UNUSUALLY HIGH INDOOR RADON CONCENTRATIONS FROM A GIANT ROCK-SLIDE

In a village in western Tyrol, Austria (Umhausen, approximately 2600 i nhabitants) unusually high indoor radon concentrations were measured. The medians were found to be 3750 Bq/m3 (basements) and 1160 Bq/M3 (gr ound floors) in winter, and 361 Bq/M3 (basements) and 210 Bq/m3 (groun d floors) in summer. Maximum radon concentrations of up to 274000 Bq/m 3 were registered. The unusually high radon concentrations are due to the geology of the locality. The part of Umhausen with the highest rad on concentrations is built on an alluvial fan of a giant rock slide (g ranitic gneiss). Measurements of the radon exhalation rate from soil s howed a median of 0.4 Bq/m2/s, measurements of the radium content of r ock samples yielded a median of 125 Bq/kg. The material of the rock sl ide is heavily fractured so that an elevated emanating power and an in creased diffusion coefficient for radon in soil must be assumed. Given a diffusion coefficient of 8 X 10(-6) m2/s and an emanating power of 0.3, the median exhalation Tate of 0.4 Bq/m2/S is obtained at a radium concentration of 125 Bq/kg. The rock slide is therefore considered to be the main source of radon. The abnormally high radon concentrations in Umhausen coincide with a statistically significant increase in lun g cancer mortality (age and sex standardized mortality rate = 3.9, 95% C.I.: 2.9-5.1); the control population is the population of the entir e Tyrol (630000 inhabitants).