Measurement of Environmental Radioactivity and Assessment of Doses to the General Public in Rechna Doab, Pakistan
By
Abdul Jabbar CIIT /SP05-PPH-001/ISB PhD Thesis
COMSATS Institute of Information Technology Islamabad, Pakistan
Fall, 2010
In The Name Of Allah, The Beneficent The Merciful
Measurement of Environmental Radioactivity and Assessment of Doses to the General Public in Rechna Doab, Pakistan
By
Abdul Jabbar CIIT /SP05-PPH-001/ISB
120 PhD Thesis 107 100 100 93 86.5 81 ) -1 80 70 75 h 68 65 60 51.5 54 46.1
40 Doserate (nGy Department of Physics 20 COMSATS Institute of Information 0 Technology n y b a e a h g a d k j s n i n e n r r n e o s a g a n n y o u u d K y w a t ta a J T P a la i r is s t d . Islamabad,l g a Pakistana e i s tu n g n T k k i N a n M v a k s i a o a P a a t d H d , P P n n B l , , e I r b b s o ja ja re e W n o r u n h P P u a . P L September, 2010S Measurement of Environmental Radioactivity and Assessment of Doses to the General Public in Rechna Doab, Pakistan
A Thesis Presented to COMSATS Institute of Information Technology, Islamabad In partial fulfillment of the requirement for the degree of Doctor of Philosophy in Department of Physics
By
Abdul Jabbar CIIT /SP05-PPH-001/ISB September, 2010
ii
Measurement of Environmental Radioactivity and Assessment of Doses to the General Public in Rechna Doab, Pakistan
A Post Graduate thesis submitted to the Department of
Physics
As partial fulfillment for the award of Degree of Doctor of Philosophy
Name Registration Number
Abdul Jabbar CIIT/SP05-PPH-001/ISB
Supervisor:
Prof. Dr. Arshad Saleem Bhatti, Dean, Faculty of Science CIIT, Islamabad Campus
Co-Supervisor:
Dr. Syed Salman Ahmad, Advisor to DG DOS Pakistan Atomic Energy Commission (PAEC) Islamabad
COMSATS Institute of Information Technology, Islamabad
iii
Final Approval
This thesis titled
Measurement of Environmental Radioactivity and Assessment of Doses to the General Public in Rechna Doab, Pakistan
By Abdul Jabbar
has been approved
for the COMSATS Institute of Information Technology, Islamabad
Supervisor: ______Prof. Dr. Arshad Saleem Bhatti CIIT, Islamabad
Co-Supervisor: ______Dr. Syed Salman Ahmad Advisor to DG DOS, PAEC, Islamabad
External Examiner: ______Dr. Gul Feroze Tariq
External Examiner: ______Dr. Masood Iqbal
HoD: ______Dr. Ishaq Ahmed
Dean: ______Prof. Dr. Arshad Saleem Bhatti
iv Declaration
I Abdul Jabbar, hereby declare that I have produced the work presented in this thesis, during the scheduled period of study. I also declare that I have not taken any material from any source except referred to wherever due. If a violation of HEC rules on research has occurred in this thesis, I shall be liable to punishable action under the plagiarism rules of the HEC.
Date: ______Signature of the student:
______(Abdul Jabbar) (CIIT /SP05-PPH-001/ISB)
v
Certificate
It is certified that Mr. Abdul Jabbar has carried out all the work related to this thesis under our supervision at the Department of Physics, CIIT, Islamabad.
Supervisor: Co-Supervisor:
Prof. Dr. Arshad Saleem Bhatti Dr. Syed Salman Ahmad Dean, Faculty of Science Advisor to DG DOS CIIT, Islamabad, Pakistan Pakistan Atomic Energy Commission (PAEC), Islamabad, Pakistan
Submitted through:
Dr. Ishaq Ahmed Head, Department of Physics CIIT, Islamabad
Prof. Dr. Sajid Qamar Chairman, Department of Physics CIIT, Islamabad
vi
Dedicated To My beloved parents (late) (May Allah rest their souls in eternal peace!) and my caring wife & children
vii ACKNOWLEDGEMENTS
All praises are for ALMIGHTY ALLAH, the most Benevolent, the most Compassionate, whose blessings and graciousness flourished my ideas and endowed me with the strength required to complete this work. My humble respects are for the Holy Prophet (Peace Be Upon Him) who enlightened our scruples with the essence of faith in ALMIGHTY ALLAH and emphasized to seek knowledge, from cradle to the grave, for betterment of oneself and the humanity at large. The research work presented in this thesis has been carried out under the kind supervision of worthy Prof. Dr. Arshad Saleem Bhatti, Dean, Faculty of Science, CIIT, Islamabad. His kind attitude, positive and thoughtful criticism, sincere advices, and valuable suggestions always guided me and served as source of encouragement throughout my studies. I would also like to pay gratitude to Dr. S. Salman Ahmad, Co-supervisor, advisor to DG DOS, Pakistan Atomic Energy Commission, Islamabad for his keen interest, scholarly comments and constructive promptings during my studies. I acknowledge the cooperation, technical guidance, valuable suggestions and encouragement extended by Dr. M. Tufail, DCS, DNE, PIEAS, Islamabad and Dr. Shahid Manzoor, PS, PD, PINSTECH. I am also thankful to Dr. Waheed Arshed, DCS, Head SSDL, Health Physics Division, PINSTECH, Islamabad, for his much needed guidance and his keen involvement in my work, which resulted in completion of this thesis. I am thankful to Dr. I.E. Qureshi, Executive Director COMSATS who was instrumental in establishing a MoU between CIIT and PINSTECH, which facilitated tuition fee concession and accomplishment of PhD studies smoothly. I am thankful to
viii Dr. S.M. Junaid Zaidi, Rector CIIT for providing a dynamic scientific research environment, Head of Department and the faculty members of the Department of Physics, CIIT, Islamabad, for their nice cooperation. I am obliged to PAEC and PINSTECH authorities who allowed me to complete this study and provided support in performing the field work. I pay special gratitude to Dr. Perveen Akhter, CS, Head Health Physics Division, PINSTECH for extending experimental facilities required to accomplish this research work. My heartiest thanks to my colleagues at HPD and PhD fellows at CIIT, specially Mr. M. Dilband, Mr. M. Iftikhar, Mr. Tanveer Ahmad, Dr. M. Munir, Dr. Jahan Zeb Khan, Mr. Qaiser Bashir, Mr. Zahid Hussain, Mr. Ijaz Haider, Mr. M. Tariq, Mr. M. Hanif, Mr. S.U. Rehman, Mr. Zafar Wazir, Mr. Faisal, Mr. Rizwan, Dr. Narjis, Mr. Shahid, Mr. Hafeez and Mr. Awais for their cooperation and valuable suggestions. I acknowledge the nice cooperation extended by Dr. Manzoor Ahmad, Technical Officer, IAEA and Dr. Masood Iqbal, PS, NED, PINSTECH, Islamabad. Last but not the least; I am greatly indebted to all my relatives, friends and well-wishers. I can never forget my caring wife and lovely children for their love, support and special attention throughout my PhD studies. I would like to pay special tribute to my beloved father (Allah rest his soul in eternal peace) and my teacher Mr. Muhammad Younis (Retd.); both played a vital role in my early education.
(Abdul Jabbar)
ix CONTENTS
List of Figures ------xv List of Tables ------xviii Publications ------xxi Abstract ------xxiii
Chapter 1: INTRODUCTION 1
1.1 Environmental radioactivity ------2 1.1.1 Radioactivity in air ------3 1.1.2 Radionuclide concentration in soil ------4 1.1.3 Radionuclide concentration in water ------5 1.1.4 Transfer of radioactivity from soil to vegetation ------6 1.1.5 Radioactivity levels in staple food ------7 1.1.6 Strontium-90 levels in different environmental media ------9 1.2 Measurement techniques ------10 1.2.1 Gamma measurement ------10 1.2.2 Beta measurement ------11 1.3 Motivation of study ------12 1.4 Objectives of study ------12 1.5 Thesis layout ------13
Chapter 2: AREA UNDER STUDY AND SAMPLING 14
2.1 Area under study ------15 2.1.1 Area ------16 2.1.2 Location ------16 2.1.3 Geology ------16
x 2.1.4 Climate ------18 2.1.5 Irrigation System ------18 2.1.6 Agriculture ------19 2.1.7 Population ------19 2.2 Sampling of different environmental media ------20 2.2.1 Soil sampling ------20 2.2.1.1 Representative soil sampling ------20 2.2.1.2 Benefits of representative soil sampling ------21 2.2.1.3 Methodology involved in soil sampling ------21 2.2.1.3.1 Site selection criteria ------21 2.2.1.3.2 Compilation of background information ------21 2.2.1.4 Systematic grid sampling approach ------22 2.2.1.5 Core methododology for soil excavation ------23 2.2.2 Water sample collection------25 2.2.3 Vegetation sample collection ------25 2.2.4 Staple food sample collection ------25 2.3 Sample processing ------25 2.3.1 Pre-treatment of soil samples ------26 2.3.1.1 Drying process ------26 2.3.1.2 Homogenization ------27 2.3.2 Pre-treatment of water samples ------27 2.3.3 Pre-treatment of vegetation samples ------28 2.3.4 Pre-treatment of staple food samples ------28 2.4 Conclusion ------29
Chapter 3: GAMMA RADIOACTIVITY MEASUREMENTS 30
3.1 Gamma Spectrometry ------30 3.1.1 Gamma-spectrometric equipment ------31 3.1.2 Sample containers ------32 3.1.2.1 Packing of samples for measuring purposes ------33
xi 3.1.2.2 Establishment of secular equilibrium ------33 3.2 Detector shielding ------35 3.2.1 The graded shielding ------36 3.2.2 Laboratory background level 37 3.3 Analytical accuracy, IAEA standards ------37 3.4 Counting uncertainties ------37 3.5 Minimum Detectable Activity ------38 3.6 Energy calibration ------39 3.7 Peak efficiency calibration ------40 3.8 Calculation of radioactivity per unit volume or mass ------42 3.8.1 Corrections for contributions from other radionuclides and background ------44 3.9 Analysis of natural and fallout radionuclides ------44 3.9.1 Determination of Radium-226------46 3.9.2 Determination of Thorium-232------47 3.9.3 Determination of Potassium-40 ------47 3.9.4 Determination of Cesium-137 ------47 3.10 Conclusion ------48
Chapter 4: RADIOACTIVITY LEVELS IN SOIL, WATER, VEGETATION AND STAPLE FOOD 49 4.1 Radioactivity levels in soil media ------50 4.1.1 Radioactivity levels in northern Rechna Doab ------50 4.1.2 Radioactivity levels in mid Rechna Doab ------55 4.1.3 Radioactivity levels in southern Rechna Doab ------59 4.1.4 Comparison of radioactivity levels in soil ------62 4.2 Radioactivity in surface water ------65 4.2.1 Concentration of radionuclides in surface water ------66 4.3 Soil-to-plant uptake of radionuclides ------67 4.3.1 Radioactivity levels in vegetation ------67 4.3.2 Transfer of radionuclides from soil to plant ------70
xii 4.4 Radioactivity levels in staple food ------73 4.4.1 Radionuclide concentration in staple food ------73 4.5 Conclusion ------75
Chapter 5: DETERMINATION OF STRONTIUM-90 IN DIFFERENT ENVIRONMENTAL MEDIA 76 5.1 Sample collection and pre-treatment ------77 5.2 Radiochemical processing ------77 5.2.1 Strontium carrier solution ------78 5.2.2 Yttrium carrier solution ------78 5.2.3 Radiochemical separation of 90Y ------78 5.2.4 Extraction of Y from Sr and other elements ------79 5.2.5 Precipitation as Yttrium Oxalate ------80 5.3 Liquid scintillation counting ------82 5.4 Results and discussion ------84 5.5 Conclusion ------87
Chapter 6: HEALTH RISKS AND RADIATION HAZARD ASSESSMENT 88 6.1 Hazards due to environmental radiation doses ------89 6.1.1 Environmental radiation doses in northern Rechna Doab ------90 6.1.2 Environmental radiation doses in mid Rechna Doab ------92 6.1.3 Environmental radiation doses in southern Rechna Doab ------93 6.2 Radiation hazards due to radionuclides present in soil ------94 6.2.1 Radium equivalent activity ------94 6.2.1.1 Radium equivalent activity in northern Rechna Doab ------94 6.2.1.2 Radium equivalent activity in mid Rechna Doab ------94 6.2.1.3 Radium equivalent activity in southern Rechna Doab ----- 95 6.2.2 Radiation hazard indices ------95 6.2.2.1 Radiation hazard indices in northern Rechna Doab ------96 6.2.2.2 Radiation hazard indices in mid Rechna Doab ------96 6.2.2.3 Radiation hazard indices in southern Rechna Doab ------96
xiii 6.2.3 Gamma dose rate ------97 6.2.3.1 Gamma dose rate in northern Rechna Doab ------97 6.2.3.2 Gamma dose rate in mid Rechna Doab ------97 6.2.3.3 Gamma dose rate in southern Rechna Doab ------97 6.2.4 Annual effective dose ------98 6.3 Radiation hazards due to radionuclides present in water ------105 6.4 Radiation hazards due to radionuclides present in vegetation ------105 6.5 Radiation hazards due to radionuclides present in staple food ------107 6.5.1 Daily intake of 40K from staple food ------107 6.5.2 Annual internal doses from staple food ------108 6.6 Cancer risk assessment ------110 6.7 Conclusion ------113
Chapter 7: CONCLUSIONS AND RECOMMENDATIONS 114
7.1 Conclusions ------114 7.2 Recommendations for future studies ------117
REFERENCES 118
xiv List of FIGURES
Fig 2.1: Map of Study Area, Rechna Doab, Pakistan along with three sub- divided parts. ------15 Fig 2.2: Soil texture of study area. ------17 Fig 2.3: Extended part of the map of the study area, as shown in figure 2.1, illustrating systematic grid sampling approach. ------22 Fig 2.4: A Global Positioning System (GPS) to record coordinates of the sampling site, used during present study. ------24 Fig 2.5: Illustration of use of hand corer for soil sampling. ------24 Fig 2.6: Illustration of systematic grid sampling approach applied at each sampling point. ------24 Fig 2.7: A view of a specially designed electric furnace to remove moisture contents and to burn plant remains in the samples. ------27 Fig 3.1: Schematic diagram of PC based high resolution gamma spectrometry system. ------31 Fig 3.2: Specially designed and manufactured marinelli beakers. ------32 Fig 3.3: Secular equilibrium showing buildup of a very short lived daughter radionuclide from a very long lived parent radionuclide. The activity of the parent radionuclide remains constant. ------35 Fig 3.4: Detector shielding, specially designed for the present study. ------36 Fig 3.5: A laboratory background spectrum counted for 65,000 seconds on gamma spectrometry system. ------37 Fig 3.6: Energy calibration curve of the gamma spectrometer. ------40 Fig 3.7: Full energy peak efficiency curve of the gamma spectrometry system for soil. ------41 Fig 3.8: Gamma ray Spectrum of a soil sample acquired using an HPGe detector. ------43 Fig 3.9: Uranium-238 decay series. ------45 Fig 3.10: Thorium-232 decay series. ------46
xv
Fig 4.1: (a) Correlation between 226Ra and 232Th concentrations; (b) correlation between 226Ra and 40K concentrations; (c) correlation between 232Th and 40K concentrations in northern Rechna Doab, Pakistan. ------52 Fig 4.2: Frequency distribution of (a) 226Ra, (b) 232Th and (c) 40K concentration in northern Rechna Doab, Pakistan. ------54 Fig 4.3: Frequency distribution of the concentrations of (a) 226Ra, (b) 232Th and (c) 40K in mid Rechna Doab, Pakistan. ------58 Fig 4.4: Frequency distribution of the activities in southern Rechna Doab, Pakistan of (a) 226Ra, (b) 232Th and (c) 40K (Bq kg-1).------61 Fig 4.5: Comparison of mean concentration of 226Ra with different countries of the World. ------63 Fig 4.6: Comparison of mean concentration of 232Th with different countries of the World.------63 Fig 4.7: Comparison of mean concentration of 40K with different countries of the World. ------64 Fig 4.8: Comparison of concentration of 137Cs with different countries of the World. ------65 Fig 5.1: Liquid scintillation plastic vials along with specifications, used for counting of environmental media on liquid scintillation analyzer. ----- 78 Fig 5.2: Different steps of radiochemical separation procedure for 90Sr. ------81 Fig 5.3: Liquid Scintillation Analyzer used for determination of 90Sr in different environmental media collected during present study. ------82 Fig 5.4: Schematic arrangement of photomultiplier tubes and associated electronics required for liquid scintillation coincidence counting. ----- 83 Fig 6.1: A view of portable FAG dose rate meter used during present study. -- 89 Fig 6.2: Comparison of measured and calculated dose rates in the study areas, (a) northern (b) mid and (c) southern Rechna Doab, Pakistan. ------102 Fig 6.3: Frequency distribution of dose rate in air (nGy h-1) for (a) northern (b) mid and (c) southern parts of Rechna Doab, Pakistan. ------103
xvi
Fig 6.4: Comparison of average dose rate in air, calculated from soil activity concentrations with different countries of the world. ------104 Fig 6.5: Comparison of daily activity intake of 40K through staple food with different countries of the world. ------108 Fig 6.6 Comparison of annual internal dose to adult population of world from intake of 40K. ------110
xvii List of TABLES
Table 2.1: Area and population of different districts in the Rechna Doab. ------19 Table 3.1: The Minimum Detectable Activity (MDA) for the radionuclides 40K, 226Ra, 232Th and 137Cs for different environmental media. ------39 Table 3.2: Gamma-ray energies used for the calibration of spectrometer and for the measurement of activity of the radionuclides of interest. ------44 Table 4.1: Activity concentrations (Bq kg-1) of 226Ra, 232Th, 40K and 137Cs in soil samples of northern Rechna Doab, Pakistan along with location parameters. ------51 Table 4.2: Statistical data for activity concentration of 226Ra, 232Th and 40K in surface soil samples from northern Rechna Doab, Pakistan. ------53 Table 4.3: Activity concentrations (Bq kg-1) of 226Ra, 232Th, 40K and 137Cs in soil samples of mid Rechna Doab, Pakistan along with location parameters. ------56 Table 4.4: Statistical data for radioactivity concentrations of 226Ra, 232Th and 40K in surface soil samples of mid Rechna Doab, Pakistan. ------57 Table 4.5: Activity concentrations (Bq kg-1) of 226Ra, 232Th, 40K and 137Cs in soil samples of southern Rechna Doab, Pakistan along with location parameters. ------59 Table 4.6: Statistical data for radioactivity concentrations of 226Ra, 232Th and 40K in surface soil samples from southern Rechna Doab, Pakistan. -- 60 Table 4.7: Activity concentrations (Bq l-1) of 226Ra and 40K in surface water samples of Rechna Doab, Pakistan. ------66 Table 4.8: Activity concentrations (Bq l-1) of 226Ra and 40K in water samples reported from different countries of the world. ------67 Table 4.9: Activity concentrations of 226Ra, 228Ac and 40K (Bq kg-1) in vegetation of Rechna Doab, Pakistan. ------69 Table 4.10: Activity concentration (Bq kg-1) of 226Ra, 228Ac and 40K in vegetation samples reported from different countries of the World. -- 70
xviii Table 4.11: Transfer coefficients from soil to vegetation of the listed radionuclides for the samples collected from Rechna Doab, Pakistan. ------72 Table 4.12: Activity concentration (Bq kg-1) of 40K in staple food samples of Rechna Doab, Pakistan. ------74 Table 5.1: The Minimum Detectable Activity (MDA) for the radionuclides 90Sr in different environmental media. ------84 Table 5.2: Strontium-90 activities measured in different environmental media collected from Rechna Doab, Pakistan. ------85 Table 5.3: Comparison of activity concentration of 90Sr (Bq kg-1) in soil and vegetation samples reported from different countries of the world. -- 86 Table 6.1: Environmental gamma radiation levels in northern Rechna Doab, Pakistan. ------91 Table 6.2: Environmental gamma radiation levels in mid Rechna Doab, Pakistan. ------92 Table 6.3: Environmental gamma radiation levels in southern Rechna Doab, Pakistan. ------93 Table 6.4: Calculated values of radium equivalent activity, absorbed dose rate, outdoor hazard index and indoor hazard index in the northern Rechna Doab, Pakistan. ------99 Table 6.5: Calculated values of radium equivalent activity, absorbed dose rate, outdoor radiation hazard index and indoor radiation hazard index in the mid Rechna Doab, Pakistan. ------100 Table 6.6: Calculated values of radium equivalent activity, absorbed dose rate, outdoor radiation hazard index and indoor radiation hazard index in the southern Rechna Doab, Pakistan. ------101 Table 6.7: Statistical data for calculated dose rates in surface soil samples from three parts of Rechna Doab, Pakistan. ------104 Table 6.8: Calculated values of radium equivalent activity, absorbed dose rate, annual effective dose and outdoor radiation hazard index in the vegetation samples collected from Rechna Doab, Pakistan. ------106
xix
Table 6.9: Daily intake of radioactivity and annual internal dose due to 40K assessed from typical staple food used in Rechna Doab, Pakistan. --- 109 Table 6.10: Estimated loss of life due to different carcinogens. ------111 Table 6.11: Fatal cancer risks for general public of the study area, Rechna Doab, Pakistan. ------112
xx PUBLICATIONS
1. Abdul Jabbar, Waheed Arshed, Arshad Saleem Bhatti, Syed Salman Ahmad, Perveen Akhter, Saeed-Ur-Rehman and Muhammad Iftikhar Anjum, Measurement of soil radioactivity levels and radiation hazard assessment in southern Rechna interfluvial region, Pakistan, Environ. Monit. Assess., 169 (1-4), 429 (2010). 2. Abdul Jabbar, Muhammad Tufail, Waheed Arshed, Arshad Saleem Bhatti, Syed Salman Ahmad, Perveen Akhter and Muhammad Dilband, Transfer of radioactivity from soil to vegetation in Rechna Doab, Pakistan, Isotopes in Environmental and Health Studies, 46 (4), 495 (2010). 3. Abdul Jabbar, Waheed Arshed, Arshad Saleem Bhatti, Syed Salman Ahmad, Saeed-Ur-Rehman and Muhammad Dilband, Measurement of soil radioactivity levels and radiation hazard assessment in mid Rechna interfluvial region, Pakistan, J. Radioanal. Nucl. Chem. 283, 371 (2010).
4. Abdul Jabbar, Arshad S. Bhatti, Syed S. Ahmad Waheed Arshed, and Perveen Akhter, Assessment of environmental gamma dose in northern Rechna Doab in Pakistan, J. of Nuclear Technology and Radiation Protection, 24, 56 (2009).
5. S.U. Rahman, Matiullah, F. Malik, M. Rafique, J. Anwar, M. Ziafat, A. Jabbar Measurement of naturally occurring/fallout radioactive elements and assessment of annual effective dose in soil samples collected from four districts of the Punjab Province – Pakistan, J. Radioanal. Nucl. Chem., 287(2), 647 (2011).
6. A. Jabbar, A. S. Bhatti, S.U. Rahman, W. Arshed, P. Akhter, S.S. Ahmad and M.I. Anjum, Assessment of environmental gamma dose in southern Rechna Doab, Pakistan, proceedings of International PIP Conference, February, Lahore, pp. 59-63 (2009).
xxi
7. A. Jabbar, S.U. Rehman, W. Arshed, A. S. Bhatti, S. S.Ahmad, P. Akhter and M. Dilband, Natural radionuclide distribution in soil samples of interfluvial region, Punjab, Pakistan, proceedings of International ESDev conference, August, CIIT, Abbottabad, pp. 59-68 (2009).
Presentations
1. Assessment of environmental gamma dose in southern Rechna Doab, Pakistan, presented in International PIP Conference, February 2009, University of Engineering and Technology, Lahore.
2. Determination of strontium-90 in environmental media samples, presented in the IAEA/ICTP workshop on understanding and evaluating radioanalytical measurement uncertainty, November 2007, Trieste, Italy.
3. Radiological environmental monitoring techniques, two presentations were delivered in 2nd Orientation Course for International relations analysts, August, 2008, International Relations Office, Islamabad.
