38 BIOMEDICAL CONSIDERATIONS WORLDWIDE EFFECTS OF ATOMIC WEAPONS Table 4 3. It has a long physical half-life. 4. STRONTIUM CONTENT OF HUMAN BONES It is a bone-seeking element in animal metabolism and therefore will have a long biological half-life. Strontium in Human Bone Ash (in %) CALCIUM AND STRONTIUM METABOLISM It is proper to point out that very little is known about the strontium pathway in the human, However, there are certain relationships estab- lished between calcium and strontium metabolism that will enable us to circumvent the constriction of “strontium ignorance” by paying attention to certain quantitative aspects of calcium metabolism. Another important point to consider is the fact that, unlike radium, Sr Ao will find its way into the human economy in mixture with its stable tsotope.” We are thus confronted with a crade tracer-type experiment in which the radioactive material of interest will be quantitatively modified by its relationship to the inert carrier, and that the inert carrier must, inferentially, be evaluated via an assumed relation to calcium metabolism. Calcium plays an important role in several body functions, but quantitatively about 99 per cent of the element is found in the bones; we may therefore restrict ourselves to bone metabolism. As strontium follows a similar metabolic pathway, our chief items of concern will be deposition and accumulation of radioactivity in bone. The strontium content of human bones, which forms the basis for subse- quent quantitave considerations,is given in Table 4. The values given in Table 4 are of considerable interest. The relatively constant amount of strontium present holds for all age groups and also for the cadavers preserved since 1914. This would indicate that the variations existing in diet, etc., between the people dying in 1914 (these were all adults) and those dying in 1949 did not appreciably affect the strontium content of the bones. Also, the data indicate a fairly uniform distribution of the strontium throughout the skeleton. anhalt and 7000 gm to be the average weight of the skeleton (50 per centof this is ash), we artive at 0.7 pm as the average content of strontium in the adult skeleton. “Except possibly through direst inhalation cf atomic bomb debris; but see Appendix IV. 39 Parietal Vertebra | Rib Femur Fetus 0.016 0.016 0.017 0.017 All ages 0.023 0.622 0.022 0.022 "1914" cadavers 0.027 ..... 0.027 0.025 Sourcn: R. M. Hodges, “The Strontium Content of Human Bones,” J. Biol. Chem., Vol. 185, 1950, p. 519. NOTE: 1. The fetal bones showed a total range of 0.015 per cent to 0.019 per cent. 2. The “All-age’’ group showed no significant increase with age when analyses were compared in five age groups. 3. Except for a 5-month-old female with hydrocephalus and with values of 0.053 per cent to 0.055 per cent, almost all values were in the range of 0.017 per cent to 0.029 per cent, Figure 3 is a plot of calcium accumulation versus age." These are experimental data taken from growth studies on boys. Assuming that strontium is deposited in bone at the samerelative rate as calcium, we can use this curve to arrive at the strontium content for any age. The right ordinate indicates the strontium values plotted for a final Sr/Ca weight ratio of 7 X 107. Figure 4 indicates the daily accretion of calcium and strontium at various ages. Here again the calcium values are experimental and the stronttum values are added, so that the above ratio applies. It is obvious from this graph that the growth years are the ones that will define the tolerance levels allowable in the environment. Figure 5 plots data regarding calcium deposition in the fetus and is included as a guide for interpreting the results of fetal samples should this ohadacpeundesiakenn Someaspects of bone formation and structure are important with regard to the Sr’ problem. The mostactive site of bone formation, and therefore the place of greatest deposition of calcium andstrontium,is tn the region of the epiphyses. It is here that the long bones grow in length by the