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GENERAL CONSIDERATIONS CONCERNING THE OCEAN AS A RECEPTACLE FOR ARTIFICIALLY RADIOACTIVE MATERIALS1 ROGER REVELLE and MILNER B. SCHAEFER, Scripps Institution of Oceanography and Inter-American Tropical Tuna Commission, La Jolla, California I. INTRODUCTION IN THIS report, we have attempted to sum- marize both the present knowledge and the areas of ignorance concerning the oceans that must be taken into account in considering the biological effects of radiation. The oceans of the world furnish essential sources of food and other raw materials, vital routes of transportation, recreation, and a con- venient place in which to dispose of waste ma- C terials from our industrial civilization. These different ways in which men use the sea, how- ever, are not always compatible. The use of the sea for waste disposal, in particular, can jeopardize the other resources, and hence should be done cautiously, with due regard to the pos- sible effects. Waste products from nuclear re- actions require special care: they constitute a hazards in extremely low concentrations and their deleterious properties cannot be eliminated by any chemical transformations; they can be dispersed or isolated, but they cannot be de- stroyed. Once they are created, we must live with them until they become inactive by natural decay, which for some isotopes requires a very long time. Waste products from nuclear reactions arise in two ways: (1) from the slow controlled re- actions involved in laboratory experimentation, in the production of materials for nuclear weapons, the production of reactor fuels, and the "burning" of fuels in power reactors; (2) from the rapid, uncontrolled reactions involved in testing of weapons or in warfare. Up to the present time, the largest quantities of fission products introduced into the aquatic environ- fi ment have been from weapons tests; most of the products from controlled reactions have been isolated on the land, and only relatively small quantities have been introduced into the 1 Contribution from the Scripps Institution of Oceanography, New Series, No. 901. sea or fresh water. In the future, however, in- cdustrial nuclear wastes will present difficult dis- posal problems and the sea is a possible dis- posal site, particularly for small, densely popu- lated nations with long sea coasts. We have, therefore, given particular attention to the long- range problems that may arise from the large- scale disposal of both high-level and low-level industrial wastes, as well as to the effects of weapons tests. Among the variety of questions generated by the introduction of radioactive materials into the sea, there are few to which we can give precise answers. We can, however, provide con- servative answers to many of them, which can serve as a basis of action pending the results of detailed experimental studies. The large areas of uncertainty respecting the physical, chemical, and biological processes in the sea lead to re- strictions on what can now be regarded as safe practices. These will probably prove too severe when we have obtained greater knowledge. It is urgent that the research required to formulate more precise answers should be vigorously pur- sued. Fortunately, the use of radioactive iso- topes is one excellent means of acquiring the needed information, and the quantities of these isotopes required for pertinent experiments are well within limits of safety. Moderate quanti- ties of the very waste products we are concerned with can, therefore, provide one means of at- tacking the unsolved scientific problems. II. THE NATURE OF THE OCEAN AND ITS CONTAINED ORGANISMS The ocean basins cover 361 x 10* square kilometers and have an average depth of 3,800 meters, giving a total volume of 1.37x10* cubic kilometers. They are characteristically bordered by a continental shelf, which slopes gently out to a depth of about 200 meters. In- side it is a steeper slope extending down to the

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Atomic Radiation and Oceanography and Fisheries deep sea floor with depths of 4,000 meters or more. The average width of the continental shelf is about 30 miles, varying from almost nothing off mountainous coasts, such as the West Coast of South America, to several hun- dred miles in the China Sea. The shelf is not everywhere smooth, but is often intersected by submarine valleys and canyons. In the deep ocean basins there are high mountains and long, deep trenches, features larger than any on land. Some of the deeper parts are isolated by sub- marine ridges which restrict the exchange of water between adjacent areas. The waters of the oceans are stratified. Within a relatively thin layer at the surface, varying in thickness in different places but averaging about 75 meters, vertical mixing caused by winds is fairly rapid and complete. In conse- quence, the temperature, salinity and density are nearly uniform from top to bottom. Relatively fast wind-driven currents exist in this upper mixed layer; these are the "surface" currents of the oceans depicted on many charts. Here also the horizontal mixing is relatively rapid. The mixed layer is the region of the sea in which most of man's activity takes place. Below the mixed layer is a zone within which the temperature decreases and the density in- creases rapidly with depth. This thermocline, or pycnocline, separates the surface mixed layer from the layers of intermediate and deep water, the latter extending to the bottom, within which there are gentle gradients of decreasing tem- perature and increasing salinity and density with depth. Vertical movement in the intermediate and deep layers is much slower than in the mixed layer, and horizontal currents are more sluggish. The strong density gradient across the pycnocline tends to inhibit physical transport across it, because work is required to move wa- ter vertically in either direction, and thus the pycnocline acts as a partial barrier between the mixed layer and the lower layers. There is, however, some interchange of both living and non-living elements; indeed the continued ex- istence of some marine resources depends on such interchange. MARINE RESOURCES Living resources The most important extractive industry based on the resources of the sea is the harvesting of its living resources. On land the cycle of life is relatively simple; we may describe it in four figurative stages. First is the grass, which by a subtle and complex chemistry captures the energy of sunlight and builds organic matter. Sheep and cows live on the grass; tigers and men eat them. The cycle is closed by bacteria, which decompose the dead bodies and the excreta of all living creatures, making their constituent substances again avail- able as building materials for the plants. In the sea, the cycle is longer. Instead of grass there are the tiny floating plants called phytoplank- ton; in place of cows, the zooplankton animals that eat the plants are small crustaceans, no bigger than the head of a pin. Many kinds of tigers eat the cows, but they are mostly also zooplankton, only a fraction of an inch in length. Other intermediate flesh-eaters exist between them and the fishes of our ocean har- vest. Because every link in this long food chain is inefficient, we reap from the sea only a small fraction of its organic production. Other characteristics of the ocean also tend to limit the harvest as compared to that from the land. One is its giant size; more than 70 per cent of all the sunlight that penetrates the atmosphere falls on the sea; moreover, this sunlight can act throughout the top 20 to 100 meters, thus the living space for plants and animals is far greater than on land. This great areal extent and volume, combined with the fluidity of the oceans, results in a low concentra- tion of organisms per unit volume and therefore inefficiency in harvesting. On land, the standing crop of plants and animals is of the same order of magnitude as the amount of organic production per year, while in the ocean the crop is very small, com- pared to the production, because of rapid turn- over. The average rate of organic production per unit area is probably about the same on land and in the sea, but the efficiency of harvesting depends more on the size of the crop than on the total amount of organic matter produced. The plants of the sea, on which all other liv- ing things depend, grow only in the waters near the surface where bright sunlight pene- trates. These waters differ widely in fertility. Like the land, the ocean has its green pastures where life flourishes in abundance, and its deserts where a few poor plants and animals barely survive. The fertility of the land depends on four things: water, temperature, intensity of sun- light, and available plant nutrients—substances

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General Considerations that usually occur in very small amounts but are essential for plant growth. In the sea, water is, of course, always abundant; the plants are well adapted to the narrow range of temperature; the intensity of sunlight determines the length of the growing season and the depth of growth, but usually not the differences in fertility. These depend only on the plant nutrients in the wa- ters near the surface. As in any well-worked soil on land, the nutrients in the waters must be replenished each year. They are continually de- pleted by the slow sinking of plant and animal remains from the brightly lighted near-surface layers into the dark waters of the depths. Men plow the soil to restore its fertility; the fertility of the sea is restored when nutrient-rich deeper waters are brought up near the surface. The "plowing" of the sea is accomplished in three ways. In some regions winds drive the surface waters away from the coast or away from an internal boundary, and nutrient-rich waters well up from mid-depths. In other areas, the surface waters are cooled near to freezing in the winter, become heavy and sink, and mix with the deep waters. Elsewhere, violent mixing occurs along the boundaries between ocean cur- rents, and deeper waters are thereby brought into the brightly lighted zone. The influx of nutrients to the upper layer, and the corresponding loss from this layer by sinking of plant and animal remains, do not directly involve the deep waters. Upwelling and vertical mixing take place only in the upper few hundred meters. The exchange between these mid-depths and the abyssal deep is a very much slower process, of the scale of hundreds of years. Most of the commercially important marine organisms are harvested in coastal waters or in offshore waters not very far from land. Several factors are involved: (1) Profitable fisheries can be conducted more easily near ports and harbors; (2) the coastal waters are of high fer- tility, because of greater upwelling and turbu- lent mixing and the ease of replenishment of plant nutrients from the shallow sea floor, and perhaps also because of the supply of nutrients and organic detritus from land; (3) the stand- ing crop of plants and animals attached to or living on the bottom in coastal areas is large, relative to the total organic production. None of the animals of the great depths are the objects of a commercial fishery. Even the truly pelagic, high seas fisheries, such as the great offshore fisheries for tuna, herring, red- fish and whales, harvest animals that live pri- marily in the surface layer. Some of these ani- mals, however, do much of their feeding in the deeper layers. The sperm whales, for ex- ample, feed on deep-sea cephalopods at great depths. Moreover, much of the food for com- mercially harvested organisms consists of small animals, including crustaceans, squids, and fishes, that perform vertical diurnal migrations from several hundred meters depth to the sur- face. The sea fisheries produce about 25 million metric tons per year of fishes and marine in- vertebrates, in addition to about 4 million tons of whales. The great bulk of the harvest is taken, at present, from the waters of the north- ern hemisphere, despite the fact that the south- ern oceans constitute 57 per cent of the world's sea area. The following table indicates the pro- duction in 1954 by latitude zones: TABLE 1 HARVEST OF FISHES AND MARINE INVERTEBRATES IN 1954, BY LATITUDE ZONES (FROM FAO, 1957) Millions of Zone metric tons % Arctic region 1.2 5 Northern hemisphere-temperate zone 17.5 72 Tropical zone 4.1 17 Southern hemisphere-temperate zone 1.4 6 Antarctic regions 0* 0* * About 4 million tons of whales were taken in the Antarctic, but few fish or marine invertebrates. The disproportionately large yield in the northern hemisphere is related to three factors: (1) Human populations are heavily concen- trated there; (2) the major fishing nations are the industrialized maritime nations, which are mostly located in the north; (3) except for some of the fisheries for tuna, salmon, her- ring, and whales, the important fisheries are located in the relatively shallow areas along the continents, and the extent of these areas is much greater in the northern than in the southern hemisphere. The sessile algae of shallow coasts are also the object of important industries in Japan, the United States, the United Kingdom, Norway, and some other countries. Some of these plants are used directly for human consumption, while

