Radioactivity in the Marine Environment (1971)

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Radiation Effects 229 dose from data on body burdens of serially killed fish fed 65Zn daily over a period of 16-18 weeks. He estimated a total absorbed dose of 25 R for trout fed 0.01 ^Ci/g of body weight and 1,200 R for trout fed 1.0 juCi/g. Watson era/. (1959) also calculated a dose to the bone, gut, and muscle of approximately 6,000 R, 1,600 R, and 800 R, respectively, in trout fed 0.06 pCi of 32P/g daily for 17 weeks. At this level, the growth rate of the fish was reduced. No deaths were attributable to radiation damage, and there appeared to be an increase in growth rate after cessation of isotope feeding. In some of the experiments involving chronic dosages to marine fish eggs, absorbed doses were measured and calcu- lated (Table 5) (V. M. Brown, 1962; Brown and Templeton, 1964). Absorbed doses calculated for anchovy eggs from the basic data of Polikarpov and Ivanov (1962) indicate that at the concentration where abnormalities become significant (10-10 Ci/liter), the dose absorbed was 0.16 mR/day. The total dose accumulated by the eggs was the same, since the period from fertilization to hatching was 20-24 hr. The cal- culated dose rate from the 40K in the seawater and in the egg was about 0.02 mR/day. However, consideration must also be given to the additional background dose within the laboratory, which would be about 0.3 mR/day, or approxi- TABLE 4 Effect of Chronic Ingestion of 32P, 90Sr-90Y, or 65Zn on Yearling Rainbow Trout (Salmo gairdneri)" Treatment (MCi/g fish/ day) Duration of Feeding (wk) Growth Depression Significant Mortality Gut Concentration at End OuCi/g wet weight) of Feeding 32p Leukopenia Damage Bone Muscle 0.006 25 no no no no - - 0.06 25 wk 17 no 4 mo no 1.8 0.23 0.60 25 wk 11 yes 1 7 days yes - - 90Sr-90Y 0.005 21 no no no no 2.1 0.0022 0.05 21 no no no no 28 0.078 0.50 21 wk 12 wk 15 wk 15 yes 248 0.27 65Zn 0.01 17 no no no no — - 0.10 17 no no no no - — 1.0 17 no no no no 4.0 0.35 10.0 10 no no wk 10 no — — "After Watson era/. (1959); Nakatani and Foster (1963); Nakatani (1966). TABLE 5 Calculated and Measured Radiation Dose Rates from Contaminated Media to Fish Eggs under Experimental Conditions" Fish Concentration Factor Nuclide Water Concentration (pCi/liter) Range of Dose Rate to Egg (per day) Dose Rate from 40K in Water and Egg (mR/day) Approximate Background Dose Rate in Laboratory (mR/day) Salmon (Salmo salar) 30 90Sr-90Y 103 1-10 mR 0.017 0.3 Brown trout (Salmo trutta) 25 90Sr.90Y 1os-1o-7 60 mR-3.0 R 0.017 0.3 Plaice (Pleuronectes platessa) 0.35 10.0 90Sr 90y 102-108 <0.1 mR-13.0R 0.02 0.3 "After Brown (1962) and Brown and Templeton (1964).

230 Radioactivity in the Marine Environment mately twice that calculated to be delivered to the egg from the 90Sr-9oY. Calculations of the dose rates from radionuclides ab- sorbed by or adsorbed on the organism in the laboratory and in the natural environment are difficult to compute ac- curately for several reasons. The radionuclide is not uni- formly distributed throughout the organisms or even throughout the volume of a single organ or cell. One organ or tissue may contribute to the dose of an adjacent organ, the concentration may change with time, and the structures of organisms are of varying size and shape. A further com- plexity is the wide variation in the energy of the emissions. Calculations for the assessment of the dose to fish eggs aris- ing from immersion in contaminated seawater have been developed by Fedorov (1965) and Adams (1968). A major advance in the determination of dose is the de- velopment of thermoluminescent dosimeters (TLD's). These dosimeters are commercially available in a variety of forms, most commonly as LiF powder in sachets or as LiF extru- sions. The lower limits of detection in routine use are of the order of 20 mR, with an error of about 10 percent, and the techniques are rapidly being improved. The small size of the dosimeters allows them to be conveniently emplaced on or in living organisms to provide the best practical means of direct measurement of the radiation dose received by the organisms in their natural habitat. These dosimeters can also be used to measure the radiation dose in sediments directly, and they can be used in water with inexpensive buoyline- anchor support systems. The performance of TLD's is very good. They are little affected by wide variations in environmental conditions and can therefore be left unattended for long periods. They are nearly energy-independent over a wide range of energies and can be reused. The principal limitations of TLD's, however, are the same as those of other dosimeters that measure accumulated dose-only the total dose can be determined without knowl- edge of the rate at any time during the exposure period or of the radionuclides contributing to the dose. Thermoluminescent dosimeters have been successfully used to measure the dose to fish in the Windscale area (Min- istry of Agriculture, Fisheries and Food, 1967, 1968) and to aquatic organisms of the Columbia River in the vicinity of the Hanford Works (Watson, personal communication). Tests of TLD's in the tropical marine environment using a 60Co source indicate that 0.7-MeV gamma emitters at con- centrations of approximately 10~3 ^Ci/ml in seawater could be detected after 48-hr exposures (Baltzo and Held, 1968). It should be expected that the results of more such studies, relating concentration to radiation dose in the aquatic en- vironment, will appear in the literature. With the wider application of this technique, the results of experimental studies and field studies, and, it is hoped, of the predictions of effect, will become more meaningful in the future. INFLUENCE OF ENVIRONMENTAL FACTORS ON RADIATION EFFECTS The potential ecological interactions and the assessment of the radiosensitivity of marine ecosystems have been dis- cussed in a previous chapter. The influence of two major en- vironmental factors-temperature and salinity—on radiation effects on marine organisms will be briefly reviewed here. The effect of oxygen on radiosensitivity of organisms has been studied extensively (Bacq and Alexander, 1961) and will not be reviewed here. The literature shows little experi- mental work on the interactions of temperature and salinity with radiation effects, but research into this subject be- comes increasingly important with greater use of nuclear energy to meet man's needs for power and for fresh water from the sea. Nuclear power and desalination plants imply not only some release of radioactive materials to the sea but also release of heat and highly saline water. As the metabolism of poikilotherms is dependent on temperature, it is easy to understand the greater radiosensi- tivity observed following elevation of the temperature dur- ing or after radiation exposure. After exposure to 28,000 R, fecundity of a freshwater snail, Physa acuta, was reduced to 30 percent of that of the control snails in 20°C water and to 12 percent in 30°C water (Ravera, 1966). The hatchability ofArtemia eggs exposed to irradiation by x rays was signifi- cantly reduced in warm water, but when cooler water was used, no significant reduction occurred (Iwasaki, 1964; Cervini and Giavelli, 1965). Goldfish, Carassius auratus, ex- posed to 8,000 R all died within 10 days when maintained at 22°C, but similarly irradiated fish survived for more than 100 days at 4°C (Hyodo, 1965). Gros etal. (1958) postu- lated that low temperatures (7°C) would protect the crucian carp, Carassius carassius, against radiation damage and that radiation, on the other hand, would protect the fish against cold by lowering the thermal tolerance. White et al. (1967) reported on the combined effects of ionizing radiation, salinity, and temperature on the estuarine fish Fundulus heteroclitus. In a factorial experiment, fish were subjected to four levels of acute radiation (500, 1,000, 2,000, and 2,500 rads), three levels of salinity (5, 15, and 250/00), and four levels of temperature (12°, 17°, 22°, and 27°C). They found that different combinations of levels of temperature and salinity yield different LD50 values. The estimated LD50 values for different experimental conditions ranged from 300-350 rads to more than 2,500 rads. The significance of the experiments is the demonstration of the importance of the environmental factors on the radiosensi- tivity of aquatic organisms. In other words, the effects of radiation on aquatic organisms can be evaluated only along with the effects of other major environmental factors. The investigations by Egami and Etoh (1966) and Etoh and Egami (1967) of the effect of temperature on the rate of damage accumulation and recovery in the fish Oryzias latipes showed that the processes of recovery from damage

