water at some distance from the atolls are shown for comparison. Table 1 indicates that there are significant spatial and temporal differences in concentrations in the lagoon water. Wherever and wheneverwater was sampledin the lagoon or on the reef, the concen- trations greatly exceeded the 0.3- -to 0.5-pCi/m* fallout background levels in the Equatorial Pacific surface waters. These results are a direct indication that 2°?*24° Pu is continuously mobilized to solution from sourceswithin the atoll and is resuspended to the water column for subsequent redistribution both within and outside the atoll. The mobilized “9?t249 py has solute-like characteristics and is available for uptake by organisms. Figure 3 showsthat different oxida- of the environment. If this state per- (which relates the activity associated with a gram of dry sedisists, mobilization of the entire in_ ment to the activity in a gram of ventory of °?*44 Du from these water) is used to estimate the quanatoll sediments will require more than 400 years. Although this is a tity of 239240 by that can be dissociated from the sediments into long period of time compared to our life span, it is a small fraction of solution. The mode! estimates the radiological half-life of agree well with the measured plutonium. . average concentrations in water at ‘both Enewetak and Bikini. Thus, our experimentally derived and The mobilization field-verified distribution coefficient of plutonium A simple mass-action model em- can be used to predict plutonium ploying an experimentally deterpartitioning between solid-liquid phases. We are determining mined distribution coefficient i a © . oO Ww Hg 239 4 240p,, 40 tion states of 739*299Py coexistin = c 2 cm 5 94% of the dissolved 2997440 py js a - a2 r the lagoon water. From 75% to in the oxidized (+5 or +6) form, while the rest is in a reduced {+3 or +4) state. The atolls have reached a chemical steady state with respect to the partitioning o f 2394240, bo. tween the solution and solid phases ou 3a 3s 238 “Pu z £0 20 a . ; 94% (+5 or +6) 4 75% (+5 or +6) 7 - % 20 a Se] E 5 o NS UO © — a - 10r- aa | oe 0 IPR 3} Ge 4 | yy fo. ty ft 10 20 30 40 50 Total activity of soluble plutonium in seawater — fCi/I Activity of oxidized 7°*“°Py in seawater at various locations in the Enewetak Lagoon compared to the total activity of 60 plutonium in the water. From 75% to 94% of the soluble plutonium is in an oxidized (+5 or +6) form, and the rest is in a reduced {+3 or +4) state. 12