[You. 91 ‘from plant ited as 0.13. (DF;) and ited as 0.25. ., the popuerived from soi to bone = (08x 1.0 rium Sr-90/ 1964] YWARTIN : RADIOECOLOGY AND STUDY OF ENVIRONMENTAL RADIATION ~Average Sr-90 in U.S. milk as. “od as expresses ue 1 =o 9 Average Sr-90 Average Sr-90 in U.S.soil cad 4e aias 315 +2.6 — deposition for : preceding month, expresse a as me/m? According to estimates based on this formula, 51% to 83% of the Sr-90 in U, S. milk (an average of 69%) during 1958 was derived from soil, and the remaining 17% to 49% (an average of 31%) was derived from worldwide fallout. Burton et al. (1960) have reported that 20% of the Sr-90 in milk produced in the United Kingdom during 1958 was derived from soil are known, a deposited tion, Allowexpression, ie fractions ces, respec- deposits and 80% from fresh fallout. The difference between Knapp’s interpretation of Sr-90 levels in U. S. milk and Burton et al.’s interpretation of data collected in the United Kingdom have not been explained, but it seems owance for ja are uni- and by Langham and Anderson (1959) and has been used by Dunning (1962) to predict the maximum possible levels of Sr-90 in U. 8. milk and in the total diet of people living in the U. 8. The soil and fallout levels used for this purpose are based on the prediction that fallout from the 1961 test series in Russia will raise the average concentration of Sr-90 in U. 8. soils from about 80 to about 125 me/mi’. Aceording to Dunning (1962): lis sort are s of radiout but are n Dret. The ry Commisthe United rograms to ods, and in s generally d bones of ;may vary concentra- l-wide fallve studied yposed emiman diets wssimilated U.S. milk and seems quite likely that a reasonable explanation of these differences could be found by making detailed studies and comparisons of the Sr-90 fallout and its eyclmg in representative pasture ecosystems in the two countries. The formula outlined below is similar to those proposed by Knapp (1961) C= aT +bR, where: C = concentration (Sr Units) in diet T = total deposition (me/mi? = 125) R = rate of Sr-90 fallout (me/mi*/yr = 45) _a & b= proportionality constants: For U. 8. milk :a=0.1 & b=0.4 For total diet :a=0.15 & b=0,2 Bycaleulation, C = (0.1 x 125) + (0.2 x 45) = 21.5 Sr Units in milk; and C = (0.15 x 125) + (0.2 x 45) = 36.75 Sr Units in the total diet of people living in the U. S. during 1962. Because the formula assumes that 100% of the fallout on the U. 8. will oceur in one year, these estimates are probably too high. Ecological models of the kind described above are particularly useful in helping to evaluate, on a nation-wide or world-wide seale, the potential shortand long-term hazards of fallout to human populations. Theyprovide a basis for predicting future levels of particular fission products in human populations and in parts of the food-chains leading to man.