-408- The first Marshall Island workshop was organized and hosted at LLL in June 1977 to discuss long-range planning for the DOE Marshall Island programs. An open exchange of information between al! program participants provided a valuable overview of the radiological problems presently being investigated and those remaining to be studied. In early summer of 1978, we plan to participate in a Woods Hole Oceanographic Institution (WHO!) cruise to the Marshall Island region. Along with Dr. V.T. Bowen of WHO!, we will conduct a variety of plutonium biogeochemical 16. studies in several regions around the atolls. TECHNICAL PROGRESS IN FY 1978: We completed the publications listed in Sec. 13, and, with the data generated by FY 1977, we began writing several other documents describing the results of our Marshal! Islands program. in various stages of completion, include the following: @ These reports, Renewal Rates of Cactus Crater Water. We describe the use of rhodamine dye to estimate the tidal flushing characteristics of Cactus crater. A simple model is developed to explain the water residence time as well as the fate of the crater water and its dissolved constituents. Cactus crater is being considered as the disposal site for radioactive waste accumulated during cleanup operations. The results of this study permit us to evaluate the impact and fate of any radionuclides remobilized to solution in the groundwater after the crater is filled. @ Remobilization of Plutonium Radionuclides from Cactus Crater Sediments at Enewetak Atoll. Data related to the rate of plutonium remobilization from sediments to the water are provided. The remobilized plutonium has solute-like behavior, passing readily through 0.45-um nucleopore filters and dialysis membranes, and can be traced in solution for considerable distances along the reef. @ Plutonium Concentrations in Reef Fish at Enewetak and Bikini Atolls. We compare concentrations in mullet tissue samples from different locations at both atolls. Plutonium available to man from the aquatic environment should be most highly concentrated in food organisms with the smallest number af plutonium transfers between abiotic sources and man. Mullet are inshore fish and in their adult stage feed on detritus extracting organic matter from sediments. This species is an excellenc indicator since the plutonium levels in mullet would be expected to be highest among reef fish commonly caught. Concentration factors, isotopic ratios in the tissues, and other relationships between plutonium concentrations in fish and in the environment are discussed. Concentrations in fish at Bikini differ from those at Enewetak but the average 3