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Chapter One INTRODUCTION A. H. Seymour The first significant release of radionuclides to the marine environment began in late 1944 with the discharge of efflu- ent from the reactors at the Hanford atomic plant to the northeast Pacific Ocean via the Columbia River. In July 1946, the detonation of two nuclear devices at Bikini Atoll introduced radionuclides into the north equatorial current system of the Pacific Ocean. Since that time, fallout from other nuclear detonations and radioactive wastes of various kinds have been added to the oceans of the world. Radio- nuclides are now found in all of the oceans; they present a potential health hazard and thus are of concern to the people of many nations. However, radionuclides as tags for chemical elements are a valuable tool for the study of bio- logical, chemical, and physical processes of the ocean, and, in this report, both the beneficial uses and the potentially harmful effects of radionuclides are considered. Studies of radionuclides in the marine environment and their impact upon populations of fish and invertebrates be- gan at Bikini Atoll in 1946. During subsequent nuclear deto- nations at Bikini and later at Eniwetok Atoll, small-scale radioecological studies provided information about the bio- logical and geographical distribution of fallout radionu- clides near the test sites, but this information was mostly semiquantitative and semiqualitative. In the 1950's, the number of nations testing nuclear devices, as well as the number of nuclear detonations, increased; the technology of radiation detection and measurement improved greatly; and public concern about fallout in both the terrestrial and marine environments grew. In 1956-1957, the National Academy of Sciences-National Research Council (NAS- NRC) published a series of reports on the biological effects of atomic radiation. One of these reports, The Effects of Atomic Radiation on Oceanography and Fisheries (NAS- NRC Publication No. 551), is an appraisal of radioactivity in the marine environment at a time when fallout from the detonation of nuclear devices was the principal source of artificial (man-produced) radionuclides in the environment. Now, 25 years after the detonation of the first nuclear device, radionuclides in the ocean continue to be a subject of worldwide concern, although attention is now centered on the input of radionuclides from the peaceful uses of nu- clear energy rather than on "fallout," which has become a nearly forgotten word. The present report, prepared by the Panel on Radioac- tivity in the Marine Environment of the National Research Council's Committee on Oceanography, provides an account of what has been learned about radionuclides in the ocean since 1957. The subjects selected by the Panel for discus- sion are sources of radionuclides; the distribution of 137Cs and other fallout radionuclides; physical processes of water movement; chemical systematics and elementary reactivi- ties in seawater; sorption and scavenging properties of sedi- ments; accumulation and distribution of radionuclides by marine organisms; radioecological interactions and consider- ations; and the effects of radionuclides on marine organisms and man.
Radioactivity in the Marine Environment Sources of natural and artificial radionuclides in the ocean are discussed by Joseph, Gustafson, Russell, Schuert, Volchok, and Tamplin in Chapter 2. Natural radionuclides include radionuclides and their radioactive daughters that have persisted since the earth's formation and radionuclides that are being produced constantly in the earth's atmo- sphere. The radioactivity of seawater from all natural radio- nuclides is about 750 dpm/liter, 97 percent of which derives from 40K. Because of the long half-lives of many natural radionuclides, all organisms living in the ocean have been and will continue to be exposed to an essentially constant level of background radiation. The principal sources of artificial radionuclides in the ocean are fallout from nuclear detonations, direct or indi- rect wastes from nuclear reactor operations, and wastes from medical, scientific, and industrial uses of radionuclides. Since the second nuclear test ban treaty in 1963, fallout has decreased markedly, and in recent years only small quanti- ties of solid radioactive wastes have been disposed of in the sea by the United States. However, the number of nu- clear reactors has increased steadily, and, at this time, wastes from nuclear reactor operations are considered to be the greatest source of radioactivity in the marine environ- ment. Only small amounts of radionuclides are released during the normal operation of nuclear reactors. The sources of these radionuclides, when they do occur, are excess pri- mary coolant, produced by expansion of the coolant during reactor warm-up, and miscellaneous wastes. The eight origi- nal production reactors at Hanford are an exception in that the primary coolant is not recycled in a closed system but is returned directly to the Columbia River. Hence, greater amounts of radionuclides are released directly to the aquatic environment from a Hanford production reactor than from other types of reactors of similar capacity. Although only a few curies of radionuclides are released directly to the envi- ronment by nuclear reactors, thousands of curies are pro- - duced within the fuel elements of the reactor. These radio- nuclides, when chemically separated from the unused fuel element, create a major disposal problem. The present policy in the United States is to convert these highly con- centrated liquid wastes into a chemically inert solid for underground storage. Previously, these liquid wastes were stored in underground tanks, and, at one time, their dis- posal in containers in the deep ocean was considered, but the policy was never adopted. The oceanic distribution of fallout