Sources of heavy metals in vegetables in Cape Town, and possible methods of remediation

270 Pages·2012·5.85 MB·English

SOURCES OF HEAVY METALS IN VEGETABLES IN CAPE TOWN,
AND POSSIBLE METHODS OF REM  EDIATION

MARŸKE MEERKOTTER

A thesis submitted in partial fulfilment of the requirements for the degree of Doctor
Philosophiae in the Department of Biodiversity and Conservation Biology, University of the
Western Cape

Supervisor: Prof LM Raitt (University of the Western Cape)
Co-supervisor: Prof L Brendonck (Katholieke Universiteit Leuven)

February 2012
SOURCES OF HEAVY METALS IN VEGETABLES IN CAPE TOWN,
AND POSSIBLE METHODS OF REM  EDIATION

MARŸKE MEERKOTTER

KEY WORDS
Cadmium
Lead
Zinc
Agricultural resources
Crop quality
Mitigation/remediation methods
Triple super phosphate fertilizer
EDTA
Vegetable farming practices
Pollution sources

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ABSTRACT

SOURCES OF HEAVY METALS IN VEGETABLES IN CAPE TOWN, AND

POSSIBLE METHODS OF REMEDIATION 
M. Meerkotter  
PhD thesis, Department of Biodiversity and Conservation Biology, University of the Western
Cape

Cape Town includes two vegetable farming areas within the city limits, the
Joostenbergvlakte/
Kraaifontein area and the Philippi area. Both areas supply produce to local markets and
further afield. Sporadically, high levels of cadmium, copper, lead and zinc have been
found to occur in some of the soils, irrigation water resources and crops. To find the
sources of specifically Cd, Pb and Zn to these agricultural systems, extensive analysis of
several heavy metals in inputs such as fertilizers, agrochemicals and supplementary
water resources to these farming areas was undertaken. Heavy metal concentrations in
soils, irrigation water resources and crops were also determined. Two mitigation
techniques that could be used to remediate Cd, Pb and Zn contamination were
investigated. The first mitigation method included immobilization of heavy metals as
phosphate complexes by using a triple super phosphate fertilizer, while the second
method involved mobilisation and thus leaching of heavy metals away from plant roots
using EDTA. These mitigation methods were tested in a pot experiment using cabbage
as the experimental crop and soil from these areas as growth medium. A survey of
common farming practices in these two areas and farmers‟ willingness to use
remediation methods was conducted. The results in general indicated that crops from
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these two areas were fit for human consumption and that raw (unprocessed) cattle
manure and chicken manure were the greatest sources of heavy metals in both farming

areas. It was found that the use of EDTA led to elevated levels of Cd, Pb and Zn in

cabbage, while the use of triple super phos phate at a low concentration contributed to
limiting the uptake of Cd, Pb and Zn, but o nly minimally. Most farmers are willing to
apply remediation methods but only when they have been proven necessary. In general,
the same farming practices occurred in both areas. Farmers from the Philippi area tended
to rely more heavily on subterranean water resources. It became clear that unprocessed
manures should be used with caution and that more appropriate heavy metal remediation
methods should be sought.

February 2012

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DECLARATION

I declare that: “Sources of heavy metals in vegetables in Cape Town, and possible methods of

remediation” is my own work, that it has n ot been submitted before for any degree or
examination in any other university, and that a ll the sources I have used or quoted have been
indicated and acknowledged as complete references.

Marÿke Meerkotter

February 2012

Signed: …………………………

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ACKNOWLEDGEMENTS

Allow me to thank the following people for their continuous support and encouragement, as

well as technical support and advice as I worke d on this thesis:

From the Biodiversity and Conservation Biology Department:
Prof. L Raitt, Prof. L Brendonck, Mr. L Cyster and Mrs. L van Heerden

Friends and family:
Miss. C Biggs, Mr. M Malan, Mrs. M Augustus, my parents and family

I give God the glory for enabling me to complete this thesis in Jesus Christ, my Lord and
strength.

