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