Radiation Effects 231 induced by external irradiations (x rays or 60Co y rays) are active to some extent at 23°C but remain almost undevel- oped at 11°C. For poikilotherms, it seems likely that low temperature not only delays the development of radiation- induced damage but also decreases the rate of recovery (Egamiera/., 1967). Fish with body burdens of 90Sr and 13II were subjected to thermal shock of 13°C from an acclimation temperature of 25°C. These body burdens did not impair their ability to withstand lethal temperatures. Indeed, there was an indica- tion that their survival time was increased. The approximate beta dose to the bone and thyroid tissues was calculated for the fish containing maximum concentrations of 90Sr and 1311. These were found to be at least 104 rads to bone tissue and 10s rads to thyroid tissues (Ophel and Judd, 1966). Blaylock and Mitchell (1969) determined that temperature was an important factor in the LD50,30 for Gambusia af- finis affinis, since a difference of only 5°C resulted in a sig- nificantly different LD50/30. Few experimental data are available to explain how tem- perature, salinity, and other physicochemical environmental factors interact to affect the radiosensitivity of different aquatic organisms. It is recognized, however, that all orga- nisms in nature have always been subject to different environ- mental stresses, including radiation, in varying degrees. The possibilities for damage to aquatic organisms will most prob- ably arise through the combination and interaction of dif- ferent environmental factors, since survival is rarely depen- dent on a single environmental factor. BEHAVIOR AND METABOLIC STIMULATION Scattered reports describe the use of behavioral criteria to determine the effects of radiation on aquatic organisms. These studies suggest that aquatic organisms apparently de- tect ionizing radiation, although the receptors have not been identified. In experiments with fish, particularly for high levels of external radiation, it has not been established whether the fish are responding directly to a radiation source or indirectly to induced products of water hydrolysis. O'Brien and Fujihara (1963) observed that larvae of the freshwater cichlid fish Aequidensportalegrensis became hy- peractive during x-ray irradiation. Doses of 50 R stimulated activity, and larvae remained active for 90 minutes after ir- radiation. These larvae are not normally free-swimming but remain in clumps on the bottom. O'Brien and Fujihara also observed the influence of a 137Cs source in the water, emit- ting less than 5 rads per hour at a distance of 1 in., on the behavior of 2-day-old cichlid larvae. The control larvae were scattered randomly around a sham source, but the experi- mental larvae avoided a 137Cs source. Pravdina (1965) re- ports that carp avoided x-ray sources providing a dose rate of 2.5 rad/min. Hyperactivity in fish has also been reported by Scarborough and Addison (1962). They observed definite periods of hyperactivity in the golden shiner, Notemigonus crysoleucas, during irradiation at doses of 7,200-18,000-R x rays given for periods of 6-12 min. Tsypin and Kholodov (1964) used y rays from 60Co at a dose rate of 0.1-0.5 rad/ sec for a duration of 5-10 sec as a conditioned stimulus, and they used electric shock as the unconditioned stimulus on fish. Four of thirteen trials resulted in a motor response to the y rays alone. A modification of the locomotor orienta- tion of the turbellarian Dugesia dorotocephala has been re- ported under low-level chronic irradiation in the range 26 juR/hr to 240 juR/hr (Brown, 1962; Brown and Park, 1964). Field et al. (1964) compared the swimming activity of rainbow trout tagged with 16-fiCi 60Co wire tags and with nonradioactive tags. Tests made 16 hours after tag- ging showed a significantly higher swimming activity in 60Co-tagged fish, which persisted for at least 26 hours. Apparent stimulation of growth by radiation in aquatic organisms is reported for periphyton, certain marine inver- tebrates, young blue crabs, and rainbow trout. The growth of periphyton during 5 months in aquaria containing mixed fission products (3 X lO"6 to 6X10-7 Ci/liter) resulted in a greater biomass and greater species diversity than in control aquaria (Timofeyeva-Resovskaya, 1958). Glass plates with 90 Y on the surface at a concentration of 3.3 Ci/cm2, with a calculated surface dose of 40 rads/day, exposed in the sea, enhanced the development of barnacles, bryozoans, calcare- ous worms, and small mussels (Dolgopolskaya et al., 1959). Engel (1967) reports that exposure of young blue crabs, Callinectes sapidus, to 60Co at 3.2 rads/hr resulted in sig- nificantly more rapid growth than that of crabs irradiated at 7.3 and 29.0 rads/hr or of control crabs. Since molting is as- sociated with growth, the percentage increase in width of molted carapaces was monitored; it was found to be related to the radiation dose rate. Crabs receiving 29.0 rads/hr, the highest dose rate, had the smallest percentage of increase in carapace width, and those that received 3.2 rads/hr had the largest increase in width, compared with the control crabs. Metabolic activity of salmon (Salmo salar) eggs and fry was increased by the presence of 137Cs at a concentration of 1 ^Ci/liter. Oxygen consumption increased gradually throughout development and was always higher in the 137Cs-treated eggs than in the controls. Upon hatching of the eggs, the oxygen consumption increased by 50 percent in the controls and 200 percent in the treated aquaria (Neustroev and Podymakhin, 1966b). Although insufficient replicate groups were maintained to provide a rigorous sta- tistical test, rainbow trout fed 0.01, 0.1, and 1.0 juCi 65Zn/g of fish daily for 17 weeks showed more rapid growth than the control group (Nakatani, 1966). Other examples of possible stimulation of organisms by radiation under laboratory conditions can be found; how- ever, little or no knowledge exists about either the mecha- nisms involved or the significance of radiation as a possible stimulus to individuals, populations, or ecosystems.