Submitted papers
1. A. Jabbar, W. Arshed, A. S. Bhatti, S. S. Ahmad, P. Akhter and M. Dilband, Radioactive contents and background doses from alluvial sediment plains between rivers Ravi and Chenab, Pakistan, submitted for publication in International Journal of Low Radiation. 2. A. Jabbar, W. Arshed, A. S. Bhatti, S. S. Ahmad, P. Akhter and M.I. Anjum, Determination of 90Sr levels in environment of Rechna Doab, Pakistan submitted for publication in Journal of Radioanalytical and Nuclear Chemistry.
xxii ABSTRACT
A systematic study in Rechna Doab, Pakistan was carried out to establish background radiation data and to assess the radiological environmental pollution and its impact on the humans and the environment. The study was carried out through the measurement of gamma and beta emitting radionuclides in different environmental media e.g. soil, surface water, vegetation and staple food. The concentration levels of primordial radionuclides 226Ra, 232Th and 40K and anthropogenic radioisotopes 137Cs and 90Sr were determined. As the study area was quite large, having different lithological components so it was divided into three parts as northern, mid and southern. Gamma ray spectroscopy technique was used to study the gamma emitting radionuclides in different environmental media. Mean radioactivity levels in soil of northern parts of the study area came out to be 226Ra, 45.0±1.3 Bq kg-1, 232Th, 59.6±2.8 Bq kg-1, 40K, 613.8±20.0 Bq kg-1 and 137Cs, 4.0±0.2 Bq kg-1. The concentration levels of radioisotopes in soil of mid Rechna Doab were 226Ra, 49.0±1.6 Bq kg-1 232Th, 62.4±3.2 Bq kg-1, 40K, 670.6±33.9 Bq kg-1 and 137Cs, 3.5±0.4 Bq kg-1. The levels of concerned radionuclides in soil of southern parts were 226Ra, 50.6±1.7 Bq kg-1, 232Th, 62.3±3.2 Bq kg-1, 40K, 662.2±32.1 Bq kg-1 and 137Cs, 3.1±0.3 Bq kg-1. The radioactivity levels in surface water collected from the study area were 226Ra, 0.9±0.2 Bq l-1 and 40K, 2.5±1.6 Bq l-1 while the levels of the concerned radionuclides in vegetation were 226Ra, 2.7±0.4 Bq kg-1 232Th, 2.2±0.1 Bq kg-1 and 40K, 172.7±4.0 Bq kg-1. Potassium-40 was the only radionuclide found in the staple food consumed by the general public of the study area, having concentration levels 174.3±2.7 Bq kg-1 (wheat) and 27.6±1.4 Bq kg-1 (rice). The radioactivity levels of 40K were found to be slightly higher than that of 232Th and 226Ra at all the places of the study area. These raised levels of 40K is an indication of the fact that most of the area under
xxiii study is fertile and fertilizers are being used copiously in large quantities to get good crops. The average values of soil to plant transfer factors in the vegetation samples collected from the Rechna Doab were 0.06, 0.26 and 0.04 for 226Ra, 40K and 232Th respectively. In most of the collected vegetation samples, the transfer factors for different radionuclides were in the order: 40K>232Th>226Ra. Average 40K daily intake through the staple food consumed by the humans residing in the study area was 64.6 Bq day-1. The levels found in staple food of the study area were on lower side than the ICRP values and other global values. Liquid scintillation counting system was used to determine the radioactivity levels of beta emitting radionuclide, 90Sr. Mean radioactivity levels of beta emitting anthropogenic radionuclide 90Sr in soil samples of the study area were 3.0 Bq kg-1 while it was 1.4 Bq kg-1 in vegetation samples. The levels of 90Sr in soil and vegetation have been compared with the same determinations in some European countries, USA and Ukraine and found less than these countries. Annual internal dose through ingestion of staple food was found to be 146 µSv y-1. The results of ingestion doses obtained were comparable with other countries of the world. Radium equivalent activity levels in three parts of the study area in north, mid and south were found to be 177.6, 189.9 and 190.8 Bq kg-1 while the absorbed dose rates in air were came out to be 85.09, 70.1 and 69.8 nGy h-1 respectively. Indoor radiation hazard index was determined as 0.60, 0.65 and 0.65 and out door radiation hazard index was 0.48, 0.51 and 0.52 while annual effective dose was 0.52, 0.43 and 0.43 mSv y-1. Fatal cancer risk assessment was made on the basis of total external dose received to the population through soil and vegetation and internal dose received through ingestion of staple food. Fatal cancer risk to the population was found to be comparable in all parts of the study area. Health risks to the population of the Rechna Doab, Pakistan due to external and internal radiation doses were much smaller than the risks associated with other activities of daily life. On the basis of the present study, it is concluded that annual radiation doses received by population of the study area neither pose any significant radiological impact on human health nor contribute towards fatal cancer risk to the population.
xxiv Chapter 1
INTRODUCTION
The Earth continues to be affected by both natural events and human activities. The global environment around us contains small amounts of radionuclides that are derived from primordial, cosmogenic, and anthropogenic sources. Radionuclides in the air, soil, water, and rocks that make up our Earth and its atmosphere can be transferred into the ecosphere by many organisms and accumulated in food [1]. A large amount of the radioactivity to which we are exposing ourselves daily, comes from natural sources occurring in our nearby environment and the buildings in which we are living. In most of the places on the Earth, the natural radioactivity levels are comparable, but in some localities it varied by large amounts because of abnormally high concentrations of radioactive contents in soil [2]. Environmental radionuclides can be grouped into three categories primordial, cosmogenic and anthropogenic. Primordial radionuclides (uranium, thorium and potassium) have very long half lives and were produced at or before the creation of the Earth. Uranium and thorium have decay chains and their decay products are referred to as daughters [3]. Cosmogenic radionuclides are formed by the interaction of cosmic rays with the Earth’s atmosphere. Anthropogenic radionuclides are formed from man made activities that create artificial radionuclides [4]. All the three types of radionuclide sources have been discussed in this chapter. The public concern and awareness about the environmental radioactivity has been increased too much. Due to these reasons the present study has been carried out to Chapter-1: Introduction measure the amount of radioactivity for the assessment of radiation doses from outside and from the ingestion of staple food. Pakistan is eager to fill the supply and demand energy gap with the development of nuclear energy. The area under study lies between two independent rivers of Pakistan and is expected to have more than one sites for nuclear power reactor installations. Putting the present study in this perspective, environmental radioactivity further enhances its importance.
1.1 Environmental radioactivity
Ionizing radiations enter into our lives in a variety of ways. Natural sources of radioactivity include cosmic rays, gamma rays from the Earth, radon decay products in the air, and various radionuclides in edibles and potables [5]. The sources of radiation deliver dose to the human beings. We cannot change our exposure to the natural sources, cosmic rays and natural radioactivity within the body [6]. Cosmic rays are a source of gamma radiation which are produced from the extra-terrestrial bodies and travelled to our planet Earth. When these radiations enter into our atmosphere, they begin to be absorbed by air and the radiation level on the ground is noticeably reduced. The radiation dose level increases with altitude and are the highest for the people in aircrafts due to cosmic rays [7]. Terrestrial radiation arises from natural processes, such as the decay of uranium and thorium in the Earth. The buildings in which human beings are living and working have been built from materials which contain uranium, thorium and potassium [8]. Radioactivity present in air or soil may be transferred to food grown on the soil. The radiation dose to human beings varies depending on the food quantities consumed and the rate at which the body excretes the radioactivity [9]. Due to nuclear weapon testing in early sixties and Chernobyl reactor accident in 1986, atmosphere contains anthropogenic radioactive materials e.g. 137Cs and 90Sr which are present in sea water and soils. The nuclear weapon tests transported radioactive fragments to the upper stratosphere from where it is coming back to the Earth. Many hospitals and industries are discharging radioactive substances to the environment in a controlled way [10].
2 Chapter-1: Introduction Radiation dose from radon decay products is also unavoidable. It is easier, in most cases, to control artificial sources of radiation but there is a balance to be made [11]. The doses that are received by the people are affected by the geology of the area [12].
1.1.1 Radioactivity in air
The air that we breathe in also contains radioactive materials which deliver whole body external dose and internal dose to the lungs [13]. External exposures arise from terrestrial radionuclides present in trace levels in all soils and from cosmic radiations. The specific levels in soils are related to the types of rock from which the soils originate. Higher radiation levels are associated with igneous rocks, such as granite, and lower levels with sedimentary rocks. The major part of radiation dose is received from radon gas; 222Rn, a daughter product of uranium decay series and 220Rn from the decay of thorium. Both uranium and thorium are present in rocks, soil and building materials [14, 15]. The levels of these radionuclides in air depend on the quantity of uranium and thorium in the ground and how much they can emanate from the ground and from building materials. Due to these reasons the radioactivity levels inside buildings may be little higher, especially in case of poor ventilation. Within buildings and other enclosed places where the air cannot be circulated, these levels may be high [16]. Mostly, gamma-ray surveys have been conducted for geological/mineral exploration, involving the measurement of the natural radionuclides, 40K, 232Th and 238U. Besides this, there has also been a continuing concern in determining the levels of anthropogenic radionuclides present in the environment. In either case, it is important to maximize the data available on the environmental impact that can be derived from these surveys. This baseline data provides radioactivity information for both natural and artificial radionuclides and improves the important role of monitoring worldwide changes in levels of radiation and their possible impact on the health of human beings [17]. Many surveys have been made worldwide to determine the background levels of radionuclides in soils, which can in turn be related to the absorbed dose rates in air. The later can easily be measured directly, and results of such measurements provide an even more extensive evaluation of the background exposure levels in different countries [18, 19].
3 Chapter-1: Introduction
1.1.2 Radionuclide concentration in soil
Naturally occurring radionuclides of terrestrial origin (also called primordial radionuclides) and artificial radionuclides that are present in the environment are main sources of radiation exposure for human beings. The primordial radionuclides have radioactive decay half-lives that are approximately the Earth’s age. These radionuclides and their radioactive decay products are an important source of the Earth’s radioactivity. Naturally occurring radionuclides are present in various degrees in all media in the environment. The cumulative fallout from nuclear weapon tests, nuclear accidents and the natural radioactivity from the primordial radionuclides, radioactivity levels in undisturbed soils can be used as a base line data [20]. The human population is exposed to radiation from these radionuclides directly, as a result of external exposure, or through incorporation of these radionuclides into the body through inhalation or ingestion. For the assessment of the radiation exposure effects, the distribution of these radionuclides is determined. Therefore, many researchers in the world are taking interest in measurements of natural radioactivity in air, soil and drinking water samples [21]. 40 Rocks, soils and minerals contain naturally occurring radionuclides such as K, 238 232 137 U and Th and the fallout radionuclides Cs and 90Sr [22]. These radionuclides contribute significantly to natural background levels of radioactivity through their radioactive progeny or daughters, which often have much shorter half-lives and lead to a chain of radioactive isotope production [23]. These naturally occurring radionuclides compose a significant portion of the natural radionuclides present on the Earth because they are significantly long-lived [24]. All the uranium isotopes are radioactive, and their decay produces a number of secondary radioactive elements that continue to decay until they reach stable nuclei. This decay chain of radionuclides is commonly referred to as the uranium decay series. Similarly thorium, another primordial isotope with a long half-life, also has a decay series that leads to the formation of numerous naturally occurring secondary radionuclides. Thus the key primordial radionuclides of uranium and thorium decay to many other radioactive isotopes that occur in the environment at different levels of abundance, depending on their own decay rates and those of their parents [25, 26].
4 Chapter-1: Introduction Other natural isotopic species on the Earth’s surface include 40K. Potassium is quite an abundant element, composing more than 2% of the Earth’s crustal mass. Because of its biological uptake, 40K is the most significant natural source of radioactivity ingested by humans [27]. The study of the background levels of 137Cs in soil is very important because it is the main source of inventory of radionuclides entering into the food cycle. Its presence in soil would clearly indicate that the area under study might have received some global fallout radioactivity in the past [28, 29].
1.1.3 Radionuclide concentration in water
Water is a medium for the transport and interaction of radionuclides with and within different parts of the troposphere: soils, sediments, crustal rocks, biota, and air are continuously exchanging their radioactive contents with water. The presence of natural and artificial radionuclides at different levels in surface waters is correlated with above mentioned different parts [30]. In fact, surface waters are coupled to subsurface aquifers, to soils, and to the atmosphere, allowing incorporation of several radionuclides following different routes. Indeed, some radionuclides previously dissolved in deep underground aquifers may reach surface waters, other radionuclides may be directly incorporated in surface waters by deposition from the atmosphere, and a large fraction of the radionuclides in aquatic systems have their origins in the underlying soils, from where they can be transported to surface waters through runoff into the groundwater. The first and the last routes are the most important ones explaining the presence of natural radionuclides in rivers and lakes, while the second and third routes, together with direct discharges from nuclear facilities [31]. Once radionuclides are incorporated in a body of water, their dispersion and behavior is hard to predict in a general or straightforward way. Each stream, river, lake, etc., has its own mixing characteristics that vary from place to place and time to time, the rate of mixing being dependent on the depth of the water, the type of bottom, the shoreline configuration, wind, etc., and on the different chemical and biological processes [32]. All these factors make it quite difficult to predict, especially in rivers, the behavior and dispersion of radionuclides. However, if sufficient information can be
5 Chapter-1: Introduction obtained about their physical characteristics, it is possible to estimate with some degree of certainty, the dispersion of some specific radionuclides. More advancement has been made in the prediction of radionuclide behavior in lakes. Models for predicting the migration of radionuclides through the biotic and abiotic components of lacustrine environments have been identified by the researchers [33]. Among the different natural radionuclides that can be found in nature, there are radionuclides belonging to the uranium and thorium series and 40K, the isotopes that may be present at higher levels in water. Uranium can be found in dissolution in most surface water systems. In contrast, thorium is quite insoluble in the majority of natural waters, being present or transported in the suspended matter of water bodies [34]. In addition to the inputs of natural radionuclides related to increased agriculture, some specific rivers around the world have not been free of anthropogenic inputs of natural radionuclides due to releases produced by nuclear and non-nuclear activities. Anthropogenic inputs of uranium associated with other mineral activities have been observed, such as the ones related with pyrite extraction. Saline water from underground coal mines contains natural radioisotopes, mainly 226Ra from the uranium decay series [35]. Furthermore, several industries generate wastes that are radionuclide enriched such as Technologically Enhanced Naturally Occurring Radioactive Materials (TENORMs). Such industries release a fraction of these radionuclides into freshwater [36].
1.1.4 Transfer of radioactivity from soil to vegetation
Soils are heterogeneous systems, combining three un-mixable phases (solid, liquid and gaseous) in different and changing proportions depending on the humidity level. Each phase is highly complex and variable in composition and physicochemical properties [37, 38]. Soil contains natural radioactivity that comes mainly from the primordial radionuclides 238U, 232Th and 40K, which are present at trace levels in the Earth’s crust and distributed in ground formations [39, 40]. Since radioactivity is present everywhere in soil, wherefrom it is transferred to plants or vegetation through uptake of radionuclides either via the root system or by external plant surfaces and the former path is more effective [41]. Uptake of
6 Chapter-1: Introduction radionuclides from soil to plant is characterized using a transfer factor (TF), which is defined as the ratio of the concentrations of radionuclides in plant (Bq kg-1 dry mass) to that in soil (Bq kg-1 dry mass) [42, 43]. This ratio describes the amount of radionuclides expected to enter a plant from its substrate, under equilibrium conditions. The TF for a given type of plant and for a given radionuclide depends on many factors such as physiochemical characteristics of a site, weather conditions and time after contamination, etc. [44]. The TF is usually used for evaluating the impact of releases of radionuclides into the environment [45]. Soil–plant–man is recognized as one of the major pathways for transfer of radionuclides to human beings [46, 47]. The migration and accumulation of radionuclides in the soil plant system is a complex phenomenon, involving processes such as leaching, capillary rise, runoff, sorption, root uptake and re-suspension into the atmosphere [48]. In terms of the radioecology of the terrestrial ecosystem, the uptake of radionuclides by vegetation has received the most attention, due to the potential food chain transfer to man [49]. In recent years a growing interest in the evaluation of fluxes of nutrients as well as contaminants through ecosystems has been expressed in many fields of environmental research, including radioecology [50-52]. The knowledge of concentration levels and distributions of the radionuclides in plants and vegetation are of interest because it provides useful information regarding environmental radioactivity [53]. The study of radionuclide transfer from soil to edible vegetation through root uptake is important, especially considering accumulation of these radionuclides in the food chains. Information on the existence and accumulation of radionuclides in vegetation, plants, etc., has gained importance because users of these products may develop a higher incidence of cancers and other health effects [54]. The assessment of radiological hazard of vegetation depends on its applications. If it is an edible then internal hazards are important otherwise there is need to estimate external hazard using some mathematical model [55].
1.1.5 Radioactivity levels in staple food
Everybody needs food to stay alive and develop. Food can be contaminated with a wide range of pollutants including radioactivity. Some radionuclides are naturally occurring in soil, rocks, underground water, oceans, and the atmosphere. Their transfer to the food
7 Chapter-1: Introduction chain is directly linked to parameters such as their chemical form and redox conditions of the environment. Chemistry within the upper layer of soil is critical in the transfer of radioactivity from soils to plants [56, 57]. Exchange of air within the atmosphere is also a major parameter for cosmogenic radionuclides available in the atmosphere, to be present in food items. The nutrient status of the soil plays an important role in natural and semi-natural ecosystems [58, 59]. For TENORMs present in soil, man-made sources (e.g., fertilizers, petroleum or mining industries) are important when considering the transfer of radioactivity to the food chain. The naturally occurring radionuclides can be seen approximately homogeneously distributed on the Earth with the exception of ore deposits. In that case, sources of contamination are the utmost important as far as transport of radionuclides to the food chain is concerned. For example, 137Cs from the Chernobyl accident has been enriched the flow paths present in soils due to heavy rain and water runoff during the deposition. Consequently more concentration of radionuclides during wet deposition in a part of the soil where roots are present in higher density led to higher activity in plants than with dry deposition [60, 61]. While looking at the presence of radioactivity in food, emphasis is given to the sources of radionuclides [61]. Potassium-40 is present in soil, a radioisotope of potassium and is transferred to the food chain. Radium-226, a decay product of 238U, is associated with uranium deposition but as a member of the alkaline Earth group, its behavior is comparable to that of calcium [62, 63]. Thus 226Ra transferred to food chain in a similar way as that of calcium. With the discovery of nuclear fission, a large number of man- made radionuclides have been produced. Some of them are produced due to fission of nuclei such as 137Cs, 131I, or 90Sr and some other are produced by activation of uranium fuel (plutonium isotopes). The discharge of anthropogenic radionuclides in the environment follows different pathways to the food chain [64]. Human beings are externally exposed to terrestrial radiation and cosmic rays, while the ingestion and inhalation of naturally occurring radionuclides result in internal exposure. Terrestrial radioisotopes, thorium and uranium series, and 40K enter the human body mainly by ingestion, while inhalation of these isotopes is limited [65]. As per UNSCEAR-2000 report, the total exposure per person resulting from ingestion of terrestrial radioisotopes was 0.29 mSv, of which 0.17 mSv was from 40K and 0.12 mSv
8 Chapter-1: Introduction was from thorium and uranium series. Exposure due to inhalation of terrestrial radioisotopes contributes 0.01 mSv [66]. Thus the internal dose of terrestrial radionuclides can be estimated from the concentrations of these radionuclides in food and from the intakes of these foods. The concentrations and internal doses of natural radionuclides within food have been determined in Europe [67], Asia [68-70].
1.1.6 Strontium-90 levels in different environmental media
Everyone is being exposed to small amounts of 90Sr, since it is widely dispersed in the environment and the food chain. Strontium-90 is a pure beta emitter having no gamma radiation. It is the most important radionuclide present in the environment. Strontium-90 is a daughter of 90Kr which is a fission product of uranium and plutonium. In a very short time period, 90Kr completely transforms to its daughter, 90Rb, which further decays into 90Sr [71, 72]. Strontium-90, 89Sr and 85Sr can be found around reactors, industry and medical centres using radioisotopes. Strontium-90 is also found in radioactive waste from nuclear reactors. It can contaminate reactor components and fluids. People who live near or work in nuclear facilities may have increased exposure to 90Sr [73, 74]. The greatest concern would be the exposures from an accident at a nuclear reactor or an accident involving high-level wastes. Large amount of 90Sr was produced during atmospheric nuclear weapons tests performed in the 1950s and 1960s and dispersed globally. The accident at the Chernobyl nuclear power plant in1986 also introduced large amount of 90Sr into the environment. A large part of the 90Sr was deposited in the Soviet Republics. The rest was dispersed as fallout over Northern Europe and worldwide [75, 76]. Strontium-90 is of special importance among the fission products because of its comparatively high retention period in the skeleton. It is chemically similar to Ca, an element essential to both plants and animals and have a low rate of excretion from the skeleton [77, 78]. Strontium-90 is also a volatile radionuclide as 137Cs and 131I, on average is assumed to be deposited locally and regionally. Measurements for the determination of 90Sr in the environment are made routinely at a number of locations around the world [65]. Strontium and cesium are potentially more dissolvable than plutonium and transport of these elements to animals in ecosystems involves a combination of physical
9 Chapter-1: Introduction and physiological processes. Strontium-90 and 137Cs transport will be more by soil particle as these are more tightly bound to them. The bioavailability of these radionuclides depends on chemical form also, local environmental conditions, structure and function of the relevant food webs [79, 80] Strontium-90 is a bone seeker. Internal exposure to 90Sr may be responsible for bone cancer, cancer of the soft tissue near the bone and leukemia [81]. When people ingest 90Sr, most of it passes through the body. Some remaining amount is deposited in the bone. Very little amount is distributed among the blood volume, extra-cellular fluid, soft tissue, and surface of the bone [82, 83].
1.2 Measurement techniques
Gamma-spectroscopy is a very important non-destructive nuclear and radioanalytical technique. Many radioactive sources produce γ-rays of various energies and emission probabilities. These gamma lines are collected in the form of a spectrum and analyzed with a γ-spectroscopy system. The analysis of this spectrum is used to identify and quantify the γ-emitters present in the source. Now-a-days most common detector used for gamma spectroscopy is High Purity Germanium detectors (HPGe). Liquid scintillation counting (LSC) is a standard analytical method widely used for measurement of beta-emitting radionuclides. A scintillator or cocktail is used in liquid samples to be counted on LSC. Cocktails absorb the energy emitted by radionuclides and re-emit it as scintillations of light. Cocktails contain two basic components, the solvent and the phosphor(s) to do these two actions, absorption and re-emission. The solvent takes away the bulk of the energy absorption. Phosphor molecules convert the absorbed energy into light.
1.2.1 Gamma measurement
Many natural and man-made radioactive sources produce gamma rays of different energies and intensities. When the samples of gamma emitting radionuclides are counted and analyzed with a gamma spectroscopy system, a gamma energy spectrum is produced. A detailed analysis of the collected spectrum is employed to identify and quantify the gamma emitters present in the samples. Nowadays, many measurement techniques are employed routinely, involving gamma spectrometry measurements [84].
10 Chapter-1: Introduction For determination of gamma emitting radionuclides in environmental samples, a PC based high resolution gamma spectrometry system is being utilized. Uranium-238 and 232Th do not have their own intense gamma lines suitable for their activity determination. These radionuclides can be detected indirectly through their progenies, which have many intense gamma lines. The activities of the progenies are equal to their parents in the state of secular equilibrium. In the case of thorium, the existence of the equilibrium can be assumed throughout the series for any soil or rock if the emanation of gaseous radionuclides is prevented. Radium-226, a member of the uranium series, is also in the state of equilibrium with its progeny if the sample is hermetically sealed. But 226Ra is generally not in equilibrium with 238U due to geochemical reasons [86]. Radium-226 and 232Th are usually determined from only one gamma line of 351.9 keV of 214Pb and 911.2 keV of 228Ac respectively which are free from interfering lines of other radionuclides. Other radioisotopes found in environmental samples, 40K and 137Cs are determined using gamma lines of 1460.7 keV and 661.7 keV, respectively [84].
1.2.2 Beta measurement
Carbon-14, 32P, 3H and 90Sr are radionuclides, emitting β- particles of low energies and are extremely difficult to detect. All these radionuclides do not emit γ-rays. The problem of self absorption exists during counting of solid samples. Converting sample material into a gas is tedious, time consuming and needs complex handling. These are the main
reasons for use of liquid scintillation counting for determination of β-emitters. In liquid scintillation counting, the radioactive sample dispersed in a suitable cocktail, photons are
emitted as a consequence of the interaction of β- particles and these photons produce scintillations which can be detected and counted [87]. Some of the beta emitting radionuclides can be analyzed on Liquid Scintillation Counter (LSC) without using any cocktail. Strontium-90 emits beta particles having energies more than 263 keV for counting in water. A beta particle counting technique without using cocktail or with only a little water is called Cerenkov counting, which is widely used in these days [85].
11 Chapter-1: Introduction
1.3 Motivation of study
Advanced countries, having nuclear infrastructure and nuclear power production programmes, have generated their country wide base line data of radioactivity levels and radiation doses on a reasonably small grid size and generated radioactivity images of their countries. Such projects have been completed through collaborative efforts of universities, research students and scientific institutes. We being one of the important nuclear countries and eager to widen our nuclear power base for contribution to the national energy needs do not have any such data. This lack of data in our case has motivated me to start work on these lines. The research intends not only to measure the amount of radioactivity but also use it for assessment of external radiation doses and ingestion doses from staple food grown and used by the local population residing in well populated and cultivated area namely, Rechna Doab, Pakistan.
1.4 Objectives of study
The study objectives were;
To assess the radiological environmental pollution into the environment of Rechna Doab, Pakistan, To establish the possible radiological risks due to dwellings made by mud bricks, using as residence by the general public in the area, To assess the natural radioactivity levels in soil, water, vegetation, staple food and levels of artificial radionuclides 137Cs and 90Sr, To estimate the radiation doses using the available theoretical models for the uniformly distributed source on ground, To determine the transfer factors of radioactivity from soil to plant, To assess the associated radiation hazards due to radioactivity intake through consumption of staple food grown on the soils. To determine any abnormal activity levels (hot spots), if exists, in the study area.
12 Chapter-1: Introduction
1.5 Thesis layout
There are seven chapters in this thesis. The first chapter depicts the introduction of radioactivity in the environmental media such as air, soil, water, vegetation and staple food and its determination. The objectives of the study have also been included in this chapter. The second chapter describes the details about the study area regarding location, geology, temperature, rain, humidity, population and irrigation. The details of sampling of different environmental media soil, water, vegetation and staple food including sample processing have been included in this chapter. Radioactivity measurement techniques of gamma emitting radionuclides in different environmental media have been described in third chapter. Chapter 4 gives the details of the natural radioactivity levels present in soils of the study area and their comparison with world values. The radioactivity levels determined in water, vegetation and staple food grown and consumed in the area have been described in the chapter 4 as well. Determination of beta emitting radionuclide 90Sr in different environmental media has been discussed in chapter 5. Health risks and radiation hazard assessment have been given in chapter 6. It covers the calculation of the radiation doses from the available theoretical models for the uniformly distributed source on ground. The calculations of absorbed dose rates in air, effective doses, radium equivalent activity and hazard indices have been determined. Cancer risk assessment to the human beings living in the study area due to external and internal doses has been evaluated and described at the end of this chapter. Conclusions of the study along with future recommendations have been depicted in the last, 7th chapter.
13 Chapter 2
AREA UNDER STUDY AND SAMPLING
Selection of study area plays a pivotal role in obtaining representative results. In present study, the Rechna Doab, Pakistan was selected as study area having some special features. The Rechna Doab is enclosed by the river Chenab and river Ravi on the Northwest and Southeast respectively with the piedmonts near the Jammu and Kashmir boundary in the Northeast. It is about 403 km long, in a Southwest direction and has a maximum width of about 113 km. It is an alluvial filled area. The alluvial sediments different have different colours and clay is also found. Agriculture is the most important industry in the area. Wheat, rice, maize, sugarcane, fruit, tobacco, cotton and many other crops are grown. Sampling strategy was planned carefully according to the experimental goal, the conditions of the study area and knowledge on how these conditions may affect results [88]. The purpose of environmental sampling and analysis is to obtain data that describe a particular site at a particular point. In this process, the collection of suitable samples is the critical first step. Sampling was done with great care. To obtain a meaningful data, sampling was carried out with a clear purpose and considering the problem to be addressed and the prevailing physical conditions. Chapter-2: Area under study and sampling
2.1 Area under study
The Punjab, a province of Pakistan consists mostly of plains, north and south of the very old Salt Range, which extend from east to west. The Punjab province can be divided into five major physical regions, such as, (I) Northern Mountains, (II) South-West Mountains, (III) Pothwar Plateau, (IV) the Upper Indus Plain and (V) The Deserts. In the north side of the Punjab there are the outer ranges of the Himalayas: Murree and Kahuta hills in the north and the Kirana hills near Faisalabad lies in the south. The Rechna Doab can be classified as one of the main regions of the Punjab. The Punjab historically has been divided into regions based on its various rivers, since the name Punjab is based on its five main rivers. The Rechna Doab area is shown in figure 2.1.
