Before we can follow the atom down into the sea, we must understand
something about the potentials, both good and bad, of this incursion of
one of our most advanced technologies into one of earth’s least
understood environments. This adventurous probing has ramifications for
studying both man-produced radioactivity in the sea and the ocean itself
as an uncontaminated environment.
TABLE I
AEC OCEANOGRAPHY PROGRAM 1968
Expenditures
Estimate
_Research Activities_
Division of Biology and Medicine $4,000,000
Studies of uptake, concentration, distribution and
effects of radioisotopes on marine life, of
geochemical cycling of elements, and of geophysical
diffusion and transport.
Division of Research 25,000
Geological dating of corals and other marine and
terrestrial materials.
Division of Isotopes Development 190,000
Radioisotope applications to devices for marine
systems, such as current meters, analysis and
recovery of sedimentary minerals, and underwater
sound transmission.
Division of Reactor Development and Technology 197,000
Studies of factors affecting dissolution and
dispersal of accidentally released radionuclides, and
site evaluations.
Division of Space Nuclear Systems 275,000
Nuclear power sources for aerospace applications.
Division of Military Applications 850,000
Ocean environmental observation and prediction.
_Total—Research Activities_ 5,537,000
_Engineering Activities_
Division of Reactor Development and Technology 5,900,000
Radioisotope and reactor power development.
Division of Naval Reactors 1,320,000
Deep submergence research vehicle.
_Total —Engineering Activities_ 7,220,000
_Total—ABC Oceanographic Activities_ 12,757,000
Radionuclides (radioactive atoms) can find their way into the sea from
natural radiation sources or from nuclear energy operations undertaken
by the United States and other countries since 1945. Specific man-made
sources in the past may have included nuclear weapons tested in the
atmosphere and under water, the cooling water and wastes of nuclear
reactors, laboratories and nuclear-powered ships, containers of
radioactive waste disposed of at sea[5], radioisotope energy devices,
and intentional injection of radioisotope tracers for scientific
research. In the future, they may also include reentry from space of
upper-stage nuclear rockets or satellite-borne nuclear energy sources.
[Illustration: _The Nansen bottle, shown being attached to a
hydrographic wire, is one of the standard tools of oceanology. When
a bottle reaches a desired depth, a sliding weight tips it upside
down to collect seawater samples. Thermometers on the sides of the
bottles record temperature. The device was designed by the Norwegian
oceanographer and explorer, Fridtjof Nansen._ (_See photo on
page 56._)]
In order to evaluate the effects of these materials in the ocean
environment, it is necessary to know many things. Just how much
radiation is introduced? In what form? Where geographically? How are
these radionuclides dispersed or concentrated physically, chemically,
biologically, and geologically? What is the net result in each case now,
and what will it be many years hence?
These questions are not answered easily. There is, as yet, no
satisfactory laboratory substitute for the open ocean. Research for the
most part must be conducted at sea, where tests and measurements are
difficult at best, and where results therefore are often suspect.
Further, if we are to study the effects of man-induced changes in a
natural environment, it would have been advantageous to have known the
nature of that environment before the changes were introduced—which, by
and large, in the case of the ocean we do not. So we must start with a
contaminated environment and try to separate what we have put there
ourselves from what would have been there anyway. It isn’t an easy task
to make the physical and biological observations that will make this
distinction.
Table II CONCENTRATION AND AMOUNTS OF 42 OF THE ELEMENTS IN SEAWATER
Element Concentration Amount of element in Total amount in
(mg/l) seawater (tons mile³) the oceans (tons)
Chlorine 19,000.0 89.5 × 10⁶ 29.3 × 10¹⁵
Sodium 10,500.0 49.5 x-10⁶ 16.3 × 10¹⁵
Magnesium 1,350.0 6.4 × 10⁶ 2.1 × 10¹⁵
Sulphur 885.0 4.2 × 10⁶ 1.4 × 10¹⁵
Calcium 400.0 1.9 × 10⁶ 0.6 × 10¹⁵
Potassium 380.0 1.8 × 10⁶ 0.6 × 10¹⁵
Bromine 65.0 306,000 0.1 × 10¹⁵
Carbon 28.0 132,000 0.04 × 10¹⁵
Strontium 8.0 38,000 12,000 × 10⁹
Boron 4.6 23,000 7,100 × 10⁹
Silicon 3.0 14,000 4,700 × 10⁹
Lithium 0.17 800 260 × 10⁹
Rubidium 0.12 570 190 × 10⁹
Phosphorus 0.07 330 110 × 10⁹
Iodine 0.06 280 93 × 10⁹
Barium 0.03 140 47 × 10⁹
Indium 0.02 94 31 × 10⁹
Zinc 0.01 47 16 × 10⁹
Iron 0.01 47 16 × 10⁹
Aluminum 0.01 47 16 × 10⁹
Molybdenum 0.01 47 16 × 10⁹
Selenium 0.004 19 6 × 10⁹
Tin 0.003 14 5 × 10⁹
Copper 0.003 14 5 × 10⁹
Arsenic 0.003 14 5 × 10⁹
Uranium 0.003 14 5 × 10⁹
Nickel 0.002 9 3 × 10⁹
Vanadium 0.002 9 3 × 10⁹
Manganese 0.002 9 3 × 10⁹
Antimony 0.0005 2 0.8 × 10⁹
Cobalt 0.0005 2 0.8 × 10⁹
Caesium 0.0005 2 0.8 × 10⁹
Cerium 0.0004 2 0.6 × 10⁹
Silver 0.0003 1 5 × 10⁸
Cadmium 0.0001 0.5 150 × 10⁶
Tungsten 0.0001 0.5 150 × 10⁶
Chromium 0.00005 0.2 78 × 10⁶
Thorium 0.00005 0.2 78 × 10⁶
Lead 0.00003 0.1 46 × 10⁶
Mercury 0.00003 0.1 46 × 10⁶
Gold 0.000004 0.02 6 × 10⁶
Radium 1 × 10⁻¹⁰ 5 × 10⁻⁷ 150
Adapted from _The Mineral Resources of the Sea_, by John L. Mero,
American Elsevier Publishing Company, New York, 1964.