232 Radioactivity in the Marine Environment 30 20 10 - 0.10 20 40 60 Exposure Dose Rate in Roentgen: Per Hour FIGURE 4 The effects of continuous gamma radiation on the intrinsic rate of natural increase of Daphnia /iu/1".,. (Reprinted with permission from Marshall, 1962.) 30 20 10 . 20 40 60 Exposure Dose Rate in Roentgens Per Houi 80 FIGURE 5 The effects of continuous gamma radiation on the life expectancy at birth, e'0, or average life-span, of Daphnia pulex. (Reprinted with permission from Marshall, 1962.) RADIATION EFFECTS ON POPULATIONS Ultimately, we are concerned with radiation effects on populations and ecosystems in the marine environment rather than with the demise of individuals. Marshall's (1962) work with Daphnia is indicative of a line study that is par- ticularly significant. He investigated the effects of gamma radiation on the intrinsic rate of natural increase, r. The dose rates used ranged from 25 to 75 R/hr, and the cultures were exposed for about 19 hr/day. Reproduction was entirely parthenogenetic. There was a continuous decrease of r as a nonlinear function of the dose rate (Figure 4). The decrease was almost entirely caused by a falling birth rate, which in turn resulted from direct ef- fects of radiation on the ovaries. Average life-span was not greatly shortened, even at the highest dose (Figure 5). Inter- estingly, growth in length of individuals increased with in- creasing dose rate, which was interpreted as due to the uti- lization for growth of energy ordinarily spent in egg pro- duction. Grosch (1962, 1966) followed the reproductive capacity of mass cultures ofArtemia for 8 years. Cultures were re- peatedly contaminated with sublethal amounts of 65Zn or 32 p (~7_30 ^Ci/liter). The following are some of Grosch's conclusions: Although the number of adults seen in mass cultures may be equivalent, subcultures of control and experimental strains react differently to radioisotope additions. Strains de- scended from ancestors exposed to 32P do not necessarily survive a second dose even though total dosage does not ex- ceed the extinction dose given as a single addition. A period of recovery involving generations must intervene. Most no- table is the consistent demonstration that the number of adults can be identical in different mass cultures, but that the reproductive potential of populations with different an- cestral histories differs considerably. On the basis of pair mating tests, maintenance of mass cultures at an observed level of 300 adults per three liters requires only 0.2% of the reproductive potential of controls. Cultures of experi- mental origin utilize 1% or more of their potential to main- tain the same total. Grosch has a detailed discussion in which he compares his conclusions with those derived from Drosophila populations (Wallace, 1956) and Tribolium (Crenshaw, 1965), which showed increased genetic fitness following the irradiation of inbred strains. ENVIRONMENTAL STUDIES Pacific Proving Grounds The first large-scale introduction of man-made radionuclides into a marine environment was at Bikini Atoll in 1946. Two 20-kiloton devices were detonated, the first an air burst and the second an underwater detonation in the 250-mi2 lagoon, which has maximum depth of about 60 m. In succeeding years, through and including 1958, Bikini and Eniwetok be- came the Pacific Proving Ground. During that time, nuclear and thermonuclear devices with a total yield of many mega- tons were detonated at the atolls. Certainly, these atolls rep- resent the most radioactively contaminated marine environ- ment in the world, as far as is known from public announce- ments. And yet today, more than 23 years since the initial contamination of the atolls, a statement by Schultz in a 1947 report on the observed biological effects of the nuclear weapon test "Operation Crossroads" still holds true: Undoubtedly, countless animal individuals have perished at Bikini because of the atomic bomb experiments and still others may perish. But, this destruction of life in a large

Radiation Effects 233 atoll like Bikini amounts to only an extremely small per- centage of the total animal life. The overall picture of life on the reefs has changed little because beneath this surface layer, and from extensive adjoining unaffected areas, indi- viduals have come forth to repopulate and occupy the reefs. The pressure of population from all sides into the damaged areas is very great and soon replaces the losses. Thus, nature begins the repopulation cycle, and, if given sufficient time, the wounded reefs will be cleansed of their contamination, biological equilibrium will be reached; and life will establish itself as in past millenniums—similar to that before man re- leased the greatest destructive force in his history. It is inconceivable that there were no radiation effects at the test sites. Evidently, where the prompt radiation at the moment of detonation was sufficiently intense to produce immediate visible effects, the concomitant effects of blast and heat virtually eliminated the populations. Furthermore, those individuals suffering sufficient injury from the residual radiation to be readily recognized are soon eliminated. In other words, gross radiation injury in marine organisms has not been seen at Bikini and Eniwetok because seriously in- jured individuals do not survive the natural rigors of the en- vironment, and the more subtle injuries are exceedingly difficult to detect. Bikini and Eniwetok were intensively studied before and following the test series (Revelle, 1954; Hines, 1962), in- cluding extensive studies of fish (Schultz et al., 1953,1960; Hiatt and Strassburg, 1960; Welander, 1957; Welander et al., 1967), corals (Wells, 1954), and algae (Taylor, 1950; Dawson, 1957), and yet in none of the reports on marine organisms is there reference to anomalous individuals. However, Gorbman and James (1963) studied the thy- roid histologically and observed thyroid tissue damage in fish collected at Eniwetok Atoll 30 days to 8 months fol- lowing nuclear detonations. Although no radioiodine was detectable in the fish at the time of examination, it seems clear from indirect evidence that the observed anomalies were caused by radioiodine. Blinks (1952) examined physi- ological functions of sessile algae at Bikini a year after the first atomic tests; at that time, the dose rate was estimated to average 20 to 30 mR/day. He concluded that there was "no noticeable alteration of many normal somatic functions." The land plants and animals were subjected to greater in- tensities of radiation both from external sources and from internally deposited radionuclides, but even here, lasting ef- fects of radiation on populations or on the ecosystem are not apparent. Jackson (1967) has reconstructed the story of the sur- vival of rat populations at Eniwetok Atoll. Engebi Islet, with an area of 260 acres, was subjected to radiation in 1948, 1952,1954, 1956, and 1958. The accumulated dose a year after contamination was 44 R (1948), 11,000 R (1952), and 118 R (1954). Prior to the nuclear tests, prob- ably only the Polynesian rat (Rattus exulans) was present at Engebi, but early in the testing period the roof rat (R. rattus) was unintentionally introduced. The former makes a nest under surface vegetation and debris, while the roof rat often burrows. Rats were killed following the detona- tions in 1948, 1952, and 1954, but a sufficient number of individuals survived to re-establish the population. In sum- mary, Jackson states: The Eniwetok story is made difficult by taxonomic confu- sion and lack of specimens. At best, a hypothetical recon- struction can be attempted. Early in the test program at Engebi Islet, the Polynesian rat (Rattus exulans) was exter- minated, probably by heavy surface radiation. Prior to the detonation of a thermonuclear detonation in 1952 [14 megatons detonated approximately 3 mi from Engebi], the roof rat (R. rattus) had become established on Engebi; and a nucleus survived the heavy initial radiation by being deep in burrows. Calculations show that repopulation by 1954 and 1955 was theoretically possible. The decline of the Engebi rat population from its high density in the mid-fifties was a result, probably, of a change in the carrying capacity of the environment. Cole (1951) reported that the insects of Bikini were studied for structural anomalies in 1947 and that none were found. He further stated that "continuing studies ofDroso- phila cultures, taken in the living form at Bikini Island, have not thus far [1947-1951] revealed genetic abnormalities in excess of normal variability." However, more detailed studies following further contamination did reveal probable genetic effects in Drosophila. Stone and his co-workers (Stone etal., 1957; Stone and Wilson, 1958, 1959; Stone et al., 1962) made extensive genetic studies of wild popula- tions of Drosophila subjected to fallout in 1954 at Bikini, Rongelap, and Rongerik Atolls, comparing them with popu- lations of uncontaminated islands. The estimated gamma dose to the Bikini Drosophila population was 3,000-8,000 R, but the absorbed dose is not known. The conclusion was reached that the genetic load of detrimental and lethal fac- tors of the irradiated Drosophila populations had been in- creased but was returning to a normal range. These tests were possible only because of the extensive and sophisti- cated genetic techniques for Drosophila. Similar established techniques are not now available for the marine organisms; hence, we can only speculate that they, too, might have had an increased deleterious genetic load but have recovered or are continuing to recover. Rongelap Atoll was heavily contaminated with radioac- tive fallout in 1954 (Glasstone, 1962; Dunning, 1957). From observations in 1956, Fosberg (1959a and b) de- scribed the condition of plants at islets where the integrated dose was approximately 3,360 R. He suggested that the situation observed might be primarily due to the radiation. Held (1963a), following further studies at Rongelap, sug- gested that other environmental factors might be more im- portant than radiation in this case. The question is not re- solved, nor is it likely to be without controlled experiments with the species involved under varying conditions.

