Radioactivity in the Marine Environment (1971)

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246 Radioactivity in the Marine Environment identified the potential concentration of radioisotopes in edible marine products as the factor that would most limit waste disposal. Maximum permissible concentrations in sea- foods were calculated for several radioisotopes on the basis of intake rates recommended by the National Committee on Radiation Protection (NCRP), which at that time did not distinguish between exposure limits for radiation workers and members of the public at large (NCRP, 1953). In es- sence, these were the NCRP recommendations for maximum permissible concentrations in drinking water adjusted for the rate of intake of seafoods and for concentration of the radioisotopes by the marine organisms. The assumption was made that individuals eating the sea- foods obtained all of their protein from this source. This is a very conservative assumption in relation to the food habits of North Americans. Other assumptions used conservative, but best available, data on the extent to which fish, shell- fish, and other edible marine products might concentrate specific isotopes from the seawater, and on the rate of dis- persion of the contaminants from packaged radioactive waste. The report specified maximum permissible concen- trations for several radioisotopes in seawater and the asso- ciated permissible rate of disposal of wastes-i.e., the dis- posal rate that would not result in greater concentrations in the seawater within disposal areas 2 miles in diameter. In June 1958, the AEC made an additional request of the Committee on Oceanography to undertake a study of the problems of disposal of radioactive wastes from nuclear- powered ships (National Academy of Sciences-National Re- search Council, 1959b). The working group appointed for this new project used basically the same approach as the At- lantic and Gulf Coast group-i.e., consideration of the rate of dispersion by ocean currents, concentration of isotopes from the seawater by edible marine products, consumption of the seafoods by humans, and maximum permissible rates of intake recommended by the NCRP. The nuclear ships study dealt with a more complex set of disposal conditions, however. The marine environment was classified into four zones: inshore waters within 2 mi of the coastline; the coastal area, between 2 and 12 mi from the shore; the outer continental shelf, beyond 12 mi from shore; and the open sea. The most stringent limits were assigned to the inshore zone because some individuals might obtain all of their pro- tein requirements from fish harvested there, and because dispersion would be relatively poor in this zone. This report also recognized that people may receive radiation exposure from other environmental sources, e.g., the atmosphere and the land, and an allocation was made for the fraction of the total that should be assigned to the sea. This allocation per- mitted radionuclide intakes one third as large as those recommended by the NCRP (1953). The International Atomic Energy Agency ad hoc panel on radioactive waste disposal into the sea has presented a reasonably detailed description of the step-by-step proce- dure that may be used in arriving at maximum permissible rates of introduction of radioactive materials into particular marine locales (IAEA, 1961), and many of these details are not repeated here. All of the studies cited above use a method that is now referred to as the "critical pathway ap- proach"-a procedure that is recommended by Committee 4 (Application of Recommendations) of the ICRP (1966a). The Critical Pathway Approach The critical pathway approach involves evaluation of a se- quence of events through which radioactive material intro- duced into the marine environment is diluted, perhaps re- concentrated, and ultimately reaches man either in food or via material with which he comes in contact. Prediction of the radiation dose that man will receive from an introduc- tion of radioactive material (or the reverse procedure, the calculation of tentative guides for acceptable rates of intro- duction) not only requires a number of source terms but also requires the use of several mathematical simulation models, transfer coefficients, and basic assumptions. Begin- ning at the point of introduction, the significant parameters are considered in the following sections. KINDS AND QUANTITIES OF RADIOACTIVE MATERIALS INTRODUCED This source data must be available in terms of rates of intro- duction (e.g., Ci/mo) of specific radionuclides. Data pre- sented in terms of concentrations (e.g.,/uCi/liter) is not very useful unless accompanied by information on the volume (flow rate) of the water involved. Further, data expressed only in terms of gross beta or alpha activity is of little value unless the calculation is being carried out solely to demon- strate that the amount of radioactive material involved is in- significant in relation to acceptable dose limits. PHYSICAL AND CHEMICAL FORM OF RADIONUCLIDES AT TIME OF INTRODUCTION These characteristics determine whether the material will be dispersed promptly in the area of introduction more or less as a solution or whether it will settle to the bottom. Once deposited on the seabed, the radioactive material may be- come a significant source of external exposure, as well as a continuing source, by dissolution, to the seawater and to marine organisms. In the absence of direct measurements on such deposited material, assumptions must be used to define the rate of dissolution. The mean residence time on the bot-

Evaluation of Human Radiation Exposure 247 torn is important in relation to the radioactive decay rates (half-lives) of the nuclides. INITIAL MECHANICAL DILUTION Initial dilution by this means depends upon the manner in which the material is introduced into the sea. It is important for the elimination of differences in densities that might delay dilution by advection and turbulent diffusion. Inade- quate initial dilution could lead to unnecessarily high con- centrations in the vicinity of the point of introduction. DILUTION BY NATURAL MIXING PROCESSES OF THE SEA These processes (advection and turbulent diffusion) are of paramount importance in accomplishing the required dilu- tion of the radionuclides within the time and distance con- straints peculiar to the disposal site. Mathematical models are ordinarily used to predict the manner in which the con- centrations of the nuclides diminish in space and time. These processes are discussed in detail in Chapter 4. For each disposal site, there will be some minimum vol- ume of seawater that will be of interest, and even though small regions within the "critical volume" will have higher concentrations, this will not affect the final outcome of the prediction. One method of identifying the size of the critical volume is to relate productivity of the critical food organism of the area to its rate of consumption by a critical popula- tion. For example, if a local population of 100 people sub- sists largely on fish produced in the vicinity of the site of introduction of the radionuclides, and if the quantity offish consumed is 50,000 Ib/yr, then the smallest area of interest is that required to produce an annual harvestable crop of the species of interest of 50,000 Ib. This might be an area of 1,000 acres. The critical volume is, then, the mass of water available in relation to this acreage. The rate of replacement of the water in the critical volume then determines the flow (i.e., m3/day) available for dilution of the radioactive ma- terials. This critical volume approach was used by a working group of the National Research Council to evaluate the po- tential hazard of a sealed nuclear power source to marine fisheries. AVAILABILITY OF INTRODUCED MATERIAL TO MARINE BIOTA Most predictive calculations assume that radioisotopes added to seawater will be adsorbed or absorbed by marine organisms in a manner identical with that of their stable counterparts already present in solution in the seawater. It is on this basis that concentration factors are usually derived. It is also on this basis that the "specific activity approach" (to be described later) is derived. In actual practice, how- ever, freshly introduced radioisotopes cannot be expected always to have the same availability as the stable isotope of the same element in seawater because the freshly introduced material is initially apt to be in a different physical and chemical state. For specific situations, it may be possible to predict whether the radioisotope will be more or less avail- able to organisms of interest. CONCENTRATION FACTORS Perhaps the greatest uncertainty in predictive calculation is the selection of an appropriate concentration factor whereby the estimated concentrations of specific radionu- clides in the seawater can be translated into the concentra- tions that will result in the marine food products of interest. This general topic is discussed in several other chapters of this volume, and several publications are now available that record values deemed appropriate by various authors (IAEA, 1961; National Academy of Sciences-National Research Council, 1962; Mauchline and Templeton, 1964; Bryan et a/., 1966: Polikarpov, 1966). The wide variations that have been observed among dif- ferent environments and even among closely related species in the same environment emphasize the need for careful consideration of the specific characteristics of each site. In dealing with radioisotopes with relatively short half-lives (days or weeks), it is also important to bear in mind that their accumulation by fish to a level that is in equilibrium with the environment requires a significant period of time and that radioactive decay will reduce the quantity present to levels substantially below those anticipated from the use of unmodified concentration factors. CONSUMPTION OF MARINE PRODUCTS It is now conventional to select or hypothesize a small popu- lation group, or even individuals, that eat extremely large quantities of the seafoods that are expected to become con- taminated through the introduction of radionuclides. Such an approach is endorsed by both the ICRP (1966a), which uses the term "Critical Group," and the FRC (1961), which refers to "the exposed population." In the absence of fac- tual data derived from dietary surveys, predictive calcula- tions have usually employed obviously safe assumptions, i.e., that the entire protein requirement is derived from the seafood of concern. Desired refinements in the estimated seafood consump- tion by the critical group include not only the true propor- tion of the diet that is made up of the seafood of interest, but also the proportion of this food that actually originates in the critical area (market dilution) and the lag time that ordinarily exists between the harvest of the food and actual

