ML12338A697

Official Exhibit - ENT00354A-00-BD01 - Soures and Effects of Ionizing Radiation

ML12338A697
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Site:	Indian Point
Issue date:	04/30/2011
From:	United Nations Scientific Committee on the Effects of Atomic Radiation
To:	Atomic Safety and Licensing Board Panel
SECY RAS
References
RAS 22138, 50-247-LR, 50-286-LR, ASLBP 07-858-03-LR-BD01
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{{#Wiki_filter:ENT00354A Submitted: March 29, 2012 United States Nuclear Regulatory Commission Official Hearing Exhibit In the Matter of: Entergy Nuclear Operations, Inc. (Indian Point Nuclear Generating Units 2 and 3) ASLBP #: 07-858-03-LR-BD01 Docket #: 05000247 l 05000286 Exhibit #: Identified: Admitted: Withdrawn: Rejected: Stricken: Other: ENT00354A-00-BD01 10/15/2012 10/15/2012 c:..\\,.~""R REGlI~;. l~'~ 0 ~ ~ ....,,1-0.... ? ~

• • • • il SOURCES AND EFFECTS OF IONIZING RADIATION United Nations Scientific Committee on the Effects of Atomic Radiation UNSCEAR 2008 Report to the General Assembly with Scientific Annexes VOLUME II Scientific Annexes C, 0 and E t_~

~ ~ ~i§ ~ UNITED NATIONS New York, 2011

NorE The report of the Committee without its annexes appears as Official Records of the General Assembly. S i x l y~lhird Session. Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations conccrning lhe legal status of any country, territory, city or area. or of its authorities. orconceming the delimitation of its frontiers or boundaries. Thecounlry names used in this document are. in most cases, those that were in use allhc time the data were collected or the text prepared. In other cases. however, the names have been updated. where Ihis was possible and appropriate, to reflect poli tical changes. UNITED NATIONS PUBLICATION Sales No. E.II.lX.3 ISBN-13: 978-92 142280- 1 e-ISBN-13: 978-92-1-054482-5 © United Nations. April 20 I I. All rights reserved. Publishing production: English, Publishing and Library Section. United Nations Office at Vienna.

CONTENTS VOLUME I, SOURCES Report of the United Nations Scientific Committee on the Effects of Atomic Radiation to the Geneml Assembly Scientific Annexes Annex A. Medical radiation exposures Annex 8. Exposures of the public Hnd workers from various sources of radiation VOLUME II, EFFECTS Annex C. RadiHtion exposures in accidents......... Annex D. Health effects due to radiation from the Chernobyll.lccident.. Annex E. Effects of ionizing radilltion on non-humnn biota.... iii 45 221

ANNEX E EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA CONTENTS INTRODUCTION...... A. Background. B. Scope of annex.

c.

Effects of exposure to ionizing mdiHtion..

1.

Individual level effects.....

2.

PopulHtion Hnd ecosystem level effects.

3.

Multiple stressors

4.

Commentary..... D. Observations from case studies E. Structure of this annex........ I. ESnMATING DOSES TO NON-HUMAN 810TA _. A. Assessing exposures of biota

1.

Choice of reference organisms......

2. Radioecological models....

3. Transfer of mdionuclides in the environment I.Ind resulting exposures B.

Transfer of radionuclides in the terrestrial environment.

1.

Dry deposition....

2.

Interception of radionuclides deposited from the air.

3. Weathering......

4.

Distribution of mdionuclides within plllnts.

5.

Uptake of mdionuclides from soil..

6.

Migration in soil...

7.

Resuspension.....

8.

Transfer to animals. C. Transfer to freshwater organisms D. Transfer of radionudides to marine organisms. E. Evaluating doses to biota................

1.

Fraction of mdiation absorbed by organism

2.

Principal relationships for internal and external exposure.

3.

Doses to non-human biota.

4.

Conclusions _..... II.

SUMMARY

OF OOSE-fFFECTS DATA FROM THE UNSCEAR 1996 REPORT. A. Dosimetry for environmental exposures....

8.

Effects of radiation exposure on plants and animals..

1.

Terrestrial plants..

2.

Terrestrial animals.

3.

Aquatic organisms. 221 P"", 223 223 224 224 224 225 226 227 227 228 229 229 229 230 231 232 232 233 233 233 233 236 237 237 238 241 242 242 244 253 254 255 255 258 259 260 261

c.

Effects of radiation exposure on populations of plants and animals. D. Effects of major accidents. III.

SUMMARY

OF DOSE-EFFECTS DATA FROM THE CHERN08YL ACCIDENT... A. Radiation exposure............

8.

Effects of radiation exposure on plants.... C. Effects of radiation exposure on soil invertebrates... D. Effects of radiation exposure on farm animals. E. Effects of radiation exposure on other terrestrial animals F. Effects of radiation exposure on aquatic organisms.... G. Genetic effects in animals and plants.............. H. Overall observations on the effects of the Chemobyl accident... IV. EFFECTS OF RADIATION EXPOSURE ON NON-HUMAN 810TA. A. Overall conclusions of the UNSCEAR 1996 Report..

8.

Evaluations since 1996.........

1.

United States DepHrtment of Energy..

2. Canndo.

3.

FASSET.

4.

ERICA...

5. Observntions from recent liternture.

6.

Effects on populntions and ecosystems. V.

SUMMARY

AND CONCLUSIONS...... A. Estimating dose to non-human biota..

8.

Summary of dose--effects dnta from the UNSCEAR 1996 Report.. C. The current evnluation. D. Conclusions. ACKNOWLEDGEMENTS. REFERENCES 222 P"" 261 262 263 263 263 265 265 266 266 268 269 272 272 273 273 274 275 278 282 288 291 291 292 293 294 295 297

INTRODUCTION A.

Background

1. The estimation of human exposure to ionizing radiation from radionuclides of natural and artificial origin is an impor-tant and ongoing function of the Conunittee. The Committee has used simplified generic models of the dispersion and transfcr of radionuclides through the environment to estimate the internal and external exposure of humans and the result-ing doses. Owing to the complexity and interactions of the underlying processes, special attention has been given to radionuclide transfcr via human food chains and the assess-ment of ingestion doses. The underlying model assumptions and parameters are kept under review and revised as neces-sary. The last revision was documented by the Committee in annexA, "Dose assessment methodologies" of the UNSCEAR 2000 Report [U3].

2. In the past decades, scientific and regulatory activities related to radiation protection focused on the radialion expo-sure of humans. The prevailing view has been that, if humans were adequately protected, then "other living things are also likely to be sufficiently protected" [18] or "other species are not put at risk" [15]. Over time, the general validity of this view has been questioned on occasion and therefore consider-ation has been given to the potential effects of exposure to ionizing radiation of non-human biota. This has occurred, in part, as a result of the increased worldwide concern over the sustainability of the environment, including the need to main-tain biodiversity and protect habitats and endangered species

[U22, U23]; in part, because it has increasingly been recog-nized that the exposure scenarios and pathways for assessing human exposure may not apply to non-human biola; and, in part, as a result of various efforts to assess the effects of expo-sure to ionizing radiation on plants and animals [C I. DI, F5, 11, 12,13, 14, 19, N6, P13, R9. TI, WI6J.

3. The Committee initially addressed the effects of radia-tion exposure on plant and animal communities in a scien-tific annex, "Effects of radiation on the environment", of the UNSCEAR 1996 Report [U4]. Prior to this, the Committee had considered living organisms primarily as part of the environment in which radionuclides of natural or artificial origin may be present and contribute to the internal exposure of humans via the food chain. Like man, however, organisms are themselves exposed internally to radiation from radio-nuclides that have been taken up from the environment and externally to radiation in their habitat In general tenns, the Committee, in its 1996 report, considered that population-level effects were of primary interest and, of those, that reproductive effects were the most sensitive indicator of 223 hann. Furthennore, it also concluded that it was unlikely that radiation exposures causing only minor effects on the most exposed individual member of a population would have sig-nificant effects at the population level; that chronic expo-sures to low-LET radiation at dose rates of less than 100 mGylh to the most highly exposed individuals would be unlikely to have significant effects on most terrestrial animal populations; and that maximum dose rates of 400 mGylh to a small proportion of the individuals in aquatic populations of organisms would not have any detrimental effects at the population level.

