Influence of Climate and Weather on the Mitigation of Radon Exposure in Two Towns of the Western Cape, South Africa

Globally, exposure to high levels of radon gas is a known health risk. Granite commonly contains high concentrations of uranium and subsequently high exhalation of radon gas. In the Saldanha Bay area of South Africa, granites dominate the underlying geology as well as the surface characteristics of the area. This implies that elevated levels of radon gas may exist in houses in the area. However, a survey of indoor radon concentrations in the town of Vredenburg in the Saldanha Bay area recorded average indoor radon concentrations well below those recommended as threshold levels by international bodies. The average radon concentrations are also significantly below those recorded in Paarl, a town about 100 km south-east of Vredenburg with a similar underlying geology, but different climatological characteristics. Indoor radon concentrations were measured in 34 homes in Vredenburg, and 62 houses in the west side of Paarl, on or near the granite outcrops. Electret ion chambers (E-PERM (TM)) from Rad-Elec Inc were used to measure indoor radon in the randomly selected houses in each area. For both surveys, the electrets were deployed for periods of between 5 and 20 days. The Paarl survey was conducted between October 2003 and March 2004, while houses in Vredenburg were surveyed during January and February 2019. In this article, researchers develop a theory to explain the lower than predicted indoor radon concentrations, as well as the difference in results obtained from the Vredenburg and Paarl surveys. They attribute these anomalies to the mitigating effect of the prevailing climatological conditions of the Saldanha Bay area and the generally mild climate experienced at both sites. The research postulates that these conditions can significantly reduce the health hazard associated with elevated indoor radon levels.