Determination of Activity Concentrations of Natural Radionuclides and Radiation Hazard Indices in the Sediments of Ogun River

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DETERMINATION OF ACTIVITY CONCENTRATIONS OF NATURAL RADIONUCLIDES AND RADIATION HAZARD INDICES IN THE

SEDIMENTS OF OGUN RIVER

BY

OKEYODE, ITUNU COMFORT

MAT. NO. 73810

B.Sc (Hons) Physics (Ibadan) 1999

M.Sc Radiation and Health Physics (Ibadan) 2002

A thesis in the Department of Physics Submitted to the Faculty of Science In Partial Fulfillment of the Requirements

for the degree of

DOCTOR OF PHILOSOPHY of the

UNIVERSITY OF IBADAN

August 2012

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DEDICATION

This reseach work is dedicated to the MOST HIGH GOD, WHO WAS, WHO IS AND WHO IS TO COME, THE ALPHA AND OMEGA OF EVERYTHING.

Also, to my wonderful, loving and best Dad, Late Prof. Theophilus Olaitan KAMIYOLE and uncomparable one in a million Mum, Mrs Christiana Adetoun KAMIYOLE.

And finally to my heartthrob, Mr Michael Adebayo Okeyode and our loving children, Oreoluwa, Ifeoluwa and Ayooluwa Okeyode.

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iii ABSTRACT

River sediments are known to contain natural radionuclides, the concentrations of which if beyond certain limits can cause adverse health effects. The sediments from Ogun river provide large quantities of sand for construction purposes in Nigeria. Despite this, data are scarce on the natural radionuclides: ⁴⁰K, ²²⁶Ra and ²³²Th distribution in the river sediments. This work was aimed at determining the spatial distribution of these natural radionuclides and their concentrations in the sediments of Ogun river, and to evaluate the radiological implications on the population living in houses built with the river sediments.

A total of 320 sediment samples were randomly collected along the course of the river; 60 in the upper region (Igboho to Idi- Ata; Oyo – Ogun axis), 90 in the middle region (Olopade to Mile 8 Oba; Ogun –Lagos axis) and 170 in the lower region (Abata to Apa Osa; Lagos axis). The number of samples collected in each region was determined by accessibility. The samples were air dried, pulverized and sieved using a 2 mm mesh size. Two hundred and fifty grams of the sieved samples were transferred into plastic containers of uniform sizes, sealed and left for 4 weeks to attain secular radioactive equilibrium. The activity concentrations of the natural radionuclides in the samples were determined using gamma-ray spectrometer comprising 76mm x 76mm NaI(Tl) detector coupled to a multichannel analyser. These concentrations together with standard equations were used to evaluate indoor effective dose rates, radium equivalent, external and internal hazard indices, representative gamma index and Excess Lifetime Cancer Risks (ELCR) and results were compared with available data from India, Egypt and Turkey. Data were analysed using descriptive statistics.

The activity concentrations (in Bq/kg) of ⁴⁰K, ²²⁶Ra and ²³²Th ranged from 371.0 (middle) – 608.0 (lower), 5.6 – 20.4 (middle) and 5.0 (lower) – 23.1 (middle) respectively. These were similar to data from other locations of the world. The upper region of the river indicated no location effect, in the middle and lower regions, significant location effects were observed and these were attributable to industrial activities. The mean annual indoor effective dose rates were 0.31 ± 0.02 mSv (upper), 0.30 ± 0.05 mSv (middle) and 0.33 ± 0.05 mSv (lower region). The radium equivalent activity for upper, middle and lower regions respectively, were 65.16 ± 4.14 Bq/kg, 64.10 ± 10.78 Bq/kg and 71.00 ± 11.78 Bq/kg, while external hazard indices were 0.18 ±

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0.01, 0.17 ± 0.03 and 0.19 ± 0.03. Internal hazard indices were 0.210.01,0.210.04 and 05

. 0 23 .

0  , representative gamma indices were 0.52  0.03, 0.51  0.08 and 0.56  0.09, whereas ELCR values were



^0.141^0.01



^103,



^0.137^0.02



^103 and



^0.148^0.03



^103.

The radiological hazard indices evaluated for Ogun river sediments were less than acceptable limits and therefore posses no radiation risk on the populations living in the houses built with materials incorporating the river sediments.

Keywords: River sediments, Ogun river, Activity concentrations, Natural radionuclides, Radiological hazard indices

Word Counts: 463

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ACKNOWLEDGEMENT

I express my intense gratitude to the ALMIGHTY GOD, (JEHOVAH EL- SHADAI), who is more than enough for me, He is my Jehovah Raah- The Lord my shepherd. Without Him, this project couldn’t have been a success.

My sincere appreciation and gratitude goes to my supervisor, under whose supervision this project was undertaken, I am greatly indebted to you Sir, Dr Nnamdi Norbert Jibiri. I really thank you for your guidance, tolerance, leadership role, fatherly corrections, encouragement and your words of advice. May the good Lord greatly reward you Sir.

I want to sieze this opportunity to appreciate sincerely the efforts of Prof. I.P Farai, the Head of Physics Department, University of Ibadan, Ibadan. I also want to thank all my lecturers and staff in the Department of Physics, University of Ibadan, most especially Dr, J.A Adegoke, Dr Awe, Dr Popoola, Dr (Mrs) Obed, Dr (Mrs) Ademola, Dr Adetoyinbo, Dr Otunla, Dr Joshua and Aunty Ope for their support, God will bless you all.

My immense gratitude goes to Dr F.O Ogundare, whom despite his tight schedule made sure that there was no stone unturned, thank you sir for your thoroughness.

I want to acknowledge Dr Pascal Tchokosa of Obafemi Awolowo University, Ile Ife, for the helping hand he rendered during the analysis of my samples, thank you and God bless you sir. Also to the divers, (Baba Bose, Baba Folake, Taoreed- Alaga, Agboluwaje Baba Iyabo) who were with me for the sample collections, God bless you all. I can not forget your efforts Pastor and Pastor (Mrs) Okeyode during samples preparation of this work, God will reward you. I am also saying a big thanks to Dr John Oyedepo, for his assistance in the area of the geographical information system used for the work. I am greatful to Dr Dayo Sowunmi, Department of Zoology, Univerity of Ibadan and Mr Akinyero, Department of Geology, Univerity of Ibadan, Ibadan, for all your positive contributons to the success of this work.

I can not afford to forget to show my sincere appreciation to Prof. J.A Olowofela for all his invaluable assistance to the successful completion of this project, I am greatly indebted to you, only God will reward you Sir.

A lot of thanks goes to my Head of Department (Physics), Federal University of Agriculture, Abeokuta, Dr Mustapha for his contributions towards the success of this work, he was always asking for the progress report of the work. Dr Bello, thank you for your assistance, Dr Adebayo G.A, thank you sir for your support in the acquisition of literatures.

