This paper reports on an enriched uranium dioxide (UO2) mass clearance study undertaken with Fischer-344 rats. The UO2 had a uranium (U) isotopic composition of 0.79% 234U, 92.8% 235U, 0.34% 236U and 6.06% 238U, by mass, with an alpha-particle activity of 1.91 Bq micrograms-1. Forty-six rats were exposed to an enriched UO2 aerosol that had an activity median particle aerodynamic diameter ranging from 2.7 to 3.2 microns. The rats were killed from 1 to 720 d post-inhalation (PI). The mass of enriched UO2 present in the trachea, lung lobes, thoracic lymph nodes, kidneys, liver, spleen, gut, and the remainder of the carcass was assessed at death. At 720 d after exposure, 82% of the total body burden of enriched UO2 was in the lung, with a further 10% in the thoracic lymph nodes. This represented 17% and 2% of the original (5 d PI) lung burden. The mass clearance of enriched UO2 from the lung was fitted to a single exponential function, normalized to 100% at 5 d PI. The rate constant (k) was 2.8 X 10(-3) d-1, giving a clearance half-time of 247 d. Although statistical comparisons with the majority of published data were not possible, it appeared that both enriched UO2 and natural UO2 particles cleared at rates that were broadly similar, with a t1/2 in the rat lung of 150 to 300 d over the 5- to 720-d PI period. As a consequence of the 234U component in the inhaled UO2 particles, the rats killed at 720 d PI received a total mean accumulated alpha-particle dose averaged over the whole lung of 5.7 Gy. Histologic investigations of the rat lungs found that widespread lung disease was only observed in animals killed at 720 d PI.
Tlwenty-four wscher 34 rts were exposed to enriched uranium dioKide (UO0) aerosols to give a mean initial lung burden of291 ± 89 (SD) yg. Groups of rats were killed at 1, 7, 180, 360, 540, and 720 days post-inhalation (PI). Their lungs were fixed and inflated. Sections cut from all five lung lobes were used to prepare CR-39 neutron-induced 23.U fission frament autoradiographs. A single traverse across a CR-39 autoradiograph of a tissue section, from the left lung of all the rats, was made using a motorized microscopic stage. The traverse was divided into 10 fields. The track counts per field were used to test for homogeneity oftrack distribution and to assess if there was any tendency for tracks to be related to the peripheral region ofthe lung. FRUl raster scans across the entiretissue image were made on left lung autoradiographs from two animals kifled at each time point toassess the homogeneity offission fgment track dition ughout the entire section. There was no evidence of any temporal change in the proportion of tracks associated with the lung periphery. At all time points PI, the trck distribution was significantly nonhomogeneous, suggesting a nonuniform pattern of tissue irradiation from the 234U a particles.At time points from 180 to 720 days PI, large clusters of macrophages were observed in some of the sections taken from anl five lung lobes. The total number of macrophage clusters increased with time PI. These macrophage clusters produced many 235U fission fragment tracks within the CR-39 autoradiographs. The tracks within these macrophage clusters represented 04%4-4% ofthe entire trackcount for the section. The mean tU a-particle dose rate within these clusters was calculated to be 0.033 and 0.13 Gy/day, depending on the size of the cluster. This compares with the estimated dose rates averaged over the whole lung of Q021 Gy/day at 4 days PI and 0.0057 Gy/day at 720 days PI.
Twenty-four Fischer 344 rats were exposed to enriched uranium dioxide (UO2) aerosols to give a mean initial lung burden of 291 +/- 89 (SD) micrograms. Groups of rats were killed at 1, 7, 180, 360, 540, and 720 days post-inhalation (PI). Their lungs were fixed and inflated. Sections cut from all five lung lobes were used to prepare CR-39 neutron-induced 235U fission fragment autoradiographs. A single traverse across a CR-39 autoradiograph of a tissue section, from the left lung of all the rats, was made using a motorized microscopic stage. The traverse was divided into 10 fields. The track counts per field were used to test for homogeneity of track distribution and to assess if there was any tendency for tracks to be related to the peripheral region of the lung. Full raster scans across the entire tissue image were made on left lung autoradiographs from two animals killed at each time point to assess the homogeneity of fission fragment track distribution throughout the entire section. There was no evidence of any temporal change in the proportion of tracks associated with the lung periphery. At all time points PI, the track distribution was significantly nonhomogeneous, suggesting a nonuniform pattern of tissue irradiation from the 234U alpha particles. At time points from 180 to 720 days PI, large clusters of macrophages were observed in some of the sections taken from all five lung lobes. The total number of macrophage clusters increased with time PI. These macrophage clusters produced many 235U fission fragment tracks within the CR-39 autoradiographs.(ABSTRACT TRUNCATED AT 250 WORDS)
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