radionuclides is dis- cussed in Chapter 3 by Volchok, Bowen, Folsom, Broecker, Schuert, and Bien. One of the important considerations is whether 137Cs and 90Sr are present at depths greater than 1,000 m. There are three expert opinions-one that they are present, another that they are not present, and a third that they are present in particulate but not in ionic form. Be- cause of the significance of this issue to the understanding of ocean-water circulation and because no consensus was reached by the Panel, the unusual procedure was adopted of allowing proponents of each view to present synopses of their arguments. The presence of 137Cs and 90Sr in deep water is also dis- cussed in Chapter 4, where the conclusion is reached that these two radionuclides could be expected at depths be- tween 500 and 2500 m at middle and low latitudes but not in quantities as great as some authors have reported. The principal subjects of discussion in Chapter 4, by Pritchard, Reid, Okubo, and Carter, are those advective and nonadvective processes of water movement that influence the distribution of radionuclides in the ocean. The simplest situation, the instantaneous release of radionuclides in a physicochemical state in which complete and immediate solution occurs, is given first consideration; more compli- cated situations are then considered, in which the radioac- tive materials are released by several methods and in dif- ferent physicochemical states. The radioactive "cloud" formed in the ocean by the in- troduction of radionuclides is moved horizontally by local currents and vertically by small-scale turbulent-motion processes. The eventual dispersion of the cloud is affected by the size of the field-of-motion eddy. Eddies larger than the cloud produce advection of the cloud as a whole, while eddies smaller than the cloud produce internal shearing and stirring. Eddies the same size as the cloud produce shear in the velocity field and in this way significantly influence the shape of the cloud and contribute to its dispersion as well. As the cloud grows in size, the scales of motion that con- tribute to its movement and mixing change. Models de- signed to predict the shape of the cloud or the concentra- tion of the radionuclides at a specific place or time must take into account the nature of these changes. The subject of "concentration factors" is considered in several chapters, and tables of concentration factors for marine organisms are given in Chapters 5, 7, and 8. Concen- tration factors are useful for the prediction of the routes and rates of transfer of radionuclides from sea to man, and also for the identification of the nonconservative elements in seawater, that is, elements whose concentration may be significantly altered by biological processes. Several conditions may limit the effective use of concen- tration factors. First, by definition, the concept loses mean- ing when applied to organisms that accumulate a chemical element or radionuclide in some way other than directly from seawater. Second, the value for the amount of the chemical element or radionuclide in the organism should be that value reached when equilibrium between the organism and seawater is reached. Third, the value for the amount of the chemical element or radionuclide in seawater should be the representative value for the entire period of accumula- tion of the chemical element or radionuclide by the orga- nism and not the value for a single sample. Also, there may
Introduction not be a single concentration factor for any common group of organisms, including those of the same species, because of the changes in concentration in the organism related to the physiological and environmental factors that influence metabolism. Further discussion of the use of concentration factors can be found in Chapter 8. Each of the tables of concentration factors in the three chapters was used for a different purpose. The table in Chapter 5, "Marine Chemistry," was used to provide some insight into the accumulation and distribution of specific elements by plants and animals. For this purpose, large er- rors were acceptable, and the marine organisms were there- fore classified only as either plants or animals and the con- centration factors were expressed as logarithms. Also, as discussed in Chapter 5 by Goldberg, Broecker, Gross, and Turekian, the concentration factors and the ratio of ele- ments in both deep water and surface water were used to identify the nonconservative elements. The nonconservative elements are identified in greater detail in Chapter 7, "Accumulation and Redistribution of Radionuclides by Marine Organisms," by Lowman, Rice, and Richards. In addition, the elements that are concen- trated by phytoplankton by a factor of 1,000 or more are listed, along with important radionuclides of these elements, that are of interest in the consideration of biological trans- port. The list includes structural, catalytic and easily hydro- lyzed elements, heavy halogens, and heavy divalent ions- some of unknown biological function-all reported to be present either in fallout from nuclear detonations or in effluent discharged into the sea from nuclear reactors or reactor fuel-processing plants. The most comprehensive table of concentration factors is given by Bowen, Olsen, Osterberg, and Rivera in Chap- ter 8, "Ecological Interactions of Marine Radioactivity," where the concentration factors for chemical elements are listed by trophic level and by plant and animal group. Although clear-cut conclusions could not be made, the authors of this chapter were of the opinion that concentra- tion factors, in general, were inversely related to trophic level. In this chapter, the use of simulation models as the ultimate method of predicting what happens to artificial radionuclides introduced into the marine environment is also discussed. Like other models of ecological systems, the applicability