234 Radioactivity in the Marine Environment In a more intensive study, Palumbo (1962) documented the recovery of land plants at a site 2% miles from a multi- megaton detonation at Eniwetok. The vegetation was de- stroyed by heat and blast, and the estimated external dose to the vegetation was 400 R in 200 days. Palumbo noted that regrowth of the vegetation occurred in 6 months and described two minor anomalies. Palumbo discusses many of the factors influencing plant growth in the island environ- ment and reviews the anomalies in plants reported by others at the test site and in other areas of the Central Pacific. He points out that similar anomalies have been observed in areas of heavy fallout and in uncontaminated areas. Again, there can be no doubt that there was damage and even the destruction of individual plants by radiation; but the spe- cific examples of damage or killing caused by radiation or by other factors, or in combination with other factors, can- not be sorted out. The important point is that although in- dividuals may be debilitated or destroyed, the ecosystem recovers. The land-dwelling hermit crab, Coenobita sp., and coco- nut crab, Birgus latro, are subject to higher levels of chronic radiation from internally deposited radionuclides than any other organism studied at the atolls. The levels of 90Sr and 137Cs were found to remain virtually constant at 4,500 pCi of 90Sr per gram of skeleton and 450 pCi of 137Cs per gram of muscle in Coenobita sp. at Eniwetok over a period of two years (Held, 1960). Parallel studies of Birgus sp. at Rongelap Atoll showed that the crabs contained more than 700 pCi 90Sr per gram of skeleton and 100 pCi of 137Cs per gram of muscle over a period of 10 years, 1954-1963. No gross anomalies were noted among these crabs, and no obvious population changes were noted during this fallout period; however, population studies as such were not made. Observations at Bikini Atoll in 1964 (Welander era/., 1967) showed that vegetation nearly covered the islet in a mass that was impenetrable without cutting. The vegetation, exclusive of roots, taken from an area 10 m in diameter in a Scaevola sp. community in 1967 yielded 108 kg/hectare (wet weight), and no gross anomalies were seen on the islet (Held, 1967, unpublished field notes). The abundance and size of fish and of spiny lobsters and coconut crabs at Bikini Atoll appear to be greater than ever, which does not, of course, reflect a beneficial effect of radiation but presum- ably results from the absence of predation by man. Irish Sea Apart from the Pacific Proving Grounds, the Irish Sea coastal area adjacent to the Windscale reprocessing plant of the United Kingdom Atomic Energy Authority probably represents the most important area known with respect to the degree of contamination in the marine environment (Mauchline and Templeton, 1964). Studies of the relationships between radionuclides and man have been of prime importance; some studies, though limited, have considered effects of radiation in the environ- ment. Morgan (1960) reported that effects of radiation had been sought in plaice (Pleuronectes platessd) caught in the region of the Windscale discharge, but none has been estab- lished so far. The area, which had been carefully surveyed before and after discharges began, showed that there were no changes in bottom organisms that could be ascribed to the effects of the discharge. Calculations (Dunster et al., 1964) of the external radi- ation dose rate to benthic organisms that would result if the seabed were at the derived working limit of 0.1 juCi/g total beta activity are about 45 mR/hr, or 1 R/day, mainly of beta radiation. In a series of experiments concerned with the uptake by plaice eggs of six radionuclides, 85Sr, 137Cs, 144Ce, 103Ru, 88Y, and 95Zr/95Nb, data were obtained on the rates of ac- cumulation and concentration factors (Woodhead, 1970). The concentration of these radionuclides in the egg can now be calculated for any concentration of the radionuclides in seawater to which they may be exposed. Tentative conclu- sions have been drawn that the dose rate to the eggs of plaice from the contaminant activity in the spawning areas off St. Bees Head, near Windscale, was 9.1 X 10~2 /md/hr compared with 7.0 X10~1 fuad/hr from the natural 40K in the seawater. Studies have also been made of the radiation dose re- ceived by fish in the Windscale discharge area (Ministry of Agriculture, Fisheries and Food, 1967). The plaice, Pleuro- nectes platessa, is a seabed resident and is known to spend its early life, up to the beginning of its third year, inshore. Calculations were made of the potential dose that a fish could receive on the basis of data from measurements of seawater, seabed, and the fish themselves over the previous 5 years at a point 2 miles south of the outfall and 1 % miles offshore from the pipeline. The radionuclides 137Cs, 106Ru, 95Zr/95Nb, 144Ce, and 90Sr were considered, since these represent the major contributions to dose in terms of the various known factors of concentration in the major seg- ments of the environment. In the calculations, allowance was made for fish movement and type of bottom, and these indicated that an annual dose of 7.3 rads could be accumu- lated, with most of the dose contributed by the seabed (Woodhead, 1968 personal communication). The seawater and internal radionuclides would only contribute about 1 percent of the total expected dose (Table 6). The annual dose might increase to 40-50 rads if the fish spent the whole year close to the pipeline outlet on a silty bottom. This calculation suggested that the use of thermolumi- nescent dosimetry was warranted, and 2,500 marked plaice were released in the vicinity of the outfall in 1967 (Ministry

Radiation Effects 235 TABLE 6 Estimates of Dose Rates to Plaice from Fission Products at Windscale" Source Type of Radiation mR/week Sea water Seabed Radionuclides in muscle 7 0 0.01 0.01 48.8 91.4 0.013 0.057 140.3* "Data from Woodhead (1968, personal communication). 6Or 7.3 R/year. of Agriculture, Fisheries and Food, 1968). Each fish carried two lithium fluoride dosimeters, incorporated in a Petersen fish tag, one to measure the accumulated dose on the upper surface and one to measure the dose on the under surface. In the first few months, over 243 marked fish were recov- ered, and preliminary data indicated an integrated exposure of 4.5 R for the bottom dosimeter. This was equivalent to a dose of 10 R per year. The ratio of top to bottom dose was 0.73. The differential response of dosimeters placed on the top and the underside of the fish indicated the expected re- sponse to beta radiation. The agreement between calculated and measured dose is extremely good. Gamma dose rates measured 1 m above the Ravenglass mud flats, near Windscale, from January 1965 to June 1967, averaged about 140/uR/hr, compared with 10-15 piR/hr background. Over sandy beaches, dose rates ranged from 11-16/uR/hr, compared with a background rate of 8-12 nR/hr. The mean dose rate over mud, from 106Ru/106Rh, 144Ce/144pr, and 95Zr/95Nb, has been calculated as about 1 mR/hr, or 8 R/yr (Jeffries, 1968). Thermoluminescent dosimetry measurements in 1965, using LiF powder in sachets implanted in the mud at a point where 106Ru/106Rh + 144Ce/144Pr levels were about half those reported by Jeffries, gave values of 100 mR/wk in the top 1 in. of mud, 50 mR/wk at a depth of 3 in., and <20 mR/wk at depths to 17 in. Organisms in the top 3 in. might then be exposed to a radiation dose of 4.0 R/yr, comparable to that received by fish near the outlet (Templeton, 1968, personal communication). Oak Ridge Very few studies have been made of natural populations ex- posed to chronic radiation higher than background. The salivary chromosomes of the larvae ofChironomus tentam, which inhabit the contaminated bottom sediments of White Oak Creek and White Oak Lake at Oak Ridge National Lab- oratory, were analyzed for 5 years for chromosomal aber- rations (Blaylock, 1966). Calculations and measurements of the adsorbed dose for the larvae living in the sediments gave values of 230-240 R/yr, or 1,000 times background for that area. More than 130 generations had been exposed to this or greater dose rates over the previous 22 years. The conclusion was that the ionizing radiation from the contaminated en- vironment was increasing the frequency of new chromo- somal aberrations in the irradiated population, but that the new aberrations were eliminated by natural selection. Also, the present level of chronic irradiation has not affected the frequency of the endemic inversions. Blaylock (1969) also studied the fecundity of a natural population of fish, Gambusia affinis affinis, that had been exposed to chronic irradiation in White Oak Creek for many generations, compared with a control population. The calcu- lated dose rate from the bottom sediments was 10.9 rads/ day. A significantly larger brood size occurred in the irradi- ated than in the nonirradiated population, although signifi- cantly more dead embryos and abnormalities were observed in the irradiated broods. These results suggest that an in- creased fecundity is a means by which a natural population having a relatively short life cycle and producing a large number of progeny can adjust rapidly to an increased en- vironmental stress caused by radiation. We return then to a concept that has recurred in this report: Man, as an individual, is the critical biological target in predicting the consequences of introducing radioactive materials into marine environments. If the radionuclides are present in concentrations acceptable for man, the individual, then it is difficult to conceive that there will be more than subtle effects on ecosystems-perturbations that would probably be indistinguishable from those due to causes other than radiation. On the other hand, it is not only con- ceivable, but probable, that with increasing uses of atomic energy, accidents will occur that will result in damaging con- centrations of radionuclides. In preparation for these con- tingencies, there is a pressing need to increase the sensitivity of methods for studying the response to radiation of popu- lations and ecosystems in the marine environment. EFFECTS ON RESOURCES The extrapolation of the results of laboratory experiments into the practical terms of their effects on marine resources must be made with care since, without evaluation of the natural variations related to changes in fecundity, mortality, and recruitment, quite erroneous conclusions can be reached. Polikarpov (1966) suggests "inhibition and degen- eration of a number of food fishes and other radio-sensitive organisms" and "rapid development and multiplication of