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The following people are wonderful people who helped either through their prayers and words of advice which kept me going, Dr and Dr (Mrs) Akintokun, Tunrayo Oladosu, Pastor and Pastor (Mrs) Ayoola and Dr V Makinde, thank you all.

Also to my siblings who were always given suggestions and asking me when the work will be over, Seun Abiodun, Segun Kamiyole, Dupe Igbafen, Juwon Kamiyole and Funmi Ajasa, thanks alot for all your prayers and suggestions.

My warmest regards to my lovely Husband, Mr Michael Adebayo Okeyode, who, through the help of God, gave me all his support, spiritually, financially, emotionally and physically to his ability just to see that God sees me through the work, his words of encouragements can not be under-estimated, thank you dear.

Lastly, my profound gratitude goes to my children: Oreoluwa, Ifeoluwa and Ayooluwa Okeyode, for your understanding during the course of this project when I would not be able to spare time to prepare delicacies for you.

Thank you all and God bless.

Okeyode, I.C August 2012

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CERTIFICATION

I certify that the work described in this thesis was carried out under my supervision by Okeyode Itunu Comfort (73810) in the Department of Physics, University of Ibadan, Ibadan, Nigeria.

...

(Supervisor) Dr. N.N.Jibiri

B.Sc. (Jos). M.Sc., Ph.D (Ibadan) Senior Lecturer Department of Physics

University of Ibadan, Nigeria.

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TABLE OF CONTENTS

Title Page i

Dedication ii

Abstract iii

Acknowledgement v

Certification vii

Table of contents viii List of figures xiii List of tables xvi CHAPTER ONE: INTRODUCTION 1.1 Natural radioactivity... 1

1.2 Sources of natural radioactivity ... 2

1.2.1 Cosmogenic radionuclides and radiation ... 3

1.2.2 Terrestrial radionuclides ... 4

1.2.2.1 Series radionuclides ... 4

1.2.2.2 Non-series radionuclides ... 4

1.3 Sources of artificial radioactivity ... 10

1.4 Transport of radionuclides in the environment ... 10

1.5 Biological effect of radiation ... 14

1.5.1 Classification of radiation effects on biological system ... 14

1.6 Aims and objectives of the study ... 15

CHAPTER TWO: LITERATURE REVIEW 2.1 Radioactivity in river sediments ... 17

2.2 Sands and muds ... 22

2.3 Environmental radiation monitoring ... 23

2.4 Radioactivity in building materials ... 24

2.5 Sediments and minerals ... 29

2.6 The geography of the study area ... 29

2.6.1 The upper Ogun river ... 32

2.6.2 Middle Ogun river ... 32

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2.6.3 The lower Ogun river ... 33

2.7 Geology of the study area ... 33

2.8 Social- economic activities of the study area... 35

CHAPTER THREE: RADIATION DETECTION TECHIQUES 3.1 Interaction of electromagnetic radiation with matter ... 37

3.2 Radiation detection technique ... 40

3.2.1 Principle of scintillation counters ... 41

3.2.2 Gamma ray spectrometers ... 44

3.2.3 Stabilized high- voltage power supply (HVPS) ... 46

3.2.4 Preamplifier ... 46

3.2.5 Main amplifier ... 47

3.2.6 Analog – Digital Converter (ADC) ... 47

3.2.7 Dead time ... 48

3.2.8 Multi channel analyzer ... 48

3.3 Gamma spectrometer system used in this work ... 49

3.3.1 Detector efficiency ... 51

3.3.2 Energy resolution of a detector ... 51

3.4 Counting statistics (Statistical nature of radioactive decay) ... 54

CHAPTER FOUR: MATERIALS AND METHODS 4.0 Experimental techniques and radioactivity measurements ... 56

4.1 Calibration of detector system ... 56

4.1.1 Energy calibration ... 56

4.1.2 Efficiency calibration ... 59

4.2 Sample collection ... 62

4.3 Detection limit ... 64

4.4 Sample preparations ... 64

4.5 Measurements of activity concentrations of ⁴⁰K, ²²⁶Ra and 232Thin the sediment samples ... 64

4.6 Grain size and heavy mineral analysis of the sediments ... 66

4.6.1 Grain-size analysis ... 66

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4.6.2 Heavy mineral determination ... 68

4.63 Petrographic analysis of the sediments ... 68

CHAPTER FIVE: RESULTS 5.1 Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K for the upper, middle and lower Regions of Ogun river . ... 70

5.2.1 Radium equivalent activity (Bq/kg) of the sediments ...70

5.2.2 The external hazard index (HEX) ... 76

5.2.3 The internal hazard index ... 79

5.2.4: The representative gamma index ... 79

5.2.5: The indoor gamma dose rate ... 80

5.2.6 The indoor effective dose rate ... 80

5.2.7 Excess lifetime cancer risk (ELCR) ... 85

5.2.8 Thorium to Uranium ratio ... 86

5.3 Grain size analysis of the sediments ... 89

5.3.1 Graphic mean ... 89

5.3.2 Sorting ... 89

5.3.3 Skewness ... 89

5.3.4 Kurtosis ... 89

5.4 Heavy mineral, provenance and distribution along the river ... 92

5.4.1 Heavy mineral and provenance ... 92

5.4.2 Mineralogical composition ... 92

CHAPTER SIX: DISCUSSION AND CONCLUSION 6.1 Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K for the upper, middle and lower regions of Ogun river .. ... 96

6.2 Determination of radiological hazard indices ... 103

6.2.1 Radium equivalent activity (Bq/kg) of Ogun river sediments ... 103

6.2.2 The external hazard Index (HEX) ... 108

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6.2.3 The internal hazard index ... 108

6.2.4 The representative gamma Index ... 112

6.2.5 The indoor gamma dose rate ... 112

6.2.6 The indoor effective dose rate ... 116

6.2.7 Excess lifetime cancer risk (ELCR) ... 120

6.2.8 Thorium to uranium ratio ... 120

6.3 Statistical test on concentrations of the radionuclides ... 127

6.3.1 Variational tests on the concentrations of the radionuclides of the sediments taken from the upper, middle and lower regions of the river ... 127

6.3.2 The location effects size measures for the three regions ... 130

6.3.3 Pearson correlation analysis between the concentrations of radionuclides and hazard indices ... 133

6.3.4 Cluster analysis of the radionuclides in Ogun river sediments ... 141

6.4 Grain size analysis of the sediment ... 146

6.4.1 Graphic mean ... 146

6.4.2 Sorting ... 146

6.4.3 Skewness ... 148

6.4.4 Kurtosis ... 148

6.5 Heavy mineral, provenance and distribution along the river ... 148

6.5.1 Heavy mineral and provenance ... 148

6.5.2 Mineralogical composition ... 149

6.6 Conclusion ... 153

6.7 Recommendation for further studies ... 155

REFERENCES ... 156

APPENDIX Appendix I: Activity concentrations of each radionuclides for 10 typical sites in the 32 locations... 176

