ca 1332. FALLOUT FROM NUCLEAR WEAPONS TESTS RESULTS AND DISCUSSION. Cestuml3? mcretion Levels and Sody Burden The urinary excretion levels of cesiuml3? for the years 1954, 1957, and 1958 are shown in Tables 1 - 4. On 24 - 25 March, 1954, the mean excretion level of cesium 37 for all age groups was 4C5 uve per liter. With an excretion rate of 0.46 percent (4) of cesium!37 pody burden per 24 hours, the mean body burden from fallout 24 - 25 days after exposure was 405/4.6x1073 x 10° (+ 54 percent). 6 or 88 me This value is about 20 times the average body burden reported by E. C. Anderson, et al (5, 6) for people measured during 1956 - 1957 in the United States. The cesium37 urinary excretion levels for the six months follow- . ing exposure can be expressed as an exponential function, and a best line of fit drawn through the data resulted in a half time for elimination of about 110 days (Pig 1). A biological half time of about 140 days has been observed on volunteers who ingested one microcurie of radio-cesium (4). From the 1957 Cs+37 excretion levels (Table 2) the Rongelap group exposed to fallout was estimated to have an average burden of about 7 mic, whereas the Rongelap control group was about 2 mc. Body burden in either group in 1957 ie comparable to levels measured in the U. S. population (6). With a half time for elimination of the order of 150 days, the body burden of the exposed Rongelap group should have decreased from the March 1954 level to 7 muc in about 550 days, or late in 1955. A body burden of 7 mc for this group in March 1957 could then indicate a continuing exposure to cal 37 during 1956 of the order of 32 micromicrocurics per day from stratospheric-tropospheric fallout while residing on Majuro. Since the Utirik group was returned to their atoll in 1954, the mean body Dunien in 1957 was elevated to an eatimated 337 mc, some 48 times the Csl37 burden of the exposed Rongelap people who resided on Majuro. time on Utirik atoll after fallput contamination, This long residency as compared to the excretion