209 7 Effects of Radioactivity on Plants and Animals Kathryn A. Higley CONTENTS 7.1 Introduction 209 7.2 Physics, Chemistry, and Biology of Radiation Interactions 209 7.2.1 Types of Ionizing Radiation 210 7.2.2 Physical and Chemical Aspects of Ionizing Radiation Interactions 210 7.2.3 Direct and Indirect Radiation Interaction 211 7.2.4 Biological Consequences of Radiation Interaction 212 7.3 Effects of Radioactivity on Individual Plants and Animals 215 7.4 Ecological Consequences of Radiation Exposure 219 7.5 Conclusion 222 References 222 7.1 INTRODUCTION The literature on the effects of ionizing radiation on plants and animals spans nearly a century. Early studies of radiation effects on drosophila were used to determine that it is a mutagen [1]. The primary intent of these early studies was to better elucidate the nature of radiation interactions to understand their impacts on people. A consequence of the development of nuclear weapons was the developing awareness of the existence and global distribution of radionuclides. Interest grew in understanding where radionuclides went in the environment and helped support numerous studies of radiation effects on species, populations, and ecosystems [2]. While the bulk of the studies have focused on the response of the individual, accidents such as Chernobyl have allowed ecosystem-level inves- tigations to be conducted. Many of these studies are ongoing. 7.2 PHYSICS, CHEMISTRY, AND BIOLOGY OF RADIATION INTERACTIONS Understanding the effect radiation has on living tissues requires that one first examine the physics and chemistry of the initial interaction. Living cells are DK594X_book.fm Page 209 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 210 Radionuclide Concentrations in Food and the Environment composed in large part of water. The remainder consists of organic compounds — lipids, proteins, carbohydrates, and nucleic acids [3]. When ionizing radiation interacts within a cell it rapidly sets in motion a series of events that can lead to chemical and ultimately biological changes. The subsequent damage can be traced to the chemical changes that have come about due to the initial interactions of radiation. The nature and time frame for these events are discussed below. The magnitude of radiation exposure necessary to cause the effects is discussed later in this chapter. 7.2.1 T YPES OF I ONIZING R ADIATION There are two types of ionizing radiation: electromagnetic and particulate. X and γ rays are the ionizing electromagnetic radiations. They differ primarily in their origins (atomic vs. nuclear transitions), but are otherwise similar in properties. When X or γ rays are absorbed in matter, energy is deposited — unevenly and in discrete packets. The amount of energy is generally sufficient to break chemical bonds. Hence these radiations are termed “ionizing.” The other type of ionizing radiation is particulate. The most common partic- ulate radiations encountered in environmental settings are α and β particles. α particles are highly energetic helium nuclei lacking orbital electrons. They have a +2 charge when they are initially ejected from the nucleus during decay. β particles are highly energetic electrons that originate in the nucleus and may carry either a –1 or +1 charge. 7.2.2 P HYSICAL AND C HEMICAL A SPECTS OF I ONIZING R ADIATION I NTERACTIONS Absorption of ionizing radiation energy occurs through indirect and direct mech- anisms. Charged particles such as α and β particles have enough kinetic energy to directly dislodge electrons and cause ionization of the atoms and molecules with which they interact. Electromagnetic radiation (X and γ rays) is classified as indirectly ionizing. The radiation must be absorbed in order to transfer its energy to an electron. The end result is virtually the same — the production of an excited or ionized atom. The result of this interaction is the production of secondary electrons with some kinetic energy (energy of motion). In water, and other low atomic number materials, these secondary electrons have energies on the order of 10 to 70 eV [4]. The life span of these secondary electrons is very brief (approximately 10 –15 sec) and during that time they transfer their energy to the surrounding environment as they move through it. The initial transfer of energy to water results in the formation of ionized and excited water molecules, most notably H 2 O + (ionized water) and an electronically excited version of water, H 2 O * . These are accompa- nied by free electrons that have insufficient energy (less than 7.4 eV) to cause any additional excitation. DK594X_book.fm Page 210 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Effects of Radioactivity on Plants and Animals 211 Following the initial interaction, the three species that have been created undergo additional