toot
C
Radioecology
Page 168
not all organisms at Rongelap but that the levels
at which they occur are extremely low and so escape
detection.
Passing from the soil to the soil solution,
the term being used here to mean leachates collected in the field from lysimeters, strontium-90,
cesium-137, and antimony-125 are the principal nu-
clides found, although Rul06-Rn106, cerium-144,
and europiun-155 are also detectable (Cole et al.,
from the sea water or algae.
The possibility that
most of the zinc-65 radioactivity in fish is residual
appears
to be ruled out by the fact that young
fish contain relatively high levels.
consisting almost exclusively of parent material,
The marine invertebrates taken ag a whole contain a wider spectrum of radionuclides than do the
fish.
These are manganese-54, cobalt-57,60, zinc-
There 1s to us no evident explanation for this
difference.
only invertebrates in which strontium-90 has been
1961). Here differences exist with respect to soil
type in that the leachates from immature soil,
contained only antimony-125 and strontium-90.
The ground water probably contains these nuclides since their movement has been detected in
leachates to depths of 30 inches, but the levels
are so low in ground water that special techniques
would have to be developed to detect them.
The land plants contain principally cesium-137
and strontium-90.
Manganese-54 and zinc-65 have
been found in plants from the more heavily contaminated iSlets but are present in relatively insignificant amounts.
In general, cesium-137 accounts
for yO per cent or more of the radioactivity in the
land plants and strontium-90 for the remainder.
This 1S unlike the situation usually found on continental soils and is a consequence of the low
potassium content of Rongelap soil.
Amendments of.
potassium to Rongelap soil reduce the uptake of
cesium-137 by plants (Walker et al., 1961), and
affect the distribution of cesium-137 within the
°
- me
vertebrates containing zinc-65 are known to be consumed by fish found to contain zinc-65, but, in
general, no definite sources of zinc-65 are known
to exist five years after fallout.
It is possible
that there is concentration of undetectable levels
plant.
There are, of course, differences between
plant species and plant parts with respect to the
relative amounts of cesium-137 and strontium.
For
example, copra contains very little strontium-90
as compared with Pandanus fruit, and the basal
leaves of various plants contain more strontium-90
relative to cesitum-137 than do the terminal leaves.
This variation is related to differences in mobil-
ity between cesium and potassium, and strontium
and calcium.
The rats contain cesium-137 and strontium-90,
reflecting the radionuclides present in the plants
on which they feed,
The coconut crab and the land
hermit crab (Coenobita perlatus) contain the same
nuclides but Concentrate strontium-90, as has been
Topp for Coenobita from Eniwetok Atoll (Held,
0).
The occurrence of radionuclides in man at
Rongelap has been summarized by Cohn et al. (1960).
In 1958 these nuclides were cesium-137 and strontium-90 coming form the food plants, and zinc-65
coming to man from marine products.
The birds, which feed almost exclusively on
marine organisms, contain primarily zinc-65 and
occasionally small amounts of manganese-54 and
cobalt-60. Strontium-90 is also found in small
amounts in bird bone and may reflect direct uptake
from the ingestion of soil, although there is no
direct evidence that this occurs.
Radionuclides in fish are limited to manganese54, cobalt-60, anda zinc-65, the latter being pre-
dominant.
On a dry-weight basis for a sample of
goatfish (Mulloidichthys samoensis) testes have the
highest levels,
e
ver, gastrointestinal tract,
and eyes are lower by about an order of magnitude,
and the muscle and bone lower by still another
order of magnitude.
If the total amount of radio-
activity by tissue is considered, then bone is tne
principal depository
of zinc~-65 (Joyner, 1961, personal communication).
The sources of zinc-65 for
fish are open to question.
In some tnstances in-
65, strontium-90, cerium-144, and probably europium155. The corals contain cobalt-60 and are the
consistently detected. From limited data available thus far it appears that these nuclides were
deposited in the skeletal material soon after fallout and have remained localized in portions of the
coral colony actively growing at that time.
The
clams contain mostly zinc-65. cobalt-57 and cobalt60.
Weiss and Shipman
(1957) originally reported
the concentration of cobalt-60 in the kidney of
Tridacnid clams collected at Rongelap in 1956.
Animals such as the sea cucumber
(Holothuria,
Stichopus) and spider snail (Lambis, Strombus),
whic
ngest large amounts of bottom sediments,
contain ruthenium-106, cerium-144, and probably
europium-155.
Of several species of algae sampled in 1959
the only radionuclides detected were ruthenium-106,
cerium-144 and europium-155.
In general,
the
levels of radioactivity in the aigae are lower
than in the fish or invertebrates.
The plankton contain manganese~54, cobalt§7,60, zinc-65, zirconium-95, ruthenium-106, and
cerium-144, but all in minute amounts. [In 1959
plankton samples collected by pumping a total of
two and a half million gallons of water were
pooled for gamma-ray spectrum analysis and were
found to contain only enough of these nuclides
for qualitative analysis without resorting to
chemical separations.
Further analysis has been
deferred until other studies with the individual
samples can be completed.
The lagoon sediments contain strontium-90,
ruthenium-106, cerium-144, and europium-155.
The
radioactivity is associated mainly with the fines
and is concentrated in the top two to four inches,
dropping off rapidly with depth.
Radionuclides other than naturally occurring
potassium-40 were not detected in sea water al-
though larger samples and more sensitive techniques
undoubtedly would have revealed their presence.
In sum, on land the present distribution of
long-lived fission products, strontium-90 and
cesium-137, can be expected to remain very much
as it is now. The levels of radioactivity will be
reduced primarily by physical decay of the radic-
nuclides so long as other factors such as changed
agricultural practices or a catastrophic storm
do not occur.
In the lagoon, the levels of radioactivity will decline more rapidly than on land
because of the presence of shorter-lived radionu-
clides, with the exception of strontium-90. The
latter does not enter the marine food web to any
significant extent and may remain as a label useful in evaluating the long-term effects of physical
forces in the lagoon.
SUMMARY
The qualitative distribution of radionuclides
at Rongelap Atols 19 determined approximately five