Many sea creatures are efficient, selective concentrators of “trace
elements”, which occur in seawater only in minute portions. These
elements are difficult enough to detect qualitatively and all but
impossible to analyze quantitatively. Yet among the elements the sea’s
plants and animals concentrate are the very materials with which we are
apt to be most concerned: Strontium, cesium, cerium, ruthenium, cobalt,
iodine, phosphorus, zinc, manganese, iron, chromium, and others.
Radioisotopes[6] of all these elements occur as by-products of human
nuclear activities. Many concentrating organisms are microscopic in size
and are frequently impossible to raise in captivity. It is apparent that
we are faced with a research program of considerable challenge and
proportion.
We need to know _how_ each marine species concentrates. Is it from the
food it eats, by absorption from the water, or both? Does it concentrate
an element by continuous accumulation, or is there a constant turnover
of the material in the organism’s system? (In the first case, once the
creature became radioactive it would remain so throughout its life or
until the radioactivity decayed. In the second case, however, the
radioactivity might be a transient condition, assuming the creature
could find its way into uncontaminated water and were able to flush
itself.) Obviously, both the cycling time of the radioisotope in the
organism and its radioactive half-life[7] must be taken into account.
Even if we should manage to identify all the marine concentrators and
gain some insight into their metabolic processes, this would be only a
first step. For example, one tiny form of planktonic protozoan,
_acantharia_, concentrates up to 15% of its own weight of strontium,
including the radioisotope strontium-90. It is eaten by larger
zooplankton (animals), such as copepods, which are eaten by little fish,
which, in turn, are eaten by bigger fish, etc. Somewhere along this food
chain, perhaps, a fish will come along that is favored for human dinner
tables. How much strontium-90 has _that_ fish accumulated through
swallowing its prey and by absorption from the water? Is the
radioactivity in its scales, bones, viscera, and other usually uneaten
portions, or in its flesh?
It is probable, though as yet by no means proven, that among the million
or so oceanic species of plant and animal life, there are concentrators
of virtually all the 60 or more elements found in seawater. To identify
and study them is an enormous undertaking, which is often possible only
by using radioisotopes as tools.
And what of the immediate and genetic effects of radiation on each
species? Studies of reef fish in the nuclear testing area in the
Marshall Islands have shown that radioiodine in the water caused thyroid
gland damage long after the amount of radioiodine remaining in the water
was too low to be detected. Studies of salmon in the Columbia River have
shown some physiological variations between those fish whose eggs and
young were reared in radioactive waters and those that were not, though
these variations have not been determined to be statistically
significant or different from variations caused by other contaminants.
Studies are being made of the reproductive efficiency and patterns of
sea creatures in a radiation-contaminated environment, compared with
those in an uncontaminated environment, to learn such things as the
numbers, survival rates, and sex ratios of the offspring, and any
genetic abnormalities or mutations. Many more studies are needed.
Always, the task is made difficult by insufficient detailed knowledge of
the original natural environment, the limitations of laboratory
experiments, and the mechanics of trying to follow the reproductive
cycles of free-floating or swimming organisms in any statistically
meaningful manner through successive generations.
One obviously important kind of research deals with the rate, pattern,
and means by which radionuclides are distributed into the sea from a
point source, such as the mouth of a river or a nuclear test site.
Transport and diffusion of radioactivity can be, and are, influenced by
physical, chemical, biological, or geological means, separately or all
at once. This has led the AEC to support scientific studies of currents,
upwelling, downwelling, convergence, diffusion, mixing rates, air-sea
interactions, chemical and geological processes in the sea, and the
horizontal and vertical migrations of sea life.