changes. The ionized water molecule can interact with an adjacent water molecule to form the following compounds: H 2 O + + H 2 O → H 3 O + + OH. The excited water molecule, H 2 O * , can lose energy in two ways: H 2 O * → H 2 O + + e or H 2 O * → H + OH. This process, although not as rapid as the initial ionization event, occurs in the time frame of 10 –12 sec. The molecule H 2 O + is an ion radical (it is both electrically charged and contains an unpaired electron). It has a short life span (less than 10 –10 sec) and decays to form the highly reactive hydroxyl radical (OH·), which has a life span of approximately 10 –5 sec. Once these species have been produced, they go on to react chemically with their environment, based on diffusion-con- trolled reaction kinetics [4]. 7.2.3 D IRECT AND I NDIRECT R ADIATION I NTERACTION Radiation interactions within cells are typically characterized as direct or indirect in nature. This characterization stems from the historical assessment that DNA is the principal target of concern with regard to radiation damage [3–5]. When radiation interactions occur in the cell, they may do so directly with the atoms of the target or with other atoms or molecules in the vicinity. For α particles, which are considered high linear energy transfer (LET) radiations, direct action is the dominant process by which the critical targets are affected. Sparsely or indirectly ionizing radiations such as β particles and X or γ radiation produce free radicals that can then diffuse and damage the critical target. This mode of delivering radiation damage is called indirect action. It accounts for roughly two- thirds of the damage caused by sparsely ionizing radiations [4]. Although DNA has generally been viewed as the most important target from the perspective of radiation damage, there is a wide range of molecules within the cell that can be adversely affected. These molecules vary in both size and molecular weight, and they too are impacted by the same direct and indirect effects of radiation discussed earlier. Broken chemical bonds, cross-linkages, and conformational changes are the resultant products of radiation interaction within the cell [4,5]. These altered molecules may hinder the molecule’s biological function. For example, a change in the orientation of an enzyme or protein (a conformational change) could limit its ability to perform a function in a metabolic pathway. The result could be the interruption or cessation of certain functions [5]. DK594X_book.fm Page 211 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 212 Radionuclide Concentrations in Food and the Environment 7.2.4 B IOLOGICAL C ONSEQUENCES OF R ADIATION I NTERACTION The consequences of ionizing radiation interaction can be seen at all levels of biological organization (molecule, cell, organ). However, it is important to note that while events may transpire at the molecular level, impacts do not automati- cally flow through to the higher levels of organization (individual, population, community, or ecosystem) [6–10]. When DNA is considered the critical target, the impacts of concern are the nature and extent of damage caused by charged particle tracks (or resultant chemical species). Single breaks in a strand of DNA, as well as ruptures in both strands (double-strand breaks), are the immediate products of ionizing radiation interaction within cells. As previously noted, ionization produces highly reactive products that break chemical bonds, including DNA molecules as well as cell membranes. Cell killing, mutation, and carcinogenesis are the longer-term con- sequences of these events. However, to complicate matters, many living cells have systems in place to repair damage to the DNA [11]. There are several characteristics of radiation that are important in determining the extent of the biological response. These include •Type and energy of radiation (e.g., α , β , or γ ). As noted previously, these can be densely ionizing radiations (i.e., α ) that directly impact critical targets, or sparsely ionizing radiations (X or γ rays, or β par- ticles), which have an indirect effect as their principle mode of radiation damage. These radiations are not the same with respect to their effec- tiveness in causing biological damage [12]. An absorbed dose of α particles, for example, can cause more biological damage than an equal absorbed dose of photons. In translating absorbed dose to a measure of biological effect, radiation “weighting” factors have been developed for humans. They have been assigned a value of 1 for photons and electrons and 20 for α particles. However, they account for the potential to cause cancer, a stochastic effect, and do not address deterministic effects. Data on deterministic radiation effects for α particles have been reviewed and evaluated by the