ABSTRACT
The study was carried out to assess heavy metal concentrations in soil and their accumulation in cassava plant parts at the metal waste dumpsite in Umuahia South Local Government Area, Abia State, Nigeria. Soil samples were collected randomly at depths of 0 – 10 cm, 11 – 20 cm, 21 – 30 cm, 31 – 40 cm and 41 – 50 cm from nine (9) sampling points, three (3) each at entry, middle and exit positions within the site. Cassava plant samples were collected randomly at nine points from the nearby farmland, about 1m away from the dumpsite. The chemical properties of soil and macro elements assessments were carried out to examine heavy metals and polycyclic aromatic hydrocarbons (PAHs). Soil chemical properties analysed were pH, organic matter and electrical conductivity. Macro elements studied were zinc (Zn), calcium (Ca), sodium (Na) and potassium (k). Heavy metals were assessed using Agilent FS240AA Atomic Absorption Spectrophotometer (AAS). PAHs were assessed using Gas chromatography (GC-MS). In soil, total heavy metal levels ranged from (mg/kg), 0.01 to 0.13 for Cr, 0.27 to 1.28 for Cu, 0.93 to 2.57 for Pb, and 0.11 to 0.26 for Cd. Their mean values were (mg/kg), 0.062 for Cr, 0.606 for Cu, 1.544 for Pb, 0.212 for Cd. The rank profile of the metals were Pb > Cu > Cd > Cr. In the cassava plant, total heavy metal levels ranged from (mg/kg), 0.018 to 0.051 for Cr, 0.10 to 4.01 for Cu, 0.82 to 2.08 for Pb, 0.20 to 3.24 for Cd. The result shows that high Pb content was obtained for the different cassava plant parts when compared with the FAO/WHO permissible limit, whereas other metals were well below their permissible limits, except Cd which exceeded its permissible limit of 0.7 – 1.1mg/kg in the root only. Eleven PAHs were detected across the different soil depths, they include, fluorine, flouranthene, benzo(a)flouranthene, benzo(b)flouranthene, benzo(ghi)perylene, 1– 2benzanthrene, xylene, phenanthrene, naphthalene, anthtacene and dibenzyl(ah)anthracene. The root accumulated the most mean concentration for PAHs (0.003μg/g), followed by the leaf (0.00224μg/g), then the stem (0.0016μg/g). The results show that the levels of heavy metals and polycyclic aromatic hydrocarbons in the soil and cassava plant were small and were way below their permissible limits, only Pb exceeded its permissible limit at all parts of the cassava plant. The result also shows that at 41 – 50cm, there were concentrations of the studied contaminants. This could be call for concern as further contamination deeper into the soil horizon could pose threat on underground water quality. Therefore, proactive measures should be adopted to remediate contamination.
TABLE OF CONTENTS
Title
Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements vii
Table
of Contents viii
List
of Tables ix
List
of Figures x
List
of Plates xi
Abstract xii
CHAPTER 1: INTRODUCTION 1
1.1 Background of the Study 1
1.2 Statement of Problems 3
1.3 Scope of the Study 4
1.4 Aim and Objectives of the Study 4
1.5 Research Questions 5
1.6 Significance of the Study 5
CHAPTER 2: LITERATURE REVIEW
2.1 Scrap Metals Generation and Management 6
2.2 Soil Properties Affecting Metals Availability
and Mobility 8
2.2.1 Hydrogen ion (H+) concentration 8
2.2.2 Soil electrical conductivity 8
2.2.3 Organic matter 9
2.3 Selected Heavy Metals 9
2.3.1 Cadmium (Cd) 9
2.3.2 Chromium (Cr) 11
2.3.3 Lead (Pb) 12
2.3.4 Copper (Cu) 14
2.3.5 Zinc (Zn) 15
2.4 Polycyclic Aromatic Hydrocarbons (PAHs) 20
2.4.1 Sources of PAHs 21
2.4.2 PAHs in soil 22
2.4.3 Routes of exposure to PAHs 23
2.4.4 PAHs in foods 23
2.4.5 PAHs health effects on humans 24
CHAPTER 3: MATERIALS AND METHODS
3.1 Study Area 28
3.1.1 Location 28
3.1.2 Climate 28
3.1.3 Vegetation 28
3.1.4 Geology and soil 29
3.1.5 Major human activities 29
3.2 Sources of Data 34
3.3 Selection of Sample Site 34
3.4 Experimental design 37
3.4.1 Soil samples collection and Pre-treatment 38
3.4.2 Plant sampling and pre-treatment 39
3.5 Some Chemical Analysis of Soil 40
3.5.1 pH 40
3.5.2 Electrical conductivity 40
3.5.3 Organic matter 40
3.5.4 Method for heavy metals analysis 41
3.5.5 Method for GC analysis of PAHs 42
3.6 Experimental Design and Statistical
Analysis of Data 43
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Results 44
4.2 Discussion 68
4.2.1 Some
physico-chemical properties of the soil 68
4.2.2 Macro
elements content in soil 69
4.2.3 Macro Elements in Cassava Plant Parts 70
4.2.4 Heavy Metal Content in Soil 73
4.2.5 Heavy Metals Content in Cassava Plant 76
4.2.6 Polycyclic Aromatic Hydrocarbons in Soil 78
4.2.7 Polycyclic Aromatic Hydrocarbons in Cassava
Plant Parts 80
4.2.8 Correlation Analysis of Data 81
4.2.8.1 Correlation between heavy metals and macro
elements content in soil 81
4.2.8.2 Correlation between heavy metals and macro
elements content in
cassava
plant 81
4.2.8.3 Correlation between heavy metals in soil and
cassava plant 82
4.2.8.4 Correlation between polycyclic aromatic
hydrocarbons in soil and