[Illustration: _This sound instrument record reveals the layers of
planktonic sound scatterers on the continental slope east of New
England. Each peak originates from an individual group of
organisms._]
In much of the ocean there is an acoustic “floor”, known as the _deep
scattering layer_ (because of what it does to sound waves), which is
believed to consist primarily of zooplankton. Every 24 hours the layer
migrates up and down through several hundred feet of water. At night the
countless small animals graze in the rich sea-plant pastures near the
surface; during daylight, back at the lower level, they undoubtedly are
heavily fed upon by larger animals. Over a period of time, the layer
accounts for considerable vertical transport of materials. (See figure
above.) Other life forms may move materials still farther down, or, in
some instances, back up—as when the sperm whale descends to the depths
to fight and best a giant squid, and then returns to the surface to eat
it.
Constantly drifting downward is a great volume of material—the dead
bodies, skeletons, excrement, and other waste from sea life at all
depths. As it sinks there is a constant exchange of matter between it
and the surrounding water through chemical, physical, and biological
processes. Eventually, the molecules of material added to the bottom
sediments may be returned to the water mass by bacteriological action or
the eating and living habits of sea floor animals.
[Illustration: _A school of skipjack tuna photographed from an
underwater observation chamber on the research vessel_ Charles H.
Gilbert.]
Biological transport works in other ways, too. Most pelagic
(free-swimming) fish are great travelers. They account for a tremendous
movement of material, namely themselves, from one place to another.
Tuna, swordfish, whales, porpoises, and sea birds may travel thousands
of miles in a single year. Such migrations may serve, variously, as
mechanisms for either dispersal or concentration of elements or
nutrients. The anadromous (river-ascending) fishes, such as salmon,
herring, sturgeon, and shad, concentrate in freshwater streams in untold
numbers to spawn. After hatching, the young seek the ocean and scatter
widely until they, too, feel the urge to return to the rivers and lakes
whence they came, to spawn and die there as did their ancestors.
Ocean currents may transport concentrations of radionuclides essentially
undiluted for thousands of miles. Surface currents move at speeds of up
to five knots (nautical miles per hour). Normally current waters do not
mix readily with the water mass through which they pass. Because of the
slowness of vertical circulation in the ocean, radionuclides deposited
on the surface of the ocean may take a thousand years to reach the
bottom. But the vertical transport sometimes is much more rapid: When
the wind piles too much water against a coastline, the resultant
downwelling (sinking) may move radionuclides suddenly into the deeper
ocean. Or, conversely, when the wind and the rotation of the earth
combine to force the surface water _away_ from the coast, deep water may
suddenly rise to replace it, a process known as upwelling.
[Illustration: _Mechanisms of nutrient turnover in the sea._]
Light energy
Dissolved gases
Birds and man
Rivers and ice
Wave action
Surface mixed layer 20-100m
Suspended matter
Elements in true solution
Plants phytoplankton
Animals
Deep water
Elements in true solution in deep water
Buried in sediment
Physical Processes
_Transport by wind_
_Transport by current_
_Turbulent mixing_
_Sedimentation_
_Transport_ by animals
_Volcanic action_
_Diffusion_
Chemical or Biological Processes
_Photosynthesis_
_Dissolving_
_Upwelling_
_Decomposition and respiration_
_Sorption_ by sediment surface
_Redissolving_ from sediment
_Chemical precipitation_
Combined Processes
_Sedimentation and decomposition_ by bacteria
_Scavenging_
Some recent evidence indicates that the passage of a hurricane across
the ocean drives surface water out from the storm center in all
directions. This, too, produces upwelling. If radionuclides fall on the
Arctic ice pack or on the Greenland or Antarctic ice caps, it may be
years before they are released to the sea. In more or less stable
conditions at sea, radionuclides may remain trapped above the
thermocline (a layer of sharp temperature change usually less than 100
meters below the surface) for a considerable period. Then a severe storm
may destroy the thermocline and mix the waters to much greater depths.
The process of diffusion in the ocean is not well understood, due both
to the difficulty of the measurements that have to be made and to the
variety of other factors affecting both vertical and horizontal
transport of materials. Here again, however, the existence of
radionuclides, introduced artificially at a known time and place, is
materially aiding these investigations by making a particular water mass
detectable and traceable.
[Illustration: _Winds of 100 knots (about 115 mph) whip high waves
in the Caribbean Sea east of Guadeloupe Island during a hurricane._]
In chemical oceanography, the AEC is concerned with the fact that in
some instances our society is introducing elements, ions, and compounds
that have not been naturally found in the sea, as well as natural
materials in greater concentration than is normal. These may combine
with other materials in the sea, changing into new forms or substances,
or removing them from solution entirely. Any change in the chemical
composition of the ocean is quite likely to have biological effects,
some of which may prove detrimental to man.
A disturbance of the chemical balance of the sea is thought to be
responsible, at least in part, for the periodic, disastrous plankton
“blooms” known as “red tides”. Such a sudden, explosive overpopulation
of plankton is a natural phenomenon, but one that can be triggered by
man-made pollution. When it occurs, plankton multiply so rapidly that
the oxygen in the water is depleted and many fish die from suffocation.
Fortunately, nuclear energy operations account for an extremely small
portion of the chemical contamination of the sea, when contrasted with
the tremendous volume of poisons dumped daily into it in the form of
other industrial and municipal waste and agricultural pesticides.