1041 R RADIATION ECOLOGY Radiation Ecology or Radioecology is a term that came into common usage in 1956 to denote that area of the broad field of ecology concerned with the assessment of radioactivity in the environment. More specifically, radiation ecology has come to be recognized as that area of ecology concerned with radioactive substances, radiation and the environment. The development and subsequent expansion of nuclear energy for military and peaceful purposes has been accom- panied by environmental problems, some of which are typi- cal of other facets of industrialization and some unique to atomic energy. The unique problems primarily concern the fate and ecological effects of radionuclides released into the environment. The major environmental problems introduced by the Atomic Age may be grouped into several areas of scien- tific and public concern. Underlying each of these is the worry about the effects of ionizing radiation—on man, his domesticated plants and animals, and on the environment and its living components, Fallout from weapons testing, reactor radioactive waste effluents, radioactive waste dis- posal, nuclear war, and use of nuclear explosives for major engineering and related technological projects of large scale comprise the activities which have concerned society and which, because of potential impact on the environment and man, have stimulated the development of radiation ecology. Understanding the manner in which our ecological systems (ecosystems) distribute, assimilate, and affect the environ- mental behavior of radioactive substances, and the effects of radiations emitted from those substances, are the concern of the radioecologist. RADIONUCLIDES OF ECOLOGICAL IMPORTANCE Radionuclides which are of interest to the ecologist are listed in Table 1. These radioactive elements represent the major naturally-occurring and man-made sources of radia- tion in the environment. Principal sources of exposure from background (natural) radiation are represented by the ura- nium, thorium and actinium decay series. Internal exposure to man results primarily from 40 K, 14 C, 226 Ra, and 228 Ra and their daughter products that are deposited in the body. Radionuclides such as 222 Rn and 220 Rn and their daughter products represents sources of internal radiation exposure to man from inhalation. Radionuclides produced by the fissioning of uranium (fission products) are of the greatest current concern. These man-made isotopes are not essential to organisms, but they constitute the major sources of radiation in the environment whether it be from fallout or waste disposal from reactor operations. All of these radionuclides may enter ecosystems where they become part of the flux of systems that are being circulated within and between systems. Some of the fission products which are chemically simi- lar to biologically essential elements are of special inter- est. They vary greatly in their physical half-life and in the extent to which they participate in metabolic processes of living organisms. The most important radionuclides affecting plants and animals on land are strontium-90, cesium-137, and iodine-131. Strontium-90 remains in the environment for a long time. Its half-life is 28 years. Strontium is chemically similar to calcium, and it can enter living organisms as a replace- ment for calcium. In weapons fallout strontium-90 is usually deposited in the root systems of plants. the amount of 90 Sr that a plant absorbs from soils depends on several factors, particularly on the quantity of calcium in the soil, the relative quantities of calcium and strontium at the depth where the roots are located, and the ability of the plant to discriminate between the two elements. The plant is the base for 90 Sr to enter the human food chain. This chain is a short and simple one consisting of plants, cows, and man, with cow’s milk being the chief source of entry into man. There is consider- able discrimination against the transfer of strontium at each step in this food chain, but the small amount that is trans- ported to man tends to concentrate in bone tissue. It remains there, undergoing radioactive decay and emitting its radia- tion. Its danger is related to the fact that bone contains blood forming (erythropoetic) tissue. In sufficient quantities the radiation can cause leukaemia and bone cancer. C018_001_r03.indd 1041C018_001_r03.indd 1041 11/18/2005 11:04:27 AM11/18/2005 11:04:27 AM © 2006 by Taylor & Francis Group, LLC 1042 RADIATION ECOLOGY Strontium-90 accumulation normally is greater in children than in adults, because