STUDY OF THE RADIOLOGICAL IMPACT OF SMALL-SCALE MINING ACTIVITIES AT DUNKWA-ON-OFFIN IN THE CENTRAL REGION, GHANA

ABSTRACT

Small-scale (and artisanal) mining has been defined differently around the world. However, in Ghana, small-scale (gold) mining is defined as ―mining (gold) by any method not involving substantial expenditure by an individual or group of persons not exceeding nine in number or by a co-operative society made up of ten or more persons‖. The activities in the mining sector have increased in recent times and as at 2008, a total of 212 mining companies were awarded mining leases and exploration rights. These mining operations consequently turn out large volumes of solid and liquid wastes in the form of waste dams; slime dams, tailings dams, which could contain elevated levels of NORM. Small-scale mining activities pollute rivers and streams nearby that serve as sources of drinking water for communities downstream. These activities are common in the study area. The general aim of the studies is to assess the radiological exposure to members of the general public living in Dunkwa community and its surrounding communities due to NORMS as a result of the small-scale mining activities. Direct gamma spectrometry and iMatic P-F Gas-less Automatic Gross Alpha/Beta counter was used to determine the concentration of naturally occurring radionuclides 226Ra, 232Th and 40K, and gross alpha and gross beta activity concentration respectively in the soil and water samples. The mean values of the gross-α and gross-β activity concentrations in the water sources were 0.002±0.001 Bq/L and 0.029±0.016 Bq/L respectively which are also below the WHO recommended guideline values for drinking water. The gross-α and gross-β activity concentrations of most soil samples in the study area are below the activity concentration of the control sample. The mean activity concentrations measured for 226Ra (238U), 232Th and 40K in the soil samples were 25.4±11.1, 29.4±15.6 and 225.9±93.8 Bq/kg respectively. For the water samples the mean activity concentrations were 4.7±1.5, 2.7±0.4, 53.9±11.6 Bq/L for 226Ra (238U), 232Th and 40K respectively. The total annual effective dose to the public was estimated to be 0.95 mSv. The results obtained in the study area are within the recommended world average values with the exception of mean activity concentration 232Th and committed annual effective dose of the water samples. The results thus indicate an insignificant exposure of the general public. The radiological hazard assessment as a result of 226Ra (238U), 232Th and 40K were also established. The radium equivalent activity (Raeq), External hazard index (Hex) and Internal hazard index (Hin) varied in the range 32.8-173.4 Bq/kg, 0.1-0.4 and 0.1-0.6 with mean values of 87.0±38.9 Bq/kg, 0.2±0.1 and 0.3±0.1 respectively. The values of the Raeq, Hex and Hin are below the acceptable values. Hence soils from the study area that could be used for building purposes might not pose any significant radiological hazard.