236 Radioactivity in the Marine Environment bacteria, microphytes and radio-resistant forms of inverte- brates" as a result of radiation modification of the marine environment. Zaytsev and Polikarpov (1964) and Polikarpov (1966), based on their previously discussed laboratory data, have calculated the time needed to halve the stocks of various species of Black Sea fishes in relation to the proportion of the eggs damaged by radiation. These workers conclude that there is reason to assume that the fisheries will be adversely affected, and may, in many instances, cease to function if fish stocks are reduced to one half or less. They consider that from the commercial standpoint, radiation damage must not affect more than 10 percent of the eggs, though even at this level, catches will be perceptibly reduced. Garrod (1966) points out the fallacy of this argument. For marine mammals or for certain fish species with low fecundity, a 50 percent mortality of the young or of the eggs will be reflected as a 50 percent reduction in recruits to the stocks, though this does not generally occur in the marine environment. In the general case of organisms with high fecundity, reduction in the spawning stock does not necessarily result in a decrease in the number of recruits. The capacity of the environment to support young fish is limited, and this capacity can be satisfied by the eggs from a small number of adults, the superfluous eggs and larvae being reduced by density-dependent mortality. The magnitude of the mortality is also pertinent in the evaluation of the effects of radiation on marine resources. Garrod indicates that for stocks of arctic cod with high fe- cundity, survival is 1 in 104 and can be as low as 1 in 105. The addition of 50 percent mortality in the egg stage due to the effects of radioactive contamination of the environment would not noticeably alter the existing mortality rate of 99.99 percent. This would also be true of all highly fecund species. While it may be true that the fecundity of both the indi- vidual and the population could be reduced by radiation ef- fects, it is extremely doubtful that these would influence stock size beyond the normal range related to environmental changes, except in very heavily exploited stocks. It is cer- tain, however, that with the techniques of assessment now available, it would not be possible to obtain an unbiased measure of the effect attributable to radiation alone. RESEARCH NEEDS • Further studies are required concerning the concen- trations of naturally occurring radionuclides and natural background radiation doses in the environment as a baseline for studies of the effects of radiation. • Time curves for acute exposures of lethal doses should be extended, with particular attention to exposure as a function of age. • Because of the conflicting nature of the present ex- perimental data on the effects of low-level chronic irradi- ation on developing embryos, more studies should be estab- lished under rigorous, controlled experimental conditions. The effects of other environmental "stress" factors, such as salinity, temperature, oxygen, and pollutants, must be studied and expanded to include the interaction of these factors with radiation effects. • More sensitive parameters of radiation effects on indi- viduals, populations, and communities should be developed. Long-term studies, in which factors such as rates of growth, morphological abnormalities, onset of maturity, and repro- ductive capacity are considered, for example, should be em- phasized. Chromosomal studies under experimental and field conditions should be extended, and the somatic and genetic consequences of such changes on populations and ecosystems should be evaluated. • Measurements of absorbed dose using microdosimeters should become standard practice in experimental work. In areas subject to radioactive contamination, studies should be initiated to determine the radiation regime in the environ- ment. The data obtained should be closely correlated with measurements of concentration of radionuclides in order that the historical radiation regime can be determined. SUMMARY Radiation is not a recent introduction to the marine environ- ment, since low levels from environmental and cosmic sources have been present throughout geological time. Lethal amounts of acute radiation differ widely among ma- rine organisms and are related to variations such as species, age, physiological status, and body size. These variations are further complicated by the interaction of environmental fac- tors such as temperature and salinity. Exclusive of the eggs of fish and larvae of invertebrates and fish, most marine or- ganisms for which data exist are relatively radioresistant. Limited studies on the effects of chronic exposure have been conducted. These have been limited to selected devel- opmental stages and indicate that, with the possible excep- tion of some Russian data, the dose necessary to evoke an unequivocally detectable biological response is considerably above that of concentrations of radionuclides in the environ- ment as a result of controlled waste disposal operations. Studies on the genetic consequences of radiation expo- sure to population indicate that, despite larger numbers of mutations, increased utilization of reproductive capacity maintains a population at preradiation density. Field studies on the effects of radiation indicate that our best technologies and methods cannot demonstrate effects on marine ecosystems, at prevailing dose rates, that are clearly and uniquely attributable to ionizing radiation.

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Chesapeake Sci. 7:36-39. White, J. C., Jr., J. W. Angelovic, D. W. Engel, and E. M. Davis. 1967. Interactions of radiation, salinity, and temperature on estuarine organisms, p. 29-35. In Annual report of the Bureau of Com- mercial Fisheries Radiological Laboratory. Circ. 270. Beaufort, N.C. Woodhead, D. S. 1970. The assessment of the radiation dose to developing fish embryos due to the accumulation of radioactivity by the egg. Radiat. Res. 43:582-597. Zaytsev, Yu. P., and G.G. Polikarpov. 1964. Problems of the radio- ecology of the hyponeuston. Okeanologiya 4(3):423-430. Also Translation of Okeanologiya, Joint Publications Research Service 25(966): 28-41. GENERAL BIBLIOGRAPHY Angelovic, J. W., and D. W. Engel. 1968. Interaction of gamma irradiation and salinity on respiration of brine shrimp (Artemia salina) nauplii. Radiat. Res. 35:102-108. Angelovic, J. W., J. C. White, Jr., and E. M. Davis. 1969. Interaction of ionizing radiation, salinity and temperature on the estuarine fish, Fundulus heteroclitus, Part III, p. 131-141. In D. J. Nelson and F. C. Evans [ed.] Symposium on radioecology. CONF- 670503 (TID^500). USAEC, Oak Ridge, Tenn. Bennett, B. G., and H. L. Beck. 1969. External radiation on Bikini Atoll. Nature (London) 223:925-928. Blaylock, B. G., and P. G. Koehler. 1969. Terminal chromosome rearrangements in Chironomus riparius. Amer. Natur. 103(933): 547-551. Engel, D. W. 1969. The comparative radiation sensitivities of some estuarine decapod Crustacea, p. 202-209. In Annual report to USAEC of the Bureau of Commercial Fisheries Radiobiological Laboratory. Beaufort, N.C. Hoppenheit, M. 1969. Strahlenbiologische Untersuchungen an Gammeriden (Crustacea, Amphipoda). Helgolander Wiss. Meerensunters. 19:163-204. Riel, G. K. 1962. Operation Swordfish Project DUNC(U). U. S. Nav. Ord. Lab. Tech. Rep. 62-151. 40 p. Yermolayeva-Makovskaya, A. P., L. A. Pertsov, and D. K. Popov. 1969. Polonium-210 in the human body and in the environment. Contribution from the Academy of Sciences, USSR, to the UN Scientific Committee on the effects of atomic radiation. A/AC. 82/G/L.1260. [Transl. USAEC HASL, USSR reps, on natural and fallout radioactivity.]

