Incidence of Brain Tumours in Rats Exposed to an Aerosol of239PuO2

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Abstract
Incidence of brain tumours was investigated in 3390 famale and male Wistar rats exposed to an aerosol of 239PuO2, or as sham-exposed controls. Lung doses ranged from 0·05 to 22 Gy. In females, six brain tumours were found in 1058 control rats (incidence, 0·6%) and 24 brain tumours in 2134 rats exposed to Pu (incidence, 1·1%); the survival-adjusted level of significance was p = 0·29 for comparing control with exposed females. In males, two brain tumours were found in 60 control rats (incidence, 3·3%) and seven brain tumours in 138 rats exposed to Pu (incidence, 5·1%); the survival-adjusted level of significance was p = 0·33. Brain tumour incidence was about five times greater in male than in female rats (p = 0·0001), demonstrating a highly significant sex difference in brain tumour incidence. Tumour types were distributed similarly among control and Pu-exposed groups of both sexes; most tumours were astrocytomas. Mean lifespans for rats with brain tumours were not significantly different between control and Pu-exposed rats. Plutonium was not detected on autoradiograms of the brain. These results, like those for plutonium workers, show an increase of brain tumours which cannot be demonstrated statistically to be related to radiation exposure.