Evaluation of the Level of Norms and Associated Radiological Hazards & Risks from Mining Activities of Kenticha Tantalum Mines in Ethiopia

Abstract

In this study radiological hazards to members of the public and workers from exposure to natural radioactivity as a result of mining activities from Kenticha Tantalum Mines in Ethiopia, have been studied through several exposure pathways using direct gamma spectrometry to determine 238U, 232Th, 40K, 226Ra and 222Rn in tantalum ore, soil, waste, waste tailing and water samples. Additionally, cancer risk assessment associated with NORM was estimated. The average activity concentrations of 238U, 232Th, 40K, 226Ra and 222Rn in tantalum ore were 78.653±1.431 Bq/kg, 24.945±0.492 Bq/kg, 603.170±55.013 Bq/kg, 69.478±31.0 Bq/kg and 112.554±50.249 kBq/m3, respectively. In soil the activity concentrations were 69.354±1.081 Bq/kg, 15.479±0.231 Bq/kg, 718.880±65.531 Bq/kg, 68.923±1.7 Bq/kg and 111.655±2.681 kBq/m3, respectively and in solid waste samples 110.496±1.907 Bq/kg, 15.009±0.274 Bq/kg, 607.269±55.375 Bq/kg, 98.300±38.6 Bq/kg and 159.246±62.607 kBq/m3 respectively. The values were generally above the worldwide average activity concentrations in all samples, except thorium-232. This might be due to the high contents of 238U decay families and 40K in the granite – pegmatite rocks of Kenticha area. The corresponding average external dose rate at 1m above the ground in air for tantalum ore, soil and solid waste samples were 76.407 nGy/h, 71.337 nGy/h, 85.408 nGy/h, respectively which were above worldwide average value of 60 nGy/h. The annual equivalent doses were also estimated as 0.021±0.003 mSv, 0.020±0.001 mSv and 0.023±0.004 mSv for ore, soil and solid waste samples, respectively and were found to be lower than the worldwide average of 2.42 mSv/y. Likewise, the radon emanation coefficient which is the fraction of radon generated within the grains of materials and escaped to the pore space, varied from 82±2% to 85±2% for ores, from 82±2% to 84±2% for soil, and from 53±15% to 83±15%for solid waste samples. Also, the radon exhalation rate varied in the range of 41.7±25.7 to 87.3±25.7 mBq/m2.s for ores, from 56.2±1.4 to 58.1±1.4 mBq/m2s for soil and from 53.3±32.1 to 120.2±32.1 mBq/m2s for solid waste, respectively. The radium equivalent activity, external hazard index, internal hazard index and representative gamma index, for all samples were estimated and generally found to be within recommended international values. Annual effective dose was evaluated from only external gamma dose rate. However, the relatively high values in all the other parameters measured implies that the Kenticha tantalum mine and its environments shown the significance of naturally occurring radioactive material. Therefore, the results from this study will ignite in decisionmaking for future set-up of further research for the management of NORM wastes in Kenticha tantalum mine and for the emerging mining industry in Ethiopia.