The toxicity of90 Sr administered by the inhalation route was studied in young adult Beagle dogs exposed once to aerosols containing <tex-math>${}^{90}{\rm SrCl}{}_{2}$</tex-math>. Due to its relatively soluble chemical form,90 Sr was rapidly translocated from lung to bone where a substantial portion was retained for a long period of time. This resulted in only a brief radiation exposure of the respiratory tract and a protracted exposure of the skeleton. The long-term retained burdens ranged from 0.037 to 4.4 MBq <tex-math>${}^{90}{\rm Sr}/{\rm kg}$</tex-math> body wt. Dogs were subsequently observed throughout their life span. Six dogs with long-term retained burdens of 1.7 to 4.1 MBq <tex-math>${}^{90}{\rm Sr}/{\rm kg}$</tex-math> died at less than 32 days after exposure from radiation-induced bone marrow hypoplasia. Review of hematological parameters of all dogs showed a similar, consistent, and dose-related pancytopenia in those animals having a long-term retained burden of greater than 0.37 MBq <tex-math>${}^{90}{\rm Sr}/{\rm kg}$</tex-math>. Thrombocytopenia and neutropenia persisted in all exposed dogs through 1000 days after exposure. For reference purposes, a burden of 0.37 MBq <tex-math>${}^{90}{\rm Sr}/{\rm kg}$</tex-math> is calculated to deliver an average radiation dose to the skeleton over 30, 100, and 1000 days after intake of 1.0, 2.8, and 17 Gy, respectively. The hematologic changes were similar to those seen in people exposed to high doses of whole-body external radiation.

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