Toxicity of Inhaled 144 CeO 2 in Mice

One hundred and seventy-eight mice, exposed by inhalation to an aerosol of ${}^{144}{\rm CeO}{}_{2}$ particles, were observed for their lifespan and their survival compared with those of 200 unexposed control mice. Approximately 91% of the initial whole-body burden of ${}^{144}{\rm Ce}$ was cleared within 6 days. The whole-body burden at 6 days was estimated to be equivalent to the initial lung burden (ILB) of which 32% was retained with an effective half-time of 7 days, 49% with a half-time of 28 days, and 19% with a half-time of 145 days. Cerium-144 retained in the lungs as a percentage of whole-body burden at death was determined through day 454 postinhalation exposure to be 84%. Mean survival time and cumulative percentage of survival were related to the estimated ILBs; ILBs of 4-5 μCi or greater resulted in 62% or more shortening of lifespan and ILBs of 3-4 μCi resulted in a 24% shortening of lifespan. The dose of beta radiation to the lung to the day of deat...