UNUSUALLY HIGH INDOOR RADON CONCENTRATIONS

Measurements of indoor radon concentrations in the village Umhausen (2 600 inhabitants, Otztal valley, Tyrol, Austria) revealed unusually hig h indoor radon concentrations up to 274,000 Bq m-3. The medians measur ed on the basements were 3750 Bq m-3 in winter and 361 Bq m-3 in summe r, those on the ground floors were 1180 Bq m-3 and 210 Bq m-3, respect ively. Seventy-one per cent of the houses showed basement radon concen trations above the Austrian action level of 400 Bq m-3 in winter, 33% in summer. There are indications that the high radon concentrations ar e due to a giant rock slide about 8700 years ago. The unusually high r adon concentrations in Umhausen coincide with a statistically signific ant increase in lung cancer mortality. For the period 1970-1991 the ag e 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).