International Commission on Radiolog- ical Protection (ICRP) [13] and appear to lie in the range of about 5 to 10 [12]. A weighting factor of one is typically used for electrons and photons, even for deterministic effects. • Spatial distribution of delivered energy, both micro- and macroscopic. At the macroscopic scale, the physical unit that describes energy dep- osition is the absorbed dose (in Gy or rads). It is defined as the average energy absorbed in a target tissue or organ divided by its mass. How- ever, this average value does not depict the enormous variability in energy deposition that occurs at the microscopic (e.g., cellular and molecular) level due to the stochastic nature of energy deposition events. DK594X_book.fm Page 212 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Effects of Radioactivity on Plants and Animals 213 •Total dose (energy per mass) delivered. With moderate to high doses of sparsely ionizing radiation (greater than 100 mGy), cells and tissues receive a nearly uniform exposure [14]. However, for substantially lower doses (approximately 1 mGy) more than a third of the cells remain undamaged [11]. The number of cells struck by an ionizing event depends significantly on the radiation energy as well as the type of radiation (i.e., α , β , or γ ). • Rate at which the dose is delivered. It is well known that dose response can be modified by changing the duration of exposure [5]. The biolog- ical effects from low-LET radiation are smaller when low dose rates are used than for higher ones (0.5 to 1.0 Gy/min). Fractionation also can reduce the impact. High-LET radiations, because of the direct nature of the damage they inflict, do not show the same degree of dose- rate response. Radiobiological studies have shown that, in general, cells most sensitive to the effects of ionizing radiation are those that are undifferentiated, well oxygenated, are highly metabolically active, and rapidly reproduce. In mammalian cells, the most sensitive are spermatogonia and erythroblasts, epidermal stem cells, and gastrointestinal stem cells [3,4,15,16]. The least sensitive are the highly differ- entiated and mitotically inactive nerve cells and muscle fibers. Interestingly, oocytes and lymphocytes are also very sensitive, although they are resting cells and consequently do not match the criteria noted earlier. The reasons for their sensitivity are unclear. There are also several areas of radiobiological research that are challenging our fundamental understanding of radiation damage at the cellular level (where DNA has historically been viewed as the principal target of concern). Three of these areas are • Genomic instability. Also known as genetic and chromosomal insta- bility, it refers to genetic change occurring serially and spontaneously in cell populations as they replicate. The concept of genomic instability is that radiation can induce a genome-wide process of instability in cells. This instability is transmitted over many generations of cell replication, leading to an enhanced frequency of genetic changes occur- ring among the progeny of the original irradiated cell [17]. The phe- nomenon has been observed with cell systems in vivo and in vitro and for low- as well as high-LET radiation [18]. These effects have been noted not only in cells that have been hit by ionizing radiations, but by adjacent, unirradiated cells (see the section below on bystander effects). While genomic instability is generally accepted, there are many unanswered questions concerning the mechanisms, in particular how it is initiated and how it is maintained over many generations of cell replication [17,18]. DK594X_book.fm Page 213 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 214 Radionuclide Concentrations in Food and the Environment • Bystander effects. The conventional model of radiation-induced dam- age requires damage of DNA either from direct interactions of radiation or from free radicals created nearby. Recent studies have demonstrated damage (such as altered gene expression) occurring in cells not directly exposed to radiation [18,19]. This is known as the bystander effect. There is evidence that this damage may be a consequence of intercel- lular signaling, production of cytokines, or free radical generation. It is also thought that these effects are related to inflammatory-type responses. The significance of the bystander effect as it relates to organisms and environmental consequences of radiation exposure is not yet known [17,18]. • Adaptive response. The technical literature contains an increasing num- ber of studies that show that adaptive protection responses occur in living cells after single as well as protracted exposures to X or γ radiation at low doses [20]. This has been observed both in vivo and in vitro and has been documented across a