The AEC supports oceanographic research conducted by its own
laboratories and by other federal agencies, as well as by non-government
research scientists. The Environmental Sciences Branch of the Division
of Biology and Medicine has begun the long and complex task of
unraveling the mystery of the fate of radionuclides in the ocean.
Valuable techniques have been developed for the intentional injection of
radioisotopes into the sea for specific research. Scientists are now
able to conduct investigations that were never before possible. In some
instances, traditional scientific concepts and theories have been
shattered, or at least severely shaken, by new evidence gathered by
radioisotope techniques.
Since 70% of the earth’s surface is water, at least 70% of the
radioactive debris lofted into the stratosphere during atmospheric
nuclear weapons tests falls into the ocean. An additional small
proportion finds its way into the sea as the run-off from the land. In
the case of tests at sea, the majority of radiation immediately falls
into the water nearby. For this reason, the ocean around the sites in
the Marshall Islands where U. S. tests were conducted has provided a
unique opportunity to study the effect of large concentrations of
radionuclides. Particularly significant studies have been conducted of
the absorption of radionuclides by plants and animals living on nearby
reefs and islands, and of both lateral and vertical diffusion rates of
elements in the open ocean.[8]
The 1954 nuclear test at Eniwetok Atoll produced heavier-than-expected
local radioactive fallout. Since then, both American and Japanese
scientists have studied water-mass movement rates, using the fallout
radionuclides strontium-90 and cesium-137 themselves as tracer elements.
These nuclides produced in the test have been detected at depths down to
7000 meters in the far northwestern Pacific in the vicinity of Japan.
[Illustration: _Autoradiograph of a plankton sample collected from a
Pacific lagoon a week after a 1952 nuclear test, showing
concentration of radioisotopes (bright areas)._]
If this results from simple eddy diffusion, as some scientists believe,
it is a case of diffusion at a very high rate. Other scientists suggest
that other factors may have contributed to the vertical transport of the
radionuclides to these depths. Still others believe that the
strontium-90 and cesium-137 might not have originated with the U. S.
Pacific tests at all, but rather with Russian tests in the Arctic taking
place at about the same time. They propose the theory that a syphoning
effect in the Bering Strait causes a current to flow out of the Arctic
Ocean and down under the surface waters of the western Pacific. In
support of this, Japanese researchers cite a dissolved oxygen content
where these measurements were made that is different from that of other
deep water in the area. If this theory should be proved correct, it
would be the first indication that such a current exists.
Similar investigations have been conducted of the variations in depth of
strontium-90 concentration in the Atlantic Ocean. In February 1962, when
fallout from 1961 nuclear tests was high, tests south of Greenland
showed that mixing of fallout was fairly rapid through the top 800
meters of water. At greater depths a colder, saltier layer of water
contained only about half as much strontium-90, confirming other
evidence that interchange between water masses of different physical and
chemical properties is comparatively low.
Work such as this has emphasized the difficulty in making meaningful
measurements of man-made radiation in the ocean. One problem is to
separate the artificially produced radiation from the natural radiation,
namely that from potassium-40 (which accounts for 97% of oceanic
radiation) and from the radionuclides, such as tritium, carbon-14,
beryllium-7, beryllium-10, aluminum-26, and silicon-32, created in the
stratosphere naturally by cosmic-ray bombardment.
[Illustration: _In 1955 a scientific team aboard the U. S. Coast
Guard vessel_ Roger B. Taney _conducted a survey of ocean fallout in
the western Pacific. They collected marine organisms and water
samples at various depths on their 17,500-mile, 7-week journey._]
Another problem is the sheer physical size of the water sample required
to get any measurements at all. Up to now there has been no truly
effective radiation counter that can be lowered over the side of a ship
to the desired depth. It is often necessary to collect a sample of many
gallons at great depths and return it to the surface without its being
mixed by any of the intervening water. This is difficult at best, and
only rather primitive methods have been developed. None is more than
partly satisfactory. A standard system is to lower a large, collapsed
polyethylene bag to the desired depth, open it, fill it, and close it
again, all by remote control, and then gingerly and hopefully return it
to the surface. Results do not always agree among samples taken at the
same location by different methods or by different scientists. There is
still no universal agreement among scientists as to the quantitative
validity of any of the measurements, although as more and better data
are gathered there tends to be a greater concurrence.
[Illustration: _Fifty-gallon sampler ready to be lowered over the
side of the research vessel_ Atlantis II _in the North Atlantic.
Such devices are used to obtain samples at fixed intervals from the
sea surface to the bottom. The water is analyzed for radioisotope
content._]
Recently, under an AEC contract, a detector for direct measurements of
gamma radiation[9] in the deep ocean was developed for the Institute of
Marine Sciences, University of Miami, by the Franklin GNO Corp. (See
figure above.) This unit incorporates two of the largest plastic
scintillation counters[10] ever used in the ocean—each is 16 inches in
diameter by 12 inches thick. This apparatus may permit direct
qualitative and quantitative measurement of radiation at great depths by
techniques that will be eminently more satisfactory than water sampling.
Already tests with the detector have disclosed the existence of
cosmic-ray effects at much greater depths than heretofore known.
