Assessment of Heavy Metals Concentration in Soil and Food Crops Growing Around Etelebou Flow Station in Bayelsa State, Nigeria

ABSTRACT

The concentration of Zinc, Lead, Copper, Iron and Chromium in soils, tuber crops (cassava, cocoyam and plantain fruit), within the vicinity of Etelebou flow station operated by Shell Petroleum Development Company (SPDC) were determined in order to assess the concentration level of heavy metals around the flow station. Twenty (20) soil samples were collected from the flow station environment, 50m apart. This consists of 10 top soils (0cm to 15cm) and 10 bottom soils (15cm to 30cm). Also Tuber crops cocoyam tuber (Xanthosoma mataffa), cassava tuber (Manihot esculenta), and plantain fruit (Musa sapientum) grown within the farmlands of the flow station were collected 3 samples each. Samples were prepared (Digested) and analyzed with the aid of Atomic absorption spectrophotometry technique. The result obtained showed the concentration level of 6.82mg/kg to 8.3mg/kg for Zn 0.64mg/kg to 2.3mg/kg for Pb, 1.81mg/kg to 3.3mg/kg for Cu, 16.02mg/kg to 27.10mg/kg for Fe and 0.1mg/kg to 0.81mg/kg for Cr for top soil sample. Bottom soil samples contain as much as 6.30mg/kg to 9.90mg/kg Zn, 0.91mg/kg to 3.33mg/kg Pb, 3.01mg/kg to 4.41mg/kg Cu, 18.50mg/kg to 27.10mg/kg Fe, 0.40mg/kg to 1.02mg/kg Cr. The levels reported on soil samples had an abundance ratio in the order of Fe, > Zn > Cu > Pb > Cr. The result of the concentration levels of heavy metals on food crops were found to be relatively high and gradually accumulating. Their accumulation in tuber crops were found to be higher than the background values (or controls). Furthermore, the concentration level in the soil samples were found to be higher compared to heavy metal concentration in tuber crops.

TABLE OF CONTENT

Title Page ..................................................................... i

Certification .................................................................. ii

Dedication .................................................................... iii


Acknowledgement..................................................... iv


Abstract ....................................................................... vi

Table of contents 

CHAPTER ONE: INTRODUCTION

1.0 Background Of Study ................................................ 1

1.1 Statement Of Problem............................................... 9

1.2 Aim And Objectives................................................... 11

1.3 Justification of study ................................................. 12

1.4 Scope Of Study ........................................................ 14

CHAPTER TWO: LITERATURE REVIEW

  1. 2.0  Pollution.................................................................. 16

  2. 2.1  Types Of Pollution..................................................... 16

  3. 2.2  Land Pollution .......................................................... 17

  4. 2.3  Air Pollution............................................................. 18

  5. 2.4  Water Pollution ........................................................ 20

  6. 2.5  Transport Of Environmental Contaminants In Onshore Flow Stations. ........................................................ 22

