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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.

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.

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.

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 …