soil of each radionuclide on the island. The concentration ratios of each radionuclide in each food were developed from data obtained from Lawrence Livermore National Laboratory (LLNL) test plots on Janet Island at Enewetak Atoll and Eneu Island at Bikini Atoll, and from coconut, breadfruit and Pandanus trees planted on Bikini Atoll in 1970 by the Trust Territory Government. When sufficient data were collected to ensure confidence in the concentration ratios of each radionuclide in each food, the concentration ratio could be mulitiplied by the average concentration in the soil on each island to predict the radionuclide concentration in a specific food item on that island. For example, the concentration ratio of !8%Cs in coconut meat is 6 in the 0-40 em soil profile encompassing the root zone. The average concentration of 137Cs in the 0-40 em profile on Janet Island is 12 pCi/g; thus the estimated average concentration of 137Cs in coconut meat of trees growing on Janet Island is predicted to be about 72 pCi/g. This approach was used almost exclusively in the entire assessment for Enewetak Atoll and therefore required a very detailed analysis of the concentration of radionuclides in the soil on each of the islands after the cleanup project. 6.11.2 Significant Radionuclides and Exposure Pathways The most significant radionuclides in order of the magnitude of their contribution to the total estimated dose are given in Table 6-7. The exposure pathways in the order of the magnitude of their contribution to the total estimated dose are: Terrestrial foodechain External gamma radiation Marine foodchain Inhalation Drinking water TABLE 6-7. RADIONUCLIDES CONTRIBUTING TO THE ESTIMATED DOSE OF RADIOACTIVITY TO THE POPULATION ON ENEWETAK ATOLL THROUGH LOCALLY GROWN CROPS Radionuclide* Half Life, y 137C¢ 30.9 905, 60Co 29.12 5.27 239,240py 24,000 24lam 432.2 *Radionuclides are listed in the order of the magnitude of their contribution, as of 1980. The most significant radionuclide is 137Cs because it constitutes a considerable part of the total estimated dose in both the terrestrial and external gamma pathways. Strontium-90 is a major component of the radiological dose through the ingestion pathway but most of the contribution from 60Co is through external gamma exposure. The transuranic radionuclides will contribute very little to the total dose over the next few decades; the exposure will be primarily through the inhalation pathway by resuspension processes and secondarily through the marine pathway. The potential re exposure to transuranic elementsis long term, but the estimated doses are very small. 199