248 Radioactivity in the Marine Environment consumption. This lag time can allow substantial radioactive decay of short-lived nuclides. STANDARD MAN The ICRP and the FRC have computed the daily rates of intake of radionuclides that will eventually lead to the al- lowable radiation dose rates in various organs of the body. In making these calculations, it was necessary to fix a num- ber of physiological and anatomical characteristics that are implicit in the calculations. These "standard man" parame- ters include such things as body and organ sizes, chemical composition, metabolic rates, and intake and excretion rates (ICRP, 1959). To the extent that individuals differ from the standard man, the dose estimates that are associated with specified intakes of particular radionuclides will also differ. The greatest differences will obviously occur for infants and children, and the ICRP is therefore developing an additional set of parameters associated with the "standard child." For predictions of radiation dose from marine foods to critical population groups, there appears to be no need for concern that deviations from the standard man assumptions will in- troduce serious errors, except perhaps when some foods are fed to infants in quantities approaching or exceeding those eaten by adults. The capability of accurately calculating the dose received from seafoods by the critical population group improves as the identity of the group, and thus the physical and metabolic characteristics of its members, becomes better defined. EXTERNAL EXPOSURE In addition to the reconcentration of radioactive materials in food chains leading to man, accumulations or reconcen- trations may also occur by physical, chemical, and biological processes that will lead to external exposure. Such accumu- lations can result from the deposition of undissolved particu- late material on the seabed and beaches, the adsorption of ions from solution onto sediments or suspended matter that will later settle out, and the adsorption or "growth" of con- taminated materials onto fishing gear and other equipment immersed in the sea. Prediction of the magnitude of the ex- ternal exposure that will result from these sources involves not only estimation of the concentration factors that will occur on the sources of exposure but also the amount of time that members of the critical population group will be exposed (e.g., the number of hours during a season that a fisherman handles his nets). APPLICATIONS The critical pathway approach to evaluating the dose to critical population groups has been used for several radio- active waste disposal operations throughout the world: Nation Use United Radioactive waste disposal into Atlantic and Gulf States coastal waters Radioactive waste disposal from nuclear-powered ships Hanford (now Richland) plutonium production plant discharge to Columbia River Oak Ridge National Laboratory discharge to the Clinch River United Atomic Energy Authority sites Kingdom Windscale (Irish Sea) Dounreay (north coast of Scotland) Winfrith (southern coast of Britain) Civil nuclear power stations (total of 9) Royal Navy nuclear submarine base (Chatham) U.S. Navy nuclear submarine base (Holy Loch) Nuclear shipping France Commissariat a 1'Energie Atomique site (Cap de la Hague) Sweden A.B. Atomenergi Studsvik India Bhabba Atomic Research Center Tarapur Atomic Power Station Rajasthan Atomic Power Station The Specific Activity Approach The National Research Council's Committee on Oceanog- raphy was asked by the AEC in 1958 to consider the prob- lems of disposal of low-level radioactive wastes in the Pacific Ocean off the North American coast (National Academy of Sciences-National Research Council, 1962). The approach used by the group set up for this study was basically differ- ent from that used by others. Rather than using the NCRP recommendations on rates of intake of radioisotopes, they used the NCRP (1959) values for maximum permissible body burdens of individual radioisotopes in combination with expected amounts of the nonradioactive isotopes of the same elements in the body. This resulted in a set of maximum permissible "specific activities," e.g., microcuries of radioactive 90Sr per gram of stable 88Sr ordinarily pres- ent in the body. They pointed out that, if the maximum permissible specific activity were not exceeded in the envi- ronment where foods were grown, there was no mechanism by which the specific activity in the foods, or in the humans who ate the foods, could exceed the limit. Therefore, maxi- mum permissible concentrations of radioisotopes in sea- water could be calculated on the basis of the specific activi- ties in the seawater. The advantage of the specific activity approach is that it eliminates the need for speculation on the extent to which marine organisms might concentrate isotopes from the wa- ter, and it eliminates the need for apportioning some frac- tion of the total intake of radionuclides to marine foods. Such an approach can be used to evaluate the disposal of radioisotopes into the sea because the chemical content of the seawater is quite uniform.

Evaluation of Human Radiation Exposure 249 The specific activity approach is very conservative, es- pecially for North Americans, because it assumes that an individual's entire food supply is derived from the sea. It also has limitations for elements that are not common in the human body, and the working group found it necessary to use "stand-ins" for a number of elements for which hu- man data were unavailable. They also postulated that some elements, such as zinc, cobalt, iron, and copper, might enter the sea as complexes that would not permit complete iso- topic dilution with the element in the seawater prior to up- take by marine organisms. To allow for this, an additional safety factor of 10 was introduced. Another limitation of the specific activity approach is that it is not applicable when the gastrointestinal tract is the critical organ. Here, the principal exposure is from food that passes through the gut rather than from the radioisotope after deposition in the body. The working group resolved this problem by reverting to the critical pathway approach of estimating the concentration that might occur between the seawater and the marine organisms (i.e., as used by the Committee on Oceanography working group for nuclear- powered ships) and assuming a generous consumption rate for the seafoods. In making a predictive calculation using the specific ac- tivity approach, many of the same parameters used in the critical pathway approach must still be applied. These are Detailed knowledge of the kinds and quantities of radio- active materials introduced Knowledge of or assumptions about the physical and chemical form of the radionuclides introduced Calculation of the initial dilution by mechanical mixing Calculation of the dilution that will result from natural mixing processes of the sea Assumptions about the relative availability of the intro- duced material to the marine biota Parameters used in the critical pathway approach that are not needed with the specific activity approach are Assumptions about the concentration of radionuclides by marine organisms from the seawater Knowledge of the kinds and quantities of marine prod- ucts used as food. (It is assumed that the entire food supply has its origin in the marine environment of interest.) Follow-up Evaluations Estimation of the mode and magnitude of radiation expo- sure to people that might result from the introduction of radioactive materials into the marine environment is pre- requisite to the deliberate discharge of waste and to the as- sessment of risks that may be associated with large-scale ac- cidents. It must be remembered, however, that the actual exposures received by people after a new radioactive waste disposal operation has begun, or after the occurrence of an accident, may differ substantially from early predictions, both in terms of the critical pathways of exposure and in terms of the magnitude of the dose. Once the introduction of radioactive materials into the sea from a new installation has started, the preoperational predictions will, in large mea- sure, have served their purpose, and attention should be shifted to a determination of the actual concentrations of radionuclides that are accumulating. This means that pro- visional limits placed on the rates of introduction of con- taminants will very likely need to be revised, and it may be possible to dismiss safety factors that were added solely be- cause of uncertainties in rates of dispersion and of biological reconcentration. Follow-up evaluations should, insofar as practical, be based on measurements of the materials directly responsible for human exposure. This means the species of fish, shellfish, and seaweed actually consumed by the public, the beaches used by the public, and the gear handled by the fishermen. Measurements made of the concentrations of contaminants in seawater, in plankton, and in the sediments of the seabed are useful as reference points from which interrelationships can be developed, but they have only limited use in evalu- ating radiation exposure to people. Once the critical exposure pathways and the critical populations have been confirmed by measurements made after waste disposal has begun, estimates of the dose re- ceived can be refined by comprehensive investigation of seasonal trends in the levels of contamination and in the use of the marine products and zones of interest. Greater atten- tion can also be given to the size, age composition, and hab- its of the critical population. If gamma emitters are involved, it may be possible to measure the actual body burdens in individuals that make up the critical population. This tech- nique is now being used at the Hanford plant to determine the quantities of 65Zn acquired by people who drink water and eat fish from the Columbia River or who eat oysters from the coasts of Washington and Oregon (Foster and Soldat, 1966). The determination of actual body burdens of radionu- clides acquired from environmental sources represents some- thing of an ultimate technique for evaluating the radiation dose from internally deposited sources. When such methods are feasible, they should be favored over the estimation of dose from the sampling and analysis of water and foodstuffs. However, practical considerations will ordinarily dictate that the measurements be made on the water and foodstuffs and, thus, that dose estimates be made using assumed rates of in- gestion and the ICRP metabolic models. Where the concen- trations of radionuclides in foods are so low that radio- chemical analyses are difficult and imprecise, it may be desirable to sample some other organism or group of orga- nisms (e.g., plankton) that concentrate the radionuclides of