4. The lnternational Commission on Radiological Protec-tion (ICRP), the International Atomic Energy Agency (IAEA) and other international organizations have encour-aged the exchange of information on the effects of radiation exposure on non-human biota [119. N6J. The IAEA's action plan on the protection of the environment was discussed at the 2003 Stockholm Conference [Ill. which concluded that "While accepting that there remain significant gaps in knowledge and that there needs to be continuing research.

there was an adequate knowledge base to proceed and (the Conference) strongly supported the development of a frame-work for environmental radiation protection". It also found that the time is ripe for launching a number of international initiatives to consolidate the present approach to conlrolling radioactive discharges to the environment by taking explicit account of the protection of species other than humans".

5. in 2000, the ICRP, recognizing that environmental pro-tection is a global matter, sel up a Task Group to examine the issues. It considered that an approach to environmental protection from ionizing radiation "should relate as closely as possible to the current system for human radiological protection, and that these joint objectives could therefore best be met by the development of a limited number of Ref-erence Animals and Plants" [19]' Subsequently, the ICRP decided to establish a new Commiuee (lCRP Committee 5) on the Protection of the Environment. The ICRP further noted that "as radiation effects at the population level---or higher-are mediated via effects on individuals of that pop-ulation, it seems appropriate to focus on radiation effects on the individual for the purpose of developing a framework of radiological assessment that can be generally applied to environmental issues" [110],

6. Since the preparation of the UNSCEAR 1996 Report

[U4], the approaches to evaluating radiation doses to non-human biota have been reviewed and improvements made [e l, EI, FI, F5, U26], Infonnation on the levels of radiation

224 UNSCEAR 2008 REPORT: VOLUME II exposure below which biological effects are not expected or, alternatively, above which such effects might be expected, has been developed. This has been obtained, in part, for the projects on the Framework for Assessment of Environmental Impact (FASSET) fF 11 and the Environmental Risk from Ionising Contaminants: Assessment and Management (ERICA) [EI], in particular, as part of the development of the FASSET Radialion Effects Database (FRED) [F3]. This information was subsequently integrated with the database on the effects of radiation exposure from the project on Envi-ronmental Protection from Ionising Contaminants in the Arctic (EPIC) [826] resulting in the so-called FREDERICA database [F20]. B. Scope of annex

7. The scientific information given in the FRED [F20]

combined with that obtained in the subsequent ERICA pro-gramme [G II. J61 and thai from more recent studies, espe-cially those undertaken around the site of the Chernobyl accident, provided the basis for the Committee's review of the effects of exposure to ionizing radiation on non-human biota given in this annex. In particular, the Committee used the information from ils review to re-evaluate ils recom-mendations on dose rates below which exposure to ionizing radiation is unlikely to result in detrimental effects on popu-lations of non-human biota, given in the UNSCEAR 19% Report [U4],

8. This annex only provides the Committee's overview of the current data and methods to assess doses to non-human biota and a brief discussion of the nature of effects of radiation exposure on individual organisms and populations.

Detailed discussion of these topics is beyond the scope of this annex. C. Effects of exposure to ionizing radiation

9. Since the preparation of the UNSCEAR 1996 Report

[U4], a number of radiobiological phenomena have been described, including genomic instability (genomic damage expressed post irradiation after many cell cycles) and the bystander effect (whereby non-irradiated cells in proximity to irradiated cells exhibit effects similar to those seen in the irradiated cells). These phenomena were discussed in annex C, "Non-targeted and delayed effects of exposure to ionizing radiation". of the UNSCEAR 2006 Report [U I], While such phenomena are relevant to understanding mech-anisms for the development of effects on non-human biota after exposure to ionizing radiation, a discussion of such phenomena is beyond the scope of this annex.

10. The immediate effects of ionizing radiation exposure may be seen al various levels of organization from the sub-cellular through individual organisms to populations and ecosystems [GI61. Responses of various biological func-tions to radiation exposure (e.g. reproductive success, metabolic impairment and changes in genetic diversity) can be traced to events al the cellular or subcellular level in specific tissues or organs.

t.

Individual level effects II. Even though mutational events in somatic cells are pri-marily responsible for cellular transformation and tumour formation, the occurrence of cancer in individual organisms is normally of low relevance to the ecosystem as a whole. except in the case of endangered or protected species [A 13]. However, mutational effects in germ cells may lead to repro-ductive impairment [AI4J. Genotoxic stressors, including ionizing radiation, may alter reproductive success by decreasing fertility via c1astogenic,md mutagenic effects in genn cells resulting in a decrease of the number of gametes. Such stressors may also increase the frequency of develop-mental abnormalities, e.g. when mutations are induced in germ cells and the progeny of exposed parents develop abnormally.

12. There are a number of weaknesses in the data on which to base estimates of the dose rates below which effects on non-human biota are not considered likely. In addition, there are also issues in extrapolating from the effects observed at cellular and subcellular levels to effects thai might be observed in individual organisms. populations and ecosystems. Moreover, it is only under controlled condi-tions in the laboratory thai organisms can be exposed to a single stressor. This presents a further source of uncertainty in extrapolating the results to real ecosystems where multi-ple stressors exist. Although beyond the scope of this annex, the Committee acknowledges that improved understanding of the mechanisms of radiation damage. of how to extrapo-late information from lower to higher trophic levels, and of the possible consequences of multiple stressors is of great interest and worthy of further study.

13. The scientific literature provides many examples of adaptive responses to and hormetic effects of exposure to ionizing radiation. Annex B of the UNSCEAR 1994 Report

[U5] provided a comprehensive discussion of adaptive responses. In that report, the Committee concluded that there was evidence of an adaptive response in selected cellular processes following exposure to low doses of low-LET radiation but went on to suggest that it was premature to con-elude that adaptive cellular responses had beneficial effects that outweighed the harmful effects of exposure. Subsequent to the UNSCEAR 1994 Report [U5], there have been numer-ous papers and considerable discussion concerning the possibility of hormetic responses to low doses of ganuna radiation. For example, Boonstra et al. [B39[ reported pos-sible honnetic effects of gamma radiation exposure on popu-lalions of meadow voles. These authors suggested that increases in glucocorticoid levels associaled with chronic gamma irradiation at a rate of about I mG y/d may be an important factor in the increased longevity of exposed meadow voles compared to non-exposed ones. Mitchel et al.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 225 [M9] found that a single dose of 10 mGy to radiation-sensitive mice (frp53 heterozygous) reduced the risk of both lymphoma and spinal osteosarcoma by greatly delaying the onset of malignancy. Further discussion of adaptive responses and potential honnetic effects of low dose and low dose-rate gamma radiation exposure is beyond the scope of this annex.

14. The various life stages of organisms differ in their sen-sitivity to exposure to ionizing radiation. It is often assumed that a population will be protected if the most sensitive stage of the life cycle is protected. For a large number of stressors, this assumption seems to be widely true [F9].

However, the most sensitive life stage is often difficult to identify a priori. Consequently, if data on effects only exist for one or two life stages, it may not be possible to know for certain if these data represent infonnation for the most sen-sitive life stage, even though most of the available infor-mation indicates that gametogenesis and embryonic development are among the most radiosensitive stages of the life cycle [14]. For example. Anderson and Harrison [A 15] showed that the synchronous spawning in polychaete worms rendered the organisms susceptible to low-level cumulative impact of ionizing radiation exposure. Because they spawned synchronously and died, oocytes were formed all at once, and damaged gametes could not be replaced.

