= 14 In obtaining the derived values in Tables I and II, MPLB anc MPC, for Pu-239, a QF=10 was employed. implies, 25 mentioned above, This QF that the particles of Pu-239, wiich emit alpha particle radiation, are 10 times more effective in inducin¢e cancer than X-rays. Although the irradiation of tissue by insoluble plutonium particles is highly nonuniform, no DF value has been assigned to these particles and hence, a DF=1 was enployed in determining the derived values in Tables I and II. Ideally, the DF should be determined by the ratio of the cbserved effects in an organ following uniform and nonunizor= radiation of the tissue with the same radionuclide; For #xamcle: oF = Numer of cancers ° Number of cancers; (nonuniform irradiation) {uniform irradiation) Since Girect exserimental data are not available, it is = mecessary ic derive the DF for insoluble Bu-239 particles from teral cata. In a subsequent section, we shall sresent the bioicgical evidence that strongly suggests that a DF=l crossiv underestimates the DE for insoluble particulates of . this . . radionuclide, are greatly . 20 in error. $12 be shown that the biological data strongly I~ * that the derived standards, MPLB t I~ it itr it a3 iw cr et Q ur cr lh fu " fs atd ath th wi Hi J anda MPC, consecuently, ft Q rg Pu-239 and, such parzicles one shovld use a DF=115,000. t@s as well to other aloha-emitting actinices reticulate form.