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CONTENTS
Title Page 1

Key words 2

Abstract   3
Declaration   5
Acknowledgements 6

CHAPTER 1: INTRODUCTION TO THE STUDY ‘SOURCES OF HEAVY METALS
IN VEGETABLES IN CAPE TOWN, AND POSSIBBLE METHODS OF
REMEDIATION’ AND A LITTERATURE REVIEW 16
1.1. Aims of the research 16
1.2. Background to the vegetable farming areas of Cape Town 18
1.3. Literature review on global examples of heavy metal contamination on vegetable farms
and methods of remediation 23
1.4. The research problem and hypotheses for the study „Sources of heavy metals in
vegetables in Cape Town and possible methods of remediation‟ 33
1.5. Delimitation of the research 35
1.6. Overview of the research methodology 36
1.6.1. Analysis of various inputs to farms as possible sources of heavy metals 37
1.6.2. Assessment of mitigation techniques (Pot experiment) 37
1.6.3. Farming practice survey 38
1.7. Outline of chapters in this thesis 39
1.8. References 40

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CHAPTER 2: A SURVEY OF HEAVY METAL CONTENT IN WATER, SOIL AND
VEGETABLES PRODUCED IN THE AGRICULTURAL AREAS OF PHILIPPI,

KRAAIFONTEIN AND JOOSTENBERGVLAKTE AND POSSIBLE SOURCES OF

HEAVY METALS   54
2.1. Introduction   54
2.2. Materials and Methods 64
2.3. Results 71
2.4. Discussion 90
2.5. Conclusion 102
2.6. References 104

CHAPTER 3: PHOSPHATE FERTILIZER AND EDTA TREATMENTS AS MEANS
OF MITIGATING THE UPTAKE OF CADMIUM, LEAD AND ZINC BY CABBAGE
GROWN ON SOIL FROM CAPE TOWN’S AGRICULTURAL AREAS 111
3.1. Introduction 111
3.2. Materials and Methods 115
3.2.1. Preparation of the growth medium 116
3.2.2. Heavy metal altering of the growth medium 117
3.2.3. Addition of soil amendments 119
3.2.4. Soil incubation period 122
3.2.5. Planting of cabbage seedlings 122
3.2.6. Harvesting of cabbage 122
3.2.7. Chemical analysis of samples 123
3.3. Results 124
3.4. Discussion 156
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3.5. Conclusion 171
3.6. References 173

CHAPTER 4: SURVEY OF AGRICULTUR  AL PRACTICES IN CAPE TOWN’S
VEGETABLE FARMING AREAS   184
4.1. Introduction 184
4.2. Materials and Methods 199
4.2.1. Survey ethics statement 199
4.2.2. Survey method 200
4.2.3. Survey questionnaire 202
4.3. Results 204
4.4. Discussion 222
4.5. Conclusion 229
4.6. References 231

CHAPTER 5: GENERAL DISCUSSION AND CONCLUSION: WHAT IS THE
HEAVY METAL SITUATION ON CAPE TOWN’S VEGETABLE FARMS? 237
5.1. Introduction 237
5.2. Analysis of inputs to the farms as possible heavy metal sources 238
5.3. Assessment of mitigation techniques (Pot experiment) 242
5.4. Farming practice survey 244
5.5. Final conclusion 247
5.6. References 248

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LIST OF TABLES AND FIGURES
CHAPTER 1

Table 1: Human body systems affected adversely by excess amounts of cadmium, copper,

lead and/or zinc intake   24

CHAPTER 2
Table 2.1: Comparison of samples collected from the Joostenbergvlakte/Kraaifontein and
Philippi agricultural areas 66
Table 2.2: Mean heavy metal concentrations in samples collected from irrigation water
holding dams measured in mg.l-1, from the farming areas of Joostenbergvlakte, Kraaifontein
(J/K) and Philippi (Plp). 73
Table 2.3: Mean heavy metal concentrations in supplementary water resources measured in
mg.l-1, for samples collected in the summer of 2006 in the farming areas of
Joostenbergvlakte, Kraaifontein (J/K) and Philippi (Plp). 75
Table 2.4: Mean heavy metal concentrations in mg.kg-1 for soils planted with cabbage, from
Joostenbergvlakte/Kraaifontein and Philippi farms. 76
Table 2.5: Mean heavy metal concentrations in mg.kg-1 for soils planted with carrots, from
Joostenbergvlakte/Kraaifontein and Philippi farms. 77
Table 2.6: Mean heavy metal concentrations in mg.kg-1 for soils planted with lettuce, from
the Joostenbergvlakte/Kraaifontein and Philippi farms. 78
Table 2.7: Mean heavy metal concentrations in mg.kg-1 in crop sprays, manures and soils
from Joostenbergvlakte/Kraaifontein and Philippi farms. 80
Table 2.8: List of common agrochemicals used on Cape Town‟s agricultural soils and their
heavy metal content 83
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