Figure 2.1: Map of Study Area, Rechna Doab, Pakistan along with three sub-divided parts.
As the study area, the Rechna Doab, Pakistan is quite large; having different lithology and alluvial deposition in northern, mid and southern parts, likewise the said
15 Chapter-2: Area under study and sampling
area was further divided into three parts. To develop a base line natural background radioactivity levels and radiation dose data for various regions of the Rechna Doab, Pakistan, comprising of districts Sialkot, Gujranwala, Narowal, Hafizabad, Sheikhupura, Nankana Sahib, Faisalabad, Toba Tek Singh and Jhang [89], a detailed radiation study was made by distributing the whole study area, Rechna Doab into spacial grids of 24×28 square km.
2.1.1 Area
The Rechna Doab is spread over 28,500 square kilometer. It is linked with the piedmonts near the Jammu and Kashmir boundary in the Northeast [90]. The area is interfluvial and is Southwesterly sloped. In the upper part of the Rechna Doab, the slope is about 38 cm/km to about 29 cm/km. Physiographically, the Rechna Doab can be characterized by the following units: ¾ Kirana hills - though minor features as compared with the alluvial complex but very prominent, ¾ Active flood plains in the vicinity of the rivers Ravi and Chenab, ¾ Abandoned flood plain, ¾ Bar upland - an elevated land beyond the reach of flood waters of the rivers. In the study area, controlled irrigation system started with the construction of Marala, Khanki, Qadirabad and Trimmu Head Works on the river Chenab [90, 91].
2.1.2 Location
The Rechna Doab lies between longitude 71o 48' to 75o 20' East and latitude 30o 31' to 32o 51' North. It is one of the most ancient and intensively developed irrigated areas of the Punjab Province of Pakistan.
2.1.3 Geology
The consolidated exposed rocks near Chiniot, Sangla and Shahkot represent the remains of the buried ridge of metamorphic rocks forming the basement of the alluvial deposits in the Rechna Doab. These hardened rocks are known as Kirana Hills and are of Precambrian age (700-570 million years ago). These rocks cover the mid part of Rechna
16 Chapter-2: Area under study and sampling
Doab making the longitudinal section across its width. These loose and un-stratified alluvial deposits are of Pleistocene (about 1.65 million until 10,000 years ago) to Recent in age and are overlying the Precambrian basement rock. These were deposited in a settling trough by the very old and present tributaries to the river Indus. This alluvial filling is more or less consistent in nature and has little persistence vertically or laterally, indicating various depositional environments from time to time, caused by constant change in the stream courses [92].
Figure 2.2: Soil texture of study area.
As shown in figure 2.2, the alluvial deposits mainly consist of gray, a grayish brown, fine to medium sand, silt and clay, gravel or very coarse sand are uncommon. Kankers, a calcium carbonate material of secondary origin are related with fine-grained strata. Clay is normally found in lenses. The origin of clay has not been assured but presumably it is repeatedly reworked un-stratified accumulation of clay and silt deposited by the wind. Of the alluvial deposition, sand forms the areas of fairly transmissive geological formation material in which ground water occurs under water table conditions [93].
17 Chapter-2: Area under study and sampling
2.1.4 Climate
Climate of the area is sub-humid in the northeast to sub-arid in the southwest and is characterized by seasonal changes in temperature and rainfall. The rainfall has a marked seasonal instability and also differs considerably across the area increasing from south to north. In the high relief area, the rainfall may exceed 89 cm per year but in the southwest it decreases to about 20 cm per year near the convergence of the rivers Ravi and Chenab. About 70 percent of the average annual rainfall happens in the period from June to September. During summer (June to August) the average day temperature is more than 40 oC while the maximum temperature during winter (December to February) is between 15.5 and 21.1 oC and minimum temperature is between 3 to 7 oC. The average annual temperature is about 32 oC; the hottest day may reach 49oC while the minimum summer reading may be as low as 21 oC [90, 94].
2.1.5 Irrigation System
Due to inadequate rainfall as well as its unfavorable seasonal division, agriculture is not possible without irrigation in the Rechna Doab. The modern irrigation system was initiated in the Rechna Doab through making the Lower Chenab Canal (LCC) in 1892. Presently, the Rechna irrigation network consists of five main canals and many inter-river link canals. The normal flow period for the relentless canals is about 340 days per year. The outlets from the distributaries are designed to carry a fixed quantity of water when the canal is flowing at full swing. Each farmer is allotted a fixed quantity of water proportional to his land holding on a weekly or 10-day turning round period. This system was designed to irrigate a limited amount of canal water over the entire area to maintain approximately 65 percent cropping strength during a year. The major design purpose of irrigation expansion at that time was to protect against crop failure and prevent food scarcity. However, the cropping strengths have drastically increased due to immense groundwater development and after the completion of the Indus Basin Works that were initiated after signing of the Indus Basin Treaty between India and Pakistan under United Nations/World Bank patronage in 1960 [94].
18 Chapter-2: Area under study and sampling
2.1.6 Agriculture
The Rechna Doab falls in the most cropped zones of the Punjab province. The soil of the area is flexible to a wide variety of crops and temperatures allow continual cropping. Rice, maize, cotton and fodder dominate the summer season, while wheat is the major winter crop, sugarcane, an annual crop, is also cultivated in this area [94].
2.1.7 Population
The Rechna Doab (interfluvial region) is the most populous region of Pakistan. About 21.1 million people dwell the Rechna Doab, with a population density of nearly 599 persons per square kilometer [95]. Out of the total population, 25 percent lives in Faisalabad, while 16 and 15 percent in Gujranwala and Sheikhupura, respectively. Other districts, such as Jhang, Sialkot, Toba Tek Singh, Narowal, Hafizabad and Nankana Sahib have 13.29, 12.74, 7.6, 6, 4 and 4 percent of the population, respectively [95]. The population density of these districts is also presented in Table 2.1.
Table 2.1: Area and population of different districts in the Rechna Doab
Area Population Male Female Population Urban Rural Literacy District (km2) (Million) (Million) (Million) density population population ratio (per km2) (Million) (Million) (%) Faisalabad 5,856 5.43 2.83 2.60 927.2 2.32 3.11 51.9 Jhang 8,809 2.83 1.47 1.36 321.8 0.66 2.17 37.1 Toba Tek 3,252 1.62 0.84 0.78 497.6 0.28 1.34 50.5 Singh Sheikhupura 3,627 2.64 1.37 1.26 557.9 0.80 1.84 47.8 Nankana 2,332 0.68 0.35 0.33 411.5 0.07 0.61 35.9 Sahib Narowal 2,337 1.27 0.64 0.63 541.3 0.15 1.12 52.6 Sialkot 3,016 2.72 1.40 1.33 903.0 0.71 2.01 58.9 Gujranwala 3,622 3.40 1.77 1.63 939.0 1.72 1.68 56.5 Hafizabad 2,366 0.83 0.43 0.40 351.9 0.23 0.60 40.7
19 Chapter-2: Area under study and sampling 2.2 Sampling of different environmental media
Sampling of different environmental media e.g. soil, surface water, vegetation and staple food was made with proper care and as per pre-defined methodologies in the litterature so that the results obtained after analysis would be true representative of the study area. As sampling techniques contribute in the final results of study so it was given the same attention as that of analysis.
2.2.1 Soil sampling
Soil sampling is a valuable approach to determine the cumulated amounts of airborne long-lived radioactive and stable contaminations that deposit on the ground. Historically, soil sampling procedures for radionuclides were inferred from techniques used in agriculture. Normally enough emphasis is not given on the importance of a proper sampling method to take the representative sample. The objectives of the study were taken into account and the degree of precision required was considered before sampling as well. Site characteristics, such as soil type, topography, source and current dispersion of the contaminations were considered also when the study was being planned [88, 96]. The most direct use of soil measurements is the determination of the inventory of the material deposited over a given area. These inventories require the choice of a sufficient number of representative sites, with the concentration of the sites depending on the accuracy required [97].
2.2.1.1 Representative soil sampling
The main aim of representative soil sampling was to obtain accurate data about the soil quality of a particular site but the crucial objective was the purpose for which the study was being carried out [98]. The objectives of the representative sampling of soil were:
• Establishment of radiation risks to public health and to the environment, • Assessing the possible sources of contamination if any, • Determining the magnitude of contamination.
20 Chapter-2: Area under study and sampling
2.2.1.2 Benefits of representative soil sampling
• It helps to safeguard the environment, and the generated data serve as a reliable database to authenticate fulfillment to local and national laws and regulations, • It helps in deciding compensation and responsibility, in case of accidents, • It helps in deciding boundaries for clean areas and deciding precedences to clean-up of affected sites, • It assists in overall financing priorities for development of different areas, • It assists in making decisions regarding the type of treatment required for cleaning affected sites, • It assists in possible cost savings including those resulting from the false results, • It also assists in assuring effective response arrangements in case of emergencies.
2.2.1.3 Methodology involved in soil sampling
The basic objectives of soil sampling was the monitoring of environmental contaminants and different other wide ranging aspects. Different parameters considered and general principles involved in soil samplings during present study, are summarized below:
2.2.1.3.1 Site selection criteria
To determine the accumulated deposition over a given time period by soil sampling, selected an undisturbed area for sampling. It was difficult to obtain the accurate history of the site after a long time. Secondly the selected sampling site was chosen at the center of a large and flat open area. The sampling sites under the foot of slopes, in low spots, in flooded areas, close to the buildings or trees and very close to dusty roads had been avoided. The sampling site was vegetated, having moderate to good permeability [99, 100].
2.2.1.3.2 Compilation of background information
All possible information related to the sampling site and the parameters to be measured in the samples were collected before starting the field work [101]. The background data collected was as under:
21 Chapter-2: Area under study and sampling
1. Soil type of the site location and climate in the vicinity. 2. Present and past agricultural activities existing in the area. 3. Knowledge regarding the wastes generated from the various activities and its disposal routines. 4. Details of any past radiological environmental monitoring studies. 5. Site location map and other available related documents.
2.2.1.4 Systematic grid sampling approach
After studying and analyzing different soil sampling approaches as random, stratified, search and systematic random sampling through the literature, systematic grid sampling approach was selected for the present study. The whole sampling area was divided into rectangular grids of 24×28 square km and samples were collected from the nodes. The origin and direction for placement of the grid was done using starting random point.
Sampling point
Figure 2.3: Extended part of the map of the study area, as shown in figure 2.1, illustrating systematic grid sampling approach
Grids were made over the whole site from that random point by taking help of the site maps. The distance between sampling points in the systematic grid was decided by the population density, the size of the area, and the number of samples to be taken. Figure 2.3 describes a systematic grid sampling approach.
22 Chapter-2: Area under study and sampling
2.2.1.5 Core methododology for soil excavation
Different versions of soil excavation techniques e.g. coring and template etc. studied before selection of coring technique. The sample excavation technique employed keeping in mind site specific features and as per study objectives [102, 103]. A hand corer used during present study, had 10 cm diameter and could excavate soil up to the depth of 5 cm on a flat grassy lawn. Total ninety nine (99) soil samples were obtained using the aforementioned technique from the whole study area. Different steps involved in this procedure are being described as follows [98, 104]; 1. After selecting an undisturbed site, a straight transect line 3 m long was drawn and thus 3×3 m2 area was marked at every sampling location. Site coordinates were also recorded for the purpose of traceability of the sampling place in future by using a Global Positioning System (GPS), as shown in figure 2.4. 2. The top 0.5 cm surface along with vegetation cover was removed prior taking the sample. 3. Soil sample was taken using a 5 cm depth hand corer as shown in figure 2.5. The sample core placed into a plastic sampling bag. 4. The same process repeated to collect five numbers of cores as per methodology shown in figure 2.6. Compositing all soil samples to make a larger sample volume and a more representative of the area. About 2 kg of soil sample collected from selected area and mixed thoroughly to make one representative sample. 5. Pebbles, plant remains and other non relevant things were removed as per standard sampling methodology. These samples were packed into neat polyethylene bags and marked for later identification. Then placed the sample bags in a canvas bag and tied firmly.
23 Chapter-2: Area under study and sampling
Figure 2.4: A Global Positioning System (GPS) to record coordinates of the sampling site, used during present study.
Figure 2.5: Illustration of use of hand corer for soil sampling
Figure 2.6: Illustration of systematic grid sampling approach applied at each sampling point
24 Chapter-2: Area under study and sampling
2.2.2 Water sample collection
The sampling procedure was established according to the methodologies recommended by the “Standard Methods for the Examination of Water and Waste water'' [105]. Twenty three (23) raw water samples were collected in polyethylene bottles using a muslin cloth as a strainer, from each selected site in the Rechna Doab as shown in figure 2.1. Ten litres water sample was collected from each point. The samples were properly marked for later identification.
2.2.3 Vegetation sample collection
Twenty nine (29) samples of vegetation (sacrificial grass) were collected from different locations of study area, the Rechna Doab, Pakistan as shown in figure 2.1. About ten kg of sacrificial grass (dab), vegetation sample was taken from each sampling point. The coordinates of each sampling site were also recorded for traceability purpose. Samples were packed in plastic bags carrying identification marks.
2.2.4 Staple food sample collection
One method of food monitoring is to obtain individual food sample at the point of production. This is most useful for relating contaminations to local conditions of fallout, soil content or farming practice being carried out. Although it is quite difficult to compare the concentration level of a contaminant in samples collected at the point of production to the dietary intake of any particular group of people [101]. This sampling system was used during the present study. Fifty eight (58) samples of staple food (wheat and rice) were collected through out the area under study, the Rechna Doab, Pakistan as shown in figure 2.1. Sampling mass was 5 kg each of wheat and rice. The collected samples were properly packed in polyethylene bags and marked for future reference.
2.3 Sample processing
The collected different environmental media were processed as per their described standard protocols in the literature. The basic purpose of the sample processing is to make the sample look like the standard that was used for efficiency calibration. The
25 Chapter-2: Area under study and sampling
sample had been prepared in a manner that properties like dimensions, density and particle size and its distribution were similar to that of calibration standards.
2.3.1 Pre-treatment of soil samples
The processes followed for a soil sample to obtain a representative sub-sample for analysis depends to some extent on the radionuclide of concern and the size of the sample. The soil samples oven dried, pulverized, sieved, blended for more homogenous distribution of particle sizes. This process reduced the soil to a standard particle size. [106]. Global fallout is comparatively homogeneous in particle size and distribution in the sample is uniform. Sub-sample for analysis was taken with great care that it was a representative of the total sample. It was similar and homogeneous just like total sample. Cross contamination was also avoided during sample processing. In addition, careful cleaning of the equipment between samples was done also [107].
2.3.1.1 Drying process
The drying process was used during present study comprised of following steps; 1. Vegetation, roots, large organic pieces, stones, etc. were separated from soil and discarded. The samples were screened using an appropriate sieve. 2. The sample were spread out on a plastic sheet and allowed to air dry for 2-3 days. The soil was turned up during the drying process. 3. The samples were heated in an electric oven at 110 oC up to 24 hours to remove further moisture contents and then put the samples in an electric furnace as shown in figure 2.7, which was specially designed and manufactured, to burn the plant remains up to 350 oC for 48 hours. 4. The samples were weighed when completely dried.
26 Chapter-2: Area under study and sampling
Figure 2.7: A view of a specially designed electric furnace to remove moisture contents and to burn plant remains in the samples
2.3.1.2 Homogenization
For homogenization of soil samples close attention was paid for every sample to avoid cross-contamination. Equipment was disassembled and cleaned between samples. The treated samples were then passed through a sieve having 2 mm mesh size [108]. Homogenized samples having weight of 200 g were packed in recommended containers for gamma spectrometric measurements, plastic marinelli beakers as shown in figure 3.2, specially designed and manufactured for the present study, having same geometry as that of reference materials. These beakers were hermetically sealed for a period of 30 days to establish secular equilibrium as discussed in section 3.1.2.2.
2.3.2 Pre-treatment of water samples
The collected water samples concentrated by evaporation at 100 oC in a controlled environment in the laboratory, the sample volume were reduced to 300 ml. The pre- treated samples then packed in marinelli beakers having 200 ml capacity and about 20 ml of HNO3 (65%) was added to prevent losses by sorption of the radionuclides in the beakers. These beakers were hermetically sealed and left for 30 days before counting to establish secular equilibrium between Uranium and Thorium series.
27 Chapter-2: Area under study and sampling
2.3.3 Pre-treatment of vegetation samples
The collected vegetation samples were washed and dried on plastic sheets at room temperature for 1-2 weeks [109]. To remove moisture further, these samples were heated o o in an electric oven at 110 C up to 24 hours and then ashed to 350 C in an electric furnace for 48 hours as shown in figure 2.7. The ashed samples, 100 gm each were packed in marinelli beakers, having identical geometry as that of reference material as dictated by the calibration requirements. These beakers were sealed hermetically so that the overpressure produced inside the containers by the 222Rn from 226Ra decay would not 238 result in gas leakage. After assuring secular equilibrium among the progenies of U and 232 Th series (for 30 days), these sealed samples were ready for counting.
2.3.4 Pre-treatment of staple food samples
The collected staple food samples were washed with water to remove dust particles, and weighed. The samples were air dried at room temperature for 1-2 weeks and then oven- dried at 105 oC for 24 hours and later on ashed in an electric furnace at 350 oC for 48 hours to remove organic matter. These ashed samples were homogenized and weighed. For determination of concentration of 40K and other gamma emitting radionuclides, the homogenized samples were transferred to marinelli beakers. These samples were hermetically sealed and left for a period of one month to establish a secular radioactive equilibrium.
28 Chapter-2: Area under study and sampling 2.4 Conclusion
This chapter provides the information regarding the two key steps of the present study. Salient features of the study area, the Rechna Doab have been described. Site selection has been carried out. The selected sites were located in nine districts of the Rechna Doab of Punjab Province, Pakistan. The study area lies in the alluvial sediment plains of the Rechna Doab, which have most fertile soils in the area. The whole area is irrigated by the canales. The sampling procedures have been discussed for soil, water, vegetation and staple food. Samples were pre-treated by drying, sieving and crushing to attain desired particle size. These pre-treated samples were packed into plastic marinelli beakers. The beakers were properly closed and plastic tape was wrapped over the lids.
29 Chapter 3
GAMMA RADIOACTIVITY MEASUREMENTS
The samples of different environmental media soil, water, vegetation, etc. are measured to determine background levels of radiation, or to assess the levels of contamination as a consequence of manmade radioactivity. The radionuclides usually measured by gamma spectrometry are terrestrial radionuclides 40K, 238U, 232Th and cosmogenic radioisotopes. Uranium-238 and 232Th are accompanied by their daughter radionuclides. Gamma spectrometry of environmental media is not an easy task due to a number of reasons. The activity levels are quite low and if statistically better results are required it needs long counting times. Other difficulty is to minimize the background radioactivity levels around spectrometer. In addition, annihilation peaks and fluorescence X-rays contribute in the background. Any activity in the environmental sample itself must be detected above the background activity. There lie also a large number of mutual spectral interferences between many radionuclides in the decay series of uranium and thorium. Details of gamma spectrometric system and methodologies for analysing different environmental media are being discussed in this chapter.
3.1 Gamma Spectrometry
The activity of gamma-emitting radionuclides present in the environmental samples was determined using gamma spectrometric system based on the analysis of the energies and the peak areas of the gamma lines. This technique allowed the identification and the quantification of the radionuclides [110, 111]. The nature and geometry of the detectors Chapter-3: Gamma radioactivity measurement as well as the samples demanded for an appropriate energy and efficiency calibrations [112, 113].
3.1.1 Gamma-spectrometric equipment
The equipment of gamma-spectrometric system was consisted of:
• a high purity germanium semiconductor detector with a cooling system (liquid nitrogen, cryogenic assembly, etc.), • a lead shielding to minimize the effect of ambient radiation on the sample counts, • a highly efficient electronics (high-voltage power supply; spectroscopy amplifier an analogue-to-digital converter), • a multi-channel analyser (MCA), • a personal computer to acquire the spectra and then process the accumulated data.
The semiconductor detector used was made up of P-type high-purity germanium crystal (HPGe).The detector was coaxial in shape having relative efficiency 30% with respect to NaI(Tl) detector and active volume of 180 cm3 fitted with beryllium-end 60 window. The energy resolution was 2.0 keV (FWHM) at 1332 keV from Co [114, 115].
HV supply Shielding
Pre- PC amplifier Amplifier ADC based MCA
HPGe
detector Bias supply
Figure 3.1: Schematic diagram of PC based high resolution gamma spectrometry system
31 Chapter-3: Gamma radioactivity measurement
A schematic diagram of the PC based high resolution gamma spectrometry system used, is shown in figure 3.1. The system included a low-noise electronic preamplifier and amplifier. The measuring system was installed in the middle of the room having dimensions 18×30 square feet, with the maximum distance available to the room walls, as the walls were made up of cement and bricks, a source of natural radioactivity. [116, 117].
3.1.2 Sample containers
Specific sample containers were used for gamma spectrometric measurements of radioactivity levels in different environmental media. The chosen containers for present study had the following characteristics: • made of materials with low absorption of gamma radiation, • having volume accommodated to the shape of the detector for the maximum efficiency, • air tight and not reacting with the sample contents, • having a wide-necked opening to facilitate fillings, and • unbreakable material.
The beakers used for the present study were specially designed and manufactured. These marinelli beakers for gamma spectrometric measurements were used.
Figure 3.2: Specially designed and manufactured marinelli beakers
32 Chapter-3: Gamma radioactivity measurement
These containers were designed for the most symmetrical sample-detector geometry that can be attained for this type of marinelli beakers. The beakers had lids with a unique interlocking design which helped in precluding spillage or leakage of samples [118]. The schematic of such beaker used is shown in figure 3.2 along with its dimensions.
3.1.2.1 Packing of samples for measuring purposes
The environmental media packed for gamma spectrometric measurements after ashing, drying, crushing, and homogenizing, as discussed in section 2.3. The packing procedure was carried out as follows: a) The container was closed after filling the material. To decrease self-absorption effects, the height of the contents was kept at the minimum level, b) The sample mass was noted, this information was used during the preparation of specific activity results, c) The upper level of the sample was checked visually and it was assured that it was horizontal before measuring, d) The containers were sealed hermetically, e) The containers cleaned from outside to remove potential contamination during the filling process.
When measuring 226Ra through decay products of 222Rn, the sealed container should be stored for 30 days to allow radioactive equilibrium to be reached [115]. This time period to attain secular equilibrium was assessed through calculation and a curve was drawn as shown in figure 3.3.
3.1.2.2 Establishment of secular equilibrium
The quantitative relationship between the parent and daughter radionuclides in secular equilibrium can be derived using following equation 3.1:
ABC⎯⎯⎯⎯λAB→⎯⎯⎯⎯λ → 3.1 where the half-life of parent radionuclide A is very much greater than that of daughter
radionuclide B. The decay constant λA of A is much smaller than the decay constant λB for B. C is a stable isotope and is not transformed. Due to very long half-life of A relative to
33 Chapter-3: Gamma radioactivity measurement
B, the rate of production of B can be regarded as constant and equal to K. Under these circumstances, the net rate of change of radionuclide B with time, if NB is the number of atoms of B present at time ‘t’ is given by equation 3.2;
dNB =− 3.2 dt K λBBN
As the production rate of B from A is equal to the rate of transformation of A, so K is equal to λANA. Solving equation 3.2, mathematically, equation 3.3 is obtained;
λAAN −λ B t NeB =−()1 3.3 λB
If λN is the transforming atoms per second, then multiplying both sides of equation 3.3 with to convert the activity into becquerels or millicuries and equation 3.3 can be λ B written as;
=−1 −λB t QQBA( e ) 3.4 where QA and QB are the respective activities in becquerels or millicuries of the parent and daughter radionuclides [119, 120]. Equation 3.4 expresses a buildup of 222Rn from zero to a maximum activity, which is equal to that of 226Ra, its parent radionuclide. This buildup of daughter radionuclide activity can be shown graphically by plotting equation 3.4. A curve showing the buildup of daughter radionuclide activity under conditions of secular equilibrium is −λt shown in figure 3.3. With the increase in time the e decreases and QB approaches to QA. For practical purposes, equilibrium can be regarded to be established after about seven half-lives of the daughter radionuclides. As 222Rn has half life of 3.8 days, during present study, samples were kept for 30 days (approximately equal to 8 half lives of 222Rn) before counting to establish secular equilibrium between daughter and parent radionuclides. In case of equilibrium;
λ=λAAN BBN 3.5
34 Chapter-3: Gamma radioactivity measurement
Figure 3.3: Secular equilibrium showing buildup of a very short lived daughter radionuclide from a very long lived parent radionuclide. The activity of the parent radionuclide remains constant.
Equation 3.5 shows that under the conditions of secular equilibrium, the activity of the parent radionuclide is equal to that of the daughter radionuclide and the ratio of the decay constants of the parent and daughter radionuclides are in the inverse ratio of the equilibrium concentrations of the parent and daughter radionuclides.
3.2 Detector shielding
Most of the radionuclides found in soil, are similar to that in building materials. Due to this reason the detector was shielded against natural background radiation. The detector was shielded with lead being a high Z material to absorb background radiation, to reduce the number of gamma-rays arising from outside. Lower-energy radiations can be affectively stopped by 50 mm of lead but it is requisite to remove high energy gamma- rays also. Because if relatively low energies are to be measured, Compton scattering of high-energy gamma lines will contribute to the background continuum at low energy [121, 122]. Modern lead has radioactive impurities such as 210Pb which cannot be removed by refining processes. Due to this reason hundred years old lead is preferred for shielding of
35 Chapter-3: Gamma radioactivity measurement
HPGe detector, in which the activity is much lower than modern lead. This material is apparently short in supply and expensive. Aged lead can be likely to have less than 25 Bq of 210Pb per kg of lead [123].
