Iron and Cobalt in Ecology
which
they
were taken had been contaminated,
The plankton contained only a small fraction
of the total radioactivity, however, the amounts
of radioactivity per unit volume, ine luding
radioactive iron and cobalt, were much greater in
plankton than water, In Table 3 the average percentage of total radioactivity contributed by the
principal radionuclides in sea water and plankton
at times less than 48 hours, one week, and six
weeks after contamination are shown, At 48 hours
the percentage compositions of water and plankton
were Similar,
indicating little or no selectivity.
However, at one week cobalt-57,58,60, and
jron-55,59 contributed 43 percent and 16 percent,
respectively, of the total radioactivity in
plankton and 0,05 percent each of the total ra-
dioactivity in the water, Therefore, at one week
the radioisotopes of iron and cobalt accounted
for 59 percent of the radioactivity in the plankton but only 0.1 percent in the water.
were
At six weeks, radioactive tron and cobalt
present in plankton at a level which ac-
counted for 48 percent of the total radioactivity,
each element contributing 24 percent of the total
radioactivity. In the water, iron and cobalt accounted for 0,93 and 0.67 percent respectively of
the total,
The concentration factors exhibited by the
plankton at six weeks after contamination were approximately 90,000 for iron and 100,000 for co-
balt. The iron value is approximately one half
of that reported by Krumholz and Foster (1957),
for freshwater phytoplankton which have a much
larger surface to volume ratio than do the zooplankton,
The plankton considered
primarily two trophic levels
the phytoplankton or primary
zooplankton. The zooplankton
orous fishes (flying fishes)
above comprise
in the food chain,
producers and the
are eaten by omnivwhich are in turn
eaten by the carnivorous fishes
(tunas).
The
radionuclide composition of the two types of
fishes have been discussed in another paper of
this series (Lowman, 1962), and will not be conSidered in detail, however, the distribution pattern of cobalt-57,58,60, and iron-55,59, in the
three trophic levels are as follows:
Per cent of total Radioactivity
Tine
Total radioactivafter
ity (disintregracontam-—
tions per minute
imation
CobaltIronper gram of dry
Plankton
Onnivorous
fish
Muscle
Liver
Carnivorous
fish
Muscle
;
Liver
(weeks)
57,58,60
55,59
1
43
16
1
10
1
6
6
9
0.9
to
2,5
09.0
to
2.3
31
81
6
to
8
15
to
25
weight)
2.3 x 10°
22x 104
1.1 x 108
3.3 x
to
1.2 x
3.6 x
to
2.9 x
107
4
10,
10
5
10
On a dry weight basis the total radioactivity
in the plankton was approximately two and 100 times
that in the liver and muscle respectively of the
omnivorous fish, The levels of radioactivity in
the plankton and omnivorous fish cannot be comPared directly with those in the carnivorous fish
(tuna) because the latter fishes are capable of
"igrating great distance in short periods of time
ond the length of time they had been in the area of
Outamination before they were taken cannot be
etermined,
Page 565
_
If the per cent of total radioactivity contributed by cobalt-57,58,60, and iron-55,59 are
compared in the plankton,
the omnivorous fish, and
the carnivorous fish, however, a pattern of accumulation may be seen. Whereas in the plankton
radiocobalt contributed 43 per cent of the total
radioactivity, in tissues of the omnivores it con=-
tributed only nine to ten per cent and in the
carnivores zero to 2.5 per cent. Radioiron accounted for 16 per cent of the total radioactivity
in the plankton, 31 to 81 per cent in the omnivores, and six to 25 per cent in the carnivores.
The reduction in the percentage of total
radioactivity contributed by radioiron in the
carnivorous fish was caused by a high concentration factor for zinc-65 in the tissues of these
shes.
Thus, the percentage of total radioactivity
contributed by radiocobalt decreased through the
two higher trophic levels, Radioactive iron, however, increased in percentage of total radioactivity in the muscle and liver of the omnivorous fish over that in plankton and was concentrated in the liver at an absolute level double
that found in the plankton.
In addition to the food chain represented by
the plankton, omnivorous fishes, and carnivorous
fishes, another food chain is comprised primarily
of the plankton, omnivorous fishes, and sea
birds, Among the birds at Eniwetok are the terns
or sea swallows (fairytern, Gygis alba; common
noddy tern, Anous stolidus) which feed primarily
upon small fish and to a lesser degree upon
squid. Analyses for iron-55,59 have not been
made on the tissues of these animals,and in gamma
Spectra of the liver, gut, kidney, muscle, and
lung tissues of the terns, only the gamma peak of
Zinc-65 was detected (Lowman, et al., 1957).
Tron-55 is probably present in the tissues of the
terns in large amounts, however, Indirect evidence has been found that this is the case in
analyses of soil samples from areas in which
these birds nest (Palumbo and Lowman, 1958). A
comparison is shown below of soil samples taken
in bird nesting areas and from an island where
nests were not present,
Per cent of Total Radioactivity in Soil
Ce 144_p, 144 |
Iron - 55,59
Cobalt - 57,58,60
Manganese - 54
Zinc - 65
Non-nesting area
(Lowman, et al.,
1957)
43.6
Nesting area
(Palumbo and
_Lowman, 1958)
41.7
0
40.6
1 to 2
0
0
0.4
0.8
0
In the non-nesting area the soil did not
contain the radioisotopes of iron, manganese, or
zinc, but did contain one to two per cent of
radiocobalt. In the nesting area, zinc-65 was
not found in the soil, which contained excretory
products from birds although it was present in
high amount in the tissues of the birds. Har~
ever, approximately 41 per cent of the total
radioactivity in the soil was contributed by
iron-55,59 with only trace amounts of radiocobalt
and manganese, On the basis of the soils data
and the gamma spectrum data on the birds, these
animals excreted high amounts of iron-55,59, almost all of the cobalt-57,58,60, and manganese54, and retained the zinc-65, The fact that the
gamma peaks of cobalt-57,58,60, and manganese-54
were not found in the bird tissues and that
these radionuclides were present in low amounts
in the soil, indicates that the birds ingested
relatively low amounts of radioactive cobalt and
manganese and large amounts of iron-55,59 and
Zinc-65 and retained the radiozinc to a
par A
AVES