Appendix II: Granulometric analysis data ... 177

Appendix III: Cummulative frequency curves and histogram plots of grain size data ... 178

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xii Appendix IV: Published article I

Appendix V: Published article II

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LIST OF FIGURES

Fig. 1.1 A schematic diagram of the uranium -238 series ... 5

Fig. 1.2 A schematic diagram of the Thorium -232 series ... 6

Fig. 1.3 A schematic diagram of Uranium-235 radioactive decay series (actinium) . 7 Fig. 1.4 Simplified pathways for airborne releases to man ... 12

Fig. 1.5 Simplified pathways for waterborne releases to man ... 13

Fig. 2.1 Map of South Western Nigeria showing study area and the three states the river traversed ... 30

Fig. 2.2 Geology of South Western Nigeria Showing the distribution of the major rocks ... 34

Fig. 3.1 The interaction of gamma rays with matter ... 39

Fig. 3.2 Schematic diagram of the sequence of events in the detection of gamma ray photon by a scintillation detector ... 42

Fig 3.3 Block diagram of a gamma ray spectrometer ... 45

Fig. 3.4 The set up of the gamma ray spectrometer used for this work ... 50

Fig. 3.5 The energy resolution of a gamma ray spectrometer ... 52

Fig. 3.6 A typical gamma ray spectrum showing the positions of the energy windows for a NaI(Tl) detector... 53

Fig. 4.1 Energy (keV) – Channel number calibration curve ... 58

Fig. 4.2 Detection efficiency curve of the detector ... 61

Fig. 4.3 Locations where sediment samples were collected ... 63

Fig. 6.1a Chart of the average values of the three radionuclides in each location from upper region of the river ... 99

Fig. 6.1b Chart of the average values of the three radionuclides in each location from middle region of the river ... 100

Fig. 6.1c Chart of the average values of the three radionuclides in each location from lower region of the river ... 101 Fig. 6.2(a-c) Surface interpolation plots of the concentrations of each

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radionuclides along the river ... 102

Fig. 6.3a Distribution of the mean radium equivalent activities in the upper region of Ogun river ... 105

Fig. 6.3b Distribution of the mean radium equivalent activities in the middle region of Ogun river ... 106

Fig. 6.3c Distribution of the mean radium equivalent activities in the lower region of Ogun river ... 107

Fig. 6.4a The distributions of the radiological assessment for upper Ogun river... 109

Fig. 6.4b The distributions of the radiological assessment for the middle Ogun river . 110 Fig. 6.4c The distributions of the radiological assessment for lower Ogun river ... 111

Fig. 6.5a The indoor gamma dose rate in the upper region of Ogun river ... 113

Fig. 6.5b The indoor gamma dose rate in the middle region of Ogun river ... 114

Fig. 6.5c The indoor gamma dose rate in the lower region of Ogun river ... 115

Fig. 6.6a The indoor effective dose rate in the upper Ogun river ... 117

Fig. 6.6b The indoor effective dose rate in the middle Ogun river ... 118

Fig. 6.6c The indoor effective dose rate in the lower Ogun river ... 119

Fig 6.7a Distribution of the Excess Lifetime Cancer Risks For Upper Region ... 121

Fig. 6.7b Distribution of the Excess Life Cancer Risks For middle Region ... 122

Fig 6.7c Distribution of the Excess Life Cancer Risks For Lower Ogun River ... 123

Fig. 6.8a Th/ U ratio for Upper Ogun River ... 124

Fig. 6.8b Th/ U ratio ror middle Ogun River ... 125

Fig. 6.8c Th/ U Ratio For Lower Ogun River ... 126

Fig. 6.9a Dendrogram for classifying sample locations as groups according to the concentrations of ⁴⁰ K in the sediments from Ogun river ... 142

Fig. 6.9b Dendrogram for classifying sample locations as groups according to the concentrations of ²³²Th in the sediments from Ogun river ... 143

Fig. 6.9c Dendrogram for classifying sample locations as groups according to the concentrations of ²²⁶Ra in the sediments from Ogun river ... 144

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Fig. 6.10a The composition of feldspar (%) with ²³²Th 2 and ²²⁶Ra (Bq/kg) against locations along the river ... 151 Fig. 6.10b The composition of quartz (%) with ²³²Th and ²²⁶Ra (Bq/kg) against

locations along the river ... 151 Fig. 6.10c The composition of rock fragments and rock cement (%) with ²³²Th and

226Ra (Bq/kg) against locations along the river ...152 Fig. 6.10d The composition of mica and rock matrix (%) with ²³²Th and

226Ra (Bq/kg) against locations along the river ...152

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LIST OF TABLES

Table 2.1 Activity concentrations (Bq/kg) of naturally occuring radionuclides

obtained by researchers from different parts of the world... 21 Table 2.2 Activity concentrations (Bq/kg) of naturally occuring

radionuclides of some building materials obtained by researchers

from different parts of the world... 28 Table 4.1 Energy (keV) – Channel number calibration ... 57 Table 4.2 The radionuclide energy and detection efficiency ... 60 Table 5.1 The range and mean of the activity concentrations of the

radionuclides (⁴⁰K, ²²⁶ Ra and ²³²Th) in the upper region of Ogun river 71 Table 5.2 The range and mean of the activity concentrations of the

radionuclides (⁴⁰K, ²²⁶ Ra and ²³²Th) in the upper region of Ogun river ... 72 Table 5.3 The range and the Mean of the activity concentrations of the

radionuclides (⁴⁰K, ²²⁶R and ²³²Th) in the Lower region of Ogun river ... 73 Table 5.4 Range and mean of radium equivalents (Bq/kg) for each

location in the upper, region of Ogun river... ... 74 Table 5.5 Range and mean of radium equivalents (Bq/kg) for each location

in the middle, region of Ogun river ... 74 Table 5.6 Range and mean of radium equivalents (Bq/kg) for each site

in the lower regions of Ogun river ... 75 Table 5.7 Range and mean of external hazard and internal hazard indices

in the upper region of Ogun river ... 77 Table 5.8 Range and mean of external and internal hazard indices

in the middle region of Ogun river ... 77 Table 5.9 Range and mean of external and internal hazard indices

in the lower region of Ogun river ... 78 Table 5.10 The range and the mean of the representative gamma index

for the upper region ... ... 81 Table 5.11 The range and the mean of the representative gamma index

for the middle region ... ... 81 Table 5.12 The range and the mean of the representative gamma index

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for the lower region ... ... 82

Table 5.13 The range and the mean of the indoor gamma dose rates, and indoor effective dose rates for the upper region ... 83

Table 5.14 The range and the mean of the indoor gamma dose rates, and indoor effective dose rates for the middle region ... 83

Table 5.15 The range and the mean of the indoor gamma dose rates, and indoor effective dose rates for the lower region ... 84