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Atomic Radiation and Oceanography and Fisheries others are employed indirectly in pharmaceutical and food products. Petroleum and natural gas It is estimated that about 30 million cubic meters of possible oil-bearing sediments underlie the 11.8 million square miles of the submerged continental shelves. These sediments contain some 400 billion barrels of recoverable crude oil. Exploitation of these deposits of petroleum and the associated natural gas has commenced in the waters of the Gulf of Mexico; intensive geophysical prospecting has been conducted off- shore from California and in the Persian Gulf. It may be expected that this source of fossil fuels will be extensively utilized in the near future. The resource is confined to the subsoil of the marginal seas, since only there do we find oil- bearing sediments. Minerals Extraction of sea salt for sodium chloride is an ancient industry, and is now highly developed also for production of sodium sulfate, potas- sium chloride, and magnesium chloride. Bro- mine is extracted directly from sea water for the manufacture of ethylene dibromide. Magnesium metal has been produced commercially from sea- water by chemical and electrolytical procedures for nearly two decades. All of these industries use sea water taken from near the surface at the shore but the quantity of water utilized is insignificant. For example, a single cubic kilometer of sea water contains over a million tons of magnesium, about five times the peak world annual produc- tion of this metal. The floor of the deep sea is known to contain low-grade deposits of cobalt, nickel and copper (0.1 to 0.7 per cent by weight of the metals) associated with deposits of iron and manganese. The problems of mining these materials, in the face of the great depths and pressure, have not been solved, and they certainly will not soon be economically useable. Ocean transportation Long-distance transportation of large cargos by sea is the indispensable basis of international commerce. The economy of the United States and of other industrial nations is in large part dependent on the sea-borne commerce that flows through the seaports. Contamination of the sea by nuclear wastes will certainly not present a hazard to shipping, since acceptable levels of such materials in the surface layer of the sea will be limited by other considerations (such as the effects on the fish- eries) to much lower levels than would consti- tute a hazard to ships' personnel. On the other hand, it is almost certain that nuclear power plants will be extensively used in merchant ves- sels ; they are already in use in naval craft. Serious hazards may arise in confined waters from collisions in which the reactor is damaged and the fuel elements with their contained fis- sion products are lost in the water. Suppose for example that a 50,000 kilowatt reactor (prob- ably fairly typical for a large fast freighter) has been in service without refueling for one year on a ship that has spent half its time under way. Approximately 10 kilograms of fission- able material will have been used up and the total amount of fission products will be ap- proximately 10T curies. If, owing to a collision, the reactor is lost in a harbor, say 8 miles long by 3 miles wide by 50 feet deep, and the fis- sion products become uniformly distributed, the water in the harbor would contain 10-2 curies per cubic meter giving an almost constant radia- tion dose of about 0.5 r per day on the surface. Dock pilings, ship bottoms and other structures covered with fouling organisms would accumu- late a much higher level of radioactivity, and local concentration in the water might be ex- tremely high. Recreation For coastal populations in the temperate, sub- tropical, and tropical regions, the sea and its contents provide healthful sports and satisfac- tion of men's curiosity and their desire for beauty. Boating, swimming, sport fishing, and other recreations are engaged in by millions of people, and are the basis of tourist and service industries of very considerable monetary value. Waste disposal Disposal of domestic sewage and industrial wastes is often conveniently accomplished near coastal population centers by running them into the sea. The large volume and rapid mixing of the ocean waters dilute the wastes, and the bac-

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General Considerations teria in the sea break down the organic con- stituents. Unless care is exercised, however, this discharge into inshore sea areas may be dele- terious to other resources. Dumping of excess volumes of sewage and industrial wastes, with- out proper regard to the local characteristics of the sea bottom, currents, and other factors, has already resulted in ruining some harbors and beaches for recreation, damage to the living resources of adjacent areas, and even serious problems of corrosion to ships. The use of the sea for the disposal of atomic wastes has, fortunately, been so far approached with great caution and with due regard to the possible hazards. The problems, because of the dangerous character of small amounts of atomic wastes, are of a different order of magnitude than those of the disposal of other kinds of wastes. III. POTENTIAL HAZARDS FROM RADIOACTIVE MATERIALS Direct hazards A direct hazard to human beings from radia- tion may exist if the levels of radiation in the environment are sufficiently high. The natural radioactivity of the sea is very much lower than that of the land. According to Folsom and Harley (Chapter 2 of this report), a man in a boat or ship receives only about half a millirad per year from the radio isotopes in the sea, compared with about 23 millirads per year from sedimentary rock or 90 millirads per year from granite. Thus, it would be necessary to increase the radioactivity of the sea many fold to equal the radiation that man normally receives from the land on which he lives. Due to the rather rapid mixing in the upper layers of the sea, and to its very large volume, even large quantities of activity introduced at the sur- face in the open sea become sufficiently dis- persed to constitute no direct hazard after a relatively short time, as has been shown by the dispersion of the activity resulting from weap- ons tests in the Pacific. If the direct hazard were the only consideration, sea disposal of radioac- tive wastes would give rise to difficulties only in small areas near the disposal sites. Some radioactive wastes have been disposed of in the sea by placing them in containers de- signed to sink to the sea bottom. In this way, the wastes are isolated and not dispersed by the ocean currents. Direct hazards could arise if the containers in some manner were to come into contact with humans, such as through ac- cidental recovery during fishing or salvage op- erations or if, through improper design, the containers were to float to the surface and come ashore. Indirect hazards 0 The most serious potential hazards to human beings from the introduction of radioactive products into the marine environment are those that may arise through the uptake of radio iso- topes by organisms used for human food. There are several reasons why these indirect hazards are more critical than the direct hazards: (1) The radiation received from a given quantity of an isotope ingested as food is much greater than the dose from the same quantity in the external environment; (2) many elements, in- cluding some of those having radioactive iso- topes resulting from nuclear reactions, are con- centrated by factors up to several thousand by the organisms in the sea; (3) the vertical and horizontal migrations of organisms can result in transport of radioactive elements and thereby cause distributions different from those that would exist under the influence of physical fac- tors alone; for example, certain elements may be carried from the depths of the sea into the upper mixed layer in greater amounts than could be transported by the physical circulation. It is quite certain that the indirect hazard to man through danger of contamination of food from the sea will require limiting the permis- sible concentration of radioactive elements in the oceans to levels below those at which there is any direct hazard. Any part of the sea in which the contamination does not cause danger- ous concentrations of radioactive elements in man's food organisms will be safe for man to live over or in. A reduction of the harvestable living re- sources of the sea could conceivably occur through the effects of atomic radiations on the organisms that are the objects of fisheries, or on their food. This might result from mortality in- duced by somatic effects, or from genetic changes. There is no conclusive evidence that any of the living marine resources have yet suf- fered from either of these, and they are not likely to be undesirably influenced at radiation levels safe from other standpoints. The knowl-

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Atomic Radiation and Oceanography and Fisheries edge of radiation effects on marine organisms is, however, inadequate for firm conclusions. Pollution in general The introduction of atomic wastes into the aquatic environment is but one aspect of the general problem of pollution. Man's record with respect to pollution of lakes, streams, and parts of the sea by sewage and industrial wastes has not been good. In many places, the waters have been ruined for recreation and useful living resources have been destroyed or made unfit for human consumption. This unhappy record results from two factors: (1) the insidious nature of pollution of the aquatic environment, and (2) the fact that the waters and most of their resources are not pri- vate property, but are the common property of a large community (in the case of the high seas, the whole world) ; what is everyone's business often becomes no one's business. The ruin of an aquatic resource by pollution seldom has been rapid. Quantities of waste products, at first very small, increase year by year until finally the concentrations become so large as to have obvious deleterious effects. For example, in the depletion of oxygen by organic wastes, sharp critical levels of tolerance of low oxygen content exist for some of the living re- sources, so that there is little adverse effect until a critical concentration of pollutant is reached, whereupon catastrophic mortality occurs. In other cases, the effects are more or less propor- tional to the concentrations. The destruction of a resource may then proceed gradually and it may not even be clear whether the pollutant has, indeed, been the cause rather than some other environmental change. For these reasons, it is necessary that the introduction of waste materials of any kind into the aquatic environ- ment be carefully monitored, so that the effects may be detected before they become serious. Unfortunately, such monitoring is seldom the concern of those who produce the pollutants. The record of the control and monitoring of the disposal of atomic pollutants has, so far, been excellent. We are, however, at the thresh- old of a tremendous growth of the atomic energy industry, and it behooves mankind to make sure that as much caution is exercised in the future as in the past. Ordinary pollutants in sewage and industrial wastes are rapidly neutralized by the chemical and biological processes in the sea, and when effects of pollution are detected they can be rather quickly reversed by the cessation of intro- duction of the waste. A number of the radio isotopes, on the other hand, are very long-lived. Having reached harmful concentrations in the sea, they will diminish only by very slow decay, so that the effect of any serious pollution is not reversible. For this reason, the prevention of D atomic pollution is of paramount importance. URGENCY OF THE PROBLEM Estimates of the rate of economic develop- ment of nuclear power vary widely. This source of power is already competitive with conventional sources in some places, and re- search on reactor development with consequent reductions in cost is proceeding rapidly. Thus, we can expect that very large quantities of nu- clear power will be generated in the quite near future, even though the relative urgency of nuclear power requirements differs greatly in different countries. In countries with high costs from conventional (fossil) fuels there is en- couragement to proceed immediately with the commercial construction of reactors of proved design. In such countries as the United States, where conventional power costs are low, major efforts are being devoted to experimental con- struction of new types of reactors that hold promise of economical operation in the future. One megawatt-year of heat produced by a nuclear reactor results in 365 grams of fission products. The Committee on Disposal and Dis- persal of Radioactive Wastes, also a part of the National Academy of Sciences' study of the bio- logical effects of atomic radiation (1956), es- timates that by 1965 the United States will be generating about 11,000 megawatts of reactor heat, some 20 per cent of which will be for naval vessels. This will result in the produc- tion of about 4 tons per year of fission products. According to recent statements of government officials, reported in Nucleonics (1957), the United Kingdom has a 1965 target of 6,000 megawatts of electricity from Calder Hall-type reactors; "Euratom" has a goal of 15,000 mega- watts by 1967, and Japan will produce 1,000 megawatts by 1965 and 10,000 megawatts by 1975. If the reactors are of 25 per cent ef- ficiency in conversion of heat to electricity (the Calder Hall reactor has a net thermal efficiency of 21.5 per cent, Nucleonics 1956), for each