wide range of organisms from bacteria and viruses to plants and animals. Two types of protection are identified. One prevents and repairs DNA damage, the other removes damaged cells. The adaptive response mechanism is not immediate, but develops, presumably in response to physiologic stress. It manifests within hours and may persist weeks to months. However, there are no strong data supporting adaptive response following expo- sures to high-LET radiation [5]. By convention, the delivery of radiation dose has been categorized as acute (short term) or chronic (protracted). The resultant impacts of exposure are further apportioned into deterministic or stochastic effects. There is some confusion in the application of the terminology, as well as imprecision in describing both. In general, large radiation doses (the definition of large depends upon the organism) delivered within a short period of time (an acute dose) leads to short-term, acute (deterministic) effects. The expression of acute effects does not preclude the later occurrence of stochastic impacts (stochastic meaning an effect for which the probability of occurrence, rather than the severity, is a function of dose without a threshold). The most notable stochastic effects are cancer and genetic effects. Impairment of reproductive capability is one example of a deterministic effect [21]. A more severe one is death. Many effects, such as skin reddening or sterility, only appear when a threshold dose has been exceeded. There are also confounding factors (noted earlier) such as total dose, dose rate, fractionation, and partial body irradiation that can alter an organism’s response. Protracted (chronic), lower-dose radiation exposures that do not exceed the threshold for deterministic effects can still lead to increased probability for stochastic impacts. The definition of chronic depends on the life span and metab- olism of the receptor, but it is generally on the order of days to weeks (or longer). Chronic irradiation effects data are generally given in terms of the daily dose (e.g., mGy/day) rather than the total dose (e.g., Gy). DK594X_book.fm Page 214 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Effects of Radioactivity on Plants and Animals 215 7.3 EFFECTS OF RADIOACTIVITY ON INDIVIDUAL PLANTS AND ANIMALS When radiation effects at the level of the organism are examined, it becomes apparent that radiosensitivity generally increases with increasing organism com- plexity [2,21,22]. The generally accepted hierarchy of radiosensitivity to acute radiation doses has mammals, including man, among the most radiosensitive, and primitive organisms (bacteria, protozoa, viruses) among the most resistant [2]. Extrapolations and generalizations of effects must be made with caution. Even within similar species, radiosensitivity can vary by more than an order of magnitude [21]. During the course of their life span, individuals may also exhibit a range of radiosensitivities, based on a number of factors, including age, health, and genetic predisposition. In general, the young are more radiosensitive than adults (which can be attributed to cell proliferation being higher). However, considering the wide range of organisms (plants, animals, viruses, bacteria) found in the environment, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) [21] noted that the data do not allow one to “reliably predict the potential radiation effects in the wide variety of organisms likely to be present in a contaminated area.” The difficulty in providing clear-cut evaluations of the effect of radioactivity on plants and animals is that much of the available radiation effects data are based on short-duration (e.g., seconds to hours), high-dose exposures, which are expressed in terms of the total dose rather than a dose rate. These data, unaltered, do little to help address the issue of radiation exposures at low dose rates and in chronic conditions. In a sweeping study, Rose [16] conducted an extensive, critical review of the published literature to summarize and categorize the levels at which radiation- induced changes were detected in organisms following both acute and chronic exposures. Three broad categories of impact were examined: death, behavioral or developmental, and teratogenic or genetic. This review encompassed more than 600 citations and included data from all five kingdoms: protista, animalia, monera, fungi, and plantae. Viruses were also examined. The bulk of the work examined by Rose was conducted with animals and plants and utilizing X or γ radiation. It is interesting to note that considering the large dataset, only a few species were represented; the majority were mammalian. Most also focused on acute, high-dose exposures in laboratory. Past approaches to addressing the absence of chronic exposure data have been