-409- concentration factor for plutonium in fish muscle is similar at both atolls. Thus plutonium concentrations determined in fish at one atoll can be used to predict levels at other atolls. , Gamma-Emitting Radionuclide Concentrations in the Reef Fish, Mullet, from Enewetak and Bikini, We describe radionuclide concentrations, other than the transuranics, in fish tissue at the atolls. Bikini mullet have higher 137¢5 levels associated with muscle tissue than average values found for Enewetak fish. The mean ©9Co levels in muscle tissue of fish from both atolls is similar, and the highest concentrations are associated with reproductive organs. In addition, *°7Bi levels in Enewetak fish exceed those in comparable fish tissue at Bikini, whereas levels of !92Rh above detection limits are found in fish from the islands of Enidrik and !roij of the Bikini Atoll. Residence Time of, Radionuclides in the Groundwater of Enewetak Atoll. Results are summarized on the rates of radionuclide recharge and migration in the groundwater at islands of Enewetak Atoll. The chemical characteristics of plutonium remobilized to groundwater solution are different from those of plutonium found in solution in the lagoon. Radionuclides at Pacific Atolls - Concentrations in the Sedimentary Components and Benthic Organisms at Enewetak and Bikini. We report on al! available radionuclide data for sediment cores, surface sediments, and benthic organisms. Much of the data presented in our report for the forthcoming DOE publication Transuranic Elements in the Environment (see Sec.. 13) were derived from this document. An_!tmproved Thiocyanate Anion-ExchangeProcedure for the Separation of Americium from the Rare Earths. We describe a pressurized separation procedure developed in 1977 that requires less than 2 h to purify americium from 10 to 50 mg of rare earths with an average recovery greater than 90%, Assessment of Potential Dose to Populations from the Transuranic Radionuclides at Enewetak Atoll. This is an expanded report ofan assessment requested by DBER in 1977 and written with W. Robison and W. Phillips, describing the expected transuranic doses to population from the various pathways at the atolls. Data from our work on plutonium concentrations in mullet at Bikini and Enewetak Atolls were used to evaluate the potential dose via the marine foodchain. As a result of a more detailed andcareful analysis, computed plutonium doses from the marine food chain were revised to well below the levels established during the 1972 radiologica} survey.