Assessment of Factors Affecting Indoor Radon -222 Concentration in Dome and its Environs - Greater Accra Region of Ghana

Abstract

The objective of this study was to evaluate the contributions of the main factors of indoor radon concentration. This was achieved by measuring indoor and soil gas radon in three localities (Dome Afghanistan, Achimota Mile7 and Achimota ABC) in and around Ga East. 60 houses were selected in the three localities for the indoor measurements. Five sites were located in each of the localities for soil radon measurement at 75 cm depth. LR-115-type II plastic track detectors were used for the measurement in two different seasons – dry and wet. The indoor radon concentration measurement was carried out for three months in each season and the soil measurement was also carried out in a 14-day cycle for four cycles. The LR- 115-type II plastic track detectors were collected, etched at 60 0C and counted using the image j software and v-600 perfection scanner. The track densities obtained were converted into radon concentrations. The International Commission on Radiological Protection (ICRP) publication 115 model was used to estimate the annual absorb dose and effective dose to the lungs. Significant seasonal variations were observed in the radon concentrations of the dwellings studied. Indoor radon concentrations for the rainy season showed relatively high values than that of the dry season. This was expected as the sliding windows used for the dwellings are not opened during the rainy season. This might have resulted in the accumulation of radon gas in the rooms. Regular opening of windows and other means of providing air exchanges in the rooms during the dry season could have also accounted for the low levels of indoor radon concentration. The mean indoor radon concentration in the rainy season for Dome Afghanistan, Achimota Mile7 and Achimota ABC were determined to be 165 Bq/m3, 115 Bq/m3 and 119 Bq/m3 respectively. The corresponding dry seasons were 71 Bq/m3, 73 Bq/m3 and 66 Bq/m3 respectively for the three localities. The annual effective dose (AED) in the dwellings for Afghanistan ranges from 4.8 mSv/y to 20.2 mSv/y and that of Achimota Mile7 and Achimota ABC ranged from 3.23 to 13.9 mSv/y and 3.5 to 10.74 mSv/y respectively. According to ICRP Publication 115 (2010) statement on radon, the upper value for radon reference level of 300 Bq/m3 corresponds to an AED of 17 mSv/y. Thus the three localities are generally found to fall within the ICRP (2010) limit; however, dwelling AF H17 of Dome Afghanistan recorded indoor radon concentration of 334.10 Bq/m-3 with a corresponding AED of 20.2 mSv/y. These are relatively higher than the ICRP limit. The soil radon measured in both seasons was higher than the corresponding indoor radon concentrations. The concentration ranges from 0.37 to 1.19 kBq/m3 and 1.43 to 4.23 kBq/m3 in the rainy and dry seasons respectively. The concrete floors and blocks of the dwellings seemed to have provided shielding and prevented high radon diffusion from the ground and outdoor into the dwellings. Works already done on the same building materials showed that the radon exhalation rate from these materials ranged from 17.5 to 42.6 Bq/m3. This suggested that the major possible contributing factor to indoor radon concentration in dwellings is lack of ventilation which leads to the build-up or accumulation of radon. A linear correlation analysis for the influence of soil radon concentration on indoor radon concentration in rainy and dry season, gave an Rsquared value of 0.0032 and 0.0021 respectively, indicating a weak negative correlation between soil radon concentration and indoor radon concentrations. This confirms that the indoor radon concentration is weakly linked to the soil radon, possibly as a result of the concrete floor and blocks which provided good shielding.