to use the acute effects data to estimate which effects are expected from chronic exposures. This approach is very conservative because, as noted earlier, a much larger total dose can be tolerated if it is received gradually rather than all at once [16]. Repair and compensation mechanisms that can be used at low dose rates are overwhelmed if the dose is received rapidly. One example cited by Rose [16] is an acute:chronic ratio of 10 or more observed for the most sensitive stages of fish development, growth reduction in plants, and damage to somatic organs in mammals. DK594X_book.fm Page 215 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 216 Radionuclide Concentrations in Food and the Environment As part of the EPIC project (Environmental Protection from Ionizing Con- taminants), a database of approximately 1600 records spanning 440 publications on dose-effects relationships for wildlife in northern temperate climate zones was recently published [23]. This database is built on records from Russian/FSU experimental field studies and addresses what had previously been a large gap in knowledge on low to moderate dose rate effects. As a consequence, much more information is now being made available on the effects of chronic radiation in animals. The data are still being reviewed, but some of the results are noted here. In an article examining radiation protection criteria for northern wildlife, Sazykina [23] proposed that five potentially measurable parameters be considered when assessing the potential impacts of radiation exposure in the environment. Three of these categories were similar to those identified by Rose [16]. These five were • Cytogenetic effects. Radiation interaction in tissue can leave indica- tions at the cellular and subcellular level. One example of a molecular endpoint is reciprocal chromosome aberrations [25]. The advantage of examining this molecular marker is that the abundance of such aber- rations can be related to cell killing, mutation and carcinogenesis, and also reproductive successes (for germ cells). The problem is that there are insufficient data at the present time to relate the chromosome aberrations to individual and population-level effects. • Radiation hormesis. Similar to the mechanism of adaptive response, radiation hormesis is considered to be the consequence of stimulation of the immune system from low-level irradiation. While results have been observed, the data are inconsistent, and at this time do not appear to be useful as a measure of assessing impacts of dose. • Morbidity. In the context of Sazykina [23], morbidity as a parameter referred to the appearance of illness and the general deterioration of specific aspects of an organism such as suppression of the immune sys- tem, changes in blood/lymph systems, and an overall decline in health. • Reproductive effects. Reproductive organs are known to be sensitive to radiation exposure. Sazykina [23] included damage to both the reproductive organs of adults as well as its eggs and embryos. In its literature review of radiation effects on biota, the International Atomic Energy Agency (IAEA) [22] suggested that reproduction was an impor- tant endpoint for assessing the effects of radiation on plants and ani- mals, within the context of developing guidelines for radiation protection. Cataloging the doses necessary to cause sterility is impor- tant because for some organisms a dose which may cause complete sterility may result in only minor changes within the organism [23]. And while sterilization may not directly impact the organism’s life span, it may indirectly effect the population in which it lives [7]. While tissues and organs within an organism vary in their radiosensitivity, DK594X_book.fm Page 216 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Effects of Radioactivity on Plants and Animals 217 reproductive processes and the early stages of development are seen as the most radiosensitive due to the ongoing activities of cell division and differentiation. • Mortality and life shortening. The classic measure of radiation impact has been to measure mortality. Within confined experimental settings, determination of mortality and comparison of the life span of control as compared to exposed animals is relatively straightforward. In the natural environment, confounding factors may make the analysis more complicated [7,14,23–26]. While obscuring some of the finer points, it is possible to combine the work of Rose [16] and the summary of Sazykina [23] and an earlier summary of Brechignac [15] to develop an overall assessment of radiation exposure on organ- isms. These will be examined using the five-kingdom convention of Rose [16] and incorporating the effects analyses of Sazykina [23]. Rose noted that within individual kingdoms there was a wide range of sensitivity