250 Radioactivity in the Marine Environment interest to levels that are easily detected. Such organisms are often termed "indicator species" because they can be used to indicate the relative levels of contamination in the envi- ronment (including the concentration in edible species) and because they can show increasing or decreasing trends in these levels. In order to use the concentrations of radioac- tive materials observed in indicator species to estimate dose to people, it is first necessary to establish the relationship between concentrations in the indicator species and in spe- cies actually used by man. In situations where the dose to man is of any real significance in respect to limits, it will be possible to make the measurements directly without the use of indicator species. The Windscale Evaluation: An Example of Acceptable Dose in Relation to the Radioactive Contamination of Coastal Waters The preoperational evaluation at Windscale, on the Cumber- land coast of Britain, was the first detailed evaluation of radioactive material in the marine environment using the critical pathway approach. It involved an assessment of the rate of dilution of activity, its reconcentration in materials previously identified as playing an important role in man's use of the local environment, and a carefully controlled pe- riod of experimental discharges of radioactivity during which a safety factor of 10 was introduced between the cal- culated maximum rates of discharge and those employed in the study (Seligman, 1956; Dunster, 1956; Fair and McLean, 1956; Dunster, 1959). The results of these studies completely substantiated the preoperational estimates of discharge rates and confirmed the major pathways by which radioactivity is returned to man. The results of subsequent surveillance programs at the site have continued to demonstrate the acceptability of the Windscale sea discharges in terms of the criteria discussed in earlier parts of this chapter (Mitchell, 1967b; Dunster, 1959; Morgan, 1964; Dunster era/., 1964; Morgan, 1965;Langley and Templeton, 1965; Templeton and Preston, 1966; Howells, 1966; Preston and Jefferies, 1967). The consumption of laverbread (an edible product manu- factured from seaweeds of the genus Porphyra) is the limit- ing route or critical pathway by which radionuclides dis- charged by the Windscale plant (particularly 106Ru) return to man. This critical pathway for human radiation exposure is described in detail by Preston and Jefferies (1967, 1969). The maximum rate of consumption of laverbread, found in a sample of consumers obtained by local survey, was 75 g per day, but the distribution of observations indicated the possible existence of a few consumers who might be eating laverbread at a greater rate than this. A recent survey (Preston and Jefferies, 1969) of laver- bread consumption rates identified the heavy consumers more accurately. In the sample obtained, rates of consump- tion ranged between 75 g and 388 g per day. The median rate of consumption of this group, based on the distribution of observations in the sample, is 160 g per day, or approxi- mately twice the previous maximum rate. The group is com- posed of adults of both sexes and is estimated to comprise 170 individuals in a total laverbread-consuming population of about 26,000 persons. The survey also reviewed the supply, distribution, and processing of the seaweed, and confirmed that the concen- tration of 106Ru in the laverbread was only about half that in the seaweed because of the incorporation of extra water during processing (Preston and Jefferies, 1967). Parallel in- vestigations of market dilution based on market sampling of the processed foodstuff revealed an average 106Ru dilution factor of 5 between the activity as measured in seaweed in the vicinity of the outfall and the concentration of the ra- dionuclide in laverbread (Preston and Jefferies, 1969). The calculations that follow are based on the results of the recent surveys but ignore the market dilution factor, since this varies from year to year with the particular mar- ket situation and has in recent years tended to decrease in value as Windscale seaweed has come to occupy a larger fraction of the market. The calculations that follow are de- signed to illustrate the degree of somatic exposure experi- enced by the critical group and to compare this exposure with the genetic exposure received by the South Wales population. CRITICAL SOMATIC EXPOSURE: ESTIMATED DOSE TO LOWER LARGE INTESTINE The average annual dose to the gastrointestinal tract (lower large intestine) between 1959 and 1965 was estimated by Preston and Jefferies (1967) at 0.35 rem. This estimate was based on a consumption rate of 75 g of laverbread per day. Adopting the new median consumption rate of 160 g per day for the critical group, this estimate becomes 0.74 rem per year, compared with the ICRP recommended dose limit of 1.5 rem; the range of estimated doses experienced by the critical group as a whole was 0.35 to 1.78 rems (Preston and Jefferies, 1969). (See Figure 1.) GENETIC EXPOSURE IN THE SOUTH WALES POPULATION The mean acceptable annual genetically significant dose is calculated as follows: The size of the laverbread-consuming population based on the 1962 (Preston and Jefferies, 1967) and 1967 (Preston and Jefferies, 1969) laverbread surveys is

Evaluation of Human Radiation Exposure 251 ICRP REC0MMENDED DOSE LIMIT FIGURE 1 Estimated annual dose (rads) to the lower large intestine of adults eating 160 g/day of laverbread manufactured from Cumber- land Porphyra. (Modified from Figure 4 of Preston and Jefferies, 1967.) 2.6X 104 persons. The population of South Wales, in the laverbread area, is 1 X106 persons. Therefore, on the basis of ICRP recommendations, the mean acceptable annual ge- netically significant dose, D, is 2.6X104/lX106X30yrX£> = 0.1 rem D = 0.13 rem This calculation carries the conservative assumption that South Wales has a semiclosed population, with restricted interchange of genetic material with the rest of the U.K. population, and allots 1/10 of the U.K. recommended ge- netic exposure rate from radioactive waste disposal (U.K., Minister of Housing and Local Government, Minister for Welsh Affairs, and Secretary of State for Scotland, 1960) to the Windscale sea disposal operation. The genetically significant dose actually received by the whole laverbread-eating population is computed as follows: From above, the average annual gastrointestinal tract dose for the critical group consuming 160 g of laverbread per day is 0.74 rem. The average rate of consumption of the whole laverbread-eating population is 14.6 g per day. By ratio, the average gastrointestinal tract dose for the population is 0.065 rem. From the ratio of ICRP permissible intakes, the gonad receives a dose of 1 /600 of that to the lower large in- testine. Hence, average gonad dose is 0.065 X1/600 = 0.0001 rem. SOMATIC AND GENETIC DOSES IN RELATION TO RECOMMENDATIONS From the above calculations, the ratio of the dose estimated for the gastrointestinal tract of the critical population to the ICRP limit is 0.74 rem/1.5 rem = 1/2, and for the genetic dose is 0.0001/0.13=1/1,000. CONCLUSIONS Without allowing for dilution of Windscale-contaminated seaweed with seaweed from other sources entering the South Wales laverbread market, the average annual dose to the critical organ (gastrointestinal tract) of laverbread eaters over the years 1959-1965 was 50 percent of the recom- mended dose limit. The somatic dose is 500 times more re- strictive than is the genetic dose, even though calculations for the genetic case were based on very conservative assump- tions for the mixing of the South Wales population with the total U.K. population. HUMAN EXPOSURE FROM RADIONUCLIDES IN THE SEA Natural Radioactivity Compared to the land, the sea presents a relatively friendly radiation environment. In the sea, natural radionuclides are present in lower concentrations than in most rocks and soils (Folsom and Harley, 1957), and the only ones of signifi- cance in seawater that enter food chains leading to man are 40K and 87Rb. The dose from 87Rb is insignificant, and the dose from the burden of 40K in the body will be about 17 mrems per year regardless of whether it is acquired from seafood or from food of terrestrial origin. Worldwide Fallout Some fraction of the radiation exposure received by man from fallout radionuclides results from his use of the sea and of food from the sea. For most of the world's popula- tion, this marine-derived exposure constitutes only a small fraction of the total exposure from fallout. The major frac- tion of internally deposited fallout radionuclides is derived from terrestrial food chains (United Nations Scientific Com- mittee on the Effects of Atomic Radiation, 1964). Calculations by the Food and Agriculture Organization (FAO) of the United Nations (1960) for 90Sr indicate that fish contribute less than 0.5 percent of the total daily intake

