Pulmonary tumours in Syrian hamsters following inhalation of 239PuO2.

Syrian hamsters were exposed to various levels of aerosolized 239PuO2 particles to attain a range of initial lung burdens (medians ranged from 40 to 144 nCi). They were allowed to live without sacrifice and had gross and microscopic tissue examinations at death. Over a range of median lung doses from 4-12 000 rad there was an average 2 per cent incidence of malignant tumours (adenocarcinomas) and 9 per cent incidence of total tumours (primarily adenomas). Some of these results are consistent with those from other laboratories using plutonium oxide aerosols but they represent considerably lower lung tumour incidences than previously observed in this laboratory using aerosols of 238PuO2-ZrO2 particles.

Lung response to localized irradiation from plutonium microspheres.

Uniform spherical 10-micrometer diameter particles of ZrO2 ceramic, containing various concentrations of PuO2, have been injected into the jugular vein of Syrian hamsters with subsequent permanent lodgement in the lung capillaries. The number of particles injected has varied from 2000 to 2 000 000 and the specific activity has been from 0.16 to 59 pCi/sphere so that lung burdens range from 0.2 to 700 nCi. To date, approximately 3000 hamsters have been committed to the experiment and two-thirds have died--the expected rate for normal animals. Little biological damage has been observed, and only five primary lung tumours have been found that may be due to radiation delivered to the lung. To provide a comparison to more uniform radiation, soluble polonium has also been instilled intratracheally. Results from the microspheres suggest that localized lung irradiation alone is not sufficient cause for tumour induction and is much less hazardous than diffuse exposure.

The effects of dose protraction on hematopoiesis in the primate and dog.

The modifying effects of dose protraction by fractionation or continuous low dose-rate exposure are not well known in the primate. Comparative studies between the two mammalian species dog and monkey with widely differing acute LD50 values have not been made. A program to study dose-rate effects on injury and recovery of the bone marrow in dogs and monkeys under simultaneous and similar exposure conditions is in progress. The equivalent residual dose (ERD) assumptions of 10% irreparable injury and a 28-day recovery half-time for the reparable portion (90%) of radiation were studied in dogs (beagles) and monkeys (Macaca arctoides) using variable recovery times and appropriate fractionated exposures to attain but not exceed theoretical effective residual body burdens of 200 rads over a 1-year period. The ERD assumptions were tolerated by the dogs but resulted in death to 7 of 8 monkeys tested. The same ERD assumptions were tested with monkeys (Macaca mulatta) using a fixed recovery time span and an upper ERD limit of 100 rads. Monkeys in this study have tolerated 1900 rads of gamma-ray exposure (approximately 3 times the acute lethal dose) with minimal suppression of the hematopoietic system.