Assessment of Heavy Metal Concentrations in Food Crops from Pece Wet Land in Gulu Township, Northern Uganda

ABSTRACT

The present study is aimed at assessing the concentrations of heavy metals in food crops from pece wet land Gulu town ship. The study investigated heavy metals which include Copper, Zinc, Lead, and Cadmium in the soil and in selected crops which were banana fruit, sugar cane, coco yam and green vegetables (Amaranthus dubius). Metals are essential for maintaining human health throughout life however, at high concentrations they become poisonous. In Gulu town ship, waste disposal and management is still a challenge, wastes are dumped anywhere and when it rains they are taken by runoffs into pece wet land which is also used as a dumping site and on the other hand utilized for agriculture. Intake of heavy metal contaminated crops may pose a risk to the human health. Plants take in minerals from soil media or air through their roots or foliage. Understanding the distribution of some trace metals in some common food crops is important for establishing baseline concentrations from which anthropogenic effects can be measured. This will provide a basis for encouraging people to undertake proper care in the handling and disposal of solid wastes in addition to providing analytical data for further research. Soil and plant samples were collected from Pece wet land Gulu Township which was used as a dumping site and other samples from Katikamwe wet land in Bushenyi district which served as a control site. The samples from both sites were transported to the laboratory well prepared, soil parameters pH and electrical conductivity determined using a pH meter and a conductivity meter bridge respectively Samples were digested using acids and the concentrations of heavy metals Cadmium, Copper, Lead and Zinc determined using Atomic Absorption Spectrophotometer. The results showed that the soils in municipal waste dump sites are higher in heavy metals: Cd (1.35 ± 0.44)mg/kg, Cu (36.23 ± 4.04)mg/kg, Pb (46.23 ± 1.68) mg/kg and Zn (151.36 ± 2.22)mg/kg compared to those of the control site Cd (0.65 ± 0.0l)mg/kg, Cu (18.22 ± 3.22)mg/kg, Pb (12.56 + 3.36)mg/kg, and Zn (7.50 ± 2.76)mg/kg, suggesting possible mobility of metals from dumpsites to farmlands through leaching and runoffs. Soils from Gulu town ship had higher pH and EC values than the control site 6.35±0.07 compared to 5.47±0.09 and 167 ± 6 compared to 143 ± 3 respectively. xi Heavy metal concentrations in crops grown in these soils from both sites were determined and it was found out that heavy concentrations in crops from urban wet land were generally higher than those from the control site For both cases translocation factors from soils to crops were calculated accordingly. The translocation factors for the same metal and plant were significantly different from those of the control site suggesting their mobility from the dumpsites to the plants. . Despite the higher values of these metals in food crops from Pece wet land than those from the control site, its only lead and cadmium that exceeded the World Health Organization maximum permissible levels, and may pose serious human health risks. I would recommend that further studies be carried out in pece wet land to determine the levels of heavy metals in other food crops such as beans, cassava that were not looked at and also establish the relationship between the seasonal changes and the levels of heavy metals. Research should be done to quantify the levels of heavy metals present in the urban atmosphere To minimize heavy metal load in soils from dump sites, sorting of wastes at source, treatment and constitution of a proper dump site should be carried out. It was observed that heavy metal uptake depend on plant species and soil quality. Heavy metal pollution in the Pece wet land Gulu municipality may eventually enter the food chain There were relatively high levels of soil heavy metal contamination in the Gulu town ship (pece wet land) compared to the control site.

TABLE OF CONTENTS

DECLARATION A

DECLARATION B ii

DEDICATION

TABLE OF CONTENTS iv

LIST OF TABLES vii

LIST OF FIGURES viii

ACKNOWLEDGMENT ix

LIST OF ABBREVIATION / ACRONYMS x

CHAPTER ONE 1

1.0. INTRODUCTION 1

1.1 BACK GROUND TO THE STUDY 1

1.2 PROBLEM STATEMENT 7

1.3 OBJECTIVES 7

1.3.1 General objective of the study 7

1.3.2 Specific objectives 7

1.4 SIGNIFICANCE OF THE STUDY 8

1.5 SCOPE OF THE STUDY 8

1.6 JUSTIFICATION 8

CHAPTER TWO 9

2.0 LITERATURE REVIEW 9

2.1 INTRODUCTION 9

2.2 HEAVY METAL POLLUTANTS 10

2.2.1 Zinc 11

2.2.2 Cadmium 14

2.2.3 Copper 19

2.2.4 Lead 20

2.3 EFFECTS OF HEAVY METALS 21

2.3.1 On the Soil 21

2.3.2 OnP~~ts.22

2.3.3 On human health 23

2.4. FACTORS THAT AFFECT THE RATE OF HEAVY METAL UP TAKE BY PLANTS 24

2.5 BIOAVAILABILITY OF HEAVY METAL IN THE VEGETABLE GARDEN SOIL 25

CHAPTER THREE 27

3.0 MATERIALS AND METHODS 27

3.1. SAMPLING IN THE WET LAND CULTIVATION STUDY SITES 27

3.1.1 Soil sampling and chemical analysis 31

3.1.2 Plant sampling and chemical analysis 31

3.1.3 pH and conductivity measurements of the soil 34

3.2 HEAVY METAL ANALYSES 34

3.3 QUALITY CONTROL 35

3.4 STATISTICAL ANALYSIS 35

CHAPTER FOUR 36

4.0 RESULTS AND DISCUSSION 36

4.1 HEAVY METAL CONCERTRATION LEVELS IN RURAL AND URBAN WETLAND CULTIVATED SOILS 36

4.1.1 Zinc (Zn) concentrations in the soil 40

4.1.2 Cadmium (Cd) concentrations in the soil 40

4.1.3 Lead (Pb) concentrations in the soil 41

4.1.4 Copper (Cu) concentrations in the soil 41

4.1.5 Cadmium (Cd) concentrations in cocoyam conns 41

4.1.6 Cadmium (Cd) concentrations in Sugarcane stems 42

4.1.7 Cadmium (Cd) concentrations in green vegetable (Amaranthus dudius) 42

4.1.8 Cadmium (Cd) concentration in banana fruit 42

4.1 .9Zinc (Zn) concentration in cocoyam corms 43

4.1.10 Zinc (Zn) concentrations in sugarcane stems 43

4.1.11 Zinc (Zn) concentration levels in green vegetable (Amaranthus dudius) 44

4.1.12 Zinc (Zn) concentration levels in banana fruit 44

4.1.13 Lead (Pb) concentrations in Sugarcane stem 44

4.1.14 Lead (Pb) concentrations in cocoyam corms 45

4.1.15 Lead (Pb) concentrations in banana fruit 45

4.1.16 Lead (Pb) concentrations in green vegetable (Amaranthus dudius) 46

4.1.17 Copper (Cu) concentration levels in cocoyam corms 46

4.1.18 Copper (Cu) concentration in sugar cane stems 46

4.1.19 Copper (Cu) concentration in green vegetable (Amaranthus dudius) 47

4.1.20 Copper (Cu) concentrations in banana fruit 47

CHAPTER FIVE 51

5.0 CONCLUSION AND RECOMMENDATIONS 51

5.1 RECOMMENDATIONS 51

5.2 CONCLUSIONS 51

REFERENCES 52

APPENDICES 60

APPENDIX A: Heavy metal calibration curves 60

APPENDIX B: pH calibration graphs 61

Appendix C: correlations of food crops and soil samples 62