of the model is inversely related to the amount of pertinent information left outside the model. The success of models in the management of certain fishery resources and the special promise that the use of simulation models has for marine ecology indicate the possible success of models for describing the dynamics of radionuclides in the marine environment. However, before present models can move beyond the "early model" stage, as defined in Chap- ter 8, much more information is needed. Radionuclides can be removed from seawater by the biota and also by sediments and sedimentary particles, as described by Duursma and Gross in Chapter 6. The sorp- tion capacity of a sediment for a radionuclide appears to be controlled by the physicochemical state of both the sedi- ment and the radionuclide. After sorption, especially to a clay-mineral particle, the radionuclide may move within the structure of the particle while the particle is being moved by currents and wave action. Bottom grazers and burrow- ing organisms are important factors in the translocation of radionuclides in the surface layer of bottom sediments. The use of sediments to scavenge radionuclides from sea- water after an accidental release of radionuclides has been suggested. By this process, the radionuclides would merely be transferred from the water to the bottom sediments, which may or may not be advisable. The large quantity of sediments that would be needed under the most favorable circumstances raises the question of practicability and cost. The effects of radionuclides in the ocean on marine orga- nisms and man are discussed in the last two chapters. The discussion of the effects on marine organisms in Chapter 9 by Templeton, Nakatani, and Held points out that the re- sults of laboratory experiments in various countries are not in agreement about the sensitivity of fish larvae to ionizing radiation. The results of some experiments indicate that there was no significant increase in abnormal larvae in fish exposed to 90Sr + 90Y concentrations a million times greater than the 90Sr + 90Y concentrations that in other experi- ments were reported to have produced significant increases in abnormal larvae. The concentration of 90Sr + 90Y in the experiments in which effects were observed was only one third the concentration of naturally occurring 40K in sea- water. These investigators also believe that embryo mortal- ity greater than 10 percent will significantly reduce the population size of the adult stock. For fecund species, the accuracy of this statement is not obvious. The radiosensi- tivity of the embryos and larvae of fishes is pertinent to the question of radioactive-waste disposal in the sea: hence, the need for further study of the radiosensitivity of fish larvae is evident. The radiation dose to plaice, a bottom fish, living in the vicinity of the discharge of radioactive effluent into the Irish Sea from the Windscale Chemical Reprocessing Plant is exceptionally well documented and can be extrapolated in a general way to other species and other areas. The dose was predicted from calculated values for the concentrations of radionuclides in seawater and later determined empiri- cally by use of thermoluminescent dosimeters (TLD's). The contribution of natural radionuclides to the total dose of 7.4 rad for a plaice 2 miles from the discharge point was 1 percent; the major contribution was from the bottom sediments, with a small contribution from seawater and in- ternal radionuclides. The dose to a fish living in surface water would be considerably less, because the contribution by bottom sediments would be essentially zero. The predicted doses and the doses measured by the
Radioactivity in the Marine Environment TLD's attached to plastic tags on the fish were in good agreement. The small size of TLD's permits their use either internally or externally for fish, oysters, and other organisms of a similar or larger size. Future use of TLD's for in situ measurement of radiation doses to living organisms is ex- pected to provide information not previously available. In considering the effects of ionizing radiation on marine organisms, the primary concern is with populations, not in- dividuals. Unless deaths by radiation reduced the stock be- low the level for maximum sustained yield, these deaths would not jeopardize the population and would merely be another type of mortality. In the appraisal of the genetic effects of ionizing radiation on marine organisms, it should be recognized that genetic damage at the population level is reparable by natural selection. A quotation in Chapter 9 from Purdom (1966) summarizes the effect of ionizing radi- ation on marine organisms as follows: It would seem likely that the genetic response of popula- tions is relatively unimportant and that general mortality and infertility would be the limiting factors in the extent to which populations may overcome radiation exposure. The primary concern about the presence of radionuclides in the ocean is their effect on man, as discussed by Foster, Ophel, and Preston in Chapter 10. Man may be exposed to ionizing radiation from seawater in various ways. Swim- ming, walking on beaches, and handling contaminated fish- ing gear are some of the ways, but none is as important as the ingestion of seafoods. The question, "How much sea- food can be eaten safely?" then arises and leads to the con- cept of an "acceptable dose." The acceptable-dose concept implies that exposure to ionizing radiation from any source entails some risk of a biological effect; therefore, a dose is considered acceptable only if the benefits are greater than the risks and the risks are acceptable both to the individual and to society as a whole. The acceptable dose recommended by the International Commission on Radiological Protection (ICRP) is 5.0 rem per 30 years or 0.17 rem per year. This dose is the accept- able average