growing children are building bone at a greater rate and use a larger amount of calcium. A study of species in the deer family (cervidae) graphically demonstrated the effects of 90 Sr fallout. The levels of 90 Sr in the antlers of deer rose continually from 1947 through 1955, then remained constant for 2 yrs, and rose again in 1958. The concentration of 90 Sr was more than 8 ϫ as high in 1958 as it was in 1947. With the cessation of major weapons tests in the 1960’s, the levels began to drop off. Cesium-137 is another major fission product that is found in fallout and untreated radioactive waste effluents. Cesium behaves chemically very much like potassium and follows the same metabolic route in plants and animals as potassium does. It enters plants directly through the leaves after being deposited by rain, and so it appears in plant tis- sues more quickly than does 90 Sr. From there on the route of 137 Cs is much the same as 90 Sr; it appears in the milk and muscles of cattle that eat contami- nated plants, and it enters the human body in food. Once in the human body, it becomes part of muscle tissue and so has an almost uniform distribution throughout the body. It stays there for only about 4 months. Since its half-life, like that of 90 Sr, is about 28 yrs, little of the 137 Cs undergoes radioactive decay while in the body. The transfer of 137 Cs and 90 Sr from plants to animals also has been observed in species that are not important as food sources for man. The coconut crab, a land animal that lives on a diet of fruit and nuts on islands in the Pacific, was found to have accumulated radioactive materials as a result of the Pacific test explosions. Strontium-90 was found in the skeleton, and 137 Cs was found in the soft body parts—direct results of eating contaminated vegetation. The third radionuclide or fission product of importance in fallout is radio-iodine ( 131 I). The chemistry of radioactive 131 I is exactly like that of natural 127 I, which is not radioac- tive. Therefore, its concentration in the body depends only on the concentration in the source material. Iodine becomes concentrated in the thyroid glands of vertebrate animals, where it can cause cancer of the thyroid and damage to other tissues. Like 90 Sr and 137 Cs, it enters plants as a result of radioactive fallout and then enters humans either by way of the plants themselves, or by way of contaminated milk from cows that eat the plants. The radioactivity of thyroid glands removed from certain animals can serve as a sensitive indi- cator of 131 I in the environment, because the concentration of 131 I in the thyroid can be as much as 10,000 ϫ higher than the concentration in nature. The black-tailed jack-rabbit is a useful animal for such measurements. It has a large thyroid gland that is easy to remove and weigh. The level of radioac- tivity in each gram of its thyroid tissues varies directly with the fallout on vegetation. Finally there are man-made radionuclides (activation products) which are important because they are the isotopes of elements which may be essential to plants and animals. Some of these also may enter the environment as activation products resulting from reactor operations or nuclear explo- sives. Examples of activation radionuclides are cobalt-60 and zinc-65. In aquatic or marine environments these radio- nuclides have been found to accumulate in food organisms especially shellfish and mollusks. Generally 60 Co can be anticipated to be accumulated by organisms or to be retained in organically enriched materials such as forest floor humus and organic sediment. Zinc-65 is of particular concern in marine environments where it is likely to be accumulated in clams and oysters. However, being an activation rather than a fission product its presence depends more on appropriate stable elements present which in turn are exposed to fast neutrons than on fissionable material. RADIOSENSITIVITY OF ECOLOGICAL SYSTEMS Although there is much current concern about the possible effect of low level, chronic radiation on ecological systems, there is relatively little comprehensive scientific data on TABLE 1 Radionuclides of ecological importance Category Major radionuclides Ecological importance Naturally occurring radionuclides Uranium Thorium Actinium series elements Potassium-40 Carbon-14 Major contributors to background radiation (long half-lives) Fission products Strontium-89, 90, 91 Yttrium-90, 91 Zirconium-95 Niobium-95 Ruthenium-103, 106 Rhodium-106 Iodine-131 Cesium-137 Barium-137, 140 Lanthanum-140 Cerium-141, 144 Praeseodymium-143, 