Repeated inhalation exposure of rats to aerosols of 144CeO2. II

The effects of protracted beta radiation of the lungs of gnotobiotic female and male Fischer-344 rats are being studied. Rats are being exposed seven times by inhalation to aerosols of 144CeO2 to reestablish lung burdens of 0.04, 0.20, 1.0 or 5.0 μCi of 144Ce at 60 day intervals. The observations in these rats are being compared with those in rats exposed once to 144CeO2 to achieve similar initial lung burdens of 144Ce. Control rats were either unexposed, sham exposed once or repeatedly, or exposed once or repeatedly to stable CeO2. Less than 12% of the rats in any group have died through approximately 500 days after initial inhalation exposures. Apparent lung tumors were evident at necropsy in three rats in the group repeatedly exposed to reestablish a 5 μCi lung burden that had died