tropospheric latitudinally localized world-wide fallout have occurred from subsequent weapons tests by the Russians and the Redwing series completed last summer at the Eniwatok Proving Grounds. II. A. RESEARCH FINDINGS Amount of Fallout and Expected gr90 Body Burden from Weapons Fired to Date. ~ Since our last report ,2/ further data on the actual magnitude of fallout in various places in the world and in various selected spots in the food chain have bee come available. We shall summarize the results. Some human bona now contains radioactive strontium at levels of about 1/1000 of maximum permissible concentration (0.001 MPC; the MPC is 1 microcurie of Sr90 for the standard man and proportionally less for children and is the maximum permissible ccncentration) in the northern latitudes where the bombs have been fired and the world-wide tropospheric fallout has occurred. There is evidence in the data on human material that age is a factor, e.g., older _ people having had their calcium deposited prior to the weapons tests show lower concentrations, though in some instances exceptions to this rule are te be found. Lower levels are found in the Southern Hemisphere where the major contamination is due solely to the world-wide stratospheric fallout which in the northern latitudes of 10°N to 50°N is generally less than one-half or onequarter of the total fallout. The deposition in the human body seems roughly to parallel the levels of the total fallout. More data are necessary to fully validate this point. At the end of 1955, the total deposition in the upper midwest of the United States was some 13 mc/mi2 of Sr90. In the spring of 1956, this total rose to about 16 mce/mir. 2/ "Radioactive Strontium Fallout," W. F. Libby, Proc. Nat. Acad. Sci., &2, 365 (1956). (more)