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CHAPTER 9 ACCUMULATION AND RETENTION OF RADIOACTIVITY FROM FISSION PRODUCTS AND OTHER RADIOMATERIALS BY FRESH-WATER ORGANISMS1 Louis A. KRUMHOLZ, Department of Biology, University of Louisville, Louisville, Kentucky and RICHARD F. FOSTER, Biology Operation, Hanford Laboratories, General Electric Company, Richland, Washington Introduction RELATIVELY little is known about the mech- anisms of uptake, concentration, retention, and excretion of fission products and other radio- materials by fresh-water organisms. These or- ganisms include many biological forms such as the vascular plants, algae and phytoplankton, protozoans, zooplankton and other invertebrate forms, and representatives of each of the five vertebrate classes. The complex interrelationships of the fresh- water biota, together with their diverse indi- vidual anatomies, physiological processes, and life histories indicate the enormous scope of the problem of determining the role of radioma- terials in the metabolic processes of such a community. In addition, there is extreme ur- gency for obtaining information on many as- pects of this problem within a relatively short period of time. Within the next 10 years sev- eral power-producing reactors will undoubtedly be in operation; many placed, in all probability, near the large industrial and/or population centers of the United States where the only ready means of disposal of large quantities of liquid effluent will be into fresh waters. Any near-by rivers and lakes may be subject to rather severe contamination by radioactive ma- terials in the event of accidents. Owing to the complex interactions of the factors involved, any estimates of the levels of radioactive contamination that may occur in a particular situation may be in error by as much as one or two orders of magnitude. For purposes of hazard control, estimates must therefore be 1 Contribution No. 10 (New Series) from the De- partment of Biology, University of Louisville. based on pessimistic assumptions with the hope that field sampling and experimentation will reveal a more desirable situation. An estimate of the worst situation can be ob- tained by comparing the concentration of a par- ticular element in the water with its concentra- tion in an organism or tissue under study. Since the radioisotope of the element will behave in much the same manner as its stable counterpart (for purposes of this paper), there will be no greater concentration of the radioisotope than of the stable form. Sources of information At the present time there are three primary sources of information available regarding the uptake, concentration, retention, and excretion of radiomaterials by fresh-water organisms. They are: 1. The long-term program of the Biology Labo- ratories of the General Electric Company at Richland, Washington. This program has been primarily concerned with the accumulation of radioactive materials in the flora and fauna of the Columbia River. The effluent water released to the Columbia from the plutonium-producing reactors at the Hanford Operation contains ra- dioelements induced when the "impurities" in the cooling water pass through the high neutron flux. The Hanford program was designed as a radiological-ecological study with four main ob- jectives: (1) to determine the geographical dis- tribution of the radioactive materials, (2) to find out how the radioisotopes became dis- tributed in the various kinds of aquatic organ- isms from the phytoplankton on through the fishes and, to some extent, to the land animals 88

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Chapter 9 89 Uptake by Fresh-water Organisms which feed on fresh-water organisms, (3) to study the seasonal distribution of the radioac- tive materials throughout the biota, and (4) to determine whether the aquatic forms were ad- versely affected. 2. A three-year study at the Oak Ridge Na- tional Laboratory, Oak Ridge, Tennessee. That work was performed by the Fish and Game Branch, Division of Forestry Relations, Ten- nessee Valley Authority, under contract to the Atomic Energy Commission and consisted pri- marily in an ecological survey of White Oak Creek and its drainage area. In that study, principal emphasis was placed on the effects on the biota and its environment from radioma- terials that consisted of both fission products and wastes with induced radioactivity from the processing of different materials in the prepara- tion of radioisotopes. The Ecological Survey of White Oak Creek was divided into three main categories: botany, limnology, and vertebrate biology (Krumholz, 1954). Because of a virtual absence of rooted aquatic plants in the area, the fresh-water bi- ology was largely covered in the studies on limnology and vertebrate biology. That program was designed to find out what radiomaterials had accumulated in the biota of the drainage area, in which organisms and tissues they had accumulated, and what, if any, had been the effects of such levels of accumulation on popula- tion balances and on the various types of indi- vidual organisms. 