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General Considerations 1,000 megawatts of electrical power there will be produced 1.46 tons per year of fission prod- ucts. Thus, the fission products from the fore- going programs will amount to: United King- dom 8.8 tons, "Euratom" 21.9 tons, Japan 1.5 to 14.6 tons. If we further assume that all other areas of the world will in the next ten years develop nuclear power equal to the sum of that gen- erated in the United States, Japan, the United Kingdom, and "Euratom," there will be a total of some 80 tons per year of fission products. This represents, after 100 days' cooling, accord- ing to the values given by Renn (see Chapter 1, Tables 2 and 3), 3.9 x 104 megacuries of beta r. radiation and 2.5 x 104 megacuries of gamma radiation, or over M.O of the total natural radio- activity of all the oceans (Revelle, Folsom, Goldberg and Isaacs 1955). The annual pro- duction of the isotope of greatest long-range hazard, strontium 90, will be 200 megacuries. Craig (Chapter 3) has shown that a thousand tons of fission products per year would result from a 2.7-fold increase in the present world energy consumption of about five million mega- watts, if 10 per cent of this energy were derived from the heat of nuclear fission at 50 per cent efficiency. World energy consumption is now doubling once every thirty years and a 2.7-fold increase would be expected by about the year 2000. An annual production of a thousand tons of fission products corresponds to an equilibrium quantity of 7.7 x 105 megacuries of radiation or about 1.6 times the total natural radioactivity of the oceans. The equilibrium amount of strontium 90, plus its daughter yttrium 90, would be 2.2 x 105 megacuries. Carritt and Harley (Chapter 6) have made calculations based on an annual production of 4,000 tons of fission products, corresponding to two million megawatts per year of nuclear heat production from fission. If no new sources of power, such as thermonuclear reactions, become available, this production would be expected in the very early part of the twenty-first century because of the limited world fossil fuel reserves. Our knowledge of just what share of these fission products can be safely introduced into the oceans is woefully incomplete because we simply do not know enough about the physical, chemi- cal, and biological processes. If the sea is to be seriously considered as a dumping ground for any large fraction of the fission products that will be produced even within the next ten years, it is urgently necessary to learn enough about these processes to provide a basis for engineer- ing estimates. As shown in the several chapters of this re- port, the necessary information can be obtained only by extensive fundamental research. In the next decade we should attempt to learn far more about the ocean and its contents than has been learned since modern oceanography began 80 years ago. Some of the required investigations of physi- cal, chemical, and biological processes involve the employment of naturally occurring or ex- perimentally introduced radioactive tracers. Pol- lution of the seas by the dumping of atomic wastes, even at levels that are "safe" from the standpoint of human health hazards, will make such experiments progressively more difficult because the presence of introduced pollutants will add an unknown background variability. The sooner the work can be commenced and the cleaner our oceanic laboratory, the more precise will be the experimental results. At the very least, it is urgent that the details of any interim introductions of radio isotopes be carefully doc- umented, so that researchers can take account of them in their investigations. INTERNATIONAL IMPLICATIONS The oceans and their resources cannot be separated into isolated compartments; what hap- pens in one area of the sea ultimately affects all of it. Moreover, the greater part of the oceans and their contained resources are the common property of all nations. Even the rela- tively narrow territorial seas are amenable only to juridical and not physical control; no nation can effectively modify the natural interchange of the biological and physical contents of its terri- torial sea with those of the high seas or of the territorial seas of other nations. The continuity of the oceans, and their status as international common property require that the oceanic dis- posal of radioactive wastes be treated as a world problem. It is, first of all, urgent that the nations of the earth formulate agreements for the safe oceanic disposal of atomic wastes, based on ex- isting scientific knowledge. Second, because of the vastness, complexity, and immediacy of the underlying scientific problems, it is important that pertinent oceanographic research be intensi- fied on a world-wide basis. Third, from the

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Atomic Radiation and Oceanography and Fisheries standpoint both of research and of proper con- trol of this new kind of pollution, careful rec- ords should be maintained of the kinds, quanti- ties, and physical and chemical states of all radio isotopes introduced into the seas, together with detailed data on locations, depths and modes of introduction. This can probably best be done by national agencies reporting to an international records center. Although we are urgently concerned with preventing possible deleterious effects of atomic wastes, atomic radiations can also be of benefit. Large-scale experiments employing radioactive isotopes might contribute importantly to our knowledge of the flux of materials through the food chains from the phytoplankton to the harvestable fishes, invertebrates, and whales (Schaefer, Chapter 13 of this report). Such knowledge will not only make possible assess- ment of the ocean's potential for providing food to mankind, but is a basic prerequisite for the effective conservation of marine populations, to permit maximum harvests to be taken year after year. Other experiments using radioactive trac- ers could lead to improved knowledge of the processes of circulation and mixing in the sea (Folsom and Vine, Chapter 12; Craig, Chap- ter 11). In both types of experiments, inter- TABLE 2 ELEMENTS IN SOLUTION IN SEA WATER (EXCEPT DISSOLVED GASES)1, * me/ke Element Cl = 19.00%. Total in oceans (tons) Nuclide Total (tons) Curies Chlorine 18,980 2.66 X 10" Sodium 10,561 1.48 X 10" Magnesium 1,272 1.78 X 10U Sulfur 884 1.23 X 10" Calcium 400 5.6 X 10" Potassium 380 5.3 X10" K" 6.3 X10U 4.6 X K Bromine 65 9.1 X 10" Carbon 28 3.9 X 10" C" 56 2.7 X K Strontium 13 1.8 X 10" Boron 4.6 6.4 X10U Silicon 0.02 -4.0 0.028-5.6 X 10U Fluorine 1.4 2 X 1011 Nitrogen (comp.) . 0.01 -0.7 0.14 -9.8 X 10U Aluminum 0.5 7 X 10U Rubidium 0.2 2.8 X 10" Rb" 1.18 X 10U 8.4 X K Lithium 0.1 1.4 X 10" Phosphorus 0.001-0.1 0.014-1.4 X 10" Barium 0.05 7 X10" Iodine 0.05 7 X10U Arsenic 0.01 -0.02 1.4 -2.8 X 10U Iron 0.002-0.02 0.28 -2.8 X 10" Manganese 0.001-0.01 0.14 -1.4 X 1010 Copper 0.001-0.01 0.14 -1.4 X 1010 Zinc 0.005 7 X10* Lead 0.004 5.6 X 10* Selenium 0.004 5.6 X 10* Cesium 0.002 2.8 X 10* Uranium 0.0015 2.1 X 10* LI8"8 2.8 X 10* 3.8 XK Molybdenum 0.0005 7 X 10* ll"" 2.1 X 101 1.1 X K Thorium < 0.0005 <7 X 10* Thm 1.4 X 107 8 XK Cerium 0.0004 5.6 X 10* Silver 0.0003 4.2 X 10* 0.0003 4.2 X 10* Lanthanum 0.0003 4.2 X10* Yttrium 0.0003 4.2 X10* Nickel 0.0001 1.4 X 10' Scandium 0.00004 5.6 X 10' Mercury 0.00003 4.2 X 10' Gold 0.000006 8.4 X10* Radium 0.2-3 X 10'" 28 -420 Ra2* 4.2 X 10* 1.1 X K 1 Sverdrup, H. U., M. W. Johnsoi i, and R. H. Fleming, OCEANS (1942). 2 Revelle, R., T. R . Folsom, E. D. Goldberg, and J. D. Isaacs (1955).

