Unusually high indoor radon concentrations

Measurements of indoor radon concentrations in the village Umhausen (2600 inhabitants, Ötztal valley, Tyrol, Austria) revealed unusually high indoor radon concentrations up to 274,000 Bq m^?3. The medians measured on the basements were 3750 Bq m^?3 in winter and 361 Bq m^?3 in summer, those on the ground floors were 1180 Bq m^?3 and 210 Bq m^?3, respectively. Seventy-one per cent of the houses showed basement radon concentrations above the Austrian action level of 400 Bq m^?3 in winter, 33% in summer. There are indications that the high radon concentrations are due to a giant rock slide about 8700 years ago. The unusually high radon concentrations in Umhausen coincide with a statistically significant increase in lung cancer mortality. For the period 1970–1991 the age and sex standardized mortality rate is 3.85 (95% confidence interval: 2.9 to 5.1). The control population is the total population of Tyrol (630,000 inhabitants).