15. The propagation of effects on individuals to the popula-tion as a whole depends greatly on the characteristics of the specific life history. The relative importance of each stage in the life history also varies between species, depending on the specific reproductive characteristics (short generation time versus long generation time, iteroparous versus semelpa-rous, sexual versus asexual reproduction, etc.). Changes in the value of an individual parameter such as age of reproduc-tion (i.e. generation time) often have much stronger conse-quences for species with fast population growth rates (i.e.

with short generation time and high fecundity rate) than for those with slow population growth rates [G3]. On the other hand, the National Council of Radialion Protection and Measurements (NCRP) [N8] noted that when natural causes of deaths are considered collectively on a biologically com-parable lime scale, nalural mortality occurs at a biologically comparable age, as illustrated in figure I. Figure I. Cumulative survival curves of the mouse, beagle and human for natural causes of death 1.0 Beagle ~ O.S ~ Human " 0.* ~ ~ \\ " ~ 0.4 " 0.2 u 0 100 300 500 700 900 1100 1300 1500 AGE AT DEATH (mouse days) 1000 2000 3000 4000 5000 .000 7000 AGE AT DEATH (dog days) 20 40 60 so 100 120 AGE AT DEATH (human years)

2.

Population and ecosystem level effects

16. Whatever the stressor considered, population-level effects are valuable indicators of ecological hazard (e.g.

[F9]). However, because of experimental constraints, most available data describe the effects on the individual traits of irradiated organisms. Many studies have documented the effects of radiation exposure at the cellular, tissue and indi-vidual levels. The consequences have been found to be increases in morbidity and mortality. decreases in fertility and fecundity, and increases in mutation rate [WIO]. These types of effect. observed at the individual level. may have consequences for a population of a species.

17. Matson et al. [M 12] and Baker et al. [829] investigated the possible genetic and population effects resulting from the chronic radiation exposure of bank voles, Clethrionomys glareolus, inhabiting contaminated sites near Chemobyl.

226 UNSCEAR 2008 REPORT: VOLUME II Both groups reported that genetic diversity was elevated in the contaminated sites when compared to relatively uncon-taminated sites but were unable to attribute any significant detrimental effects among the bank vole populations to radiation exposure.

18. Ionizing radiation does not appear to have any direct effects at the population or higher ecological levels (i.c.

community or structure and function of ecosystems). At present, it appears that all such effects are mediated by effects at the individual or lower levels. In addition, indi-reel effects through food-web mediated processes may occur [0 16]. One approach to extrapolating from the effects on individuals to effects at the popuJation level is to integrate the effects on survival and reproduction in temlS of population growth rate. Population growth rate is one of the most important characteristics of a population and is defined as the population increase per unit lime divided by the number of individuals in the population. Population models are used to extrapolate from the toxic effects on individuals. expressed as modifications to values of life-cycle parameters. to effects at the population level. This method has been used, for example, by Woodhead [WI OJ in a theoretical way and was implemented through experi-ments within the ERICA project for the chronic exposure of two invertebrates exhibiting contrasting life cycles: the earthworm and the daphnid [A26, G3].

19. An ecosystem has complex interactions between biotic and abiotic components and among biotic components. The latter are called interspecific interactions and include compe-tition, predation and association. These interactions conlrib-ute to the flow or cycle of energy, materials and infonnation in the ecosystem, and thus provide the ecosystem with its fundamental property of self-organization. It is possible that if one species is directly damaged by a toxic agent, another species more resistant to that agent is also indirectly affected by the depletion of interactions with the directly damaged species. As a result, the entire ecosystem can be affected in extreme cases. These indirect effects have been observed in ecosystems exposed to ultraviolet radiation IE37J and some chemicals [C23, H24. M24, T24, W20J. Similarly, some indirect effects through inter-species interactions have been observed in irradiated ecosystems, as reviewed in the UNSCEAR 1996 Report [U4]. Given this backdrop, tbe importance of indirect effects has been considered in reviews of the effects of exposure to ionizing radiation on ecosys-tems IE38, C21, 12, 13, 14, NI, U4]. Since these indirect effects cannot necessarily be deduced from effects on indi-viduals and populations, ecosystem-level effects are evalu-ated using mathematical modelling, model ecosystem experiments and field irradiation experiments.

3.

Multiple stressors

20. In general tenns, the modifying effects of multiple stressors can be considered in one of two broad categories, namely (a) the modification by the other slressors of the organism's uptake of radioactive material and the distribu-tion of radioactive material within the organism, and (b) the influence of the other slressor:s on the radiosensitivity of the species [AI8. B28, F5, G18. L8. P9. R19. S17. S18].

21. Metabolic manifestations of exposure to ionizing radia-tion include impainnent in enzyme function, altered protein turnover, impainnent in general metabolism and inhibition of growth. Sugg et al. [S 171 showed that the body condition of largemouth bass exposed 10 mercury and mCs in different lakes near the Savannah River site could be related to DNA damage. Changes in lipid metabolism in fish liver and a stimulation of the ventilation rate of a lamellibranch species have also been shown to occur at low doses in this mixed exposure scenario [P22, P23].

22. Experiments involving multiple exposures to metals (cadmium and zinc), organic pollutants, such as polychlo-rinated biphenyl (PCB). polycyclic aromatic hydrocarbon (PAH), endocrine disruplOrs, and radionuclides (radioactive isotopes of cobalt, caesium, and silver) have been conducted both under controlled conditions and in the field [G 17].

Experiments using a freshwater bivalve (Dreissena poly-morpha) and a carnivorous fish (Oncorhynchus mykiss) exposed under chronic conditions to water containing con-centrations of 1-4 jJgIL of cadmium and/or 170-250 jJglL of zinc showed a 60% decrease in the bioaccumulation of the isotopes of silver and caesium in the bivalve and a 30% decrease in the fish. However, no effect was observed for other radionuclide/organism pairs (such as cobalt for the fish). On the other hand, prior exposure to organic micro-pollutants enhanced both the uptake and retention of '1CO and 'l4Cs in the fish. Several possible explanations, linked to a modification of the health status of the animal by the pres-ence of stable pollutants, were advanced by the authors and supported by biomarker measurements: an increase in respi-ratory activity by alteration of the global metabolism; a decrease in the Na+/K+-ATPase in gills and therefore modi-fication of the ionic flux; or an alteration of the epithelium permeability [AI6, A17, FI5].

23. Genotoxic/cytotoxic damages are not specific to ioniz-ing radiation and may also be initiated by other toxins [S 18].

indeed, most biochemical techniques for delecting DNA danlage at the molecular or cellular level lack specificity for radiation-induced DNA damage [T9]. However, Tsytsugina [T8] and Tsytsugina and Polikarpov [T6] analysed the distri-bution of chromosome aberrations in cells and the frequency of the different types of aberrations in order La discriminate between the contributions of radiation and chemical factors to the total damage to natural populations in aquatic organ-isms. These studies showed that the chromosome damage observed in aquatic wonn populations exposed to dose rates of I 0 ~Gylh or more in lakes located in the vicinity of the site of the Chernobyl accident was mainly caused by radioactive contamination. Hinton and Brechignac [H20], however. cau-tioned that, while there is a great potential value in using biomarkers for assessing risks to non-human biota, there remain many challenges in linking changes in biomarkers at

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 227 the molecular or cellular levels to effects on individual organisms and populations of organisms.

24. The antioxidant status modified by exposure to various stressors may influence the radiosensitivity of organisms.

The cellular damage due to radiation exposure is mainly associated with oxidation. This oxidative stress may also be caused by other stressors, such as chemical pollutants, and cellular defence mechanisms against reactive oxidative species (ROS) that may be solicited are not stressor specific [S27]. Therefore, the interaction of heavy metals and radio-nuclides, and the resulting modification of radiosensitivity, may depend on tbe capability of the antioxidant defence systems of the organism LC13, C14, CIS, S27, VI].

25. The potential effects of exposure to uranium in lhe environment may arise from the chemical toxicity of the metal and its radiotoxicity (arising from the uranium alpha particles) and thus, such situations can be regarded as being due to a mixture of stressors coming from a single element

[830, C19, P24]. Thus, while an evaluation of the chemical toxicity of uranium to non-human biota is beyond the scope of this annex, it is important to recognize that the chemical toxicity and the radiological effects of uranium occur con-currently, and that both may need to be considered in a practical assessment of risks to non-human biota.

4.

Commentary

26.