3. Many studies of lesser magnitude carried on at other installations of the Atomic Energy Commission and at different colleges and uni- versities throughout the United States. Such studies usually are not integrated with one an- other but are separate studies designed to an- swer specific questions. Rather intensive studies of the phosphorus cycle in fresh-water lakes have been carried out by workers at Dalhousie University (Coffin, et al., 1949, and Hayes, et al., 1952), at Yale Uni- versity (Hutchinson and Bowen, 1950), and at Atomic Energy of Canada, Ltd. (Rigler, 1956). These studies have increased our knowl- edge of the role of phosphorus in the economy of fresh-water lakes, particularly at the lower trophic levels. Much work has also been done on the economic aspects of such aquatic insects as the mosquitoes (Bugher and Taylor, 1949; Hassett and Jenkins, 1951) and also on such aquatic forms as the frog (Hansborough and Denny, 1951). These animals have been tagged with radioisotopes (usually radiophosphorus) either by direct feeding of substances which contained the radioactive material, or by im- mersing them in radioactive solutions. Concentration of radioactive materials in aquatic organisms m (nc/fi of organism) The concentration factor ^ /&, . ° '- fie/ml of water for any radioelement cannot exceed the ratio between the normal concentration of that ele- ment in the organism and the concentration of the element in the surrounding water. Thus, if the element in question is not normally used by a particular organism, it is unlikely that any of the radioisotopes of that element will be con- centrated in the tissues. Each organism in each environment has spe- cific requirements for the different chemical elements. However, it is necessary to know the chemical composition of the organism and its parts, as well as that of its aquatic environment, in order to understand those requirements and to interpret the role played by each element in the metabolic processes. At present, there is very little information available on the chemical composition of any of the fresh-water organ- isms or their tissues, and consequently there is virtually nothing known of the concentration factors to be expected for the different elements by the organisms. Some data on the chemical composition of fresh-water lakes and streams are available, but these waters differ so widely from one another that no generalizations can be made. The total dissolved solids in fresh waters range from less than five parts per mil- lion to well over 400 parts per million. In addition, the elements which make up these dissolved solids seldom occur in exactly the same percentage composition in any two bodies of fresh water. The concentration of any par- ticular element in the water is directly depend- ent upon the chemical characteristics in the drainage area. Because of these differences in the requirements of organisms and in the chemi- cal compositions of the different fresh waters, it is necessary to consider each situation as a separate case. An indication of the differences in the orders

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90 Atomic Radiation and Oceanography and Fisheries TABLE 1 CONCENTRATION (PPM WET WEIGHT) OF SOME ELEMENTS IN SELECTED ORGANISMS AND IN SOME MAJOR RIVERS OF THE UNITED STATES Organism' Water 2 Algae Insect larvae Fish , Element (Spirogyra) , 1,500 (Caddis fly) 20 (Minnows) Low High 20 10 3 , 6,500 300 1 <0.01 6.0 1,500 300 3,000 2 200 250 2,000 6,000 <0.001 1.5 2 0.2 0.3 Sodium . 1.500 700 1,000 1 200 These values are only estimates of orders of magnitude. They are recorded here to illustrate differences which can exist and are not intended for use in precision work. 1 Values are from unpublished results obtained by spectrophotometric analysis at the Hanford Laboratories. * Abstracted largely from Moyle (1956) and Clark (1924). of magnitude of the concentrations of a few of the common elements in some organisms and in water is shown in Table 1. However, the con- centrations of particular elements in specific structures or tissues of those organisms may deviate widely from those values. For instance, the concentration of calcium as calcium car- bonate in the shells of some molluscs or that of silicon in the siliceous tests of some diatoms may be greater than the listed values by more than one order of magnitude. Field studies in the Columbia River at the Hanford Operation and in White Oak Lake at the Oak Ridge National Laboratory have pro- vided an opportunity to study the uptake and accumulation of a variety of radioactive ma- terials by organisms in those waters under natural conditions. Omitting those radionuclides which have half-lives shorter than ten hours, there are measurable amounts of Na24, Cr51, Cu04, P52, As7a, and rare earths in effluent from the Hanford reactors. The composition of the wastes from