3.2.1 The graded shielding
Graded shielding plays an important role in reducing Pb X-rays at 72 to 87 keV. Lining thickness of the graded shielding is a compromise between reducing the background by absorbing X-rays and 210Pb on the one side while increasing the background by increasing backscattering [124, 125]. To make a reasonably good graded shielding, different materials have been studied and ultimately tin and copper were selected as an inner lining of lead. During the present study, the detector was shielded by 15 cm thick lead wall provided with 3 mm thick copper and 4 mm thick tin inner lining as shown in figure 3.4 in order to effectively reduce the natural background. The inner size of the shielded circular cavity was 530 cm2.
Figure 3.4: Detector shielding, specially designed for the present study
36 Chapter-3: Gamma radioactivity measurement
3.2.2 Laboratory background level
By using the graded shielding described in section 3.2.1, the background of the measuring instruments e.g. HPGe detector was achieved as low as possible. Recurrent measurements of the background levels verified its stability. This was necessary because the peaks of the background spectrum have to be subtracted from those of a sample spectrum. Such laboratory’s background spectrum taken by gamma spectrometry system for 65,000 seconds is shown in figure 3.5.
Figure 3.5: A laboratory background spectrum counted for 65,000 seconds on gamma spectrometry system
3.3 Analytical accuracy, IAEA standards
Four reference materials were made available through the International Atomic Energy Agency (IAEA), soil 326, soil 375, soil 6 and ash 156 to ensure the quality of the results. Upper limits of the radioactive concentrations were known and used to monitor laboratory’s contamination and background counting rates [109].
3.4 Counting uncertainties
Statistical counting uncertainties could not be neglected but always taken into account within the spectrum analysis [126, 127]. Because these uncertainties differ from sample
37 Chapter-3: Gamma radioactivity measurement to sample, from radionuclide to radionuclide within the sample and even from peak to peak of each radionuclide, these are variables and have been taken into account by estimating counting uncertainties [128, 129]. The activity concentration results presented have a confidence level of 68% characterized by ±1σ values. The following formula shown in equation 3.6 was used to calculate uncertainty in activity concentration values,
()22+ () σ= σσSB 3.6 TYV××ε × where σ combined uncertainty in activity concentration
σS uncertainty in sample counts
σB uncertainty in background counts T counting time in seconds ε counting efficiency Y gamma emission probability of the radionuclide at a particular energy V the sample volume (or mass)
The standard error for 226Ra, 232Th and 40K were in the range of 2.7% to 6.2%. while for 137Cs ranged from 26.8% to 95.2%. The higher errors in 137Cs may be attributed to low activity levels and scarcity of data points.
3.5 Minimum Detectable Activity
The minimum detectable activity (MDA) is the minimum amount of radionuclide that can be detected with certain confidence level. The minimum detectable activity is not the minimum activity detectable [130, 131]. To find out MDA for gamma spectrometry, the region in the spectrum was examined, where the peak was expected to be. The net peak area, its uncertainty and the uncertainty of the peak-background correction was determined. When the net peak area was significant it was assumed that it was detected. Due to this technique the same calculation was performed whether the peak was present or not. If the peak was not present in the spectrum then the upper limit was realistic
38 Chapter-3: Gamma radioactivity measurement
[132, 133]. The Minimum Detectable Activity (MDA) values for 226Ra, 232Th, 40K and 37Cs were determined using following equation 3.7 and are given in table 3.1.
4.66 Continum counts+ Background peak counts MDA = 3.7 TYV××ε ×
Table 3.1: The Minimum Detectable Activity (MDA) for the radionuclides 40K, 226Ra, 232Th and 137Cs for different environmental media
Soil Water Vegetation Staple food Radionuclide -1 (Bq Kg ) (Bq l-1) (Bq kg-1) (Bq Kg-1) 40K 6.70 1.32 1.74 2.20 226Ra 3.60 0.62 0.96 0.53 232Th 2.25 0.46 0.62 0.29 137Cs 1.35 0.35 0.37 0.23
3.6 Energy calibration
Energy calibration was performed to derive a relationship between peak position in the spectrum and the corresponding gamma-ray energy. This was normally performed before taking measurements. Energy calibration was carried out by measuring the spectrum of a gamma source of specific energy and comparing the measured peak position with energy. For environmental media, different available IAEA reference materials were used for calibrating the system. The spectrum of the reference material was collected for 65,000 seconds in order to achieve good statistical precision for the peaks to be used for the calibration. After determining the peak locations for each of the required peaks for calibration purpose, software (Genie-2000) was used for the energy calibration:
Energy (E) in keV as a function of channel number x is shown below in equation 3.8:
2 3 E = C0 + C1x + C2x + C3x 3.8
where C0, C1, C2, and C3 are the coefficients to be determined. C0 represents the
energy offset, C1 represents the “gain”, and C2 and C3 account for the system non-
linearity. Only C0 and C1 were calculated automatically. The other coefficients were calculated based on selections made during an interactive calibration session. Three
39 Chapter-3: Gamma radioactivity measurement
calibration peaks were selected to calculate C2, and four calibration peaks were
taken to calculate C3 [134]. Energy calibration curve obtained is shown in figure 3.6.
1600
1200
800
Energy (keV) 400
0 0 600 1200 1800 2400 3000 3600 Number of Channels
Figure 3.6: Energy calibration curve of the gamma spectrometer
3.7 Peak efficiency calibration
In gamma spectrometry, relative efficiency is used to relate the efficiency of HPGe detector of the 60Co gamma-ray peak at 1332 keV to that of a standard sodium iodide scintillation detector. While the full-energy peak efficiency associates the counts under the peaks in the spectrum to the number of gamma-rays incident on the detector. Peak efficiency depends on the detector and is not depending on the source/detector geometry [135, 136]. Detection efficiency varies with energy and energy/efficiency relationship was determined for a full calibration of the detector system. The peak detection efficiency at a given energy [134] is defined in equation 3.9;
ε(E) = S 3.9 TKyVAW Uf where ε(E) the efficiency at energy E, S the net peak area of the calibration peak, T the live time of the measurement, V the volume (or mass) of the reference material,
40 Chapter-3: Gamma radioactivity measurement
Y the gamma emission probability of the calibration nuclide at this energy, A the source activity at the source reference time,
Uf a factor to convert the activity ‘A’ from other activity units into units of Bq (if applicable), and
Kw the decay correction factor to correct the activity ‘A’ to the activity at the time of the start of acquisition (if applicable); that was calculated using equation 3.10,
ln(2) − t W = 1 3.10 K W e T 2 where
tw decay time of the calibration source (time being elapsed between the start of the acquiring data and the time at which the calibration source activities to be reported) and
T1/2 half-life of the calibration radionuclide
The peak efficiency was calculated for a set of well defined single peaks using a standard calibration source. Furthermore, it was ensured that the selected peaks covered the entire energy range of interest. Figure 3.7 shows an efficiency curve after measuring gamma-rays and plotting efficiency against energy. Figure 3.7 shows that the relationship is close to linear over most of the commonly used energy range e.g. from 130 to 1600 keV.
Figure 3.7: Full energy peak efficiency curve of the gamma spectrometry system for soil
41 Chapter-3: Gamma radioactivity measurement
3.8 Calculation of radioactivity per unit volume or mass
After completion of the counting of an environmental media, spectra were obtained, one of these of soil samples is shown in figure 3.8, the net peak area was calculated by subtracting linear background. The activity per unit volume (or mass) of the sample ‘A’ was calculated using equation 3.11 [134, 137, 138];
= S A / 3.11 TKKyε VUf cW where S the net peak area, V the sample volume (or mass), ε/ the efficiency after attenuation correction was determined using equation 3.12;
/(E)t−μρ εε= .e 3.12 where ε the detection efficiency before attenuation correction of the peak energy in question µ(E) the mass attenuation (cm/g) at gamma energy E, ρt average sample mass per unit area, y gamma emission probability of the peak energy, T live time of the collection in seconds,
Uf conversion factor to convert the activity in µCi (if applicable),
Kc correction factor for the radionuclide decay during counting process was determined (if applicable) using equation 3.13,
1 ⎡⎤ln(2)tc T 2 − − =−⎢⎥1 1 3.13 K c e T 2 ln(2)t c ⎣⎦⎢⎥
where
T1/2 the half-life of the radionuclide in question, and
tc the elapsed real clock time during the measurement
42 Chapter-3: Gamma radioactivity measurement
Figure 3.8: Gamma ray Spectrum of a soil sample acquired using an HPGe detector
Kw the correction factor for the radionuclide decayed from the time the sample was collected to the start of the data collection was calculated (if required) using equation 3.14;
ln(2) − − t W = 1 3.14 K W e T 2 where
tw the elapsed time from the time the sample was taken to the beginning of the data collection
For long lived radionuclides in equation 3.11, Uf, Kc and Kw are taken as one when the sample and the reference material being used for calibration have the same geometry, volume, quantity and density. The activity measurements (Ax) were also cross checked using comparative method as shown in the following equation 3.15;
StXRm R AAXR= ×× × 3.15 StRXmX where
SX net sample peak area
SR net reference material peak area
tX sample counting time
43 Chapter-3: Gamma radioactivity measurement
tR reference material counting time
mX sample mass
mR reference material mass
AR activity concentration of reference material
3.8.1 Corrections for contributions from other radionuclides and background
During present study, corrections for two types of contributions during counting were considered as well [139]: a) The contribution from other radionuclides to the gamma line was estimated taking into account the emission probabilities of the respective gamma lines. b) Net counts of the gamma line were corrected by subtracting background counts of the respective peak.
3.9 Analysis of natural and fallout radionuclides
The activities of many radionuclides belonging to natural decay series can be measured using gamma spectrometry. This includes 40K and 238U, 226Ra and 210Pb of the uranium decay series (see figure 3.9) and 232Th, 228Ra and 228Th of the thorium decay series [140] (see figure 3.10). Parent radionuclides and their corresponding daughter radionuclides and their respective gamma lines [141] are shown in table 3.2.
Table 3.2: Gamma-ray energies used for the calibration of spectrometer and for the measurement of activity of the radionuclides of interest.
ray energy Gamma emission-ץ Parent nuclide Daughter nuclide (keV) probabilities (%) 226Ra 214Pb 351.9 37.6 232Th 228Ac 911.2 26.0 40K - 1460.7 10.7 137Cs - 661.7 84.6
Radioactive equilibrium can be interrupted within the sampled media being counted due to the different chemical or biochemical behaviour of the respective radionuclide. Due to this reason the samples were kept for a sufficiently long period before measuring them to establish secular equilibrium as discussed in section 3.1.2.2.
44 Chapter-3: Gamma radioactivity measurement
Both the radioactive decay of the respective radionuclide and its decay products were taken into account. Examples of such radionuclide pairs are 232Th/228Ra, 228Ra/228Th etc. Another problem for the gamma spectrometric determination of natural radionuclides is due to the fact that some radionuclides have gamma lines that are identical and so close to each other that make it impossible to resolve them.
Figure 3.9: Uranium-238 decay series
45 Chapter-3: Gamma radioactivity measurement
When the decay series are in equilibrium, the listed emission probabilities refer to the decay of the parent radionuclide.
Figure 3.10: Thorium-232 decay series
3.9.1 Determination of Radium-226
Radium-226 has a half-life of 1600 years and is a long lived radionuclide in the uranium decay series. The short lived decay radionuclides 214Pb was measured after the
46 Chapter-3: Gamma radioactivity measurement establishment of radioactive secular equilibrium between 226Ra, 222Rn and 214Pb assumed, for the determination of 226Ra in different environmental media by gamma spectrometric analysis rather considering 226Ra peak at 186.1 keV line. The contribution of the 235U peak overlapping at 185.7 keV could not be ignored while considering 186.1 keV line [142]. For the determination of 226Ra the gamma line of 214Pb at 351.9 keV was used because the summation effects become negligible using this gamma line otherwise summation correction had to be made if all the detectable gamma lines of 214Pb and 214Bi were used. [143, 144].
3.9.2 Determination of Thorium-232
Thorium-232 has a half-life of 1.41×1010 years and is the parent radionuclide of the thorium decay series as shown in figure 3.10. Thorium-232 has a gamma ray line at 63.81 keV which overlaps a line of 234Th at 63.28 keV. Due to this reason 232Th cannot be determined directly by gamma spectrometry in environmental media. Its determination through its daughter radionuclides 228Ac was made as shown in table 3.2, assuming that it was in radioactive secular equilibrium with 232Th due to its short half-life of 6.15 h. [145].
3.9.3 Determination of Potassium-40
Potassium-40 is much prominent in background spectrum. It is present in wood, building materials and even in the bodies of the gamma spectrometrists. The substantial presence of 40K in the detector background and in environmental samples, with its long Compton continuum, makes it difficult in detection of many radionuclides emitting gamma rays at lower energies. The gamma spectrometry of 40K is carried out using gamma ray line at 1460.7 keV [146, 147].
3.9.4 Determination of Cesium-137
Cesium-137 is a fallout radionuclide which is formed mainly during nuclear fission. It is also widely used in industry. Its half-life is 30 years. It mainly came into the world’s environment from atmospheric nuclear weapons tests in the 1950s and 1960s and later on by Chernobyl reactor accident in 1986. It decays with the emission of beta particles
47 Chapter-3: Gamma radioactivity measurement accompanying strong gamma rays. It decays to 137mBa, having half-life of 2.5 minutes and is responsible for all gamma ray emissions, which in turn decays to a non radioactive form of barium. Cesium-137 is determined through 137mBa having gamma energy 662 keV using gamma spectrometric techniques [23].
3.10 Conclusion
Gamma spectrometry is a non destructive technique used for determination of gamma emitting radionuclides. The system became capable to detect gamma emitting radionuclides in different environmental media after calibrating it with IAEA reference materials soil-375, soil-6, soil-327 and ash-156. For radiometric measurement techniques, gamma spectrometry is the preferred method which allows the simultaneous determination of a wide range of natural and man made gamma emitting radionuclides without requiring any radiochemical separation.
48 Chapter 4
RADIOACTIVITY LEVELS IN SOIL, WATER,
VEGETATION AND STAPLE FOOD1
Gamma spectrometric technique for analysis of different environmental media is widely used worldwide. It is a non destructive technique which has proved its capableness in the field and within the laboratory. Gamma spectrometry system comprises of HPGe detector, MCA and necessary electronics. The study of primordial and man-made radionuclides is very important due to their radiological hazards. Some of these radionuclides have tremendous biochemical and geological tracers in the environment. Moreover, soil behaves as the probable source of radionuclides through which these can enter into food chain and then eventually into human beings. In this perspective, activities of radionuclides 226Ra, 232Th, 40K and 137Cs are being determined worldwide and the data is available in literature for many countries. The radioactivity levels of the above mentioned gamma emitting radionuclides have been assessed through gamma spectrometric technique using soil, water, vegetation and staple food of Rechna Doab, Pakistan and discussed in this chapter.
1 The work presented in this chapter resulted in the following publications: i.) Abdul Jabbar, Waheed Arshed, Arshad Saleem Bhatti, Syed Salman Ahmad, Perveen Akhter, Saeed-Ur-Rehman and Muhammad Iftikhar Anjum, Measurement of soil radioactivity levels and radiation hazard assessment in southern Rechna interfluvial region, Pakistan, Environ. Monit. Assess., 169 (1-4), 429 (2010). ii.) Abdul Jabbar, Muhammad Tufail, Waheed Arshed, Arshad Saleem Bhatti, Syed Salman Ahmad, Perveen Akhter and Muhammad Dilband, Transfer of radioactivity from soil to vegetation in Rechna Doab, Pakistan, Isotopes in Environmental and Health Studies, 46 (4), 495 (2010). iii.) Abdul Jabbar, Waheed Arshed, Arshad Saleem Bhatti, Syed Salman Ahmad, Saeed-Ur-Rehman and Muhammad Dilband, Measurement of soil radioactivity levels and radiation hazard assessment in mid Rechna interfluvial region, Pakistan, J. Radioanal. Nucl. Chem. 283, 371 (2010). Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
4.1 Radioactivity levels in soil media
The terrestrial radioactivity contains the primordial radionuclides, 238U and 232Th series and 40K. These radionuclides are found in all rock and soil types. Secondary radionuclides are derived from radioactive decay series. Uranium-238 and 232Th decay series are the most important from radioactivity point of view. Members of these decay series are important either as contributors to human exposure or due to other radioactive characteristics. In order to determine the activity levels of terrestrial and anthropogenic radionuclides, the collected soil samples from the study area have been analyzed.
4.1.1 Radioactivity levels in northern Rechna Doab
The northern parts of the study area, Rechna Doab (see figure 2.1) comprising of districts Sialkot, Narowal, Gujranwala and Hafizabad. Soil samples were collected from this area described in section 2.2.1. The collected soil samples were processed and counted on PC based high resolution gamma spectrometry system as described in section 3.8. Radioactivity levels of 226Ra, 232Th, 40K and 137Cs measured and presented in table 4.1.
50 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
Table 4.1. Activity concentrations (Bq kg-1) of 226Ra, 232Th, 40K and 137Cs in soil samples of northern Rechna Doab, Pakistan along with location parameters.
Activity concentration (Bq kg-1) Sampling location Latitude Longitude 226Ra 232Th 40K 137Cs Gujranwala 32o 09/ N 74o 07/ E 32.8±1.5 41.8±2.7 480.2±19.5 2.1±0.1 Wazirabad 32o 28/ N 74o 05/ E 39.3±1.5 57.5±2.8 652.8±20.2 ≤MDA Aiman Abad 32o 01/ N 74o 13/ E 31.7±1.1 49.8±2.7 465.9±19.5 1.6±0.1 Dhaunkal 32o 23/ N 74o 08/ E 51.5±1.2 61.5±2.8 695.9±20.3 3.2±0.2 Ahmad Nagar 32o 20/ N 73o 59/ E 38.6±1.2 53.5±2.8 566.5±19.9 1.8±0.1 Head Khanki 32o 22/ N 73o 59/ E 62.8±1.3 74.8±2.9 624.0±20.1 ≤MDA Rasul Nagar 32o 19/ N 73o 47/ E 60.1±1.3 72.7±2.9 609.6±20.0 ≤MDA Kalianwala 32o 17/ N 73o 44/ E 55.3±1.3 60.3±2.8 595.3±19.9 1.6±0.1 Kot Hara 32o 16/ N 73o 41/ E 47.5±1.2 63.1±2.8 537.7±19.8 ≤MDA Rasulpur Tarar 32o 03/ N 73o 27/ E 44.5±1.6 59.5±2.8 638.4±20.1 1.8±0.1 Gajar Gola 32o 04/ N 73o 43/ E 54.3±1.6 59.1±2.8 739.0±20.5 ≤MDA Uddowali 32o 06/ N 73o 54/ E 48.2±1.2 59.5±2.8 624.0±20.1 2.9±0.2 Qillah Didar Singh 32o 07/ N 73o 59/ E 43.8±1.2 59.1±2.8 638.4±20.1 ≤MDA Nosherah Virkan 31o 59/ N 74o 09/ E 50.9±1.6 58.7±2.8 695.9±20.3 2.9±0.2 Kamoke 31o 56/ N 74o 13/ E 40.0±1.5 53.1±2.7 566.5±19.9 2.4±0.1 Sadhuke 31o 53/ N 74o 14/ E 56.6±1.3 67.5±2.9 695.9±20.3 ≤MDA Manguke 31o 47/ N 74o 01/ E 53.9±1.2 62.3±2.8 739.0±20.5 4.7±0.2 Hafizabad 32o 03/ N 73o 42/ E 52.1±1.2 57.5±2.8 681.5±20.3 ≤MDA Pindi Bhattian 31o 53/ N 73o 15/ E 51.5±1.2 67.9±2.9 595.3±19.9 ≤MDA Winekay Tarar 32o 13/ N 73o 35/ E 46.5±1.7 61.5±2.8 667.2±20.2 1.6±0.1 Chak Bhatti 32o 05/ N 73o 24/ E 47.9±1.5 69.1±2.9 595.3±19.9 ≤MDA Jalal Pur Nau 32o 03/ N 73o 23/ E 44.9±1.2 59.9±2.8 624.0±20.1 ≤MDA Sukhay Ki 31o 49/ N 73o 35/ E 44.5±1.2 52.3±2.7 595.3±19.9 3.3±0.2 Kishan Garh 31o 47/ N 73o 26/ E 58.5±1.8 73.6±2.9 739.0±20.5 5.5±0.2 Sialkot 32o 27/ N 74o 33/ E 36.2±1.1 51.0±2.7 580.9±19.9 6.3±0.2 Sambrial 32o 30/ N 74o 20/ E 33.2±1.1 47.4±2.7 451.5±19.4 2.2±0.1 Kulu Wal 32o 34/ N 74o 21/ E 49.5±1.2 66.3±2.8 652.8±20.2 5.6±0.2 Head Marala 32o 40/ N 74o 28/ E 42.2±1.2 55.9±2.8 624.0±20.1 3.6±0.2 Chaprar 32o 34/ N 74o 29/ E 41.2±1.2 55.9±2.8 537.7±19.8 4.6±0.2 Chuvinda 32o 21/ N 74o 37/ E 36.9±1.1 60.7±2.8 609.6±20.0 8.1±0.3 Mundeki 32o 17/ N 74o 32/ E 43.0±1.2 69.9±2.9 695.9±20.3 3.8±0.2 Daska 32o 17/ N 74o 21/ E 46.0±1.2 60.3±2.8 638.4±20.1 4.2±0.2 Dharamkot 32o 11/ N 74o 22/ E 46.8±1.2 64.7±2.8 667.2±20.2 6.9±0.2 Sutra 32o 09/ N 74o 28/ E 40.8±1.2 56.3±2.8 480.2±19.5 ≤MDA Merajke 32o 24/ N 74o 46/ E 38.0±1.2 51.8±2.7 580.9±19.9 5.6±0.2 Norowal 32o 06/ N 74o 51/ E 37.5±1.1 59.1±2.8 667.2±20.2 2.0±0.1 Zafarwal 32o 20/ N 74o 55/ E 36.0±1.1 48.2±2.7 566.5±19.9 7.3±0.2 Chak Amro 32o 15/ N 74o 08/ E 41.8±1.2 62.7±2.8 537.7±19.8 6.1±0.2 Noor Kot 32o 11/ N 74o 06/ E 39.9±1.2 59.9±2.8 537.7±19.8 3.0±0.2 Jassar 32o 05/ N 74o 55/ E 39.3±1.2 59.5±2.8 710.3±20.4 7.2±0.2 Talwindi Bhindran 32o 06/ N 74o 40/ E 39.2±1.2 60.3±2.8 566.5±19.9 ≤MDA
It can be seen in the table 4.1 that the activity of 226Ra ranges from 31.7±1.1 Bq kg-1 in Aiman Abad to 62.7±1.4 Bq kg-1 in Head Khanki. The activity of 232Th ranges from 41.8±2.7 Bq kg-1 in Gujranwala to 74.8±2.9 Bq kg-1 in Head Khanki.
51 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
(c)
800.00 2 R = 0. 2874 750.00
700.00 ) -1 650.00
600.00
550.00
500.00
K Concentration (Bq kg (Bq Concentration K 450.00 40
400.00
350.00
300.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00 75.00 80.00 232Th Concentration ( Bq kg-1)
Figure 4.1: (a) Correlation between 226Ra and 232Th concentrations; (b) correlation between 226Ra and 40K concentrations; (c) correlation between 232Th and 40K concentrations in northern Rechna Doab, Pakistan.
52 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
The activity of 40K ranges from 451.5±19.4 Bq kg-1 in Sambrial to 739.0±20.5 Bq kg-1 in Kishan Garh. The radioactivity levels of artificial radionuclide 137Cs were found to be the maximum in Chuvinda (8.1±0.3 Bq kg-1). The radioactivity levels of 40K were seen to be higher than those of 232Th and 226Ra at all the places of study area. In order to determine the existing ratio between the activity concentrations of three natural radionuclides in soil samples, correlations between them were drawn. Figure 4.1(a-c) represents correlations between the activity concentrations of 226Ra and 232Th, 226Ra and 40K and 232Th and 40K respectively, with a trend line drawn amo ng the d at a poi n ts using regression technique. In all the three cases, linear and positive regression was found. The correlation coefficient between 226Ra and 232Th was 0.6 where as between 226Ra and 40K and similarly between 232Th and 40K, it was quite low. It indicated that 226Ra and 232Th came from a common origin where as 40K had source that was independent of both 226Ra and 232Th. However a positive correlation may still be attributed to property of the soil in retaining these radionuclides under varying weather conditions. The results shown in table 4.1 also indicate that the mean value of 40K is the highest and that of 226Ra is the lowest. The statistics of the values measured for 226Ra, 232Th and 40K in the surface soil samples are enlisted in table 4.2. It shows the respective mean value, range, skewness, and kurtosis coefficients.
Table 4.2: Statistical data for activity concentration of 226Ra, 232Th and 40K in surface soil samples from northern Rechna Doab, Pakistan.
Activity concentration (Bq kg-1) 226Ra 232Th 40K Mean 45.0 59.6 613.8 Std. Dev. 7.7 7.2 74.4 Skewness 0.41 -0.01 -0.29 Kurtosis -0.49 0.27 -0.37 Range 31.7 – 62 .8 41.8 – 74 .8 451.5 – 73 9.0
53 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
12
10
8
6 Frequency 4
2
0 30 35 40 45 50 55 60 65 (a) Ra-226 concentration (Bq/kg)
12
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6 Frequency 4
2
0 40 45 50 55 60 65 70 75 (b) Th-232 concentration (Bq/kg)
12
10
8
6 Frequency 4
2
0 450 500 550 600 650 700 750 (c) K-40 concentration (Bq/kg)
Figure 4.2: Frequency distribution of (a) 226Ra, (b) 232Th and (c) 40K concentration in northern Rechna Doab, Pakistan.
54 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
Positive skewness coefficient was observed for 226Ra, it meant that activity levels had increasing trend. The reasons of this trend might be due to use of phosphate fertilizers in cultivated land and some amount of it had been leached out into the sampling sites. Thorium-232 having approximately null skewness, indicating the existence of normal distribution and the activity concentration was practically symmetrical. Potassium-40 had negative skewness indicating decreasing trend. It meant that less potash fertilizers were used in the agricultural land or it had been leached out from the sampling sites. Figure 4.2(a–c) shows above mentioned reasons. The existence of a broad range in the variation of the activities of radionuclides was also observed (see table 4.2). This was due to the wide variety of lithological components existing in the zone under study. Cesium-137, although in very low concentrations, was detected at most of the places. Its concentration ranged from 1.6±0.1 to 8.1±0.3 Bq kg-1 with an average value of 4.0±0.2 Bq kg-1. At some locations its concentration was quite low and less than minimum detectable activity. Cesium-137 is one of the important fission products and is a prominent indicator of fallout from nuclear weapon tests during fifties and sixties of the last century and the fallout due to the Chernobyl reactor accident.
