31 variety of sediments, 32 Considering the difference in the types of two. Although this is not a large discrepancy, the average environmental samples represented in Table 6, it is striking that the Ky concentration, as was mentioned previously, probably does not represent for plutonium differs so little. the real mean for the lagoon at the time sampled. Table 1 shows that the mean plutonium inventory associated with the sediment components in the top 2.5 cm at Enewetak is 249 Ci. sediment has an average density of 1.8 g/om? of 933 km’ The lagoon (—m54) and occupies an area The mean depth of the lagoon is 47.4 m, Using this data Using the appropriate dimensions for the Bikini Lagoon, sediment data from Table 1, and the Ky fo r 2394240, u, the average inventory in the water column and concentration computed at Bikini are 1.7 Ci and 60 fCi/1, respectively. During December 1972, the mean soluble 2594240), inventory and and the Ka for plutonium of 1,8 x 10°, a simple model can be constructed concentration in the lagoon water were 1.2 Ci and 42 + 21 fCi/], to predict the average concentration expected in the lagoon water by respectively (No74), and in January 1977 the respective values were 1.4 assuming that the plutonium in solution is in equilibrium with that in Ci and 49 + 21 {Ci/l (No78b), the sediments. with the amounts predicted, At any time the amount of plutonium in solution is limited by the saturation of the solution under equilibrium conditions, These average values also are consistent For many reasons, it may be argued that some of this agreement is The rate at which water and the dissolved plutonium is flushed from the fortuitous. lagoon is balenced by input of uncontaminated ocean water, which is computed and twice-measured average concentrations in both lagoons rapidly saturated with remohilized plutonium from the Atoll source between 1972 and 1977, the general usefulness of this simple equilibrium terms. model in predicting long term average concentrations in lagoon water is If plutonium is cycled through an intermediate host such as the Nevertheless, having found peneral agreement between Halimeda, the rate at which plutonium is released from decaying plants demonstrated. must be balenced by uptake in the new growth, thereby maintaining a coral sections (No?75, No78a), State of equilibrium. with dissolved species is estimated to be exchanged approximately twice Given that equilibrium conditions exist, the mean From radiclogical records retained in yearly prowth of Bikini and Inewetak Lagoon water along, plutonium inventory in the lugoon water and concentration expected in per yr. solution computed from the basic equation relating Ka to water and slightly more than 250 yr will be required té reduce the plutoniur sediment concentrations are 1.4 Ci and 32 £Ci/l, respectively. inventory in the sediment by 50%, There is At this rate of exchange under stecdy state conditions, The rates of the mobilization and general agreement between the average quantity of 23942405, predicted migration processes of plutonium away from the Atoll to the equatorial and measured in solution (see Table 5). Pacific waters are much faster than the rate of radfoactive decay, In 1976 the computed value differed from the measured mean soluble concentration by a factor of These figures and results should be considered when the consequenccs of