cassava
plant 82
CHAPTER 5: CONCLUSION AND
RECOMMENDATIONS
5.1 Conclusion 84
5.2 Recommendations 85
References 86
Appendices 104
LIST
OF TABLES
4.1 Means
and standard deviation of selected chemical properties of
the soil 45
4.2 Means
and standard deviation of macro elements content in soil 47
4.3 Means
and standard deviation macro elements content in
Manihot
esculenta 49
4.4 Means and standard deviation of heavy
metals content in soil 51
4.5 Means and standard deviation of heavy
metals content in
Manihot esculenta 53
4.6 Means
and standard deviation of polycyclic aromatic hydrocarbons
(PAH) in soil 55
4.7 Means and standard deviation of polycyclic
aromatic hydrocarbons (PAH)
in
Manihot esculenta 57
4.8 Correlation
between macro elements in soil and macro elements in
Manihot esculenta 59
4.9 Correlation
between heavy metals and macro element content in soil 61
4.10 Correlation between heavy metals and macro
elements content in Manihot esculenta 63
4.11 Correlation
between heavy metals in soil and heavy metals in
Manihot
esculenta 65
4.12
Correlation between polycyclic
aromatic hydrocarbons in soil and
Manihot
esculenta 67
LIST
OF FIGURES
3.1 Nigeria showing Abia State 30
3.2 Abia
State showing Umuahia South 31
3.3 Umuahia
South showing the study area, Ohiya Mechanic
Village 32
3.4 Ohiya
mechanic village showing samples collection points 34
3.5 Experimental
design 37
LIST
OF PLATES
1 Showing
collection of reusable metal waste at the site 34
2 Showing dumped metal
wastes at the site 35
3 Showing
burning activity at the dumpsite 35
4 Showing
farmland next to the site. 36
CHAPTER
1
INTRODUCTION
1.1
BACKGROUND
OF THE STUDY
The
environment is exposed to continuous contamination due to inevitable
commercial, social and domestic activities by humans such as agriculture,
mineral exploitation, industrial production and food processing. These
anthropogenic activities release heavy metals and polycyclic aromatic
hydrocarbons into the environment (Demirezen and Aksoy, 2006)
Heavy metal
contamination is an environmental issue, globally recognized, threatening human
lives immensely. The increase in population and high demand for food has
resulted in the release of various contaminants into the environment. These
contaminants eventually enter the food chain. Edible plants are the major
source of diet, and their contamination with toxic metals may result in
disastrous health hazards. Heavy metals affect human health directly and/or
indirectly; one of the indirect effects is the change in plant nutritional
values, changes such as, insufficient production of chlorophyll on the leaves
of plants giving rise to yellow leaves (chlorosis), stunted growth,
deficiencies in the formation of grains and maturity, root formation, etc.
(Khan et al., 2015).
Heavy
metals are important constituents for plants and humans but only in small
amount. Some micronutrients or trace elements may also be toxic to both animals
and plants at high concentrations; such as copper (Cu), chromium (Cr), fluorine
(F), molybdenum (Mo), nickel (Ni), selenium (Se) or zinc (Zn). Other trace
elements such as arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) are
toxic even at small concentrations. They are known to be persistent in the
environment as they are neither removed by normal cropping nor easily leached
by rain water (Enenche et al., 2016).
Plant
species growing on metal contaminated soil are exposed to contamination by
absorption and translocation processes. The roots of the plant species absorb
metals from soil solution and translocate the metals to the stems and leaves.
This process results to bioaccumulation of metals in the plant tissues (Amusan et al., 2005), depending on the type of
metal, plant species and plant part (Juste and Mench, 1992).
According
to Patel et al. (2015), “Polycyclic
aromatic hydrocarbons (PAHs) are a large group of chemical compounds, with a
similar structure made up of two or more joined aromatic carbon rings”. The
compounds are formed by combustion of fuels, biomass and waste mate rials. Polycyclic aromatic compounds are
known to be carcinogenic and mutagenic compounds, causing irreversible changes
in the structure and functioning of living organisms (Patel et al., 2015). Some
PAHs are at the same time persistent, bioaccumulative and toxic for humans and
other organisms. Persistence means that the substances are not easily broken down
hence remain in the environment for a long time. Bioaccumulative chemicals
accumulate in organisms, including the human body. Substances having these
three characteristics (persistent, toxic and bioaccumulative) show a certain
level of concern under an environmental aspect. PAHs enter the atmosphere by binding
to dust and soot particles. Due to their persistence, they can be transported
over long distances. Dusts eventually return to the earth’s surface via rain,
fog, or snow and are deposited on soil, plants, as well as surface waters
(Quiroz et al., 2010).