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General Considerations national scientific cooperation will often be essential for optimum results. IV. CHEMICAL PROCESSES AND RADIOACTIVE MATERIALS Elements in sea water Sea water is a solution of a large number of dissolved chemicals containing small amounts of suspended matter of organic and inorganic ori- gin. The ratios of the more abundant elements are very nearly constant, despite variations in absolute concentrations in different parts of the sea. Lower than average absolute amounts are encountered in coastal areas and near river mouths, while higher amounts are encountered in areas of high evaporation, such as the Red Sea. Vertical variations are usually small; in general, in the open ocean in mid-latitudes, the quantity of dissolved materials, measured by the salinity, first decreases slightly with depth, then increases slowly in the deep water. Table 2 (from Carritt and Harley, Chapter 6) shows the concentrations of some of the ele- ments in solution in sea water at a chlorinity of 19.00%0, which is near average for the sea, and the total amounts in the ocean as a whole. Also shown are the total amounts and total radioactivity of the principal naturally occur- ring radio isotopes. In addition to the listed elements, there are variable amounts of dis- solved gases, including nitrogen, oxygen, and the noble gases. A range of values is given for some elements present in small quantities, such as nitrogen, phosphorus, silicon, iron, and cop- per. These are substances necessary for living organisms, and the inorganic phases may be re- duced to nearly zero in surface waters where they have been almost completely removed by organic uptake. Behavior of introduced materials A number of things can happen to materials introduced into the sea either in solution or as particles. The particles may go into solution. The dissolved substances may be precipitated as particles of colloidal or larger size either by co- precipitation with other elements, by sorption on organic or inorganic particles already present in the sea, or by interaction with other sea water constituents. Both dissolved materials and par- ticles may be ingested by organisms and enter into the biochemical cycles. Particles in the sea are continually removed by settling out on the bottom. The rates of settling depend on the size and density of the particles, as modified by various physical and biological factors. Normal removal of elements from sea water The results of geochemical studies provide very approximate estimates of the fractions of some elements supplied to the ocean that are eventually removed from solution. In Table 3 TABLE 3 GEOCHEMICAL BALANCE OF SOME ELE- MENTS IN SEA WATER (FROM GOLDSCHMIDT, QUOTED IN RANKAMA AND SAHAMA, 1950, TABLE 16.19) Amount present in ocean (ppm) 10,560 380 Element Na .... K Total supplied (ppm) 16,980 15,540 Transfer percentage 62 2.4 Rb .... Ca .... 186 0.2 400 13 0.1 14 7.2 Sr 21,780 180 Ba .... Fe .... Y 150 30,000 16.9 0.05 0.02 0.0003 0.03 0.00007 0.002 La Ce .... 11 0.0003 0.0004 0.003 0.001 27.7 are listed a number of elements, including some of the elements having long-lived fission-product isotopes, with their concentrations in the supply to the ocean and in the ocean itself. Assuming steady-state equilibrium, the ratio of the con- centration in the ocean to the concentration in the supply, the transfer percentage, indicates what share of the supply stays in solution. Large values of the transfer percentage indicate that a relatively large fraction remains dissolved; small values indicate that relatively much is removed. These data give no information on the re- moval processes or on the time rate of removal. The latter can be obtained from estimates of rates of natural sedimentation together with chemical analysis of sediments or from study of rates of sedimentation of radio isotopes follow- ing weapons tests or waste disposal operations (Carritt and Harley, Chapter 6). Goldberg and Arrhenius (in press), from a study of natural sediments, have estimated resi- dence times in the ocean for several elements. They conclude that one half the amount of

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10 Atomic Radiation and Oceanography and Fisheries strontium present at a given time is deposited in the sediments in about ten million years. For other elements the residence times relative to strontium are roughly proportional to the trans- fer percentages. Thus they estimate that the residence time for iron is of the order of a hun- dred years. Introduction of radioactive materials Radioactive materials in large quantities can be introduced into the sea from reactor wastes, from weapons tests, or in warfare. gradients of specific activity decreasing from the sites of introduction, and depending on the mixing characteristics of the ocean. Q Nuclear explosions have been the principal source of fission products introduced into the sea to date. The total quantity of fission power from such explosions so far may be estimated at 40 to 60 megatons of TNT equivalent, from the data summarized by Lapp (1956). This corresponds, with 20 kilotons equal to 1 kilo- gram of fission products (Libby, 1956a), to two to three metric tons of fission products. TABLE 4 FISSION PRODUCT ACTIVITY AFTER 100 DAYS COOLING FROM 10" MEGAWATT HOURS OF NUCLEAR POWER PRODUCTION » Isotope Half-life Tons (metric) Kr* ... 94y 7.3 Sr* ... 55 d 86 Sr" ... 25 y 463 Y"> ... 62 h — Y" ... 57 d I11 Zr" ... 65 d 152 Nb- .. 35 d 161 Ru"" .. 45 d 46 Rh1M .. 57 m — Ru1M . . 290 d 35 Rh1M . . 30 sec — I1" ... 8.0 d — Csm ., 33 y 705 Ba1" .. 2.6 m — Ba1" .. 12.5 d 2 La1" 1.7 d — Ceul .. 28 d 4) Pr"1 .. 13.8 d 2 Ce"4 .. 275 d 490 Pr14* .. 17m — Pm"7 . 94 y 7.3 Sm"1 . 73y 0.7 1 Adapted from data of Culler (1954) and Revelle et al. (1955) 2 Based or i tonnage shown in Table 2. Curies at 100 days 3.3 X101 2.3 X 10U 7.5 X 1010 7.48 X 10'° 2.8 X 10" Xio" X 10" Xio" Xio" Xio" 5.15 X 10" 5.2 XIo* 5.63 X 1010 5.1 X 1010 X10U Xio" X iou xio" X 10" Xiou X to* X 10' 3.2 6.3 1.3 1.3 1.5 1.5 2.5 1.5 1.4 1.6 2.4 3.3 2.0 Specific activity curies per ton 2 0.128 0.0042 178 6,660 0.0743 20.1 0.728 2.14 595 268 386 In Table 4 is a listing of the important fis- sion products, their half-lives, and the quantities resulting from 1011 megawatt hours of nuclear power production (Carritt and Harley, Chapter 6). The column "specific activity" shows the ratio of the quantity of radioactivity of a par- ticular isotope to the total amount of isotopes of that element in the sea for this amount of energy. The specific activity will, of course, be lower for smaller amounts of fission. It is also obvious that a uniform specific activity in all parts of the sea would be obtained only if the fission products were evenly distributed. Since, under any practical method of introduc- tion, this will not occur, there are bound to be The amount of fission products reaching the sea from nuclear explosions depends on a num- ber of factors such as the location of the burst, the distance above (or below) the surface, and the size of the weapon or device. For the smaller devices with a TNT equivalent of several kilotons, most of the fallout is immedi- ate and local, although an appreciable fraction remains in the troposphere for a few weeks (Libby, 1956a, b). Subsurface explosions will result in local deposition of a larger fraction of the fission products; a deep underwater burst will deposit practically all of the activity locally, with nearly J being in the surface layer and about § below (Revelle, 1957). In the case of

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General Considerations 11 large, megaton devices, half or more of the total fission products are injected into the strato- sphere from which there is a slow leakage into the troposphere (of the order of 10 per cent per year) and subsequent fallout fairly evenly over the entire northern hemisphere, with lesser amounts in the southern hemisphere (Libby, 1956a, b). Of this long-term fallout, up to 71 per cent falls on the oceans, since this is the proportion of the earth's surface covered by them. (The proportion of land to sea is higher in the northern hemisphere than in the south- ern, and since most of the long-term fallout occurs in the northern hemisphere, the amount entering the ocean will be less than 71 per cent.) On the other hand, some of the fallout on the land will eventually reach the sea through land drainage or river runoff. Except in the case of deep underwater bursts, all of the fission products reaching the sea from weapons tests are deposited in the upper layer of the ocean. Removal into the deeper water is relatively slow. Despite the rapid mix- ing within the upper layer by vertical and hori- zontal wind stirring, the products from a large weapon remain in measurable concentrations over many months. A survey made 13 months after the 1954 weapons tests in the Pacific showed low-level activity over a vast area (Har- ley, 1956). Radio isotopes in fallout on the land remain largely in the upper few inches of the soil. Fall- out on the sea, on the contrary, is rapidly dif- fused through the upper mixed layer, some 75 meters deep on the average. Consequently, for conditions of equal fallout, the concentrations of radio isotopes in the part of the sea from which they are taken up by man's food organ- isms are less than in the soil. Thus, even though the calcium concentration of sea water is lower than in most soils, the ratio of stron- tium 90 to calcium in the marine environment is now much less than in agricultural lands of the mid-western United States. In 1955 (Libby 1956b) these soils contained about .025 micro- curies of strontium 90 per kilogram of calcium available to growing plants. Revelle (1957) has calculated that for an equal amount of widely distributed fallout (from approximately 25 megatons TNT equivalent of fission) about .00015 microcuries of strontium per kilogram of calcium would be present in the upper mixed layer of the sea, half of one percent of the amount in soils. In addition to fission products, neutron ir- radiation of elements in the environment im- mediately after the detonation produces other radioactive isotopes. With ordinary land or marine materials, the amounts of this neutron- induced radioactivity are small (Libby, 1956a). However, soon after the 1954 tests in the Pacific, quantities of zinc 65 were discovered in marine fishes, and subsequently cobalt 60 was recovered from clams in the Marshall Islands. These isotopes probably originated from neu- tron irradiation of metals, other than the fis- sionable materials, in the test device. Comparison of table 2 and table 4 demon- strates that the mass of radioactive isotopes in- troduced into the sea from weapons tests, or which might be introduced from disposal of waste products, will be very small compared with the amounts of their normal isotopes al- ready present. The introduction of the radioac- tive material does not, therefore, appreciably modify the chemical and physical properties of normal seawater, so that the chemistry of the introduced radioactive substances is the same as for the corresponding non-radioactive isotopes in the sea. Introduced radioactive isotopes will partition into a soluble and an insoluble fraction. The physical states of a given element under equi- librium conditions depend upon whether or not the solubility product of the least soluble com- pound has been exceeded. Since the ionic ac- tivities of the elements in the complex chemical mixture that is sea water are not accurately known, it is difficult to attack this problem from theory. Greendale and Ballou (1954) have de- termined the distribution among soluble, col- loidal, and particulate states of important fission product elements by simulating the conditions of an underwater detonation; their results are given in Table 5. Elements of Groups I, II, V, VI and VII usually occur as ionic forms, while other elements, including the rare earths, occur as solid phases. Some of these results have been confirmed by field observations following weap- ons tests (see Chapter 6 of this report by Carritt and Harley, and Chapter 7 by Krumholz, Gold- berg and Boroughs). Those elements in Table 5 that have sufficiently long half-lives to con- tribute a significant share of the total activity after one year of decay are marked with an asterisk. Cesium 137 and strontium 89 and 90

