Page 147
Radionuclides in Pacific Plankton and Tuna
eo
‘tration of these radionuclides by the organisms
was evident.
In the food chain under consideration, the
on are fed upon by omnivorous fish. Carnivpious fish, in turn, feed upon the omnivores and
probably, to a lesser degree, on the plankton.
During the 1958 surveys samples of plankton
and omnivorous flying. fish were taken at the same isampling station in an area which had been contam
tuna
nated by fallout about one week earlier. The west
(carnivores) samples were collected south and
of the sampling station, described above, about
five weeks later.
The plankton and omnivorous fish may be as-
sumed to have remained in the contaminated body of
water during the week following fallout and the to-
tal radioaetivity and the levels of individual
radionuclides contained in these organisms may be
directly compared.
However, the total radioactivi-
ty in the tissues and organs of the tunas cannot be
directly compared with that in the plankton or om-
nivorous fish. Tunas are pelagic fishes and are
capable of migrating great distances, in comparison
to the size of the main mass of the contaminated
area, in short periods of time.
Thus the length of
time that the fish remained in the contaminated
area
prior to being taken cannot be determined.
The levels of individual elements in the organos and
tissues of the tunas can be compared with those in
the other organisms, however, if the total time
spent in the contaminated area by the tunas is rela-
tively long in comparison to the biological half-
life of the elements in these fish.
The tunas were
taken in a mass of water that had been contaminated
for about six weeks. During this time the contaminated body of water had been dispersed over an
area with a diameter of several hundred miles al-
though a central area of higher radioactivity still
persisted.
If one assumes a more or less random
movement of the tunas and if a similar distribution
of radionuclides is found in the same organs of
different fish, it is probable that the tunas had
sufficiently long for the individual radionuclides
within the tissue and organs to have reached a
State of equilibrium with the radionuclides in the
food items. The average level of radioactivity in
the food items would not necessarily be the same,
however, as those of the food items taken at the
above described sampling station.
In Table 2 is shown the percentage of fotal
radioactivity contributed by individual radionu-
.clides in plankton and flying fish at one week and
in tunas and water at six weeks after contamination.
they were present only in trace amounts
vorous flying fish.
In the tuna tissues and organs
the only fission product that was detected was cesium-137 which was present in one sample of white
muscle. The cesium-137 in this sample accounted
for only 1.1 per cent (36 disintegrations per minute per gram of dry weight) of the total radioactivity and was present at about the same percen~
tage value of total radioactivity as that in the
water.
Cesium-137 is present in solution in sea
water and would be expected to follow the w/t@es
of naturally occurring potassium which is c§ncentrated in muscle tissue.
Radioisotopes of manganese,
iron,
cobalt, and
zinc contributed 62 per cent of the total radio-
activity in the plankton and almost 100 per cent
in the omnivorous and carnivorous fishes.
Metabolism is similar in all forms of life at
the cellular level in both plants and animals al-
though they may differ significantly in form and
complexity. Marine plants and animals tend to con-
centrate the stable transition elements manganese,
iron, copper, cobalt, and zinc which become tightly
bound to the organisms (Krumholz et al., 1957).
The details of the processes involved in the uptake of these elements have been discussed elsewhere (Lowman, 1960) and will not be reviewed
again. However, observations by Korringa (1952)
and Lehninger (1951) indicate that marine organisms
tend to concentrate positive polyvalent ions but
not positive monovalent ions although the latter
may be present in the environment in high amounts.
The ability of the transition elements to form
complexes with biological materials is usuaily not
affected by the chemical composition of the biolobiological complex is usually in the following
‘biological order.
“
"Mn
< Fe++
<cot* < mitt < cut | > mnt
Uptake of the radioisotopes of these elements from
sea water by the plankton probably reflects the
stability of the metal-biological substrate described above. In plankton samples taken at approximately one and six weeks (Table 1) the order of uptake in relation to the levels of radioisotopes in
Percentage of total radioactivity contribdted by fission products and by the neutroainduced isotopes uranium-237, cobalt-57, 58, 60; iron-55, 59; zinc-65, and manganese54 determined in plankton and fish samples collected at the Eniwetok Proving Ground
in 1958.
The total radioactivity per gram dry weight is also shown.
Water! Plankton
Ruthenium, zirconium and uranium
Barium-140; lanthanum-140
Cesium-137; barium-137m
Cobalt-57, 58, 60
pron-55, 59
Zinc-65
anganese-54
Total radioactivity
(disintegrations per minute
per gram dry weight)
the plankton,
in the white muscle and liver samples of the omni-
gical sustrate, and the stability of the metal-
remained in some part of the contaminated area
Table 2.
The total disintegration rates for the radioactivity
in the biological samples are also given. Aithough
the fission products plus uranium-237 accounted
for 36 per cent of the radioactivity associated with
Flying Fish
White
muscle
Liver
White muscle
A
B
trace
0.0
0.0
8.7
81.3
9.9
0.0
0.0
0.0
1.1
0.9
5.8
91.9
0.2
0.0
0.0
0.0
2.5
8.1
89.0
0.4
0.0
0.0
0.0
0.0
25.5
74.5
0.0
0.0
0.0
Q.0
2.3
15.0
82.6
0.1
0.0
0.0
0.0
1.t
12.4
86.3
0.2
9.0
0.0
0.0
2.1
9.7
38.0
0.2
1.1
:
x
.
33
1.2
xX
.
376
.O
>.
.
53
.
2°
52.0
18.0
0.08
0.67
0.93
0.84
0.12
13.0
23.0
0.0
43.0
16.0
3.0
0.0
trace
0.0
0.9
19.0
31.3
58 .8
0.0
-
2.3
.
x
2.2
:
x
108
Tuna
104
10°
107
104
Liver
10?
D
~=s_-0°
Dark musclg
A
B
10°
107
vat six weeks.
from four different fish: A = big
fin tuna; D = big eye tune. &
= yellow
Cauples
e ey e tuna
(Thunnus obe us) ;:.B =
yellow fin tuna (Thunnus albacares) ;’
DOE ARCIUVES