Effects of Single and Repeated Inhalation Exposure of Syrian Hamsters to Aerosols of 144 CeO 2

Male Syrian hamsters (84 days old at the time of the initial exposure) were repeatedly exposed by inhalation at approximately 60-day intervals for 1 year (seven exposures) to aerosols of ${}^{144}{\rm CeO}{}_{2}$ to reestablish lung burdens of 0.4, 2.0, or 10 μCi of ${}^{144}{\rm Ce}$. Other hamsters were exposed once when either 84, 220, or 360 days old to achieve similar initial lung burdens. Primary lung tumors were observed in 7 of 197 hamsters repeatedly exposed to ${}^{144}{\rm CeO}{}_{2}$ that died between 177 and 685 days after the initial inhalation exposure. The cumulative absorbed β-radiation doses to the lungs of these hamsters were 14,000 to 50,000 rad. Primary lung tumors also were observed in 6 of 153 hamsters exposed once to ${}^{144}{\rm CeO}{}_{2}$ when 84 or 220 days old that died between 270 and 675 days after exposure. The cumulative β-radiation doses to the lungs of these hamsters were 6000 to 21,000 rad. Lung tumors were not observed in hamsters exposed when 360 days old or in contr...