Chapter Ten EVALUATION OF HUMAN RADIATION EXPOSURE R. F. Foster, I. L. Ophel, A. Preston The presence of artificial radioactive materials in the marine environment must be considered in relation to radiation ex- posure of people who use the sea and its products. Some exposure is inevitable and, indeed, has always existed from naturally occurring radionuclides. To this natural back- ground exposure must now be added some additional radia- tion dose as a consequence of man's entry into the age of atomic energy. The magnitude of exposure that is likely to result from artificially produced radionuclides depends upon many complex relationships. These relationships involve how, where, what kinds, and in what amounts radioactive mate- rials are introduced into the seas, and the ways and extent to which the seas and their resources are used by man. It is the purpose of this chapter to identify the relationships that are now recognized as important in assessing human radiation exposure, to discuss ways in which the presence of radioactive materials can be translated into estimates of radiation dose to people, to provide perspectives on the magnitude of exposure from marine sources in relation to acceptable dose limits, and to summarize the status of radio- active contamination in the seas after the first quarter cen- tury of use of atomic energy. USE OF THE SEA IN RELATION TO RADIATION EXPOSURE Influx of Radioactive Materials The seas have been the intended or casual recipient of sig- nificant quantities of artificial radionuclides since 1945, when the fissioning of 235U and 239Pu was first undertaken on a massive scale. The earliest additions consisted mostly of short-lived neutron activation products present in the cooling water of the plutonium-producing reactors at the Hanford Works in the State of Washington. This radioactive material reached the North Pacific Ocean via the Columbia River. Only a few months after the startup of the reactors, atomic weapons were detonated in the atmosphere, and the oceans of the world began to receive the fallout of fission products and other debris. In the following year, atomic devices were exploded underwater at Bikini Atoll. In a general sense, the ways in which radioactive mate- rials were added to the marine environment in the first year and a half of the atomic age characterize the types of addi- tions with which we are still concerned: 240

Evaluation of Human Radiation Exposure 241 Chronic discharges of low-level wastes from operating reactors and fuel processing plants. Such discharges are planned and monitored and can be controlled at the source. They result in a gradual buildup of longer-lived isotopes to some equilibrium level, and the area of greatest concern is ordinarily in the region close to the discharge point. Worldwide fallout from detonations that inject debris into the atmosphere. In this case, the source is widespread, fluctuates greatly in intensity at different times, is not under control, and results in low-level, but worldwide, con- tamination in the oceans. Acute releases from single incidents at or below the sea or ground surface. Such releases may result in high levels of contamination in local regions-contamination that de- creases with time but spreads in area. In the early years, acute releases occurred from weapons tests. In future years, they may result from accidents at shore installations, to ships, or to isotopic power sources. Several large-scale engi- neering projects that have been proposed under the Plow- share Program of the U.S. Atomic Energy Commission (AEC) could also cause acute releases. These differ from the accident cases in that the place, time, and nature of the incident is under control. The magnitude of the release is likely to be substantially greater than in most accidents, however. Additions of radioactive materials to the sea that are more characteristic of contemporary uses of atomic energy also include The disposal of low-level packaged waste and intermittent releases from nuclear-powered ships. Such disposal repre- sents an intermediate case between the chronic discharge of liquid wastes from fixed installations and the acute releases TABLE 1 Consumption of Fish and Shellfish Direct Consumption (g per capita per day) Country or Area Area Average Specific Locality Surveys Oceania (Cook Is.) 260" Southern Nigeria 244a - Norway 105" - Portugal 1006 - Japan 606 - United Kingdom 306 807c Finland 30* 308d United States IS6 390« India 56 18f/ "Rao (1962). 6Food and Agriculture Organization of the United Nations (1960). cPreston (1966). dJokelainen (1967). ^Hanson et al. (1967). hat era/. (1967). from single incidents. Repetitive disposal into designated dump areas requires administration comparable with that for chronic discharge. The use of sealed radioisotope power sources for such purposes as navigational lights and space satellites, which in- creases the potential inventory of radioisotopes in the ma- rine environment; however, these radioisotopes are not bio- logically available except after accidents. Radiation exposure of man as a result of the introduction of artificial radioactive contaminants into the marine envi- ronment may occur by one or more of several pathways, and only careful evaluation can determine the most impor- tant or critical pathways in particular situations. The fol- lowing pathways are the ones that normally merit consid- eration, however. Pathways of Exposure FOODSTUFFS The consumption of contaminated marine foodstuffs, including fish, seaweeds, and manufactured products, is ordinarily the exposure pathway of greatest importance. This is particularly true of the heavily populated northern hemisphere, where sea fisheries produce over 70 percent of the world's sea harvest. Closely related is the use of the sea as a source of fresh water, a use that is expected to increase with the application of nuclear desalination. Desalination processes tend to exclude radioactive materials from the finished water. On the other hand, waste water from nuclear desalination plants will contribute to the burden of radio- active contaminants in the marine environment. The levels of contamination in the edible portions of marine plants and animals may be many times higher than that in the seawater because of biological reconcentration processes. The levels that are acceptable for any specific situation depend upon the rates of consumption of locally derived marine foods, and these rates vary widely. Statistics for countries as a whole are usually of little relevance with respect to specific regions, and only surveys of local con- sumption habits can provide the data required to determine permissible concentrations in particular dietary items. The data in Table 1 illustrate the wide range of consumption rates. The rate for a specific locality within a country may be 30 times that of the national average, and the national average for some countries is 50 times that of others. SAND AND SEDIMENTS Some radioactive debris enters the sea as particulates, and some radionuclides in solution are easily adsorbed to the