Most of the data on the effects of exposure to ionizing radiation on non-human biota are from observations made on individual organisms. Radiation effects on populalions occur as a result of the exposure of individual organisms. The propagation of effects from individual organisms to popula-tions is complex and depends on a number of factors. How-ever, as suggested in the UNSCEAR 1996 Report [U4], the most important effects appear to be those on reproduction and repnxluctive success. Many questions remain with respect to the following: the mechanisms whereby radiation exposure can cause hann; inter-species extrapolation; propa-gation of hann from nuclear DNA to the population; and the effects of multiple stressors. Moreover the possibility of honnetic effects at low doses and dose rates of gamma radia-lion, the relation between changes in biomarkers at the molecular and cellular level and the effects on individual organisms or populations of organisms, and the effects of multiple stressors continue to be of considerable interest. D. Observations from case studies

27. Ecological risk assessments (ERAs) have been con-ducted for a wide variety of situations where non-human biota are exposed to enhanced levels of radiation or radio-active material. ERA studies are available for a wide variety of nuclear fuel cycle activities from uranium mining to waste management, as well as for sites with enhanced levels of naturally occurring radioactive materials, and for sites con-taminated as a result of accidents. Table I outlines the key elements of an ERA framework for assessing the effects of exposure to ionizing radiation on non-human biota. Various approaches for perfonning ERAs have been outlined includ-ing those of the lAEA [12. 13, 14], NCRP [NI], the United States Department of Energy (DOE) [U26], Jones et al. [J1],

Environment Canada and Health Canada [E2], FASSET [Fl. LA] and ERJCA [817]. All of the approaches necessarily involve simplifications of the knowledge about the actual environment. A common approach to the assessment of the effects of radiation exposure on non-human biota involves the use of a screening index (SI), where SI is simply a dimen-sionless ratio of the estimated dose rate (to an individual organism) to the reference radiation dose rate. viz.: SI = estimated dose rate reference doserate (I) Table 1. Key elements of a framework for the assessment of the effects of radiation exposure on non"human biota B_", Consiriemrions Exposum of biota

• Spatial arnllOOlporal pati9ITIS of radiooucliOO concentrations in oovironrnootll malorial
• Uptake by organism
• Non-unrtorm di~lribution withm organism RelorlHlCQ biota
• Nol possible 10 IIV3lootll all biota
• NilIId to ~eklcl mfllrOOCe biota or indicalor spocies approprialll fnr aUla of irrtllr9st and oosirablo basis fnr soJoction
• Possi!Jie flOOd to coosidoJ indMdual biota pIlJ so whoo spocios aJIl oodan!J9flld Dosimetry mod9I for (rnfeJ9J'Ce) biota
• Absorbod dose 110 whole body or to lissoo/organ)
• Goometry cormctions
• RoIaliw biologicaleffocliwooss (RBE): the effects of different qualiOOs of radiation on biota Endpoints ill radiological assessment
• SGkiction of appropfiale pop!llation-illvol (determirislicl "umbmlla" Bifocls such as mortalrty or mproducliw capacity and cormsponding millr!lllC9 dosBS Bfocls on biota
• Connoction betwoon radiation offocls on "lrnbmlla-ondpoinl in individual. and consllqoonl"possi!Jie-offocls on population
• Roo of badground radiation Iovels
• Nalural population 't'iIriabilrty

228 UNSCEAR 2008 REPORT: VOLUME II

28. The reference dose rate refers to the chronic dose rate (commonly expressed in milligray per day) below which potential effects on populalions of organisms are not expected. The ratio. SI, assumes that the estimated dose rate and the reference dose rate relal'e to the same endpoint (e.g.

mortality, reproductive capacity). The estimation of dose rate to an individual organism is discussed in seclion I of Ihis annex. As there are many complex factors involved, caution is needed in extrapolating [.rom the effects of radiation expo-sure on an individual organism to those on a population of organisms [817].

29. The reference radiation dose rates for particular end-points developed by the Committee in the UNSCEAR 1996 Report [U4] have been the most commonly used for the denominator of the 51 calculation. However, other guidance has also been developed [CI, EI, E2, F5, 14, NI] and, more recently, the concept of species sensitivity distributions (5SDs) has been introduced [B 17. G3]. These developments may necessitate a re-evaluation of the reference dose rates obtained in the ERA case studies.

30. Because of the sparsity of peer-reviewed literature, all of the various sources of infonnation on reference dose rates (e.g. various reports and supporting environmental assess-ments in Canada, technical reports of government agencies in various countries and conference proceedings) have been considered in this annex.

31. Of the numerous reports [A24, A25. B17, CI, C2, C20, C22, E2, E3, ES, En, E23, F2, G2, G3, 027, 12, SID, 511, 532, S33, U26, WI9], only a few provide studies of the radia-tion exposure of non-human biota arising from radioactive waste management activities or accidents involving dose rates close to or exceeding the reference dose rates [A25. E8, E22]. For exanlple, one study [539] which involved investi-gation of the risks to biota from exposure to ionizing radia-lion from nuclear fuel cycle activities in Canada concluded that the largest risk is associated with past uranium mining activities; that discharges of radioactive material from power reactors under nonnal operating conditions are not expected to cause environmental hann; that organisms within one of the waste management areas examined may be hanned by exposure to ionizing radiation; and that current radioactive discharges from uranium refineries and conversion plants are not expected to cause environmental hann. Similar results can be derived from a consideration of the case studies reported in ERICA [B17] of a wide variety of nuclear fuel cycle and other activities.

32. One study in which the estimated dose rates to biota exceeded the reference dose rates, at least over a limited area, was of the radioactive waste management site at the Chalk River Laboratories (CRL) located on the shore of the Ottawa River, 160 km north-west of Ottawa, Ontario, Canada [E23].

The CRL site was established in the mid-l94Os and has a his-tory of various nuclear operations and facilities, primarily related to research. An ERA was conducted to assess the doses to biota arising from elevated levels of tritium, 1-1(:, ~I Ar, 'lOSr, III I, 117CS and 2J9Pu and [rom radionuclides that are naturally present in the environment, for example, the ura-nium series radionuclides, using standard methods for evalu-ating the uptake of these radionuclides by biota from the affected aquatic and terrestrial environments [B 12]. A refer-ence dose rate of I mGy/d was used for all organisms [B36]. Dose rates to some aquatic organisms such as frogs, small fish, snails and aquatic plants within the on-site waste man-agement areas were estimated to be above the reference dose rate of I mOy/d; however, outside of the actual waste man-agement areas, dose rates were estimated to be below the ref-erence dose rate. The main contributor to the estimated dose rales to invertebrates and terrestrial plants was IlI.lSr in surface soil, while that 10 the woodchuck (estimated al 51 mOy/d) was inhalation in Ihe burrow of m Rn decay products from background levels of 116Ra in the soil. A few individual inver-tebrates and terrestrial plants actually within the confines of small on-site waste management facilities were also esti-mated to have been subjected 10 dose rates above I mOy/d. Based on the limited spatial extent of the estimated dose rates that exceeded the reference dose rate and environmental observations, the authors considered that significant effects at the population level were unlikely.

33. Much of the new infonnation on the effects of exposure to ionizing radiation on organisms has arisen from studies in the area surrounding Ihe site of the Chernobyl accident.

where dose rates to organisms were above the reference dose rate suggested in the UNSCEAR 1996 Report [U4]. A sum-mary of the results of these studies up 10 1996 is provided in this annex. Section III of this annex provides a comprehen-sive review of the more recent data from studies of non-human biota in the area surrounding the site of the Chernobyl accident. E. Structure of this annex

34. The prime purpose of Ihis annex is to build on the infonnation reported in Ihe UNSCEAR 1996 Report [U4];

to compile data that has since become available on the effects of exposure 10 ionizing radiation on non-human biota; and to determine if the reference dose rates need to be updated. However, it is necessary first to provide some gen-eral information on the relationships between the levels of radiation in the environment in which the biota live and the consequent dose (or dose rate) to biota as a whole or selected tissues and organs. Table I provides a summary of five key elements that form the basis for assessing the effects of exposure Lo ionizing radiation on non-human biota.

35. The relationships between the levels of radiation expo-sure and the activity concentration of radioactive material in the environment and the dose to an organism living in that environment is the subject of section I.

36. Section n provides a summary of the infonnation con-sidered in the UNSCEAR 1996 Report [U4] and the key observations from that report.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 229

37. Section m provides an overview of Ihe findings of the studies of non-human biota in the area surrounding the site of the Chernobyl accident. It includes the work of the Chernobyl Forum [E8].