Table 5.16 Range and mean of excess life cancer risk (ELCR) and thorium to uranium ratio for the upper region of Ogun river... 87

Table 5.17 Range and mean of excess life cancer risk (ELCR) and thorium to uranium ratio for the middle region of Ogun river... 87

. Table 5.18 Range and mean of excess life cancer risk (ELCR) and thorium to uranium ratio for the upper region of Ogun river... 88

Table 5.19 Percentile Values for Grain Size Analysis... 90

Table 5.20 Summary of Results obtained from Grain Size Analysis and its Interpretation ... 91

Table 5.21 Data of Heavy Minerals showing Z, T, R and ZTR index ... 93

Table 5.22 Composition of Sediments based on visual estimates in Percentage (Modal Analysis) ... 94

Table 5.23 Calculated percentage composition of QFL in the sediments ... 95

Table 6.1 The range and (mean) of activity concentrations of the radionuclides in (Bq/kg) estimated by different authors in comparison to the present study ... 98

Table 6.2 Analysis of variance for the upper region ... 128

Table 6.3 Analysis of variance for the middle region ... 128

Table 6.4 Analysis of variance for the lower region ... 129

Table 6.5 The Location Effects Size measures on the concentrations of the radionuclides in the upper, middle and lower regions ... 131

Table 6.6 Pearson Correlation matrix of measured parameters in upper Ogun river ... 135

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Table 6.7 Pearson Correlation matrix of measured parameters

in middle Ogun river ... 136 Table 6.8 Pearson Correlation matrix of measured parameters

in lower Ogun river ... 139 Table 6.9 Classification of sands ... 147

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1 CHAPTER ONE INTRODUCTION 1.1 NATURAL RADIOACTIVITY

All matter are made up of atoms and their effective diameters are about 3x10^-10 m.

Nearly all the mass of the atom is concentrated in the nucleus which is centrally place within the atom. The nucleus of an atom is composed of protons and neutrons, these are bound together by the nuclear force which is a very strong and short- range force (Jibiri, 2000).

There exists a limit to the stability of the nuclei which is determined by the balance between the nuclear force and electrostatic force. This stability depends largely on the ratio of number of neutrons (N) to number of protons (Z) (Cember, 1989). For light nuclei, the ratio of N to Z being unity is the ideal situation for their stability while for heavy nuclei, the ratio N to Z being about 1.5 is ideal for stability (Jevremovic, 2005 and Isinkaye, 2009). Any departure from these usually results in nuclear instability. When the nucleus is unstable, it experiences a spontaneous nuclear transformation (disintegration), which shifts the N to Z ratio to a more stable configuration and in the process emitting nuclear particles. This process is known as radioactivity or radioactive decay and it always results in the formation of new nuclides which may be stable or radioactive. The particles emitted in natural radioactivity include the heavy charged particles (He⁺⁺) and the light - particles (e⁺,e^-) accompanied by the nuetral and much light particles –the neutrinos. In the process of - decay, an atom with the atomic mass A and atomic number Z would be transformed into a new atom with atomic mass A-4 and atomic number Z-2. In the case of a  -decay, it transforms the same atom into a new atom with a change in Z but no change in A, causing an increase in Z by 1 (Z+1) or a decrease in Z by 1(Z-1). These particles are released with great energies and are usually accompanied with the emission of a highly penetrating electromagnetic radiation, -rays (Jibiri, 2000). The process of radioactive decay is random in its nature. It can not be predicted precisely when an atom will decay in a radioactive material. The rate at which a particular radionuclide decays is directly proportional to the number (N) of radioactive nuclei present at a given time (t). The constant of proportionality called decay constant λ, (s^-1) represents the probability that a radionuclide will decay in a unit time. Radioactive decay is a

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nuclear process that originates in the nucleus and is therefore not determined by the chemical and physical states of the radioisotope. The radioactive decay obeys the exponential law:

e t

N

N  ₀ ^ (1.1)

Where N is the number of nuclei remaining at a later time t.

No is the number of unstable nuclei at time t=0 t =time

The time taken for the number of radioactive nuclei to reduce to half of its initial value is known as half life (

12

T ) and can be expressed as

 693 . 0

12 

T (1.2)

The half-lives of naturally occuring radionuclides can range from fractions of second to billions of years. For example, the radionuclides ⁴⁰K, ²³⁸U, ²³²Th and ²³⁵U have half-life of 1.3 x 10⁹ years, 4.5 x 10⁹ years, 14 x 10⁹ years, and 0.7 x 10⁹ years respectively.

1.2 SOURCES OF NATURAL RADIOACTIVITY

Radionuclides, radiation and radioactivity have been an essential constituent of the earth since its creation. Radionuclides are classified according to their origins. Radionuclides classified as natural are referred to as Naturally Occurring Radioactive Materials (NORM), technologically enhanced radiouclides as Technologically Enhanced Natural Occurring Radioactive Material (TENORM) and the artifically induced known as man-made or anthropogenic radionuclides. Both NORM and TENORM have the same natural origin except that TENORM exists as a result of human activities, such as tobacco smoking, uranium and phosphate mining and milling, air travel, coal fired power plants, oil exploration and others, that could enhance and modify the concentration of NORM, their environmental distribution and radiation exposure dose to human-beings. Generally, some of the non- nuclear industrial processes causes a considerable contribution to the radio-ecological pollution such as phosphate ore mining and phosphate fertilizers manufacture and

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agricultural applications (UNSCEAR,1988; Oosterhuis,1992), and they also contribute technologically. In term of population radiation dose, the sources of natural radiation are most significant and the main contributor to the population collective doses (UNSCEAR,1988; Abdulkareem, 2009). Natural radiation sources are classified into three categories; cosmic radiation, cosmogenic radionuclides and primordial (terrestrial) radionuclides.

1.2.1 Cosmogenic radionuclides and radiation

Cosmogenic radionuclides are produced following result of collision of highly energetic cosmic ray particles with stable elements in the atmosphere and in the ground. The entire geosphere, the atmosphere and all parts of the earth that directly exchange material with the atmosphere contains cosmogenic radionuclides with the major production being from the interaction of cosmic rays with atmospheric gases (Alatise, 2007). These radionuclides are formed primarily through bombardment of the upper atmosphere by high energy heavy particles. The cosmogenic radionuclides include tritium, ¹⁴C, ⁷Be, and ²²Na.

Only tritium and ¹⁴C really contribute to any significant exposures to the worldwide population. The exposures from these sources are relatively low and uniform over the surface of the planet (Bennett, 1997). Carbon-14 is present in carbon dioxide in the air, in the terrestrial biosphere, and in bicarbonates in the ocean. This radionuclide is produced in the atmosphere by the ¹⁴N capture of neutrons. The neutron spectrum covers a wide energy range in the lower atmosphere, from thermal to 100 MeV ( UNSCEAR, 1993).

