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