Page 168
Radioecology
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 collec-
ted in the field from lysimeters, strontium-90,
cesium-137, and antimony-135 are the principal nu-
clides found, although Rul@6-Rn106, ceriun-i44,
.mc
uropium-155 are also detectable (Cole et al.,
1961). Here differences exist with respect to soil
type in that the leachates from immature soil,
consisting almost exclusively of parent material,
contained only antimony~-125 and strontium-90.
There is to us no evident explanation for this
difference.
The ground water probably contains these nuclides since their movement has been detected in
leacnates to depths of 30 inches, but the levels
are so low in ground water that special techniques
would have to be developed to detect then.
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
tor ¥O per cent or more of the radioactivity in the
land plants and strontium-90 for the remainder.
This 18 unlike the situation usually found on continental soils and is a consequence of the low
pot: sSium 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
plant.
There are, of course, differences between
plant species and plant parts with respect to the
relative amounts of cesium-137 and strontium. For
«xample, copra contains very little strontium-90
as compared with Pandanus fruit, and the basal
leaves of various plants contain more strontium-90
relative to cestum-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
rlatus) contain the same
nuclides but concentrate strontium-90, as has been
igported for Coenobita from Eniwetok Atoll (Held,
1960).
The occurrence of radionuclides in man at
Rongelap has been summarized by Cohn et al. (1960).
In 1258 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
vertebrates containing zinc-65 are known to be con-
sumed 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
from the sea water or algae.
The possibility that
most of the zinc-65 radioactivity in fish is resid-
ual appears to be ruled out by the fact that young
fish contain relatively high levels.
The marine invertebrates taken as a whole con-
tain a wider spectrum of radionuclides than do the
fish.
These are manganese-54, cobalt-57,60, zinc65, strontium-90, cerium-144, and probably europium-
155.
The corals contain cobalt-60 and are the
only invertebrates in which strontium-90 has been
consistently detected. From limited data available thus far it appears that these nuclides sere
deposited in the skeletal material soon after fall-
out 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 ag the sea cucumber (Holothuria,
Stichopus) and spider snail (Lambis, Strombus),
which Pagest 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 ruthenius-106,
cerium-144 and europium-155.
In general, the
levels of radioactivity in the algae 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 strontius-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 although 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
marine organisms, contain primarily zinc-65 and
occasionally small amounts of manganese-54 and
cobait-60.
Strontium-90 is also found in small
amounts in bird bone and may refiect direct uptake
from the ingestion of soil, although there is no
direct evidence that this occurs.
cesium-137, can be expected to remain very much
Radionuclides in fish are limited to manganese54, cobalt-60, and zinc-65, the latter being predominant.
On a dry-weight basis for a sample of
because of the presence of shorter-lived radionuclides, with the exception of strontium-90. The
latter does not enter the marine food web to any
goatfish (Mulloidichthys samoensis) testes have the
highest levels, the liver, gastrointestinal tract,
and eyes are lower by ahout an order of magnitude,
and the muscle and bone lower by still anotver
order of magnitude.
If the total amount
of radio-
aciivity by tissue is considered, then bone is tue
princ:pal depository
of zine-65 (Joyner. 1361, person.) communication).
The sources of zinc-65 for
fisn are open to question.
In some instances in-
as it is now.
reduced
The levels of radioactivity will be
primarily by physical decay of the rauic-
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
significant extent and may remain as a label useful in evaluating the 1ong-term effects of physical
forces in the lagoon.
SUMMARY
The qualitative distribution of radionuclides
at Rongelap Atola .s determined approximately five