23 from sediments (No78b) at higher concentrations than those in the weight, and the concentrations in the water where the algae were overlying bottom water at Enewetak Atoll, obtained ranged from 10 to 116 fCi/]. By equilibration, small quantities of 2394240), | from the sediments are exchanged and released . Surface sediment concentrations at the stations (No78a, Ne75) were compared to the algae concentrations Vertical diffusion moves the radionuclides to the sediment water at these sites. interface where the plutonium mixes with the lagoon water mass. associated with the Halimeda spectes (pCi/g dry weight) Remobilized plutonium can then be concentrated by members of the marine top 2.5-em sediment layer (pCi/g dry weight) was 0,24 + 0.13 aud the food chain. 24d concentration ratio wus 0.32 # 0.24, Vertical diffusion can also move the exchanged plutonium in the interstitial fluid deeper into the sediment column, Exchange of The average ratio of the 2394240), concentrations to that in the Concentrations and 24d an in the sediment ranged from 9 to 0? pli/y and irom 1.1 Plutonium with exposed carbonate surfaces might account for the pCi/g, respectively, concentrations associated with material decper in the sediment column, algae have lower PSO cmd PAT Ay levels than sediments immediate environment. TRANSURANICS ASSOCTATED WITH THE CALCAREOUS ALGAE, HALIMEDA Debris from the calcareous algae, Halimeda, is the second most of 23924, ratio of 2394240 On an equivalent werght baste the te 67 live henthic in the The average plant to sedinent concentration 24 : : Pu and * Van are uot statistically different. . ‘Thus, 2394240, and 24d in processes there is no discrimination between abundant component of Enewetak Lagoon sediments (£m54) and covers an beginning with remobilization of the transuranics fron tie envaronrent estimated 26% of the lagoon floor (Im54). and ending with concentration by the algac. Live species were collected by divers and during dredging operations from numerous locations at both Enewetak and Bikini. Because algae were shown previously to concentrate Table 4 summarizes data on transuranic concentrations in alae, water, and sediment from Cactus Crater at Emnewetak, The data show that plutonium (No72), the role of this benthic algae is recycling the the 238), 23240, ratio in the plants, water, and sediment are transuranics at the Atoll should be assessed. identical. The mean concentration factor for 2394240 Pu associated with algae In this crater ecosystem marine alyae do not discrinuinate among the plutonium isotopes in the environment. Tho plaunt:isedivert species from both Atolls is 6 x 10° and ranges from 1 x to 32 x 104 concentration ratios of 2394240), and 241, are neariy (No78a). again shows that the processes of environmental release and plant uptake To within the precision of our Measurements, the concentration factors for plutonium at the two atolls and of different Halimeda species from both atolls do not differ (No78a). 239+ 24 Concentrations of OBy associated with the live algac ranged from 0.4 to 22 pci/g wet iventiceal, which of the two transuranics are similar, The mean surface sediment inventory of Ci (Table 1). The lagoon is 933 km” Pu et FPrneretak is 249 in area and the average specific