the Oak Ridge National Labo- ratory varies from day to day but there are rela- tively large amounts of Sr<"», SrBO-Yso, Cs"T, Ce144-Pr144, Ru106, and other fission products present at all times. In addition, there are rela- tively large amounts of other radionuclides such as P" and Co40 present on occasion. In spite of this large variety of radionuclides available to the organisms of these two aquatic communi- ties, only a few appear to be utilized to any great extent. Observed concentrations of the radionuclides most frequently used by the or- ganisms through their natural food webs in the Columbia River and White Oak Lake are listed in Table 2. From these data it is evident that some elements are utilized in much greater quantities than others. Rather large variations occur from one collecting site to another and between species, however. For example, the concentration factor for P22 in filamentous algae of White Oak Lake is listed as 850,000. This figure is for a sample from a large mat of Spirogyra that lie on the bottom near the upper end of the lake. In other parts of the lake Spirogyra contained less radiomaterial. Fur- thermore, radioactivity in other filamentous algae, such as Oedogonium, was consistently lower than for Spirogyra. Comparable differ- ences in the amounts of radioisotopes accumu- lated by the different phytoplankton and insect larvae were also found. Very few data have been published which indicate the importance of the physical and chemical states of the various elements in the TABLE 2 ESTIMATED CONCENTRATION FACTORS FOR VARIOUS RADIONUCLIDES IN AQUATIC ORGANISMS AS OBSERVED FROM FIELD STUDIES ON THE COLUMBIA RTVER AND WHITE OAK LAKE Radionuclide Site Na1* Columbia River Cu" Columbia River Rare Earths Columbia River Fe°* Columbia River P" Columbia River P" White Oak Lake Sr"-Y«> white Oak Lake Filamentous Insect Phytoplankton algae larvae Fish 500 500 100 100 2,000 500 500 50 1,000 500 200 100 200,000 100,000 100,000 10,000 200,000 100,000 100,000 100,000 150,000 850,000 100,000 30,000-70,000 75,000 500,000 100,000 20,000-30,000

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Chapter 9 91 Uptake by Fresh-water Organisms physiological processes of fresh-water organ- isms. Coffin, et al. (1949) and other workers have shown that a large fraction of the P22 which was added to fresh-water lakes under natural conditions was quickly fixed in the bot- tom sediments where it was essentially unavaila- ble to the organisms. Thus it is apparent that elements which are introduced into an environ- ment as insoluble or tightly fixed compounds, or become parts of such compounds shortly after their introduction, may be of little or no use to the organisms even though the particu- lar element involved normally enters into their metabolic processes. Another factor in the concentration of radio- materials by fresh-water organisms about which there is only limited information available is the effect of the presence of one chemical on the uptake of another. For example, it was Methods of accumulation of radiomaterials by organisms Radiomaterials may become associated with fresh-water organisms in one of three ways: (1) through adsorption to surface areas, (2) through absorption from the surrounding me- dium, or (3) through ingestion as food. The first of these methods is primarily a physical process whereas the last two are largely bio- logical in nature and make up an integral part of the physiological processes necessary for the metabolism of the population. In some instances, especially in those organ- isms which have a large surface-to-volume ra- tio, adsorption to surfaces is very important. For example, Foster and Davis (1955), working with organisms from the Columbia River, showed that the amounts of radioactivity in TABLE 3 ABSORPTION OF VARIOUS ELEMENTS FROM SOLUTION By FRESH-WATER FISH Element Organism Strontium Goldfish Barium-Lanthanum Goldfish Sodium Goldfish Calcium Guppy Probable concentration factor 150 150 30 1000 Investigator Prosser, et al., 1945 Prosser, et al., 1945 Prosser, et al., 1945 Estimated from Rosenthal, 1956 shown by Prosser and co-workers (1945) that the amount of calcium present in the water af- fected the amount of strontium taken up by goldfish; as the amount of calcium was in- creased, the uptake of strontium decreased. The amount of a radionuclide taken up by an aquatic organism is dependent not only upon the concentration of the nuclide in the water (microcuries per milliliter) but also upon its specific activity.1 As the specific activity is de- creased by increasing the concentration of "car- rier" over a certain range, the stable form of the element becomes more readily available to satisfy the requirements of the organism, and the amount of radioisotope taken up by the organ- ism will generally decrease. Such isotopic dilu- tion has a non-linear relationship, however, and may be ineffective in instances where low con- centrations occur (Whittaker, 1953; Kornberg, 1956). 