ABSTRACT
The levels of Cd, Zn, Mn, Cr and Pb were investigated in spinach plant irrigated with pond water using Atomic Absorption Spectroscopy. The physico-chemical parameters and the levels of the metals in the pond water samples were analyzed also. The temperature, salinity, conductivity and dissolved oxygen of the pond water were within permissible limits; however, the pH was slightly above the permissible limit. The levels of Cd, Mn and Cr 0.53, 0.94 and 5.22mg/L respectively (all through the months) in the pond water were higher than the US permissible limits for irrigation water (0.01, 0.2 and 0.1mg/L respectively), while the level of Zn was higher in the month of May only and Pb was higher in the months of May and April. The concentration of the metals in the soil samples from the three farmlands was generally of the order Mn>Cr>Pb>Zn>Cd and the mean concentrations of Cr (26.8mg/kg), Pb (20.3mg/kg) and Zn (12.7mg/kg) were below the WHO/FAO recommended maximum limits of (100, 85 and 200mg/kg) respectively except for Mn(91.9mg/kg) and Cd(1.7mg/kg) with allowable limits of 80 and 0.8mg/kg. The general trend of the metals in the spinach samples was observed to be Mn>Zn>Cr>Pb>Cd, the mean concentrations of Cd(1.52mg/kg), Cr (17.37mg/kg) and Pb (13.73mg/kg) were higher than the WHO/FAO allowable limits of 0.30mg/kg, 1.50mg/kg and 10.0mg/kg for Cd, Cr and Pb respectively. On the other hand, the mean concentrations of Zn (21.8mg/kg) and Mn (40.0mg/kg) were below the WHO permissible limits (50.0, 200.0mg/kg).The transfer factor of the metals from the soil to the spinach plant in farm 1 followed the order Zn>Cd>Cr>Mn>Pb while orders of Zn>Cd>Pb>Cr>Mn and Cd>Zn>Pb>Cr>Mn were observed for farms 2 and 3 respectively. Since the concentrations of the metals in the spinach (vegetable) were higher than permissible limits, consumption over time
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might present problems as the tendency for the soil to accumulate and transfer metals to the spinach cultivated increases which will subsequently get to man through the food chain.
TABLE OF CONTENTS
Title Page………………………………………. …………………………………………………i
Declaration…………………………………….. …………………………………………………iii
Certification…………………………………………………………………………………………iv
Dedication…………………………………………………………………………………………..v
Acknowledgments………………………………………………………………………………..vi
Abstract……………………………………………………………………………………………viii
Table of Contents…………………………………………………………………………………..x
List of Tables………………………………………………………………………………………xv
List of Figures……………………………………………………………………………………xvi
List of Plates……………………………………………………………………………………xvii
List of Acronyms………………………………………………………………………………xviii
List of Symbols…………………………………………………………………………………xviii
CHAPTER ONE: INTRODUCTION…………………………………………………. ……..1
1.1 Background ………………………………..…………………………………………………1
1.2 Statement of the Problem…………………………………………………………….2
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1.3 Justification ………………………………………………………………………………………………..3
1.4 Aim………………………………………………………………………………………..3
1.5 Objectives………………………………………………………………………………….4
1.6 Scope /Limitations of the Research…………………………………………………….…………….4
1.6.1 Scope………………………………………………………………………………………………………………………….4
1.6.2 Limitations………………………………………………………………………………………………………………….4
CHAPTER TWO: LITERATURE REVIEW…………………………………………………5
2.1 Heavy Metals and their occurrence……………………………………………………………………….5
2.2 Sources of heavy metal contamination……………………………….…………………………6
2.3 Methods for investigating heavy metals in environmental samples…………………………8
2.3.1 Atomic Absorption Spectroscopy (AAS)………………………………………………………………..9
2.4 Sample collection Technique………………………………………………………………………………11
2.4.1 Water Sample Collection Technique……………………………………………………….……11
2.4.2 Soil Sample Collection Technique………………………………………………………………….13
