PUBLIC EXPOSURE TO HAZARDS ASSOCIATED WITH NATURALLY OCCURRING RADIOACTIVE MATERIALS IN MINING: DOSE ASSESSMENT AND CANCER RISK ESTIMATION

ABSTRACT

Human beings are always exposed to background radiation that comes both from natural and man-made sources. Natural radioactivity is widespread in the earth environment and it exists in various geological formations such as earth’s crust, rocks, soils, plants, water and air. Mining has been identified as one of the potential sources of exposure to naturally occurring radioactive materials (NORM). However, mining activities are not being monitored and regulated for NORM in Ghana. Most of the NORM industries such as mining and mineral processing are located in developing countries such as Ghana. Adamus Goldmine is one of the gold mining companies in Ghana and has been in operation since 2007 with no data on radioactivity levels. The mine currently undertakes only surface mining and the process produces large volumes of tailings and waste that may contain NORM. Some of the NORM are soluble in water and can leach into water bodies and farm lands. Mining activities lead to pre-concentration and accumulation of NORM in stockpiles, waste piles (tailings), water bodies and finally leading to exposure of humans through the food chain, as a result it is important to investigate and provide scientific data for the assessment of exposure of the general public. The objective of this study was to evaluate the contents of radionuclides 238U, 232Th and 40K and outdoor terrestrial gamma dose rates in the Adamus Gold mine. To assess the radiological hazard of soils, the radiological hazard indices such as absorbed dose rate, annual effective dose equivalent (outdoor), hazard indices (Hex and Hin), activity utilization index (Iɣ) and estimated excess life time cancer risk (ELCR) are calculated. Gamma spectrometry technique was used to analyse for Uranium, Thorium and K-40 in soil, water and food crop samples from the mining environment. A total of one hundred and twelve (112) samples from thirty-one (31) sites were analysed. The absorbed dose rates, the corresponding annual effective dose and radiological hazard due to 226Ra, 232Th and 40K in the soil materials that might possibly be used as building materials were carried out. The mean ambient gamma dose rate from direct measurement and calculation were 55.90 nGy h-1 and 46.75 nGy h-1, respectively. The mean activity concentrations measured for 238U, 232Th and 40K in the soil samples were 8.09 Bq kg-1, 45.16 Bq kg-1 and 397.77 Bq kg-1, respectively. The mean activity concentrations measured for 238U, 232Th and 40K in the mine tailings were 7.41 Bq kg-1, 33.35 Bq kg-1 and 370.97 Bq kg-1, respectively. For the water samples (ground and surface), the mean activity concentrations were 0.15 Bq l-1, 0.75 Bq l-1 and 0.71 Bq l-1 for 238U, 232Th and 40K, respectively. For the mine processed water samples, the mean activity concentrations were 0.17 Bq l-1, 1.45 Bq l-1 and 0.86 Bq l-1 for 238U, 232Th and 40K, respectively. The mean activity concentrations of 226Ra, 228Th and 40K in the food crop samples were 5.90 Bq kg-1, 12.20 Bq kg-1 and 279.58 Bq kg-1, respectively. The food crop samples have higher estimated lifetime fatality cancer risk (ELCR) value. These values are comparable to concentrations reported for other countries. The total annual effective dose to the public was estimated to be 0.46 mSv. The results in this study compared well with typical world average values. The results indicate an insignificant exposure of the public to technologically enhanced NORMS from the activities of the Goldmine. The radiological hazard indices obtained in this study for the materials considered for use as construction materials for dwellings by the inhabitants are below the internationally recommended values. The results also show that the background radiation levels are within the natural limits and compared well with similar studies for other countries.