Cosmic radiation refers to both the primary energetic particles of extra- terrestrial origin and to secondary particles generated by the interaction of primary particles with the atmosphere.The annual external dose rates from cosmic rays depend slightly on latitude and strongly on altitude. Biehl et al., (1949) studied the effects of geomagnetic latitudes on the total cosmic ray and found that the ratio of latitude effects at low geomagnetic latitudes to those at higher latitudes is roughly 65 : 100. Spatial variations of cosmic-rays with altitude and latitude have also been reported in the works of Light et al., (1973) and Merker et al., (1973). The dose rate at sea level from ionizing component of cosmic rays is estimated to be 32 nGy/h (UNSCEAR, 2000), which is about 15% of natural radiation in the environment.

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4 1.2.2 Terrestrial radionuclides

Terrestrial radionuclides are the radionuclides found in the earth. They are long-lived nuclear species, which have been present on earth since the formation of the earth about 4.5x10⁹ years ago. They are classified into two series: Series radionuclides and non-series radionuclides.

1.2.2.1 Series radionuclides

These are radionuclides that are headed by parent radionuclides that decay in sequence to other radionuclides with different half lives and decay modes, and finally end to stable isotopes (NCRP, 1992). There are three natural decay series. There are Uranium-238 series, Thorium-232 series and Uranium-235 series. These series and their main members are shown in Figures 1.1, 1.2 and 1.3 respectively.

1.2.2.2 Non-series radionuclides

The non-series decays directly to stable nuclide. The most important radionuclides in this category are the isotopes of Potassium-40, Vanadium-50, Rubidium-87, Cadmium-113 and Indium-115. In term of population dose, the most significant radionuclides are Potassium-40 and Rubidium-87 (NCRP, 1992).

The radionuclides ²³⁸U, ²³²Th and ²³⁵U have half-life of 4.5 x 10⁹ years, 14 x 10⁹ years, and 0.7 x 10⁹ years respectively. These radionuclides do not decay to a stable isotope in one step, but give rise to decay series (Figures 1.1 and 1.2 and 1.3). For ²³²Th it takes about ten steps to reach stable ²⁰⁸Pb, with 346 possible -ray emissions. The decay of ²³⁸U (Uranium – Radium ) series takes about 14-16 steps to reach ²⁰⁶Pb, with 458 possible -rays.

The decay of ²³⁵U (Uranium – Actinium) series leading via 11-14 radionuclides to ²⁰⁷Pb.

When an unstable nuclide decays, it is nearly always emitting  or β radiation. Most of  or β decays leave the final nucleus in an excited state. These excited states decay rapidly to the ground state through the emission of one or more  rays (Firestone, 1998). The average number of emitted photons per decaying nuclide equals 2.628 for ²³²Th and 2.197 for ²³⁸U (NCRP, 1992). Not all nuclides of the series emit -radiation, and the detection of thorium and uranium depends on -rays emitted by some of their decay products. The most important

-rays for ²³²Th are the 0.58 and 2.61 MeV transitions from ²⁰⁸Tl, and for ²³⁸U the 0.61, 1.12 and 1.74 MeV -rays from ²¹⁴Bi (NCRP, 1992). All decay products have half-lives shorter

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Fig. 1.1: A schematic diagram of the uranium -238 series (Harb, 2004)

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Fig. 1.2: A schematic diagram of the Thorium -232 series [Harb, 2004]

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Fig. 1.3: A schematic diagram of Uranium-235 radioactive decay series (actinium) [Harb, 2004].

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than ²³²Th and ²³⁸U, so in a closed systems secular equilibrium develops. Secular equilibrium in the decay series of ²³⁸U can be distorted by the escape of ²²²Rn. This radionuclide has a half-life of 3.8 days and is an inert gas, allowing it to move out of the system, for example in the sediment or soil. Decay products of radon once escaped from the soil can be deposited again by precipitation. These processes affect the activities of the radon decay products in the sediment and at the soil surface. The main -rays that are used for the detection of ²³⁸U are emitted by decay products of ²²²Rn. Therefore, the possibility of radon escape should be taken into account when detecting ²³⁸U. In a laboratory setting the escape can be prevented by sealing samples in radon-proof containers and leaving them for some time, to establish secular equilibrium. Another radionuclide that can cause a break in secular equilibrium in the Uranium series is ²²⁶Ra (t1/2 = 1600 yr), which is soluble in water. Radon also appears in the decay series of ²³²Th, but its isotope, ²²⁰Rn, has a half-life time of 55.6 secs which is too short for significant escape.

Among the primordial radionuclides, ⁴⁰K, ²³⁸U and ²³²Th and any of their decay products such as radium and radon mainly contribute to the total dose from natural backgound radiation. These primordial radionuclides are found in trace amount in drinking water, coal, phosphate rocks, sediments and plants resulting in internal exposure by ingestion, in addition to these is the low exposure by inhalation of airborne suspended particles.

Potassium -40 has been found to be the most significant primordial radionuclide of terrestrial origin. It has a half- life of 1.3 x 10 ⁹ years and the main decay modes of ⁴⁰K are β- decay to stable ⁴⁰ Ca and electron capture to an excited state of ⁴⁰Ar, emitting 89% of 1.314 Mev of β- particles most of the time (Kathren, 1998). ⁴⁰Ar decays to its ground state by the emission of a -ray of 1.461 MeV, which happens in 10.67% of all decays. This photon value makes it easy to identify and quantify ⁴⁰ K by - ray specrometry. It is also an excellent calibration point because of the presence of potassium in essentially all environmental samples (Alatise, 2007).

Thorium is essentially insoluble. Therefore, concentrations of this radionuclide in biological material is almost negligible. This radionuclide also is not mobile in the environment. The highest concentrations of thorium in the body have been found predominantly in the pulmonary lymph nodes and lungs. The presence of high concentrations

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in this area of the body indicates that infiltration occurs mainly as a result of inhalation of soil and dust particles (NCRP, 1992).

The isotope of ²³⁸U occurs with a natural abundance of 99.28%, ²³⁵U occurs with a natural abundance of 0.71%, and ²³⁴U occurs with a natural abundance of 0.0058%. Uranium is prevalent to some degree in all common types of rock and soil. Common rock types contain concentrations of uranium in the range of 0.5 ppm to 4.7 ppm. These concentrations, however, do not only just refer to ²³⁸U itself, but also to the daughter products inherently contained in the uranium decay chain. Each radionuclide in this decay chain emit several different types of radioactive particles and photons. Over a sufficiently long time, the decay chain essentially behaves as a single, large source of ionizing radiation. Considerable energy releases occur as a result of the decay of Uranium series. Uranium radionuclide is present in food and human tissues. The annual intake of Uranium from all dietary sources averages approximately 320 pCi (13 Bq) (Eisenbud, 1987). The specific levels of terrestrial environmental radiation are related to the geological composition for each lithologically separated area, and to the content of Uranium, Thorium and Potassium in the rock from which the soil originated in each area (Merdanoglu and Altinsoy, 2006; Chowdhury et al., 2006). These radionuclides when ingested or inhaled enter the human body and are distributed among body organs according to the metabolism of the element involved. The organs normally exhibit varying sensitivities to the radiation and thus, varying doses and risks result from their consumption or inhalation. UNSCEAR (1993) and Mettler and Sinclair (1990), showed that terrestrial sources are responsible for most of man‘s exposure to natural radiation and Kullab et al., (2006) reported that the natural radionuclides concentration in soil and rock would affect the natural radioactivity level of river sediments.

