DISCUSSION AND CONCLUSIONS Comparison Between Atolls ~ Moving in a northerly direction, radioactivity values were least in the samples from Wotje Atoll, increased slightly at Ailuk Atoll and increased significantly at Utirik. From Utirik, radioactivity values increased to the west. Thus, Rongelap Atoll had higher values than Utirik and Bikini had the highest values of any atoll sampled during this survey. This pattern has been noted previously (Nelson, 1977) and is a result of the fallout distribution from the 1 March, 1954 Bravo test on Bikini Atoll. The south to north increase in radioactivity is also apparent at Rongelap Atoll where the southern islands have radioactivity levels about a factor of ten lower than the northern islands. Differences Due to Sample Type As noted previously (Nelson, 1977) 9°Sr and 137Cs are the predominant radionuclides in biological and soil samples from the terrestrial environment. In addition, 2%!Am and 239°240Py are important in soils from Rongelap Atoll and Bikini Atoll? (Nelson, 1977) because of the quantity of these radionuclides and because they are alpha-emitters, which have a higher potential health hazard than most of the gamma-emitters. Pandanus leaves continue to be the best indicator species for !37Cs because they concentrate 137Cs and are abundant and available through the year. These leaves may also be used as an indicator for 9°Sr, if coconut crabs are not available. The exoskeleton of these crabs contains more 9°Sr than any other biological sample measured; however, these crabs are often absent or scarce on the more populated islands. In the marine environment, “°K is the predominant radionuclide. Cobalt-60 was the only fallout radionuclide present in a significant number of the marine samples and the values for this radionuclide were usually Tess than a pCi. 15