bone., The figure of 0.7 grams for the "Standard Man" is being borne out by more recent studies. Thus theonly really important correction to the SUNSHINE model which can be madeate this time, then, relates to the first paramoe, ofuniform @istribution. Calculations indicative of howthis cen “affect the results have been given above. It is important to recognize, however, that the SUNSHINE model deliberately strove to make the most "pessimistic" assumption possible; i.e., where a parameter value was in doubt, the value which led to the lowest possible estimate of fission yield was chosen. ‘The range of uncertainty involved is such ‘that had the upper limit been sought instead, it would have been greater than the lower limit of 25,000 MI by as much as a factor of a thousand. Evaluation of the Strontium-90 MPC. As indicated previously, the 1.0 microcurie of strontium-90 maximum permissible concentration _ in man is based essentially on the following relationship: groo Mouse _ (sr?y Human ) eK (sr? Human ) ee Mouse " Ra Human Ra Human The non-bracketed values are observed and the others are calculated. The factor K is introduced to convert the strontium-89 experience to the strontium-90 equivalent. The data leading to the establishment of 1.0 microcurie as the MFC for strontium-90 in man derive from the mouse experiments at the Argonne National Leboratory and the acceptance of 0.1 pgm of radium as being 0.1 of the lowest amount of that element in humans that has been found to be associated with tumor formation. The strontiwn-90 MFC value, therefore, is critically dependent upon the strontium-89 effects data originating from one laboratory and on the strontium-89/radium effects ratio derived from one species of lower animal and the extrapo- lation of this ratio to strontium-90 equivalent in man. This is obviously a rather tenuous basis for establishment of such an important standard. able. In addition, the radium experience in man is far from reli- The clinical data are sparse; the collection of cases is not 120