Description
CONTENT PAGE
Title Page…………………………………………………………………………….i
Certification ………………………………………………………………………………………………….
ii
Dedication ……………………………………………………………………………………………………
iii
Acknowledgement ………………………………………………………………………………………..
iv
Table of Contents ………………………………………………………………………………………….
v
List of Figures …………………………………………………………………………………………….
viii
List of Tables………………………………………………………………………………………………..
ix
Abstract ………………………………………………………………………………………………………..
x
Chapter One
1.0 Introduction ………………………………………………………………………………………………
1
1.1 Justification ………………………………………………………………………………………………
3
1.2 Aim and Objectives ……………………………………………………………………………………
4
Chapter Two
2.0 Literature Review ………………………………………………………………………………………
5
2.1 Ecosystem…………………………………………………………………………………………………
5
2.2 Environmental Pollution …………………………………………………………………………….
6
2.2.1 Types of Environmental Pollution …………………………………………………………….
7
2.2.1.1 Air Pollution ………………………………………………………………………………………..
7
2.2.1.2 Water Pollution ……………………………………………………………………………………
7
2.2.1.3 Land/Solid Waste Pollution …………………………………………………………………..
8
2.3 Heavy Metals…………………………………………………………………………………………….
8
2.4 Heavy Metal Poisoning ………………………………………………………………………………
9
2.4.1 Routes of Heavy Metal Exposure ……………………………………………………………
10
2.4.2 Classifications of Heavy Metal Exposure …………………………………………………
10
2.4.3 Mechanism of Action of Heavy Metals ……………………………………………………
11
2.5 Heavy Metals Contamination of Soils ………………………………………………………..
11
2.5.1 Sources of Heavy Metal Contamination of Soils ……………………………………….
12
2.5.1.1 Fertilizer ……………………………………………………………………………………………
12
2.5.1.2 Pesticides …………………………………………………………………………………………..
12
2.5.1.3 Biosolids and Manures ………………………………………………………………………..
13
2.5.1.4 Wastewater ………………………………………………………………………………………..
14
2.5.1.5 Metal Mining and Milling Processes and Industrial Wastes …………………….
14
2.5.1.6 Air-Borne Sources ………………………………………………………………………………
15
2.6 Heavy Metal Contamination of Vegetables …………………………………………………
15
2.7 Selected Heavy Metals ……………………………………………………………………………..
16
2.7.1 Zinc (Zn) ……………………………………………………………………………………………..
16
2.7.2 Chromium (Cr) ……………………………………………………………………………………..
17
2.7.3 Cobalt (Co) …………………………………………………………………………………………..
18
2.7.4 Lead (Pb) ……………………………………………………………………………………………..
18
2.7.5 Cadmium (Cd) ………………………………………………………………………………………
19
2.7.6 Copper (Cu) ………………………………………………………………………………………….
20
2.7.7 Iron (Fe) ……………………………………………………………………………………………….
21
2.7.8 Mercury (Hg) ……………………………………………………………………………………….
22
2.7.9 Manganese ……………………………………………………………………………………………
23
2.7.10 Aluminium …………………………………………………………………………………………
23
2.7.11 Titanium …………………………………………………………………………………………….
24
2.7.12 Strontium ……………………………………………………………………………………………
25
2.8 Selected Vegetables …………………………………………………………………………………
26
2.8.1 Fluted Pumpkin (Telfairia Occidentalis) ………………………………………………….
26
2.8.2 African Spinach (Amaranthus Hybridus) …………………………………………………
27
2.8.3 Waterleaf (Talinum Triangulare) …………………………………………………………….
27
2.9 Remediation of Heavy Metal Contamination ………………………………………………
28
2.9.1 Immobilization Techniques …………………………………………………………………….
29
2.9.2 Soil Washing ………………………………………………………………………………………..
30
2.9.3 Phytoremediation ………………………………………………………………………………….
31
2.10 X-Ray Fluorescence Technique ……………………………………………………………….
31
Chapter Three
3.0 Materials and Methods ……………………………………………………………………………..
33
3.1 Materials …………………………………………………………………………………………………
33
3.1.1 Study Locations …………………………………………………………………………………….
33
3.1.2 Vegetable Samples ………………………………………………………………………………..
35
3.1.3 Soil Samples …………………………………………………………………………………………
35
3.2 Methods ………………………………………………………………………………………………….
35
3.2.1 Preparation of Vegetable Samples …………………………………………………………..
35
3.2.2 Preparation of Soil Samples ……………………………………………………………………
35
3.2.3 Determination of Heavy Metals ………………………………………………………………
