TRANSURANIUM RADIONUCLIDES IN COMPONENTS OF THE BENTHIC catastrophic events, little alteration in the present distribution of transuranics in the sediment is anticipated during the next few decades, ENVIRONMENT OF ENEWETAK ATOLL The Atoll seems to have reached a chemical steady state in the V.E. partitioning of 23942405, between soluble and insoluble phases of the Noshkin environment. Lawrence Livermore Laboratory the concentrations in the sediment agrees well with recently measured Environmental Sciences Division California Ob 23942405 amount of dissolved radionuclides predicted to be in equilibrium with University of California Livermore, Using an experimentally determined Ka for average concentrations in the water at both Fnewetak and Pikini Atolls. 94550 The remobilized 2394240 Pu has solute-like characteristics. 1t passes readily and rapidly through dialysis membranes and can be traced ag a solute for considerable distances in the water. the present inventory of We estimate that 50” of 2394240, in sediment wil] be remobilized in solution and discharged to the North Equatorial Paeific aver the next ABSTRACT Data on the concentrations and distributions of transuranium 250 yr. radionuclides in the marine environment of Enewetak Atoll are reviewed, INTRODUCTION The distributions of the transuranics in the lagoon are very heterogeneous. The quantities of transuranics generated during the Nuclear test years at the Atoll and now associated with various sediment components are discussed. Whenever possible, concentrations of Alan and 23942405, are compared. The lagoon is the largest reservoir of tranguranics at the Atoll and radionuclides are remobilized continuously to the hydrosphere from the solid source terms and are cycled with components of the biosphere. Although 2394240, is associated with filterable material in the water column, the amount that is relocated and redeposited to different areas in the lagoon is small. Barring Large inventories of several transuranium radionuclides (Ne73) persist in the marine environment of Enewetak Atoll]. Forty-three nuclear weapons tests were con acted by the United States at Enewetak between 1948 and 1958. ‘he testing produced close~in fallout debris that was contaminated with transuranics and that entered the aquatic environment of the Atoll. More transuranics were transported westward to Enewetak in airborne debris and water contaminated from nuclear testing at Bikini Atol], Global fallout deposited a small] additional amount of transuranics to the Atoll. Presently the largest inventory of E CHI por AR