Radon and radon progeny outdoors in a valley of enhanced natural radioactivity

Results of a pilot study of 222Rn and 222Rn progeny outdoors and indoors in a valley of enhanced radioactivity, affected by uranium mining and milling have been summarized. Diurnal and spatial variations have been followed, and 222Rn concentrations in soil-gas have been determined. High outdoor concentrations of radon progeny during nights and at early mornings have been observed under the conditions of high air stagnation. The indoor concentrations were greater than the outdoor ones, however in most of the studied houses, the contribution of outdoor radon to the total exposure was found to be dominating. The cumulative exposure (for over 90% of the inhabitants) due to outdoor radon was estimated to be about 0.9 WLM per annum. These results reveal that lung-cancer risk excess by about 80% could be attributed to outdoor radon, provided that one assumes the risk coefficients (the cancer risk per unit of exposure) determined for occupational exposures. The study of different radon sources suggests that except for the uranium mining and milling, the generally enhanced natural radioactivity and meteorological conditions in this valley are of substantial importance. Valleys, such as the questioned one, may give an opportunity to check up the hypothesis about the existence of health effects at low doses of 222Rn progeny exposure.