1 Specific activity as used here refers to the ratio be- tween the amount of radioisotope present and the total amount of all other isotopes, both radioactive and stable, of that same element. sponges and diatoms remained comparatively high at a season when the amounts of radio- activity in other organisms were quite low. All of the nutrient materials, and thus the biologically important radioisotopes, that are metabolized by plants are absorbed directly from the environment (Rediske, Cline, and Selders, 1955). Direct absorption of a few radionu- clides by fresh-water organisms has been ob- served under laboratory conditions. Gross es- timates of concentration factors which appear to have occurred in these studies are listed in Table 3. For the most part, these are short- term tests in which the particular test organism was immersed in the radioactive solution. En- tirely different values would result if the organ- ism had also acquired the isotope through the food web. The principal mode of accumulation of ra- diomaterials by fishes is through ingestion. Ol- son (1952) found that young trout which had been immersed in dilute effluent from the Han- ford reactors failed to concentrate radiophos- phorous, whereas similar fish, which were fed

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92 Atomic Radiation and Oceanography and Fisheries organisms that had been grown in the effluent, accumulated substantial amounts of P22. Fish living in the Columbia River downstream from the reactors and which fed on organisms that had assimilated the radioactive materials con- tained over 100,000 times more radiophos- phorus than the surrounding water during the late summer. Krumholz (1954, 1956) at- tributed the high concentrations of Sr90 and Cs1" in the fishes of White Oak Lake to the ingestion of contaminated food organisms. In addition, it was shown that the different kinds of animals which served as food for the fishes accumulated different amounts and kinds of ra- diomaterials. For instance, although a high per- centage of the radioactivity in the food organ- isms, such as larval Chaoborus, emanated from radiophosphorus, only a relatively small portion of the radioactivity in the fish was traceable to that radioelement. Similarly, although only a relatively small amount of radioactivity in the plankton organisms was attributable to Sr°°, about 80 per cent of the radioactivity in the fish skeleton emanated from that radioisotope. From these findings it is apparent that the ability of the various organisms in the food web to con- centrate the different radionuclides is of the ut- most importance to the predatory species. If the animals which serve as food were unable to take up the radiomaterials, there would be con- siderably less chance of the predators becoming contaminated. The food habits of fishes and other fresh- water organisms determines, to a great extent, which radioelements they may accumulate. In a study of the food habits of the black crappies and the bluegills of White Oak Lake (Krum- holz, 1956) it was found that the diets of those two species were considerably different. Marked differences also occurred in the concentration and relative proportions of the radiomaterials in the tissues of the two kinds of fish. Greater amounts of radiomaterials were concentrated in the soft tissues of the bluegills than in the crappies, and greater amounts of radiomaterials were concentrated in the skeleton and other hard parts of the crappies than in the bluegills. Furthermore, there were relatively greater amounts of radiophosphorus in the bones of the bluegills and relatively greater amounts of radiostrontium in the bones of the crappies. These differences may well have resulted from the dissimilar diets or, perhaps, from different physiological demands. Unpublished data of the Hanford Laboratories shows that 50 to 75 per cent of the radiophosphorus ingested by fish is assimilated and retained. Unfortunately, there is virtually no other information available on the efficiency of transfer of radioisotopes from food organisms to aquatic predators. Concentration of radioactive materials in dif- ferent organisms In unpublished results from the studies at White Oak Lake, it was shown that bacteria may have the greatest powers for concentrating radiomaterials of any of the fresh-water organ- isms, their concentration factors for certain iso- topes may exceed 1,000,000. However, it is not definitely known for all radionuclides whether or not they actually enter into the metabolism of the bacteria or are adsorbed to surface areas. Labaw, Mosley, and Wyckoff (1950) showed that the measured radioactivity in Escherichia colt, which had been cultured on a medium that contained P22 (as Na2HP*O4), was not due to adsorption of the P22 on the bacterial surfaces nor to residues from the radio- active culture. The data from the Columbia River and White Oak Lake indicate that the phytoplankton usu- ally concentrate greater amounts of