Studies have been carried
out on metal waste generation, movement and dumping in terms of poverty
alleviation (Magaji and Dakye, 2011), quality of work life of metal waste scavengers
(Engler et al., 2009), recovering and
recycling of metal wastes (USGS, 2002; Norgate et al., 2007; Onwughara et
al., 2010). Research also shows that there is paucity of data on metals and
PAHs contamination in soil and their accumulation in plants at metal waste
dumpsites in Umuahia. This study,
therefore, attempts to fill this gap by assessing the concentrations of selected
metals and Polycyclic aromatic hydrocarbons in soil and cassava plant at the
major metal waste dumpsite in Ohiya mechanic village, Umuahia South, Abia
state, Nigeria. This research was necessary to ascertain the level of
contamination of heavy metals and Polycyclic Aromatic hydrocarbons in soil and
cassava plant.
1.2 STATEMENT OF PROBLEM
Due to the global growing
campaign for recovering, reusing and recycling of solid wastes such as metal
wastes, there has been an increase in the above mentioned processes of waste
management. These environmental management processes have helped to manage the
environment, provide source of income to skilled and unskilled individuals
(Adebola, 2006; Nzeadibe, 2009), improve the economy (Papp, 2001). However, the
methods used in the the recovering of reusable or recyclable materials has on
the other hand contributed to the contamination of the environment (soil, air,
water, plants, animal and humans). During the recovering of metals wastes,
waste scavengers are exposed to health hazards (Nzeadibe, 2009). Metal wastes
are collected from different parts of a region (homes, MSW, construction site,
landfills, etc) and assembled at a provided site for the purpose of recovering
useful components of the metal waste, thereafter they are moved to the
recycling facility. The soil and other surrounding environmental media at the
host site for salvaged metals may be exposed to contaminants. Air quality
becomes threatened by air pollutants, water bodies are contaminated by
leachates via run-off (Enenche et al., 2016). Plants
growing within the affected environment may take up metals via the roots (Amusan
et al., 2005). Furthermore, human beings who come in contact with the
contaminated soil and who depend on the contaminated plants for food may be
exposed to health hazards (Kim et al.,
2013). Animals which feed on the contaminated plants will absorb the metals and
PAHs into their system, and further transferred to humans who feed on them.
This process results to bioaccumulation (uptake from the ambient environment)
and biomagnification (uptake along the food chain) (Chaphekar,
1991).
The issue of the
contamination of the environment in Umuahia via the activities involved in
recovering reusable and recyclable metals wastes at the metal wastes dumpsite
may be a call for concern, hence the need for this study.
1.3 SCOPE OF THE STUDY
The study focused mainly
on determining the level of heavy metal and Polycyclic Aromatic hydrocarbons
concentrations in soil and cassava plant (Manihot
esculenta) (Root, stem and leaves), sampled within the scrap metals
dumpsite at Ohiya mechanic village in Umuahia South Local Government Area of
Abia State Nigeria.
1.4
AIM
AND OBJECTIVES OF THE STUDY
The
aim of the study was to assess the heavy metal concentration (Pb, Cd, Cr, Cu)
and Polycyclic Aromatic Hydrocarbons (PAHs) in soil and their accumulation in Manihot esculenta at the scrap metal
dumpsite in Ohiya mechanic village, Umuahia South Local Government Area. The
following specific objectives were to assess:
i.
The physic-chemical properties (pH,
electrical conductivity and organic matter) of soil at the study area
ii.
The macro elements (Zn, Ca, Na, K) in the soil
and Manihot esculenta at the study
area
iii.
Heavy metals (Cr, Cu, Pb, Cd) in the soil
and Manihot esculenta at the study
area
iv.
Some Polycyclic Aromatic Hydrocarbons in
the soil and Manihot esculenta at the
study area
1.5 SIGNIFICANCE OF THE STUDY
The
study provides baseline data on the levels of selected metals, chromium (Cr),
cadmium (Cd), lead (Pb) and copper (Cu); macro elements, zinc (Zn), calcium
(Ca), potassium (K) and sodium (Na); and polycyclic aromatic hydrocarbons (PAHs),
in soil and Manihot esculenta parts at
the scrap metal dumpsite in Ohiya mechanic village, Umuahia South, Abia State.
The information will provide basis for further studies or monitoring of their
concentrations in soil and plants within the study area.
The findings will help to
expose the level of metals and PAHs contamination in soil at the site and the
potential threats of heavy metal uptake and PAHs contamination on plant growing
around the study area. This will awaken the consciousness of people who depend
on plants growing around the study site for food. Also, findings from this study
will be a good working tool for the Ministry of Environment and other environmental
agencies in Abia State.
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