Assessment Of Radiological Hazards Associated With Indoor Norm Dose Exposure In Residential Houses In Nairobi, Kenya

Abstract

Indoor air quality has profound impact on health worldwide; effects on respiratory, circulatory and immune systems due to sick building syndrome. This study examined the radiological hazards associated with indoor air quality in selected residential houses in Nairobi City for exposure to NORM. In situ measurements were done using Gamma Spectroscopy Multichannel NaI (Tl) analyzer on the type of building materials (for floor, walls and ceiling), used in three hundred and thirty (330) residential houses. Indoor NORM radioactivity content, ambient gamma equivalent dose were measured and the ventilation rate of the main living rooms evaluated. The radiological hazards assessed were; absorbed dose, effective dose and excess life time cancer risks. The results indicate potential exposure associated with NORM within the type of building materials. The dominant radionuclide identified was 40K; mean 107 kBq (103 -163) kBq (floor), mean 140 kBq (97 -344) kBq (walls) and mean 120 kBq (84 -167) kBq (ceiling) and dose rate of 0.32 mSv/yr (floor) and 0.34 mSv/yr for both walls and ceiling. Other NORMs were below their detection limits. For indoor ambient gamma dose rate, the ceiling was the dominant source of exposure for most residential houses and exceeds 2 mSv/yr. The indoor absorbed dose ranged from 60.34 - 272.73 nGy/h with a mean value of 113 nGy/h and varies with type of building material used with correlation significance of 26%. The results of mean absorbed dose rate show that residence within Kapiti Phonolites regions are relatively at risk of high exposure than those in Nairobi Phonolites. The indoor annual effective dose obtained from the floor, ceiling, and walls are 0.55 ± 0.18 mSv, 0.63 ± 0.21 mSv and 0.71 ± 0.24 mSv and are within the UNSCEAR indoor annual exposure of 0.41 mSv for adults, 0.45mSv for children and 0.53 mSv for infants, respectively. The findings of this study indicate potential exposure from tiled floors (1.34 mSv/a) and concrete roof (1.06 mSv/a). The estimated excess lifetime cancer risk ranges from 0.2 to 0.6 % with a mean value of 0.28%. The three parameters of ventilation namely; ventilation rate, air exchange rate per hour, and ventilation per area were studied. Most main living room residential houses had ventilation openings areas less than 5%, air change rate per hour ranges between 0.48 to 0.61 h-1 with mean value of 0.51 h-1, and are not compliant to the local minimum requirement of 0.5 - 1 h-l. This findings are in agreement with indoor air quality and exposure dependency on ventilation systems. However, there is indication of poor indoor air quality in some Nairobi residence whose exposure rate is dependent on; the type of building materials used, ventilation area opening, ventilation rate, the floor level, locations of residences, the size of the rooms, indoor occupancy and lifestyle. The study therefore recommends incorporation of radiation protection and safety standards of NORM in building materials of residential houses and indoor air quality standards, and policies for the building and construction industry of residential houses. Further investigations of the associations between indoor air quality and respiratory diseases or allergies and the air change rate in homes could be considered and public ventilation awareness campaigns.