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1.3 SOURCES OF ARTIFICIAL RADIOACTIVITY

Artificial radioactivity are created via human activities that vary with time and location according to domestic and/or world activities. Sources of man-made radionuclides include nuclear tests, nuclear power plants and reprocessing facilities, sources used for medical, industrial and agricultural applications, and sources used for research purposes (UNSCEAR, 1988; Eisenbud, 1987). Most of these radionuclides find their ways into the environment through transport, routine release, accidents, loss and inproper disposal or misuse of radioactive materials. Man made sources of radiation can only affect a small fraction of the population at any time under controlled management. Radiation used in medicine for both diagnostic and therapeutic purposes especially the management of cancer in humans make a significant contribution to man‘s exposure (Pascal, 2006).

Some common consumer products enhance man‘s exposure, like the luminous watches and clock which contain ³H, ¹⁴⁷Pm or ²²⁶Ra as the activating agent (UNEP, 1991; NCRP, 1977).

Television sets produduce x-rays, but modern sets have been designed to produce negligible amounts when used correctly and serviced appropriately (Larmash, 1983). Also, smoke detectors contain alpha-emmiting sources such as Americium-241. Some porcelain dentures and eye glasses which contain Uranium and Thorium (NCRP, 1977) also enhance exposure.

Starters for fluorescent tube lights and some electrical appliances contain sealed radionuclides although they do not cause any hazard unless they are broken (NCRP, 1977), X-ray machines used for screening travelers (Mettler and Sinclair, 1990), cigarette smoke and tobacco which contain Pb-210 and Po-210 (Larmash, 1983; NCRP, 1977, Pascal, 2006) and combustible fuels as well as building materials which could be mixed with Uranium, Thorium and Pottasium containing waste etc (NCRP, 1977). All these radiation sources could contaminate the human body through irradiation, inhalation and ingestion leading to varying doses of radiation to man (Pascal, 2006; NCRP, 1997).

1.4 TRANSPORT OF RADIONUCLIDES IN THE ENVIRONMENT

Radionuclides in the environment can give rise to radiation doses to humans. External irradiation is exposure from environment to human directly. Internal irradiation means uptake by human via a variety pathway such as inhalation of contaminated dust, ingestion of

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dirt and dust, inhalation of radon diffusing from the material and skin contamination (see Figures 1.4 and1.5). Radioactive materials can be released into air or directly into water or soil. When released in the air, they can travel some distance, depending upon such factors as wind speed and direction and altitude of the release. The products of airborne releases can be transported to humans by a variety of paths. First, direct inhalation is possible. Secondly, the materials will eventually deposit themselves on the ground, where they will find their way into plant and animal life and thereby, into the food chain. Third, deposition of airborne contaminants into water can reach humans either by direct ingestion or via the food chain.

Similarly, direct soil and water depositions find their way into the food chain via both plant and animal life. Rain water runoff can carry soil into rivers and streams, thereby transporting any soil (sediment) contamination to water. Additionally, radioactive materials can leach into porous soils and into ground water (

Doendara

, 2007). Apart from all these pathway radionuclides in the aquatic environment could cause external exposure through the use of riverbed sand (sediment) as building materials. It is now a common knowledge that sediment from rivers, lakes and beaches are used as materials for the construction of buildings (Xinwei and Xiaolan, 2006).

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Fig. 1.4: Simplified pathways for airborne releases to man (Doendara, 2007).

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Fig. 1.5: Simplified pathways for waterborne releases to man (Doendara, 2007).

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1.5 BIOLOGICAL EFFECTS OF RADIATION

The human body is made up of many organs which are composed of tissues. The tissues are made up of cells while the cells are made up of nucleus and cytoplasm. The cells contains 70% of water. When radiation transfers energy to a biological medium, some chemical reactions take place. Most of the energies are absorbed by the water content of the cell thereby causing excitation and ionization. Following these process is the breakage of chemical bonds of water as follows:

H20 ... OH^- + H⁺ (1.3) H20 ... OH⁺ + H^- (1.4) H20 ... OH^o + H^o (1.5) H20 ... H20⁺ + e^- (1.6)

The end products of the breakage of the bonds of water (H20) are formation of free radicals (OH^o H^o) and the release of aqueous electrons. These free radicals are highly reactive and they may recombine to form stable ions and molecules or the reactive species may attack the molecules present in the cellular environment, mostly the biologically important molecules, Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA). The concentration of the reactive species at a sight determines which of the above two competing mechanisms will occur. This in turn depends on the linear energy transfer (LET) of the incident radiation, and on the nature of the biological system. The effectiveness of a radiation in destroying cells is called Relative Biological Effectiveness (RBE) and it depends on LET. It is important to note that radiation does not result into biological effects that are new, unique or characteristic, rather it increases the frequency of diseases which are already known to occur in human race.

1.5.1 CLASSIFICATION OF RADIATION EFFECTS ON BIOLOGICAL SYSTEM There are various criteria for the classification of the detrimental biological radiation effects on biological system. The most recent depends on presence or absence of a threshold radiation dose to produce the effect. Radiation effects that occur after a threshold of dose are called deterministic effects and those that occur without a threshold of dose are called

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stochastic effects. A deterministic effect occurs only after a threshold dose and the severity depends on magnitude of the dose, dose rate and fractionation. There are some other deterministic effects which normally show after a latent period, usually some few years after the exposure to radiation, these are the delayed deterministic effects, example is cataract.

Cataract is a change in transluscency of the optic lens and it is due to the damage of the individual cell of the lens epithelium. Abnormal cells and resultant debris accumulate at the poles of the lens, after a threshold dose that falls within the range 0.2 Gy and 0.5 Gy.

Cataracts would manifest within three years of initial exposure. Also, radiation infertility, is the cell damage to the gonads, depending on the dose, it could be temporary or permanent damage. The cummulative effects of radiation caused infertility, raise the possibility of gradual human extinction. It was found that those living on the high radiation backgound had twice the rate of couples who want children but are unable to have children compared to those living on the normal backgroung soil.

The stochastic effects have no evidence of causative threshold dose and the chance of occurence is basically probabilistic. Severity of the effect is not a function of magnitude of dose but the probability of occurence or risk is a linear function of the magnitude of the dose.

