44 WORLDWIDE EFFECTS OF ATOMIC WEAPONS BIOMEDICAL CONSIDERATIONS problem in a tissue such as the skeleton, the estimation of the concentration, and so the radiation dose, was considered too uncertain. ) analysis figures have been questioned, this calculation is included as an illustration and any quantitative implications should be deferred until an acceptable average amount for available strontium in the soil is at hand. If we consider 27,000 gm (60 Ib) of strontium to be available per acre of land, then approximately 200 yg of Sr°° maintained will define an acre's contribution to the diet as one that eventually will result in the maximum permissible body-burden level. The published data on radium exposure in man indicate that an oste- ogenic sarcoma has been found with a radium burden as low as 1.2 pg. Thus, the maximum permissible body burden has been set at one-tenth of the lowest amount known to be carcinogenic. However, skeletal changes have appeared in roentgenograms of people with body burdens as low as 0.4 pg. It appears probable that the radium safety level will have to be reduced as more cases are followed and evaluated. It is also important to remember that the International Commission on Radiological Protection was considering occupational exposure. This means that they were interested in evaluating the risk of a limited number of adults. In considering a worldwide population exposure we must remember that children are at risk, that the total years of exposure are also greater, and that a safety factor that is acceptable for, say, one hundred thousand people might not be acceptable for three billion people. In summary, then, it would seem that, from the medical point of view, there are enough uncertainties in the picture to indicate that the presently accepted maximum permissible body burden may have to be lowered. (For another point of view, see “Remarks on Calculation of Worldwide Contamination,” Appendix I, page 71.) SOME CALCULATIONS If we accept the maximum permissible concentration of Sr°* as being 1 pc (i.e, 5 X 10° pg) and the amount ofstrontium in the adult skeleton as being 0.7 gm, then ratio of ) (=) a ( Sr = 7 Sr On the basis of uniform distribution, the maintenance of the earth, including arable land, at this level will require 2.5 10’ gm of Sr. This amount of Sr” is created by nuclear detonation totaling 2.5 & 10‘ MT. SUMMARY AND CONCLUSIONS 1. The importance of Sr’ as a hazard to human beings has been discussed. 2. The reasons why Sr” is the limiting factor relative to human hazard from nonimmediate effects of the atomic bomb have beenindicated. 3. The relationship between calcium,inert strontium, and Sr°® has been presented and a method for quantitatively assessing the hazard problem has been suggested. 4. The uncertainties regarding safety standards have been pointed out. 5. The lack of firm quantitative chemical analyses with regard to strontium in the soil, etc., is indicated, and it is strongly suggested that these data be obtained. 6. In view of all the uncertainties involved, it is suggested that a food and water monitoring system be set up to assay the Sr essentially at the point of ingestion. - = noll 45 body x 10 REFERENCES , in the ingested material (each in a form of equal availability) will bring a epenmissibleeromtb period of Ota 20 years. It is also possible to calculate the amount of St°" that, when deposited in the agricultural soil, will bring people living off the products of that soil to the level of the MPC. In view of the fact that the strontium soil- 1. MrrcuHert, H. H., “The Chemical Composition of the Adult Human Body and Its Bearing on the Biochemistry of Growth,” J. Biol. Chem., Vol. 158, 1945, p. 625. 2. Best, C. H., AND N. B. Tayior, The j , Wilkins Company, Baltimore, 1950, p. 823. illiams & 3. Pecner, C., “Biological Investigations with Radioactive Calcium and Strontium,” Pharmacology, Vol. 2, University of California, 1942, p. 117. -