252 Radioactivity in the Marine Environment of this radionuclide. This small uptake applies even in Japan, where marine fish are an important part of the total diet (Table 1). Because the 90Sr/Ca ratio in marine fish is much lower than in other items in the human diet (FAO, 1960), the marine contribution to 90Sr actually deposited in hu- man bone would be much less than 0.5 percent. The marine contribution to 137Cs intake by people is also small—probably considerably less than 10 percent (United Nations Scientific Committee on the Effects of Atomic Radiation, 1962). The 137Cs/K ratio in marine fish is much lower than that in milk and meat, so that the per- centage contribution to retained 137Cs (and hence to the internal radiation dose) is even less. From the dose commitment calculations made by the United Nations Scientific Committee on the Effects of Atomic Radiation (1966), the worldwide average dose from 90Sr to human bone (actually to "cells lining bone sur- faces") up to the year 2000 is almost exactly 5 mrem per year. The marine-derived portion of this dose can then be approximated as less than 0.5 percent of 5 mrem per year, or an average of less than 0.025 mrem per year. A similar calculation for 137Cs whole-body dose results in less than 10 percent of 0.5 mrem per year, or an average of less than 0.05 mrem per year. The above calculations refer to average doses for the world population. In some parts of the world, there are small population groups that depend on fish and other ma- rine organisms for most of their food. An approximate upper limit for the marine-derived ^Sr and 137Cs dose rate to such people can be calculated by using the maximum fish- consumption rate (807 g/day) found by Preston (1966) for English fishermen together with the concentrations of these radionuclides measured in the flesh of commercial fish (0.04 pCi 137Cs/g wet weight; 0.007 pCi 90Sr/g wet weight) (Mitchell, 1967b). These lead to possible daily intakes of 32 pCi 137Cs/day and 6 pCi 90Sr/day. Using conservative biological parameters, these intakes could result in dose rates as high as 0.36 mrem/year to the whole body and 30 mrem/year to parts of the skeletal bone. In addition to 90Sr and 137Cs, many other fallout radio- nuclides reach the sea; these include 22Na, 54Mn, 60Co, 65Zn, 95Zr-95Nb, 103Ru, 106Ru, 1311,141Ce,and 144Ce- 144Pr. Most of these have short half-lives, and their concen- trations in the marine biota that are used for human food are transitory and usually very low (Morgan, 1965). One exception is the radionuclide 55Fe (half-life of 2.6 years), which by 1965 had been recorded in humans, marine fish, and plants (Palmer and Beasley, 1967). Concentrations found in marine fish flesh are much higher than those in ter- restrial animals. Consequently, small population groups that have a high proportion of fish in their diet have been found to have body burdens of 55Fe approaching 1,000 nCi. The resulting internal radiation dose to the red blood cells in these individuals (if they retain this body burden) has been estimated to be about 30 mrem/year (Palmer and Beasley, 1967). The other marine radionuclides mentioned above con- tribute only a small fraction to the external dose received by the world's population. Although the exact fraction cannot be calculated at this time, from our knowledge of the world population distribution and habits, we know it is small. Local Fallout Many studies of radionuclide concentrations found in ma- rine organisms as a result of local fallout from nuclear ex- plosions have been published (e.g., Japan Society for the Promotion of Science, 1956; Hines, 1962, p. 341 et seq.). Much of the information gathered is not directly usable for the estimation of the marine-derived fraction of the total radiation dose received by persons living in the local fallout zone. However, some generalizations can be made with re- gard to the relative importance of fallout radionuclides to man. In the edible portions of marine fish, the major radionu- clides found (Lowman, 1960, 1963) have been 65Zn, 55Fe, "Co, 58Co, 60Co, and 54Mn. None of these elements are fission products. They presumably result from neutron acti- vation of materials in and around the device. Fission-product concentrations in fish are very low in comparison with the above radionuclides even some years after the contaminating event (Lowman, 1960). Other edible marine organisms, such as shellfish, contain much the same spectrum of radionuclides as fish in which the cobalt radioisotopes predominate. The fission products i06RU + 106Rh an(J 95Zr + 95Nb have a]so been found ^ clams (Lowman, 1960). One example is available in which it was possible to de- termine the dose contribution from marine food in a popu- lation exposed to "close-in" or local fallout from a nuclear explosion. In this case, a group of people from Rongelap Atoll were returned to their homes several years after the atoll had been heavily contaminated by local fallout. From data given by Cohn et al. (1960), it is possible to estimate that about 10 percent of the 90Sr bone dose to these people was 0.36 nCi (Cohn et al., 1960), which would deliver ap- proximately 30 mrem per year internal whole-body irra- to include the land crabs in their diet, this would reduce the marine food contribution of 90Sr to 2 percent of the total 90Sr intake. For whole-body radiation, the marine contribution was somewhat greater. Virtually all of the body burden of 65Zn was contributed by fish in the diet. This 65Zn body burden was 0.36 y£i (Cohn et al., 1960), which would deliver ap- proximately 30 mrem per year internal whole-body irra- diation. However, terrestrial food chains contributed

Evaluation of Human Radiation Exposure 253 0.68 u.Ci of 137Cs, resulting in a dose of about 110 mrem per year. Consequently, the marine contribution would amount to some 20 percent of the total internal whole-body dose. Since this small native population had a relatively high proportion of seafood (including fish viscera) in its diet, these percentage contributions to internal radiation dose are probably near a maximum for similar occurrences. The contribution of marine radioactivity to external dose was very small, the gamma dose rates over the sea being much lower than those over land (Dunning, 1957). Plowshare Program Calculations of the marine-derived radiation exposure to humans are being made for proposed nuclear excavation projects associated with the Plowshare Program of the U.S. Atomic Energy Commission (Martin, 1969). Disposal of Radioactive Wastes There are a considerable number of locations in the world where radioactive wastes are discharged into the sea, or where such disposals are planned. Most of these discharges are associated with experimental or power reactors, but the best-documented case is the multifacility U.K. Windscale site. Fuel-processing wastes are included in the effluent from Windscale, which is discharged directly into the coastal waters. The discharge of reactor cooling water from the Hanford plant in the State of Washington is also well- documented. The Hanford reactor effluent enters the Co- lumbia River about 360 miles upstream from the Pacific Ocean, but some nuclides persist and can be detected in the sea beyond the mouth of the river. (For information on the kinds and quantities of radioactive waste discharged to the marine environment, see Chapter 2.) Waste discharges differ from worldwide fallout in a num- ber of important characteristics: Waste discharges are planned and controlled with respect to both time of disposal and amounts of materials. Wastes are made up of relatively concentrated solutions and are discharged from point sources, usually into coastal waters. A smaller spectrum of radionuclides is present in the wastes, and, except for fuel-processing plants, neutron acti- vation products often predominate (at least qualitatively) over fission product radionuclides. Other chemicals or heat present in the waste discharge may have a greater biological effect than the waste radio- nuclides. The number of people exposed to measurable amounts of radiation as a consequence of waste discharge is a very small fraction of the total population exposed to worldwide fallout. Radiation exposure of humans has been accurately as- sessed in relation to the discharge of radionuclides from sev- eral atomic energy installations, and the experience at these sites is summarized in the following paragraphs. LARGE NUCLEAR INSTALLATIONS Windscale An assessment of radiation exposure resulting from discharges of the U.K. Atomic Energy Authority fac- tory at Windscale, Cumberland, was detailed earlier. The radionuclide in the effluent of this fuel-processing plant that most restricts the total discharge of radioactive waste is a fis- sion product, 106Ru. The critical pathway that limits the amount of 106Ru discharged is the consumption by a small population in a distant area of contaminated seaweed (Porphyra) collected near Windscale (Figure 2). Discharge rates of radionuclides are accurately recorded (U.K. Atomic Energy Authority, 1965, 1966, 1967), and regular assessments are made of radiation doses received by members of the public (Preston and Jefferies, 1967, 1969). Disposal rates in the years 1964-1966 of 2,000 Ci/mo of 106 Ru via the effluent pipeline resulted in intestinal doses, as a result of eating Porphyra, of 0.67, 0.61, and 0.57 rad/yr (i.e., about 40 percent of the recommended dose limit) in the three respective years. (Dose rates for other years are shown in Figure 1.) Other routes of exposure and other radionuclides present in the discharged wastes result in much lower fractions of recommended dose limits for members of the public. For example, the average external gamma dose rate on mud flats near Windscale was 140^R/hr during 1964-1967, and this resulted largely from the discharge of 95Zr-95Nb (Jefferies, 1968). Allowing for occupancy factors, this would result in a whole-body dose to some people (fishermen) of 10 per- cent of that recommended by the ICRP. These are, of course, not the same people who receive internal radiation from eating Porphyra. Dounreay Limited amounts of radionuclides are discharged from the Dounreay Experimental Reactor Establishment on the coast of Scotland (Morgan, 1967). Because of the kinds of radionuclides of major significance in the discharge (141Ce, 144Ce 103Ru, 106Ru 95Zr) and 95^) and the ab- sence of seaweed harvesting, it has been found that the major source of radiation exposure to man is the handling of fixed nets by fishermen in nearby bays. Discharge rates from the offshore pipeline varied from 600 to 2,000 Ci (total radionuclides) a month in 1965- 1966 (U.K. Atomic Energy Authority, 1966, 1967). Beta radiation dose rates measured at experimental nets during

254 Radioactivity in the Marine Environment WATER T0 5EAWEED C0NCENTRATI0N FACT0R -1800 C0NSUMPTI0N 160n/DAY D0SE T0 G.I. TRACT tt 7 REWYEAR (50*0f LIMIT) THE 1°6Rij EXP0SURE PATHWAY Hjl AT WINDSCALE. UK FUEL PROCESS ING PLANT SEAWATER 0.08 pCi/ml Ru DILUTED WITH WATER IN PROCESSING IN S0UTH WALES FIGURE 2 The critical exposure pathway associated with the U.K. atomic energy plant at Windscale is the release of ".""Ru to the Irish Sea, its accumulation by seaweed, and the consumption of the seaweed by man. this period (Mitchell, 1967b) were less than 150 /uR/hr (i.e., less than 2.5 percent of the acceptable dose rate when han- dling times for commercial fishing gear are considered). Hanford Project The Hanford Project (now known as Rich- land Operations) discharges substantial quantities of radio- nuclides into the Columbia River. Some of these radionu- clides reach the mouth of the river and enter the Pacific Ocean (Soldat and Essig, 1966). Of those radionuclides that reach the sea, only 65Zn and 32P warrant consideration as sources of exposure to humans in nearby communities. Oysters grown in a bay several miles north of the river mouth contain higher concentrations of these radionuclides than other common seafoods. Estimated human dose rates from an assumed consumption rate of 230 g of oysters per week are 5 mrem per year to the intestinal tract and 3 mrem per year to the whole body (Soldat and Essig, 1966). These represent 0.3 percent and 0.6 percent, respectively, of the acceptable dose rate to individual members of the public. Other marine fish and shellfish in the vicinity also con- tain measurable concentrations of 65Zn, but human expo- sure from these sources is much less than from oyster consumption. Within the Columbia River, near the point of discharge of the effluent from the reactors, the uptake of 32P by fish is the critical pathway. This is illustrated in Figure 3. OTHER INSTALLATIONS Radionuclides are discharged into the sea at a number of other research centers, including Trombay, India (Pillai and Ganguly, 1961); Studsvik, Sweden (Agnedal and Bergstrom, 1966); and Petten, Netherlands (Van Dam and Davids, 1966). Discharges at all these locations have been small in amount, and the critical pathways for human radiation ex- posure have been evaluated only as a preoperational exercise. At Trombay, the critical radionuclide is 32P, and the critical pathway is expected to be the eating of marine fish. At Studsvik, the composition of the discharged effluent is uncertain. Present indications are that external exposure from 60Co on fishing gear will be the critical pathway for neutron activation products, and internal exposure from 106 Ru in fish will be the critical pathway for fission prod- ucts. At Petten, the critical pathways are assumed to be fish and shellfish consumption. No critical radionuclides have been identified. NUCLEAR POWER REACTORS Bradwell The nuclear power station at Bradwell, England, discharges radionuclides into a river estuary. Here, the criti- cal pathway is the consumption of contaminated oyster flesh, and the critical radionuclide in the effluent is 65Zn (Preston, 1967) (Figure 4). Preoperational and follow-up assessments have been made (Table 3). The radiation dose received by the small critical population group is 0.17 per- cent of the acceptable dose rate for the total body and 0.08 percent of that for the intestinal tract (Preston, 1968). Other U.K. Power Reactors At five other power reactor sites in the United Kingdom that began operation in 1968, preoperational assessments had been made of the critical pathways and critical radionuclides (Table 4). Actual dis- charges at Berkeley and Hinkley have been so low in relation to the maximum rate permissible for the site that only very small concentrations of radionuclides have been detected in the environment. At Berkeley, 137Cs has been measured ex-