36
Chapter Four
4.0 Results and Discussion ……………………………………………………………………………..
37
4.1 Results ……………………………………………………………………………………………………
37
4.2 Discussion ………………………………………………………………………………………………
42
4.2.1 Heavy Metal Concentrations …………………………………………………………………..
42
4.2.1.1 Chromium …………………………………………………………………………………………
43
4.2.1.2 Zinc …………………………………………………………………………………………………..
44
4.2.1.3 Manganese …………………………………………………………………………………………
45
4.2.1.4 Iron …………………………………………………………………………………………………..
46
4.2.1.5 Titanium ……………………………………………………………………………………………
47
4.2.1.6 Strontium …………………………………………………………………………………………..
47
4.2.1.7 Aluminium …………………………………………………………………………………………
48
4.2.2 Transfer Factors ……………………………………………………………………………………
48
Chapter Five
5.0 Conclusion and Recommendations …………………………………………………………….
50
5.1 Conclusion ………………………………………………………………………………………………
50
5.2 Recommendations ……………………………………………………………………………………
51
References …………………………………………………………………………………………………..
52 LIST OF FIGURES
2.1: Typical fluted pumpkin leaves (Telfairia occidentalis) ………………………………….
26
2.2: Typical African spinach Spinach (Amaranthus hybridus) ………………………………
27
2.3: Typical waterleaf (Talimun triangulare) ……………………………………………………..
28
2.4: Schematic Diagram of X-ray Fluorescence (XRF) Spectrometer…………….32
2.5: Typical X-ray Fluorescence (XRF) Spectrometer …………………………………………
32
3.1: Map of Ondo State showing Owo Local Government Area ……………………………
34
3.2: Map of Edo State showing Etsako-West Local Government Area ………………….
34 4.1: Bioavailability of heavy metals in the soil samples
………………………………………. 40
4.2: Bioaccumulation of heavy metals in the vegetable samples obtained from St.
Louis Farm …………………………………………………………………………………………….. 40
4.3: Bioaccumulation of heavy metals in the vegetable samples obtained from Osuma
Layout Farm …………………………………………………………………………………………… 41
4.4: Bioaccumulation of heavy metals in the vegetable samples obtained from Water-
Board Farm…………………………………………………………………………………………….. 41
4.5: Bioaccumulation of heavy metals in the vegetable samples obtained from
Iyerekhu Farm …………………………………………………………………………………………
42 LIST OF TABLES
4.1: Heavy metals of soil and vegetable samples from Saint Louis, Owo Local
Government Area ………………………………………………………………………………….. 37
4.2: Heavy metals of soil and vegetable samples from Osuma Layout, Owo Local
Government Area ………………………………………………………………………………….. 37
4.3: Heavy metals of soil and vegetable samples from Water-Board, Etsako-West
Local Government Area …………………………………………………………………………. 38
4.4: Heavy metals of soil and vegetable samples from Iyerekhu, Etsako-West Local
Government Area ………………………………………………………………………………….. 38
4.5: Transfer factor of the vegetable samples relative to their soil sources ……………
39
ABSTRACT
The soils and leaves of fluted pumpkin (Telfairia occidentalis), African
spinach, "Green" (Amaranthus hybridus) and water leaf (Talinum triangulare) were
collected as randomly composite samples from four (4) different study locations of
two (2) each from Owo Local Government Area and Etsako-West Local
Government Area. The samples were examined for heavy metal concentrations,
using X-ray fluorescence (XRF) technique. Chromium (Cr), zinc (Zn), manganese
(Mn), iron (Fe), titanium (Ti), strontium (Sr) and aluminium (Al) of both soil and
vegetable samples were detected at higher proportions than the permissible limits of
WHO/FAO and EU for soils and plants. Exceptions were obtained for Cr in SL 3
(Talinum triangulare from St. Louis farm), and Zn in WB (soil from Water-Board
farm), IY (soil from Iyerekhu farm) and IY 3 (Talinum triangulare from Iyerekhu
farm). Toxic heavy metals, such as nickel (Ni), lead (Pb), cobalt (Co), cadmium (Cd)
and copper (Cu) were not detected in both soil and vegetable samples. Generally, the