144 Neodymium-147 Promethium-147 Enter ecological systems through fallout or waste disposal (half-lives ranging from a few hours to 30 yrs) Radioisotopes of elements essential to organisms Hydrogen-3 Cobalt-60 Carbon-14 Sodium-22, 24 Phosphorus-32 Sulfur-35 Potassium-42 Calcium-45 Manganese-54 Iron-59 Copper-64 Zinc-65 Used as tracers in both radionuclide cycling and radiation effects studies on organisms and ecological systems C018_001_r03.indd 1042C018_001_r03.indd 1042 11/18/2005 11:04:28 AM11/18/2005 11:04:28 AM © 2006 by Taylor & Francis Group, LLC RADIATION ECOLOGY 1043 this problem. Much more is known about the radiosensi- tivity of organisms exposed to radiation doses which are much higher than we expect to contend with in the normal environment. In general, higher animals are far more sensi- tive to radiation than are lower animals, and the very young and the aged are more sensitive than mature, healthy ani- mals. For example Table 2 gives estimated acute doses of gamma of X-radiation necessary to kill 50% or more of the adult members of several groups of organisms. These data should be considered only as an indication of rela- tive radiosensitivity as they represent generalized ranges. Half the humans exposed to a single dose of 500 R will die. For other mammals the lethal dose ranges from less than 300–1200 R. Frogs and newts can survive higher radiation levels, depending on their body temperatures at the time of exposure. Insects can survive doses of up to 100,000 R in a few instances; most have lethal doses in the 10,000–20,000 R range. These kinds of data do not reflect the more complex responses of organisms subjected to ion- izing radiation under natural conditions. For example, most organisms go through several stages of development from egg to adult. These stages may take place in different parts of the ecosystem. Likewise, the radiosensitivity of these organisms may differ in different stages of the life cycle. In radioresistance groups such as insects, 10% or less of the lethal dose to adults may be effective at juvenile or egg stages. For example, in the bagworm a dose of 450 R is sufficient to kill 50% of 1-day old eggs, whereas a dose of approximately 10,000 R was required to produce the same effect in the larvae. Effects other than lethality also may be produced by radi- ation, especially in ecosystems where all organisms are linked through various interactive processes. Aside from genetic or reproductive effects, changes in number, growth, disease resis- tance, life span or response to physical environmental factors are of interest to the ecologist. Radiation-induced changes can affect the role of organisms or populations within the ecosystem. Predator–prey relationships, food chain transfers, and other ecological processes which depend on the continu- ing interaction between different organisms may be altered by the impact of ionizing radiation. The effect of ionizing radiation on plants has been studied both outdoors and in greenhouses. One indoor test field consists of 10 acres of land with a 60 Co source located at the center. It is installed in a vertical tube, which can be raised to different heights for irradiation and then lowered by remote control into a lead case when not in use. Various species of plants grow in the soil in concentric circles around the source. Each species is arranged in a wedge-shaped area so that the plants are located at various distances from the source and receive various intensities of radiation. Plants are exposed to radiation for 20 hr a day. Radiation effects on plants are complex and depend on a number of factors, including the plant species, the maturity of a plant, its physical condition, the parts of the plant exposed to radiation, the kind and amount of radiation, and the rate at which the radiation dose is applied. Woody plants gener- ally are more sensitive to radiation than are herbaceous plants (Table 2). Gymnosperms are more sensitive to radiation than angiosperms. A pine tree shows severe growth inhibition at a level of about 10 R/day, while the same degree of inhibition in a gladiolus plant requires about 5000 R/day. Some ecologists have speculated that radiation from a nuclear attack would destroy all pine trees and other gymnosperms in irradiated areas, leaving other plants relatively unharmed. It is possible to predict some radiation effects in plants. The meristematic or growth regions in plants are the most radiosensitive tissues. It is the absorption of radiation energy in these regions that alters plant growth and development. Ecologists