Stochastic effect results from damage due to low –level radiation on the genetic material of the cell which is transferred to the descendant of the cell. Apart from hereditary effects which are due to chromosome aberations and gene mutation in gonadal cells, cancer of different forms is much the most important ultimate effect of damage to a cell by low level radiation. Major concern is based on the general public and radiation workers since the effects may manifest immediately after exposure and through accidental exposure of the public.

1.6 AIMS AND OBJECTIVES

River sediments are known to contain natural radionuclides, the concentrations of which if beyond certain limits can cause adverse health effects. The sediments from Ogun river provide large quantities of sand for construction purposes in Nigeria. Despite this, data are scarce on the natural radionuclides: ⁴⁰K, ²²⁶Ra and ²³²Th distribution in the river sediments.

The measurement of radioactivity of Ogun river sediment from the source in Oyo state around Ago Fulani through Ogun state, down to the sink in Lagos Lagoon was designed

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to establish the trends of the distribution of radionuclides through the measurement of the concentrations of these natural radionuclides in the river sediments and to establish the current status of the radiological implications of that environment. The assessment involves the measurement of radiation dose equivalents for reasons related to the radioactivity in the sediments of the river since sediments are derived from weathering and erosion of rocks and soil, these sediments contain certain concentrations of naturally occurring radionuclides which will depend on the concentrations of such radionuclides in rocks and soil of their origin. Human and industrial activities around the river may also increase the level of radioactivity in the sediments. The three states through which the river passes, are heavily industrialised cities: Lagos and Sango – Ota (Ogun state) for instance, about six major industries including Vitabiotics, Nestle, Glaxos, Smith kline, Sona Breweries and Nigerian German chemicals discharge their wastes into the river. The aim of this work is to investigate the extent of radioactive pollution in the river, if any, and to assess if sediment materials obtained from this river used for the construction of dwellings are radiologically safe. The aim is achieved through the following objectives:

i. To investigate and interpret the distribution of radionuclides in the sediments along Ogun river course.

ii. To provide a baseline data on the distribution of natural radionuclides in sediments from Ogun river.

iii. To investigate if there are obvious/significant variations in the radionuclides‘

concentrations due to different locations based on economic activities.

iv. To evaluate the environmental gamma dose rates and other radiation hazard indices for determining the health implications through the use of the sediments from the river for construction purposes.

v. To determine the excess lifetime cancer risk associated with the use of the sediments as building material.

vi. To carry out geotechnical study of the sediments.

vii. To determine the distribution of basic mineral composition and heavy minerals (opaque and non- opaque) in the river sediments.

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17 CHAPTER TWO

LITERATURE REVIEW 2.1 Radioactivity in River Sediments

A river is a natural watercourse usually freshwater, flowing toward an ocean, a lake, a sea or another river. In few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be termed by several other names, including stream, creek and brook. In the United States a river is generally classified as a watercourse more than 18 metres wide. The water in a river is usually in a channel, made up of a stream bed between banks. In larger rivers there is also a wider floodplain shaped by flood-waters over-topping the channel. Flood plains may be very wide in relation to the size of the river channel. Rivers are a part of the hydrological cycle. Water within a river is generally collected from precipitation through surface runoff, groundwater recharge, springs, and the release of water stored in glaciers and snowpacks (Marriam, 2010).

Rivers are of immense importance geologically, biologically, historically and culturally although they contain only about 0.0001% of the total amount of water in the world at any time. They are vital carriers of water and nutrients to areas around the earth (Murugesan, 2004). They are crucial components of the hydrological cycle, acting as drainage channels for surface water. The world‘s rivers drain nearly 75% of the earth‘s land surface (Iwena, 2000). Rivers play vital roles in the provision of habitat, nurishments and means of transport to many organisms, travel routes for exploration, recreation and even commerce, importantly they leave valuable deposits of sediments, such as gravel and sand, even forming floodplains where many cities were built (Murugesan, 2004).

Sediments are particles of organic or inorganic matter that accumulate in a loose, unconsolidated form that settles at the bottom of water bodies as a result of the erosive force of water‘s contact with rock, soil and plant materials (Thompson, 2007). There are two primary sources for particles accumulating as sediments today, the detrital sediments – originated and are transported as solid particles derived from weathering of the land accumulations and the other is known as the chemical sediments originating from the dissolved materials derived from weathering which are precipitated from water streams, lakes, or the ocean accumulations (Murugesan, 2004; Oyebanjo, 2010).

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Radioactivity in river sediments originates from the near surface, from exposed igneous, volcanic and sedimentary rocks. Some of these rocks are easily eroded and others most especially the crystalline and the metamorphic rocks are affected by streams only when altered in the surface layers, (Joshua and Oyebanjo, 2010). Radionuclides have an affinity for silts and clays in the soils. These soils and attached radionuclides are subject to sheet erosion and transport into streams and rivers, the fine sediments are most representative of the sediment transport of radionuclides (Purtymun et al., 1980). In spite of the low concentrations in the aquatic environment, the aquatic behaviour of radionuclides plays an important role in the ecosystem, since water is crucial to life and it is one of the prime agents that help to move and distribute elements on the earth (Khan et al., 2003; Isikaye, 2009).

Distribution of sediments is determined by climate (temperature), environmental factors (nutrients, possible chemical reactions, activity of physical environment) supply, size and rate of accumulation (Thompson, 2007). Resources from sediments are sand and gravel for construction, phosphorite for fertilizers, sulphur for sulphuric acid for industry, coal for energy, oil and gas for energy and transportation. Manganese nodules for Mn, Fe, Co, Cu and Ni, etc (Thompson, 2007).

Sand whether found on beaches or in rivers and streams, is mostly quartz grain (Ramasamy et al., 2010). The weathering of rocks such as granites form the quartz grain, grains of other weather-resistant minerals too are found in quartz sand as well. The use of sand and gravel are of two categories, some are used in construction where it may be mixed with other materials or used as it is. The second use is the industrial use, where the sand and gravel are used in some way in the production of other materials (Murugesan, 2004).

Along with industrial development of the world, water reservoirs, such as soil become, although in considerably smaller degree, the place of accumulation of different kind of contaminants. Introduction of organic, inorganic, and radioactive substances produces dramatic, often irreversible changes of physicochemical and biological properties of these reservoirs. The geochemical composition of sediments, gathering on the bottom of rivers and water reservoirs is a very good indicator of quality of surface waters and the presence of contaminants (Jan et al., 2006).

