Determination of Polycyclic Aromatic Hydrocarbons(PAHs) in Soils of Selected Farmland Cleared By Bush Burning

ABSTRACT

Polycyclic Aromatic Hydrocarbons are some of the known organic pollutants resulting from incomplete combustion of organic matter. They have been found to be carcinogenic, mutagenic and teratogenic. Much of the previous works on Polycyclic Aromatic Hydrocarbons have been on foods, water, dumpsites and on soil generally. However, this study focuses particularly on soils contaminated with Polycyclic Aromatic Hydrocarbons as a result of a widely used agricultural practice of farmland clearing by bush burning.

Soil samples were collected from five selected farmlands in Ogun state and were subjected to extraction procedure using, soxhlet extractor, to isolate the Polycyclic Aromatic Hydrocarbon contents of the respective samples. The concentrations of Polycyclic Aromatic Hydrocarbons in the soil samples were determined with a standard analytical procedure using Gas Chromatography equipped with Flame Ionization Detector (GC-FID). The result showed that low molecular weight PAHs and high molecular weight PAHs were detected in the soil samples. The total concentration of the PAHs ranges from 3.0 x 10-5 Mg/Kg to 2.3 x 10-3 Mg/Kg in which Benzo (g,h,i)perylene, an high molecular weight PAH  has the highest concentration than Acenaphthylene and Fluorene which are low molecular weight PAHs. 

It is recommended, based on the outcome of this research that further studies be carried out on soil, to identify other anthropogenic activities that could generate PAHs. It is imperative however that bush burning as agricultural cultivation method is discouraged.

TABLE OF CONTENT

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

Certification……………………………………………………………………………...............ii

Dedication……………………………………………………………………………………….iii

Acknowledgement………………………………………………………………………………iv

Table of Content………………………………………………………........................................v

List of Tables…………………………………………………………………………………..viii

List of Figures…………………………………………………………………………………...ix

Abstract………………………………………………………………………………………......x

CHAPTER ONE

 Introduction…………………………………………………………………………………1

1.1 Background of Study………………………………………………......................................1

1.2 Problem Statement and Justification…………………………………………………….….5

1.3 Aim and Objectives…………………………………………………………………………5

1.4 Contribution to Knowledge…………………………………………………………………5

1.5 Scope of Study………………………………………………………………………….......6

CHAPTER TWO

Literature Review……………………………………………………………………………7

2.1 Role of Soil in Ecosystems…………………………………………………………….........7

2.1.1 Soils and the Carbon Cycle……………………………………………………………......7

2.1.1.1 Quantitative Amounts of Organic Carbon Stored in Soil……………………………….9

2.1.1.2 Nature and Formation of Soil Organic Carbon……………………………………….....9

2.1.1.3 Factors Influencing Soil Carbon Storage………………………………………………11

2.1.1.4 Biotic and Abiotic Factors…………………….…………………………………….....12

2.1.2 Soil and Nutrients Cycle………………………………………………………………....13

2.1.2.1 The Nutrient Cycle: Knowledge Gaps and Research Needs…………………………..16

2.1.3 Soil and Water Cycle………………………………………………………………….....16

2.2 Polycyclic Aromatic Hydrocarbons …………………………………………………..…..19

2.2.1 Sources of Polycyclic Aromatic Hydrocarbons in the Environment……………….........20

2.2.2 Physicochemical Properties of Polycyclic Aromatic Hydrocarbons …….………….......21

2.2.3 Toxicity of Polycyclic Aromatic Hydrocarbons ………………………………………...22 

2.2.4 Methods of Determining Polycyclic Aromatic Hydrocarbons …………………….........22

2.2.5 Distribution of Polycyclic Aromatic Hydrocarbons in the Environment…………….......23

2.2.6 Degradation of Polycyclic Aromatic Hydrocarbons …………………………………….23

2.2.7 Biodegradation of Polycyclic Aromatic Hydrocarbons ……………………………….....24

2.2.8 Harmful Effects of Polycyclic Aromatic Hydrocarbons …………………………………24

2.2.9 Toxic Levels and Bioaccumulation of Polycyclic Aromatic Hydrocarbons ……………..25

2.3 Studies showing the Extraction Techniques of Polycyclic Aromatic Hydrocarbons…….....27

2.3.1 Soxhlet Extraction………………………………………………………………………...27

2.3.2 Ultrasonic Agitation/Sonication……………………………………………………..…....29

2.3.3 Mechanical Agitation……………………………………………………………………..30

2.3.4 Accelerated Solvent Extraction or Pressurized Fluid Extraction…………………………30

CHAPTER THREE

Methodology…………………………………………………………………………….….32

3.1 Instruments and Reagents…………………………………………………………………..32

3.2 Sampling……………………………………………………………………………………32

3.2.1 Site location and Samples Collection…………………………………………………….32

3.3 Labelling…………………………………………………………………………….……..32

3.4 Sample Pretreatment……………………………………………………………………….32

3.5 Extraction Procedure of Polycyclic Aromatic Hydrocarbons from Soil Samples…………32

3.6 Clean-up Procedure………………………………………………………………………..33

3.7 Gas chromatography/Mass spectrometry (GC/MS) Analysis……………………………..34

CHAPTER FOUR

4.0 Results and Discussion………………………………………………………………........35

4.1 Polycyclic Aromatic Hydrocarbons Concentration in Soil Samples………………..........35

CHAPTER FIVE

5.0 Conclusion and Recommendation……………………………………………………….38

5.1 Conclusion……………………………………………………………………………….38

5.2 Recommendation………………………………………………………………………...38

REFERENCES………………………………………………………………………………40

APPENDIX………………………………………………………………………………….52