2.6 Previous researches on heavy metals contamination on environmental samples…..14
2.7 Allowable limits of heavy metals in various samples……………………………………….19
CHAPTER THREE: MATERIALS AND METHODS………………………………..22
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3.1 Description of the Study Area…………………………………..…………………………………22
3.2 Samples Collection, Preparation and Analysis……………………………………………27
3.2.1 Water Samples……………………..…………………………………………………………27
3.2.2 Soil Samples……………….……………………………………………………………..28
3.2.3 Vegetable Crop(Spinach) Sample…………………………….………………………………29
3.3 Preparation of stock solutions…………………………………………………………………….29
3.3.1 Stock solutions………………………………………………………………………………….29
3.3.2 Standard working solutions…………………………..………………………………………30
3.4. Determination of the metals…………………………………………………………………………………..30
3.4.1 Transfer factor……………………………………………………………………………………………………………31
3.5 Statistical Analysis…………………………………………………………………………………………………..32
CHAPTER FOUR RESULTS……………………………………………………….……………………33
4.1 Physico-chemical parameters of the pond water ………………………………….…………..34
4.2 Concentrations of Zn, Cd, Mn, Cr and Pb in the Pond Water Samples…………….35
4.3 Correlation of Physico-chemical Parameters with the Concentration of Metals in the Pond Water Samples……………………………………………………………………………………………..36
4.4 Correlation Coefficients of the Metals in the Water Samples………………………38
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4.5 Concentration of Heavy Metal in Soil Samples from Three Farmlands Irrigated with the Pond Water………………………………………………………………………………………….40
4.6 Correlation Coefficients of Heavy metals in the Soil Samples……………………………….41
4.7 Concentration of Heavy Metal in Spinach Samples Cultivated at the Farms………..43
4.8 Correlation Coefficients of Heavy Metals in the Spinach Samples ……………………..44
4.9 Soil/ Plant Metal Transfer Factor……………………………………………………………………….46
CHAPTER FIVE: DISCUSSION……………………………………………………………………………………50
5.1 Physico-chemical Parameters and Levels of Heavy Metals in the Pond Water (Irrigation Water)…………………………………………………………………………………………………..50
5.2 Levels of Heavy Metals in the Soil Samples……………………………………………..………54
5.3 Levels of the Metals in Edible Parts of Spinach ………………………………………………….57
5.4 Transfer Factors of Metals from Soil to Spinach………………………………………………….59
CHAPTER SIX: SUMMARY, CONCLUSION AND RECOMMENDATION………………..60
6.1 Summary and Conclusion………………………………………………………………………………….60
6.2 Conclusion………………………………………………………………………………………………………..61
6.3 Recommendation……………………………………………………………………………………………….62
REFERENCES…………………………………………………………………………64
APPENDIX……………………………………………………………………………..71
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CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND
Heavy metals are general terms, which apply to the group of metals and metalloids with atomic density greater than 4 g/cm3, (Huton and Symon, 1988; Nriagu, 1999; Garbarino et al., 1995; Hawkes, 1997). This classification includes transition metals and higher atomic weight metals of group III to V of the periodic table. Heavy metals include lead, cadmium, zinc, copper, Iron to mention a few (Duruibe et al., 2007).They are among the major contaminants of food supply and are considered as problem to the environment (Zaidi et al., 2005). Heavy metals contamination may occur due to irrigation with contaminated water, the addition of fertilizers, metal-based pesticides, industrial emissions, transportation, harvesting process and storage. Advancement in technology has lead to high levels of industrialization leading to the discharge of effluent bearing heavy metals into our environment. The various activities by man in recent years have increased the quantity and distribution of these heavy metals in the atmosphere, land and water bodies (Gustar, 1974).
