ASSESSMENT OF RADIATION EXPOSURE LEVELS ASSOCIATED WITH GOLD MINING IN SAKWA WAGUSU, BONDO DISTRICT, KENYA

Abstract

The concentrations and distribution of natural radionuclides in soils from Sakwa Wagusu area, Kenya were investigatedwith an aim of evaluating the environmental radioactivity and radiological health hazard. Thirty nine rock and soilsamples were collected from ten sites of Sakwa Wagusu area, Bondo district to measure their natural radioactivityconcentrations due to 226Ra, 232Th and 40K radionuclides. Measurements were done by use of gamma spectrometrymethod with a high purity germanium (HPGe) detector. To evaluate the radiological hazard of the natural radioactivity,the radium equivalent activity, the external hazard index, internal hazard index, the absorbed dose rate and the effectivedose rate were calculated and compared with internationally approved values. The calculated radio activities for 226Raranged from 7.2 – 113.8 Bqkg-1 (mean: 44.2Bqkg-1), for 232Th, 4.6 – 100.7 Bqkg-1(mean: 40.3Bqkg-1) and 119.3 –1611.8Bqkg-1 (mean: 639.6Bqkg-1) for 40K. The mean absorbed dose rate for the ten pits/mines, measured at 1m belowthe surface was 141.6nGyh-1 while the mean calculated total absorbed dose rates was 69.8nGyh-1. The natural activityvalues were more than the accepted world average values; hence this area should be considered High BackgroundRadiation Area (HBRA). The radium equivalent activity values of all samples were lower than the limit of 370Bqkg-1. Thecalculated mean outdoor effective dose rate was 0.17mSvy-1 and which is less than 1mSvy-1 upper limit recommendedfor the public by ICRP. An excess cancer risk of 0.02% was achieved with an assumption of 30% occupancy factor, themean annual effective dose rate of 0.17mSvy-1. It is recommended that proper ventilation be put in the buildings in thisarea.