to radiation. Sometimes the response appeared beneficial rather than harmful at low radiation exposures. • Animalia. The bulk of the literature on radiosensitivity is for mammals, and they have been observed to be the most radiosensitive, with lethal doses, of 6 to 10 Gy for small mammals and 1.5 to 2 5 Gy for the largest wild and domestic animals [15]. The lowest dose rate observed to cause death was in the range of 3 to 6 Gy/yr for several species of rodents [16]. Protraction of the lethal dose such that it is delivered over the life span of the organism substantially decreased its impact. UNSCEAR [27] noted that if a mouse was given the lifetime equivalent of its lethal dose, 7 Gy, the mean reduction of the life span was estimated to be 5% from cancer induction. In summarizing the literature on radiation effects for animals, Brechignac [15] noted that while there was a variation between species, if dose rates were less than 4 Gy/yr the mortality rate of the corresponding population would not be seriously affected. The lowest chronic exposure to produce a detectable change in behavior or development was about 10 2 Gy/yr (detected in planarium worms and mud snails) [16]. For acute exposures, a dose of only 10 –6 Gy could be visually detected in cockroaches. Reproductive capacity is more sensitive to the effects of radiation than life expectancy [2,15,16,26–29]. The lowest chronic exposure to produce a reliable teratogenic or genetic change (reduced birth mass and increased brain mass of laboratory rats irradiated as fetuses) was 3 × 10 –3 Gy/yr. Acute exposures of 10 –2 Gy to pregnant rats impaired the reflexes of their offspring. The lowest lethal dose rate was 3.6 Gy/yr and was found for several species of American rodents. The lowest dose rate found for detectable teratogenic or genetic effects was 3 × 10 –3 DK594X_book.fm Page 217 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 218 Radionuclide Concentrations in Food and the Environment Gy/yr. This dose rate reduced the birth mass and increased the brain mass of laboratory rats irradiated as fetuses toward the end of the intrauterine life. The lowest single dose to cause a teratogenic effect was 10 –2 Gy, which impaired reflexes in the offspring of irradiated pregnant rats [15,16]. It is important to note that while mammals have comprised the bulk of studies, work has been done on birds, reptiles, aquatic organisms, and invertebrates. The radiosensitivity of birds is similar to those of small mammals. Studies on reptiles, while appearing to show them as less radiosensitive, are being reexamined because of differences in physiology that may not have been appropriately accounted for [15]. Invertebrates, while less sensitive, still exhibit age-specific radiosensi- tivity, with gametogenesis, egg development, and their young being most sensitive. In the aquatic environment, fish are the most sensitive. Doses of 10 to 25 Gy to ocean species are lethal, although embryos are substantially more sensitive (e.g., 0.16 Gy for salmon) [15,26]. Embryo development in fish and the process of gametogenesis appear to be the most radi- osensitive stages of all aquatic organisms tested [22]. • Plantae. It has been noted that the plant kingdom contains the most radiosensitive species. The lowest acute dose, 0.8 Gy, killed a small proportion of young Douglas fir trees ( Pseudotsuga douglasii ). Yet a different species, eastern white pine ( Pinus strobus ), required doses of 2.7 Gy [16]. In his review of the literature, Brechignac [15] observed that literature values of lethal radiation doses are between 10 and 1000 Gy for plants. As has been reported several times, larger plants appear more radiosensitive than small ones. The order of radiosensi- tivity, from greatest to least, is conifers to deciduous trees, thicket species, herbaceous plants, lichens, and mushrooms. The review by Rose [16] indicated that dose rates on the order of 6 Gy/yr were found to kill red pine ( Pinus resinosa ), but a 50% reduc- tion in dose rate had no observable effect on pitch pine ( Pinus rigida ). Nonlethal effects on plants have also been observed, as well as variable sensitivity in plant structures. Nonlethal effects observed include inhi- bition of growth and seed production, delay in bud opening, increased leaf dormancy, and greater susceptibility to infestation [15]. Examples of ranges of sensitivity include seeds (very insensitive) and apical mer- istems (most sensitive). The data of others [15,26] is in general agree- ment with that of Rose [16], and dose rates of approximately 4 Gy/yr will produce only minor effects on sensitive plants and have minimal impacts on the large majority of plants in natural communities. The literature has provided limited data on the radiosensitivity of other organ- isms. The data provided below are summarized from Rose [16]. DK594X_book.fm Page 218 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC [...]