38. Section IV provides a sununary of the effects of exposure to ionizing radiation on non-human biota derived from the material given in earlier sections and reviews carried out by other scientific organizations and groups, namely, the IAEA [14], Bird et al. [BIJ, the DOE [JI, U261, Environment Canada and Health Canada [E2J, Canada's former Advisory Committee on Radiological Protection (ACRP) [All. the UK Environment Agency

[CIJ, the FASSET group [FI, F5, Ll, IAJ, and the ERICA group [EI, GIl, G151. The published literature was also reviewed.

39. Section V provides an overall summary of the data reviewed and, based on these data, the Committee's evalua-tion of the dose rates below which effects on non-human biota are not considered likely. A few important areas for potential future study are also noted.

I. ESTIMATING DOSES TO NON-HUMAN BIOTA

40. Data on the effects of radiation exposure on non-human biota have been obtained from experimental studies carried out in the laboratory and in the field. Additional data have been obtained from the results of studies on environments with elevated levels of radiation or of radioactive material resuJting from nonnal operations of nuclear facilities, waste management activities, or accidents. The interpretation of the results of these studies requires an understanding of the relationship between the levels of radiation and the activity concentrations of radionuclides in the various environmental media in which the organism resides, the consequent dose rate to an organism (or a tissue or organ of the organism) that lives in the environment, and the biological effect of interest.

For example, radionuclides in the ambient environment may lead to external irradiation and internal irradiation as a result of radionuclides being taken into the organism via inhala-tion, ingestion, or uptake through its skin or membrane. Empirically detennined concentration factors and transfer factors are commonly used to estimate contaminant concen-trations in the organism (e.g. expressed for wet or dry weight in units of Bqlkg) from concenlrations in the ambient envi-ronment (e.g. expressed in units of Bqlkg for sediment or soil, or BqlL for water). Dosimetric models can then be used to derive, for selected organisms, dose conversion coeffi - cients (DCCs) that relate ambient concenlrations to internal or external exposure, as appropriate, and hence to dose. A. Assessing exposures of biota

1.

Choice of reference organisms

41. In view of the enonnous variety of living organisms, it would be impossible to consider all species of flora and fauna as part of an environmental impact assessment even for a limited area. Instead, a concept has been developed involving the selection of reference organisms that are repre-sentative of large components of common ecosystems and for which models are adopted for the purpose of deriving doses and dose rates to organisms, tissues, or organs from radionuclides in the environment. The results of such dose assessments for these predefined reference organisms will allow a basic assessment to be made concerning the possible biological effects. This approach provides a strategy that allows the modelling effort to be reduced to a manageable level. It further provides infonnation on the exposures of dif-ferent organisms under varying exposure conditions, which allows the estimation of the impacts on those components of the environment for which data may be sparse or absent.

42. The reference organism approach of the ICRP had its genesis in some earlier publications [P6, P13j. In the frame-work of the FASSET project [F20, lAJ. reference organisms were defined as "a series of entities that provide a basis for the estimation of radiation dose rate". The idea was that these organisms would provide a basis for assessing the doses to organisms and consequential effects in general due to radio-nuclides in the environment. The main criterion for the selec-tion of reference organisms within the FASSET project was that the habitats and feeding habits should be such that the external and internal exposures are maximized.

43. The ICRPis assembling databases that relate to a limited number of "reference animals and plants". These are defined as "hypothetical entities with the assumed basic characteristics of a specific type of animal or plant, as described to the gener-ality of the taxonomic level of family, with defined anatomi-cal, physiological. and life-history properties that can be used for the purposes of relating exposure to dose, and dose to effects, for that type of living organism" [l12J.

44. Both the FASSET and the ICRP approaches were intended to simplify the process of estimation and evaluation of exposures to ionizing radiation of non-human biota.

Whereas reference organisms in FASSET were specifically selected for different ecosystems (e.g. agricultural, semi-natural, freshwater, and marine), ICRP [1101 described the reference animals and plants in groups (family or taxonomic level). The reference organisms selected cover a range of eco-systems and taxonomic families (table 2). The generic (refer-ence) organisms that are explicitly considered in this annex are summarized in table 2. Organisms similar to those adopted by the leRP were selected for consistency. The features of the selected organisms are described in reference [II OJ.

UNSCEAR 2008 REPORT: VOLUME II Table 2. Comparison of reference organisms defined by different international bodies Defined by fASSET TerrostJial ocosystGms [lll fASSET Aquatic OCosystllfllS [lll ICAP Proposal on A%ronco Animals and Plants [1101 This anno~

2.

RadioecologiclIl models

45. Three classes of radioecological model can be distin-guished and are presented here in tenns of increasing COffi-plexity---equilibrium models, dynamic models and research models.

Refoo!flCfl organism:; Soil mK:roorganisms Soil invoit9bratos Plants and fufl!Ji ",,_M Grassos. horbs afld craps Shrubs Abovo grlMld invDrtebrato Burrowing mammal Hmbivorous mammals CamNOfOUs mammals Aeptile Vortobrato 999s Amphibians Birds Troos Banlhic bactllfia 8anlhic invortobratos Molluscs Cruslacoans Vascular plants Amphibians Fish fish oggs Wading birds Sea mammals Phytoplan(ton ZoopIan(ton Macroalgaa 0_ fIot Doc' IT", r,rut Flatfish 800 Crnb EartlrNorm Pino lreo Wdd grass Brown soowood Earthwoml/so ~ inv9rlobrato flatftmrrowing mammal 8ooIabovo ground invilflobrato Wild grass/grasses. ItGrbs and crops Pino troo/hoo Ooor~orbivorous mammal O!.cl;ftJird frog/amphibian Brown soowood/macHlalgao Trwl/pOOgic fish Flatlislvbonlhic fish Crab/crustaceans

46. Equilibrium models are primarily intended for the assessment of exposures due to routine discharges of radio-active material into air or water. They are based on two funda-mental assumptions: (a) theemission rates of the radionuclides are constant in time; and (b) the duration of the discharges is long compared to the time needed for radionuclide transfer

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 231 along the environmental pathways considered. With these assumptions, the radionuclide concentrations reach equilib-rium within each of the compartments into which the environ-ment is subdivided for modelling purposes, and the transfcrs between compartments are easily characterized by time-invariant ratios of concentrations between the acceptor and donor compartments.

47. Since equilibrium radionucLide concentrations in the environment are typically attained after considerably long operational times of a nuclear faci lity, the equilibrium models are likely to give conservative exposure estimates.

This type of radioecological mooel has been used to deter-mine compliance of routine discharges from nuclear facilities with authorized limits [H4, Ill, N3, U3].

48. Ciffroy et al. [C22] tested the influence of the time-dependence assumption frequently uscd in radioecological mooels in a case study conducted on the Loire River in France. For routine discharges of radionuclides from nuclear power plants, their main conclusions were that:

(a) attention must be paid to the temporal variations in the discharges, and gaps between actual instantaneous dis-charges and maximum discharges on a yearly time scale must be analysed; (b) the equilibrium assumption at the water-suspended matter interface must be justified and eventually corrected when equilibrium conditions are not expected; and (c) for organisms showing slow uptake/elim-ination rates, a kinetic approach to the bioaccumulation process can avoid some overestimation of radionuclide concentrations. The assumption of equilibrium led to over-estimations of one to two orders of magnitude in predicting 6OCO concentrations in invertebrates.

49. A number of inherent advantages have contributed to the proliferation of equilibrium models. The model structure can be kept simple, but there is flexibility to allow more detailed structure, if necessary. Under equilibrium condi-tions, dispersion of trace amounts of radionuclides in the atmosphere or rivers is adequately represented by analytical solutions of more general physical mooels; transfer via food chains is represented by simple multiplicative chains of concentration ratios.

50. A major conceptual limitation of radioecological models is that many of thc parameters involved (e.g. con-centration ratios) have to be established empirically.