    2.6 Heavy Metals ........................................................... 27

    2.7 Sources Of Heavy Metals ........................................... 30

    2.8 Industrial Effluent..................................................... 31

    2.9  Geological Weathering.............................................. 31

    2.10  Domestic Effluent .................................................. 32

    2.11  Atmospheric Source ................................................ 32

    2.12  Mining Effluents...................................................... 33

    2.13  Petroleum Industry ................................................ 34

    2.14  Toxicity Of Heavy Metals.......................................... 35

    2.15  Effect Of Metal On Ecosystem ................................... 36

    2.16  Effect Of Metal On Man ............................................ 37

    2.17  Effect Of Metal On Animals ....................................... 37

    2.18  Effect Of Iron ......................................................... 38

    2.19  Effect Of Lead ........................................................ 40

    2.20  Effect Of Zinc ......................................................... 41

    2.21  Effect Of Copper ..................................................... 43

    2.22  Effect Of Chromium................................................. 45

    2.23  Atomic Absorption Spectrophotometer In Heavy Metals Pollution Studies. ................................... 47 

    CHAPTER THREE: RESEARCH METHODOLOGY

    3.0 Study Area .............................................................. 50

    3.1.1 Location And Site................................................... 52

    3.1.2 Climate And Vegetation .......................................... 52

    3.1.3 Population And Activities......................................... 54

    3.1.4 Infrastructures ...................................................... 54

    3.2 Research Design ...................................................... 54

    3.3 Sources Of Data ....................................................... 55

    3.3.1 Primary Data......................................................... 55

    3.3.2 Secondary Data..................................................... 55

    3.4 Data Collection Technique ......................................... 61

    3.4.1 Sampling ............................................................. 61 

    3.4.2 Sampling Period .................................................... 61

    3.4.3 Sampling Site Locations ......................................... 62

    3.5 Sample Collection Techniques..................................... 62

    3.5.1 Soil Samples ......................................................... 62

    3.5.2 Edible Plant Samples:............................................. 62

    3.6 Sample Handling And Treatment ............................... 63

    3.7 Sample Preservation And Treatment ........................... 63 

    3.8 Preparation Of Samples ............................................. 64

    3.8.1 Determination Of Metals In Soil Samples .................. 64

    3.8.2 Determination Of Metals In Edible Plant Samples ........ 65

    3.9 Preparation Of Standard Solution ............................... 66

    3.10 Instrumentation...................................................... 67

    3.10.1 Principal Of Atomic Absorption Spectroscopy ........... 67

    3.10.2 Atomic Absorption Spectroscopy Component ............ 68

    3.11 Laboratory Equipment And Experimental Materials ....... 69

    3.11.1 Apparatus And Equipments.................................... 69

    3.11.2 Reagents And Chemicals ....................................... 70 

    3.12 Analytical Method And Techniques ............................ 72

    3.12.1 Analytical Method................................................. 72

    3.12.2. Analytical Techniques .......................................... 78

    3.12.3 Choice Of Analytical Techniques ............................. 81 

    CHAPTER FOUR: RESULTS

    4.0 Results ................................................................... 82

    4.1 Results Analysis ....................................................... 89

    4.1.1 Zinc..................................................................... 89

    4.1.2 Lead .................................................................... 89

    4.1.3 Chromium ........................................................... 90 

    4.1.4 Iron .................................................................... 90

    4.1.5 Copper................................................................. 91 

    CHAPTER FIVE: DISCUSSION

    5.1 Discussion .............................................................. 107

    CHAPTER SIX: CONCLUSION AND RECOMMENDATION

    6.1 Conclusion ............................................................. 113

    6.2 Recommendation.................................................... 115 

    REFERENCE: ...................................................................118

    APPENDIX .................................................................. 122 


    LIST OF TABLES

    Table 3.1: Concentration Limits For Heavy Metals.............................. 56

    Table 3.2: Maximum Recommended Heavy Metal Concentration In Soil .......................................................................................... 57

    Table 3.3: Roles Of Trace Metals In Plants And and Animals ............... 59

    Table 3.4: Flame Absorption Data For Heavy Metal Under Study.......... 73

    Table 3.5: Flame Atomic Absorption Data For The Common Elements .. 74

    Table 4.1: Concentration Of Zn, Pb, Cu, Fe And Cr In Mg/Kg In Soil Samples, Where T Represent Topsoil And B Represent Bottom Soil. ................................................................................. 84

    Table 4.2: Concentration Of Zn, Pb, Cu, Fe And Cr In Cocoyam, Cassava And Plantain Fruit In Mg/Kg ............................................................ 86

    Table 4.3: Minimum And Maximum Concentration Of Heavy Metal In Food Crops In Mg/Kg ......................................................... 87 

     Table 4.4: T-Test And F95 Confidence Interval Of Zn, Pb, Cu, Fe, And Cr In Mg/Kg ......................................................................................... 92

    Table 4.5: Calculation Of Standard Deviation For Lead Pb In Top Soil .. 93

    Table 4.6: Calculation Of Standard Deviation For Lead Pb Bottom Soil....94 Table

    4.7: Descriptives..........................................................................................97

    Table 4.8: F-95 Confidence Interval For Mean Of Heavy Metal Concentration In Food Crops..............................................................................102

    Table 4.9: Discriptives Of Food Crops............................................... 103 


    LIST OF FIGURES

    Figure 3.1: Map of study area showing the impacted gas flaring sites and boundary...................................................................................... 51

    Figure 3.2: Schematic diagram showing the disposition of essential components of a single – beam atopmic absorption spectroscopic
    System ........................................................................................ 69

    Figure 4.1: Mean concentration (mg/kg) of Zn, Pb, Cu, Fe, and Cr in soil sample, ........................................................................................ 85

    Figure 4.2: Concentration of heavy metals in food crops in mg/kg ...... 88