(iy ees -lé £ ve vie . case the dissolved plutonius would fiffuse away From the hot particles. However this dissolved plutonium undoubtedly would be slowly redistributed fn the lung in the seme fashion as chat revorted Dy Meskalev (34) for inhaled soluble compounds of plutonium, resulting in a highly non-uniform << distribucica, with hot spets located predominantly of the lungs. in the sub-pleurai region This gradual conversion ef the soluble plutonium compounds to small colloidal size particles at focal points of activity may be the result of the self-chelating preperties of terravalent plutonium in solution. ; & . (11) In recent studies of rat inhalation of 73 Pud,s Sanders has demoustrated a substantially increased risk per rad for small lung burdens of aged, "crushed" 73%puo, 2 microspheres. In this case the inhaled particles involve smaller particles and a correspondingly larger surface area. The observed nore rapid rate of translocation to other organs can be attributed vatiously to the hicsher mobility of the smaller particles, or te the highe~ rate of surface ablation (or dissolution) for the increased surface area, or both. The higher tumor incidence can be attributed to the fact that the greater mobility and wider redistribution of the 238Pu0, microspheres and their breakdown products subject a much larger number of cells to a limited number of alpha interactions. The correctness of the ebove interpretation is reinforced by the results of the Los Alamos ceramic sphere experiments reported by Richmond et a y, (12513) and further discussed by Bair et al, 2 | In these experi- ments 2090 Zirconium oxide microspheres of 10 um diameter, each set containing a specified amount of plutonium, were injected into the lungs of groups of experimental animals. The total plutonium per microsphere | ranged from 0.07 to 1.6 pCi of ??°Pu and from 4.3 to 59.4 pCi of 73% pu, with identical activity for each of the 2000 microspheres in each of eight animal exposure groups of 70 animals per group. The local dose rate,