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General Considerations 15 brought to the surface by this process. Upwell- ing occurs along the western coasts of continents in intermediate and low latitudes, wherever the wind-driven circulation removes surface water from the coast. This water is replaced by deeper water moving upward. Such coastal upwelling has been found to be of the order of 1 to 3 meters per day. Upwelling also occurs in mid- ocean where there are surface current diver- gences, most notably along the equator in the eastern and central Pacific. In regions of surface convergence, where sinking waters may extend to the oceanic depths, or may spread out at intermediate levels, ac- cording to their density. In tropical and tem- perate latitudes such sinking is confined to the upper few hundred meters, but at high latitudes the waters may reach great depths. Indeed, it is in the convergence regions of high latitudes that much of the intermediate and deep water of the oceans are formed. In regions where increase of surface density by evaporation, freezing out of ice, or cooling, causes the surface waters to sink and be replaced by the formerly deeper water. Deep thermal convection occurs in high latitudes and extends in some areas to the bottom; for example, Ant- arctic bottom water is formed in the Weddell Sea by the cooling and sinking of the surface waters, and the Atlantic deep water is formed in a similar manner east of Greenland. Haline convection takes place in regions where evapora- tion exceeds precipitation or where freezing prevails over melting. The latter in high lati- tudes increases the intensity of the thermal convection. Haline convection in winter is re- sponsible for the characteristics of the deep water of the Mediterranean Sea. This water flows out into the North Atlantic at depths of 1,000 to 1,500 meters, and can easily be identi- fied even on the western side of the ocean. The exchange between the surface layer of the ocean and the deeper layers may be either continuous or discontinuous. Some idea of the rate of exchange can be obtained from various estimates of the "age" or average residence time of the water in the deeper layers. These es- timates, which differ widely depending on the data and assumptions used, have been sum- marized by Wooster and Ketchum (Chapter 4 of this report) and by Craig (Chapter 3). Three estimates for the water in the inter- mediate layer of the Atlantic Ocean give resi- dence times between 7 and 140 years. Estimates for the water below 2,000 meters vary from 50 to 1,000 years. An estimated upper limit based on the measured heat flow through the sea floor under the Pacific Ocean indicates that the Pacific deep water is replenished in less than 1,000 years. The deep water in the Pacific may be older than in the Atlantic because of the larger volume of the Pacific. EXCHANGE FROM CONFINED BASINS The few data available for estimating the age of water in confined basins have been considered by Wooster and Ketchum (Chapter 4). These indicate that the mean residence time of water in the Mediterranean Sea is about 75 years. In the Caribbean Sea the mean age cannot be less than 6 years and, in the deeper part, may be as much as 140 years. The deep waters of the Black Sea apparently remain isolated for very long periods. Transport considerations lead to an estimated age of at least 2,500 years, while, from consideration of phosphorus accumulation, the age has been estimated at 5,600 years. VI. BIOLOGICAL PROCESSES AND RADIOACTIVE MATERIALS Uptake and accumulation of elements in organ- isms Organisms take up from their environment and their food and incorporate into their bodies those elements required for their maintenance, growth, and reproduction. The proportion of various elements required by the organisms are different than the proportions in the environ- ment, and this results in concentrations of some elements in the biosphere. The energy that drives the whole life cycle is the energy of sunlight. This energy is bound chemically in organic compounds by the photo- synthesis of plants, and is passed along, through the food chain, in the food of all the organisms beyond the plants. The flux of energy, and hence the flux of carbon, through the various trophic levels measures the productivity of the organisms at each level. Since the efficiency at each stage of the chain is low (of the order of 10 per cent to 30 per cent) the flux decreases at each step. The standing crop, or biomass, of organisms at the different levels, or, in other words, the amount of carbon present in the or- ganisms at each level, may be greater or less

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16 Atomic Radiation and Oceanography and Fisheries than the amount at the next lower level, de- pending on the rates of turnover of the popula- tions involved. In addition to the abundant elements carbon, oxygen and hydrogen, the bodies of organisms contain a number of elements in smaller amounts, such as nitrogen, phosphorus, calcium, strontium, copper, zinc, and iron, which are essential to the life processes. These may be ob- tained by organisms above the plants in the food chain either from their ingested food, or by direct uptake from the sea water. Since the requirements for different elements are different in different kinds of organisms, the fluxes of the of the populations of a particular part of the sea, and any quantities added will be soaked up by the biosphere very rapidly. Both dissolved and particulate materials can be taken up from the environment. Iron, for example, occurs in the sea almost entirely in particulate form and is used in that form by diatoms. Fishes can take up ionic calcium and strontium directly from the sea water. Observa- tions in conjunction with weapons tests, re- ported in Chapter 7 of this report, have shown that particulate feeders among the zooplankton ingest particles of inorganic compounds and retain them. TABLE 6 APPROXIMATE CONCENTRATION FACTORS OF DIFFERENT ELEMENTS IN MEMBERS OF THE MARINE BIOSPHERE. THE CONCENTRATION FACTORS ARE BASED ON A LIVE WEIGHT BASIS (FROM KRUMHOLZ, GOLDBERG AND BOROUGHS, CH. 7 OF THIS REPORT) Concentration factors < Algae (non-cal- careous) 1 25 1 10 20 100 100 20,000 500 10 1,000 1,000 300 10,000 10 10,000 *1. < III. .Ilil. M Invertebrates Vertebrates Element Na Form in sea water (i in sea water micrograms/1) 10' 380,000 0.5 400,000 7,000 10 3 10 2 10 2 1 0.05 70 900,000 50 Soft 0.5 10 10 10 10 5,000 5,000 10,000 200 100 100 1,000 Skeletal 0 0 Soft 0.07 5 10 1 1 1,000 1,000 1,000 100 20 20 40 Skeletal 1 20 K Cs . . Ca . . . . . . Ionic 1,000 1,000 1,000 5,000 100,000 200 200 50 30,000 1,000 5,000 0 Sr . . . . Ionic Zn , . . . Ionic Cu . . . . Ionic Fe . . . . Particulate Ni * . . . . Ionic Mo . . . . lonic-Particulate V t Ti j Cr j p , . . . Ionic 10,000 5 100 10,000 1 50 40,000 2 10 2,000,000 s I . * Values from Laevastu and Thompson (1956). various elements are variable from one to an- other, and at different trophic levels. The concentration factors of some of the im- portant elements in different kinds of organ- isms are tabulated in Table 6, taken from Krum- holz, Goldberg and Boroughs (Chapter 7 of this report). Certain elements, for example, sodium, occur in some organisms at lower con- centrations than in the water; they are selected against. On the contrary, those elements, such as phosphorus, that are essential to the organ- isms but occur in low concentration in the sea water, are concentrated by several orders of magnitude. In some parts of the sea, the phos- phorus may be nearly completely removed from the water by the organisms. Such elements are often limiting constituents for further increase The uptakes of various elements by organ- isms are not entirely independent of one an- other. Elements of similar chemical properties tend to be taken up together very roughly in the same proportions as they exist in the environ- ment. This is true, for example, of calcium and strontium. Sometimes one element has an in- hibiting effect on another. There can also be synergistic effects, such as the enhancement of phosphorus uptake of diatoms by increased concentration of nitrogen. Certain elements are deposited, in large part, in particular organs. Perhaps the best known examples are the deposition of iodine in the thyroid glands of vertebrates, or the deposition of calcium and strontium in the bones of verte-

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General Considerations 17 brates and in the shells and other hard parts of invertebrates. The length of time an organism retains the average atom of a given element varies greatly from one element to another. This is some- times measured as the biological half-life, al- though the relative rate of loss is not a simple linear function of time as is the case with radio- active decay. Much is known about the reten- tion times of different elements in man (see, for example, Handbook 52 of the National Bureau of Standards, 1953), but there are few data for most marine organisms. The rate of excretion of an element and the amount ulti- mately retained, will be quite different if the element is taken up quickly from a single dose or is taken up slowly over a long time. The processes of uptake, accumulation, and loss of elements by marine and other aquatic organisms, are discussed in more detail by Boroughs, Chipman and Rice (Chapter 8 of this report), Krumholz, Goldberg, and Boroughs (Chapter 7), and by Krumholz and Foster (Chapter 9). Effects of organisms on spatial distributions of elements in the sea Those elements of which a large proportion is cycled through organisms are modified pro- foundly in their spatial distributions by the ef- fects of the biosphere, so that they are quite differently distributed in the sea than elements in which the distribution is determined only by physical and inorganic chemical processes. We have already mentioned phosphorus as a notable example. Ketchum (Chapter 5 of this report) has written a detailed discussion of the general effects of the ecological system on the distribu- tion of elements in the sea. The marine biosphere acts as a reservoir for those elements that are removed selectively from sea water by organisms. This reservoir is not stationary in space, however, because many of the living organisms make both vertical and horizontal migrations of large extent, while their dead bodies and fecal materials continu- ally fall toward the bottom under the influence of gravitation. The effects of the living reser- voir in the distribution of elements vary not only from one part of the sea to another, but also seasonally in the same area. Because organisms in the sea are more abun- dant in the upper layers than deeper down, those elements in scarce supply that are essen- tial to life tend to be retained by the biosphere in the upper layers and to be returned to solu- tion in the deeper layers. Stationary popula- tions, such as attached benthic organisms, act as a fixed reservoir. Where there are currents at different levels in opposite directions, the accumulation of ele- ments by pelagic organisms, together with grav- ity effects on their dead bodies and fecal ma- terials, can result in local concentrations of ele- ments at intermediate depths greater than the concentrations in either the overlying or the deeper waters. This pattern, as noted by Ketchum, is common in estuaries, continental shelves, and in the vicinity of coastal upwelling. Migration of organisms may result in a net transport of elements from areas of high con- centration to areas of lower concentration. Thus, for example, the vertical migrations of the or- ganisms of the deep scattering layer can result in a transport from the deeper layers into the upper mixed layer. Salmon which spawn and die in fresh waters after accumulating elements in the sea can transport significant quantities of some elements from the sea to fresh waters. Finally, the remains of organisms, falling out as particulate matter, are an important com- ponent of the sedimentation process in the deep sea, and are thus important in the geochemical cycle, as noted by Carritt and Harley (Chapter 6) and others. Although we have some understanding of the various processes involved, data for making useful quantitative assessments are almost en- tirely lacking. Effects of introduction of radioactive elements Since the isotopes of most chemical elements are similar in chemical behavior, it can be as- sumed that organisms do not appreciably dis- tinguish between the radioactive and non-radio- active isotopes, and that, to a good degree of approximation, the path of a radioactive element through the biological system is the same as that of its non-radioactive isotopes. The accumulation of radio isotopes in organ- isms will, therefore, depend on the same factors as the accumulation of normal isotopes (their concentration in the water where the organisms are located, the concentrations of other elements by which uptake is influenced, the size of the population of organisms concerned, the concen-