4.1.2 Radioactivity levels in mid Rechna Doab
Mid parts of the study area, Rechna Doab (see figure 2.1) comprising of districts Sheikhupura and Nankana Sahib while tehsils Jaranwala (District Faisalabad) and Chiniot (District Jhang). Soil samples were collected from this study area as described in section 2.2.1.
55 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
Table 4.3: Activity concentrations (Bq kg-1) of 226Ra, 232Th, 40K and 137Cs in soil samples of mid Rechna Doab, Pakistan along with location parameters.
Activity concentration (Bq kg-1) Location Latitude Longitude 226Ra 232Th 40K 137Cs Shaikhupura City 31o 42/ N 74o 01/ E 48.9±1.6 65.5±3.2 739.0±30.8 1.5±0.3 Hitcher 31o 59/ N 74o 32/ E 52.1±1.6 68.3±3.3 566.5±34.6 2.9±0.3 Narang Mandi 31o 54/ N 74o 26/ E 38.0±1.5 50.6±3.1 566.5±49.5 4.9±0.4 Muridke 31o 49/ N 74o 16/ E 40.6±1.5 59.9±3.2 566.5±33.2 4.7±0.4 Shahdra 31o 37/ N 74o 17/ E 48.2±1.6 58.7±3.2 739.0±31.0 4.2±0.3 Khanpur 31o 40/ N 74o 05/ E 45.0±1.6 69.5±3.3 638.4±31.3 ≤MDA Damamkay 31o 36/ N 74o 03/ E 50.9±1.6 69.9±3.4 681.5±29.8 2.4±0.4 Sharkpur 31o 29/ N 74o 05/ E 50.6±1.6 67.9±3.3 868.4±38.9 ≤MDA Mangtanwala 31o 21/ N 73o 51/ E 36.6±1.5 56.7±3.2 695.9±34.2 6.2±0.4 Buchiki 31o 18/ N 73o 37/ E 53.1±1.6 67.9±3.3 753.4±30.6 2.7±0.3 Mananwala 31o 28/ N 73o 42/ E 47.9±1.5 59.9±3.4 652.8±29.4 1.7±0.3 Shahkot 31o 34/ N 73o 42/ E 52.8±1.6 61.5±3.2 753.4±29.1 5.6±0.6 Jhabran 31o 47/ N 73o 59/ E 50.5±1.5 64.3±3.3 739.0±34.4 2.6±0.3 Khankah Dogran 31o 50/ N 73o 36/ E 49.1±1.6 60.7±3.2 652.8±32.3 3.0±0.4 Marar 31o 44/ N 73o 23/ E 49.2±1.6 68.7±3.2 552.1±38.9 ≤MDA Sanglahil 31o 42/ N 73o 21/ E 45.8±1.7 61.9±3.2 566.5±32.3 ≤MDA Nankana Sahib 31o 26/ N 73o 41/ E 48.9±1.5 63.9±3.2 681.5±35.8 ≤MDA Syedwala 31o 07/ N 73o 29/ E 46.9±1.6 58.7±3.2 695.9±31.5 2.3±0.3 Maoza Sial 31o 05/ N 73o 20/ E 52.1±1.9 61.7±3.2 652.8±33.4 2.4±0.3 Chiniot 31o 41/ N 72o 57/ E 54.6±1.9 61.9±3.2 710.3±33.1 3.8±0.3 Bukharian 31o 39/ N 72o 49/ E 53.5±1.6 59.5±3.2 710.3±36.0 4.2±0.3 Bhawana 31o 33/ N 72o 38/ E 52.6±1.6 60.7±3.2 624.0±36.5 ≤MDA Jhok Ditta 31o 05/ N 73o 13/ E 56.9±1.6 66.3±3.2 667.2±32.5 2.6±0.3 Chak-239, 31o 17/ N 73o 26/ E 54.6±1.6 68.7±3.3 724.7±33.5 4.5±0.4 Jaranwala Jaranwala 31o 20/ N 73o 19/ E 46.6±1.5 45.8±3.1 566.5±35.6 2.2±0.3
The collected soil samples were processed and counted on PC based high resolution gamma spectrometry system as described in section 3.8. Radioactivity levels of 226Ra, 232Th, 40K and 137Cs were measured in the soil of the present study area and presented in table 4.3. It can be seen in the table 4.3 that the activity of 226Ra ranged from 36.6±1.5 Bq kg-1 in Mangtanwala to 56.9±1.9 Bq kg-1 in Jhok Ditta. The activity of 232Th ranged from 45.8±3.1 Bq kg-1 in Jaranwala to 69.9±3.4 Bq kg-1 in Damamkay. The activity of 40K ranged from 552.1±38.9 Bq kg-1 to 868.4±38.9 Bq kg-1 in Marar and Sharkpur, respectively. The radioactivity levels of 40K were observed higher than 232Th and 226Ra at all the places of the study area. In order to determine any synergistic behaviour, correlations between them were drawn. Correlations between the concentrations of 226Ra and 232Th, 226Ra and 40K and 232Th and 40K respectively were also checked. In all the
56 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
three cases, the regression was found linear and positive in a similar pattern as shown in figure 4.1. The statistical data of the values calculated for 226Ra, 232Th and 40K in the surface soil samples are enlisted in table 4.4. Table 4.4 shows the respective mean value, range, skewness and kurtosis coefficients.
Table 4.4: Statistical data for radioactivity concentrations of 226Ra, 232Th and 40K in surface soil samples of mid Rechna Doab, Pakistan.
Activity concentration (Bq kg-1) 226Ra 232Th 40K Mean 49.0 62.4 670.6 Std. Dev. 5.0 5.8 78.2 Skewness -1.02 -1.04 0.26 Kurtosis 0.96 1.59 0.15 Range 36.6 – 56.9 45.8 – 69.9 552.12 – 868.4
Negative skewness was observed for 226Ra and 232Th in the present study area, indicating decreasing activity levels. It shows that 226Ra and 232Th might be leached out or less phosphate fertilizers were used in the adjacent agricultural land to the sampling points. Positive skewness was observed in case of 40K, indicating increasing trend of activity levels. It might be due to use of potash fertilizers in the adjacent agricultural fields. The trends discussed above have been shown in figure 4.3(a–c). The existence of a vide range in the variation of the activities of radionuclides was also observed (as shown in table 4.4). This might be due to the wide variety of lithological factors existing in the study area. Very low concentrations of 137Cs were detected at most of the places. Its concentration ranged from 1.7±0.3 to 6.2±0.4 Bq kg-1 with an average value of 3.5±0.4 Bq kg-1. At some locations its concentration was quite low and less than minimum detectable activity.
57 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
12
10
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6 Frequency 4
2
0 35 40 45 50 55 60 65 (a) Ra-226 concentration (Bq/kg)
12
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6 Frequency 4
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0 45 50 55 60 65 70 (b) Th-232 concentration (Bq/kg)
12
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6 Frequency 4
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0 550 600 650 700 750 800 850 900 (c) K-40 concentration (Bq/kg)
Figure 4.3: Frequency distribution of the concentrations of (a) 226Ra, (b) 232Th and (c) 40K in mid Rechna Doab, Pakistan.
58 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
4.1.3 Radioactivity levels in southern Rechna Doab
Southern parts of the study area, Rechna Doab (see figure 2.1) comprising of districts Jhang, Faisalabad and Toba Tek Singh. Soil samples were collected from the study area as described in section 2.2.1.
Table 4.5: Activity concentrations (Bq kg-1) of 226Ra, 232Th, 40K and 137Cs in soil samples of southern Rechna Doab, Pakistan along with location parameters.
Activity concentration (Bq kg-1) Location Latitude Longitude 226Ra 232Th 40K 137Cs Jhang City 31o 16/ N 72o 20/ E 60.1±1.6 66.7±3.3 724.7±34.6 ≤MDA Khewa 31o 28/ N 72o 29/ E 57.5±1.8 73.2±3.3 681.5±36.9 2.6±0.3 Mochiwala 31o 17/ N 72o 23/ E 57.9±1.7 62.3±3.3 710.3±33.5 2.6±0.3 Bagh 31o 13/ N 72o 19/ E 60.2±1.7 67.5±3.3 724.7±36.3 ≤MDA Head Trimon 31o 08/ N 72o 09/ E 49.8±1.7 60.3±3.2 624.0±32.5 2.4±0.3 Qaim Bhawana 30o 51/ N 72o 08/ E 48.6±1.6 61.1±3.2 494.6±30.7 4.3±0.4 Garh Maharaja 30o 49/ N 72o 02/ E 43.0±1.7 58.7±3.2 595.3±31.9 ≤MDA Basti Islam 30o 47/ N 72o 03/ E 51.9±1.7 61.9±3.2 609.6±29.2 ≤MDA Darkhana 30o 47/ N 72o 05/ E 56.1±1.6 59.5±3.2 710.3±30.7 1.9±0.4 Azadpur 30o 49/ N 72o 10/ E 50.6±1.6 53.1±3.2 710.3±32.1 ≤MDA Wariam Wala 30o 54/ N 72o 17/ E 43.5±1.7 57.1±3.2 609.6±29.7 ≤MDA Pir Mahal 30o 45/ N 72o 25/ E 46.6±1.6 64.7±3.2 580.9±34.1 3.2±0.3 Chatiana 30o 52/ N 72o 21/ E 45.8±1.6 53.9±3.2 638.4±27.4 3.3±0.4 Sandilianwali 30o 39/ N 72o 22/ E 49.5±1.6 65.5±3.3 782.2±37.2 ≤MDA Wahgi Adda 30o 41/ N 72o 31/ E 46.5±1.7 61.5±3.2 667.2±29.4 ≤MDA Dwakhri 31o 15/ N 72o 45/ E 52.5±1.7 63.9±3.2 695.9±31.9 ≤MDA Korian Gojra 31o 12/ N 72o 43/ E 42.6±1.6 51.8±3.1 580.9±30.4 4.2±0.3 Kala Pahar 31o 03/ N 72o 35/ E 57.6±1.6 69.1±3.3 638.4±35.4 1.9±0.3 Dabanwala 30o 55/ N 72o 30/ E 53.6±1.6 67.9±3.2 667.2±35.6 ≤MDA Khidarwala 30o 56/ N 72o 50/ E 54.5±1.7 68.7±3.3 681.5±31.4 2.2±0.3 Ghatwala 31o 40/ N 73o 17/ E 41.8±1.6 57.1±3.2 580.9±27.7 2.1±0.3 Mamon Kanjan 30o 48/ N 72o 47/ E 50.6±1.6 53.9±3.2 724.7±34.8 ≤MDA Garh 30o 48/ N 72o 50/ E 50.8±1.6 65.1±3.2 624.0±32.4 ≤MDA Kanjwani 30o 55/ N 72o 56/ E 56.1±1.6 65.9±3.3 695.9±29.3 ≤MDA Samundri 31o 03/ N 72o 59/ E 48.5±1.9 59.9±3.2 767.8±32.9 6.5±0.4 Saloni Jhal 31o 10/ N 72o 59/ E 48.6±1.8 58.7±3.2 624.0±32.4 6.1±0.4 Sirshamir Road 31o 17/ N 72o 53/ E 53.3±1.6 70.7±3.3 681.5±25.2 2.6±0.3 Dandianwala 31o 20/ N 71o 47/ E 52.9±1.9 60.3±3.2 710.3±35.6 3.6±0.3 Tandlianwala 31o 00/ N 73o 06/ E 52.5±1.7 67.5±3.3 638.4±28.3 2.9±0.3 Lundian Adda 31o 18/ N 73o 34/ E 42.8±1.7 56.3±3.2 624.0±33.7 2.1±0.3 Chak Kundian 31o 19/ N 73o 35/ E 42.3±1.6 61.5±3.4 839.7±33.7 1.7±0.3 Khurarianwala 31o 39/ N 73o 14/ E 51.6±1.6 69.9±3.3 552.1±29.2 ≤MDA
The collected soil samples were processed and counted on PC based high resolution gamma spectrometry system as described in section 3.8. Radioactivity levels
59 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
of 226Ra, 232Th, 40K and 137Cs measured in the soil of different areas collected in the present study are presented in table 4.5. It can be seen that the activity of 226Ra ranged from 41.8±1.6 Bq kg-1 in Ghatwala to 60.2±1.7 Bq kg-1 in Bagh. The activity of 232Th ranged from 51.8±3.1 Bq kg-1 in Korian Gojra to 73.2±3.3 Bq kg-1 in Khewa. The activity of 40K ranged from 494.6±30.7 Bq kg-1 in Qaim Bhawana to 839.7±33.7 Bq kg-1 in Chak Kundian. The radioactivity levels of artificial radionuclide 137Cs were found to be the maximum in Samundri (6.5±0.4 Bq kg-1). The radioactivity levels of 40K were seen to be higher than those of 232Th and 226Ra at all the places of study area. Correlations between the concentrations of 226Ra and 232Th, 226Ra and 40K and 232Th and 40K respectively were also checked. In all the three cases, the regression was found linear and positive in a similar design as shown in 4.1 The statistical values determined for 226Ra, 232Th and 40K in the surface soil samples of southern Rechna Doab are enlisted in table 4.6. Table 4.6 shows the respective mean value, range, skewness and kurtosis coefficients.
Table 4.6: Statistical data for radioactivity concentrations of 226Ra, 232Th and 40K in surface soil samples from southern Rechna Doab, Pakistan.
Activity concentration (Bq kg-1) 226Ra 232Th 40K Mean 50.6 62.3 662.2 Std. Dev. 5.3 5.6 71.6 Skewness -0.03 -0.07 0.12 Kurtosis -0.84 -0.77 0.41 Range 41.7 – 60.2 51.8 – 73.2 494.6 – 839.7
It can be observed that the values of skewness coefficient for 226Ra and 232Th were very close to zero, indicating the existence of normal distribution. Positive skewness was observed in case of 40K, indicating little increasing trend of activity levels. It might be due to use of potash fertilizers in the area. Figure 4.4(a–c) shows the above mentioned results. The existence of a vide range in the activities of radionuclides was also observed (see table 4.6). It might be due to the wide variation in geological and lithological constituents existing in the zone under study.
60 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
12
10
8
6 Frequency 4
2
0 40 45 50 55 60 (a) Ra-226 concentration (Bq/kg)
12
10
8
6 Frequency 4
2
0 50 55 60 65 70 75 (b) Th-232 concentration (Bq/kg)
12
10
8
6 Frequency 4
2
0 450 500 550 600 650 700 750 800 850 (c) K-40 concentration (Bq/kg)
Figure 4.4: Frequency distribution of the activities in southern Rechna Doab, Pakistan of (a) 226Ra, (b) 232Th and (c) 40K (Bq kg-1).
61 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
Very low concentrations of 137Cs were detected at most of the places. Its concentration ranged from 1.7±0.3 to 6.5±0.4 Bq kg-1 with an average value of 3.1±0.3 Bq kg-1. At some locations its concentration was quite low and less than minimum detectable activity.
4.1.4 Comparison of radioactivity levels in soil
As we can see from figures 4.2, 4.3 and 4.4 that 226Ra levels in northern parts of the study area were slightly lower than other parts of the region while the mid and southern parts were comparable. It was observed that 226Ra had increasing trend from northern to southern parts, it might be due to its leaching. As northern parts have more slope than other parts of the study area and chemical nature of 226Ra, justifies its leaching as well. While the levels of 232Th in all parts of the study area were comparable as it is not readily dissolvable due to its chemical nature. Potassium-40 levels were slightly less in northern parts than other two parts of the region, it indicates that it might had leached out due to more slope of northern parts as compared to other parts of the study area. The fallout radionuclide 137Cs was determined at most of the places and its levels were found to be comparable within three parts of the study area. As shown in figure 4.5, the mean activity of 226Ra measured in soil of the Rechna Doab (48.2.0±1.5 Bq kg-1) was higher than that of many countries like Venezuela [148], Southern Jordan [149], Bangladesh [150], Taiwan [151], Syria [65], China [65] and USA [65]. However, it was lower than that of Turkey [152], Indian Punjab and Himachal Pradesh [16], Malaysia [65], Hong Kong [65] and Zanjan, Iran [153]. The World average [65] was comparable with the values determined in present study. Some Pakistani areas like Lahore [154], Punjab Province [155] and Southern Punjab [156] have higher 226Ra levels than present study. Similarly, the levels of 232Th in Rechna Doab were 61.4±3.0 Bq kg-1. As shown in figure 4.6, its values were more than those in Bangladesh, Southern Jordan, USA, Taiwan, Venezuela, Syria, China and World average but lower than that of Malaysia and Indian Punjab and Himachal Pradesh. The determined levels were comparable with Turkey and Hong Kong. Some Pakistani studies carried out like Lahore, Punjab Province and Southern Punjab have lower 232Th levels than present study.
62 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
100 95
) 88.5 -1 79 80 67
60 56.7 50 42.5 48.2 40 35 35 33 30 32 27 25.8 20 21.7 20 Mean concentration (Bq kg (Bq Mean concentration 0
n y n a g b e a i n A h n la ia e n da k Ir s S ja s a e r na g a n n r , y o U e w y a t ta ta or la K d i u hi r s s s udy J Tu n a un a z S C e i i i t . ja g P Ta v k k k s S n M n n ne a a a a t a o a ngl e P P P n H i a V ld , e Z B b, b, e s Ind or a a r re W nj ho P u unj a P P L S
Figure 4.5: Comparison of mean concentration of 226Ra with different countries of the World.
100 )
-1 87.4 82 80 62 59 61.4 60 50 49.2 44 40 41 41 40 31.1 26.7 31 20 20 16
Mean concentration (Bq kg concentration Mean 0
n y ia A b a e ng h n la ia n d k s S ja s a e r na ge n n r r y o U n e w y ta ta a dy o la K d i u hi ra s s t u J Tu a u a z S C e i i is t . g P Ta v k k k s S M n n ne a a a a t o a ngl e P P P n H i a V ld , e B r b, b, e s Ind o a a r re W nj nj o P u u h P P La S
Figure 4.6: Comparison of mean concentration of 232Th with different countries of the World.
63 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
The levels of 40K in the study area were 648.9±28.7 Bq kg-1. Its values were comparable (see figure 4.7) with those for Turkey, Bangladesh and some Pakistani studies like Punjab Province and Lahore etc. but higher than Southern Jordan, Zanjan (Iran), Malaysia, Hong Kong and World average etc. These increased values of 40K may be attributed to the fact that the largest part of the study area is fertile and fertilizers are being used most abundantly to get good crops. Along with nitrogen and phosphate, potash is a major soil fertilizer, so levels of 40K in soils were strongly influenced by fertilizers used.
800
) 648.9 -1 615 574 574 562 600 530 497 500 431 440 393 370 357 400 310 291 270
200 143 Mean concentration (Bq kg concentration Mean
0
n y n a g A b h n a a a e n n n y a e a i n a s a l ri n g a a a d k r s S j e e i a t t t rd r I y o U n w u y h r s s s tu u , a K u d i z S e i i i s o n l la a e C v k k k J T a a g P T n a a a t . j M n g a P P P n S n o n n e d , , , e a ia a V l e s Z H d B r b b r e n o ja ja o r I W n n h P u u a P P L S
Figure 4.7: Comparison of mean concentration of 40K with different countries of the World.
As shown in figure 4.8, 137Cs determined in the present study (0-8.1 Bq kg-1) had lesser values than Majorca (Spain) [157], Louisiana (USA) [158], Montenegrin Coast (Yugoslavia) [159], Cairo (Egypt) [160], Anatolia (Turkey) [161] and northern Taiwan [162]. Its values were comparable with Eastern India [163], Dhaka (Bangladesh) [150] and a Pakistan study carried out in Punjab province [158]. The levels of 137Cs indicates
64 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
that the study area might have received global fallout from past nuclear tests and Chernobyl reactor accident.
80 ) -1 60 58 60
40 28.4 25 27 19.1 18.5 20 Concentration (Bg kg Concentration 10 7.5 10 8.1 5 6.4 1.6 2 1.5 0 1.5 1.8 3 1.1 0 0
) t) ) ) ) n n a ) n y in p y A ia a a i h a d e S v d s t u a y k d iw n e s t p g r (U la u I d i s S E u s S a n a k ( ( (T a o T r l a nt a o n g n te g P e c ir ia ia u r s n , s r a l s Y e a a b e jo o i ( h B ja r a C t u t rt E ( P a o s o a n M n L a k u A o N a P C h t D n o M
Figure 4.8: Comparison of concentration of 137Cs with different countries of the World.
It is believed that the data collected and presented in this study will act as a ready reference for any future activity/development wherein each study is a regulatory requirement e.g. construction of a nuclear power plant.
4.2 Radioactivity in surface water
Water is one of the most important constituent of the environment. Water can be classified in four groups. They are, with respect to the increasing effect on of human activities: Seawater, rainwater, surface water and waste water. Water is used for direct consumption, production of food and many industrial activities, etc. Being the best solvent water has always dissolved impurities in it. The concentration of these impurities varies widely. Thus radioactivity present in water can reach humans and the environment through different mechanisms.
65 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
4.2.1 Concentration of radionuclides in surface water
The radioactivity levels in the water samples collected from the study area, Rechna Doab (as shown in figure 2.1) were determined and tabulated in table 4.7.
Table 4.7: Activity concentrations (Bq l-1) of 226Ra and 40K in surface water samples of Rechna Doab, Pakistan.
Activity concentration (Bq l-1) Sampling location 226Ra 40K Wazirabad ≤MDA 2.1±1.7 Head Khanki ≤MDA ≤MDA Kalianwala ≤MDA ≤MDA Rasulpur Tarar 0.8±0.2 2.7±1.3 Uddowali 0.9±0.2 2.4±1.7 Qillah Didar Singh 0.9±0.2 3.0±1.7 Head Marala ≤MDA 2.3±1.7 Mundeki 0.8±0.2 2.4±1.2 Zafarwal ≤MDA ≤MDA Noor Kot ≤MDA ≤MDA Khewa 0.9±0.2 2.6±1.7 Head Trimon ≤MDA ≤MDA Sandilianwali ≤MDA 2.7±1.4 Dwakhri ≤MDA 2.5±1.7 Ghatwala ≤MDA ≤MDA Mamon Kanjan 0.9±0.1 2.1±1.5 Kanjwani 0.8±0.2 1.8±1.5 Khurarianwala 1.0±0.2 2.5±1.7 Shaikhupura City 0.9±0.2 3.1±1.8 Sharkpur ≤MDA 2.5±1.7 Mangtanwala 0.9±0.4 ≤MDA Nankana Sahib 0.8±0.2 ≤MDA Chiniot 0.9±0.2 ≤MDA
It can be seen in above table 4.7 that the activity of 226Ra ranged from 0.8±0.2 Bq l-1 in Rasulpur Tarar town to 1.0±0.2 Bq l-1 in Khurarianwala town with an average value of 0.9±0.2 Bq l-1. The activity of 232Th was below the MDA (see table 3.1). The activity of 40K ranged from 1.8±1.5 Bq l-1 in Kanjwani to 3.1±1.8 Bq l-1 in Shaikhupura City with an average value of 2.5±1.6 Bq l-1. While the radioactivity levels of artificial radionuclide 137Cs were found below the MDA. The radioactivity levels of 40K were higher than that of 226Ra at all the places of study area. The increased values of 40K were
66 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
due to the fact that most of the study area is crop producing and fertilizers are used to get good crops and it was leached into the surface water adjacent to the crop fields.
Table 4.8: Activity concentrations (Bq l-1) of 226Ra and 40K in water samples reported from different countries of the world.
Country Mean activity concentration (Bq l-1) Reference 1 226Ra 40K Safaga-Quseir (Egypt) 0.11 - [168] China 0.01 - [169] Turkey 0.04 5.7 [166] SaÄo Paulo, Brazil 0.24 - [165] Northeast Spain 0.03 0.13 [167] Catalonia, Spain 0.96 - [164] Rechna Doab, Pakistan 0.9±0.2 2.5±1.6 Present study
As shown in table 4.8, the mean activity of 226Ra measured in surface water of study area (0.9±0.2 Bq l-1) was higher than that of many countries like Safaga-Quseir Egypt [168], Northeast Spain [167], China [169], Turkey [166] and SaÄo Paulo, Brazil [165] etc. However, it was lower than that of Catalonia Spain [164].
4.3 Soil-to-plant uptake of radionuclides
Natural radioactivity comes mainly from the primordial radionuclides 238U, 232Th, their decay products, and 40K, which are present in all ground formations. The radionuclides that occur naturally in soil are metabolically incorporated into plants. Artificial radionuclides introduced into soil behave in a similar manner. These radionuclides can be incorporated into vegetation through uptake of radionuclides by the root system or due to activity interception by external surfaces of plants. To determine the radioactivity levels in vegetation and soil to plant transfer factors of radionuclides (226Ra, 228Ac and 40K) sacrificial grass (dab) was selected as a study tool in Rechna Doab, Pakistan.
4.3.1 Radioactivity levels in vegetation
Table 4.9 gives the experimentally measured values of 226Ra, 228Ac and 40K activities in the vegetation samples collected from the study area. The minimum activity of 226Ra was determined as 1.0±0.3 Bq kg−1 in Ahmad Nagar while maximum activity was found in Dwakhri. Actinium-228 was found in quite few samples, with most of the samples having values less than the MDA (see table 3.1). For 228Ac, minimum and maximum activity
67 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
values were 1.6±0.4 and 2.6±0.8 Bq kg−1 found in Daska and Syedwala areas, respectively. Thorium-232 has a long half life, it cannot be determined through its daughters in vegetation/plants. Due to this reason 228Ac was determined in vegetation. The minimum activity of 40K was found to be 53.1±2.2 Bq kg−1 in Head Marala and the maximum value of 469.2±6.6 Bq kg−1 was observed in the samples of Khewa. Cesium-137 was also found below the MDA in the all samples collected from the study area. The mean activity levels of 226Ra, 228Ac and 40K in vegetation of the Rechna Doab were 2.7, 2.2 and 172.7 Bq kg−1, respectively. A comparison between the activity concentrations in vegetation have been made with those reported for different countries of the World is presented in table 4.10.
