Radon, radioactive

CAS RN: 10043-92-2

Toxicity Summary

IDENTIFICATION AND USE: Radon, a naturally occurring gas formed from the decay of uranium in the earth. Radon was produced commercially for use in radiation therapy, but for the most part has been replaced by other radionuclides. Some radon is produced in research laboratories and universities for use in experimental studies. HUMAN STUDIES: Radon and its isotopic forms radon-222 and radon-220 are known to be human carcinogens based on sufficient evidence of carcinogenicity from studies in humans. Increased incidences of lung cancer have been reported in numerous epidemiological studies of groups occupationally exposed to radon at high doses. In one of the largest prospective studies, two cohorts totaling 3,400 white and 780 Native American uranium miners and millers in Colorado were followed from 1950 to 1977. Among white males, the risk of lung cancer was significantly increased 4- to 6-fold. In some other cohorts, radon exposure was also associated with increased risks of tracheal and bronchial cancer. Smaller case-control studies also suggested an association between lung-cancer risk and indoor residential exposure to radon, mainly from ground sources. There is evidence of association between chronic exposure to indoor radon and the occurrence of chromosome damage in human oral epithelial cells. In an effort to mimic human in vivo exposures to ionizing irradiation, G(0) phase T lymphocytes from human peripheral blood samples were utilized for in vitro studies of the genotoxic effects of radon-222 irradiation. The spectrum of radon-222 irradiation-induced mutation was characterized by an increase in small alterations, especially multiple single base deletions/substitutions and micro-deletions. However, radon therapy is clinically useful for the treatment of pain-related diseases. Radon bath is a well-established modality of balneotherapy for the management of degenerative musculoskeletal disorders. ANIMAL STUDIES: In male rats, inhalation exposure to radon caused lung cancer (adenoma, adenocarcinoma, alveolar/bronchiolar carcinoma, and squamous-cell carcinoma). In dogs of both sexes, inhalation exposure to a combination of radon, radon decay products, and uranium ore dust caused lung cancer and nasal cancer. A review of studies in rats exposed to radon by inhalation also reported increased incidences of tumors of the upper lip and urinary tract. In a study in hamsters, only three animals developed features of squamous-cell carcinoma after 16 to 17 months of exposure to radon decay products or radon decay products and uranium ore dust. The cytotoxic and mutagenic effects of radon and its progeny in murine lymphoblast L5178Y-R16 cells were compared after exposure in vitro to a steady-state ratio of radon and its progeny (radon-222:polonium-218:polonium-214=1:3.5:4.5) under various experimental conditions. In all cases, a dose-dependent increase in the induced frequency of mutation at the thymidine kinase locus was found. However, radon inhalation activates antioxidative functions in the liver and inhibits carbon tetrachloride-induced hepatopathy in mice. Radon inhalation activates superoxide dismutase (SOD) inhibiting transient global cerebral ischemic injury in gerbils. ECOTOXICITY STUDIES: Radon retention by the bluegill increased much more rapidly with time after injection than did radon retention by the mouse.
Find more information on this substance at: PubChem, PubMed