Evaluation of Human Radiation Exposure 255 THE 32P EXPOSURE PATHWAY AT HANFORD WASHINGTON C0LUMBIA RIVER DIRECT C00LED REACT0R WATER T0 FISH C0NCENTRATI0N FACT0R WINTER <1 SUMMER ~ 5.000 FIGURE 3 The critical exposure pathway associated with the Hanford plutonium- producing reactors is the release of P to the Columbia River, its uptake by fish, and the consumption of the fish by man. DOSE T0 BONE 0.3REM/YEAR 120% 0F LIMIT) AVERAGE C0NCENTRATI0N IN SPECIES EATEN IN GREATEST AM0UNTS -40 pCi3ZP^ THE 65Zn EXP0SURE PATHWAY AT BRADWEIL PDWER STATI0N, U.K 0YS ~5pci/s D0SE T0 WH0LE B0DY ~1 mrem/YEAR (0.2% 0f LIMIT) FIGURE 4 The critical exposure pathway associated with the nuclear power station at Bradwell, U.K., is the release of 65/n to the Blackwater Estuary, its uptake by oysters, and the consumption of the oysters by man. tensively in silt (1-2 pCi/g dry) taken from the Severn Estu- ary, but at levels that have made no measurable contribution to gamma whole-body dose rates-the controlling feature of this type of contamination-and at Hinkley, 65Zn has been detected in seaweed taken from the vicinity of the outfall (0.1-0.5 pCi/g wet). Two of the other three stations have only recently become operational. The critical pathway for human exposure at two of the sites is predicted to be ex- ternal radiation from silt contaminated by activated corro- sion products. At the three other sites, the critical pathway is irradiation of the human intestinal tract by neutron acti- vation products concentrated in fish flesh (Preston, 1966). Humboldt Bay The nuclear power station on Humboldt Bay in northern California began operating in 1962. The quantities of radionuclides discharged to the estuary each year with the cooling water have been substantially below the authorized limit of 20 Ci (0.1 pCi/ml). The nuclides of principal interest in the discharge are 65Zn, 60Co, 54Mn, and 137Cs. A preoperational survey and assessment indi-

256 Radioactivity in the Marine Environment TABLE 3 Permissible Discharge Rate of 65Zn from the Bradwell Power Station to the Blackwater Estuary" Preoperational Estimate Follow-up Assessment Estimated concentration of 65Zn in estuary Average 65Zn discharge per month 16.6 mCi per curie released per day 1.5X10-7MCi/ml Average 65Zn concentration in oyster flesh Concentration factor-oyster flesh/seawater 100,000 at nearest commercial bed 3.4 pCi/g Daily intake 65Zn in 75 g of oysters 1.1 MCi ICRP maximum permissible daily intake 0.22»iCi Maximum daily intake of oyster flesh 75g/day ICRP maximum permissible daily intake 0.22 nd Maximum permissible concentration of 65Zn in oyster flesh 2,900 pCi/g Estimated maximum daily discharge rate 0.2Ci Calculated maximum daily discharge rate 0.5 Ci "Adapted from Preston (1967). TABLE 4 Comparison of Critical Parameters for Five Civil Nuclear Power Station Sites" Central Electricity Generating Board Site Parameters Berkeley Hinkley Dungeness Sizewell Wylfa Site dilution factor 10 I02 I03 10 I02 Water-MCi/ml/Ci of discharge/day 1o-7 io-8 10-* io-7 io-8 Nuclides 65Zn,60Co 65Zn, 60Co 65Zn, 60Co 65Zn, 60Co 60Co, 65Zn, 32P Material Silt and salmon flesh Silt and fish flesh Fish flesh Fish flesh Fish and shellfish Concentration factor IO4 IO4 IO4 10* I04 Population size 10 10 10 10 10 Critical organ Total body Total body Gastrointestinal tract Gastrointestinal tract Bone, gastrointestinal tract Ingestion rate (g/day) 23 195 807 130 205 Exposure (hr/yr) 340 (silt) 750 (silt) - - - "Adapted from Preston (1966, p. 735) and Mitchell (1967b). cated that the critical exposure pathway would be via the accumulation of 65Zn in oysters that are grown commer- cially in Humboldt Bay. Postoperational surveys have never shown levels of radionuclides in oysters of the Bay that were significantly above background. Under experimental condi- tions, oysters have been held directly in the plant discharge water, and at one time, their concentration of 65Zn reached 175 pCi/g. The level has since declined (Salo, 1968). Inas- much as the shellfish consumed by the public have only background amounts of the radionuclides, the radiation dose is negligible. Tarapur A preoperational assessment of critical pathways and radionuclides has been carried out for the Indian power station at Tarapur (Kamath et al., 1966). Neutron activation products (mainly 65Zn) in marine fish consumed by fisher- men and families are expected to contribute most to human exposure.

Evaluation of Human Radiation Exposure 257 NUCLEAR-POWERED VESSELS Studies have been made of the amounts and the fate of waste radionuclides discharged to coastal waters by U.S. Navy nuclear-powered submarines and ships at 13 U.S. docking facilities (Vaughan and Miles, 1966) and of con- ditions in harbors used by the civilian ship NS Savannah (Flora and Wukasch, 1966). (Discharges from the U.S. Naval ships are listed in Chapter 2.) No measurable transfer to man of the discharged radionuclides has occurred, and external radiation dose rates near the facilities have shown no mea- surable increase. The accidental loss of the Thresher in 1964 was followed by extensive radiation monitoring in the vicinity of the hulk. No detectable escape of radionuclides into the sea was found, and no human exposure resulted. SOLID-WASTE DISPOSAL United States Sea disposal of contaminated solid wastes was carried out along both the Pacific and Atlantic coasts of the United States during the years 1946-1963. The total quantity disposed in the Pacific was approximately 15,000 Ci, and in the Atlantic, 46,000 Ci (Belter, 1965). Radiation monitoring of the two areas (Pneumo Dynamics Corpora- tion, 1961; Brown etal., 1962) has been carried out. No de- tectable concentrations of waste radionuclides were found in seawater or marine organisms. United Kingdom Contaminated solid wastes containing approximately 1,500 Ci of beta-gamma radionuclides are disposed of yearly by the U.K. Atomic Energy Authority into the Atlantic deeps at a depth of not less than 1,500 fathoms. The amounts of waste disposed are considered to be too small to have an appreciable effect on the environ- ment; therefore no radiation monitoring is undertaken (U.K. Atomic Energy Authority, 1966). Asia Some radioactive wastes have been disposed of in the North Pacific near Japan. One of several measurements made by Akiyama (1965) suggested the presence of arti- ficial contamination near the bottom in the vicinity of the disposal site. The measurement was only slightly above the expected background level, and one would not expect it to have any radiological implications. CONCLUSIONS Over the past decade, the use of atomic energy for peaceful purposes, and especially the production of electric power, has moved from the stage of planning and technical develop- ment to the stage of demonstration and competitive appli- cation. This application has been accompanied by the dis- charge of low-level radioactive waste into rivers and directly into the sea. In every case, the proposed discharge has re- ceived careful study in advance of operations, and prudent restrictions have been specified on the kinds and amounts of radioactive materials that could be released. Follow-up sur- veys show that the restrictions have been entirely adequate to keep human exposure well within the guidelines specified by the ICRP and FRC. A continuation of the policies and practices concerning the control of low-level waste disposal that have been established during these formative years should assure that radioactive contamination of the marine environment will not reach unacceptable levels. SUMMARY The addition of artificial radioactive materials to the marine environment results in some added radiation exposure to people who use the sea and its products. The magnitude of the additional exposure that results depends upon many complex relationships, however, and involves the kinds and quantities of radioactive materials added and the manner and place of their introduction. Over the past quarter century, the major sources of arti- ficial radioactive materials to the sea have been worldwide fallout from the testing of nuclear devices in the atmosphere and the chronic discharge of low-level wastes from operating reactors and fuel processing plants. Much less significant ad- ditions have resulted from nuclear detonations below the surface of the sea, from the disposal of low-level waste in packages, and from the inadvertent loss of radioactive materials. Radioactive contaminants can follow a variety of path- ways in the sea that may bring them into contact with man and contribute to the radiation exposure that he receives from the environment as a whole. Only careful evaluation of each individual situation can determine the most important or critical pathway, but the following ones are likely to be of greatest importance: The accumulation of certain radionuclides in fish, shell- fish, and seaweeds that are eaten by man in substantial quantities The deposition of radioactive particles on the seabed in places where people may contact them either in the course of their occupations or in pursuit of recreation The adsorption of certain radionuclides on fishing gear. A large number of other pathways have been identified or postulated, but at this point in time their contribution to the radiation exposure of people has been much smaller than the ones listed above. The significance of the radiation exposure contributed by all of the pathways is dependent on the intensity (concen-

