Abstract:
Radiation is energy travelling through space. Exposure to radiation is a hazard to human health and in some situations it is known to be carcinogenic. In Kenya there is scanty information on radiation levels at various workplaces. The objective of the study was to analyse the radiation levels within Nairobi Central Business District (CBD) and the industrial areas. This was based on the fact that the study area has a huge population and the mining, quarrying and constructions taking place around this area can result to enhanced human exposure to radiation. Environmental radiation monitor model Horiba PA- 1100 was used to measure the air absorbed dose rates 1m above the ground. Soil samples were collected across the study area and were analysed qualitatively and quantitatively using gamma spectrometry to determine and quantify the activity of the radionuclides in the environment. Using energies of the spectral lines obtained from the gamma spectrometry, the radionuclides were identified and their respective activity concentrations were calculated from their respective intensities. The mean activity concentrations values for soil in 232Th, 226Ra and 40K were 117.14, 75.91 and 928.55 Bqkg-1 respectively as compared to 30, 35 and 400 Bqkg-1 which are the accepted values for 232Th, 226Ra and 40K respectively as reported (UNSCEAR 2008). The average for air absorbed dose rate was 1064.92 nGyh-1. Average calculated absorbed dose rate 263.05 nGyh-1 was 6 times higher than the world acceptable effective radiation dose 43 nGyh-1 according to UNSCEAR, 2000. The averages for both the external and internal hazard indices were 0.88 and 1.09 respectively. The external and internal hazard indices for the areas around Mwiki dumpsite and Tetrapak industries exceeded 1 which is the world acceptable value. This means that the residents of these areas are at high risks of both internal and external radiation exposure. The mean annual effective dose 0.96 mSvy-1 is less than the acceptable limit 1mSv/y for members of public though residents of Mwiki and Tetrapak areas are experiencing higher values of 1.33 and 1.89 mSvy-1. The study concludes that of the various sampled site, residents of Mwiki and people working around Tetrapak Industries are exposed to huge doses of radiation and could be at higher risks of radiation related health problems.