radiomateri- als than the zooplankton. Here, again, it is not known for all species whether the radiomateri- als actually enter into the metabolism or are adsorbed to surfaces. Some of the filamentous algae are known to concentrate PS2 at least 850,000 fold (Krumholz, 1954), whereas for other algae the concentration factor may be as little as 300,000. Some zooplankton have con- centration factors for radiophosphorus of as much as 250,000 but in others it may be less than 100,000. Fresh-water invertebrates of all classes studied in the Columbia River and White Oak Lake ex- hibited maximum concentration factors which ranged from less than 100 to more than 100,- 000 depending on the radioelement involved. It is believed that most of the radioactive ma- terials accumulated actually enter into the me- tabolism of these invertebrates. Some of the insect larvae concentrate radioelements by fac- tors upwards of 100,000; some of the micro- crustaceans by factors of nearly 200,000; some mollusks may concentrate fission products as ef-

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Chapter 9 93 Uptake by Fresh-water Organisms fectively, if not to a greater extent, than some crustaceans. This may be especially true for those long-lived isotopes which are incorporated into the shell. The length of exposure to water that con- tains radioisotopes will also greatly affect the concentration in different organisms. The con- centration of isotopes in phytoplankton and other micro-organisms will reach equilibrium with the water in a relatively short period of time. For radiophosphorus, this is estimated at about 15 hours (Whittaker, 1953). The larger animals, such as fish, will approach equilibrium much more slowly, however. Coffin, et al. (1949) found that radiophosphorus introduced into an acid bog lake did not appear in the fish until two days later. Several weeks of chronic exposure to an environment containing long- lived, bone-seeking isotopes is undoubtedly necessary before maximum concentrations will result in large fish. Variations with season, age, and growth So far as is known, all cold-blooded fresh- water organisms exhibit seasonal changes in the assimilation of radiomaterials through metabolic processes. There is a direct correlation between an increase in temperature and an increase in the accumulation of radiomaterials through metabolic processes in the invertebrates and fishes of the Columbia River (Foster and Davis, 1955) and the fishes of White Oak Lake (Krumholz, 1954, 1956). However, in White Oak Lake it was found that the amounts of ra- diomaterials in all fish tissues decreased mark- edly after August 1, even though the tempera- tures at that time were similar to those during the early summer when there was a rapid in- crease in the accumulation of radioactive ma- terials. This may well be a suggestion that some warm-water fishes enter a period of estivation or summer dormancy. A decline in radioactivity of Columbia River organisms during the winter months correlates with cessation of feeding. No seasonal pattern of change in the ac- cumulation of radiomaterials has been demon- strated for any of the warm-blooded aquatic vertebrates, but this may well occur. It is known, for example, that the I1S1 content of rabbit thyroid glands changes markedly with the season (Hanson and Kornberg, 1955). Among the fishes, it has been established by Olson and Foster (1952) that the younger, more rapidly growing individuals accumulate relatively greater amounts of radioactivity than the older, more slowly growing ones. This phenomenon is probably a reflection of the more rapid anabolism that accompanies the growth of younger fish. It is not known whether any of the other fresh-water vertebrates or inverte- brates exhibit this same phenomenon. Any accumulation of radioactive materials in an organism is subject to biological dilution. Such dilution results from cell division and growth. It is especially manifest in rapidly growing organisms and is particularly notice- able following an acute short-term exposure to the radiomaterials. Retention and elimination Radioisotopes will be deposited and retained in the organisms according to the physiological behavior of the particular element involved. Highly mobile isotopes, such as tritium, may be eliminated in a matter of minutes or hours (Foster, 1955), but certain bone-seekers, such as strontium or phosphorus, may be so tightly fixed that little loss occurs, except by radioac- tive decay, during the life of the organism. The metabolism of the radiophosphorus in trout has been studied by Hayes and Jodrey (1952) and by Watson (Hanford Laboratories, unpub- lished). Little information is available on the metabolism of other isotopes in other aquatic animals, however. The recognized methods of elimination of radiomaterials are: (1) through surface ex- change, (2) excretion through the natural physiological channels, (3) through moulting where this occurs, and (4) through death. In any of these processes of elimination, the radio- materials are released into the environment and can be immediately taken up by other organ- isms. Discussion Based on our present knowledge, there can be no broad statement to the effect that "aquatic organisms will concentrate radioactivity in their tissues." Rather, each individual situation must be appraised separately in the light of the fol- lowing basic considerations which are concerned with the accumulation of radiomaterials by fresh-water organisms: (1) the particular ele-

