Effect of239PuO2Particle Number and Size on the Frequency and Distribution of Chromosome Aberrations in the Liver of the Chinese Hamster

Chinese hamsters were injected intravenously with239Pu citrate or239PuO2particles. There were four particle sizes injected: 0.17, 0.30, 0.44, and 0.84 μm which would vary the local radiation dose and dose rate to the surrounding cells. Additional hamsters were injected with graded levels of activity from$6\times 10^{-5}$to$6\times 10^{-3}\ \mu {\rm Ci}/{\rm g}$using 0.30 μm239PuO2particles. This changes the particle number and the average dose rate. An experiment was also conducted to determine the retention and distribution of the particles using51Cr to trace the239PuO2particles. The particles were concentrated in the reticuloendothelial system with 90% of the injected activity in the liver, 3% in the spleen, and the remainder in either the bone or bone marrow. Autoradiographic studies with239Pu showed that there was particle clumping causing high local doses to the liver cells in all particle sizes studied. The239Pu citrate produced a linear increase in the chromosome aberration frequency with a slope of$4.8\times 10^{-3}$aberrations/cell/rad. The chromosome aberration frequency increased with increasing average dose following injection of the239PuO2particles. This increase in response plateaued at higher average doses. There was little evidence of an effect of particle size on the aberration frequency. When local dose was related to aberration frequency, the smaller the particles the greater the effectiveness in producing chromosome damage. Following injection of all particle sizes, the nonuniform distribution of dose was reflected in a nonuniform distribution of chromosome damage in the cell population with up to 13 aberrations in an individual cell. The number of cells at risk following particulate deposition is much less than from uniform distribution of the same total activity. This may indicate that long-term risks from239PuO2particles would be less than that from uniformly distributed239Pu citrate.