68 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
Table 4.9: Activity concentrations of 226Ra, 228Ac and 40K (Bq kg-1) in vegetation of Rechna Doab, Pakistan.
Sampling location Activity concentration (Bq kg-1) 226Ra 228Ac 40K Wazirabad 2.0±0.2 ≤MDA 125.5±3.2 Ahmad Nagar 1.0±0.3 ≤MDA 80.4±2.3 Kalianwala 1.3±0.2 ≤MDA 123.1±1.9 Rasulpur Tarar 1.0±0.3 ≤MDA 111.7±2.3 Uddowali 1.3±0.4 ≤MDA 172.9±3.5 Qillah Didar Singh 1.2±0.4 ≤MDA 114.8±3.3 Sukhay Ki ≤MDA ≤MDA 53.2±2.2 Head Marala 3.1±0.3 1.6±0.4 131.0±4.1 Mundeki ≤MDA ≤MDA 104.9±4.2 Daska ≤MDA ≤MDA 113.7±2.3 Zafarwal ≤MDA ≤MDA 58.0±1.9 Noor Kot ≤MDA ≤MDA 144.3±2.7 Talwindi Bhindran ≤MDA ≤MDA 121.0±2.4 Shaikhupura City ≤MDA ≤MDA 93.8±3.2 Hitcher ≤MDA ≤MDA 108.9±2.1 Sharkpur 2.6±0.2 ≤MDA 69.4±2.5 Mangtanwala ≤MDA ≤MDA 103.1±2.4 Mananwala ≤MDA ≤MDA 115.2±4.4 Sayedwala 6.9±0.7 2.6±0.8 357.3±9.6 Chiniot 4.3±0.5 ≤MDA 355.9±7.3 Khewa ≤MDA ≤MDA 104.1±3.7 Head Trimon ≤MDA ≤MDA 102.1±4.4 Garh Maharaja 2.6±0.4 ≤MDA 330.9±6.2 Sandilianwali 2.3±0.6 ≤MDA 469.2±6.6 Dwakhri 3.5±0.4 ≤MDA 213.1±5.8 Kala Pahar ≤MDA ≤MDA 226.5±3.3 Khidarwala 2.8±0.4 ≤MDA 428.1±6.1 Ghatwala 6.4±0.8 2.6±0.6 215.1±7.5 Khurarianwala 2.0±0.4 ≤MDA 261.5±4.9
69 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
Table 4.10: Activity concentration (Bq kg-1) of 226Ra, 228Ac and 40K in vegetation samples reported from different countries of the World.
Mean activity concentration (Bq kg-1) Country Reference 226Ra 228Ac 40K
Egypt - 2.6 326.2 [171] North America (USA) 2.4×10-2 1.8×10-2 - [170] China 1.6×10-2 2.3×10-2 - [170] Indian Punjab 1.2 0.2 141.1 [172] Greece - - 399.8 [86] Southern Punjab, 1.7 3.7 303.7 [170] Pakistan Rechna Doab, Pakistan 2.7±0.4 2.2±0.6 172.7±4.0 Present study
It can be seen from table 4.10, the activity levels of naturally occurring radionuclides determined in the present study were on the higher side than those reported for North America, China and India, whereas these were comparable to the values reported for Egypt, Greece and southern Punjab, Pakistan.
4.3.2 Transfer of radionuclides from soil to plant
Due to the complexity and spatial variability of the soil-plant system, the uptake of radionuclides in vegetation from soil is difficult to quantify. Transfer coefficient (TF) is a useful parameter to determine radiological assessment and is defined as the steady-state concentration ratio between one physical situation to another, e.g., the ratio of the concentration of a radionuclide in dry vegetation to that in dry soil as follows [49, 173].
Vegetation specific activity(Bq kg−1 ) TF = 4.1 Soil specific activity(Bq kg−1 )
Transfer coefficient depends on vegetation type, soil properties and the type of radionuclides [174, 175]. From the activity concentrations in vegetation (see table 4.9) and soil (see tables 4.1, 4.3 and 4.5), the transfer coefficients have been calculated for the samples studied and the results obtained are listed in table 4.11. For 226Ra, TF was minimum (0.02) in Kalianwala and it was the maximum (0.14) in Syedwala. The transfer coefficient of 40K was minimum (0.09) in Head Marala and maximum in Khewa (0.69).
70 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
TF of 228Ac ranged from 0.03 (Daska) to 0.044 (Syedwala). The mean values of transfer coefficients in vegetation samples were 0.06, 0.26 and 0.04 for 226Ra, 40K and 228Ac respectively. Actinium-228 (a daughter of 232Th) was not detected in most of the vegetation samples of the study area, it is understandable as 232Th does not readily dissolve in water. A considerable amount of 226Ra was found in many of the samples as radium can be readily dissolved in water. It is removed from water by adsorption of clay particles and precipitation [176]. The TF values for 228Ac were found normally about 10 times lower than for 226Ra [41]. Like soil samples, 40K is also found in relatively higher concentrations in the vegetation. As potassium activity concentration was higher in soil, therefore relatively more 40K has been up taken during the absorption process by the plants. The uptake of radionuclides from soil to plants depends upon various interrelated soil properties including texture, clay content, dominant clay minerals, cation exchange capacity, exchangeable cations, pH and organic matter contents. It also varies with physical and chemical forms of the radionuclides, plant species, part, stage of growth, etc. [177].
71 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
Table 4.11: Transfer coefficients from soil to vegetation of the listed radionuclides for the samples collected from Rechna Doab, Pakistan
Sampling location Transfer coefficients 40K 226Ra 228Ac Wazirabad 0.19 0.05 - Ahmad Nagar 0.14 0.03 - Kalianwala 0.19 0.02 - Rasulpur Tarar 0.27 0.03 - Uddowali 0.18 0.03 - Qillah Didar Singh 0.19 0.03 - Sukhay Ki 0.09 - - Head Marala 0.21 0.07 0.03 Mundeki 0.15 - - Daska 0.20 - - Zafarwal 0.11 - - Noor Kot 0.25 - - Talwindi Bhindran 0.16 - - Shaikhupura City 0.17 - - Hitcher 0.13 - - Sharkpur 0.12 0.06 - Mangtanwala 0.16 - - Mananwala 0.17 - - Sayedwala 0.51 0.14 0.04 Chiniot 0.52 0.08 - Khewa 0.18 - - Head Trimon 0.19 - - Garh Maharaja 0.47 0.05 - Sandilianwali 0.69 0.04 - Dwakhri 0.34 0.07 - Kala Pahar 0.38 - - Khidarwala 0.55 0.06 - Ghatwala 0.31 0.12 0.04 Khurarianwala 0.41 0.04 -
72 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
4.4 Radioactivity levels in staple food
The purpose of analyzing staple food items was to determine the radioactivity levels and the potential dose to either individuals or to particular groups of individuals through their intake of food. This was carried out by sampling at the point of yield. The processes through which radionuclides are becoming the part of human diet can be complex. Radionuclides in air can be deposited onto agricultural land and some of it may deposit directly on to the plants growing on the land. The transfer of radionuclides through the foodchain to human beings is influenced by the existing agricultural and dietary habits.
4.4.1 Radionuclide concentration in staple food
The activity concentration of only naturally occurring radionuclides detected in staple food samples is presented in table 4.12. The radionuclide detected was 40K while other naturally occurring radionuclides were also checked but found below the MDA (see table 3.1). In wheat, the minimum activity concentration of 40K was 91.5 Bq kg-1 in Chiniot and the maximum was 266.2 Bq kg-1 in Garh Maharaja, while the average activity concentration was 174.3 Bq kg-1. In rice, the minimum activity concentration of 40K was 11.4 Bq kg-1 in Uddowali and the maximum was 62.6 Bq kg-1 in Hitcher, while the average activity concentration was 27.6 Bq kg-1. It was found world wide that among the natural radionuclides in staple foods, the activity concentration of 40K comes out to be highest; it might be due to the activity concentration of 40K in soil [178]. The transfer coefficient of 40K also comes out to be higher than other natural radionuclides [179, 180].
73 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
Table 4.12: Activity concentration (Bq kg-1) of 40K in staple food samples of Rechna Doab, Pakistan.
Activity concentration of 40K -1 Sampling location (Bq kg ) Wheat Rice Wazirabad 200.9±3.4 28.5±1.2 Ahmad Nagar 179.4±1.7 44.1±1.2 Kalianwala 104.1±2.1 32.9±1.2 Rasulpur Tarar 127.8±2.2 37.4±1.4 Uddowali 143.5±2.4 11.4±1.0 Qillah Didar Singh 166.5±3.1 19.5±1.1 Sukhay Ki 242.8±3.1 11.6±1.1 Head Marala 229.9±2.9 19.1±1.1 Mundeki 231.1±2.7 13.2±0.9 Daska 200.5±2.3 25.8±0.9 Zafarwal 241.5±3.1 26.7±0.9 Noor Kot 172.17±1.5 36.7±1.1 Talwindi Bhindran 129.1±1.17 38.2±1.1 Shaikhupura City 127.4±1.2 13.7±1.0 Hitcher 147.9±1.4 62.6±1.2 Sharkpur 136.4±1.4 13.7±1.0 Mangtanwala 176.9±3.3 17.5±1.4 Mananwala 192.9±3.5 27.8±1.4 Sayedwala 138.3±3.1 26.7±1.4 Chiniot 91.5±2.9 36.9±1.5 Khewa 119.8±3.3 24.5±1.0 Head Trimon 221.6±3.4 21.6±2.0 Garh Maharaja 266.2±3.8 17.3±2.0 Sandilianwali 258.2±3.5 59.5±2.3 Dwakhri 51.0±3.1 26.5±2.0 Kala Pahar 124.0±3.3 49.2±1.5 Khidarwala 142.0±3.0 22.4±2.0 Ghatwala 185.9±3.1 17.3±2.0 Khurarianwala 215.2±3.1 16.6±2.0
74 Chapter-4: Radioactivity levels in soil, water, vegetation and staple food
4.5 Conclusion
The present systematic study shows that the measured radionuclide concentrations in soil, surface water, vegetation and staple food were comparable with other global radioactivity determinations. The radioactivity levels of primordial radionuclides were comparable in soils of northern, mid and southern parts of the study area. The radioactivity levels of anthropogenic radionuclide 137Cs were comparable also with in three parts of the study area. It was an indication that the study area had also received global fall out radioactivity from atomic tests and Chernobyl reactor accident. Radium-226 and 40K radionuclides were determined in surface water samples and the radioactivity levels of these radionuclides were found to be little higher than global values. The activity concentration measured in vegetation during the present study was relatively higher than those were reported for other countries of the world. In general, in most of the vegetation samples, the transfer coefficients for different radionuclides were in the following order: 40K>226Ra >228Ac. In staple food, the only radionuclide detected was 40K during present study.
75 Chapter 5
DETERMINATION OF STRONTIUM-90 IN DIFFERENT ENVIRONMENTAL MEDIA
Strontium-90 is an important fission product artificially produced through fission of 235U. It is found globally at varying concentrations since nuclear tests have been performed and its levels have increased in some areas of the world after Chernobyl reactor accident in 1986. Strontium-90 is a pure beta emitting radionuclide and decays to 90Y, which further decays through beta emission to stable 90Zr as shown below;
Determination of 90Sr in environmental samples is not so simple due to its low energy beta emission, slow decay rate and interference from other beta-emitting radionuclides, especially its daughter radionuclide, 90Y. To obtain the accurate results, strontium-90 from other beta-emitting radionuclides is separated and long counting times are required to have acceptable statistical accuracy. There are two types of techniques that are being used for radiometric analysis of 90Sr, liquid scintillation counting and other is Cerenkov counting. Cerenkov counting technique for liquid samples is applicable to beta particles having endpoint energies greater than 263 keV. The samples are contained in suitable plastic counting vials, which are then positioned between two photomultiplier tubes at an angle of 180°. In liquid scintillation analyzer, a pair of photomultiplier tubes in combination with a coincidence circuit is used for sample counting. Chapter-5: Determination of 90Sr in different environmental media
A number of studies throughout the world have been carried out to determine the levels of 90Sr which are rising with time in the environment. These levels may be responsible for increase in cancers, especially in children. It is supposed that radioactive effluents from nuclear power plants are directly responsible for the increases in 90Sr levels. In the present study, radioactivity levels of 90Sr were determined in different environmental media e.g. soil, vegetation and water collected from different locations of Rechna Doab, Pakistan and results are discussed in this chapter.
5.1 Sample collection and pre-treatment
Soil, water and vegetation samples were collected from different locations of the study area as shown in figure 2.1 and as described in section 2.2. Samples were packed in plastic bags carefully, carrying identification marks. The collected samples were dried on plastic sheets at room temperature for 3-5 days [181]. To remove moisture further, the o samples were dried in an electric oven at 110 C up to 24 hours. After drying, the samples were ashed in an electric furnace at 450 oC till complete burning of organic matter. These ashed samples were processed radiochemically as explained in section 5.2.
5.2 Radiochemical processing
Due to relatively very short half life (64.2 hours) of 90Y as compared to its parent 90Sr (28.8 years), the buildup of 90Y in the sample is very fast to attain secular equilibrium with parent and it further decays to stable 90Zr [21, 182]. To determine 90Sr in the environmental samples, Cerenkov counting technique was used. One of the main advantages of Cerenkov counting is related to sample preparation; a colourless aqueous solution of the radioactive material is required for counting. No chemical quench is observed with Cerenkov counting [85, 183]. The sample is not diluted with any scintillation cocktail and therefore the whole volume of the counting vial can be used for the sample material. The sample remains unchanged and it can be used subsequently for other purposes after counting [184, 185]. As the amount of liquid in the counting vials greatly affects the counting efficiency, the vials were filled with 15 ml solution to achieve maximum efficiency.
77 Chapter-5: Determination of 90Sr in different environmental media
Plastic vials as shown in figure 5.1, were preferred over glass vials, because glass absorbs the Cerenkov light of low wave lengths [186].
Vial height = 5.8 cm Vial diameter = 2.6 cm Cap diameter = 2.2 cm Capicity = 20 ml
Figure 5.1: Liquid scintillation plastic vials along with specifications, used for counting of environmental media on liquid scintillation analyzer.
The radiochemical separation procedure used was solvent extraction method that requires 2-3 days for analysis, to determine 90Sr [187] and is described as follows:
5.2.1 Strontium carrier solution
First of all, a strontium carrier solution (10 mg of Sr/ml) was prepared; added 12.08 g of
Sr(NO3)2 to a 500 ml graduated flask. During next step 100 ml distilled water and 10 ml
of 14.4 M HNO3 was added in the above-mentioned flask. The flask was shaken well to dissolve the salt contents and that was filled to 500 ml mark with distilled water.
5.2.2 Yttrium carrier solution
20.52 g of Y(NO3)3.5H2O was taken into another 500 ml graduated flask. Then 100 ml of
distilled water and 10 ml of 14.4 M HNO3 was added in the above mentioned flask. The flask was shaken well to dissolve the salt contents and that was filled to 500 ml mark with distilled water.
5.2.3 Radiochemical separation of 90Y
For radiochemical separation of 90Y, different steps involved are described below: a) 10 g carbon free ashed sample of soil or vegetation was taken in a 500 ml beaker and added 100 ml distilled water along with 1 ml (1mg/ml) of already prepared Sr
78 Chapter-5: Determination of 90Sr in different environmental media
carrier solution as described in section 5.2.1. The solution was heated and stirred for a few minutes to disintegrate the lumps.
b) Another aliquot of 100 ml of distilled water was added along with 5 g of Na2CO3 in the solution. Again boiled the solution for 30 minutes with stirring to prevent bumping. c) Above solution was cooled and then it was centrifuged and discarded the supernatant.
d) The residue was washed from centrifuge tube twice with 50 ml of 0.1 M Na2Co3 solution. Again centrifuged the obtained solution and discarded the supernatant.
e) 25 ml of 14.4 M HNO3 was added to the centrifuge tube and shaken it well. Transferred the above solution to a 250 ml beaker. Washed the centrifuge tube three
times with 14.4 M HNO3 in order to retrieve the entire sample contents. The washed residues were collected in a beaker. f) 10 ml of Y+3, carrier solution (1mg Y+3/ml) was added along with 1 ml each of Ba+2, Cs+1, La+3 carries comprising each 1 mg element/ml.
g) 0.5 ml of H2O2 was added drop wise with stirring in the sample solution if it contained large amount of carbon contents. h) The sample was boiled for 2 hours to leach/dissolve the sample contents. The beaker was placed sideways for thirty minutes to cool it properly. i) The suspension was filtered through a fiber glass filter paper (whatman, GF/A) by placing in Buchner funnel. Vacuum was applied to drain all the liquid in the
sample. Sample contents were washed twice with 10 ml of 14.4 M HNO3. Vacuum was applied each time to drain out the whole liquid of the sample. The washed out material was collected along with the main solution and discarded the solid contents. 75 ml of desired solution was obtained. It was ready for extraction of 90Y with Tri Butyl Phosphate (TBP).
5.2.4 Extraction of Y from Sr and other elements
a) Ytterium-90 solution was transferred into 250 ml separating funnel and further
added 30 ml of TBP pre-equilibrated with 14.4 M HNO3. The funnel was shaken for five minutes and allowed to settle down the two phases of the solution.
79 Chapter-5: Determination of 90Sr in different environmental media
b) The lower aqueous phase was transferred into another separating funnel and noted the first extraction time. 30 ml of TBP was added, again. The solution containing funnel was shaken for five minutes and allowed to settle down the two phases. c) The step (b) was repeated again as described above. d) The above mentioned lower aqueous phases were collected into a beaker and then
added 10 ml of 14.4 M HNO3 into a third separating funnel along with collected aqueous phases. After shaking for 1 minute, transferred the lower aqueous layer into the second separating funnel. Again after shaking for 1 minute, separated the two layers and transferred the lower aqueous into the first separating funnel. After shaking for 1 minute again and separated the lower aqueous layer. Then combined all the organic phases from separating funnels into one flask.
e) The organic phase was washed three times with 10 ml of 14.4 M HNO3 and discarded the lower aqueous phase. f) 20 ml of distilled water was added into separating funnel containing organic phases. The solution was shaken for 5 minutes. The lower aqueous phase was transferred into another separating funnel and repeated three times the afore- mentioned step. g) The aqueous phases were combined and washed with 30 ml of carbon tetrachloride and carbon tetrachloride layer was discarded. Yttrium was present in the obtained solution.
5.2.5 Precipitation as Yttrium Oxalate
a) The sample was put into a 500 ml beaker and NaOH was added with stirring to bring the pH of the solution up to 4-5. b) 200 ml of distilled water was added to dilute the solution and 80 ml of 2%
C2H2O4.2H2O (oxalic acid) dehydrated solution was added. A white cloudy precipitate was appeared and the pH was adjusted between 1.5-2.5. c) The solution was heated in water bath for an hour to coagulate the precipitate and boiling was not allowed. The solution containing beaker was set aside for two hours before filtration.
80 Chapter-5: Determination of 90Sr in different environmental media
d) The yttrium oxalate was filtered through a pre-weighed fiberglass filter paper (GF/C) using a filter chimney and filtration suction. The precipitate was washed two times with 10 ml of distilled water and then with 10 ml of ethanol. e) Then the chimney was removed and the yttrium oxalate precipitate was air dried for one hour. The gravimetric factor was obtained as follows: Y / ⎡⎤Y C O 9H O== 177.81/ 603.01 0.29438 2 ⎣⎦2( 2 4)3. 2 f) The net weight of yttrium oxalate was determined by difference of the weights of loaded and blank filter. The percentage chemical recovery of yttrium was calculated by using the following expression: [0.29438×− weight of air dried Y Oxalate / weight of yttrium carrier added]× 100
Different steps of radiochemical separation are summarized in figure 5.2. Radiochemically prepared samples were counted on the liquid scintillation counting system.
Figure 5.2: Different steps of radiochemical separation procedure for 90Sr
81 Chapter-5: Determination of 90Sr in different environmental media 5.3 Liquid scintillation counting
If the energy of a beta particle, emitted by a radionuclide, is higher than 263 keV, this particle can produce Cerenkov radiation when it travels in water at a speed greater than the speed of light in the same medium [188]. At this speed of travel, the beta particle causes local polarization along the path of travel with the resultant emission of electromagnetic radiation when the polarized molecules return to their original states. The radiation is named after Cerenkov the discoverer of this phenomenon. The radionuclide, 90Y (daughter of 90Sr) emits beta particle having maximum endpoint energy 2.27 MeV, which is more than the 263 keV threshold level and can be detected in aqueous solutions by the Cerenkov measurement. The advantages of this technique are its simplicity, convenience and low cost [189, 1190]. The activity concentration of 90Sr in the samples was determined through its daughter (90Y). 90Y activity was determined through measurement of the Cerenkov radiation using a liquid scintillation analyzer Tri-Carb 3170TR/SL as shown in figure 5.3.
Figure 5.3: Liquid Scintillation Analyzer used for determination of 90Sr in different environmental media collected during present study
82 Chapter-5: Determination of 90Sr in different environmental media
These photons escape from the vial and impinge on the face of the photomultiplier tube. About one third of the photons which strike the face of the photomultiplier tube, cause the release of a photoelectron inside the tube. Each of the photoelectrons is then multiplied over a million-fold within the tube. This multiplication process results in the production of a measurable electrical signal which can be processed. The process of photon production within the sample and its detection by the photomultiplier tube is fundamental to any liquid scintillation analyzer. In this process the radiation energy released by the radioactive decay event in the sample is converted into electrical energy by the photomultiplier tube [85, 191, 192]. The commercially available liquid scintillation analyzers have a system of two photomultiplier tubes which records a count only when scintillation is detected by both photomultiplier tubes simultaneously.
Figure 5.4: Schematic arrangement of photomultiplier tubes and associated electronics required for liquid scintillation coincidence counting.
This technique is called coincidence counting. It is very effective in discriminating the scintillation pulses which are recognized by both photomultiplier tubes simultaneously against the noise pulses which occur randomly in both of the two photomultiplier tubes. A schematic arrangement of photomultiplier tubes and associated electronic units are shown in figure 5.4. During present study a spike of 90Y in equilibration with 90Sr (un-separated) from standard solution was measured directly. A spike of 100 micro litres of stock solution
83 Chapter-5: Determination of 90Sr in different environmental media was prepared in 15 ml of 2M HCL in liquid scintillation vial and measured directly for the Cerenkov radiation by liquid scintillation analyzer. For the determination of efficiency of liquid scintillation analyzer, standard sample was measured three times and the calculated efficiencies {(cpm/dpm)x 100} were 60.12 %, 58.99 %, 59.42 % . An average efficiency of 59.51 % was taken as the appropriate value. The contribution of 90Sr to this efficiency was assumed to be negligible. The prepared samples in plastic vials were counted on liquid scintillation analyzer as described above and results were confirmed by repeating the sample counting and it was observed that the decay of 90Y over the course of one week was being followed. The MDA was calculated by using equation 3.7 and values obtained are presented in table 5.1
Table 5.1: The Minimum Detectable Activity (MDA) for the radionuclides 90Sr in different environmental media
Environmental media MDA (Bq kg-1) Soil 2.0 Water 1.5 Vegetation 1.0
5.4 Results and discussion
Thirty three collected samples of soil, vegetation and water from the study area were counted for 90Sr activity levels and results are presented in table 5.2. The 90Sr activity concentration results have 68% confidence level. It can be observed that the activity of artificial radionuclide 90Sr in soil ranges from ≤MDA to 3.66±0.09 Bq kg-1 in Daska. The activity in vegetation samples ranges from ≤MDA to 1.55±0.08 Bq kg-1 in Daska while the activity levels found in all water samples were below MDA. The radioactivity levels of 90Sr were detected in most of the soil samples of the study area while it was not detected in most of the vegetation samples. No correlation was observed between 90Sr activity values determined for soil and vegetation samples collected from the study area.
84 Chapter-5: Determination of 90Sr in different environmental media
Table 5.2: Strontium-90 activities measured in different environmental media collected from Rechna Doab, Pakistan.
Activity (Bq kg–1) Sampling location Soil Vegetation Water
Head Marala ≤MDA ≤MDA ≤MDA Khewa ≤MDA ≤MDA ≤MDA Head Trimon 2.91±0.09 ≤MDA ≤MDA Syedwala 2.98±0.08 1.19±0.07 ≤MDA Dwakhri ≤MDA ≤MDA ≤MDA Khidarwala ≤MDA ≤MDA ≤MDA Sukhay Ki 2.82±0.08 ≤MDA ≤MDA Daska 3.66±0.09 1.55±0.08 ≤MDA Zafarwal ≤MDA ≤MDA ≤MDA Chuvinda 2.93±0.08 1.35±0.08 ≤MDA Zafarwal 2.72±0.09 ≤MDA ≤MDA
Even for these small detected levels, it can be assumed that it may originate from past atmospheric nuclear weapon tests and also the accident at the Chernobyl Nuclear Power Plant in 1986. Absence of 90Sr in surface layer of some soil samples may also be attributed to its high mobility in the soil column. It was reported that 90Sr migrated quite rapidly from the surface to the lower layer of soil [193]. A comparison of 90Sr activity concentration levels in soil and vegetation samples with reported values of the world was also made and the results are shown in table 5.3. It can be seen that 90Sr contents in the soil and vegetation samples of Brookhaven National Laboratory (BNL) and Savannah River site of USA are greater than those were determined in the present study. The soil samples from Ukraine showed also greater activity levels of 90Sr. This enhanced levels of 90Sr in BNL Site and Savannah River site in USA were may be due to the nuclear waste disposal, site releases and atmospheric fallout. Activities of 90Sr in Ukrainian soils are mainly attributed to Chernobyl Nuclear Reactor accident in 1986. Spain, Germany and Hanford site (USA) have comparable 90Sr concentration values with those of the present study.
85 Chapter-5: Determination of 90Sr in different environmental media
Table 5.3: Comparison of activity concentration of 90Sr (Bq kg-1) in soil and vegetation samples reported from different countries of the world.
