ASSESSMENT OF RADIOLOGICAL HAZARDS AROUND RIRIWAI TIN MINES, KANO STATE, NORTH WESTERN NIGERIA
ASSESSMENT OF RADIOLOGICAL HAZARDS AROUND RIRIWAI TIN MINES, KANO STATE, NORTH WESTERN NIGERIA
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Date
2017-06
Authors
ABDULLAHI, MUHAMMAD ATTAHIRU
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Abstract
Mining industry in Nigeria provides economic benefits of wealth creation and employment opportunities. Presently there are numbers of artisanal and large scale mining activities going on across Nigeria and most of these artisanal miners currently under take only surface mining and the process produced large volumes of tailings and waste that may containnaturally occurring radioactive materials (NORMs). Some of the NORMs are soluble in water and have the tendency to leach into water bodies and farm lands. This study assessed the radiation exposure to the public from NORMs around Ririwai Tin mine in Kano state Nigeria. A total of one hundred and four (104) environmental samples comprising of 28 soil, 15 cereals, 11 vegetables, 10 dust and 40 water samples were collected. The samples were analysed using Direct Gamma Spectroscopy (NaI (Tl)), Instrumental Neutron Activation Analysis (INAA) and Liquid Scintillation Analysis (LSA). The exposure pathways considered were external irradiation due to activity concentration of 40K, 226Ra and 232Th in soil and dust, ingestion of food (cereals and vegetables) containing 40K, 226Ra and 232Th and ingestion of 222Rn in domestic water. The results show that the mean activity concentrations of 40K, 226Ra and 232Th in soil samples were 296.87±8.25Bq/kg 49.66±6.56Bq/kg and 257.24±6.53Bq/kg respectively. For the cereals samples the mean activity concentrations of 40K, 226Ra and 232Th were 59.99±2.76, 25.95±2.55 and 46.81±1.99Bq/kg respectively. The mean activity concentration in vegetable samples were 261.84±4.93, 28.65±4.92 and 56.3±1.66Bq/kg respectively for 40K, 226Ra and 232Th, in dust the activity concentration were 385.90±5.70, 54.31±2.51 and 146.64±0.91Bq/kg for 40K, 226Ra and 232Th respectively. The results in this study are higher when compared withthe worldwide average concentrations of 420Bq/kg, 33Bq/kg and 45Bq/kg for 40K,226Ra and 232Th respectively. The high values obtained in cereals and vegetables could be attributed to the fact that they are also used as phytoremediators of uranium contaminated soil due to their high bioaccumulation of 222Ra and 232Th. The mean absorbed dose for the soils cereals, vegetables and dust sample were 170.04±4.61, 32.562±1.450, 4632±1.43 and 119.85±9.700nGyh-1 respectively. The absorbed dose rate obtained in this study are also higher than the worldwide average values of 60nGy/h (UNSCEAR). The total annual effective dose calculated in this study was 4.23mSv/year with the highest contribution of 60.20% (2.540mSv/year) coming from cereals, 31.20% (1.320mSv/year) from vegetable, soil contributed 4.93% (0.209mSv/year), dust 3.47% (0.147mSv/year) and the least is 0.04% (0.0163mSv/year) 222Rn in water. The total annual effective dose is higher than 1mSv/year dose limit recommended by ICRP.The mean 222Rn concentration in soil samples was 78.799±10.197kBq/kg while the mean 222Rn Emanation fraction was 1.22±0.013.The average value of the emanation fraction obtained in soil in this study is more than the typical range of 0.05 to 0.7.Similarly, 222Rn concentration in three (3) water sources in the study area were determined but high consideration was given to the domestic water sources which has a mean 222Rn concentration of 2.23±0.11Bq/L. The result obtained in this study is below the 222Rn concentration of 10Bq/L recommended by WHO, UNSCEAR and the maximum permissible value of 11.1Bq/L by USEPA and adopted by Standard Organization of Nigeria (S.O.N). The result of hazard indices shows that the mean Raeq values in these samples were 436.92±16.950 and 266.98Bq/kg respectively for soil and dusts, only soils samples has Raeq value above 370Bq/kg recommended maximum value while the dust samples are below the maximum recommended value. Similarly the values of external and internal hazard indices for dust are below unity (1) which is the recommended maximum value, soil samples that has mean values of 1.192±0.051 and 1.326±0.062 for external and internal hazard indices respectively are higher than the recommended values. The total fatality cancer risk from all the exposure pathways considered was 2.33 x 10-4 ranging from 9.0 x 10-7 to 1.34x 10-4 the total lifetime fatality cancer risk was 1.63 x 10-2 in a
range of 6.30 x 10-5 – 9.38±10-3the total severe hereditary effect was 8.44 x 10-6 ranging from 3.20 x 10-8 – 5.10 x 10-6 while the total lifetime severe hereditary effect was 5.92 x 10-4 in a range of 2.24 x 10-6 – 3.57 x 10-4. The negligible cancer fatality risk value recommended by USEPA is in the range of1 x 10-6 to 1 x 10-4. The total risks estimated in this study were above the acceptable limit by the UNSCEAR, however, public in the study area may not necessarily be exposed to all the exposure pathways considered in this study at the same time.On the basis of the results from this study, water for consumption do not pose any significant radiation hazards to the population. However consumption of food (cereals and vegetables) grown around the study area could pose radiological hazard due to the bioaccumulation of 226Ra and 232Th in them.
Description
A Dissertation submitted to the School of Postgraduate Studies, Ahmadu Bello University, Zaria in partial fulfillment of the requirements for the Award of Doctor of philosophy in Nuclear Physics, Department of Physics, Faculty of Physical Sciences Ahmadu Bello University, Zaria Nigeria
Keywords
ASSESSMENT,, RADIOLOGICAL HAZARDS,, RIRIWAI TIN MINES,, KANO STATE,, NORTH WESTERN,, NIGERIA