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18 Atomic Radiation and Oceanography and Fisheries tration factors of the organisms for each ele- ment, and the rates of excretion, and in addition will depend on the decay rates of the radioactive isotopes). The most important radio isotopes from the standpoint of accumulation in organisms are, therefore, those which are concentrated in large degree by organisms, are retained by them for relatively long periods of time, and have slow decay rates. An additional consideration from the standpoint of human hazards is the uptake and biological half-life of the elements in hu- mans who may consume the marine organisms as food. The most important fission product from all these considerations is strontium 90 and its daughter yttrium 90. This isotope has a large fission yield and a long physical half-life, is concentrated by organisms, and can be tolerated in human food only in very low amounts. Ce 144 is another isotope with a large fission yield, which is concentrated by organisms (Har- ley, 1956), and has a moderately slow decay rate. Due to its small uptake and low retention by humans, it can, however, be tolerated in human food in much greater concentrations than Sr 90. Zn 65 and Co 60, although not fission prod- ucts, are sometimes produced in relatively large quantities in weapons tests. They are concen- trated by very large factors in fish and mollusks used for human food, but fortunately they possess a relatively high tolerance level in humans. Because of its biological role both in marine organisms and in humans, strontium 90 dom- inates consideration of depositing mixed fission products in the sea. For other radioactive wastes, and for mixed fission products from which Sr 90 has been removed, other elements will be the critical determinants, but in most cases, prior removal of Sr 90 will permit the safe disposal in the sea of larger quantities than would otherwise be possible. The safe quantity of fission products depends on the concentrations that reach man's food or- ganisms. The quantity will be greater if sites of introduction are chosen to give either long periods of isolation of the wastes or high dis- persion (and thus low concentration) of the fractions that come into the environment (both physical and biological) of human food organ- isms. Somatic and genetic effects on marine organisms It is sometimes suggested that sufficient quan- tities of radioactive elements may be accumu- lated by marine organisms to endanger their populations, either by direct somatic effects or through genetic changes. Some aspects of this problem are discussed by Donaldson and Foster in Chapter 10 of this report. So far as somatic effects are concerned, ex- perimental data indicate that primitive forms are more resistant to ionizing radiation than the more complex vertebrates. It has not been possi- ble to demonstrate any large-scale radiation damage to marine populations in the vicinity of large weapons tests. Levels of radiation safe from the standpoint of human hazards are also probably safe for the populations of marine organisms that are used as human food. By analogy with results from genetic studies on laboratory animals, it may be inferred that significant genetic population effects will occur in marine organisms at much lower levels of radiation than will produce somatic effects. These genetic effects might be related to the in- crease in amount of total body radiation above the natural background. As shown by Folsom and Harley (Chapter 2), the normal radiation background of organisms in the deep sea is very low, so that appreciable quantities of radioactive wastes would significantly increase the radiation received by them. Craig (Chapter 3) has shown that the deposition of 1,000 tons per year of fission products in the deep sea would, at secular equilibrium, almost triple the average radiation level in the deep water. This could, conceivably, result in genetic effects in the marine popula- tions in these waters, which might seriously up- set the ecological system of the oceans. At the present state of knowledge, however, this is pure speculation. The matter does require, nevertheless, serious investigation. VII. PREDICTED EFFECTS OF INTRODUCED RADIOACTIVE MATERIALS Prediction of the effects of the introduction of radioactive materials into the different do- mains of the oceans must take into account the various physical, chemical, and biological proc- esses discussed above. While our knowledge of these processes is very imperfect, we can make rough evaluations of the effects of disposal of fission products in different parts of the sea. Because of the limitation of knowledge, these

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General Considerations 19 evaluations must, of necessity, be conservative. Under some circumstances this necessity could involve considerable cost to society. Those sites and methods of disposal, both on the land and in the sea, that provide the least hazard may also involve the greatest disposal costs, so that, to the extent we must include a safety factor be- cause of ignorance, there can be economic loss. In disposing of radioactive materials in the sea, we aim at two things: (1) isolation of the materials, so that their entry into the part of the sea and its contents used by man is limited, (2) dispersal of the materials that do enter the domain important to man, to keep the concen- trations of radioactive elements at tolerable levels. Depending on the quantity of materials to be dealt with, we may need to consider either or both of these possibilities. Introduction in the upper mixed layer Radioactive materials introduced into the up- per mixed layer will, because of the rapid transport and large horizontal and vertical mix- ing within this layer, be carried away from the site of introduction and rapidly dispersed. Dis- persion may be more rapid in coastal areas than in the open sea, but in some situations there may be a net transport inshore, particularly in or near estuaries, if the materials are introduced below the surface. Direct evidence of near-surface transport and dispersion of fission products in the open sea has been obtained by the surveys of the "Shunkotsu Maru" (Miyake, Sugiura and Kameda, 1955) and the "Taney" (Harley, 1956), respectively four and thirteen months after the Pacific weap- ons tests of March 1954. The indicated trans- port of these products was in good agreement with current velocities measured by conven- tional means. These data from the open sea and earlier measurements on the partially confined waters of Bikini Lagoon (Munk, Ewing and Revelle, 1949) demonstrate the rapid dispersal of fission products in the surface layer. Dispersion in an inshore situation (the Irish Sea) was measured with fluorescein by Selig- man (1955) as a preparatory study for the dis- charge of low-level wastes from a power reactor installation. Subsequent experience with libera- tion of the radioactive wastes (Anon., 1956) confirmed that they were rapidly dispersed. Radioactive materials introduced into coastal waters enter directly into that part of the ocean most utilized by man, from which he removes the greater share of his harvest of marine food organisms. The sessile algae, bottom living in- vertebrates, and fishes of these waters heavily concentrate certain of the elements, such as strontium, cesium, zinc, and cobalt that has radioactive isotopes most hazardous to man. While dispersion due to physical transport and dispersion in these waters is high, they are usually shallow, so that the volume is limited and there can also be considerable accumula- tion in shallow bottom sediments from which the isotopes can be again taken up by man's food organisms. In some coastal areas the combination of physical and biological processes can result in local concentrations of radioactivity in the wa- ters themselves (Ketchum, Chapter 5). Because of the above considerations, the quantity of radioactive materials that can be in- troduced safely into coastal waters near shore is very limited, of the order of a few hundred curies per day. The particular physical, chemi- cal, and biological factors vary so widely from one coastal area to another, that careful study is required to determine the safe amount in any particular locality, arid continuous monitoring should be conducted to guard against effects of unforeseen variability in environmental factors. The rather low level of discharge of radioac- tive products that can be tolerated in coastal waters imposes the necessity of providing ade- quate safeguards against discharge of high-level atomic wastes from accidents to power reactors, either at locations on the shore or shipborne reactors. The quantity of radioactive material that can be safely deposited in the mixed layer in the open sea depends on such local characteristics as the direction and rate of transport, the rate of horizontal dispersion, the rate of uptake by organisms, and the contiguity of fishing areas. However, in general, the quantities will be much greater than those permissible for coastal waters. An idea of the order of magnitude of mixed fission products that can be safely intro- duced in a fairly typical situation is given by the results of weapons tests in the Pacific where a quantity of mixed fission products of the order of half a ton was introduced into the mixed layer in a short time period. That this was near the limit of safety is evidenced by the capture in adjacent areas of specimens of tunas and other fishes with sufficient radioactivity to be doubt-

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20 Atomic Radiation and Oceanography and Fisheries ful for human consumption (Kawabata, 1956, and Hiyama and Ichikawa, 1956). Deep water introduction The only place in the ocean in which we can be confident at this time that radioactive wastes of the order of some tons a year can be safely deposited is in the depths of the sea. Knowl- edge is, however, insufficient to determine whether radioactive materials of the order of the expected production from power reactors in the next few decades could be disposed of in this way. Radioactive materials introduced into the deeper layers will be partially isolated from the upper layer for time periods related to the resi- dence time of the water in the deeper layer. During this time there will be a decrease of radioactivity due to decay, and dilution due to dispersion. Since, as we have noted above, the residence times are variable in different depths and different locations, a much greater time of isolation will be obtained in some places than others. The longest average time of isolation will be obtained in deep nearly enclosed basins such as the Black Sea. It has been suggested by Wiist (1957) that there may also be a long isolation period in the abyssal trenches of the central equatorial regions, such as the Romansch Deep or the Tonga Trench, but no data on currents in these deeps are now available. Craig (Chapter 3 of this report), assuming an estimated average residence time in the deep sea of 300 years, the introduction into the deep sea of 1,000 tons per year of fission products after 100 days cooling, and complete uniform mixing within the deep water, has calculated the activity in the deep and surface layers at secular equilibrium. This calculation indicates that the total fission product activity in the mxed layer would be about equal to that at present from natural sources (primarily K<0). The concentra- tion of Sr 90 would, however, be about 6.5 x 10-5 microcuries per liter, or 0.16 microcuries per kilogram of calcium in solution in sea water. Studies of the uptake of strontium by marine fishes indicate a discrimination against strontium with respect to calcium approximately by a fac- tor between 3 and 10. Thus for human popula- tions such as the Japanese (Hiyama, 1956), in which much of the dietary calcium is obtained from marine fishes (including the bones and skin of some species), the amount of strontium 90 ingested per unit weight of calcium would be of the order of .04 microcuries per kilogram of calcium. A human population that obtained all its calcium from marine fishes after equilib- rium was established with about 1,000 tons of fission products per year (1.1 x 105 megacuries of strontium 90) in the deep sea would have a burden, primarily in the bones, of approxi- mately .005 microcuries of strontium 90 per kilogram of calcium. This is 5 per cent of the maximum permissible concentration for the population at large, estimated by the National Bureau of Standards (1955). Weapons tests resulted in an average amount of .025 microcuries of strontium 90 per kilo- gram of calcium available to growing plants in the United States in 1955. By 1970, the amount will be .08 microcuries per kilogram of calcium even in the absence of further weapons tests (Kulp, Eckelmann, and Schulert, 1957). Be- cause of discrimination against strontium with respect to calcium in food grains and grasses, and the additional discrimination in cows' milk and in human beings, it is expected that by 1970 an average of about .002 microcuries of strontium 90 per kilogram of calcium will exist in the United States population, 2 per cent of the maximum permissible concentration. From the above considerations it is uncertain whether reactor-fuel wastes of the order of 1,000 tons a year could be deposited safely in the deep sea. Craig's calculation is most useful in orienting our thinking, but is, of course, very much oversimplified. No account is taken of the removal of activity from the sea by sedi- mentation. On the other hand, it does not take into account any biological transfer of material across the pycnocline, nor can we assume that effective concentration of Sr 90 per unit weight of calcium for some commercially important or- ganisms will not be greater than the values we have taken. Moreover, such a calculation assumes even distribution of the radioactive materials through- out the deep layer. This could only occur if they were evenly distributed when introduced, or if there were uniform and complete mixing in all parts of the deep layer. A priori we should expect that neither the physical circulation and mixing in the deep sea nor the transfer between the deep layer and the mixed layer would be uniform. There is