Mean activity concentration of 90Sr (Bq kg-1) Country Reference Soil Vegetation USA (BNL Site) 52.0 330.0 [194] USA (Savannah river site) 15.9 27.8 [195] Spain (Island of Majorca) 4.5 - [196] USA (Hanford site) 5.5 - [197] Ukraine (Korosten) 34.1 - [198] Germany 2.8 - [199] Pakistan (CHASNUPP site) 1.5 - [200] Pakistan (Eastern Salt 0.5 - [201] Range) Pakistan (Sawat) - 2.9 [202] Rechna Doab, Pakistan 3.0 1.4 Present study
The comparison of the present study with other studies carried out in Pakistan, showed slightly higher deposition of 90Sr in soil samples than CHASNUPP (Chasma Nuclear Power Plant) site, Eastern Salt Range and Sawat. The activity levels of 90Sr in vegetation samples were on lower side than in Sawat. From table 5.3, it is apparent that there is no clear pattern of 90Sr distribution for different areas of the world. This inhomogeneous geological distribution of 90Sr may be due to several factors including surface run-off as well as its transport and vertical migration to deep inside the soil. Therefore, it is expected that the population residing in the study area and other parts of Pakistan is not exposed to the high doses or activity levels of 90Sr.
86 Chapter-5: Determination of 90Sr in different environmental media
5.5 Conclusion
The average activity levels of 90Sr found in soil samples of the study area was 3.0 Bq kg-1. The average activity levels found in vegetation samples were 1.36 Bq kg-1 while in all water samples the activity levels were below MDA. The presence of 90Sr concentration in the soil and vegetation samples indicates that this region has also received small inventories of this radionuclide from fallout activity due to nuclear weapon testing or nuclear reactor accident such as Chernobyl in the past. This is the first study of its nature and no background data is available for the study area. Thus a base line background data for 90Sr concentration in soil, vegetation and water has been established for the area under study, which will be helpful in any radiological or nuclear emergency. The results were found on lower side as compared to other areas of the world and almost similar within the Pakistan. The presence of 90Sr in some soil and vegetation samples of Rechna Doab demands further investigations on large scales.
87 Chapter 6
HEALTH RISKS AND RADIATION HAZARD
ASSESSMENT1
Radioactivity levels in the environment vary from point to point. Radionuclides present in air, soil, water, vegetation and rocks that make up of our planet Earth and atmosphere can be shifted into the ecosphere by many organisms and can also be accumulated in the food chain. This can be one of the reasons in increasing radiation doses to the general public, which needs to know the environmental behaviour of different radionuclides and estimation of their health risks. The radiation hazards to humans and the environment depend on the nature of the radioactive contaminant, contamination levels and the extent of the spread of contamination. Since humans cannot detect the presence of radiation with any of sensory pathways so it is detected through different means to recognize its presence. Thus, awareness of possible radiological hazards to people at large may be accomplished through its proper knowledge. The soil of the study area is also used to build mud dwellings and fabricate bricks used for construction in the area. Different theoretical models available in the literature were followed to assess the radiological environmental impact on public. The radium equivalent activity, the radiation absorbed dose rate, radiation hazard indices and effective dose have been calculated for soils, vegetation, water and staple food of the
1 The work presented in this chapter resulted in the following publication: Abdul JABBAR, Arshad S. BHATTI, Syed S. AHMAD, Waheed ARSHED and Perveen AKHTER, Assessment of environmental gamma dose in northern Rechna Doab, Pakistan in Nuc. Tech. and Rad. Protec. 1, 56 (2009). Chapter-6: Health risks and radiation hazard assessment
study area under study. Radioactivity transfer factors from soil to vegetation were also calculated. Daily intake of radioactivity by the general public was estimated as the consumption of food by humans gives rise to the internal radiation dose. All above mentioned factors were used to assess the health risks to the humans residing in the area and discussed in this chapter.
6.1 Hazards due to environmental radiation doses
Cosmic rays, cosmogenic radionuclides and radioactivity in soil, water and air are different forms of environmental radiation that contribute in background radiation doses. Other forms of background radiation include sources of radiation observable by the detector or contamination of samples. The in-situ gamma dose rate at 100 cm above the ground has also been measured using a standard calibrated environmental radiation dose rate meter, FAG, Germany model FH40F4 (see figure 6.1). It employed a G.M. tube as active detector having energy independent response from 45 keV to 1.3 MeV.
Figure 6.1: A view of portable FAG dose rate meter used during present study
The reliability of the dose rate meter results was assured by its calibration in the Secondary Standard Dosimetry Laboratory (SSDL), PINSTECH, Pakistan, whose measurements are traceable to Primary Standard and are ensured by the International
89 Chapter-6: Health risks and radiation hazard assessment
Atomic Energy Agency (IAEA) through postal dose inter-comparison [203-205]. The measurements were made during the period of April-June, 2008 and the sampling points were the same as that of soil, described in section 2.2. Ten to fifteen readings were taken at each location for this purpose and their mean value was converted to absorbed dose rate in air (nGy h-1). Minimum, maximum and mean values of absorbed dose rate in air and outdoor effective annual dose from terrestrial origin derived from these measurements.
Average absorbed dose rate in air was calculated using the following relation:
D (nGy h-1) = 9.15× dose(μ R / h) 6.1
where 9.15 included calibration factor and conversion from Roentgen to Grey.
Annual Effective Dose (AED) in mSv was estimated using following equation [65]:
AED() mSv =×× D24 365 × 0.7 × 10-6 6.2
where 0.7 is Gy to Sv conversion factor
6.1.1 Environmental radiation doses in northern Rechna Doab
The absorbed dose rates in air (including cosmic ray contribution) in northern parts of the -1 -1 study area have been found to vary from 86.0 nGy h to 139.1 nGy h with a mean value of 109.1 nGy h-1 (see table 6.1). Mean annual external effective dose due to natural exposure of population to the 40 238 232 external terrestrial ionizing radiation ( K and decay products of U and Th) with contribution of cosmic radiation in the annual effective dose, came out to be 0.67 mSv.
90 Chapter-6: Health risks and radiation hazard assessment
Table 6.1: Environmental gamma radiation levels in northern Rechna Doab, Pakistan
Average absorbed dose rate Annual effective dose Location in air (nGy h-1 ) (mSv) Gujranwala 132.6 0.81 Wazirabad 120.8 0.74 Aiman Abad 112.5 0.69 Dhaunkal 106.1 0.65 Ahmad Nagar 114.4 0.70 Head Khanki 93.3 0.57 Rasul Nagar 87.8 0.54 Kalianwala 113.4 0.70 Kot Hara 122.6 0.75 Rasulpur Tarar 105.2 0.65 Gajar Gola 105.2 0.65 Uddowali 96.9 0.59 Killah Didar Singh 123.5 0.76 Noshehrah Virkan 130.8 0.80 Kamoke 86.0 0.53 Sadhuke 89.7 0.55 Manguke 86.9 0.53 Hafizabad 112.5 0.69 Pindi Bhattian 119.8 0.73 Wainkay Tarar 122.6 0.75 Chak Bhatti 102.5 0.63 Jalalpur Nau 96.9 0.59 Sukhayki 93.3 0.57 Kishan Garh 126.3 0.77 Sialkot 129.9 0.80 Sambrial 114.4 0.70 Kulu Wal 94.2 0.58 Head Marala 102.5 0.63 Chaprar 114.4 0.70 Chuvinda 86.9 0.53 Mundeki 139.1 0.85 Daska 103.4 0.63 Dharam Kot 105.2 0.65 Sutra 115.3 0.71 Merajke 101.6 0.62 Norowal 96.1 0.59 Zafarwal 130.8 0.80 Chak Amro 111.6 0.68 Noor Kot 119.9 0.74 Jassar 98.8 0.61 Talwindi Bhindran 105.2 0.65
91 Chapter-6: Health risks and radiation hazard assessment
6.1.2 Environmental radiation doses in mid Rechna Doab
The absorbed dose rates in air (including cosmic ray contribution) in mid Rechna Doab -1 -1 were found to vary from 94.2 nGy h to 129.9 nGy h with a mean value of 113.0 -1 nGy h . Mean annual external effective dose including cosmic radiation, was found to be 0.69 mSv (see table 6.2).
Table 6.2: Environmental gamma radiation levels in mid Rechna Doab, Pakistan
Average absorbed dose rate Annual effective dose Location in air (nGy h-1 ) (mSv) Shaikhupura City 113.4 0.70 Hitcher 112.5 0.69 Narang Mandi 113.4 0.70 Muridke 97.9 0.60 Shahdra 103.4 0.63 Khanpur 119.8 0.73 Damamkay 103.4 0.63 Sharkpur 94.2 0.58 Mangtanwala 115.3 0.71 Buchiki 123.5 0.76 Mananwala 110.7 0.68 Shahkot 122.6 0.75 Jhabran 129.9 0.80 Khankah Dogran 124.4 0.76 Marar 102.5 0.63 Sanglahil 123.5 0.76 Nankana Sahib 123.5 0.76 Syedwala 105.2 0.65 Maoza Sial 97.9 0.60 Chiniot 118.0 0.72 Bukharian 104.3 0.64 Bhawana 112.5 0.69 Jhok Ditta 114.4 0.70 Chak-239, Jranwala 115.3 0.71 Jranwala 123.5 0.76
92 Chapter-6: Health risks and radiation hazard assessment
6.1.3 Environmental radiation doses in southern Rechna Doab
Table 6.3 shows the results of absorbed dose rates in air (including cosmic ray contribution) in southern parts of the study area have been found to vary from 89.7 -1 -1 -1 nGy h to 129.9 nGy h with a mean value of 111.0 nGy h . Mean annual external effective dose with contribution of cosmic radiation, came out to be 0.68 mSv.
Table 6.3: Environmental gamma radiation levels in southern Rechna Doab, Pakistan Average absorbed dose rate in Annual effective dose Location air (nGy h-1 ) (mSv) Jhang City 114.4 0.70 Khewa 115.3 0.71 Mochiwala 103.4 0.63 Bagh 122.6 0.75 Head Trimon 113.4 0.70 Qaim Bhawana 97.0 0.59 Garh Maharaja 105.2 0.65 Basti Islam 120.8 0.74 Darkhana 106.1 0.65 Azadpur 122.6 0.75 Wariam Wala 104.3 0.64 Pir Mahal 115.3 0.71 Chatiana 122.6 0.75 Sandilianwali 104.3 0.64 Wahgi Adda 124.4 0.76 Dwakhri 123.5 0.76 Korian Gojra 89.7 0.55 Kala Pahar 96.1 0.59 Dabanwala 124.4 0.76 Khidarwala 114.4 0.70 Ghatwala 112.5 0.69 Mamon Kanjan 102.5 0.63 Garh 95.1 0.58 Kanjwani 104.3 0.64 Samundri 114.4 0.70 Saloni Jhal 124.4 0.76 Sirshamir Road 97.0 0.59 Dandianwala 113.4 0.70 Tandlianwala 103.4 0.63 Lundian Adda 114.4 0.70 Chak Kundian 104.3 0.64 Khurarianwala 129.0 0.79
93 Chapter-6: Health risks and radiation hazard assessment
6.2 Radiation hazards due to radionuclides present in soil
Radiation hazards related to the radionuclides present in soil are calculated through assessment of radium equivalent activity, air absorbed dose rates, annual effective doses, outdoor and indoor radiation hazard indices.
6.2.1 Radium equivalent activity
The radiation hazards associated with the radionuclides present in the soil were also estimated by calculating the radium equivalent activity (Raeq). The Raeq is a weighted sum of activities of the three natural radionuclides 226Ra, 232Th and 40K which is based on the assumption that 370 Bq kg-1 of 226Ra, 259 Bq kg-1 of 232Th and 4810 Bq kg-1 of 40K produce the same gamma radiation dose rate [206] and is defined as: 370 370 Ra = A++ A A 6.3 eq Ra 259Th 4810 K
226 232 40 where ARa, ATh and AK are the activity concentrations of Ra, Th and K, respectively. Using Equation 6.3, radium equivalent activity was calculated in three parts of the study area.
6.2.1.1 Radium equivalent activity in northern Rechna Doab
Radium equivalent activity (Raeq) in northern Rechna Doab, Pakistan was calculated using equation 6.3. The results obtained in northern parts of the study area are shown in table 6.4. It is clear from table 6.4 that the levels of radium equivalent activity were the minimum in Gujranwala (129.5±6.8 Bq kg-1) whereas these were the maximum in Head Khanki (220.6±7.5 Bq kg-1).
6.2.1.2 Radium equivalent activity in mid Rechna Doab
Radium equivalent activity (Raeq) in mid Rechna Doab, Pakistan was calculated using equation 6.3 and results obtained are shown in table 6.5. It is clear from table 6.5 that the levels of radium equivalent activity were the minimum in Narang Mandi (154.1±9.8 Bq kg-1) whereas the maximum were in Sharkpur (214.6±9.3 Bq kg-1).
94 Chapter-6: Health risks and radiation hazard assessment
6.2.1.3 Radium equivalent activity in southern Rechna Doab
Radium equivalent activity (Raeq) in southern parts of the study area was also calculated using equation 6.3 and results obtained are presented in table 6.6. Table 6.6 shows that the levels of radium equivalent activity were the minimum in Korian Gojra (161.5±8.4 Bq kg-1) whereas the maximum in Khewa (214.6±9.3 Bq kg-1).
6.2.2 Radiation hazard indices
The hazard index (HI) used for assessment of potential hazards associated with both radiological and non radiological hazards. The hazard index represents the summation of ratios or hazard quotients, each quotient being a determined value for a particular pollutant divided by a reference value for that pollutant. The reference value represents an amount that is linked with an acceptable level of risk or dose for the exposure duration of concern. Radiation hazards due to naturally occurring radionuclides 226Ra, 232Th and 40K may be indoor or outdoor depending upon the location of a receptor, indoor (inside a dwelling) or outdoor (outside a dwelling) on the ground. These hazards are defined in terms of indoor and outdoor radiation hazard indices and are denoted by Hin and Hout, respectively. These are computed by using the expressions 6.4 and 6.5 [207];
=++A Ra AATh K 6.4 Hin 185 259 4810
=++A Ra AATh K 6.5 H out 370 259 4810
It may be noted here that indoor hazard index was calculated to determine the radiation hazard threat to respiratory organs due to 222Rn; decay product of 226Ra, and its short-lived decay products. To account for this threat the maximum permissible concentration for radium must be reduced to half of the normal limit [208]. If the value of indoor or outdoor radiation hazard index is found to be less than unity, then there is no potential indoor or outdoor radiation hazard.
95 Chapter-6: Health risks and radiation hazard assessment
6.2.2.1 Radiation hazard indices in northern Rechna Doab
226 The values of Hout and Hin calculated from the measured activity concentrations of Ra, 232Th and 40K in the northern parts of study area as shown in columns 5–6 of table 6.4.
The maximum indoor hazard index (Hin) was found to be 0.76 in the soil of Head Khanki while it was the minimum in Gujranwala having value of 0.44 with an average value of
0.60. The minimum outdoor hazard index (Hout) was found to be 0.35 in Gujranwala and the maximum in Kishan Garh at a value of 0.60 with an average value of 0.48.
6.2.2.2 Radiation hazard indices in mid Rechna Doab
226 The values of Hout and Hin calculated from the measured activity concentrations of Ra, 232Th and 40K in mid areas of Rechna Doab as shown in columns 5–6 of table 6.5. The maximum indoor hazard index (Hin) was found to be 0.72 in the soil of Sharkpur while it was the minimum in Narang Mandi having value of 0.52 with a mean value of 0.65. The minimum outdoor hazard index (Hout) was found to be 0.42 in Narang Mandi and Jaranwala and the maximum in Sharkpur at a value of 0.58 with a mean value of 0.51.
6.2.2.3 Radiation hazard indices in southern Rechna Doab
226 The values of Hout and Hin calculated from the measured activity concentrations of Ra, 232Th and 40K in southern parts of the study area are shown in columns 5–6 of table 6.6.
The maximum indoor hazard index (Hin) was found to be 0.74 in the soil of Bagh while it was the minimum in Korian Gojra having value of 0.55 with a mean value of 0.65. The minimum outdoor hazard index (Hout) was found to be 0.44 in Korian Gojra and the maximum in Khewa at a value of 0.58 with a mean value of 0.52. The mean values of the indoor and the outdoor radiation hazard indices in all parts of the study area, Rechna Doab were found to be less than the critical value of unity. This indicated that the soils of Rechna Doab were free from the radiation hazards. Radiation hazards presented in tables 6.4 to 6.6 indicates that indoor radiation hazard indices were greater than outdoor radiation hazard indices at every sampling site. These variations may be due to 222Rn inside the dwellings.
96 Chapter-6: Health risks and radiation hazard assessment
6.2.3 Gamma dose rate
Gamma dose rates (D) in the outdoor air at 100 cm above the ground level using the conversion factor published in UNSCEAR-1988 [209] were calculated. The following equation 6.6 [210] was used;
-10 -1 D = (6.62ATh+4.27ARa+0.43AK)×10 Gy h 6.6 where ATh, ARa and AK are the average activity concentrations of thorium, radium and potassium, respectively.
6.2.3.1 Gamma dose rate in northern Rechna Doab
The results tabulated for gamma dose rate in northern parts of the study area are presented in table 6.4. The absorbed dose rate ranged from 62.3 nGy h-1 in Gujranwala to 105.4 nGy h-1 in Kishan Garh. The average dose rate calculated from soil measurements for the same area was 85.09 nGy h-1, which was less than the in-situ measurements as shown in figure. 6.2 (a).
6.2.3.2 Gamma dose rate in mid Rechna Doab
The calculated values of gamma dose rate (D) for mid parts of the study area are summarized in table 6.5. The absorbed dose rate ranged from 54.7 nGy h-1 in Jaranwala to 82.3 nGy h-1 in Sharakpur. The average dose rate calculated from soil measurements for the same area was 70.1 nGy h-1, which is less than the in-situ measurements as shown in figure 6.2 (b).
6.2.3.3 Gamma dose rate in southern Rechna Doab
The calculated values of gamma dose rate (D) for southern Rechna Doab, Pakistan are shown in table 6.6. The absorbed dose rate ranged from 59.3 nGy h-1 in Korian Gojra to 77.7 nGy h-1 in Khewa. The average dose rate calculated from soil measurements for the same area was 69.8 nGy h-1, which is less than the in-situ measurements as shown in figure 6.2 (c).
97 Chapter-6: Health risks and radiation hazard assessment
The average dose rate calculated from soil measurements for each part of the study area were less than the in-situ measurements as shown in figures 6.2 (a-c). It was observed that measured absorbed dose rates were 1.2 to 1.3 times higher than the calculated values. This difference was expected as FAG dose rate meter is also responsive to cosmic rays, high energy beta particles and X-rays. Table 6.7 shows the respective mean values, ranges, medians, skewness, kurtosis coefficients and the types of theoretical frequency distribution that best fits in each empirical distribution. Negative skewness coefficients were observed for calculated dose rates in the whole study area, indicating decreasing trend. It meant that radioactivity levels present in the soils of the study area were not posing any radiological threat to the population. These trends have been shown also in figures 6.3 (a-c). Figure 6.4 shows the comparison of calculated dose rates through soil with the same determinations in different countries. Dose rates determined during present study were found to be less than Malaysia [65], Hong Kong [65], Indian Punjab [16], Bangladesh [150] and Turkey [152] and found higher than Northern Jordan [149], Taiwan [151] and Southern Punjab, Pakistan [156] etc. Present study findings were comparable with Punjab, Pakistan [29] and World average [65].
6.2.4 Annual effective dose
To check and calculate how much effective dose due to activity in soils will be received by the general public residing in the area, the annual effective dose was calculated using the formula given in equation 6.2.
The calculated values of annual effective dose (AED) are shown in table 6.4 to 6.6. Annual effective dose in northern parts of the study area lies in the range 0.38-0.65 mSv with a mean of 0.52 mSv. Annual effective dose in mid parts of the study area lies in the range 0.34-0.50 mSv with a mean of 0.43 mSv. Annual effective dose in southern parts of the study area remained in the range 0.36-0.48 mSv with a mean value of 0.43 mSv. All these values were quite low as compared to the value of 1 mSv as reported in ICRP publication no. 103 [211, 212]. When these values were compared with those found through insitu measurements, it was observed that calculated AED values were little smaller than measured values. It was also as expected because dose rate meter was also responsive to cosmic rays and X-rays.
98 Chapter-6: Health risks and radiation hazard assessment
Table 6.4: Calculated values of radium equivalent activity, absorbed dose rate, outdoor hazard index and indoor hazard index in the northern Rechna Doab, Pakistan.
Radium Annual Outdoor Indoor Absorbed dose Location equivalent -1 effective dose hazard index hazard index -1 rate (nGy h ) -1 activity (Bq kg ) (mSv y ) (Hex) (Hin) Gujranwala 129.5±6.9 62.30 0.38 0.35 0.44 Wazirabad 171.8±7.1 82.91 0.51 0.46 0.57 Aiman Abad 138.9±6.5 66.58 0.41 0.38 0.46 Dhaunkal 192.9±6.8 92.61 0.57 0.52 0.66 Ahmad Nagar 158.7±6.6 76.23 0.47 0.43 0.53 Head Khanki 217.7±6.9 103.12 0.63 0.59 0.76 Rasul Nagar 211.0±6.9 100.01 0.61 0.57 0.73 Kalianwala 187.4±6.8 89.13 0.55 0.51 0.66 Kot Hara 179.1±6.8 85.16 0.52 0.48 0.61 Rasulpur Tarar 178.7±7.1 85.82 0.53 0.48 0.60 Gajar Gola 195.7±7.2 94.09 0.58 0.53 0.68 Uddowali 181.3±6.7 86.79 0.53 0.49 0.62 Qillah Didar Singh 177.4±6.7 85.24 0.52 0.48 0.60 Nosherah Virkan 188.4±7.1 90.50 0.55 0.51 0.65 Kamoke 159.5±6.9 76.58 0.47 0.43 0.54 Sadhuke 206.8±6.9 98.80 0.61 0.56 0.71 Manguke 199.9±6.8 96.04 0.59 0.54 0.69 Hafizabad 186.7±6.8 89.58 0.55 0.50 0.64 Pindi Bhattian 194.4±6.8 92.54 0.57 0.53 0.66 Winekay Tarar 185.8±7.2 89.24 0.55 0.50 0.63 Chak Bhatti 192.6±7.1 91.81 0.56 0.52 0.65 Jalal Pur Nau 178.6±6.7 85.65 0.53 0.48 0.60 Sukhay Ki 165.0±6.6 79.17 0.49 0.45 0.57 Kishan Garh 220.6±7.5 105.44 0.65 0.60 0.75 Sialkot 153.9±6.6 74.21 0.46 0.42 0.51 Sambrial 135.7±6.5 64.97 0.40 0.37 0.46 Kulu Wal 194.6±6.8 93.09 0.57 0.53 0.66 Head Marala 170.1±6.7 81.83 0.50 0.46 0.57 Chaprar 162.5±6.6 77.69 0.48 0.44 0.55 Chuvinda 170.6±6.7 82.14 0.50 0.46 0.56 Mundeki 196.6±6.8 94.60 0.58 0.53 0.65 Daska 181.4±6.7 87.02 0.53 0.49 0.61 Dharamkot 190.7±6.8 91.49 0.56 0.51 0.64 Sutra 158.2±6.6 75.30 0.46 0.43 0.54 Merajke 156.9±6.6 75.54 0.46 0.42 0.53 Norowal 173.3±6.7 83.79 0.51 0.47 0.57 Zafarwal 148.6±6.5 71.67 0.44 0.40 0.50 Chak Amro 172.8±6.7 82.46 0.51 0.47 0.58 Noor Kot 166.9±6.7 79.80 0.49 0.45 0.56 Jassar 179.1±6.7 86.71 0.53 0.48 0.59 Talwindi Bhindran 169.0±6.7 81.00 0.50 0.46 0.56
99 Chapter-6: Health risks and radiation hazard assessment
Table 6.5: Calculated values of radium equivalent activity, absorbed dose rate, outdoor radiation hazard index and indoor radiation hazard index in the mid Rechna Doab, Pakistan.
Outdoor Indoor Radium Absorbed Annual radiation radiation Location equivalent dose rate effective dose hazard index hazard index activity (Bq kg-1) (nGy h-1) (mSv y-1) (Hout) (Hin) Shaikhupura City 199.5±8.6 75.2 0.46 0.54 0.67 Hitcher 193.4±8.9 69.6 0.43 0.52 0.66 Narang Mandi 154.1±9.8 57.9 0.35 0.42 0.52 Muridke 169.9±8.6 64.0 0.39 0.46 0.57 Shahdra 189.0±8.5 70.6 0.43 0.51 0.64 Khanpur 193.6±8.6 73.5 0.45 0.52 0.64 Damamkay 203.9±8.8 75.6 0.46 0.55 0.69 Sharkpur 214.6±9.3 82.3 0.50 0.58 0.72 Mangtanwala 171.2±8.7 67.4 0.41 0.46 0.56 Buchiki 208.2±8.6 77.4 0.47 0.56 0.71 Mananwala 183.8±8.6 67.7 0.42 0.50 0.63 Shahkot 198.7±8.5 73.1 0.45 0.54 0.68 Jhabran 199.3±8.8 74.4 0.46 0.54 0.67 Khankah Dogran 186.1±8.6 68.2 0.42 0.50 0.64 Marar 189.9±9.2 69.2 0.42 0.51 0.65 Sanglahil 177.9±8.7 65.3 0.40 0.48 0.60 Nankana Sahib 192.8±8.9 71.6 0.44 0.52 0.65 Syedwala 184.4±8.5 68.8 0.42 0.50 0.62 Maoza Sial 190.8±9.0 69.0 0.42 0.52 0.66 Chiniot 197.8±9.1 71.5 0.44 0.53 0.68 Bukharian 193.2±8.9 69.9 0.43 0.52 0.67 Bhawana 187.5±9.0 67.0 0.41 0.51 0.65 Jhok Ditta 203.1±8.7 72.6 0.45 0.55 0.70 Chak-239, Jaranwala 208.7±8.8 76.7 0.47 0.56 0.71 Jaranwala 155.8±8.7 54.7 0.34 0.42 0.55
100 Chapter-6: Health risks and radiation hazard assessment
Table 6.6: Calculated values of radium equivalent activity, absorbed dose rate, outdoor radiation hazard index and indoor radiation hazard index in the southern Rechna Doab, Pakistan.
