c e Oo nonuniform alpha radiation cose distribution in the lung. The authors of this study take exception to the conclusions and recormendations of Seesaman, Tamplin ai:d Cochran ¢ As 28) and concluce that “the nonuniform dose distribution of plutonium particles in the lung is mot more hozardous end “ay be less hazarctus than 4f the plutonium were unifernly distributed and that the mean dose iung model is a radi obiologicaliy sound basis for establishment of plutonium standards." Bair et ai, (15) fail to take into account the full implications of gome of the recent published results: in particular, the observed higher tumor risks for ?3°Pu0, than for 22%yo, 11) the apparently limited | biological response of mammal lung cells from *?°Pu and 7?°Pu incorporated into ceramic microspheres (17+3) and the tobacco smoke radioactivity results ‘14, The latter results imply that as little as a few picocuries of insolubie alpha emitting particles in the iung may give rise to a “ significant risk cf lung cancer and other serious heaith eifects in the chronic exposure case. " On the basis of a brief review of the known effects of alpha inter- . actions with cells (below) it will become evident that alpha radiation induced cancer in mammals and man must be brought about by subjecting a large number of living cells to a limited number of alpha interactions. Thus, in principie, the hignest risk would be associated with a uniferm distribution of the alpha dose, in accordance with the conclusion of Bair et al. However, in fact, we are almost always concerned with a highly irregular tissue distribution of alpha emitting particles. For hot particles, the tumor incidence must be due to the low dose irradiation of a large number of cells by a very small fraction of the hot particle burden. And for lone tern exposures, unacceptably high tumor risks appear to be associated with picocurie burdens of internal alpha emitters. This serious possibility calls for a drastic downward revision of permissible ee les: ee ape 3LTSoe strats. TETSeraes Meroy' a weedZ tae te ‘a ” aah ay : a ayes ‘ ¢' atefee ay et an ed)Pas +vasime‘WeiheMea. en os 38 hae 4. “te (¥ % A . akyeWw Mee gy pecs ORO PION re yl4 ate’ ey ¢ e on eeeeesys aaf psnapersr8 “| eeeea + map a ne he ieaewh