19 DISCUSSION AND CONCLUSIONS Comparison of Radioactivity between Atolls In order to compare the radioactivity found in biological and environmental samples from the seven atolls and Christmas Island, the results of the analyses of selected samples of soil, plants, and animals were summarized for each atoll. These data are shown in Tables 4 and 5 and in Figure 7. The mean concentration of 13765 | 20H, 241am and 2392405, in surface soil (Table 4) varies significantly between atolls. Soils from Bikini and Rongelap atolls (excepting Rongelap Island and probably other southern islands which were not surveyed) hayg7similar amounts and kinds of radionuclides. In these two areas amounts of 4°’Cs and 90sr usually range from 20 to 300 pCi/g and amounts of 241am and 239,240Pu range from 10 to 80 pCi/g. Soil from a second group of atolls, Rongerik and Ailinginae, plus Rongelap Island has radionuclide concentrations which are about an order of magnitude tess than those noted above. Radioactivity amounts on Utirik, the easternmost atoll sampled in the Marshal] Islands, are 5 to 10 times less than amounts on Rongerik and Ailinginae, but are still higher than amounts found in the single soil sample from Wotho Atoll. This atoll was south of the main pattern of fallout from Bravo which contaminated the other atolls. Kwajalein Atoll is further south and has even lower amounts of radioactivity. With slight variations, the differences between atolls exhibited by the soils can also be seen in Pandanus leaves, a representative plant sample (Figure 7) and in mullet, a representative fish (Table 5). Christmas Island which was contaminated by a different series of tests than the Marshall Islands had lower amounts of fallout radionuclides than any atoll we surveyed in the Marshalls during 1974 and 1975. The naturally occurring radionuclides 40K and 238U were the predominant radionuclides in samples from Christmas Island. Comparison of Radioactivity between Islands in Bikini Atoll Differences in the radioactivity between areas of Bikini Atoll are most apparent in the soil data in Table 4. Soil from Nam Island next to Bravo Crater contains the highest amounts of 137c¢s, 90sr, 241Am and 239,240py of any soil we collected in 1974 and 1975. Samples of soil from Bikini Island contained about one-third the 90Sr and 137cs, and one-tenth the 241Am and 239,240py found in soil from Nam. The 137¢s/90Sr and 241Am/239,240py ratios are similar in the soil from Nam and Bikini (between 1 and 2) indicating that the major source of radionuclides on these two islands was the same test and was probably the Bravo test of 1 March 1954. Enidrik Island in the southern part of Bikini Atoll had less 20Sr, 137Cs and 24lam in the surface soil than did Bikini Istand, but Enidrik soil had about twice as much 239»240py, The ratios of these radionuclides in the soil from Enidrik were 0.25 for 137cs/90Sr and +10 241Am/239»240pu. These ratios are quite different from those found in soil from Nam or Bikini islands and indicate a different source for the fallout on Enidrik. The most likely source was the test series on the west end of Eneman Island, which lies about 1000 meters east of Enidrik. Radioactivity in fish collected from the shallow areas around four islands of Bikini Atoll does not vary as markedly or as consistently as does the radioactivity in the soil. Mullet (Table 5) collected near Bikini Island had higher