[Illustration: _Scintillation counter for use in the deep ocean._]
[Illustration: _Constituent parts. The plastic discs are the
radiation detectors._]
Biologists from Woods Hole Oceanographic Institution in Massachusetts
for the first time have been able to measure the rate of excretion of
physiologically important fallout radionuclides by several species of
zooplankton—_pteropods_, _pyrasomes_, _copepods_, and _euphausids_.
Radioactive zinc and iodine, it was learned, are excreted as soluble
ions, while iron and manganese appear as solid particles. However, the
extent to which the intake and excretion of radionuclides and the
vertical migration of zooplankton contribute quantitatively to the
transport of radioactivity across the thermocline (and into the ocean
deeps) still can only be guessed.
[Illustration: _Zooplankton, mostly copepods, collected with
automatic underwater sampling equipment on board the nuclear
submarine_ Seadragon _while cruising under the Arctic ice_.]
Other plankton research at Woods Hole uses radioactive carbon-14 and
phosphorus-32 as tracers to evaluate rates of growth and nutrient
assimilation by algae (floating green plants). These investigations have
revealed that the presence or absence of minute quantities of nutrient
minerals in seawater affects the rate at which the algae produce oxygen
by the process of photosynthesis. Since the energy of all living
things—including man—is also made available by photosynthesis, and since
most of the photosynthesis on earth is performed by algae afloat in the
oceans, it is apparent that this research is of more than academic
interest. Algae, the original energy-fixers of the “meadows of the sea”,
are also the original food source for the billions of aquatic animals,
and may some day prove a source of food for a mushrooming human
population.
In a project with more immediate application, extensive biological and
environmental studies of the Eniwetok Atoll area in the Pacific were
conducted prior to the first nuclear testing there in 1948, and these
studies have continued ever since. Early in the test series the
Japanese, who were at first concerned with the possible contamination of
their traditional marine food supplies, were invited to participate in
these studies. Fisheries radiological monitoring installations were
established in Japan and the U. S. (The latter was established by the
AEC and administered by the U. S. Food and Drug Administration.) Neither
station encountered any radiological contamination of tuna or other food
fish, and the American unit has now been closed.
[Illustration: _This shell of the giant clam_ Tridacna gigas _shows
the position of a layer of strontium-90 absorbed in 1958 (black
line) and in 1956 (white line). The inside of the shell (light
layers) was deposited in 1964 when the clam was collected at Bikini
Atoll by scientists from the University of Washington, Seattle._]
Groups that have cooperated with the AEC in marine radiobiological
research are the University of Hawaii, University of Connecticut,
Virginia Fisheries Laboratory, University of Washington, U. S. Office of
Naval Research, and U. S. Bureau of Commercial Fisheries.
At the Bureau of Commercial Fisheries Radiobiological Laboratory in
Beaufort, North Carolina, a cooperative effort of the AEC and the BCF is
concerned with learning the effects of radioactive wastes on one of
America’s most valuable marine resources—the tidal marshlands and
estuaries that are essential to the continued well-being of some of our
important commercial fisheries.
Table III RADIOISOTOPES THAT MIGHT BE FOUND IN AN ESTUARINE
ENVIRONMENT
Isotope Half-life
Iodine-131 8.05 days
Barium-140—Lanthanum-140 12.8 days—40 hours
Cesium-141 32.5 days
Ruthenium-103—Rhodium-103 10 days—57 minutes
Zirconium-95—Niobium-95 65 Days—35 days,
Zinc-65 245 days
Cerium-144 285 days
Manganese-54 314 days
Ruthenium-106—Rhodium-106 1 year—30 seconds
Cesium-137 30 years
Potassium-40 1.3 × 10⁹ years
(Reprinted from _Radiobiological Laboratory Annual Report_, April, 1,
1964, page 50.)
The project has determined that radionuclides are removed from waters in
an estuarine environment by several physical, chemical, and biological
means. For example, radionuclides are absorbed in river-bed sediments at
a rate varying directly with sediment particle size. Mollusks, such as
clams, marsh mussels, oysters, and scallops, not only assimilate
radionuclides selectively, but do so in sufficient quantity and with
sufficient reliability to be useful as indicators of the quantity of the
isotopes present. Clams and mussels are indicators for cerium-144 and
ruthenium-106, scallops for manganese-54, and oysters for zinc-65 (most
of which winds up in the oyster’s edible portions). It was learned that
scallops assimilate more radioactivity than any other mollusk. Of the
total radioactivity, manganese-54 accounts for 60%: The scallop’s kidney
contains 100 times as much manganese-54 as any of the other tissues and
300 times as much as the muscle, the only part of the scallop usually
eaten in this country.
[Illustration: _On the left are mussels collected near the Columbia
River in an environment containing abnormal amounts of zinc-65._]
[Illustration: _Mussels suspended in seawater in research to
determine how fast they lose their zinc-65 radioactivity._
(_Photograph taken at low tide._)]
In a surprising unintended result, it was determined that one acre of
oyster beds, comprising 300,000 individual oysters, may filter out the
radionuclides from approximately 10,000 cubic meters (18 cubic miles) of
water per week!
