Excess Lifetime Cancer Risk from Measured Background Ionizing Radiation Levels in Active Coal Mines Sites and Environs

Abstract

A study of the terrestrial Background Ionizing Radiation (BIR) levels of Bunker and Okpara mining site environment in Enugu state has been carried out to estimate the excess lifetime cancer risk. A radiation monitoring meter (digilert 100) and a geographical positioning system (GPS) for GIS mapping were used. The monitoring of the BIR levels was carried out in one calendar year after delineating the environment of the two mining sites into four monitoring locations each. Average BIR levels measured ranged from 0.009 mRh⁻¹ (0.76 mSvy⁻¹) in Enugu new market (Bunker) mine site to 0.039 mRh⁻¹ (2.52 mSvy⁻¹) in Okpara mine site with overall mean value of 0.017 ± 0.007 mRh⁻¹ (1.39 ± 0.60 mSvy⁻¹). The computed average outdoor absorbed dose rate for the study area ranged from 113.10 ± 34.80 ηGyh⁻¹ in Bunker mining area to 217.50 ± 78.30 ηGyh⁻¹ in Okpara mining area, with a mean value of 143.55 ± 52.20 ηGyh⁻¹. The mean annual effective dose equivalent (AEDE) calculated for the study coal mining sites was 0.18 ± 0.07 mSvy⁻¹, while the mean excess lifetime cancer risk (ELCR) was (0.61 ± 0.14) ×10⁻³ mSvy⁻¹. The dose received by organs was highest in the testes (0.12 mSvy⁻¹), while the liver had the lowest dose values of 0.06 mSvy⁻¹. The study revealed that of the 8 sampling locations and 3840 exposure measurements made, 74.1 % exceeded the world ambient standard levels of 0.013 mRh⁻¹ (1.0 mSvy⁻¹) recommended by UNSCEAR, and the recorded values were higher compared to values reviewed in literature. But the reported results may not constitute any immediate health risk to the residents and coal miners in the study area. The calculated Excess Lifetime Cancer Risk values indicates that the chance of developing cancer by residents and workers in the mine sites of the study area is low and the effective dose for adult organs investigated is insignificant to cause any health related sicknesses or damage to the investigated organs from the present exposure rate.