Chromosome aberrations induced by${}^{238}{\rm PuO}{}_{2}\text{-}{\rm ZrO}_{2}$ microspheres after inhalation have been observed in Syrian hamsters (Mesocricetus auratus). The animals had initial lung burdens of approximately 140 nCi of${}^{238}{\rm Pu}$. Twenty-four hours after exposure to the particles in an inhalation chamber, the lungs were removed and placed in tissue culture for chromosome analysis. The incidence of chromosome aberrations 63 and 138 hr after cell cultivation increased (0.18 and 0.24 aberration per cell, respectively) above controls. Growth rate and mitotic indices were depressed greatly 1 and 3 weeks later, compared to 63 and 138 hr after culture. Autoradiographs of the cultured cells at these times demonstrated many star clusters from alpha tracks of the microspheres, indicating an abundance of microspheres retained in the lungs which caused continuous irradiation during the culture period.

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