EFFECTIVENESS OF RADON RELATIVE TO ACUTE CO-60 GAMMA-RAYS FOR INDUCTION OF MICRONUCLEI IN-VITRO AND IN-VIVO

Because radon and its progeny (referred to collectively here as radon) emit alpha particles with a wide range of energies, as well as beta p articles and gamma-rays, it is important to quantitate the relationshi p between initial damage induced by radon and that by acute low-LET ra diation. We have evaluated dose-response relationships for induction o f micronuclei both in vivo and in vitro following exposure to radon or Co-60. TO determine if isolation procedures altered the cells' respon siveness to Co-60 gamma-ray exposures, animals were exposed before cel l isolation, or cells were isolated and then exposed. The data were de scribed by linear dose-response functions and were not significantly d ifferent when the radiation exposure was in vivo or in vitro (respecti vely micronuclei/1000 binucleated cells = 1.6+/-65+62+/-2.7 D; micronu clei/1000 binucleated cells=15.4+/-26.0+54.6+/-11.4 D, where D is in G y). Primary rat lung fibroblasts (RLF) or Chinese hamster ovary (CHO-K l) cells were exposed in vitro to either radon or Co-60 gamma-rays. Ra don was 10(-9)+/-2.6 and 12.5+/-2.4 times as effective per Gy of radia tion dose in producing micronuclei as was Co-60 in RLF and CHO-Kl cell s respectively. To determine the relative biological effectiveness of in vivo radon exposure, animals were exposed to either radon or Co-60, and lung fibroblasts were isolated and evaluated for radiation-induce d micronuclei. In vivo radon exposure was 10.6+/-1.0 times as effectiv e as acute whole-body Co-60 exposure in producing micronuclei in lung fibroblasts. Different cell lines and exposure conditions resulted in similar effectiveness factors. Such ratios help evaluate the biologica l damage, hazard and risk associated with radon inhalation.