258 Radioactivity in the Marine Environment tration) of the source, on the frequency and length of time that people are exposed to the source, and on the number of people that may be exposed. It is generally held that any exposure to ionizing radiation entails at least some small risk of a deleterious biological effect. Therefore, the radi- ation dose must be held to such a low level that the very small risk involved is acceptable to society as a whole in re- lation to the benefits derived from the use of atomic energy. The Federal Radiation Council, the National Council on Radiation Protection and Measurements, the International Commission on Radiological Protection, and other authori- tative groups have recommended doses that they believe should be considered as the maximum acceptable for con- tinuous exposure. In all cases, they recommend restricting exposure to the lowest practicable level compatible with economic and social considerations. For radioactive mate- rials deposited in the body, dose rates are related to a per- missible body (or organ) burden for specific radionuclides, and these in turn are related to a permissible continuous daily intake sufficient to establish and maintain that body burden. When an introduction of radioactive material into the marine environment is being considered, it is now conven- tional to identify the probable critical pathway of exposure and the individuals or critical population likely to receive the greatest exposure. Preoperational guides are then calcu- lated that establish the maximum allowable rates of intro- duction of specific radionuclides. The preoperational guides are based on the critical exposure pathways and on some fraction of the internationally recognized dose limits. Fol- lowing the actual introduction of potentially significant quantities of radioactive materials, a re-evaluation of the probable dose to man can and should be made on the basis of actual measurements of the concentrations of radionu- clides in the environment. Follow-up evaluations should be based on measurements of the materials directly responsible for human exposure—the species of fish, shellfish, and sea- weed actually consumed by the public, the beaches used by the public, and the gear handled by the fishermen. The follow-up evaluations have almost always shown that the preoperational predictions were highly pessimistic and thus that the tentative discharge guides were much more restric- tive than actually necessary to maintain the radiation dose to people within the prescribed limits. The radiation dose received by people from worldwide fallout via food from the sea is very small both in magnitude and in relation to that received from the terrestrial environ- ment. Small population groups that depend on fish and other marine organisms could have received at most about 0.4 mrem per year to the whole body and 30 mrem per year to parts of the skeleton. The large nuclear installations of the U.K. Atomic Energy Authority at Windscale on the Irish Sea and of the U.S. Atomic Energy Commission at Richland on the Columbia River discharge far greater quantities of radionuclides into the sea than do nuclear power reactors. The critical expo- sure pathway for the Windscale plant is the accumulation of 106 Ru by seaweed that is eaten in quantity by a small popu- lation group in a distant area. The resulting radiation dose amounts to about 40 percent of the recommended limit. The critical exposure pathway for the Richland plant (Han- ford) is the concentration of 32P and 65Zn by fish in the Columbia River and oysters grown near the mouth of the river. The marine pathway leads to a dose to people who eat oysters of less than 1 percent of the recommended limit. 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LIST OF CONTRIBUTORS GEORGE s. BIEN, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California VAUGHAN T. BOWEN, Chemistry and Geology Depart- ment, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts WALLACE s. BROECKER, Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York HARRY H. CARTER, Chesapeake Bay Institute, The Johns Hopkins University, Baltimore, Maryland EGBERT K. DUURSMA, Laboratory of Marine Radio- activity, International Atomic Energy Agency, Monaco THEODORE R. FOLSOM, Scripps Institution of Ocean- ography, University of California, San Diego, La Jolla, California RICHARD F. FOSTER, Environmental Studies Section, Battelle Northwest Laboratories, Richland, Washington EDWARD D. GOLDBERG, Scripps Institution of Ocean- ography, University of California, San Diego, La Jolla, California M. GRANT GROSS, Marine Sciences Research Center, State University of New York, Stony Brook, New York PHILIP F. GUSTAFSON, Radiological Physics Division, Argonne National Laboratory, Argonne, Illinois EDWARD E. HELD, Laboratory of Radiation Ecology, College of Fisheries, University of Washington, Seattle, Washington ARNOLD B. JOSEPH, Division of Water Quality Research, Environmental Protection Agency, Washington, D.C. BOSTWICK KETCHUM, Associate Director, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts FRANK c. LOWMAN, Puerto Rico Nuclear Center, College Station, Puerto Rico ROY E. NAKATANI, Pacific Northwest Laboratory, Battelle Memorial Institute, Richland, Washington A KIR A OKU BO, Chesapeake Bay Institute, The Johns Hopkins University, Baltimore, Maryland JERRY s. OLSEN, Radiation Ecology, Oak Ridge National Laboratory, Oak Ridge, Tennessee IVAN L. OPHEL, Environmental Research Branch, Biology and Health Physics Division, Atomic Energy of Canada Limited, Chalk River (Deep River), Ontario, Canada CHARLES L. OSTERBERG, Oceanography Department, Oregon State University, Corvallis, Oregon ALAN PRESTON, Ministry of Agriculture, Fisheries and Food, Fisheries Radiobiologjcal Laboratory, Hamilton Dock, Lowestoft, Suffolk, England DONALD w. PRITCHARD, Chesapeake Bay Institute, The Johns Hopkins University, Baltimore, Maryland ROBERT o. REID, Texas A&M University, College of Geosciences, Department of Oceanography, College Station, Texas THEODORE R. RICE, Director, National Center for Estuarine and Menhaden Studies, Beaufort, North Carolina 261

262 Radioactivity in the Marine Environment FRANCIS A. RICHARDS, Department of Oceanography, University of Washington, Seattle, Washington "JOSEPH RAVERA, Health and Safety Laboratory, U.S. Atomic Energy Commission, New York, New York IRVING R. RUSSELL, Chairman, Chemistry Department, Boston College, Chestnut Hill, Massachusetts tMILNER B. SCHAEFER.Scripps Institution of Oceanog- raphy, University of California, San Diego, La Jolla, California E. A. SCHUERT, Information Research Associates, Berkeley, California ALLYN H. SEYMOUR, Laboratory of Radiation Ecology, College of Fisheries, University of Washington, Seattle, Washington ARTHUR TAMPLIN, Lawrence Radiation Laboratory, Livermore, California W1LLIAM L. TEMPLETON, Aquatic Ecology Section, Battelle Northwest Laboratories, Richland, Washington KARL TUREKIAN, Department of Geology, Yale Univer- sity, New Haven, Connecticut HERBERT L. VOLCHOK, Health and Safety Laboratory, U.S. Atomic Energy Commission, New York, New York *Died January. 31, 1970. ^Died July 26, 1970.