Odoh and Kolawale (2011) observed that long term irrigation with heavy metals contaminated water may lead to the accumulation of heavy metals in agricultural soils and plants. Accumulation of heavy metals in the edible and non-edible parts of vegetables creates serious environmental concern (Vousta et al., 1996). Toxicity of heavy metals such as Cd, Pb, and Hg to man, other animals and organisms are well known as they are not required by man even in small amounts (Cui et al., 2004).Vegetables constitute an important part of the human diet since they contain carbohydrates, proteins, as well as vitamins and minerals. Heavy metals are one of a
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range of important types of contaminants that can be found on the surface and in the tissue of fresh vegetables (Bigdeli and Seilsepour, 2008). A number of elements, such as lead (Pb), cadmium (Cd), nickel (Ni), cobalt (Co), chromium (Cr), Copper (Cu) and Selenium (IV) (Se) can be harmful to plants and humans even at quite low concentrations (Bowen, 1979). Soil pollution is caused by misuse of the soil, such as poor agricultural practices, disposal of industrial and urban wastes (Buchaver, 1973). Soil is also polluted through application of chemical fertilizers (like phosphate and Zn fertilizers), and herbicides (Demirezen and Aksoy, 2004). Heavy metal accumulation of soils is of concern in agricultural production due to its adverse effects on food quality, crop growth (Ma et al., 1994; Msaky and Calvert, 1990; Fergusson, 1990) and environmental health.
1.2 STATEMENT OF THE PROBLEM
Kwari pond is the only source of water used to produce substantial amount of irrigated vegetables from the surrounding farmlands. This practice has been going on for decades. Concern over possible heavy metal contamination of the pond arises following the construction of Kaduna- Kano express highway, establishment of Maraba Clinic, block making industries, the springing-up of residential houses together with their dumpsites and domestic wastewater disposal points in the vicinity of the pond. The possible sources of heavy metal pollution to the pond include storm runoff of oil spillage from hollow block producing industries and a major highway (Kaduna – Kano highway) which discharge directly into the pond and untreated hospital waste generated from Maraba Clinic which may find its way into the pond from the clinic waste disposal points. Also, the location of dumpsites and household liquid waste disposal
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points within the pond catchments further increases the likelihood of heavy metals getting into the pond through leachate and storm runoff.
1.3 JUSTIFICATION
The presence of heavy metals in irrigation water constitutes a considerable health risk to the consumers of the farm products. For example, irrigation water that is chronically contaminated with dissolved cadmium (Cd) results in kidney damage and hypertension in the consumers. Exposure to lead (Pb) impacts negatively upon intelligence and behaviour of young children (Roy, 1999).Various regulatory bodies have specified the minimum quality of water required for irrigation, the constituents of soil for farming activities and allowable metal (s) concentration in food substances in order to ensure safe practice and also to safeguard human health. Hence, the need to investigate the quality of water from Kwari pond since it is being used for irrigation of surrounding farmlands in order to ensure compliance with world standard and regulations.
1.4 Aim
The aim of this research is to investigate the levels of Cr, Cd, Pb, Zn and Mn in water, soil and spinach samples from farmlands surrounding Kwari pond and to determine the physico-chemical parameters of water samples from Kwari Pond for its stability for irrigation since reports relating to the analyses of water, soil and vegetation around Kwari pond are not available in literature.
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1.5 OBJECTIVES
The objectives of this research are to:
(i) Assess the levels of Cr, Cd, Pb, Zn and Mn in the water, soil and spinach samples from and around Kwari pond;
(ii) Compare the levels of Cr, Cd, Pb, Zn and Mn in the samples with the regulatory standards
(iii) Determine the concentration of the relevant physico-chemical parameters for water quality requirement for irrigation; and
(iv) Make recommendations on the suitability or otherwise of Kwari pond water for irrigation farming.
1.6 SCOPE AND LIMITATIONS OF THE RESEARCH
1.6.1 SCOPE
The levels of heavy metals (Cr, Cd, Pb, Zn and Mn) would be determined in samples of water, soil and spinach using Atomic Absorption Spectrometry (AAS), the physico-chemical parameters of the pond. The results obtained would be compared with regulatory standard for each metal in irrigation water, soil and spinach samples
1.6.2 .LIMITATIONS
Only the listed metals would be assessed in the water, soil, and spinach samples. A total of 72 samples of water, soil and spinach are to be collected for the purpose of this investigation.
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