Annual Outdoor Indoor Radium Absorbed dose effective dose radiation radiation Location equivalent rate (nGy h-1) (mSv y-1) hazard index hazard index activity (Bq kg-1) (Hout) (Hin) Jhang City 211.3±8.9 75.3 0.46 0.57 0.73 Khewa 214.6±9.3 77.7 0.48 0.58 0.73 Mochiwala 201.7±8.9 71.8 0.44 0.54 0.70 Bagh 212.6±9.2 75.9 0.47 0.57 0.74 Head Trimon 184.0±8.8 66.7 0.41 0.50 0.63 Qaim Bhawana 174.1±8.5 61.7 0.38 0.47 0.60 Garh Maharaja 172.8±8.7 64.4 0.40 0.47 0.58 Basti Islam 187.4±8.5 67.2 0.41 0.51 0.65 Darkhana 195.8±8.5 69.9 0.43 0.53 0.68 Azadpur 181.2±8.6 65.7 0.40 0.49 0.63 Wariam Wala 172.0±8.4 63.9 0.39 0.46 0.58 Pir Mahal 183.9±8.8 67.8 0.42 0.50 0.62 Chatiana 171.9±8.2 63.1 0.39 0.46 0.59 Sandilianwali 203.4±9.1 77.0 0.47 0.55 0.68 Wahgi Adda 185.8±8.5 69.4 0.43 0.50 0.63 Dwakhri 197.4±8.8 72.2 0.44 0.53 0.68 Korian Gojra 161.5±8.4 59.3 0.36 0.44 0.55 Kala Pahar 205.6±8.9 73.2 0.45 0.56 0.71 Dabanwala 202.1±8.9 73.7 0.45 0.55 0.69 Khidarwala 205.2±8.8 74.8 0.46 0.55 0.70 Ghatwala 168.1±8.2 62.8 0.38 0.45 0.57 Mamon Kanjan 183.4±8.8 66.8 0.41 0.50 0.63 Garh 191.9±8.7 69.9 0.43 0.52 0.66 Kanjwani 203.9±8.5 73.6 0.45 0.55 0.70 Samundri 193.2±9.0 72.7 0.45 0.52 0.65 Saloni Jhal 180.6±8.9 65.7 0.40 0.49 0.62 Sirshamir Road 206.9±8.2 76.1 0.47 0.56 0.70 Dandianwala 193.8±9.2 70.5 0.43 0.52 0.67 Tandlianwala 198.2±8.5 72.2 0.44 0.54 0.68 Lundian Adda 171.3±8.8 64.1 0.39 0.46 0.58 Chak Kundian 194.9±8.9 76.8 0.47 0.53 0.64 Khurarianwala 194.1±8.5 70.0 0.43 0.52 0.66
101 Chapter-6: Health risks and radiation hazard assessment
160 Measured dose rate 140 Calculated dose rate
120
100 Measured dose rate
80 Calculated dose rate
60
Dose rate(nGy/h) 40
20
0 4 8 12 16 20 24 28 32 36 40 (a) Sampling location numbers
160 Measured dose rate 140 Calculated dose rate
120 Measured dose rate 100
80 Calculated dose rate 60
40
Dose rateDose (nGy/h) 20
0 3 6 9 12 15 18 21 24 (b) Sampling location numbers
160 Measured dose rate 140 Calculated dose rate
120 Measured dose rate 100
80 Calculated dose rate 60
40
20 Dose rate in air (nGy/h) air rate in Dose 0 4 8 12 16 20 24 28 32 (c) Sampling location numbers
Figure 6.2: Comparison of measured and calculated dose rates in the study areas, (a) northern (b) mid and (c) southern Rechna Doab, Pakistan
102 Chapter-6: Health risks and radiation hazard assessment
7
6
5
4
3 Frequency
2
1
0 60 70 80 90 100 110 (a) Dose rate in air (nGy/h)
7
6
5
4
3 Frequency
2
1
0 50 55 60 65 70 75 80 85 (b) Dose rate in air (nGy/h)
6
5
4
3 Frequency 2
1
0 60 65 70 75 (c) Dose rate in air (nGy/h)
Figure 6.3: Frequency distribution of dose rate in air (nGy h-1) for (a) northern (b) mid and (c) southern parts of Rechna Doab, Pakistan.
103 Chapter-6: Health risks and radiation hazard assessment
Table 6.7: Statistical data for calculated dose rates in surface soil samples from three parts of Rechna Doab, Pakistan.
Calculated dose rate (nGy h-1) Northern Rechna Doab Mid Rechna Doab Southern Rechna Doab Mean 85.1 70.1 69.8 Std. Dev. 9.8 5.9 5.1 Skewness -0.24 -0.68 -0.21 Kurtosis -0.01 1.56 -0.97 Range 62.3 – 105.4 54.7 - 82.3 59.3 – 77.7
12 0 107 100 10 0 93 86.5 )
-1 81 80 70 75 68 65 54 60 51.5 46.1
40 Dose rate (nGy h (nGy rate Dose
20
0
n a y b h g e a s n ia n e rd k j e o s a n n r n d y g ta a n y o u u K iw a t ta d J T P la la a r is is u g g a e k k is t N. n n T v a a k s a n o M a a t i H P P P n d Ba ld , , , e In r b b s o ja ja re e W n n o r u u h P P P a . L S
Figure 6.4: Comparison of average dose rate in air, calculated from soil activity concentrations with different countries of the world.
104 Chapter-6: Health risks and radiation hazard assessment
6.3 Radiation hazards due to radionuclides present in water
To check and calculate how much effective dose would be received by the public residing in the area due to activity in water, the annual effective dose was calculated using the formula described in section 6.2.4 and it came out to be 0.014 mSv. As per ICRP recommendations [211] the public exposure may not exceed more than effective dose of 1 mSv y-1. The dose obtained in our study was significantly below that recommended safe limit.
6.4 Radiation hazards due to radionuclides present in vegetation
Airborne radionuclides are transported downward and settled down in the atmosphere. They gradually settle on soil surfaces as a result of different deposition processes. Vegetation and other plants are contaminated by direct deposition on aerial parts of the vegetation/plants and indirect contamination by root uptake when radionuclides deposited onto the soil are absorbed by vegetation/plants. From the measured activity levels in vegetation as shown in table 4.10, radium equivalent activity (Raeq), out door radiation hazard index (Hout) and absorbed dose rates were calculated in order to assess the radiation hazards associated with the vegetation using the equations 6.3, 6.5, 6.6 and 6.2.
105 Chapter-6: Health risks and radiation hazard assessment
Table 6.8: Calculated values of radium equivalent activity, absorbed dose rate, annual effective dose and outdoor radiation hazard index in the vegetation samples collected from Rechna Doab, Pakistan.
Radium Annual Absorbed dose Outdoor radiation Location equivalent effective dose rate (nGy h-1) hazard index (H ) activity (Bq kg-1) (mSv y-1) out Wazirabad 11.7 6.3 0.04 0.03 Ahmad Nagar 7.2 3.9 0.02 0.02 Kalianwala 9.6 5.2 0.03 0.03 Rasulpur Tarar 14.6 7.9 0.05 0.04 Uddowali 10.1 5.5 0.03 0.03 Qillah Didar Singh 10.8 5.9 0.04 0.03 Sukhay Ki 7.9 4.1 0.03 0.02 Head Marala 4.1 2.3 0.01 0.01 Mundeki 8.1 4.5 0.03 0.02 Daska 15.4 7.9 0.05 0.04 Zafarwal 8.8 4.9 0.03 0.02 Noor Kot 4.5 2.5 0.02 0.01 Talwindi Bhindran 11.1 6.2 0.04 0.03 Shaikhupura City 9.3 5.2 0.03 0.03 Hitcher 7.2 4.0 0.02 0.02 Sharkpur 8.4 4.7 0.03 0.02 Mangtanwala 8.9 4.9 0.03 0.02 Mananwala 7.9 4.4 0.03 0.02 Sayedwala 37.6 19.8 0.12 0.10 Chiniot 28.1 15.4 0.09 0.08 Khewa 38.5 21.2 0.13 0.10 Head Trimon 19.9 10.7 0.07 0.05 Garh Maharaja 17.4 9.7 0.06 0.05 Sandilianwali 35.7 19.6 0.12 0.10 Dwakhri 26.6 13.7 0.08 0.07 Kala Pahar 22.2 12.1 0.07 0.06 Khidarwala 31.7 17.1 0.11 0.09 Ghatwala 8.0 4.5 0.03 0.02 Khurarianwala 7.9 4.4 0.03 0.02
Table 6.8 gives radium equivalent activity, absorbed dose rate, annual effective dose and outdoor radiation hazard index through vegetation collected from the Rechna Doab. Radium equivalent activity was the minimum in Head Marala (4.1 Bq kg−1) and the maximum in Khewa (38.5 Bq kg−1). The mean out door hazard index was 0.04 with the minimum in Head Marala and Noor Kot (0.01) and the maximum in the area of Syedwala, Khewa and Sandilianwali (0.10). As a result the minimum and the maximum values of absorbed dose rates have been observed in Head Marala (2.3 nGy h−1) and Khewa (21.2 nGy h−1), respectively. The annual effective dose rate was also determined
106 Chapter-6: Health risks and radiation hazard assessment with an average value of 0.05 mSv y-1 with the minimum in Head Marala (0.01) and the maximum in Khewa (0.013). Radium equivalent activity was found to be less than 370 Bq kg−1 and out door radiation hazard index was less than acceptable limit of unity.
6.5 Radiation hazards due to radionuclides present in staple food
Transfer of radionuclides through the food chain to human beings can involve several stages depending upon the particular radionuclides and type of the food chain. Activity can be taken up through roots and from absorption via deposition on leaves and stems. Foodstuffs are used to determine the potential radiation doses to humans through their intake of food.
6.5.1 Daily intake of 40K from staple food
Daily 40K radionuclide intake from staple food comprising wheat and rice samples collected from the study area was assessed and presented in table 6.9. The minimum 40K daily intake by the humans of the Rechna Doab, through staple food was 37.2 Bq day-1 at Dawakhri and the maximum was 99.3 Bq day-1 determined at Sandilianwali with an average value of 64.6 Bq day-1. These determined activity levels were compared with data of different countries of the world (see figure 6.5).
107 Chapter-6: Health risks and radiation hazard assessment
140.0 124.8
) 115.9
-1 120.0 107.0 98.1 100.0 94.2 84.1 80.2 80.0 79.9 70.7 64.6 60.0 62.7 59.4 58.5
40.0 42.8
20.0 Dailyintake of 40K (Bq day 18.4 0.0
n ran ue I SR n inland nd a F Spai val US la a P st dy n an a Sudan u p zer a ndi ICR it Turkey Chi J I Paki ppine Sw ietnam li V hi P Present st
Figure 6.5: Comparison of daily activity intake of 40K through staple food with different countries of the world
The levels found in study area were slightly higher than in Philippines and Vietnam [70]. While on the lower side than found in Sudan, Switzerland [213] and in earlier studies in Pakistan [70] etc. The measured activity values were lower than the ICRP value [214] and comparable with India, China [70], Japan and Turkey [213].
6.5.2 Annual internal doses from staple food
The concentration of radionuclides in wheat and rice can be used to determine internal dose to human beings [172, 215]. The annual internal dose by 40K for a Pakistani adult residing in the study area was estimated from the measured radionuclide concentrations. The annual consumption of typical Pakistani staple food based on daily intake of 350 g wheat and 150 g rice [216], and the dose-per-unit intake coefficients published in the IAEA and ICRP reports [217, 218] using following equation:
Dose (μ×× Sv/a) = Concentration (Bq/kg) Annual int ake(kg / a)
Doseconversion factor (μ Sv / Bq) 6.7 where dose conversion factor for 40K = 6.2×10-3 µSv Bq-1
108 Chapter-6: Health risks and radiation hazard assessment
The results are presented in table 6.9. The minimum annual internal dose 84.2 µSv y-1 was received by the general public residing in Dawakhri and the maximum was 224.7 µSv y-1 received by the population at Sandilianwali. The average ingestion dose was 146.3 µSv y-1. The results obtained were compared with results as compiled in other countries (see figure 6.6).
Table 6.9: Daily intake of radioactivity and annual internal dose due to 40K assessed from typical staple food used in Rechna Doab, Pakistan.
Daily intake of 40K Annual internal dose (µSv y-1) -1 40 Sampling location (Bq day ) due to K Wheat Rice Total Wheat Rice Total Wazirabad 70.3 4.3 74.6 159.1 9.7 168.8 Ahmad Nagar 62.8 6.6 69.4 142.1 14.9 157.1 Kalianwala 36.4 4.9 41.4 82.4 11.2 93.6 Rasulpur Tarar 44.7 5.6 50.4 101.2 12.7 113.9 Uddowali 50.2 1.7 51.9 113.7 3.9 117.5 Qillah Didar Singh 58.3 2.9 61.2 131.9 6.6 138.5 Sukhay Ki 84.9 1.7 86.7 192.3 3.9 196.2 Head Marala 80.5 2.9 83.4 182.2 6.5 188.6 Mundeki 80.9 1.9 82.9 183.0 4.5 187.5 Daska 70.2 3.9 74.1 158.8 8.7 167.6 Zafarwal 84.5 4.0 88.5 191.3 9.1 200.3 Noor Kot 60.3 5.5 65.8 136.4 12.5 148.8 Talwindi Bhindran 45.2 5.7 50.9 102.3 12.9 115.2 Shaikhupura City 44.6 2.1 46.7 100.9 4.7 105.6 Hitcher 51.8 9.4 61.1 117.1 21.3 138.4 Sharkpur 47.7 2.1 49.8 108.0 4.7 112.7 Mangtanwala 61.9 2.6 64.5 140.1 5.9 146.0 Mananwala 67.5 4.2 71.7 152.8 9.4 162.3 Sayedwala 48.4 4.0 52.4 109.5 9.1 118.6 Chiniot 32.0 5.5 37.6 72.5 12.6 85.0 Khewa 41.9 3.7 45.6 94.9 8.3 103.2 Head Trimon 77.6 3.3 80.8 175.5 7.4 182.9 Garh Maharaja 93.2 2.6 95.8 210.8 5.9 216.7 Sandilianwali 90.4 8.9 99.3 204.5 20.2 224.7 Dwakhri 33.3 3.9 37.2 75.3 8.9 84.2 Kala Pahar 43.4 7.4 50.8 98.3 16.7 114.9 Khidarwala 49.7 3.4 53.1 112.5 7.6 120.1 Ghatwala 65.1 2.6 67.7 147.2 5.9 153.1 Khurarianwala 75.3 2.5 77.8 170.4 5.6 176.1
109 Chapter-6: Health risks and radiation hazard assessment
300 282 262 242
) 250 222 -1
197 190 182 178 200 179 170 160 146 141 150 128 106 101 86 100 74 74
Annual internal dose (µSv y dose (µSv internal Annual 50
0
d n n e a d n n e A y y a n a a e a a i u d a a g e d n a i e m n i n r a l n t S k i d r a i s la I p a a la d s ra U r tu h p n o n p e v n r u i e u s a I t n in S a e S k C J K e ip F P C z a v T t . i il o R it P a n S V h d d e P In IC w rl s S o re W P
Figure 6.6: Comparison of annual internal dose to adult population of world from intake of 40K
These levels in present study were little higher than those of Indonesia, Philippine, Vietnam India, Japan [219] and S. Korea [66]. While these were lower than for many countries like Finland, Iran, Spain, Canada, Switzerland [213], Sudan [215], USA [220], world average [65], earlier study in Pakistan [221] and ICRP [214] values etc and comparable with China [219] and Turkey [215].
6.6 Cancer risk assessment
Cancer is one of the main causes of mortality throughout the world. There are many cancer causing agents to which human beings may be exposed during their life. These could be during medical treatments, food consumed, tobacco smoking, etc. Solar radiation and ingestion of contaminated foodstuffs may be considered as natural sources of carcinogenesis [222-225]. Different factors causing cancer are listed below in table 6.10 in terms of estimated loss of life [226].
110 Chapter-6: Health risks and radiation hazard assessment
Table 6.10: Estimated loss of life due to different carcinogens Health risks Estimated loss of life Smoking 20 cigs a day 6 years Overweight (15%) 2 years Alcohol consumption (U.S.A.) 1 year All accidents combined 1 year Motor vehicle 207 days Home accidents 74 days Drowning 24 days All natural hazards (Earthquake, lightning, etc.) 7 days Medical radiation 6 days Occupational dose (300 mrem/yr) 15 days Occupational dose (1 rem/yr) 51 days
Ionizing radiation is also considered as one of the cancer causing agent and cancer generation following low chronic doses has been assumed to occur [227, 228] and establishes a potential hazard for workers exposed to ionizing radiation [229]. However, many studies have been made world-wide to see the impact of high doses on the human beings. These studies have shown an increased cancer risk due to that exposure [230]. Population residing in the study area is being exposed due to the natural background radiations. It is estimated by considering a linear dose effect relationship with no threshold as recommended by ICRP [211]. For low doses ICRP fatal cancer risk factor is 0.05 Sv-1 for general public. The measured annual doses in each district of the study area were used to estimate cancer risk for general public using the following equation [231] 6.9:
Fatal cancer risk = Annual effective dose (Sv)×fatal cancer risk factor (Sv·1) 6.8
The average life for general public of the study area, 60 years was used in estimating the cancer risk. Total external dose received to the population through soil and vegetation and internal dose received to the humans through ingestion of staple food was used to estimate the fatal cancer risk in all districts of Rechna Doab, Pakistan (see table 6.11).
111 Chapter-6: Health risks and radiation hazard assessment
Table 6.11: Fatal cancer risks for general public of the study area, Rechna Doab, Pakistan
Districts of Population of Average Average internal Total dose Probable Probable Rechna Doab the district external dose dose (Sv) number of number of fatal (Million) (Sv) (Sv) fatal cancer cancer risks in risks in one million different districts Gujranwala 3.40 5.70E-04 1.32E-04 7.02E-04 119 35 Hafizabad 0.83 5.90E-04 1.96E-04 7.86E-04 33 39 Sialkot 2.72 5.30E-04 1.81E-04 7.11E-04 97 36 Narowal 1.27 5.30E-04 1.55E-04 6.85E-04 43 34 Sheikhupura 2.64 4.60E-04 1.33E-04 5.93E-04 78 30 Nankana Sahib 0.68 5.50E-04 1.19E-04 6.69E-04 23 33 Faisalabad 5.43 4.60E-04 1.65E-04 6.25E-04 170 31 Jhang 2.83 5.20E-04 1.47E-04 6.67E-04 94 33 Toba Tek Singh 1.62 5.30E-04 1.36E-04 6.66E-04 54 33
As shown in table 6.11, fatal cancer risk to the humans in Sheikhupura was the minimum 78 in 2.64 million people while it was the maximum in Hafizabad as 33 out of 0.83 million. When the same figures were seen out of one million populations, these risks came out to be 30 and 39 in Sheikhupura and Hafizabad districts respectively. The fatal cancer risks determined were comparable with in the study area. Health risks to the general public of the Rechna Doab, Pakistan due to external and internal radiation doses was much smaller than the risks associated with other activities of normal daily life as tabulated in table 6.10. So it is concluded that annual radiation doses received to the population of the study area would not pose any significant radiological impact on health and fatal cancer risk to the population.
112 Chapter-6: Health risks and radiation hazard assessment
6.7 Conclusion
The environmental doses in the study area were primarily due to primordial radionuclides and cosmic radiations since no enhanced radiation levels were found any where. The measured values in air, soil, water, vegetation and staple food were comparable with other global radioactivity determinations. The estimated annual effective dose to the public was less than the recommended safe limit of 1 mSv by the ICRP. The calculated annual dose due to intake of potassium through the staple food is a small fraction of the reported world annual ingestion dose. The estimated fatal cancer risk to the general public shows that the annual radiation doses received by them would not be alarming. On the basis of results obtained it is concluded that the environment of the study area (Rechna Doab) does not pose any radiological health hazard to the human beings.
113 Chapter 7
CONCLUSIONS AND RECOMMENDATIONS
To develop a base line of natural background radioactivity levels and radiation dose data for general public residing in various parts of the Rechna Doab, Pakistan, a detailed radiation study was carried out. Radiometric analysis of the collected samples of different environmental media e.g. soil, vegetation, water and staple food was performed using a PC based high resolution gamma spectrometry system and liquid scintillation analyzer.
7 . 1 C o n c l u s i o n s
¾ Radioactivity levels of 226Ra, 232Th, 40K, 137Cs and 90Sr were measured in the soils of three parts of the Rechna Doab collected during the present study. The mean activity of 226Ra measured in the soil was 48.2±1.5 Bq kg-1 and the mean concentration levels of 232Th in the study area were 61.4±3.1 Bq kg-1. These values were very close to the measured World average. The mean activity levels of 40K were 648.9±32.5 Bq kg-1. The average value of 40K was found more than the World average. ¾ The radioactivity levels of 40K were observed higher than 232Th and 226Ra at all the places of the study area. These enhanced levels of 40K may be attributed to the use of potash fertilizers in the study area. ¾ The concentration levels of 137Cs in soil samples were found at most of the places with an average value of 3.5±0.3 Bq kg-1 which may be connected to the atomic Chapter-7: Conclusions and recommendations
tests and the Chernobyl nuclear accident. No abnormal activity levels (hot spots) were found in the study area. ¾ The activity of 226Ra in surface water samples collected from all over the study area, having an average value of 0.9±0.2 Bq l-1 which was higher than that of many countries. The radioactivity levels of 137Cs and 232Th were found below the Minimum Detectable Activity (MDA) in all surface water samples. An average activity of 2.5±1.6 Bq l-1 of 40K in surface water samples was found. The radioactivity levels of 40K were seemed to be higher than that of 226Ra at all the places of study area. The increased values of 40K were may be due to the use of potash fertilizers and it may have leached out into the surface water adjacent to the cultivated fields. ¾ Vegetation samples collected from the study area have mean activity levels of 2.7±0.4 Bq kg−1, 2.2±0.1 Bq kg−1 and 172.7±4.0 Bq kg−1 for 226Ra, 232Th and 40K respectively. No activity of 137Cs was found in any vegetation sample collected from the study area. Determined values for 226Ra and 40K during the present study were on higher side than those reported for World average. ¾ The average values of transfer coefficients in the vegetation samples collected from the Rechna Doab were 0.06, 0.04 and 0.26 for 226Ra, 232Th and 40K respectively. The transfer coefficient of 40K was also more eminent than other natural radioisotopes. ¾ The average activity concentration of 40K (the only detected radionuclide) in staple food was found to be 174.3±2.7 Bq kg-1 (wheat) and 27.6±1.4 Bq kg-1 (rice). The concentration of 40K normally comes out to be on higher side, possibly due to the high transfer coefficient of 40K from the soils. ¾ Daily intake of 40K through staple food by the people residing in the study area has an average value of 64.6 Bq day-1. These levels were with in the safe limits as recommended by the ICRP. ¾ The radioactivity levels of artificial radionuclide 90Sr were detected in the soil and vegetation samples of the study area while it was not found in the water samples. Strontium-90 activity levels in the soil and vegetation samples were on the lower side as compared to some European countries, USA and Ukraine. The inhomogeneous geological distribution of 90Sr may be due to several factors
115 Chapter-7: Conclusions and recommendations
including surface run-off as well as its transport and vertical migration. It is expected that the population residing in the study area, the Rechna Doab, Pakistan is not being exposed to 90Sr.
¾ The average radium equivalent activity (Raeq) in northern, mid and southern parts of the study area was 177.6±6.8 Bq kg-1, 189.9±8.8 Bq kg-1 and 190.8±8.7 Bq kg-1 respectively. These findings were less than the recommended safe value of 370 Bq kg-1, so the radiation hazards associated with the radionuclides present in the soil for dwellers were with in limits. ¾ The average absorbed dose rates delivered externally to the general public residing in the northern, mid and southern parts of the study area were 85.1 nGy h-1, 70.1 nGy h-1 and 69.8 nGy h-1 respectively. The in-situ average gamma dose rates at 100 cm above the ground level for the same area were 109.05 nGy h-1, 113.2 nGy h-1 and 111.0 nGy h-1 for north, mid and the southern parts respectively, which were 1.2 to 1.3 times higher than the calculated values. The higher values were may be due to the response of the gamma dose meter to cosmic rays, high energy beta particles and X-rays. ¾ The Radiation hazard indices and the annual effective doses were also calculated from the measured activity concentrations of 226Ra, 232Th and 40K in the study
area. The indoor radiation hazard index (Hin) in northern, mid and southern parts had mean values of 0.60, 0.65 and 0.55 respectively. The mean values of the
outdoor radiation hazard index (Hout) for northern, mid and southern parts had 0.48, 0.51 and 0.52 respectively. The annual effective doses for the northern, mid and southern parts had mean values of 0.30, 0.43 and 0.43 mSv respectively. All these values were found to be comparable with global values. The mean values of the indoor and the outdoor radiation hazard indices were less than the critical value of unity. This indicates that the soil of Rechna Doab, Pakistan is free from the radiation hazards. The estimated annual effective dose to the public is less than the recommended safe limit of 1 mSv by the ICRP. ¾ In the Rechna Doab, annual internal dose due to ingestion of 40K through staple food having an average value of 146 μSv y-1. The results obtained were seemed to be comparable with other countries of the world.
116 Chapter-7: Conclusions and recommendations
¾ Health risks to the general public of the study area due to external and internal radiation doses was much smaller than the risks associated with other activities of normal daily life. It is, therefore concluded that annual radiation doses received to the population of the study area would not pose any significant radiological impact on health and fatal cancer risk to the population. ¾ This radiation survey gives a flavour that the radiation levels are satisfactorily low not only for the dwellers but also for any future construction of nuclear power plants near rivers of the study area.
7 . 2 R e c o m m e n d a t i o n s f o r f u t u r e s t u d i e s
This is the first systematic study to establish a baseline data of primordial and anthropogenic radionuclides in the Rechna Doab, Pakistan. In order to make the study more comprehensive, the following guiding principles should be considered for the future studies;
The grid size to collect environmental media should be reduced to obtain the background radiation levels which are relatively more representative of the area.
The study should be expanded to cover all the food items, including maize, fruits vegetables, beans, grams, etc.
Animal based edible products received from animals found in the area, such as milk, mutton, beef, eggs and chicken should be monitored.
The presence of fission products 90Sr and 137Cs in some soil and vegetation samples of the study area demands further investigations.
A study can be made to know the levels of NORMS in soils which are being used largely through phosphate fertilizers and industries dumping their effluents in the soil.
117 REFERENCES
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