The Radiological Laboratory scientists also have found that plankton are
high concentrators of both chromium-51 and zinc-65, and that zinc
apparently is an essential nutrient for all marine organisms. Some
plants and animals appear to reach a peak of radionuclide accumulation
quickly, which then tapers off even though the radiation concentration
in the water is unchanged.
While the AEC’s oceanographic research budgets have not been large, they
have contributed materially to knowledge of the oceanic environment.
AEC-sponsored research at Scripps Institution of Oceanography has
determined by a process known as neutron activation analysis[11] that
the concentration of rare earth elements in Pacific Ocean waters appears
to be only about one hundredth of the level previously reported. By
analysis of naturally occurring radioisotopes, they have also discovered
that it takes from one million to 100 million years for lithium,
potassium, barium, strontium, and similar elements introduced into the
ocean from rivers to be deposited in the bottom sediments. Aluminum,
iron, and titanium are deposited in from 100 to 1000 years. They have
also found that sedimentation occurs in the South Pacific at a rate of
from 0.3 to 0.6 millimeter per thousand years, in the North Pacific at a
rate several times that figure, and in the basins on either side of the
Mid-Atlantic Ridge at a rate of several millimeters per thousand years.
The University of Miami has successfully developed two methods for
determining the ages of successive layers of deep ocean sediments based
on the relative abundances of natural radioelements, and thereby has
established a chronology of climatic changes during the last 200,000
years during which the sediments were laid down.
The U. S. is not alone in its use of nuclear energy as a tool of
science. The United Kingdom has carried out radiological studies of the
marine environment for many years, particularly concentrating on the
effects of radionuclides from nuclear power plants on the sea
immediately contiguous to the British Isles. Both the European Atomic
Energy Community and the International Atomic Energy Agency also
encouraged marine radiological studies. Many laboratories and government
agencies in Europe, North and South America, Africa, and the Middle East
and Far East have well-established and productive programs under way.
Scientists in many parts of the world have used both natural and
intentionally injected radiation to study the coastwise movement of
beach materials. British experimenters, for example, activate sand with
scandium-46 and are thus able to follow its movement for up to four
months. Pebbles (shingle) coated with barium-140 and lanthanum-140 are
also used as tracers and are good for 6 weeks. Scientists at the
University of California trace naturally occurring radioisotopes of
thorium, which may be introduced from deposits of thorium sands along
river banks. These studies are of immediate practical importance, for
each year the ocean moves billions of cubic yards of sand, gravel,
shingle, and rock to and from beaches and along shores. This action
destroys recreational beaches, fills channels, blocks off harbors, and
in general rearranges the terrain, often at considerable cost and
inconvenience to mariners and other people who use the coast.
In another use of radioisotopes in marine research, studies at the AEC’s
Oak Ridge National Laboratory in Tennessee have revealed radioactivity
in the scales of fish taken from waters affected by the laboratory’s
radioactive waste effluent. It was suggested that this phenomenon might
be put to use as a tagging technique in fish-migration studies, and
scientists are now working on a method using cesium-134 introduced into
the fishes’ natural diet.
[Illustration: _Isaacs-Kidd midwater trawl collects samples of
oceanic animals off the Oregon Coast. These animals are then
radioanalyzed to compare the quantity of radioisotopes associated
with animals from various depths. The recorder at the trawl mouth
indicates the volume of water filtered._]
Some of the most extensive studies of a marine environment ever
conducted are those by the AEC, the Bureau of Commercial Fisheries, and
the University of Washington in the Columbia River system and the nearby
Pacific Ocean. Operations at the AEC’s giant Hanford facilities some 300
miles upstream from the ocean result in the release of small amounts of
radioactivity to the river and also in raising the river-water
temperature. This downstream research is to determine any effects of
these changes, including any that might be detrimental to man. The
research encompasses studies of the variations and distributions of the
freshwater “plume”—the outflow from the rivermouth—extending into the
nearby Pacific, sediment analyses, studies of the population dynamics of
phytoplankton, and the transport of radionuclides through the food
chain.
[Illustration: _This core sampler is used to obtain stream bed
samples up to 5 feet long in the Columbia River. The samples are
then analyzed for radioisotope content._]
As so often happens with basic programs, this research has produced
immediate benefits. New resources of marketable oceanic fish were
discovered by the scientists at depths never before fished commercially
(from the edge of the continental shelf to depths of 500 fathoms and
greater). Similarly, commercial quantities of one species of crab have
been discovered in the deeper ocean. Other findings indicate that crab
populations may have seasonal up-and-down migrations that vary according
to sex. It appears, in fact, that, except while mating and as juveniles,
the male and female crab populations lead separate lives. This
information is important both for more efficient fisheries and for
improved conservation of the crab as a food resource.
The AEC is, in short, concerned with virtually every facet of basic
oceanography, and with study of the sea as a whole, for radionuclides,
like their nonradioactive counterparts, can and do become involved in
every phase of the vast and complex ocean ecology. In the process of
pursuing its research interests, it also provides oceanographers with a
whole new family of tools for study. Let us now see how atomic
instruments contribute to the growing knowledge of the sea.