery.
6. Compulsion the maintenance on the automobile to reduce the
emissions from it.
5.3 Recommendations for Future Works
1. Further investigations are required on the impact assessment of
heavy metals in Tigers River and the groundwater of the surrounding
region.
Chapter Five: Conclusions and Recommendations
99
2. Carrying out a study on air pollution of the same study area.
3. Studying the concentration of heavy metals in the same study area at
different times of the year to determine seasonal variation.
4. Using the Geographic Information System (ArcGIS) software in the
environmental analysis and modeling, because the GIS has become a
very powerful tool for environmental science and engineering.