Retention, excretion and translocation of 239Pu in rats following inhalation of 239PuO2 calcined at 1150 and 400 degrees C

Isotopic and elemental composition of plutonium/americium oxides influence pulmonary and extra-pulmonary distribution after inhalation in rats

The biodistribution of plutonium and americium has been studied in a rat model after inhalation of two PuO(2) powders in lungs and extra-pulmonary organs from 3 d to 3 mo. The main difference between the two powders was the content of americium (approximately 46% and 4.5% of total alpha activity). The PuO(2) with a higher proportion of americium shows an accelerated transfer of activity from lungs to blood as compared to PuO(2) with the lower americium content, illustrated by increased urinary excretion and higher bone and liver actinide retention. The total alpha activity measured reflects mostly the americium biological behavior. The activity contained in epithelial lining fluid, recovered in the acellular phase of broncho-alveolar lavages, mainly contains americium, whereas plutonium remains trapped in macrophages. Epithelial lining fluid could represent a transitional pulmonary compartment prior to translocation of actinides to the blood and subsequent deposition in extra-pulmonary retention organs. In addition, differential behaviors of plutonium and americium are also observed between the PuO(2) powders with a higher dissolution rate for both plutonium and americium being obtained for the PuO(2) with the highest americium content. Our results indicate that the biological behavior of plutonium and americium after translocation into blood differ two-fold: (1) for the two actinides for the same PuO(2) aerosol, and (2) for the same actinide from the two different aerosols. These results highlight the importance of considering the specific behavior of each contaminant after accidental pulmonary intake when assessing extra-pulmonary deposits from the level of activity excreted in urine or for therapeutic strategy decisions.

Comparative absorption parameters of Pu and Am from PuO2and mixed oxide aerosols measured afterin vitrodissolution test and inhalation in rats

PURPOSE

To compare specific absorption parameter values obtained from in vitro dissolution studies (this paper) and in vivo experiments (data published by Ramounet et al, 2000) and to determine their influence on Dose Per Unit Intake (DPUI) calculations.

MATERIALS AND METHODS

Experiments were performed on plutonium oxide (PuO2) and two Mixed Oxide (MOx) preparations containing 5% Pu (w/w) made according to the industrial process in vitro using a static test and in vivo after rat inhalation.

RESULTS

Behaviour of Pu and Am shows, in vitro, at shorter times, a greater rapid dissolution fraction f(r) for Pu (factor 10) and Am (factor 2) with MOx powders compared with PuO2, whereas in vivo results show a greater fraction f(r) for Pu (factor 5) and Am (factor 15) with PuO2 compared with MOx powders. This phenomenon has not been observed for slow dissolution absorption parameter s(s). The in vivo parameters for Pu and Am in these materials were very close to the default values recommended by International Commission for Radiological Protection for default Type S.

CONCLUSIONS

Results obtained have shown that solubility of Pu from the mixed oxide was higher than that of Pu from PuO2. Nevertheless, no significant difference was observed between the three compounds in the corresponding dose coefficients in vivo or in vitro. Therefore, for these particular compounds, variation in the chemical composition of the aerosols had no significant influence on DPUI. Consequently, in vitro, the dissolution test can provide a good estimate of the in vivo behaviour. Studies of variation of % Pu (w/w) from MOx are in progress in our laboratory to confirm these conclusions.