Indoor radon measurements in dwellings and public buildings within the KOSH gold mining region, North West Province

Abstract

A wide distribution of indoor radon levels was observed for measurements conducted in schools and homes in different areas. Schools’ results showed a minimum of 18.06 Bq.m-3 and a maximum of 154.96±20.48 Bq.m-3 with the highest concentration of 154.96±20.48 Bq.m-3 recorded at one of the schools in Khuma township during the summer season. Winter measurements in schools measured a minimum of 83.83±13.25 Bq.m-3 and a maximum activity concentration of 319.49±37.02 Bq.m-3. The highest radon concentration of 319.49 ± 37.02 Bq.m-3 was measured at a school in Khuma that recorded the highest radon concentration of 154.96±20.48 Bq.m-3 during the summer season. More than 50% of the schools had concentration above 100 Bq.m-3 which is the level that the World Health Organization (WHO) has recommended to countries to adopt as a reference level. The first set of measurements in private dwellings was conducted in six (6) locations within the KOSH region, i.e., Stilfontein, Khuma (Extension 1, 8 & 9), Orkney, and Kanana during spring and summer seasons. A minimum and maximum of 71.69±12 Bq.m-3 and 97.69± 8.09 Bq.m-3 were recorded in Khuma Extensions 8 and 1, respectively. Radon concentration of 97.69± 8.09 Bq.m-3 from Khuma Extension 1 was significant to 96.28±14.49 Bq.m-3 from Kanana township which was taken as the maximum measured concentration because, in Khuma Extension 1, detectors were deployed in one dwelling. Therefore, it could not represent the average of the whole area. The second set of measurements was conducted during the summer/autumn seasons. A minimum concentration level of 45.36±9.27 Bq.m-3 was measured at Khuma Extension 4, and a maximum of 116.33±15.56 Bq.m-3 was recorded in Jouberton. However, the measurements were conducted from only one dwelling in Jouberton; therefore, it was not taken as the average of the area. The area with the highest concentration was Khuma Extension 6, with a concentration of 83.63±13.38 Bq.m-3. The average of all locations during the first and the second sets did not exceed the action level of 100 Bq.m-3 recommended by the WHO. Still, it exceeded the World Average Indoor Radon Concentration (WAIRC) of 40 Bq.m-3 suggested by the WHO.

The third set of measurements was conducted during winter, and 75% of other data collections were done during different seasons. A minimum indoor radon concentration of 76.36±12.48 Bq.m-3 was measured from Orkney and a maximum indoor radon concentration of 108.84 ±14.53 Bq.m-3 from Khuma Extension 9. As expected, the indoor radon concentration was higher during winter than the spring and summer seasons, i.e., in 80% of the selected dwellings. Only 20%, i.e., three houses, measured slightly higher concentrations in hot and dry seasons than in winter. The highest indoor radon levels in this study were found in Khuma township. First, in a house with an average level of 212.17±26.24 Bq.m-3 and a school with 319.49 ± 37.02 Bq.m-3. The home is built near a heap of mine waste rocks, approximately 3 km away. And the school is built on a former mine tailings dam. The study suggests that the waste generated from former and operating gold mine operations in KOSH and the geology of the area could be the primary sources of elevated indoor radon concentration levels.