Although soil has always been important to humans and their health, it is also providing a resource that can be used for shelter and food production. Through ingestion, inhalation and

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dermal absorption, the mineral, chemical and biological components of soil can be directly detrimental to human health. Example of such effect to human is cancers caused by the inhalation of fibrous or radon gas derived from the radioactive decay of uranium in soil minerals (Abdulkareem, 2009). The knowledge of uranium concentration in sediments and soils is important not only to assess the contamination level but also to understand the transference processes which have occurrence at different trophic levels of the feed chain (Ricardo et al., 2009). Dim et al., (2000) determined the uranium – thoriun levels of the Kubanni river sediments in the Northern Nigerian Basement Complex and was observed to be enriched with mean values of 9.06 and 21.44 (ppm) respectively. The high geochemical mobility of radionuclides in the environments allows them to move easily and to contaminate mainly the environment with which human come in contact. Uranium -238, in particular is easily mobilized in ground water and surface water. As a result, uranium and its decay product enter the food chain through irrigation water, and enter the water supply through ground water, well and surface water streams and rivers (Otton, 1994). Igneous rock like granite has high concentration of uranium. Also the solubility of ²³²Th in natural water such as river is detected in high concentration in sediments and deposits (Arogunjo, 1994).

Moreover, ²³²Th and ²³⁸U are more abundant in sedimentary rocks than in igneous and metamorphosed sediments (Egunyinka et al., 2009). Kullab et al., (2006) determined the concentrations of some naturally occurring radioisotopes in sediments of the Kufranja river basin in Jordan, by means of γ-ray spectrometry and found that the natural radioactivity level of river sediment could be affected by the natural radionuclides concentration in soil and rock, since most of the sediments that settle in river are silts and sands derived from weathering and erosion of rock and soil. Oni et al., (2011), measured the natural radioactivity level in the coastal areas of Nigeria by gamma counting of river sediment samples and results showed that the radioactivity concentrations of ⁴⁰K, ²²⁶Ra and ²²⁸Ra in the sediment samples of oil producing areas were 122.39 ± 47.49; 18.93 ± 12.53 and 29.31 ± 18.67 Bq /kg respectively, in the sediment samples from the non oil producing areas, the respective mean values were 88.48 ± 8.22, 14.87 ± 3.51 and 16.37 ± 3.87 Bq /kg respectively. The concentrations of natural radionuclides: ⁴⁰K, ²³⁸U and ²³²Th in the sediment of rivers and streams in the Northern part of Ibadan City, Nigeria was examined by Fasewa (2007) and the mean radioactivity concentrations obtained were (0.0564 ± 0.0056), (0.0128 ± 0.0017) and

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(0.0175 ± 0.0037) kBq/kg respectively. Some other researchers from different countries in the world had also carried out different works on the measurement of activity concentrations of naturally occurring radionuclides in sediments, few of such works are presented in Table 2.1. Human activities such as application of phosphate fertilizer in surrounding farmlands and the discharge of both industrial and domestic waste into rivers and stream may also increase the radioactivity levels in water sediments (Isinkaye, 2009). Considerable amounts of natural radionuclides can be found in river sediments as the end result of fertilizer washing and industrial activities (Krmar et al., 2009; Ramasamy et al., 2009). The environmental uranium and partial thorium concentrations are increased due to the fertilizers. Usually fertilizers are considered to technologically enhance natural radiation (El Gamal et al., 2007).

The presence of radionuclides in phosphatic fertilizers have been reported by several studies (Guimond and Hardin, 1989; Khan et al., 1998; Zielinski, et al., 2000; San Miguel et al., 2003; Becegato et al., 2008).

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Table 2.1: Activity concentrations (Bq/kg) of naturally occurring radionuclides obtained by researchers from different parts the world

S/N Country ⁴⁰K ²²⁶Ra ²³²Th References

1 India (Kali river) 296.0 - 525.0 (394.7) 34.1 - 49.4 (40.1)** 4.6 - 12.2 (6.9)

Narayana et al., (2007) 2

Bangladeshi (Shango

River) 212- 292 (255) 21.6 - 28.3 (25.4)** 52.4 - 61.7 (57.5)

Chowdhurry et al., (2009)

3 Algeria (Algiers Bay) 56 - 607 (374)

4.45 - 25.04

(15.8)** 6.5 - 31.7 (19.5)

Benemar et al., (1997) 4 China (Wei River)

514.8 - 1175.5

(833.3) 10.4 - 39.9 (21.8) 15.3 - 54.8 (33.1) Xinwei et al., (2008) 5 Egypt (Eastern Desert) 298.6 – 955.8 9.7 – 19.0 10.0 – 17.7 Harb, (2008) 6 Egypt, Wadi Nugrus, 306.7 -626.0

24.7 - 86.45 (43.91)**

20.3 - 48.72

(26.62) Abdel-Razek(2008)

7 Turkey 155.7 -868.7 26.8 - 49.8 ** 17.06 - 35.62

Kam and Bozkurt (2007)

8 Bengal 118 - 608 5.9 - 27.9 10.4 - 64.0 Alam et., (1997)

9 Pakistan (647.4) (32.9) (53.6)

Matiullah et al., (2004)

** = ²³⁸U, ( ) = mean concentration

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22 2.2 Sands and Muds

The composition of a natural sediment bed is the result of various morphodynamic processes and can be characterised by its sand ( > 63 and < 2000 m) and clay ( < 2 m), silt ( < 16

m) and mud content ( < 63m) (Wijngaarden et al., 2002). Especially in delta systems where the deposition or erosion of mud and sand occurs under specific (tidal) conditions, such a classification appears often to be more functional than grain-size information expressed by a median diameter. The sand or mud content provides information with respect to:

(i) the sediment-transport processes active in a water system and

(ii) the (potential) degree of pollution of the sediments, which is strongly correlated to the mud content (Horowitz and Elrick, 1987; Zwolsman et al., 1996; Wijngaarden et al., 2002).

Sand and mud have different geochemical and physical properties and are transported in a different manner. Sand is an inorganic, silicon-rich coarse material, which is transported mainly as bedload. Mud is a fine, cohesive material, still rich in silicon, quartz and feldspars, also contains inorganic matter and clay minerals but it is transported in suspension. The main constituent of these clay minerals is Al₂O₃. Moreover, clay minerals have a high adsorption potential for trace metals and radionuclides (Ramasamy et al., 2009; Wijngaarden et al., 2002). Studies suggest that as a result of their specific adsorptive behaviour, radionuclides can function as indicators for the mud and sand content of submerged sediments (Duursma and Bosch, 1970; Duursma and Eisma, 1973; Venema and De Meijer, 2001; Wijngaarden et al., 2002).

In radiometric sedimentology, various sediment components are characterised using the concentration of natural gamma-ray emitting radionuclides. Three of the main radionuclides in the natural environment, ²³⁸U, ²³²Th and ⁴⁰K, are generally used as they have half-lives longer or comparable to the earth‘s existence. Accordingly, these nuclides form excellent indicators for intrinsic sediment properties. Their presence can be measured through the emission of gamma rays during decay, either directly (⁴⁰K) or via decay products ²³⁸U and

232Th, (Wijngaarden et al., 2002).