Evaluation of Outdoor Ambient Radiation Hazard Indices in Selected Mining Sites in Kogi State, Nigeria

Abstract

The evaluation of outdoor ambient radiation hazard indices of solid minerals in selected mining sites of Kogi State, Nigeria was carried out using radalert 100 and digilert 200 nuclear radiation monitors and a geographical positioning system (Garmin GPSMAP 76S). The sites studied include Ike Kabba (Gold), Ayedayo and Ayedera (Feldspar-Mica), Obajana (limestone), Itakpe (iron ore) and Okobo (coal). The mean background radiation exposure rates ranges from 0.023±0.004 at Ike Kabba to 0.024±0.007 mRhr-1 at Apala River while 0.024±0.006 mRhr-1 was recorded at Ayedayo and 0.029±0.008 mRhr-1 for Ayedera. Mean background radiation value of 0.018±0.006 mRhr-1, 0.021±0.009 mRhr-1 and 0.026±0.007 mRhr-1  was recorded at Obajana (limestone), Itakpe (iron ore) and Okobo (coal) mine field respectively. The obtained values are higher than world standard limit of 0.013 mRhr-1 recommended by ICRP. The mean absorbed dose rates calculated for the various mining sites are 204.2 and 211.1 nGyh-1 (gold), 206.8 and 251.9 nGyh-1 (feldspar-mica), 159.7 nGyh-1 (limestone), 181.6 nGyh-1 (iron ore), 229. nGyh-1 1 (coal). These values were observed to be higher than world permissible value of 89 nGyh-1. The annual effective dose equivalent (AEDE) for outdoor exposures values are 0.31 and 0.32 mSvy-1 for Ike Kabba gold mine and Apala River respectively. 0.32 and 0.39 mSvy-1 for Ayedayo and Ayedera feldspar-mica mine while 0.25 mSvy-1, 0.29 mSvy-1 and 0.35 mSvy-1 are for limestone, iron ore and coal mines respectively. The values were observed to be within safe values while the excess lifetime cancer risk estimated for the mine sites are 1.10 and 1.13×10-3 for gold mine and Apala River respectively, 1.11 and 1.35×10-3 for Ayedayo and Ayedera respectively. 0.86×10-3, 0.97×10-3 and 1.23×10-3 for Obajana, Itakpe and Okobo communities respectively. The recorded values are higher than the world permissible value of 0.29×10-3. The study shows that there is the probability of residents developing radiation-related illness overtime.