Expcrience gained during recent decades has amply dem-onstrated that numerical values of many of these parame-ters may vary by several orders of magnitude; this has been well documented, for example, for plant-soil rela-tionships of radiocaesium and radiostrontium concentra-tions IF7, F8, N4]. While for the purposes of screening or environmental protection as rna y be established by the ICRP or required by a national regulator, representative parameter values can be selected that ensure that the model assessments are conservative, obvious difficultics exist if a realistic assessment of exposures in specific ecosystems is necded.

51. Dynamic radioecological modcls [M4, 513, W3] are applied if the time dependence of exposures that result from varying or instantaneous releases has to be taken into account. Examples of thcir use include the assessment of the time-dependent radionuclide concentrations in the envi-ronment, such as those resulting from accidental radio-nuclide releases varying over time, and the simulation of seasonal effects, which are of major importance in terres-trial environments during the first year following deposition of radionuclides after an accidental release IM7].

52. Research models are characterized by a high dcgrec of complexity and longer computation times, and presently are limited to simulating a few of the important processes in analyses of environmental pathways for radionuclidcs IC7, P9]. Currently, therefore, they do not offer an alternative to equilibrium and dynamic radioccological mooels for envi-ronmental assessments, although they do constitute an important tool for improving understanding of the sources of variability observed empirically.

53. The scope of this annex is limited to providing a broad overview of the approach to estimating radiation exposure and subsequent doses to non-human biota. The reader inter-ested in these topics is referred to the extensive literature.

Exposure assessments are generally based on equilibrium models. However, for case studies at specific locations con-taminated by accidental releases of radionuclides, informa-tion on the levels of exposure of local biota taken from the literature is sometimes based on simulations using dynamic radioecological models.

3.

Transfer of radionuclides in the environment and resulting exposures

54. The major pathways of radiation exposure of bioia in the environment are summarized in figure n. In this schematic representation, the physical components of the terrestrial environment are air, soil and sediment; the biological components include plants, invertebratcs, and vertebrates (mammals. birds. reptiles, and land-based amphibians). The physical components of the freshwater aquatic environment include streams, rivers, lakes and sediments; the biological components are phytoplankton, zooplankton, macroinvertebrates, sessile aquatic plants and vertebrates (fi sh, water-based amphibians and some aquatic mammals). In a marine environment, the physical componenls include tidal zones, coastal waters and marine sediments; and the biological components include phytoplankton, zooplankton, macroinvertebrates, sessile aquatic plants, and vertcbrates (fish and marine mam-mals), molluscs, crustaceans and marine birds. The ter-restrial and aquatic environments are not totally separate.

Some birds and terrestrial mammals eat fish and shell-fish; moose and waterfowl feed on aquatic plants; and terrestrial animals ingest drinking water from the aquatic environment.

232 UNSCEAR 2008 REPORT: VOLUME II Figure II. Major environmental transfer routes for evaluating radiation exposure of biota I Activity in air and rain Activity in water/sediment I '\\ ----

---

-;/

I Plants Soil/sediment I ~/ Biota External Internal External exposure exposure exposure I Radiation exposure of biota I

55. The total radiation dose received by an organism (or some organ or tissue of the organism) is the sum of the con-tributions from both external and internal exposure. External exposure results from complex non-linear interactions of various factors, such as the levels of the radionuclides in the habitat, the geometrical relationships between the radiation source and the target, the shielding properties of the materi-als in the environment, the size of the organism and the radionuclide-specific decay properties (characterized by the type and energy of the radiations emitted and their emission probabilities).

56. Internal exposure is detennined by the activity concen-trations of the radionuclides in the organism, the size of the organism, the radionuclide distributions within the organism and the specific decay properties of the radionuclides. In addition, the relative biological effectivenesses (RBE) of alpha, beta and gamma radiation need to be taken into account in assessing the consequences of the exposure.

B. Transfer of radionuclides in the terrestrial environment

57. Radioactive material released into the atmosphere is dispersed and transported by the wind. Exposures of biota are calculated from the activity concentrations of radionuclides in the environmental media, such as air, soils and vegetation, and in the organisms under consid-eration. The principal processes involved in the transport of radionuclides in the terrestrial environment i.nclude dry deposition, wet deposition, interception by vegeta-tion, loss of radionuclides from plants due to weathering.

resuspension, the systemic transport of radionuclides within plants, uptake from soil, run-off to water bodies and the transfer to animals. This section discusses the factors that affect the behaviour of radionuclides in a ter-restrial environment and the uptake of radionuclides from thc environment to plants and animals.

1.

Dry deposition

58. Dry deposition per unit time is proportional to the near-surface concentration of the material in air. Usually, the dry deposition of a radionuclide from the atmosphere to soil and vegetation is expressed in tenns of the deposition velocity, v! (m/s), which is defined as the ratio of the activity deposi-tion rate per unit area and the local activity concenlration in air of the radionuclide at a reference height. This empirical quantity depends on a variety of factors such as the size of any associated particles, the characteristics of the surface-air interface. the meteorological conditions and the chemical fonn of the radionuclidc.

59. Typical estimates of deposition velocities for grass and forests are summarized in table 3. These values are used for the calculation of the exposures of biota resulting from the atmosphcric release of radionuclides.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 233 Table 3. Tvpical estimates of deposition velocities for grass and forest [P14, Rll] Chemical/physical form G,= Particles. OJ-l pm 0.001 Bemllnlal iodine 0.01 Methyl iodide 0.000 1 a Coriterous lroos 300 deciduous lroos with lulfy dlr-ialoped foIiago.

2.

Interception of rlldionuclides deposited from the lIir

60. Interception defines the fraction of radioactivity depos-ited by wet and dry deposition processes that is initially retained by the plant. There are several possible ways to quantify the interception of deposited radionuclides. The simplest is the interception fraction,f, which is defined as the ratio of the activity initially retained by the standing vegeta-tion, AI. immediately subsequent to the deposition event to the total activily deposited. A full description of the intercep-tion process is beyond the scope of this annex and the reader interested in this topic is referred to the extensive literature (e.g. see reference [H26]).

61. Radioactive material in air can be washed out by rain and snow. A fraction of the radionuclides deposited with precipitation is retained by the vegetation, and the rest falls through the canopy to the ground. Although the radioactive material retained eventually transfers to soil through weathering and is retained only temporarily by vegetation. the fraction initially intercepted is important owing to the fact that the concentration of radioactive material will be at its highest at Ihis time. Interception of wet deposits is the result of a complex interaction of the amount of rainfall. the chemical and physical form of the deposit and the actual stage of development of the plant

[M4] and thus, interception fractions for a single event may vary from 0 to I.

62. To account for its dependence on biomass in some models, the interception of wet deposited activity is model-led as a function of the biomass density, according to the approach of Chamberlain [C8]. The chemical fonn is a key factor; since the plant surface is negatively charged. the absorption of anions is less effective than that of cations [H6, H7, K4, M4, PI I). Differences between plants seem Lo be of minor importance compared to those between radionuclides, e.g. (he interception of polyvalent cations is higher than that for anions by as much as a faclor of 8 [H5]. However, in general, for the estimation of interception following the rou-tine discharge of radioactive material, very simple approaches are used in the models [FlO). Anspaugh [A22] suggested a default value for the interception f:raction of the order of 0.3 for all elements, plants and precipitation events for routine discharges of radionuclides.

Depo.sifion velocity Im/s) Fm"" c-T"",* Soil 0.005 O.!lOO 5 OJXXl8--0JXJ3 0.05 0.005 0.00&----0.02 0.000 5 0.00005 0.000 OB----O.OOO 3

3.

Weathering

63.

Following deposition on vegetation. radionuclides are removed by wind and rain. In addition, the increase of biomass during growth leads to a reduction in the activity concentration. Since growth is subject to seasonal variations, the post-deposition reduction of the activity concentration of radio-nuclides in plants depends on the season. These processes of reduction in the activity concentration of radionuclides in plants occur simultaneously after deposition. As it is difficult to quan-tify the exact contribution of each process, the net reduction in the activity concentration with time is usually called weather-ing" and expressed by the empirical weathering half-time, T",.

64. The chemical fonn of the contaminant seems to be of minor importance in weathering. After the Chemobyl acci-dent, the median weathering half-times observed for iodine and caesium on grass were approximately 8 and 10 days.

respectively [KS]. Shorter half-times were observed prima-rily in regions with fast growing vegetation, while longer half-times were found in Scandinavia, where the growth rates were lower because of the later spring in the area [KS ]. In general, longer weathering half-times are observed for slowly growing or donnan! vegetation [M8].

