Assessment of Radiological Hazards Around Ririwai Tin Mines, Kano State, North Western Nigeria
Assessment of Radiological Hazards Around Ririwai Tin Mines, Kano State, North Western Nigeria.
ABSTRACT
Mining industry in Nigeria provides economic benefits of wealth creation and employment opportunities.
Presently there are numbers of artisanal and large-scale mining activities going on across Nigeria and most of these artisanal miners currently under take only surface mining and the process produced large volumes of tailings and waste that may containnaturally occurring radioactive materials (NORMs).
Some of the NORMs are soluble in water and have the tendency to leach into water bodies and farm lands.
This study assessed the radiation exposure to the public from NORMs around Ririwai Tin mine in Kano state Nigeria.
A total of one hundred and four (104) environmental samples comprising of 28 soil, 15 cereals, 11 vegetables, 10 dust and 40 water samples were collected.
The samples were analysed using Direct Gamma Spectroscopy (NaI (Tl)), Instrumental Neutron Activation Analysis (INAA) and Liquid Scintillation Analysis (LSA).
The exposure pathways considered were external irradiation due to activity concentration of 40K, 226Ra and 232Th in soil and dust, ingestion of food (cereals and vegetables) containing 40K, 226Ra and 232Th and ingestion of 222Rn in domestic water.
The results show that the mean activity concentrations of 40K, 226Ra and 232Th in soil samples were 296.87±8.25Bq/kg 49.66±6.56Bq/kg and 257.24±6.53Bq/kg respectively.
For the cereals samples the mean activity concentrations of 40K, 226Ra and 232Th were 59.99±2.76, 25.95±2.55 and 46.81±1.99Bq/kg respectively.
The mean activity concentration in vegetable samples were 261.84±4.93, 28.65±4.92 and 56.3±1.66Bq/kg respectively for 40K, 226Ra and 232Th, in dust the activity concentration was 385.90±5.70, 54.31±2.51 and 146.64±0.91Bq/kg for 40K, 226Ra and 232Th respectively.
The results in this study are higher when compared withthe worldwide average concentrations of 420Bq/kg, 33Bq/kg and 45Bq/kg for 40K,226Ra and 232Th respectively.
The high values obtained in cereals and vegetables could be attributed to the fact that they are also used as phytoremediators of uranium contaminated soil due to their high bioaccumulation of 222Ra and 232Th.
The mean absorbed dose for the soil’s cereals, vegetables and dust sample were 170.04±4.61, 32.562±1.450, 4632±1.43 and 119.85±9.700nGyh-1 respectively.
TABLE OF CONTENT
Title Page – – – – – – – – – – ii
Declaration – – – – – – – – – – iii
Certification – – – – – – – – – – iv
Acknowledgement – – – – – – – – – v
Abstract – – – – – – – – – – vi
Table Of Contents – – – – – – – – – viii
CHAPTER ONE
1.0 Introduction – – – – – – – – – 1
1.1.0 General Introduction – – – – – – – 1
1.2.0 Statement of the problem – – – – – – – 8
1.3.0 Aims and Objectives – – – – – – – 9
1.3.1 Aims – – – – – – – – – 9
1.4.0 Justification – – – – – – – – – 10
CHAPTER TWO
2.0.0 Literature Review – – – – – – – – 11
2.1.0 Background – – – – – – – – – 11
2.2.0 Sources of exposure to NORM – – – – – – 13
2.2.1 Exposure for U,Th and K – – – – – – – 14
2.2.2 Exposure from radon – – – – – – – 16
2.3.0 Tin and Tin mineralization – – – – – – – 17
2.3.1 Tin(Sn) – – – – – – – – – 17
2.3.2 Tin mineralization – – – – – – – – 18
2.3.3 Tin mining activities in Nigeria – – – – – – 19
2.4.0 Geochemical settings of the study area – – – – – 19
2.5.0 Mineralization of the study area – – – – – – 20
2.6.0 Review of Works Carried Out in The Study Area – – – – 21
2.7.0 Review of Similar Works – – – – – – – 25
2.8.0 Review of works carried out in area with similar geochemical settings – 28
2.9.0 Review of Gamma-Ray Spectrometry Analysis – – – – 30
2.9.1 Overview of Gamma-Ray Detector – – – – – – 30
2.9.2 The NaI(Tl) Detector – – – – – – – 31
2.9.3 Neutron Activation Analysis (NAA) – – – – – 35
2.10.0 Liquid Scintillation Counting – – – – – – 38
CHAPTER THREE
3.0 Materials and Methodology – – – – – – – 39
3.1.0 Introduction – – – – – – – – – 39
3.2.0 Study Area – – – – – – – – – 39
3.3.0 Materials and methods – – – – – – – 42
3.3.1 Sample use – – – – – – – – – 42
3.3.2 Materials and Equipment – – – – – – – 42
3.4.0 Sample Collection – – – – – – – – 43
3.4.1 Soil sample – – – – – – – – – 43
3.4.2 Water – – – – – – – – – 45
3.4.3 Dust – – – – – – – – – 45
3.4.4 Cereals – – – – – – – – – 46
3.4.5 Vegetables – – – – – – – – – 46
3.5.0 Samples Preparation – – – – – – – – 46
3.5.1 Sample preparation for direct gamma spectrometry for soils, cereals and vegetables samples – – 46
