a specitic concern(®.ti plutonium, and, ta a less€extent, othor transuranics. Under a number of circumstances piutoniun forms aeroscls. The physical character of these aerosols is such that on inhalation by humans they are preverentially depesited in respiratory tissue, Because of slow clearance and because of their insoluble character, particles may experience Tong “esidence times in tissue. An appreciabtc.riass fraction of the aerosol is usually associated with particles sufficiently large that smal] but physiologically Significant volumes of tissue will be exposed to intense (i.e., orcanisn lethal or greater) radiation doses within a meaningful nhysielodical time. Studies of the effects of intense Toca] radiation to skin and kidney tisste indicate that cespite the near mitctic sterilization of the involved tissue, an enhanced carcinogenic response may occur, in the sense that energy dissipated in a limited volume may be far more carcinogenic than if the same type of radiation were to dissipate its energy over a much larger tissue mass. The question is then: do particulates of plutoniua lead to exposures that have enhanced carcinogenic potential? If they do, then present standards can be in error by orders of rlagnitude. Notice that the emphasis here is on the anomalous hazard associated with a single particle; and that if any threshold is relevant, it is nota dose 4threshold since local exposures are large, but rather a possible volumetric threshold that must be exceaded by the physical extent of the exposure. Plutonium, as-an insoluble aerosol-forming, long-lived alpha-emitter, constitutes a very special case of the Tow exposure problen. In conclusion, it is indefensible to base estimates of cancer risk on the mathod of dose’ averaging over fictitiously large volumes. Similarly, estimates based on non ‘conservative Interpretations of the Henford boayle results are highly suspect. Soper . +e, ARE,eae ie 4s . . ey gt i y hi Cal Tt Re wit whtaniN ms. *, none H Vea a i S EeBeya Ag te