242 RadIoactivity in the Marine Environment surface of particles. The result is radioactive contamination of sand and sediments. If the contamination results princi- pally from surface adsorption, then finely divided sediments, which present the greater surface area per unit weight, will exhibit the highest degrees of contamination. This mode of radiation exposure is most apt to be of significance in silted estuaries or coastal water areas with soft bottoms. Opera- tional experience in the United Kingdom (Mitchell, 1967b; Jefferies, 1968) has shown that open sandy beaches in the vicinity of effluent discharge points are not likely to be a problem, but silty estuaries up to distances of several miles from a discharge point may be of concern (Jefferies, 1968). Radioactive particulates discharged to estuaries and coastal waters, especially gamma-emitting radionuclides, may lead to quite significant exposure rates (Preston and Button, 1967; Dutton and Steele, 1966). The use of coastal waters as recreational areas has in- creased very greatly in the last decade among the affluent nations of the world. Since these nations are also the likely contributors to radioactive contamination of the same areas, the radiological implications of this use should be consid- ered. However, discharge restrictions based on the contami- nation of marine foodstuffs will, in general, also limit expo- sure from swimming and from the beaches to negligible proportions. FISHING GEAR Fishing gear-more particularly, commercial fishing gear- may become contaminated directly by adsorption of radio- active materials from the water or indirectly from radioac- tive particulates if the gear is operated on the seabed or in very silty waters. This is more likely to be of concern with static fishing gears, such as the salmon bag-nets used on the Caithness coastline in Scotland near the discharges from the Dounreay Experimental Reactor Establishment (Mitchell, 1967b; Morgan, 1967). Experience at the U.K. Atomic Energy Authority's Windscale Works has shown that trawl gear operated in the outfall area, even over soft bottoms containing up to 104 pCi of fission product radionuclides per gram of dry sediment, does not become substantially contaminated. OTHER PATHWAYS OF EXPOSURE Other pathways that may lead to very minor degrees of human radiation exposure include Seaspray driven onto land or beaches-particularly spume, which scavenges fine particulates as it travels over the water surface, leaving patches of finely divided material of in- creased radionuclide content after stranding and collapsing (United Kingdom Atomic Energy Authority, 1965). Seaweed, trash fish, and spoiled fish used as fertilizer or animal feed. Periodic inundation of pastureland with seawater that contains radioactive contaminants from nearby nuclear plants. The dredging of harbors and the maintenance of buoys in areas where radioactive wastes have been discharged. The sea as a mineral resource is already receiving consid- erable attention, particularly in continental shelf areas, with respect to the extraction of salts and drilling for oil and natural gas. The technology for the economical recovery of manganese and other valuable minerals from the bed of the deep sea may also be developed soon. Such mining of the sea might require prior consideration of possible radioactive contamination if the mineral resources are in areas where radioactive materials have been discharged. Future undersea exploitation involving underwater resi- dence by man may require advance consideration of the proximity to radioactive waste disposal areas; at present, however, radioactive contamination of the water or seabed hardly seems a credible restriction on such uses. ACCEPTABLE DOSE The Concept Exposure of man to ionizing radiation entails a risk of dele- terious biological effects, and if man wishes to benefit from the use of atomic energy, some risk will be involved. Radi- ation doses must therefore be limited to a level at which the risks involved are acceptable to the individual and to society as a whole; such doses may be termed "acceptable doses." Recommendations with respect to acceptable doses are made from time to time by the International Commission on Radiological Protection (ICRP) on the basis of the con- servative assumption that "down to the lowest levels of dose, the risk of inducing disease or disability increases with the dose accumulated by the individual," (International Commission on Radiological Protection, 1959) and that this increased risk of developing biological effects has a linear re- lation to dose. This concept assumes that there is no thresh- old dose below which no deleterious effect is produced. In light of these concepts and many years of practical experi- ence with radiations of various kinds, both with man and with experimental animals, acceptable doses are set so that there is a very low probability of biological effect. These limits, which are for continuous exposure, are not to be re- garded as absolute upper limits, but rather as guides. It will normally be quite practicable to keep the actual levels of ir- radiation very much lower, and the Commission states that every effort should be made to do so, compatible with eco-

Evaluation of Human Radiation Exposure 243 nomic and social considerations. Undue importance should not, however, be attached to occasional exposures that exceed the limits. The Commission's "permissible limits" (ICRP, 1966b) distinguish between occupationally exposed persons, mem- bers of the general public, and populations, and in the con- text of radioactive contamination of the marine environ- ment, it is the recommendations in relation to individual members of the public and of populations that will, of course, apply. These recommendations are intended to re- strict the risk to the individual of developing deleterious somatic effects. The limits for members of the public cor- respond to one tenth of the recommended maximum per- missible dose rates for occupationally exposed persons. The lower limit on dose for the public is deemed desirable in order to protect children and, among other things, in recog- nition of the absence of some controls that apply to radi- ation workers, such as employee selection, supervision, and monitoring. The limitations imposed on exposure of popu- lations are based on considerations of heredity (genetic ef- fects) and will be determined by the magnitude of the dose to individuals as well as by the number of persons exposed. No specific recommendations are made for a maximum so- matically significant population dose, but the limits for indi- viduals ensure that the frequency of somatic injury in a population will remain at a very low level. General Application For both individuals and populations, the exposures under consideration here are those that are above natural back- ground and in addition to exposures received by a patient during medical treatment. Exposure may result from either internal or external sources, and the recommended dose limits, given in Table 2, are intended to include radiation from both sources. For radioactive materials deposited in the body, dose rates are related to a permissible body (or organ) burden for specific radionuclides, and these in turn are related to a per- missible continuous daily intake sufficient to establish and maintain that body burden. The ICRP has expressed these permissible daily intakes in terms of maximum permissible concentrations in air and in drinking water (ICRP, 1959). In the case of long half-life radionuclides with slow turnover rates, the permissible body burdens and the resulting dose rates may not be achieved for tens of years. Consequently, early exposure history related to these intakes, or any body burdens derived from them, will result in only a small frac- tion of the acceptable dose. The establishment of such a model for exposure from internally deposited nuclides and the derivation of the as- TABLE 2 Recommended Dose Limits Part of Body ICRP Dose Limit" For individuals Gonads, red bone marrow, whole body (uniformly irradiated) Skin, bone Thyroid Hands, forearms, feet, ankles Other single organs (including the gastrointestinal tract) For populations Whole body 0.5 rem/yr 3.0 rem/yr 3.0 rem/yr (1.5 rem/yr children under 16) 7.5 rem/yr 1.5 rem/yr 5. 0rem/ person for 30 yr "Acceptable dose limits for members of the public recommended by the International Commission on Radiological Protection (1959). Similar limitations are recommended by the Federal Radiation Council (1960, 1961). sociated control criteria imply assumptions about the aver- age anatomy, physiology, and behavior of man. To this end, the ICRP has defined a "standard man," representing a typi- cal occupationally exposed adult. Individual variations re- lated to size, sex, age, physical condition, eating habits, and so on are not taken into account in defining maximum per- missible body burden and associated parameters. The general application of acceptable doses is intended for planning purposes and is normal for situations resulting from controlled operations. If the source of exposure is un- controlled, as it might be following a reactor accident or a nuclear explosion, abnormal exposures may arise that call for remedial action. It is unwise to stipulate action levels at which remedial measures should automatically be invoked, since the measures themselves may involve a degree of risk. However, the ICRP regards such measures as mandatory if whole-body exposures of 100 rads are likely to result from an uncontrolled situation. Some guidance concerning suit- able emergency exposures may be obtained from recommen- dations of the United Kingdom Medical Research Council (1960) and the Federal Radiation Council (FRC) of the United States (1964, 1965). Both reports suggest upper limits on the contamination levels that would result in an- nual doses to the critical organs broadly equivalent to the annual exposure permitted radiation workers. Such expo- sures are considered acceptable if they are experienced by the same population only once or twice, with some years between exposures, and if the size of this population is small compared with the total population of the country or area concerned.