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General Considerations 21 some evidence, however, from carbon 14 meas- urements made by the Lament Geological Ob- servatory that in fact fairly complete mixing occurs within the deep sea during the average residence time of a water particle. Another calculation, based on very conserva- tive assumptions concerning the mixing proc- esses, was made in the report of a meeting of scientists from the U.S. and U.K. (Anon., 1956). It was assumed that fission products deposited on the ocean floor in mid-latitudes would drift and disperse for at least 10 years before surfacing, at which time the contami- nated area would be a disc about 2 km. thick and 70 km. in diameter, which would be sub- sequently dispersed throughout the surface layer. Repeated deposits of 1 megacurie of Sr 90 (0.4 tons of mixed fission products) made at the rate of ten per year would result in an average con- centration of Sr 90 of not over 10-5 microcuries per liter in the mixed layer, or .025 microcuries per kilogram of calcium. Although we cannot say at this time with any precision what quantities of reactor-waste prod- ucts can be safely deposited in the deep sea, it appears certainly safe to employ quantities up to a few tons a year in careful experimental studies. It is not impossible that 1,000 tons a year can be safely disposed of in deep, isolated basins where the residence time is much greater than the 300-year average estimated for the deep sea generally. For quantities of the order of 100 tons a year or more, effects on the animal popu- lations of the deep sea, and resulting effects on the whole ecology of the sea could become im- portant; as to this no information is at present available. VIII. WHAT WE NEED TO KNOW Our knowledge of most of the processes in the oceans is altogether too fragmentary to per- mit precise predictions of the results of the in- troduction of a given quantity of radioactive materials at any particular place. In order to obtain the necessary knowledge, an adequate, long-range program of research on the physics, chemistry, and geology of the sea, and on the biology and ecology of its contained organisms is required. Such research must be directed toward the understanding of general principles, not simply to the ad hoc solution of a particu- lar local problem for immediate application. The latter sort of study is, of course, desirable in order to provide engineering solutions to par- ticular waste-disposal problems as they arise. Such engineering solutions must necessarily be of limited application and, moreover, they must always be conservative, at least until sufficient broad understanding is obtained. MAJOR UNSOLVED PROBLEMS Some of the major basic problems that should be included in the research program can be briefly outlined: 1. Dispersion in the upper mixed layer Fairly extensive information is available on the mean velocities and transport of the major surface currents. The transient currents and eddies that result in dispersion in both the hori- zontal and vertical directions are, on the con- trary, not understood. Some empirical param- eters approximately describing the relationships of diffusivity to time and to size of area have been developed, but understanding of the de- tailed physical principles is lacking. In con- sequence, it is not possible to predict on the basis of more elementary properties the disper- sion of materials introduced into the upper layer at a given point. Direct measurements must be made, and these are costly and not necessarily reliable. Basic research on the turbulent motion of water in the upper layer is needed. 2. Circulation in the intermediate and deep layers For the region of the sea below the surface layer, we not only do not understand the nature of the turbulent motion, we do not even have a description of the mean currents. The chart- ing of the deep currents, and investigations toward elucidating the physical principles in- volved should be vigorously pursued. 3. Exchange between the surface layer and deeper layers It is important to determine the average rate of exchange of water between the surface and the deep layers, as a basis of estimating average "hold up" times of dissolved materials deposited in the deep layer. It is probably even more im- portant to measure the heterogeneity in the ex- change system, that is to measure the rates of exchange in different areas and depths. We

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22 Atomic Radiation and Oceanography and Fisheries know that vertical exchange is much more rapid in some parts of the oceans than others, but de- scribing it in quantitative terms can be done only in a very sketchy manner. Quantitative data on this subject are required as one basis of arriving at estimates of the amount of atomic wastes that can be deposited safely in specified parts of the deep sea. 4. Sedimentation processes Sedimentation processes constitute an im- portant mechanism for removing atomic wastes from the waters of the oceans. In order to evalu- ate their role, however, we need to measure the average times that different elements remain in the sea before being deposited in the sediments, the rates of sedimentation in different parts of the deep sea, and the ability of the sediments to capture and retain various fission products. 5. Effects of the biosphere on the distribution and circulation of elements As we have noted, marine organisms have profound effects in modifying the distribution and circulation of elements in the sea. It is vitally necessary that the biological processes be studied in sufficient detail to enable their effects to be quantitatively evaluated. Such investiga- tions need to include: The flux of various ele- ments through the different trophic levels, and the variations in different ecological realms such as inshore coastal waters, offshore surface waters and the deep sea; the effects of vertical and horizontal migrations of organisms on redis- tribution of elements; the effects of the uptake, modification of the physical state, and elimina- tion of elements by members of the marine biosphere on their subsequent distribution in the sea. 6. Uptake and retention of elements by organ- isms ased as food for man Related to the foregoing, but of separate im- portance, is the study of the quantities of radio- active elements deposited in different situations in the sea that can be expected to be taken up by organisms harvested for food, the length of time such elements are retained in the food or- ganisms, and, consequently, the levels of con- centration. Some parts of some organisms are not eaten by man, but are discarded or used for other purposes. The sites of accumulation of different radioactive elements in the organisms must therefore be determined. 7. Effects of atomic radiation on populations of marine organisms In order to determine what quantities of atomic wastes can be safely deposited in the sea without upsetting the ecology of the sea through destruction of important populations of organ- isms, research is needed on the somatic and ge- netic effects of atomic radiation on marine popu- lations. This is especially important for organ- isms of the deep sea which may come in contact with very high concentrations of radioactive elements, if deep sea disposal of large quantities proves feasible in other respects. RESEARCH METHODS Much of this required research can be ac- complished by the intensive application of classical techniques of physics, chemistry, ge- ology, and biology. In addition, however, the availability of radioactive isotopes provides us with a powerful new tool, which is especially valuable for studying processes. The use of radioactive elements as tracers permits the paths of various elements, both in the physical en- vironment and within the biosphere, to be de- termined, and the fluxes of the elements through various parts of the system to be measured. Radioactive tracers are useful both in labo- ratory experiments and in field studies of vari- ous kinds. The use of tracers in the laboratory and in small scale field experiments is already familiar. Information from the tracers intro- duced into the sea by weapons tests has provided valuable information. What has not yet been done, and what we believe will be a fruitful approach, is the employment of fairly large quantities of radio isotopes to study the various processes in the open ocean in a planned fash- ion. In Chapters of this report by Folsom and Vine and by Schaefer, suggestions are made for some experiments that should be useful and are currently feasible. Naturally occurring radioactive isotopes can also provide a fruitful means of attack. Craig, in Chapter 11, discusses some of these avenues of research in detail. FACILITIES REQUIRED The Committee has not attempted to draw up detailed estimates of men, ships, and facili-

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General Considerations 23 ties which will be required for an adequate attack on this problem. These requirements will, however, be large. The problems outlined above are among the most difficult in the marine sciences. Adequate solutions will demand the collection of much more knowledge about the sea and its contents than the total obtained in the past hundred years. Because of the urgency of these problems, and because of the large costs involved, it is essential that research be coordinated on both the national and international levels. Coordina- tion among scientists engaged in these studies should be easier in the future than it has been in the past. OTHER BENEFITS OF THE RESEARCH TO MANKIND The potential requirement for disposal of atomic wastes in the sea is sufficient reason for pursuit of these investigations. However, man- kind will derive additional, and perhaps even greater, benefits in other ways. For example, the flux of materials through the various trophic levels of the biosphere is the fundamental proc- ess underlying the harvest of the sea fisheries. This process must be studied to provide part of the basis for atomic waste disposal, but its elucidation will also provide much of the scien- tific base for the optimum exploitation and con- servation of the seas' living resources by man. IX. CONCLUSIONS AND RECOMMENDATIONS We repeat here the conclusions and recom- mendations that were agreed upon by the mem- bers of the Committee at the time they prepared the Summary Report published by the Academy in 1956: 1. Tests of atomic weapons can be carried out over or in the sea in selected localities with- out serious loss to fisheries if the planning and execution of the tests are based on adequate knowledge of the biological regime. The same thing is true of experimental introduction of fission products into the sea for scientific and engineering purposes. 2. Within the foreseeable future the prob- '• lem of disposal of atomic wastes from nuclear fission power plants will greatly overshadow the present problems posed by the dispersal of ra- dioactive materials from weapons tests. It may be convenient and perhaps necessary to dispose of some of these industrial wastes in the oceans. Sufficient knowledge is not now available to predict the effects of such disposal on man's use of other resources of the sea. 3. We are confident that the necessary knowl- edge can be obtained through an adequate and long-range program of research on the physics, chemistry, and geology of the sea and on the biology of marine organisms. Such a program would involve both field and laboratory experi- ments with radioactive material as well as the use of other techniques for oceanographic re- search. Although some research is already un- der way, the level of effort is too low. Far more important, much of the present research is too short-range in character, directed towards ad hoc solutions of immediate engineering problems, and as a result produces limited knowledge rather than the broad understanding upon which lasting solutions can be based. 4. We recommend that in future weapons tests there should be a serious effort to obtain the maximum of purely scientific information about the ocean, the atmosphere, and marine organisms. This requires, in our opinion, the following steps: (1) In the planning stage com- mittees of disinterested scientists should be consulted and their recommendations followed; (2) funds should be made available for scien- tific studies unrelated to the character of the weapons themselves; (3) the recommended scientific program should be supported and car- ried out independently of the military program rather than on a "not to interfere" basis. 5. Ignorance and emotionalism characterize much of the discussion of the effects of large amounts of radioactivity on the oceans and the fisheries. Our present knowledge should be suf- ficient to dispel much of the overconfidence on the one hand and the fear on the other that have characterized discussion both within the Government and among the general public. In our opinion, benefits would result from a con- siderable relaxation of secrecy in a serious attempt to spread knowledge and understanding throughout the population. 6. Sea disposal of radioactive waste materials, if carried out in a limited, experimental, con- trolled fashion, can provide some of the in- formation required to evaluate the possibilities of, and limitations on, this method of disposal. Very careful regulation and evaluation of such operations will, however, be required. We, therefore, recommend that a national agency,

