Survival, lung clearance, dosimetry and gross pathology of rats exposed toeither NpO2 or PuO2 aerosols

Purpose: To compare survival, lung dosimetry and gross pathology after inha lation exposure of rats to either NpO2 or industrial PuO2 aerosols with sim ilar granulometric parameters. Because the specific alpha activity ratio Pu /Np is about 600, a much more homogeneous lung irradiation was expected for NpO2. Materials and methods: Male Sprague Dawley rats were exposed once and their lung burdens were measured by X-ray spectrometry at different times post-e xposure up to death. The time-course of doses delivered to the lungs were e stimated, taking into account individual lung clearance parameters and body and lung weights. Gross lung pathologies were scored at autopsy. Results: In the range of initial lung deposits (ILD) studied (0.1-4 kBq), l ung clearance impairment and reduced lifespan were only observed after expo sure to NpO2. For similar ILD or doses, the highest incidences of lung lesi ons assumed to be tumours were observed for NpO2 with a saturation of lung tumour induction for doses larger than 8 Gy (ILD: 1.5 kBq). Up to 22 gy (IL D: 3.5 kBq), such saturation was not observed for PuO2. Conclusions: NpO2 appears much more toxic than PuO2. Before saturation, lun g tumour incidence increased nearly linearly with dose, the slope of the cu rve for NpO2 being about twice as steep as that for PuO2.