Effects of continuous inhalation exposure of rats to radon and its progenyat various levels of dose and dose rate: Interim results

Studies of rats at Harwell and CEA [Monchaux et at, Radiat. Res. 152 (Suppl .), S137-S140, 1999] are currently in progress to determine the factors aff ecting the risk of induction of lung tumors after exposure to radon and rad on progeny. Knowledge of the effect of dose, dose rate and characteristics of the aerosol on lung tumor induction in rats may be used to improve estim ates of risk from domestic exposure. At Harwell, three studies are in progr ess, studying the effect of dose, dose rate, and dose rate at low total exp osures. Approximately 2000 adult male rats have been exposed. A smalt numbe r of rats were taken to determine deposition in the respiratory tract and t he early effects of exposure on cell proliferation and nuclear aberrations. The remaining animals have been held for their life span. To date 65% of t he animals in the first study have been examined. Current results (for 421 rats) suggest that exposure to radon and radon progeny causes elevated inci dences of both benign and malignant lung tumors, These findings are based o n incomplete tumor incidences, Competing causes of death may affect the res ults, and full statistical analysis is required before firm conclusions can be drawn about the effect of dose and dose rate. (C) 1999 by Radiation Res earch Society.