concentrations of the metals in the soil and vegetable samples followed the same
decreasing order: Al>Fe>Ti>Mn>Sr>Cr>Zn. The Cr concentrations varied from
54.72 to 191.52 mg/kg among the soil samples and from 0.00 to 280.44 mg/kg
among the vegetable samples. The concentrations of Zn were higher in the vegetable
samples than the soil samples, ranging from 0.00 to 184.74 mg/kg for soil samples
and from 0.00 to 795.17 mg/kg for vegetable samples. Generally, Mn concentrations
were higher in the tissues of the vegetable samples than in the soil samples except
for slight deviations observed in SL 1 (Telfairia occidentalis from St. Louis farm),
SL 2 (Amaranthum hybridus from St. Louis farm) and OL 2 (Amaranthum hybridus
from Osuma Layout farm). Iron (Fe) was the most abundant nutritionally essential
metal in both soil and vegetable samples, ranging from 22089.07 to 64282.61 mg/kg
in the soil samples and 2354.96 to 29950.57 mg/kg in the vegetable samples.
Titanium (Ti) concentrations were more predominant in the soil samples than the
vegetable samples. The peak (719.10 mg/kg) and least (118.44 mg/kg) Sr
concentrations were observed in the OL (Osuma Layout farm) and WB (WaterBoard
farm) soils respectively, which bioaccumulated, in the same trend, in their
corresponding Telfairia occidentalis samples. The Al concentrations ranged from
48333.29 – 75021.09 mg/kg in the soil samples and 30984.10 – 63407.34 mg/kg in
the vegetable samples. All the vegetable samples had significant differences in the
transfer factors of metals relative to the availability of same metals in the soil,
ranging from 0.00 to 9.47. Manganese (Mn) had the peak transfer factor (9.47) in
WB 3 (Talinum triangulare from Water-Board farm) followed by 9.33 observed in
WB 1 (Telfairia occidentalis from Water-Board farm). The vegetable samples were
recommended for possible application in phytoremediation of polluted soils.
CHAPTER ONE
1.0 INTRODUCTION
Heavy metals are generally referred to as those metals which possess a
specific density of more than 5 g/cm 3 and adversely affect the environment and
living organisms (Järup, 2003). They, without doubt, are important constituents for
plants and humans, when present only in small amount. Some micronutrient
elements may also be toxic to both animals and plants at high concentrations. For
instance, 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 (Divrikli et
al., 2006). Heavy metals, being persistent and non-biodegradable, can neither be
removed by normal cropping nor easily leached by rain water (Khadeeja et al.,
2013). They might be transported from soil to ground waters or may be taken up by
plants, including agricultural crops. For this reason, the knowledge of metal plant
interactions is also important for the safety of the environment (Divrikli et al., 2006).
There has been increasing interest in determining heavy metal levels in public
food supplied. However, their concentration in bio-available form is not necessarily
proportional to the total concentration of the metal (Opaluwa et al., 2012;
Nwachukwu et al., 2010).
The quality of ecosystem becomes altered, when heavy metals find their way,
somehow, into it through human and natural activities. These activities are one of the
most pressing concerns of urbanization in developing countries like Nigeria, which
result in the problem of solid, liquid and toxic waste management. Such waste may
be toxic or radioactive (Onibokun and Kumuyi, 1996; UNDP, 2006). Such waste
management problems include heaps of uncontrolled garbage, roadsides littered with
refuse, streams blocked with rubbish, prevalence of automobile workshops and
service stations, inappropriately disposed toxic waste and disposal sites that
constitute a health hazard to residential areas (Adewole and Uchegbu, 2005; Rotich
et al., 2006; Ebong et al., 2008).
