1.2 leukemia cases per 10 million population. Averaged over the world population of 2.6 billion, this would produce an increased leukemia burden of 300 cases per year. A world average of 100 puc of Sr® per gram of Ca would be equivalent to about 16,000 cases. The above analogy assumes that Sr” beta radiation induces leukemia of bone marrow origin at the same rate (per unit of absorbed dose) as X and gamma rays. Muchof the beta radiation from Sr® will be absorbed in the bone and not reachthe hematopoietic tissues atall. Experiments by Brueset al.®* suggest that Sr°® (half-life 55 days, Eg = 1.5 Mev) administered to mice is relatively more spectacular as an osteosarcogenic agent than a leukemogenic agent. Furthermore, leukemia was not a significant finding in the radium dial painters®®»”or in the radium-injection cases.>® Bone sarcoma is more apt to result from Sr®™ than is leukemia. Human data on radiationinduced osteogenic sarcoma are not adequate to provide even the crudest estimate of the dose response relationship, the population doubling dose, or the fraction of normal population inci- dence (about 2/100,000) attributable to natural background. Under the same conditions, the potential risk to the population from bone sarcoma, how- ever, would be less than that calculated for leukemia, since its natural incidence in the popula- tion is lower than that of leukemia. Table 9— CONCENTRATION OF Cs""" IN THE GONADS OF RATS Days after administration Concentration gonads /muscle* Testes 2 0.70 5 6.71 10 0.52 Ovaries 2 0.82 * Average of three animals per point. 5.2 Cesium-137 The present average Cs!3" level in the population of the United States is about 45 puc/g body potassium. This is equivalent to 0.006 uc per person. C87 like potassium, is concentrated in muscle and the radiation dose it delivers is essentially whole-body. The dose delivered is equivalent to approximately 1 mr/year. Taking into consideration the respective energies of their radiations, the dose from the present level of Cs'®” is about one-twentieth of that from natural K*’, or about one per cent of the average natural background. If Cs'5" i 8 entering man largely through the ecological cycle, continued testing at the past 5-year rate may result in an average radiation dose to the United States population of about 10 mr/year, or about 10 per cent of natural background, and a weighted world population average of about 7 per cent of background. Because of nonhomogeneities in fallout and uptake, a few persons may receive doses about 5 times the average. If Cs'*" ig entering man largely through direct fallout on vegetation and not through ecological integration, continued testing may not increase the average Cs'"' dose significantly above the present levels. Concern has been expressed” over the possible genetic implications of selective concentrations of Cs'** in the gonads. The data in Table 9 show the ratio of Cs*®? concentration in the gonads of rats to that in muscle. The testes and ovaries concentrate Cs'*’ to the extent of about 70 and 80 per cent of muscle, respectively, and the elimination time from the testes appears shorter. Therefore, the radiation dose delivered to the gonads is comparableto that delivered to muscle, or about 2 mr/year at present United States average Cs'*" levels. 6 DISCUSSION AND SUMMARY Past testing of nuclear weapons has produced between 5 and 6 megacuries of Sr”? (equivalent to 50 to 60 megatons of fission energy). About 90 per cent of the production has occurred 303 on