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94 Atomic Radiation and Oceanography and Fisheries ment involved and its physiological importance to the organism, (2) the physical and chemical state of the element and its acceptability to the organism, (3) the concentration of the element in the environment and the presence of other elements which may inhibit or enhance its up- take, (4) the morphology of the organism, its life history, and its particular role in the food web, and (5) the physical and chemical char- acteristics of the environment. Even though the great majority of research with radionuclides in biological fields has been performed within the past 15 years, enough data have been gathered to serve as a basis for the following general statements. 1. Radioactive materials are taken into the body of an organism either through physiological processes and incorporated directly into the tis- sues or they are attached to the surfaces of the organisms through adsorption. 2. The concentration of certain radioelements reaches a higher level in many of the lower plant and animal forms, such as bacteria, pro- tozoa, and phytoplankton, than in higher forms, such as the vertebrates. In such instances, there is an inverse correlation between the complexity of body structure and the concentration of the radioelement in question. 3. Certain plants and animals have a predilec- also concentrated in the bony skeletons of ver- tebrates, phosphorus in concentrated as adeno- sine triphosphate in the flight muscles of some birds, and potassium and other elements are concentrated in wide variety of tissues. 4. Although certain radioelements may occur in amounts acceptable for drinking water, many fresh-water organisms have the ability to con- centrate them to levels which would be harm- ful. Such deleterious effects could range from those in which only the individual organism is involved to those in which the entire popula- tion may be affected. Little information is available on the toler- ances of the various aquatic organisms to dif- ferent radioactive materials. Recently, however, D. G. Watson at the Hanford Laboratories has determined that a concentration of 65 ^c P32 per gram of bone was lethal to trout in about six weeks. A concentration of 10 ^c P'2 per gram was not lethal in 12 weeks but caused some radiation damage. This series of experi- ments is only the first step toward determining the tolerance levels for all radionuclides in each of the animals of the fresh-water fauna. The use of radiomaterials as a research tool in fresh-water biology has opened new fields which were almost impossible to explore ade- quately by other means. Determination of the metabolism of many of the elements essential tion for concentrating specific radionuclides in for proper nutrition is now possible. Further- different tissues. For instance, iodine is con-^^more, the effects of the radioactivity emanating centrated in the thyroid tissue, silicon is con- frOm isotopes deposited in the tissues can be centrated in the tests of some diatoms, calcium is concentrated as calcium carbonate in the shells of some mussels and as calcium phos- phate in others, calcium and phosphorus are studied. In the field of fresh-water biology, per- haps the greatest benefits from the use of radio- active materials can be derived from studies of the physiological processes of the organisms. REFERENCES BUGHER, J. G, and MARJORIE TAYLOR. 1949. Radiophosphorus and radiostrontium in mosquitoes. Preliminary report. Science 110:146-147. CLARK, F. W. 1924. The composition of the river and lake waters of the United States. U. S. Geol. Survey, Prof. Paper 135. COFFIN, C. C, F. R. HAYES, L. H. JODREY, and S. G. WHITEWAY. 1949. Exchange of ma- terials in a lake as studied by the addition of radioactive phosphorus. Canad. Jour. Research D. 27:207-222. DAVIS, J. J., R. W. COOPEY, D. G. WATSON, C. C. PALMITER, and C. L. COOPER. 1952. The radioactivity and ecology of aquatic organisms of the Columbia River. In Bi- ology Research — Annual Report, 1951. USAEC Document HW-25021:19-29. FOSTER, R. F., and J. J. DAVIS. 1955. The accumulation of radioactive substances in aquatic forms. Proceedings of the Inter- national Conference on the Peaceful Uses of Atomic Energy, 13 (P/280) : 364-367. FOSTER, R. F. 1955. Tritium oxide absorption and retention in the body water of some aquatic organisms. In Biology Research — Annual Report, 1954. USAEC Document HW-35917:98-100.