3.5.2 Preparation of dust samples for N.A.A – – – – – 47
3.5.3 Preparation of water samples for liquid scintillation analysis (L.S.A) – – 47
3.6.0 Samples Analysis – – – – – – – – 48
3.6.1 Analysis of samples using direct gamma spectrometry – – – 49
3.6.2 Neutron activation analysis (NAA) for dust sample – – – – 50
3.6.2.1 Long Irradiation – – – – – – – – 50
3.6.2.2 Measurements of Gamma Rays – – – – – – 51
3.6.3 Liquid scintillation analysis – – – – – – – 51
3.6.3.1 Calibration procedure of LSA for measurement of 222Rn in water – 52
3.6.3.2 Detection Limit of LSA for 2Measurement of 222Rn in water – – 52
3.6.3.3 Decay correction Factor – – – – – – – 52
3.7.0 Calculations – – – – – – – – – 53
3.7.1 Determination of activity concentration – – – – – 53
3.7.2 Calculation of annual effective dose – – – – – – 53
3.7.3 Calculation of annual effective dose in water samples – – – 54
3.7.4 Activity concentration of dust for 238U, 232Th, 40K from NAA – – 54
3.7.5 Determination of 222Rn concentration and 222Rn emanation fraction in soil samples 55
3.7.6 Calculation of effective doses and total annual effective dose – – 56
3.8.0 Determination of Hazard indices and risks – – – – – 57
3.9.0 Risk – – – – – – – – – – 58
3.10.0 Statistical analysis of samples – – – – – – 59
3.10.1 Mean differencing – – – – – – – 60
CHAPTER FOUR
4.0 Results and discussion – – – – – – – 62
4.1.0 Introduction – – – – – – – – 62
4.1.1 Direct gamma spectrometry using NaI (Tl) detector – – – 62
4.1.1.1 Activity Concentration of 40K 226Ra and 232Th in soil samples – – 64
4.1.1.2 Absorbed dose rate and annual effective dose rate – – – – 66
4.1.1.3 222Rn Concentration and222Rn Emanation fraction in soil samples – 71
4.1.1.4 222Rn activity concentration and 222Rn emanation fraction in soil – 73
4.1.1.5 Hazard indices in soil sample – – – – – – 73
4.1.2 Cereals Samples – – – – – – – – 75
4.1.2.1 Activity concentration – – – – – – – 75
4.1.2.2 Absorbed dose rate – – – – – – – 77
4.1.2.3 Committed effective dose – – – – – – – 77
4.1.3 Vegetables – – – – – – – – – 83
4.1.3.1 Activity concentration – – – – – – – 83
4.1.3.2 Absorbed dose rate – – – – – – – 85
4.1.3.3 Committed effective dose (Eing) – – – – – – 85
4.2.0 Instrumental Neutron Activation Analyses. – – – – – 90
4.2.1 Activity concentrations of 226Ra, 232Th and 40K. – – – – 90
4.2.2 Absorbed Dose rate and annual effective dose – – – – 93
4.2.3 Hazard indices – – – – – – – – 97
4.3.0 Water analysis with liquids scintillation counter – – – – 99
4.3.1 222Rn concentration – – – – – – – – 99
4.3.2 Annual effective dose – – – – – – – 106
4.4.0 Total Annual effective dose – – – – – – 110
4.5.0 Risks Estimate – – – – – – – – 112
CHAPTER FIVE
5.0 Summary, Conclusion and Recommendation – – – – 118
5.1.0 Summary – – – – – – – – – 118
5.2.0 Conclusion – – – – – – – – – 118
6.3.0 Recommendation – – – – – – – – 122
References – – – – – – – – – 129
INTRODUCTION
Mining is a global industry undertaken for its economic benefits of wealth creation and employment. In Africa, commercial scale mining provides important benefits in terms of exports/foreign exchange earnings and tax receipt to nineteen African countries (Hayumbu, and Mulenga, 2004).
Beside the socio-economic benefits of the mining industry in the developing countries such as Nigeria, the industry may be faced with three potential negative effects.
The first one is the socio-economic dislocation all ill-prepared mining communities go through at mine closure, which arise from exploitation of a non-regenerative resources (Hayumbu and Mulenga, 2004).
The second and third undesirable aspects arise when non-optimal management of mining operations results in environmental degradation and /or negative health impacts on miners and mining communities.
Principal health problems among miners and mining communities from various countries that have been cited by the literature include respiratory disease, neoplasm/cancer, chronic hypertension, mental health and genetic impact (WHO, 1999).
The major cause of these diseases can be attributed to the heavy metal contamination and naturally occurring radioactive materials NORMs (ICRP, 1994).
Mining and industrial processing are among the main sources of heavy metal contamination in the environment. Mining activities, through milling operations coupled with grinding, concentrating ores and disposal of tailings, along with mill wastewater provide obvious sources of heavy metal contamination of the environment.
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