wa 1. Introduction: The adequacy of the biomedical basis of standards for occupational and public exposure to plutonium and other internal alpha emitters have been widely discussed (145) and seriously questioned ‘© 8) | The serious uncertainties in the cancer risks attributable to internal alpha emitters must be resolved before we are irretrievably committed co a nuclear energy program. This is a matter of immediate concern in the western suburbs of Denver due to plutonium and americium .contamination of surface soils in public areas around the Rocky Flats Plutonium Plant ©?) , Many other localities are similarly affected by tranuraniun element contamination and its attendant cancer risks. Recent controversy regarding the adequacy of plutonium standards has centered on several aspects of the problem of the cancer risxs attributable to inhaled plutonium oxide particles, including such aqueetions . - as which organ and how small a tissue volume constitutes the “eritical” | organ (i.e., that experiencing the highest cancer risk), and whether the average alpha radiation dose to the critical organ or the tumor risk attributed to a given number of individual hot plutonium oxide particles provides the best guidance for the assessment of risks and standards for plutonium. , Geesaman (6) has discussed possible mechanisms of cancer induction by hot particles and concludes that the tumorigenic risk may be as high as 1/2000 per particle for submicron particles of plutonium .oxide. A recent examination of hot particle risks by Tamplin and Cochran °®), based largely on the Geesaman study, led these suthors to recommend that the occupational MPLB (maximum permissible lung burden) be reduced by a factor of 115,000, to a value of 0.14 pCi. A recent study 20) was carried out by Bair, Richmond and Wachholz at the request of the U.S. Atomic Energy Commission with the specific objective of providing an updated review of the evidence bearing on the problem of uniform vs