244 Radioactivity in the Marine Environment Application to Radioactive Contamination of the Marine Environment The Brynielssen committee of the International Atomic Energy Agency (IAEA) (1961), convened in 1958 to con- sider the problems of radioactive waste disposal into the sea, endorsed the ICRP recommendations and gave as its collec- tive opinion that radiation exposure resulting from disposals would probably be limited to small fractions of the popula- tion. It follows, therefore, that genetic exposure should not be significant and that the critical control should be based on exposure of individuals. Thus, limitations of radiation ex- posure from artificial radionuclides in the marine environ- ment may be based on the recommended ICRP dose limits for individual members of the public. The use of somatic rather than genetic criteria has been adopted by, among others, the Federal Radiation Council (1961) and the United Kingdom Minister of Housing and Local Govern- ment, Minister of Welsh Affairs, and Secretary of State for Scotland (1960). In applying these dose limits through the derived criteria, such as maximum permissible concentrations in drinking water, it must always be remembered that the actual doses received by individuals will vary, depending on variation in parameters such as age, size, and sex. Such variations can, to a large extent, be allowed for by careful selection of "critical groups" that are reasonably homogeneous with respect to age, diet, and other factors affecting dose (ICRP, 1966a), and the Commission states that "it will be reasonable to ap- ply the appropriate Dose Limit to the mean dose of this group." Some individuals may therefore receive doses higher than the dose limit, but since at the levels of risk implied such infringements will be minor in character, this approach is, in general, satisfactory. Where a critical group cannot be defined, a safety factor should be applied to the derived concentration limits. It is recognized that the value of such a factor will vary according to particular circumstances, but in the United Kingdom, for example, a safety factor of 10 is applied to preoperational assessments of waste disposal to the marine environment, and, if after some years of operation it is still not possible to accurately define a critical group, the dose limitations are applied to the habits of the most exceptional individual found through a survey of local habits. This approach has been endorsed in principle by the authorities in the United Kingdom (United Kingdom, Minister of Housing and Local Government, Minister for Welsh Affairs, and Secretary of State for Scotland, 1960), who recognize that surveys in- clude but a sample of the entire population, and conse- quently that there may exist some person with such excep- tional habits that his exposure is greater than the dose limit. Again, at the levels of risk involved, this is considered to be a satisfactory approach. The final stages in applying acceptable dose limits depend upon the results of surveys of local habits that have as their objective the identification of those individuals who will be subjected to the greatest radiation exposure. This unusually high exposure may result from their activities in the local environment or, in some cases, in an environment some dis- tance from the contaminated area. Their behavior needs to be assessed in quantitative terms-for example, in grams of marine foodstuff consumed per day or in hours per year spent on a beach or in working contaminated fishing gear. Such terms are needed to convert the ICRP maximum per- missible daily intakes, or dose rates, into derived working limits for the environment in question. After some operational experience has been gained for a particular situation, it should be possible to confirm the validity of the critical pathways predicted by the above pro- cedure and to identify the radionuclides contributing the most significant fraction of the dose limit. Field measure- ments should also permit confirmation of the critical organ or organs involved in the irradiation. When this stage has been reached, it should be practicable to pursue more de- tailed inquiries directed toward isolating the critical group of individuals. Finally, isolation of this group will permit the determination of average behavior patterns in the group and, if necessary, suitable adjustment of the provisional derived working limits. In some situations, levels of contamination are so low that they are virtually indistinguishable from natural back- ground. If calculation of absolute upper limits of exposure shows that it is far below the exposure considered as accept- able, then detailed studies need not be undertaken. In such cases, it may be possible to dispense with the routine envi- ronmental monitoring operations normally established for the areas of significant contamination. METHODS OF EVALUATION In order to put a particular level of radioactive contamina- tion in the marine environment in proper perspective, esti- mates must be made of the radiation dose to man that may result. It is now rather standard practice to make such esti- mates prior to the planned introduction of radioactive ma- terials into the sea, not only to determine whether the proposed operation is in fact feasible (safe), but also to establish preliminary guides concerning the maximum amount of such materials that might be introduced at se- lected sites over appropriate intervals of time. In making such predictions, careful consideration must be given to the exposure pathways that are most likely to result in the highest doses and to the particular individuals who will re- ceive these doses. Early identification of the critical path-

Evaluation of Human Radiation Exposure 245 ways and critical population groups is also an important prerequisite to the design of an efficient and effective en- vironmental surveillance program. Following the actual introduction of potentially signifi- cant quantities of radioactive materials into the marine en- vironment, a re-evaluation of the probable dose to man can and should be made. As pointed out in the preceding sec- tion, the evaluation made after an installation has been in operation for some months is of value not only in providing a refined estimate of the actual doses received by critical populations in relation to acceptable dose limits but also in confirming the validity of the assumptions used in making the preoperational estimates. Several cases are now available where comparisons of preoperational predictions can be made with "postoperational" experience measured after startup. These will be discussed in the section on disposal of radioactive wastes (p. 253). Usually, the preoperational predictions are shown to have been highly pessimistic and to have resulted in tentative discharge guides that were more restrictive than necessary to maintain the radiation dose to people within the prescribed limits. This was the intent, of course, and is most desirable. Nevertheless, it must be borne in mind that when postoperational assessments are made, the basic limit is the acceptable dose to man and not the tentative permissible discharge rate or permissible concen- tration in seawater calculated as a part of the preoperational evaluation. Another incentive for updating guides derived during preoperational evaluations is that a particular expo- sure pathway predicted at the outset to be critical may ulti- mately be shown to be of less importance than some other pathway. Evaluations made both before and after the planned dis- charge of radioactive materials should serve not only to pro- vide a technical basis for prudent control of the releases but also to inform both the lay and the scientific communities of the degree of risk associated with planned and actual dis- charges. Much of the public's wariness of radioactive con- tamination of the environment is justified because the true risks to man have not been published in either a timely or an easily understood manner. Dose Prediction Predictions of the radiation dose that may be received by people as a result of radioactive contamination of the ma- rine environment ordinarily begin with a comprehensive re- view of the uses that man makes of the sea in the region of interest and with the selection of a few postulated pathways by which internal and external exposures of greatest magni- tude appear most likely to occur. Comprehensive evaluation requires that the separate contributions from all pathways of significance be added together so that the combined dose can be compared with the 1CRP or FRC recommendations. This consolidation of dose contributions should include arti- ficial radioactive contaminants of the terrestrial and fresh- water environments as well as contaminants of the marine environment. In practice, it has been found that one, or a very few, pathways are so dominant that the multitude of alternate routes that can be conceived contribute only relatively in- significant doses. The pathways requiring detailed evalua- tions invariably include the possible contamination of edible products harvested from the sea in the region of interest and, where appropriate, may include the potential external exposure from beaches, fishing gear, and other pathways. Fundamentally, the mechanics of predicting the dose that may be received by people has four parts: Estimating the concentrations of the contaminants that will exist in the seawater at places and times of interest. Estimating the relationships that will exist between the concentrations in the water and in seafoods, sediments, beaches, fishing gear, and other materials that are used directly by man. Estimating the rates of consumption of particular sea- foods by critical population groups and the extent (time and distance) of exposure to materials that can deliver an exter- nal dose. Converting the estimated intakes of radionuclides and the intensity of the deposited contaminants into estimates of in- ternal and external dose (rem), consolidating these estimates with doses received from other environmental sources, and comparing them with recommended limits. In the last decade, the Committee on Oceanography of the National Research Council has had several opportunities to consider and develop in detail procedures for predicting acceptable rates of discharge of radioactive materials into the sea (National Academy of Sciences-National Research Council, 1959a, 1959b, 1962). The International Atomic Energy Agency (1961) has likewise published definitive guidance for this practice, and several nuclear installations have used these basic procedures to establish tentative limits for discharges to the sea or to provide evidence that antici- pated releases will be well below the levels that would result in dose rates of concern. The first evaluation made by the Committee on Oceanog- raphy was in response to a request by the U.S. Atomic Energy Commission that questions concerning the disposal of packaged low-level waste into coastal waters of the At- lantic Ocean and the Gulf of Mexico be examined. The rec- ommendations of the working group assigned to this study were published in 1959 (National Academy of Sciences- National Research Council, 1959a). This working group