65. In forests, weathering is more complex because of the canopy structure, which comprises several vegetation lay-ers, such as crown, trunk and understorey vegetation. Radio-nuclides lost from the crown may be retained by the understorey vegetation, thus reducing the overall loss rate of radionuclides from vegetation to soil.

4.

Distribution of radionuclides within plants

66. The currently available dosimetric models for the assessment of the exposure of bioLa do not take into account heterogeneous radionuclide distributions within plants.

Hence, any information on these distributions cannot currently be used in the assessment.

5.

Uptllke of radionuclides from soil

67.

Soil is the main reselVOir for long-lived radionuclides depos-ited on terrestrial ecosystems. lbe behaviour of radionudides in

234 UNSCEAR 2008 REPORT: VOLUME II soils controls their migration in soil, the possible transport to groundwater, and the long-tenn radionuclide concentration in vegetation and thus the exposure of soil organisms. As for all minerals. the uptake of radionuclides by planls mainly takes place via dissolution from soil. The concentration of radio-nuclides in soil solutions is the result of complex physical-chemical interactions with the soil matrix, with ion exchange being the dominant mechanism. [on exchange by its very nature is a competitive mechanism. The concentrations and composition of the major competing elements present in soil thus are of primary importance in dctennining the distribution of radionuclides between soil, soil solution and plant roots (which are able to influence the microspace in their vicinity in order to provide and maintain conditions that favour the uptake of nutrients) fE6}. 6S. The physical chemistry of sorption and desorption of radionuclides in the soil-soil solution system and their pos-sible uptake by plants are the result of complex interactions between soil type, pH, redox potential, sorption capacity, clay content, content of organic matter and soil manage-ment practice. Although these factors are qualitatively known, they are difficult either to quantify or to integrate into a universal model applicable to a wide range of soil conditions. Consequently, the approaches used include classifying the transfer according to soil types (e.g. peat, sand, loam and clay) and other physical and chemical parameters. In addition, various biological factors should be considered, especially whether or not the radionuclide is an essential element.

69. For the quantification of the root uptake of radio-nuclides, empirically derived (aggregated and greatly simpli-fied) parameters--soil-plant transfer factors or concentration Table 4.

Typical ranges of soiJ-plant transfer factors [Ttt] ratios--are usually applied despite their inherent limitations [E6]. In this case, these parameters are the ratios of the activity concentrations in the plant to those in the soil within the uppermost layer of a standardized thickness. Transfer factors were originally defined for agricultural ecosystems within which radionuclides are distributed homogeneously within the rooting depth of agricultural plants because of ploughing.

70. The aggregated transfer factor is defined as the activity concentration of a radionuclide in a material (Bqlkg) divided by the tolal deposition-activity per unit area (8 qJml)-at equilibrium. The concept of aggregated transfer factors was developed as a simplification of detailed physical and chemi-cal processes to a single value, inter alia, to avoid difficulties with detennining radionuclide concentrations in soi.ls with a multi-layered structure, such as in forests.

71. AJternatively, concentration ratios that relate to the activity concentrations of radionuclides in specific soil hori-zons exploited by the mycelium or the root system were pro-posed in the late 1980s and proved to be useful, especially in connection with the prediction of the transfer of mCs to fungi [04, RS, YI, Y4, Y5].

72. lIlustrative ranges of soil-plant transfer factors for a number of elements are summarized in table 4 [fIll. This table shows that the uptake of caesium from soil usually does not result in a simple proportional accumulation in plants. Radiocaesium is effectively sorbed by micaceous clay minerals that are present in almost all soils in varying amounts. A detailed compilation of soil-plant transfer fac-tors including data for specific plant groups, plant organs and soil types can be found elsewhere [114].

Ekm",' COOCflntratioo ratio Aggregated transfer factrJll Bq/kg plam: Id.m.) per Bq/kg soilld.m.} 8q/kg plant (d.m.) per 8q/m' wil S, 0.01-1 4 x Ht'--4 x to-' C, 0.001---0.1 4 x W' --4 x 10--' c,/> 0.1-10 4 x 10--'--4 x Ht' I 0.001-1 4x 10'-4 x lfr3 T, 0.1-10 4 x lQ--'-4 x 10"' I'b O.lXl1---O.01 4 x 10'--4 x 10-' 0.001---0.1 4 x 10'--4 x 10--' U 0.001---0.1 4 x 10'--4 x 10--' Np 0.001---0.' 4 x 10'--4 x 10--' 10"'-10-' 4 x 10-<-4 x 10' Am 1!J-'-lo-' 4 x 10-<-4 x 10' em 10-'- 10-' 4 x 10-'--4 x 10' a CaWatGd from tho COflCQntration ratio assllITlirg II mass dllflSily f()f dry mattlll (dml in tho soil rooting 1000 of 280 kg/rn' takiog ilCcoont (}f tho mass of 1110 soil within tho rooting 10110. b Qbsorwd rllngo in nalll"al lind somi-naturalocosystoms OIl acid sandy soils poor in potassium.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 235

73. Caesium uptake is particularly high from organic soils with a low pH and pronounced potassium deficits [FI I}.

Such soils are frequently found in the Russian Federation, Belarus and Ukraine, as well as in Scandinavia, the upland areas of the UK and the alpine areas of Europe. For organic maUer, the cation exchange capaci ty decreases with increas-ing acidity owing to the saturation of carboxyl groups with hydrogen ions. Furthennore, the availability of caesium for uptake is enhanced in soils that are poor in potassium. Addi-tionally, the clay content of organic soils is low and this pre-vents strong sorption and leads to persistently high caesium levels in plants [A 7, F12, F13, K6].Another important aspect is that the bioavailability of radionuclides and their uptake after deposition may change with time. This was observed in areas close to the site of the Chemobyl accident and was caused by the degradation of fuel particles, the fixation of caesium within the soil and changes in the sorption strength of the soil for caesium [N5, 514, SIS}.

74. In recent years, a number of experiments have been perfonned to detennine soil-plant transfer factors for tropi-cal and subtropical environments [C9, FII, R6. T 12, T13.

U24, U25, W 12, W 13}. The anaerobic soil condilions in flooded paddy fields change the solubility of some elements, such as I and Tc, and thus possibly their soil-plant transfer factors [M25, 1'26, Y3]. In general, however, the results do not indicate any systemalic impact of climatic conditions on the transfer of radionuclides from soil to plants, although the numbers of data are still small. Further data on the tropical and subtropical environments are therefore needed [M25}.

75.

In forest ecosystems, the transfer of radionuclides from soil 10 plants and fungal fruit bodies depends on the depth profile of the radionuclides and the vertical dislribution of fine roots and fungal mycelia in soil. At least in the case of fungi, the use of transfer factors referring explicitly to the soil layer exploited by fungal mycelia seems to be the best approach for quantifying the uptake to radionuclidcs, balancing overall simplicity with mechanistic considerations of the dynamic processes [537]. However. the concentrations of radionuclides in understorey vegetation, trees and fungal fruit bodies can be eSlimated roughly in a simplified manner using aggregated transfer factors. The ranges of aggregated transfer factors given in table 5 summarize the available observations. Table 5. Typical ranges of aggregated transfer factors for 1l1Cs from soil to vegetation and fungal fruit bodies in forest ecosystems [A8. 827. G7. 116. 117. K15. 17. Z11 Data are given on a dry weight basis unless otherwise noted Species (X genus TF. (&ilkg organism (d.m.) per Bqlm' soil) Fungal lmit bodies Agaocus 0.002--{).007 0008-> A1rniHaria 0.001 --{).2 Boletus 0.001-10 Canthamnus 0_01-2 CI~ocybe 0.01-2 Collybia 0.03----0.3 Copnnus O.OO4a Cortinarius 0.02-10 fly","m 3' Hygrophcrus 0.2-7 laccaria 0.4-10 taclarius 0006-> loccirum O.OO!>----O.!I 19pista 0.002<1 Lycopordon 0.0W----0.5 Macrolopiota 0.OOO 7--{).1 Paxinus 0.01-5 0.05-{).6 Aolit9s 0.06---10 Russula 0.04-5 0.3----0.4 SuiUus 0.02-2 Tubor 0.000 3----O.00eb Xeroctlmus 0.002-7