INDEX Accumulated radiation in fish, 235 Lithium fluoride dosimeters, 235 Activity concentration, 11 (See also Table 4), 14 Acute radiation exposure, 224 Environmental interaction, 224 Dissolved oxygen, 224 Salinity, 224 Temperature, 224 Aerospace nuclear reactors, 29 Air-cooled, 30 Water immersion studies, 30 Antarctic Circumpolar Current, 100 Antarctic Intermediate Water Fallout comparisons, 124 Artificial carbon-14 in oceans, 126 Artificial radioactive effluents Low-level sources, 106 Artificial radionuclides Seawater measurements, 75 Atlantic Ocean Cesium-137/strontium-90 ratio, 71 (See also Table 18), 72 Deep water residence time, 123 Elements vertical distributions, 172 Intermediate Water velocities, 124 Mathematical models, 202 Physical properties statistics, 92 Strontium-90 comparisons (Table 6), 50 Strontium-90 profiles (Table 20), 74 Surface water Strontium-90 mean annual concentra- tions (Table 1). 44 Temperature-salinity relationships (Table 2), 94 Tritium profiles (Table 20), 74 Atlantic Ocean contamination Depth of mixing, 54, 69 Atomic energy Applications (Table 1), 7 Sources (Table 1), 7 Bacteria-inorganic adsorption processes, 190 Baltic Sea Cesium-137/strontium-90 ratio, 72 Barents Sea Plaice radionuclide sensitivity, 226 Benthic environment Sediment-water interface, 205 Benthic organisms Sediment particles ingestion, 205 Bibliography (See end of each chapter) Bikini Atoll, 1 Vegetation-radiation studies, 234 Bikini Atoll nuclear experiments Drosophila gamma dose, 233 Drosophila genetics, 233 Insect populations, 233 Biodeposition rates, 193 Biological activity Columbia River, 154 Biological deposition Laboratory experiments, 193 Biological diffusion coefficient, 154 Biological factors variations, 163 Biological reconcentration processes, 241 Biological transport, 185 Rates, 183 Biological turnover rates, 165 Biota Trace elements transport, 161 Black Sea Cesium-137/strontium-90 ratio, 71 Blackwater Estuary Bradwell discharge limits (Table 3), 256 Bomb debris-seawater interaction, 16 Bottom sediments Exchangeable nutrients, 192 Japanese oyster farm contamination, 192 Reducing environments, 192 Box model calculations, 119 Burrowing organisms, 154 Calcareous exoskeletal material, 143 Carbon-14 concentration calculations, 127 Vertical profiles (Table 8), 128 Carbon concentrations in seawater, 172 Catalyst elements, 185, 186 Chemical composition of seawater (Table 1), 138 Chemical species I.SVr also Radionuclides in seawater), 137 Chesapeake Bay Turnover rates of phosphorus, 171 Chronic radiation dosage (See also Radiation exposure) Coconut crab (Birgus latro), 234 Hermit crab (Coenobita sp.), 234 Chronic radiation exposure (See also Radiation dosage) Chinook salmon abnormalities, 226 Cobalt-60, 225 Civilian propulsion reactors, 29 263

264 Index Clinch River Sediment radionuclide uptake, 149 Studies, 38 Cloud advection, 91 Coastal ocean (See also Marine environment) Continental shelves, 137 Estuaries, 137 Lagoons, 137 Coastal ocean characteristics, 141 Primary production, 142 Subsurface circulation, 142 Coastal plain estuaries, 130 Circulation patterns, 131 Partially mixed estuary Chesapeake Bay, 131 Physical properties, 131 Salt-wedge estuary Mississippi River, 131 Vertical homogeneity, 131 Vertical stratification, 131 Coastal waters Biological characteristics, 129 Freshwater runoff, 129 Longshore currents, 129 Meteorological conditions, 129 Near-shore environment, 129 Physical characteristics, 129 Columbia River Plankton algae radioactivity absorption, 204 Sediments Radionuclide accumulation, 189 Concentration factors, 2, 208 Comparisons, 164 Discrepancies, 164 Marine biota, 166 Nitrogen, 171 Phosphorus, 171 Stable elements, 207 Zooplankton conversion factors, 179 Concentration factors-stable elements re- lationships, 208 Concentration factors-trophic level relation- ships, 208 Contaminated wastes-radiation concentra- tion studies, 246 Contamination levels United Kingdom, 243 United States, 243 Contamination prediction, 245, 247 Concentration factors, 247 Critical volume, 247 Mathematical models, 247 Continental shelf Near-bottom currents, 157 Sedimentary characteristics, 157 Continental shelf-submarine canyon rela- tionships, 157 Conversion factor calculations, 178 Coral island surface explosions (Table 4), 14 Cosmic radioactivity, 7 Critical group (See also Exposed population), 247 Seafood consumption, 247 Somatic exposure, 250 Critical pathway, 253, 255 Studies, 254 Critical pathway approach, 4, 215, 246, 248, 249 Current measurement instrumentation Buoyant floats, 102 Current strengths, 100 Debris solubility, 17 Deep current measurements, 102 (See also Table 3), 103 Deep ocean waters Cesium-137 concentrations, 63 Strontium-90 concentrations, 62 Vertical mixing, 63 Deep water contamination, 68 Blank occurrences, 68 Data contradictions, 68, 69 Fallout calculations, 70 Half-mixing depths, 70 Ionic cesium-137 mixing, 69 Local anomaly, 68 Pump absorber instrumentation, 69 Radionuclide populations, 69 Strontium-90 Atlantic Ocean, 68 Caribbean Sea, 68 Sargasso Sea, 68 Strontium-90 inventory, 68, 70 Deep water data evaluation, 68 Deep water radionuclide deposition, 184 Deep water vertical transport Biological processes, 174 Physical processes, 174 Deep water zooplankton contamination, 176 Desalination wastes, 241 Deserts-marine ecosystems-man relation- ships, 215 Dissolved oxygen, 142 Sulfate-reducing bacteria, 142 World Ocean, 97 Distribution coefficient, 148, 153, 159 Definition, 148 Radioisotopes sorption (Table 2), 152 Distribution of properties in sea, 92 Dosimeters Sediment radiation dose, 230 Thermoluminescent (TLD), 3, 230 Dounreay radionuclides discharge Radiation exposure in fish nets, 253 Eastern Pacific Ocean surface water Strontium-90 mean annual concentration (Table 3), 47 Ecology, 200 Tracer experiments, 217 Ecology-environment relationships, 200 Ecosystem radiation exposure, 206 Ecosystems, 200 Artificial radioactive exposure, 203 Instruments-community structure rela- tionships, 201 Marine environment, 200 Physicochemical environment, 203 Simulation models, 3 Ecosystems radioactivity exposure, 204 Ecosystems-species interdependency, 213 Eddies, 91 Nonhomogeneous characteristics, 107 Nonstationary characteristics, 107 Eddy diffusion Cape Kennedy, offshore region, 115 Element concentration Biologically active, 138 Carbon depletion, 143 Deep water-surface water ratios (Table 5), 143 Depletion factors, 143 (See also Table 1), 138 Marine organisms, 144 (See also Table 6), 144 Nitrogen-phosphorus ratio, 143 Pacific Ocean, 143 Residence time in ocean, 138, 142, 143 Solubility equilibria, 138 (See also Table 3), 141 Surface water depletion, 143 Unreactive elements, 138 Element concentrations-depth relation- ships, 186 Element concentrations determination, 138 Element concentration factors, 144 (See also Table 7), 144 Ashed plankton, 144 (See also Table 7), 144 Element concentrations in ocean (See Table 2), 139 (See Table 4), 141 Element enrichment, 144 Element geochemical characteristics (Table 2), 139 Element residence time in ocean, 138 Encapsulating metals, 32 Hastelloy, 32 Eniwetok Atoll nuclear experiments Animal populations, 233 Environmental factors variations, 163 Environmental radiation Surveillance program, 245 Equatorial Current, 100 Equatorial Undercurrent, 100 Estuaries, 156 Biological productivity, 193 Box model studies, 132 Photosynthesis, 193 Radionuclide distribution, 193 Sediment movement, 156, 157 Sedimentation rates, 187 Tidal currents, 157 Turbulent diffusion, 129 Estuaries and man, 194 Food fish harvest. 194 Estuarine characteristics, 193 Estuarine circulation Numerical modeling, 132 Patterns, 130 Estuarine contaminants classification, 194 Estuarine dynamics Plume studies, 132 Estuarine numerical modeling