and botanists have shown that the response of plants to ionizing radiation is directly proportional to the interphase chromosome volumes in meristematic tissues. That is, plant species with large chromosomes are more sen- sitive; those with small chromosomes are more resistant to radiation. In general, this is an extremely useful concept, and it has been applied to predict and assess probable radiation effects on vegetation (natural and agricultural) from military uses of nuclear devices. Seeds are far less sensitive to radiation than are growing plants. A stand of pine trees exposed to a total of 12,000 R of gamma radiation was 90% destroyed, yet 95% of the seeds taken from cones on the same trees were viable. The high resistance of seeds to radiation damage is probably associated with their low water and oxygen content. The sensitivity of dry seeds varied widely among species, however. Lily seeds show practically no ability to sprout after receiving a dose of 2000 R. Yet the seeds of other plants seem to be stimulated to sprout more vigorously than normal under the same amount of radiation or more. Such differences favor the growth of certain species over others in areas where radiation is a factor in the environment. EFFECTS OF RADIATION ON ECOSYSTEMS The effects that large scale ionizing radiation such as from a nuclear attack would have on plants and animals living together in an ecosystem have concerned radioecologists ever since the first use of atomic bombs. Several studies have TABLE 2 Comparative radiosensitivity of groups of organisms Group Lethal dose range a (rads) Bacteria 100,000–1,000,000 Insects 5,000–100,000 Fish 1,000–300 Mammals 300–1,200 Herbaceous plants 5,000–70,000 Coniferous trees 800–3,000 Deciduous trees 4,000–10,000 a Estimated acute whole body gamma radiation doses required to kill 50% or more of the adult organisms. C018_001_r03.indd 1043C018_001_r03.indd 1043 11/18/2005 11:04:28 AM11/18/2005 11:04:28 AM © 2006 by Taylor & Francis Group, LLC 1044 RADIATION ECOLOGY been conducted involving small ecosystems in an attempt to determine what would happen on a large scale. In one study, 10,000 acres of land surrounding a nuclear reactor where exposed to radiation ranging from lethal levels to levels no higher than the natural background radiation. The ecosystem on this land consisted mainly of an oak-hickory-pine climax forest. The forest was exposed to a mixture of gamma radia- tion and neutrons, with an intensity similar to that expected from fallout after a nuclear attack. The radiation reached about 37,00 trees, plus many more herbaceous species and many more shrubs. Ecologists examined thousands of plants in order to differentiate between the effects of ionizing radia- tion and the effects of frost, disease, insect damage, drought, and other natural factors. In still another study, a community of spring and summer annuals was exposed to gamma radia- tion for nearly 4 months during one growing season and then was observed over the next 3 yrs. In still another study, gamma radiation was applied daily throughout one winter and spring to a forest and to an open field with a well-established cover of annual plants. On the basis of these and other studies, radioecologists have formulated a scenario depicting how ionizing radiation would affect the plants and animals of our forests and fields if a nuclear attack occurred during the summer growing season. People emerging from shelters several weeks after the attack would find little change in their surroundings, except in areas of extremely high radiation. All plants and animals, both large and small, would have been killed in these high radiation areas, and as the plants died they would subject the surrounding areas to further danger from fire. However, most fields and woodlands would appear unchanged by radiation when viewed from a distance. Closer inspection would reveal more clearly the extent of the damage. The ground would be littered with the bodies of birds and ani- mals killed by the radiation. Inspection of lakes, streams, ponds and marshes would show that the lower animals had fared better. Fish, frogs, toads and salamanders would be alive and healthy. The sound of insects would be heard as before. Among the plants the damage would be least seri- ous to those that appear early in a natural succession pattern. Mosses and lichens would be undamaged, annuals would be somewhat affected, shrubs more so, and trees most of all. The damage to pine trees would be most apparent. Pines nearest the radiation zone would have turned a