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Chapter 9 95 Uptake by Fresh-water Organisms HANSBOROUGH, L. A., and D. DENNY. 1951. Distribution of phosphorus22 in the em- bryo and larva of the frog. Proc. Soc. Exftl. Biol. Med. 78:437-441. HANSON, W. C, and H. A. KORNBERG. 1955. Radioactivity in terrestrial animals near an atomic energy site. Proceedings of the In- ternational Conference on Peaceful Uses of Atomic Energy, 13 (P/281) : 385-388. HASSETT, C. C., and D. W. JENKINS. 1951. The uptake and effect of radiophosphorus in mosquitoes. Physiol. Zool. 24:257-266. HAYES, F. R., J. A. MC.CARTER, M. L. CAME- RON, and D. A. LIVINGSTONE. 1952. On the kinetics of phosphorus exchange in lakes. Jour. Ecol. 40:202-216. HAYES, F. R., and L. H. JODREY. 1952. Utili- zation of phosphorus in trout as studied by injection of radioactive phosphorus. Physiol. Zoology 25:134-144. HUTCHINSON, G. E., and V. T. BOWEN. 1950. Limnological studies in Connecticut. IX. A quantitative radiochemical study of the phosphorus cycle in Linsley Pond. Ecology, 31:194-203. KORNBERG, H. A. 1956. Effectiveness of iso- topic dilution. In Biology Research — An- nual Report, 1955. USAEC Document HW-41500:19-28. KRUMHOLZ, L. A. 1954. A summary of the findings of the ecological survey of White Oak Creek, Roane County, Tennessee, 1950-1953. USAEC Document ORO-132: 1-54. 1956. Observations on the fish population of a lake contaminated by radioactive wastes. Bull. Am. Mas. Nat. Hist. 110 (4) :277-368. LABAW, L. W., V. M. MOSLEY, and R. W. G. WYCKOFF. 1950. Radioactive studies of the phosphorus metabolism of Escherichia colt. Jour. Bacteriol. 59:251-262. MOYLE, J. B. 1956. Relationships between the chemistry of Minnesota surface waters and wildlife management. /. Wildl. Mgt. 20: 303-320. OLSON, P. A., JR. 1952. Observations on the transfer of pile effluent radioactivity to trout. In Biology Research — Annual Re- port, 1951. USAEC Document HW- 25021:30-40 (OFFICIAL USE ONLY). OLSON, P. A., JR., and R. F. FOSTER. 1952. Effect of pile effluent water on fish. In Biology Research—Annual Report, 1951, USAEC Document HW-25021:41-52. PROSSER, C. L., W. PERVINSEK, JANE ARNOLD, G. SVIHLA, and P. C. THOMPKINS. 1945. Accumulation and distribution of radioac- tive strontium, barium-lanthanum, fission mixture and sodium in goldfish. USAEC Document MDDC-496:1-39. REDISKE, J. H., J. F. CLINE, and A. A. SELDERS. 1955. The absorption of fission products by plants. In Biology Research — Annual Report, 1954. USAEC Document HW- 35917:40-46. RIGLER, F. H. 1956. A tracer study of the phos- phorus cycle in lake water. Ecology 37: 550-562. ROSENTHAL, H. L. 1956. Uptake and turnover of calcium-45 by the guppy. Science 124: 571-574. WHITTAKER, R. H. 1953. Removal of radio- phosphorus contaminant from the water in an aquarium community. In Biology Re- search—Annual Report, 1952. USAEC Document HW-28636:14-19.