C . ES Exrerinencs in the Rocky Plats area also have shown that adout one-third of the airborne plutonium which has been resuspended from soii surfaces by wind action falls within the re.ai uble particle sise range. However only a very small fraction of the bulk surface soil is made up of insolublé particles of respiraple size. Fer this reason, surface scils with one . picocurile of plutonium per gram (the Colorado interim soil standard) should contain zn estimated 10 to 100 pCi of plutoniun per gram of insoluble soll particles of respirable size. Such a soil level should lead to plutonium lung burdens of 5 to 50 picocuries by age 20, or 15 to £50 picocuries by age 6&C, with correspondingly higher concentrations in the lymph nodes, liver, and bone. Thus the Colorado interim soil standard is hardly a safe or acceptable standard unless it can be shown that such levels of plutonium have no serious long term health effects. There are, of course, 2 nember of considerations which make it incyppropriate to equate the effects of a given burden of low specific activity alpha emitting cigarette smoke particles with the same amount of alpha activity in hot particles. The Los Alamos experiments_(12,13) make it evident that most of the alpha dose fron “hot" particles of Pud, is ° , wasted in the excessive irradiation of cells within the alpha cauge of yg, the hot particle surface. Thus the high tumor risk for the hot 7?®puo particles (11) can be variously attributed to (a) the mobility of the 2 smaller particles (b) the recoil ablation and/or dissolution rates which increase with specific activity and with surface area of hot particles and (c) the irradiation of larger numbers of cells with scattered protons (an effect that may be ‘significant for very hot particles).