brilliant red brown within a few days after the attack. Other plants in the forest and fields would undergo little change during the remainder of the summer. In the autumn the oaks, hickories and other hardwood trees would lose their leaves earlier than usual—perhaps as much as 7 weeks earlier in areas nearest the high-radiation zone. The following spring these areas would remain in their state of winter dormancy 7 or 8 weeks longer than usual. Examination of the hardwoods (oaks, hickories, etc.) at this time would reveal severe damage to the buds, resulting in the development of fewer leaves and of abnormal leaves. Near the high-radiation zones, the trees might be leafless. The distribution of annuals in the open fields and on the forest floor would also be changed from previous years. Certain species would grow in greater numbers, partly as a result of the stimulation of their seeds by radiation and partly as a result of the radiation in seed germination among other competing species. The delay in development of leaves on the trees would give these annuals an extra long growing season. In the abundance of sunshine, weeds would grow on the forest to heights of 8 ft or more. The absence of a leafy canopy would also cause changes in the forest soil. With greater wind flow through the bare trees and higher tempera- tures from direct sunlight, the soil would become drier and harder during sunny weather. In rain storms the harder impact of rain drops would wash away topsoil in areas not covered by weeds or shrubs. Throughout the first summer follow- ing the attack, birds and animals from outside the irradiated areas would move in to replace those that were killed. RADIOACTIVE TRACERS With the threat of nuclear war receding, and nuclear reac- tors being equipped with ever more elaborate safe-guards to reduce radioactive releases to the environment, the thrust of radioecology is changing. Activation products in con- trolled quantities are now being used as radioactive tracers to follow the pathways of chemical elements in the bodies of organisms and in the complex interactions of ecosystems. The radioactive materials have the advantage of being easily detected and quantitatively measured in biological materi- als without elaborate chemical separation of the elements otherwise necessary. For example, the radioisotope 137 Cs was added to the upward flow of water in trunks of yellow poplar trees in Tennessee about 18 years ago. In the ensuing years radio- ecologists have followed the movement of this relatively inert tracer into leaves of the trees, into leaf-eating insects, into the insect eating birds, into the forest litter as the dead leaves fell, into soil insects, and so forth. Periodic sam- pling has confirmed the recycling of natural materials in this forest ecosystem. The radioecologists, in concert with systems analysts, are currently developing computer simula- tion models to mimic the ecological cycles revealed by this cesium tagging experiment. Comparable information on the exchange of materials from one component of the ecosys- tem to another could never have been obtained without the knowledgeable use of radioactive materials by these trained radioecologists. Other activation products such as calcium-45 or phosphorus-32 find use in studies of metabolic processes in organisms, populations or communities. Such studies lead to an understanding of regulatory processes and struc- tural characteristics of living systems. Other examples of experimental use of radioactive tracers may range ecologi- cally, from studying the uptake of 45 Ca tagged fertilizer by corn, to following the pathways of 32 P in a stream, includ- ing its distribution in the non-living as well as the living components. Radiation ecology is now an area of ecological research and teaching that encompasses far more of the impacts of C018_001_r03.indd 1044C018_001_r03.indd 1044 11/18/2005 11:04:28 AM11/18/2005 11:04:28 AM © 2006 by Taylor & Francis Group, LLC RADIATION ECOLOGY 1045 man on his environment than the atom bomb and nuclear reactors. Understanding of nearly all pollutant chemicals in the environment is being enhanced by use of tech- niques and principles of ecological cycling developed by radioecologists. CURRENT DEVELOPMENTS IN RADIATION ECOLOGY The last several years have witnessed a major decrease of interest in, and hence support of, research in radiation ecol- ogy. In the United States the research programs and projects initiated primarily under the Atomic Energy Commission (AEC) have been mostly dismantled. The rationale behind these