whole-body radiation dose for the general pop- ulation, exclusive of radiation from natural background sources and from medical uses of ionizing radiation. The recommended dose limits, either for groups that can accept a risk greater than the acceptable risk for the general popu- lation or for single organs or tissues, are greater than 0.17 rem per year. The ICRP recommendations have been made on the assumption that dose and effect are linearly related, i.e., that there is no threshold effect. The introduction of radionuclides into the ocean neces- sitates an assessment of the environment both before and after contamination occurs. The pre-event assessment is needed to provide information for the prediction of effects, and the postevent evaluations are needed to determine the actual effects. Predictions can be made by either the "criti- cal pathway" or the "specific activity" approach. The critical-pathway approach identifies the route and estimates the concentration of the radionuclide at each step in the route from seawater to man. The specific-activity ap- proach establishes a maximum permissible value for radio- nuclides in seawater by equating the specific activity in sea- water to the specific activity in the critical organ. If the specific activity of the critical organ is not exceeded in sea- water, then the allowable body burden of the radionuclide in man cannot be exceeded, regardless of the amount of seafood eaten. The specific activity is simple to calculate and does not require the information needed by the critical- pathway approach in regard to food webs, concentration factors, transfer coefficients, and man's use of seafoods. The specific-activity approach, however, assumes that reli- able information is available for the amounts of chemical elements present in critical organs and cannot be used for radionuclides that are poorly assimilated and thus have the gastrointestinal tract as the critical organ. Values derived by this approach are unduly conservative because full compen- sation cannot be made for radioactive decay that occurs as the radionuclide moves from the sea to man and because all of man's food is assumed to come from the contaminated area of the sea. Both the specific-activity and the critical-pathway ap- proaches can be used to predict the potential dose to man from the introduction of radionuclides into the ocean. The simplicity of the specific-activity approach suggests that it be tried first if the nuclides involved do not have the gastro- intestinal tract as the critical organ. If the predicted value for the concentration of a radionuclide released in seawater is less than the maximum permissible concentration value in seawater as calculated by the specific activity approach, then the predicted release of radionuclides will not lead to a radiation exposure greater than the recommended limits. If the predicted radionuclide value is greater than the conserva- tive value derived by the specific-activity approach, or if a more precise estimate of the probable dose is needed, then the critical-pathway approach should be used. The specific-activity approach was suggested by an ad hoc committee of the National Research Council as a method for regulating radioactive waste disposal off the Pacific coast of the United States at a time when disposal of radioactive wastes to the ocean was being considered (National Acad- emy of Sciences-National Research Council, 1962). The critical-pathway approach has been used frequently: The National Academy of Sciences-National Research Council (1959a, b; 1962) and the International Atomic Energy Agency Panel on Radioactive Waste Disposal into the Sea used this method to calculate maximum permissible con- centrations of radionuclides in seafoods and in seawater, and the United States, the United Kingdom, France, Swe- den, and India have employed it in the management of the
Introduction disposal of radioactive wastes. The release of radionuclides from the Windscale Chemical Reprocessing Plant is an inter- esting example of the use of the critical-pathway approach. It was found that 106Ru released from the plant was accu- mulated by an alga that is used in the preparation of a food eaten by a community of Welshmen. As a consequence, the release of 106Ru controls the release of radioactive wastes from this plant. Significant but still incomplete data are now available for an evaluation of the biological consequences of the intro- duction of radionuclides into the ocean. The ability to pre- dict the distribution of radionuclides in the sea, as well as the ability to keep human exposure within the guidelines specified by the International Commission on Radiological Protection and the Federal Radiation Council, has been adequately demonstrated by the predictions and follow-up surveys that already have been made. These guidelines are based on many factors, not all perfectly known, and are subject to change when new and better information becomes available. Therefore, the present guidelines are subject to revision, although there is no evidence that the past and present policies and practices for radioactive waste disposal in the sea have jeopardized man or any marine species or ecosystems. REFERENCES National Academy of Sciences-National Research Council. 1959a. Radioactive waste disposal into Atlantic and Gulf coastal waters. A report of a working group of the Committee on Oceanography. NAS-NRCPubl. 655. National Academy of Sciences-National Research Council. 1959b. Considerations in the disposal of radioactive wastes from nuclear- powered ships into the marine environment. Committee on the Effects of Atomic Radiation on Oceanography and Fisheries. NAS-NRC Publ. 658. National Academy of Sciences-National Research Council. 1962. Disposal of low-level radioactive wastes into Pacific coastal waters. A report of a working group of the Committee on Oceanography. NAS-NRC Publ. 985.
