Strontium-90 in Man V The concentration in the bones of children had been dropping, but recent tests will reverse the trend

1) It is now possible to predict the strontium-90 concentration in the world population for specified modes of atmospheric contamination with moderate reliability. For example, the average adult bone level in the eastern United States 5 years after the detonation of a specified quantity of fission products into the lower polar stratosphere can probably be estimated to better than ± 50 percent. 2) The concentration of strontium-90 in fetuses reached a maximum of 1.2 micromicrocuries of strontium-90 per gram of calcium in eastern North America and began to decrease significantly in 1960 and 1961. The ratio of the strontium-90 level in the fetus to the level in the average diet of the adult is about 0.08. 3) The average rate of turnover of strontium and calcium in the adult skeleton appears to be about 2.5 percent per year, although there is considerable difference among the various bones of the body. 4) The standard deviation for strontium-90 concentration in a population of urban adults appears to be about 40 percent of the mean. The distribution curve for an interval of from 60 to 0.1 percent of the population may be approximated by the log-normal function. In urban populations of Western culture the concentration for 5 percent of the population will exceed twice the mean, that for 0.1 percent will exceed four times the mean. 5) Cities in the Southern Hemisphere showed levels in bone about half those for cities of Western culture in the Northern Hemisphere in 1960, yet the fallout in the Southern Hemisphere is only one-fourth that in the Northern Hemisphere. This is attributed to differences in diet, with a higher milk component in the Northern Hemisphere. 6) A simple model for the strontium-90 concentration in the bones of young people as a function of their age appears to fit the experimental data. 7) The coefficients of the equation describing the relative contributions of the rate of fallout (direct absorption) and the cumulative deposit (soil up-take) to the strontium-90 concentration in milk have been calculated from the observed data for 1959 and 1960. They are as follows: rate factor A = 0.65 micromicrocurie of strontium-90 per gram of calcium in milk per millicurie of strontium-90 per square mile during the growing season; cumulative-deposit factor B = 0.12 micromicrocurie of strontium-90 per gram of calcium in milk per millicurie of strontium-90 per square mile at the midpoint of the growing season. The predicted levels in milk for 1958 obtained with these coefficients are in excellent agreement with the observed levels. In 1958 and 1959 about half the strontium-90 in milk was attributable to the rate factor, whereas in 1960 the contribution of the rate factor dropped to about 15 percent. 8) Future levels of strontium-90 in man are given (i) for the next decade as a result of the nuclear tests through 1961 and (ii) under the assumption that 1.0 megacurie of strontium-90 is added to the stratosphere of the Northern Hemisphere each year. 9) The radiation doses to the skeleton to be expected from world-wide fallout on the basis of a 3000-megaton (fission yield) war are also given.