policy shifts is difficult to comprehend; however, it seems to have been associated with a perception that most of the scientific challenges associated with the ecological aspects of radiation are either sufficiently understood or can contribute little to those practical issues related to radia- tion protection that are still of concern. Despite this ratio- nale, there has been little change in the long-standing public fear of ionizing radiation and its potential consequences. In addition, the recent major accident at the Russian nuclear power station at Chernobyl (1986), in which 50–100 Mci was released into the environment, not only raised or exacer- bated fears in those public sectors already concerned about radiation problems associated with nuclear power but also served to galvanize resistance in large groups (e.g., the Soviet public and other East European populations) that hitherto had either accepted nuclear power or manifested little if any public resistance. The Chernobyl accident underscored both the inef- fectuality of political boundaries against environmental contamination and the role of food chains, both natural and agricultural, in exposing humans and other organisms to potentially harmful levels of radionuclides. Likewise, Chernobyl focused interest on the direct consequences of radiation on ecosystems in the zones of high contamination (within a radius of 18 km of the reactor site). The release of large quantities of 134 Cs and 137 Cs resulted in the contamina- tion of lakes, streams, and forests in the path of the plume. The need to understand the rates of transfer and patterns of bioaccumulation of these radionuclides in different ecologi- cal pathways became manifest in many European countries located thousands of kilometers away from the reactor. In Sweden, for example, high concentrations of 137 Cs were found in reindeer and moose (1,000 to 10,000 Bq/kg) and in several species of freshwater fish. The relatively rapid buildup of radionuclides in these organisms was the result of processes which can affect both the rate and extent of bio- accumulation in food chains. Thus the Chernobyl accident has emphasized an increased need for additional research in radiation ecology. Food chains are the ecological pathways by which many substances are moved in terrestrial and freshwater envi- ronments. In the case of radionuclides, these pathways are important in the assessment of radiation exposure to critical population subgroups and human populations. Until recently the uptake and transfer coefficients used in regulatory models were mainly generic default values intended for use in lieu of site-specific information. The Chernobyl accident demon- strated the importance of and need for geographic-specific data on individual radionuclide behavior in terrestrial and fresh-water pathways. Unlike the United States, most other countries are involved in extensive radioecological research. This research is aimed at obtaining data for predicting exposure resulting from transport of radionuclides in agricultural food chains. The processes of interest in terrestrial envi- ronments are those involving atmospheric deposition onto soils and vegetation; resuspension and leaching from these surfaces; uptake from soils by the edible portions of vegeta- tion; and transfer into meat, milk, and other animal products utilized by humans. In the aquatic environment the key pro- cesses involve the bioaccumulation of radionuclides from sediments, water, and algae into the edible components of aquatic biota. The assessment of the environmental and health impacts resulting from radiation exposure is dependent on the use of mathematical models, which, like all other models, are prone to uncertainty. The best method for evaluating uncer- tainties in the predictions of dose-assessment models is to test predictions against data obtained under real-world con- ditions. The large extent of contamination following the Chernobyl accident has provided exactly this type of oppor- tunity. Currently an international cooperative effort known as BIOMOVS (BIOspheric MOdel Validation Study) is under way to test models designed for the calculation of environ- mental transfer and bioaccumulation of radionuclides and other trace substances. More than 20 assessment models are now being tested against data collected from numerous sites throughout the Northern Hemisphere. Upon completion of the initial model testing effort of the BIOMOVS project, additional long-term testing is being planned and organized by the International Atomic Energy Agency (IAEA). Another issue of concern that has not received research attention recently in the United States in the direct effect of ionizing radiation on populations and communities of organisms. This issue invariably arises whenever there is a nuclear-related incident. In the case of the Chernobyl acci- dent, radiation exposures in the immediate vicinity of the reactor resulted in 28 human fatalities, with a larger number or persons (209) suffering varying degrees of radiation sick- ness. Pine forests within several kilometers of the reactor site received sufficient contamination to result in an accumulated dose of more than 1000 rads. According to Soviet reports, pronounced morphological damage to pine foliage was vis- ible within 5 months after the accident in the zones where the doses ranged from 300 to 1000 rads. Lethal effects in the 1000 rad zone were also manifest by this time, and by winter (7 months postaccident) 400 ha of forest was destroyed. An ecological preserve has been established in one of the natu- ral areas subjected to high levels of radionuclide contamina- tion. The Soviet government has announced its intention to carry out long-term radioecological observations and studies C018_001_r03.indd 1045C018_001_r03.indd 1045 11/18/2005 11:04:28 AM11/18/2005 11:04:28 AM © 2006 by Taylor & Francis Group, LLC 1046 RADIATION ECOLOGY in this preserve to assess the long-term impacts, if any, on the resident flora and fauna. To the Soviets’ credit, they have recognized both the need and the opportunity to obtain data on the long-term effects of ionizing radiation on plant and animal populations as manifested through genetic mechanisms. To this end, they have established experimental facilities at the accident site to carry out this research. Radioecologists have long recognized the need for hard data on the long-term conse- quences of exposure to chronic radiation to populations of organisms. Little is known about the interaction of ionizing radiation and environmental stress on populations that are subject to competitive pressures, predation, and other fac- tors that affect survival. We need to be concerned with the effects that a buildup of radionuclides in the environment would have on the eventual fate of the organisms inhabiting such an environment. Thus, despite the current lack of attention given to research issues in radiation ecology in the United States, much can be learned by collaborating with scientists in Europe and Asia who are now engaged in investigating the fates and effects of radioactive substances deposited from the Chernobyl accident. REFERENCES 1. Lansdell, Norman, The Atom and the Energy Revolution, Philosophical Library, New York, 1958. 2. Curtis, Richard and Elizabeth Hogan, Perils of the Peaceful Atom, Dou- bleday and Co., New York, 1970. 3. Bryerton, Gene, Nuclear Dilemma, Ballantine, New York, 1970. 4. Ravelle, Roger et al., The ocean. Scientific American, September 1969. 5. Russell, R. Scott et al., Radioactivity and Human Diet. Pergamon Press, London, 1966. 6. Auerbach, Stanley I. A Perspective on Radioecological Research, J. Soc. Radiol. Prot. 4(3): 100–105, 1984. 7. Izrael, Yu, A. et al., Ecological Consequences of Radioactive Contami- nation of the Environment in the Chernobyl Emergency Zone. Moscow, 1987. 8. Peterson, R. C., Jr., et al., Assessment of the Impact of the Chernobyl Reactor Accident on the Biota of Swedish Streams and Lakes, Ambio 15(6): 327–334, 1986. 9. BIOMOVS Progress Report No. 6 Swedish National Institute for Radi- ation Protection, Stockholm, 1988. 10. International Atomic Energy Agency. Coordinated Research Project on the Validation of Terrestrial, Aquatic, and Urban Radionuclide Transfer Models and Acquisition of Data for that Purpose. IAEA, Vienna. STANLEY I. AUERBACH Oak Ridge National Laboratory RADIOACTIVE WASTE MANAGEMENT: see MANAGEMENT OF RADIOACTIVE WASTE C018_001_r03.indd 1046C018_001_r03.indd 1046 11/18/2005 11:04:28 AM11/18/2005 11:04:28 AM © 2006 by Taylor & Francis Group, LLC . RADIATION ECOLOGY Radiation Ecology or Radioecology is a term that came into common usage in 1956 to denote that area of the broad field of ecology concerned with the assessment of radioactivity. Models and Acquisition of Data for that Purpose. IAEA, Vienna. STANLEY I. AUERBACH Oak Ridge National Laboratory RADIOACTIVE WASTE MANAGEMENT: see MANAGEMENT OF RADIOACTIVE WASTE C018_001_r03.indd. Co can be anticipated to be accumulated by organisms or to be retained in organically enriched materials such as forest floor humus and organic sediment. Zinc-65 is of particular concern in