... [10,15,16,23,28] A comparison of the model of Polikarpov [10] with data from Rose [16] and Sazykina [23] is provided in Table 7. 1 It is relatively straightforward to identify ranges of exposure and potential effects The difficulty arises in trying to measure them, either in the field or in a laboratory setting, and then interpret them with regard to an organism’s radiosensitivity The radiation field generated... surrounding the delivery of doses, external γ irradiation rather than internal contamination studies were favored All of these factors have contributed to an incomplete understanding of the consequences of low-level radiation exposure in natural settings [11,25, 27, 32] In the last 15 years, acute and chronic radiation effects data have been reviewed by several organizations [16,21,22,33] Based on their... of studies published in the Western literature that examined the responses of plant and animal populations to radiation exposure in their natural environments [15,23] Instead, the bulk of the research has emphasized individual over population responses Because of the ease and immediacy of information retrieval, mortality rather than reproduction was assessed Similarly, acute rather than chronic doses... damage to the underlying populations and communities is severe Polikarpov also © 20 07 by Taylor & Francis Group, LLC DK594X_book.fm Page 220 Tuesday, June 6, 2006 9:53 AM 220 Radionuclide Concentrations in Food and the Environment provided examples of environments that delivered dose rates corresponding to these zones The zones proposed by Polikarpov appear to be supported by the current and past literature... where masking of the physiological effects of radiation exposure occurs, as the dose rates can overlap with those of natural background In zone 4 (4 × 100 to 5 × 10–2 Gy/yr), there are effects on individuals, but these are masked by the interactions with the population and community Finally, in zone 5 (4 × 100 to greater than 3 × 103 Gy/yr), the consequences are catastrophic to ecosystems because the damage... Lorimore, S.A., Coates, P.J., and Wright, E.G., Radiation-induced genomic instability and bystander effects: inter-related nontargeted effects of exposure to ionizing radiation, Oncogene, 22, 70 58, 2003 20 Feinendegen, L.E., Evidence for beneficial low level radiation effects and radiation hormesis, UKRC 2004 debate, Br J Radiol., 78 , 3, 2005 21 United Nations Scientific Committee on the Effects of Atomic Radiation,... Radiation on the Environment, Report to the General Assembly, United Nations, New York, 1996 © 20 07 by Taylor & Francis Group, LLC DK594X_book.fm Page 224 Tuesday, June 6, 2006 9:53 AM 224 Radionuclide Concentrations in Food and the Environment 22 International Atomic Energy Agency, Effects of Ionizing Radiation on Plants and Animals at Levels Implied by Current Radiation Protection Standards, Technical... D.M., and Smith, G.M., Terrestrial invertebrate population studies in the Chernobyl exclusion zone, Ukraine, Radioprotection, 40, S8 57, 2005 9 Hingston, J.L., Wood, M.D., Copplestone, D., and Zinger, I., Impact of chronic low-level ionising radiation exposure on terrestrial invertebrates, Radioprotection, 40, S145, 2005 10 Polikarpov G.G., Conceptual model of responses of organisms, populations and ecosystems... 222 Radionuclide Concentrations in Food and the Environment of exposure based on reproductive effects, stochastic effects should not be significant at a population level The available stochastic effects data are difficult to interpret in regard to harm to an individual organism [21,22,33,34] The expected safe levels of exposure were based on the dose–response relationships for reproductive effects, rather... impacts on organisms and populations There are sufficient new data to help fill in many of the gaps in knowledge on the effects of chronic exposures [15,16,23,24] While remaining in general agreement with past research, some differences have been found that can be attributed to environmental conditions of exposure [23] Finally, at a very broad level, the preponderance of data suggest that the lowest dose . on organ- isms. These will be examined using the five-kingdom convention of Rose [16] and incorporating the effects analyses of Sazykina [23]. Rose noted that within individual kingdoms there was. exposure and potential effects. The difficulty arises in trying to measure them, either in the field or in a laboratory setting, and then interpret them with regard to an organism’s radiosen- sitivity Radionuclide Concentrations in Food and the Environment As part of the EPIC project (Environmental Protection from Ionizing Con- taminants), a database of approximately 1600 records spanning