National mapping survey of indoor radon levels in the Maltese Islands (2010-2011)

Abstract

Aim: To conduct a national geographically based survey to determine the distribution of the mean annual indoor radon gas concentration levels in dwellings in the Maltese Islands and map these levels; to identify any areas with annual mean indoor radon gas concentrations higher than the current proposed WHO reference level of 100 Bq/m3; to determine an advisory national reference level for radon concentration in buildings. Method: Radon measurements were carried out in 85 buildings distributed over the Maltese Islands between November 2010 and November 2011 using alpha-track radon detectors. Retrieved detectors were analysed by a Health Protection Agency-accredited laboratory in the UK. The overall annual arithmetic and geometric mean indoor radon gas concentrations for the Maltese Islands were calculated. Results: The mean annual indoor radon concentration for the Maltese Islands was 32 Bq/m3, with a geometric mean of 25 Bq/m3 (standard deviation (SD) 25). The maximum level measured was 92 Bq/m3 and the minimum 11 Bq/m3. A radon map of the Maltese Islands was produced using the geographic mean annual indoor radon gas concentration level for each building. Conclusion: The mean annual indoor radon concentration in Malta was found to be well below the lowest proposed WHO reference levels with no dwellings having a mean annual indoor radon gas concentration above 100 Bq/m3. This national mapping survey for mean annual indoor radon gas concentration in the Maltese Islands indicates that the current proposed reference level of 100 Bq/m3 by the WHO may be adopted as the national reference level for the Maltese Islands.