ww woo neutrophite counts below 2000 at some time daring the observatian Period, vtud EO per cent had th the dop and mouse 8 approximately 50 to FOO rare required to lower Che neatrophtte count by 1000 cetisstmint in the ugh sublethal dose range. (C6 these datie cai be applied ta man, an additional 50 to 100 rb would have placed the dose tu the tethucd manpe. Oo the offer hand, . however, Was clear from the present data that ueutrophile counts between LOOO and 2000 in human bemgs are well talerated. Human bemes with these levels of neut rophiles show no efint eat evidence of tliness, are physically active, and do not need prophylactic antibtatie therapy. The Rongelap people are estimated to have received 175 rias calculated from dose rate readings measured in air inthe plane fission product field. From the preceding paragraph it is seen that an additional 50 to 100 ¢ of laboratory radiation or an average of 75 r, probably would have resulted in some fatality. Correcting this average value geometry,* it follows that the minimal lethal dose (MLD) for man exposed in a fission product field is approximately 225 r measured in air. It is possible also to estimate the added increment of dose that would have resulted in some mortality among the Rongelap people fram consideration of the minimum platelet counts observed, the platelet levels in dogs exposed in the high sublethal ranyge and the estimated rate of decrease of plitelet level with increasing dose in this dosage range. Such an analysis leads to the same conclusions as those derived from neutrophile data. 4.43.7) - i Peripheral Counts as an Index of Severity of Exposure The refative value of the several hematological determinations in estimating the degree of exposure, as well as the approximate dose ranzes over which maximumsensitivity for each determination exists, can be estimated by comparing the degree of hematological change among the several exposure groups. The relative degree of change in neutrophiles, lymphocyte. and platelets can be seen in Tables 4.2 to 4.5 and Figs. 4.9 to 4.11. Lymphocyte counts were depressed appreciably even in the low-exposure Utirik group. In the higher dose groups, however, with widely different physical estimates of exposure the lymphocyte counts showed essentially identical degrees of depression. The lymphocyte counts ofthe Rongelap and Ail'nginae “roups were constantly depressed at a levei of approximately 2000 cells. Thus while sensitive at very low doses, this endpoint may be a poor index of the degree of exposure at higher doses. The total neutrophile count of the Rongelap group was consistently more depressed than was that of the Ailinginae group and the difference was of the order of 500 to 1000 cells. However, day-to-day wide fluctuations in the neutrophile counts occurred. Accordingly this endpoint appeared to be of limited usefulness as an index of relative exposure severity except when counts on groups to be compared are performed at the same time. The platelet count showed a more systematic trend than did the neutrophile count. Differ- . ‘ : . vate ences between the low-dose Utirik group and controls at the time of maximum depression for all groups could be detected, and appreciable differences existed between the means for the Marshallese higher exposure groups, Platelet counting is as easily carrted out and more reproducible than leukocyte counts.75 8? Thus the platelet ccunt may peove to be a useful index of deperee of exposure throughout the sublethal cane. The above-considerations are in accord with previous Findings on human beimes and an mals, *From geometric and depth dose considerations set forth in chapter 1, t ¢ measured in air ‘in a fission product field 1s equivalent in its effect on man to approximately 1.5 r of penetrating x- or gamma radiation under geometric conditions usually used in the laboratory. Thus the minimal lethal dose for man exposed to penetrating radiation under the usual laboratory con- . ditions would be approximately 335 r. wtoeee We J ' counts below 1000. By this criterion, then, the effective dose recerved by the Ronpelap peaple approached the ftethal range, ne etnoe re ‘