Occurrence of uncontrolled urban sewage farming is a common site in African
cities which exposes consumers of such produce to poisoning from heavy metals
(Ebong et al., 2008). Open dumps are a source of various environmental and health
hazards. The decomposition of organic materials produces methane, which may
cause explosions and produce leachates, which pollute surface and ground water. It
ruins the aesthetic quality of the land (Oyelola et al., 2009). Automobile wastes
include solvents, paints, hydraulic fluids, lubricants and stripped oil sludge; all
results of activities such as battery charging, welding and soldering, automobile body
works engine servicing and combustion processes (Adewole and Uchegbu, 2005;
Utang et al., 2013).
Soil is the most important component of the environment, but it is the most
undervalued, misused and abused one of the earth‟s resources (Gokulakrishnan and
Balamurugan, 2010). Soil contamination has become a serious problem in all
industrialized areas of the country. Soil is equally regarded as the ultimate sink for
the pollutants discharged into the environment (Shokoohi et al., 2009).
Most plants and animals depend on soil as a growth substrate for their
sustained growth and development. In many instances the sustenance of life in the
soil matrix is adversely affected by the presence of deleterious substances or
contaminants. The entry of the organic and inorganic form of contaminants results
from disposal of industrial effluents (Gowd et al., 2010). The source of the organic
and inorganic elements of the soil of contaminated area was mainly from unmindful
release of untreated effluent on the ground (Shetty and Rajkumar, 2009). The
contamination of soils with heavy metals or micronutrients in phytotoxic
concentrations generates adverse effects not only on plants but also poses risks to
human health (Murugesan et al., 2008).
Afterwards, the consumption of contaminated vegetables constitutes an
important route of heavy metal exposure to animals and humans (Sajjad et al., 2009;
Tsafe et al., 2012). Abandoned waste dumpsites have been used extensively as fertile
grounds for cultivating vegetables, though research has indicated that the vegetables
are capable of accumulating high levels of heavy metals from contaminated and
polluted soils (Cobb et al., 2000; Benson and Ebong, 2005).
1.1 JUSTIFICATION
World Health Organization (WHO) estimates that about a quarter of the
diseases facing mankind today occur due to prolonged exposure to environmental
pollution (Prüss-Üstün and Corvalán, 2006; Kimani, 2007).
Heavy metal pollution of the environment, even at low levels, and their
resulting long-term cumulative health effects are among the leading health concerns
all over the world. Heavy metals are known as non-biodegradable, and persist for
long durations in aquatic as well as terrestrial environments. They might be
transported from soil to ground waters or may be taken up by plants, including
agricultural crops (Oluyemi et al., 2008).
It is well known that high industrial and traffic activities contribute high levels
of heavy metals to the environments. Plants grown around such areas are likely to
absorb these metals either from the soil through the roots or from atmospheric
contaminants through the leaves (Fifield and Haina, 1997).
The soil contamination by heavy metals can transfer to food and ultimately to
consumers. For instance, plants accumulate heavy metals from contaminated soil
without physical changes or visible indication, which could cause a potential risk for
human and animal (Osma et al., 2012).
Based on its persistent and cumulative nature, as well as the probability of
potential toxicity effects of heavy metals as a result of consumption of leafy
vegetables and fruits, there is a need to test and analyse this food item to ensure that
the levels of these trace elements meet the agreed international requirements.
It is on this basis that this study was designed to determine the concentrations
of heavy metals in both soils and leafy vegetables from selected vegetable
plantations in Nigeria.
1.2 AIM AND OBJECTIVES
The aim of this project work is to ascertain the level of heavy metal
contaminations in the soils and vegetables of some selected vegetable plantations in
Owo and Edo Axes.
The objectives of this project work are to:
1. prepare soil samples from selected vegetable plantations;
2. prepare plant samples from selected vegetables, namely: fluted pumpkin
leaves (Telfairia occidentalis), African spinach, "Green" (Amaranthus
hybridus) and water leaf (Talinum triangulare);
3. determine the concentration levels of heavy metals in the soil obtained
from the plantations using x-ray fluorescence (XRF) spectrometer;
4. determine the concentration levels of heavy metals in the vegetable
samples obtained from the plantations using x-ray fluorescence (XRF)
spectrometer;
5. compare the levels of concentration of heavy metals in the soil and plant
samples obtained from the plantations; and
6. suggest the possible measures to manage the contamination to ensure
safety to humans and animals.