Determination of background ionizing radiation in quarries and premises around Nairobi County
Ogola, Phillip Einstein Otieno
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More recently, exposure to background ionizing radiations by the public is increasingly becoming a concern especially their contribution to the rising cancer incidences in Kenya. Such background ionizing radiations occur naturally from the sun, in rocks and soil and can cause changes in human cell including genetic mutation thus leading to cancer. Unfortunately, majority of the buildings in Kenya are usually constructed using stones and sand mined from underground rocks and river beds yet Kenya is not adequately radio-profiled to determine the levels of embedded radio-nuclides capable of emitting ionizing radiations. Conventionally, the World Health Organization (WHO) recommends that the annual exposure to the ionizing radiation to the general public should not exceed 1 mSv. This project therefore, sought to determine the levels of indoor background radiation in selected human premises and quarries around Nairobi County. Calibrated Radiation Alert'' (Digilert 200) hand held radiation detectors were used to capture the reading. The meters were held at the abdominal level (about I m above ground level) and readings were recorded in mRlh for all quarry sites and premises. Numerical data was subjected to analysis of variance using Minitab version 17.0 to determine the statistical differences of exposure levels within various areas. A total of 38 quarries were designated Q 01 to Q 38 and 400 premises were sampled. The results showed that in Ndarugo area, Q09 had the highest annual dose threshold of 1.32 mSv while Q07 had the lowest annual dose threshold of 0.91 mSv. For quarries in other parts of Nairobi County, Q23 had the highest annual dose threshold of 1.68 mSv while Q34 had the lowest annual dose threshold of 1.06 mSv. Of the 38 quarries sampled in this study, only 5 quarries had annual exposure levels below the recommended WHO standard representing a dismal 13% compliance. There were significant differences in annual dose levels between the quarries sampled in the study (p:S0.05 was statistically significant). The annual indoor readings were highest in Eastleigh (4.070 mSv) and relatively lowest in Nairobi Central Business District (CBD) at 2.763 mSv, representing a deviation from WHO recommended standard of 307.0% and 176.3%, respectively. None of the premises sampled had exposure levels below the WHO recommended standard of 1 mSv. Overall, these results indicate presence of higher levels of ionizing radiations in quarries and premises beyond the acceptable annual threshold thereby posing significant health risk to the public. Consequently, these results could find great application in guiding the formulation of the national building code to include routine surveillance of the background ionizing radiation levels in quarries and in various buildings to assess the health risk of quarry workers and general public as well as exploring appropriate mitigation approaches.