Index 265 Diffusion parameters-prediction variables relationships, 133 Transient-state solutions, 133 Estuarine nutrients Surface runoff, 187 Transport, 187 Estuarine sediment contamination, 242 Estuarine sediments Benthic organisms, 192 Trace elements distribution, 189 Estuarine tidal flow, 131 Estuary Characteristics, 187 Division Tectonically produced, 130 Flushing, 132 Pollution Concentrations, 131 Mechanical dilution, 132 Motion, 131 Tidal oscillation dispersion, 132 Subdivision Bars, 130 Drowned river valleys, 130 Fjords, 130 Estuary-open sea comparisons, 187 European Nuclear Energy Agency, 36 Waste disposal (Table 25), 38 Exometabolites Complex formers, 206 Physicochemical stability, 205 Exposed population (See also Critical group), 247 External exposure Concentration factors, 248 Critical population, 248 External radiation, 225 FAO (See Food and Agriculture Organiza- tion) Fallout Over ocean, 74 Studies Thermodynamic model, 14 Weather observations, 48 Fecal material-elements transport inter- actions, 184 Filter-feeding organisms, 147, 155,162 Sediments adsorption, 191 Fireball vapors, 12 Fish larvae Radiation sensitivity, 3 Fission explosion-isotopes production, 124 Fission-product radioactivity, 6 Florida Current, 100 Folsom in situ cesium-137 measurements, 124 Food and Agriculture Organization Radionuclides in marine fish, 251, 252 Fractionation, 11,14 Freshwater organisms. 225 Fresh water-seawater mixing Ionic radionuclides, 163 Gamma radiation in fish, 231 Gamma spectrometry Radionuclides in seawater, 77 Generating plants Nuclear powered, 6 Genetic exposure, 250 Dosage calculations, 250, 251 Windscale studies, 251 Glacial clays in seawater Radionuclide sorption, 157 Global ocean circulation, 92 Global radionuclide fallout Cesium-137 in deep ocean, 69 Strontium-90 in deep ocean, 69 Groundwater contamination, 21 Gulf of California Iodine-131 in coastal waters, 77 Gulf of Mexico Iodine-131 in coastal waters, 77 Gulf Stream currents, 100 Hanford radionuclides discharges Columbia River, 254 Oyster contamination, 254 Reactor effluents Biological effects, 228 Chemical toxicity, 228 Hexavalent chromium, 228 Radioactivity, 228 Thermal increment, 228 Hanford Reprocessing Plant, 254 Human ecology-marine environment rela- tionships, 214 Human radiation exposure, 242, 253 Hydrosphere waste deposition, 218 Hydrosphere-biosphere relationships, 161 Hyperactivity in fish, 231 (See also Radiation dosage) ICRP (See International Commission on Radiological Protection) Indian Ocean Current regime, 100 Deep water residence time, 121 Elements vertical distributions, 172 Physical properties statistics, 92 Strontium-90 comparisons (Table 9), 51 Temperature-salinity relationships (Table 2), 94 Surface water Strontium-90 mean annual concentra- tion (Table 4), 48 Initial cloud, 91 Horizontal spread, 91 Vertical spread, 91 Interactions Fireball vapors, 12 Interlaboratory comparison Strontium-90 analysis, 43 International Commission on Radiological Protection Air radionuclides concentration, 243 Critical group, 247 Behavior patterns, 244 Derived radiation working limits, 244 Drinking water radionuclides concentra- tions, 243 Human standardization, 243 Radiation accidents Remedial measures, 243 Radiation thresholds, 242 Somatic criteria, 244 Interstitial water movement, 154 Oxygen depletion, 153 Radionuclide bonding, 153 Soluble ligands, 153 Ionizing radiation, 6 Genetic effects, 4 Marine organisms effects, 4 Irish Sea Marine environment testing, 234 Iodine-131 from atmospheric explosions, 77 Iodine-131 in seawater, 77 Isotope deep ocean penetration, 124 Isotopes (.s'<v also Radionuclides) Thorium, 7 Uranium, 7 Isotopic fuels, 32 Isotopic power sources, 241 Kuroshio currents, 100 LD (See lethal dose) Lanthanides as tracers, 70 Lanthanides in seawater Residence times, 79 Laverbread consumption by man, 250 Low-level wastes, 31, 36 Man and marine food, 214 Man and radiosensitivity, 212 Marine animal contamination, 241 Marine biota Manganese-54 accumulation, 162 Radionuclides concentrations, 25 2 Exploitation Food for man, 217 Marine ecological-geochemical dynamics, 214 Marine ecology Mathematical models, 201 Marine ecosystems Benthic, 202 Classifications, 202 (See also Table 1), 203 Near-shore, 202 Pelagic, 202 Radiation as predator, 213 Radiation population damage, 213, 214 Radionuclide behavior, 207 Radiosensitivity, 208, 209, 212 Species interaction, 213 Marine ecosystems radiation effects, 209 Marine ecosystems-radiation sensitivity re- lationships, 205 Marine ecosystems-tracer experiments, 218 Marine environment Alpha activity, 224 Bikini Atoll, 232 Biota, 224

266 Index Cesium-137/strontium-90 ratio, 71 Chronic waste discharges, 241 Coastal ocean, 137, 246 Desalination wastes, 241 Ecosystems, 200, 232 Interactions, 205 Inshore waters, 246 Mixing processes, 106 Natural radioactivity, 224 Open sea, 137, 142, 246 Outer continental shelf, 246 Permissible concentration, 245 Physicochemical state of elements, 207 Populations, 223 Genetic response, 223 Radiation dosage studies Cesium-137, 224 Cobalt-90, 224 Potassium-40, 224 Radon-226, 224 Radiation dosages Black Sea, 226 Radiation monitoring, 244 Radiation-population effects, 232 Radiochemical analysis, 71 Radioecology, 200 Radioactive contamination, 245 Radioactive materials, 249 Radionuclides, 1, 232, 240 Availability, 162 Marine environment-estuarine interactions, 129 Marine environment testing Irish Sea, 234 Windscale reprocessing plant, 234 Marine fishery productivity, 217 Marine food contamination Restricted use, 194 Marine food-radiation relationships Japanese studies, 216 Marine foodstuffs, 241 Marine organisms, 224 Algae, 225 Alpha exposures, 208 Aquarium radionuclide studies, 191 Bacteria, 225 Biological activity, 169 Transport, 169 Carbon concentrations, 172 Concentration factors, 164, 178 Averages, 166, 167 (See also Table 1), 168 Element concentration factors (Table 2), 210 Element concentration groups, 167 Element concentrations, 180 Exometabolites availability, 205 Food conversion efficiency, 177 Genetic diversity, 209 Ion-exchange reactions, 166 Lethal dosage (LD), 225 Metabolic stimulation, 231 Migration Horizontal transport, 169 Vertical transport, 169 Nonstructural element uptake, 173 Protein levels, 215 Radiation Absorption rates, 247 Accumulations, 209 Behavior, 231 Radiation-genetic fitness relationships, 232 Radiation-induced mutations, 209 Radiation tolerances, 225 Ontogeny, 225 Phylogeny, 225 Radioactive concentration factors (Table 2), 210 Radiosensitivity, 230 Regeneration rates, 170 Stable elements distribution, 161 Surface adsorption, 166 Trophic levels, 208 Marine organisms-environmental equilibrium characteristics, 165 Marine organisms feeding Mucous threads, 206 Marine organisms radiation exposure Species interactions, 205 Marine organisms-radioactivity absorption, 204 Marine organisms-radionuclides accumula- tion interaction, 161 Marine phytoplankton-radioactivity absorp- tion, 204 Marine plant consumption, 241 Marine population control, 212 Marine products Consumption, 247 Contamination, 249 Laverbread contamination, 250 Marine resources studies, 235 Marine sediments, 147 Radionuclide sorption, 147 Vertical movement, 153 Marine species diversity, 212 Marine suspensoids Radioactive fallout association, 204 Radionuclide waste associations, 204 Marine-terrestrial food chains, 206 Mass balance deficiency, 17 Mathematical models Abstract phases, 201 Atmosphere, 201 Biosphere, 201 Fisheries resources, 201 Hydrosphere, 201 Hydrographic smooth curves, 202 Marine resources management, 201 Nickel in Atlantic Ocean, 202 Numerical predictions, 202 Predictive uses, 202 Psychological factors, 202 Theoretical studies, 202 Troposphere-stratosphere interchanges, 201 Use procedures, 202 Metals in seawater, 166 Microbial epiphyton-estuaries relationships, 191 Microdosimeters, 236 Natural aerosols, 11 Natural radioactivity, 7, 244, 251 Cosmic rays, 224 Natural radionuclides (Table 2), 8 Seawater radioactivity, 2 Natural vs. artificial fallout measurements, 79 Near-bottom currents, 157 Near-shore environment, 204 Sediment radioactivity, 205 Near-shore zone Coastal water exchange, 130 Radioactive materials transport, 130 Currents Wind domination, 130 Water movement Spatial variation, 129 Temporal variation, 129 Near-surface waters Wind-induced transport, 130 Nonconservative elements, 3 Nuclear debris Global distribution, 19 Nuclear desalination, 241 Nuclear detonations (Table 3), 9 Hazard to man, 20 Precipitation samples, 42 Radioactive tracers, 42 Radionuclide contaminants, 42,162 Nuclear devices Low-fission yield, 20 Nuclear excavations, 20, 22 Scavenging, 22 Nuclear excursion, 30, 31 Spacecraft reentry, 30 Nuclear explosives, 9 Peaceful applications, 9 Testing, 9 Nuclear fallout, 43 Cesium-137/strontium-90 ratio in sea- water, 71 Nuclear Power Plants (Table 10), 24 Oak Ridge National Laboratory, 235 Nuclear power stations Critical parameters comparisons (Table 4), 256 Nuclear-powered ships, 257 Civilian German, Otto Hahn, 29 Japan, NSMutsu, 29 USNS Savannah, 29 Operations, 25 Packaged wastes disposal, 241 U.S. Navy, 25 (See a/so Table 16), 29 VSS Nautilus, 28 Waste disposal (Table 17), 30 Nuclear reactors, 22 (See also Table 11), 26 (See also Table 12), 28 Accidents, 23 Aerospace programs, 30 Bradwell, England, 254 Coolants (Table 16), 29 Corrosion rates, 24 Fuel rods, 23