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24 Atomic Radiation and Oceanography and Fisheries with adequate authority, financial support, and technical staff, regulate and maintain records of such disposal, and that continuing scientific and engineering studies be made of the resulting effects in the sea. 7. We recommend that a National Academy of Sciences—National Research Council com- mittee on atomic radiation in relation to ocean- ography and fisheries be established on a con- tinuing basis to collect and evaluate informa- tion and to plan and coordinate scientific re- search.* 8. Studies of the ocean and the atmosphere are more costly in time than in money, and time is already late to begin certain important studies. The problems involved cannot be attacked quickly or even, in many cases, directly. The pollution problems of the past and present, though serious, are not irremediable. The atomic waste problem, if allowed to get out of hand, might result in a profound, irrecoverable loss. We, therefore, plead with all urgency for im- mediate intensification and redirection of scien- tific effort on a world-wide basis towards build- ing the structure of understanding that will be necessary in the future. This structure cannot be completed in a few years; decades of effort will be necessary and mankind will be fortunate if the required knowledge is available at the time when the practical engineering problems have to be faced. 9. The world-girdling oceans cannot be sepa- rated into isolated parts. What happens at any one point in the sea ultimately affects the waters everywhere. Moreover, the oceans are interna- tional. No man and no nation can claim the exclusive ownership of the resources of the sea. The problem of the disposal of radioactive wastes, with its potential hazard to human use of marine resources, is thus an international one. In certain countries with small land areas and large populations, marine disposal of fission products may be essential to the economic de- velopment of atomic energy. We, therefore, recommend: (1) that cognizant international agencies formulate as soon as possible conven- tions for the safe disposal of atomic wastes at sea, based on existing scientific knowledge; (2) that the nations be urged to collaborate in studies of the oceans and their contained organ- * The President of the Academy, Dr. Detlev W. Bronk, has requested that the present committee undertake to develop and carry forward this con- tinuing program. isms, with the objective of developing compara- tively safe means of oceanic disposal of the very large quantities of radioactive wastes that may be expected in the future.** 10. Because of the increasing radioactive con- tamination of the sea and the atmosphere, many of the necessary experiments will not be possi- ble after another ten or twenty years. The recom- mended international scientific effort should be developed on an urgent basis. 11. The broader problems concerned with full utilization of the food and other resources of the sea for the benefit of mankind also re- quire intensive international collaboration in the scientific use of radioactive material. REFERENCES ANON. 1956. Report of a meeting of United Kingdom and United States scientists on biological effects of radiation in oceanog- raphy and fisheries. Nat. Acad. Sci.—Nat. Research Council, Oct. 31, 1956, 8 pp. (mimeographed). BOWDEN, K. F. 1954. The direct measurement of subsurface currents in the oceans. Deep Sea Research, Vol. 2, pp. 33-47. CULLER, F. L. 1954. Notes on fission product wastes from proposed power reactors. ORNL Central File No. 55-4-25. DIETRICH, G. 1957. Selection of suitable ocean disposal areas for radioactive waste. (A preliminary report with 6 charts.) M.S., 10pp. FOOD AND AGRICULTURE ORGANIZATION OF UNESCO. 1957. Yearbook of fishery statistics. FAO, Rome, Vol. 5 (1954-55). GOLDBERG, E. and ARRHENIUS, G. O. S. 1957. Chemistry of Pacific pelagic sediments. In press. GREENDALE, A. E., and N. E. BALLOU. 1954. Physical state of fission product elements following their vaporization in distilled water and sea water. USNRDL Document 436, pp. 1-28. HARLEY, JOHN E. (Editor). 1956. Operation Troll. U.S., A.E.C., N.Y. Operations office 1956. 37 pp. * * As a first step in this direction an informal dis- cussion was held by members of this committee with scientists from the United Kingdom at North Fal- mouth, Massachusetts, on September 27 and 28, 1956. A brief summary of the meeting was published by the National Academy of Sciences (Anon., 1956).

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General Considerations 25 HIYAMA, Y. 1956. Maximum permissible con- centration of Sr 90 in food and its environ- ment. Records of Oceanographic Work in Japan, Vol. 3, No. 1, March 1957, pp. 70-77. HIYAMA, Y., and R. ICHIKAWA. 1956. Move- ment of fishing grounds where contami- nated tuna were caught. Japan Society for the Promotion of Science; Research in the Effects and Influences of the Nuclear Bomb Test Explosions, pp. 1079. JAPANESE FISHERY AGENCY. 1955. Report on the investigations of the effects of radiation in the Bikini region. Res. Dept., Jap. Fish. Agency, Tokyo, 191 pp. KAWABATA, T. 1956. Movement of fishing grounds where contaminated tuna were caught. Japan Society for the Promotion of Science; Research in the Effects and In- fluences of the Nuclear Bomb Test Explo- sions, pp. 1085. KRAUSKOPF, K. B. 1956. Factors controlling the concentration of thirteen rare metals in sea water. Geochim. et Cosmochim. Acta 9, pp. 1-32. KULP, J. L., ECKELMANN, W. R., and A. R. SCHULERT. 1957. Strontium 90 in man. Science, Vol. 125, No. 3241, pp. 219-225. LAEVASTU, T., and T. G. THOMPSON. 1956. The determination and occurrence of nickel in sea water, marine organisms, and sedi- ments. Jour, du Cons., Vol. 21, pp. 125- 143. LAPP, RALPH E. 1956. Strontium limits in peace and war. Bull. Atomic Scientists, Vol. 12, No. 8, pp. 287-289, 320. LIBBY, W. F. 1956a. Radioactive fallout and radioactive strontium. Science, Vol. 123, pp. 657-660. 1956b. Radioactive strontium fallout. Proc. Nat. Acad. Set., Vol. 42, No. 6, pp. 365- 390. MIYAKE, J., SUGIURA, Y., and K. KAMEDA. 1955. On the distribution of radioactivity in the sea around Bikini Atoll in June 1954. Pap. Meteorol. Geophys., Tokyo, Vol. 5, No. 3-4, pp. 253-262. MUNK, W. H. 1950. On the wind-driven ocean circulation. Jour. Meteorol., Vol. 7, No. 2, pp. 79-93. MUNK, W. H., EWING, G. C, and R. R. RE- VELLE. 1949. Diffusion in Bikini lagoon. Trans. Am. Geophys. Union, Vol. 30, No. 1, pp. 59-66. NATIONAL BUREAU OF STANDARDS. 1953. Maximum permissible amounts of radio isotopes in the human body and maximum permissible concentrations in air and water. U.S. Dept. of Commerce, Nat. Bureau Standards. Handbook 52, 45 pp. 1954. Radioactive waste disposal in the ocean. Nat. Bureau of Standards. Hand- book 58, 31 pp. NUCLEONICS. 1956. Calder Hall, over-all de- scription. Nucleonics, Vol. 14, No. 12, pp. S10-S11. 1957. Roundup of key developments in atomic energy. Nucleonics, Vol. 15, No. 6, pp. 17-28. RANKAMA, K., and T. C. SAHAMA. 1950. Geo- chemistry. Univ. of Chicago Press, 1950. REVELLE, R. R. 1957. Statement by Professor Roger Revelle before the joint Committee on atomic energy, 28 May 1957. The Na- ture of Radioactive Fallout and its Effects on Man; Hearings before the Special Sub- committee on Radiation of the Joint Com- mittee on Atomic Energy. Congress of the United States, 1957. REVELLE, R. R., FOLSOM, T. R., GOLDBERG, E. D., and J. D. ISAACS. 1955. Nuclear Science and Oceanography. Int. Conf. on the Peaceful Uses of Atomic Energy. A/Conf. 8/P/277, 22 pp. (mimeo- graphed) . SELIGMAN, N. 1955. The discharge of radio- active waste products into the Irish Sea. Part I: First experiment for the study of movement and dilution of released dye in the sea. Proc. Int. Conf. on Peaceful Uses of Atomic Energy, United Kingdom paper number 418, 25 pp. SVERDRUP, H. U., JOHNSON, M. W., and R. H. FLEMING. 1942. The Oceans. Prentice Hall, New York, 1942, 1060 pp. SWALLOW, J. C. 1955. A neutral-buoyancy float for measuring deep currents. Deep Sea Research, Vol. 3, pp. 74-81. VINOGRADOV, A. P. 1953. The elementary composition of marine organisms. Sears Foundation for Marine Research, Memoir No. 2, 647 pp. WUST, G. 1957. Report on the current veloci- ties, volume transports and mixing effects in the Atlantic deep sea as physical proc- esses important to the transport and dis- persal of radioactive wastes. M. S. (mime- ographed), 19 pp.