Potentially Toxic Elements in Food Crops Grown on Urban Waste Dump-Sites A Case Study of Wakaliga Dump-Site, Kampala City, Uganda.

ABSTRACT

This study aimed at investigating the seasonal variation in the levels of contamination in soils, food crops, and domestic spring water samples from Wakaliga dumpsite in Kampala. Potentially Toxic Elements (PTE) and physicochemical properties were analysed during the dry season (May-July 2017) and the wet season (September-November 2017) and the results compared to standard limits set by international and local agencies. The results obtained indicated that some of the elements were found in concentration levels within permissible limits, while others were above permissible set limits in the soil, crops and domestic (spring) water samples. Zinc maximum levels of 3.41±0.01 mg/kg and 3.3 1±0.04 mg/kg d.w. were found in dry-season picked spinach and sugarcane, respectively, while the lowest concentrations of 0.98±0.02 mg/kg d.w. were found in wet-season cocoyam. Copper was found to exist below permissible limits for all the crops, soil and water; concentrations of lead in spinach were found to be within a permissible limit 2.31±0.005 mg/kg d.w. while all the others were below the permissible limits. Negligible amounts of cadmium were found in all the samples. All the soil samples indicated results below permissible levels of toxic metals in the arable soils as indicated by ‘~ATHO (1996). The physiochemical parameters were all within acceptable limits for drinking water, as set by WHO and NEMA; Cadmium was not detected in the domestic water. The findings of this research indicated the presence of potentially toxic elements whose levels could be on the increase and found out that zinc concentrations were higher in both crops and soil for both the two harvesting seasons. This was followed by lead, which is attributable to the availability of discarded substances containing these elements in the environment. Proper waste management, control and disposal methods should be put in place to minimize exposure of toxic containing substances into the enviromrient.

TABLE OFCONTENTS

TITLE PAGE

APPROVAL

DECLARATION

DEDICATION

ACKNOWLEDGEMENTS

LIST OF ACROMNYS

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGUPj~S

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1 Background

1.2 Problem Statement 7

1.3 Objectives 7

1.3.1 General objective 7

1.3.2 Specific objectives 7

1.4 Scope 8

1.4.1 Content scope 8

1.4.2 Geographical Scope 8

1.4.3 Time Scope 9

1.5 Significance of the study 9

CHAPTER TWO 11

LITERATURE REVIEW 11

2.1 Introduction 11

2.2 Potentially Toxic Elements (PTEs) 13

2.2.1 Zinc 14

2.2.2 Occurrence of zinc 14

2.2.3 Uses of zinc 14

2.2.4 Zinc pollution 15

2.2.5 Zinc Toxicity 15

2.3 Cadmium ‘16

23.1 Occurances 16

2.3.2 Uses 16

2.3.3 Toxicity 17

2.3.4 Exposure 17

2.3.5 Copper 18

2.3.5.1 Occurances 18

2.3.5.2 Uses 18

2.3.5.3 Toxicity 19

2.4 Copper Exposure 19

2.4.1 Lead 19

2.4.2 Occurrence 20

2.4.3 Uses 20

2.4.4 Lead Toxicity 20

2.4.5 Effects ofpotentially toxic elements (PTEs) on the soil 21

2.4.6 Effects ofpotentially toxic elements (PTEs) on Plants 22

2.4.7 Factors that affect the rate of heavy metal up take by plants 23

2.4.8 Soils and Soil Texture 24

2.4.9 Spring water 26

2.5 Types of spring water 27

2.5.1 Flow of spring water 27

2.5.2 Classification of spring water 27

2.5.3 Spring water content 27

2.5.4 Uses of spring water 28

2.5.5 Sacred springs 28

2.6 The intolerable daily intake approach 29

2.6.1 Transfer factor (TF) 31

2.6.2 Contamination] pollution index 31

26.3 pH: Water dissociates by a very slight extent into H+ and OH- ions. It has been 32

2.6.4 Electrical Conductivity 32

2.6.5 Chemical Oxygen Demand .32

2.6.6 Total suspended solid 33

CHAPTER THREE 34

MATERIALS AND METHODS 34

3.1 Research Design 34

3.1.1 Chemical An~ilysis 35

3.1.2 Analytical procedure 35

3.1.3 pH of the water samples 36

3.1.4 Conductivity 36

3.1.5 Chemical oxygen demand (COD) 36

3.1.6 Total Suspended Solids (TSS) 36

3.2 Sampling in the wet land cultivation study sites 37

3.2.1 Soil sampling 38

3.2.2 Water sampling 38

3.2.3 Plant sampling and chemical Analysis 38

a) Sugar cane 38

b) Green vegetables(Spinach) 41

3.2.4 Soil sampling and chemical analysis 41

3.2.5 Water sampling and chemical Analysis 42

32.6 Potentially toxic element chemical analysis 43

3.2.7 Instrumentation 43

3.2.8 Quality control 46

3.2.9 Quality assurance 46

3.3 Statistical analysis 47

3.3.1 Ethical consideration 47

3.4 Limitations 47

CHAPTER FOUR 48

RESULTS AND DISCUSSION 48

4.1 Physiochemical parameters 48

4.1.1 Zinc (Zn) levels in wet and dry season spinach (Spinach) soil 50

4.1.2 Zinc (Zn) levels in wet and dry season (cocoyamn) soil 51

4.1.3 Zinc levels in wet and dry season (sugarcane) soil 51

4.1.4 Zinc levels in wet and dry season (maize) soil .52

4.1.5 Cu Levels in wet and dry season spinach (Dodoo) soil 52

4.1.6 Cu levels in wet and dry season (cocoyam) Soil 53

4.1.7 Copper levels in wet and dry season (sugarcane) soils 56

4.1.8 Copper in wet and dry season (maize) soils 57

4.1.9 Pb Levels in wet and dry season spinach (Spinach) soil 57

4.1.10 Pb level in wet and dry season (cocoyorn) soil 58

4.1.11 Lead levels in wet and dry season (sugar cane) soil 58

4.1.12 Lead levels in wet and dry season (maize)soil 59

4.1.13 Cadmium level in wet and dry Season Spinach (Spinach) soil 59

4.1.14 Cd level on wet and dry season (cocoyám) soil 59

4.1.15 Cd level on wet and dry season (sugare cane) soil 60

4.1.16 Cd Level in wet and dry season (maize) soil 60

4.1.17 Zinc level in wet and dry season spinach (Spinach) 61

4.1.18 Zinc level in wet and dry season cocoyam 61

4.1.19 Zinc levels in wet and dry season sugarcane 62

4.1.20 Zinc level in wet and dry season maize 63

4.2 Copper level in wet and dry season spinach (Spinach) 63

4.2.1 Copper level in wet and dry season cocoyam 64

4.2.2 Copper level in wet and dry season sugarcane 65

4.2.3 Copper level in wet and dry season maize 65

4.2.4 Lead levels iii wet and dry season spinach (Spinach) 66

4.2.5 Pb levels in wet and dry season cocoyarn 66

4.2.6 Pb level in Wet and Dry Season Sugarcane 67

4.2.7 Pb level in maize corn in dry and wet season 68

4.2.8 Cd levels in Spinach (Spinach) in dry and wet season 69

4.2.9 Cadmium levels in dry and wet seasons cocoyam 69

4.2.10 Cd level in sugarcane in wet and dry seasons 70

4.2.11 Cd levels in wet and dry season maize 71

4.2.12 General Discussion 73

CHAPTER FIVE .76

CONCLUSION AND RECOMMENDATIONS 76

5.1 Conclusions 76

5.1 Recommendations 77

REFERENCES 79