236 UNSCEAR 2008 REPORT: VOLUME II Species or genus TF.,.IHqlkg organism (d.m.) per EkJlm' soil} Undl!fstorey vl!Qlllalion Rubull chamaemoros IcJoudboovl. fruit VaccitOOm vitis-idaea IliflQOfiJoovl. fruit Vaccmium myrtiHus (biloony). trw Rubus idaeus Iraspbooyl. fruit Fragaria vesca Istrnwbonyl. fruit Rubu:: frutico.sus Iblackbeny). fruit Groon parts of l.fldorstorny vagetation. iflcltJdirlg the stems of booy plants Fagus sp. (hooch) Bolo wood

Loow, Picea sp. lsprl£9)

Bolli wood Nood~s Pinus:;p. (piool Bolo wood Noodles Duerr= sp. (oak) "'.wood

Loow, Betula lip. (birchl

"'.wood

Loow, f'opIJus sp. laspoo)

Bolo wood

Loow, Alnus sp. (aloor)

Bolo wood

Loow, if Onty if singlo valoo availatJIo.

b Data am giviln on if frosh wllight basis and rofGr to tho t()Jll0 em of soil.

76. Fungi are able 10 accumulate radiocaesium in their fruit bodies [014. H8]. Some species exhibit activity levels that exceed those of green plants by more than one order of magnitude. On average, the radiocaesium levels in symbi-otic fungi are higher than those in saprophytic species [R7, Y4, Y5].

77. Radionuclides in growing wood ongrnate from two sources: the initial atmospheric deposits that enler the plant by foliar absorption, and root uptake from the soil. Their relative contributions depend on the type of tree (coniferous versus deciduous) and the age IB20, E7, G5, H9], the season at the lime of deposition and the time elapsed after deposi-tion, with root uptake being the dominant pathway for grow-ing wood in the long tenn. Transfer factors or concentration ratios that are calculated on the basis of the total content of radionuclides in wood inevitably include both uptake pro-cesses and therefore are likely to overestimate root uptake (table 5) [G5].

Trees O.OO2-{L2 O.O3--{).O7 Om--{)l 0.001--0.004 O.OO4---{JOl 0.00S--0.05 0.001-1 0.001--0.002 0.002--0.003 0.000 3--0.002 0.000 6--0.02 0.000 2--{1m3 D.OO1 -{Ul4 0.002--0.004 0.006--0.01 0.000 03--0.001 0.000 3--0.04 0000 5-0.002 0."'" 0.001 11 0."'"

6.

Migration in soil

78. Vertical migration of radionuclides in the soil column is driven by various transport mechanisms. such as convec-tion, dispersion, diffusion and bioturbation. The long-tenn consequences of downward migration differ considerably, however, depending on the dominant mechanism. For convective-driven migralion, for example, the radionuclide input due to the Chemobyl accident moves down the soil as a marked peak and shows broadening with time as a result of dispersive mixing. Convective transport of radionuclides usually dominates in soils showing high hydraulic conduc-tivities, e.g. sandy soils. For further discussion of the impor-tance of downward migration of radionuclides in soil and forest litters, see section m and the references cited.

79.

For diffusive transport, the concentration is always at a maximum at the surface with a close to exponential decrease with depth. For this type of transport, which is typical in

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 237 soils of low hydraulic conductivity, the bulk of the radio-nuclides deposited from the atmosphere thus remains within the rooting zone of plants.

80. Agricultural practices have a major impact on radio-nuclide behaviour. Depending on the intensity and type of soil cultivation, mechanical redistribution of radionuclides may occur. This causes, in arable soils, a rather unifonn dis-tribution of radionuclides in the tilled horizon. Fertilization shifts the ratio of radionuclide to nutrient concentrations in soil and soil solution and thus may influence plant root uptake of the radionuclides rE6J.

81. Some investigations indicate IB21, SI6J that element-independent transport mechanisms, such as the transport of radionuclides attached to clay particles or soil colloids, may playa relevant role in detennining the migration rate of radio-nuclides in soil. Furthennore. the activity of soil animals that cause a turnover of soil, e.g. earthwonns. cannot be neglected.

The authors of references IB21. S 16J suggest that a value of 100 years for the default residence half-time for the upper 25 cm layer is adequate for all elements with low mobility, such as radium, lead, uranium, plutonium and americium. Iodine under aerobic conditions is strongly bound to organic matter and therefore a residence half-time of 100 years can also be assumed fK7J. On the other hand, iodine can be released from soil to soil solution Uflder anaerobic conditions. such as in a flooded paddy field [M25].

82. The situation with forest soil is more complex owing to the more pronounced soil horizons. Radionuclides deposited directly onto forest soil or washed from the canopy and understorey vegetation initially infiltrate the soil rather rap-idly. They are therefore initially assigned to a labile pool. In the long term, they will become immobilized through fungal or microbial activity or by mineral constituents of the soil.

The radionucHdes in the non-labile pool may be available for root uptake, e.g. via symbiotic fungi, bui are assumed not io be leached to deeper soil layers. The rate of downward migra-tion is correspondingly reduced considerably over time, and, in the organic horizons, is detennined mainly by the rates of decomposition of the organic material, and litter accumula-tion. Subsequently. downward migration of radionuclides is rather slow and partially offset by upward translocation by fungal mycelia and roots [R4]. Fungal and microbiological activity is likely 10 contribute substantially to the long-tenn retention of radionuclides, notably radiocaesium, in organic layers of forest soil. In this phase, radiocaesium is well mixed and almost equilibrated with stable caesium within the bio-logically connected compartments [Y6]. When radionuclides reach the mineral horizons of forest soil, essentially the same processes may occur as in arable soils, e.g. radiocaesium can be fixed by micaceous clay minerals.

7.

Resuspension

83. Resuspension refers to the removal of deposited mate-rial from the ground to atmosphere as a result of wind, traffic.

soil cultivation and other activities. Potentially, resuspension is a persistent source of radionuclides in air subsequent to their deposition on the ground. Furthennore, it may lead to redistribution of radionuclides and their deposition onto clean surfaces. Resuspension is influenced by a variety of factors, such as the time since deposition, meteorological conditions, surface characteristics and human activities. For biota, resus-pension is of low importance. For animals living in the soil, it is not relevant. The contribution of resuspension to the activ-ity concentration of radionuclides in plants in humid eco-systems usually is negligible compared to that of dry deposition and interception [06, H 10].

8.

Transfer to animals

84. The transfer of radionuclides to animals is usually estimated using element-dependent concentration ratios or transfer factors. The transfer factor is defined either as the ratio of the activity concentration in an organism or tissue and the intake rate under equilibrium conditions, or as the ratio of the activity concentration in an organism or tissue and the deposition density (activity per unit area). It is only applicable to an intake of a radionuclide by adult ani-mals that is constant over long periods. To account for lime-dependent (dynamic) intakes, one or more biological half-lives are considered [M4].

85. In recent decades, many data have been accumulated on the transfer factors for domestic animals. They depend on animal mass, perfom13nce level, feeding regimes and feed components. However, these data are not generally applica-ble to estimating activity concentrations in biota, since they were detennined in order to estimate activity concentrations in animal products for human food (such as meat, milk and eggs) while this annex is concerned with the estimation of activity concentrations in whole animals. Furthennore, the application of transfer factors presumes knowledge of the feed intake as well as the activity concentrations of the feed components. It has been demonstrated that highly contami-nated feed components may detennine the activity levels of game, even if consumed in low quantities. The seasonal peak activity concentration of IJ7CS in roe deer, for example, has been attributed to the ingestion of mushrooms IZI]. Fungal fruit bodies can show radiocaesium levels exceeding those of green plants by one order of magnitude or more. Wild boar ingest deer truffle (Elaphomyces gmnulatus), a pre-ferred "delicacy", which dominates theradiocacsium uptake.

despite being only a few percent of the boar's total diet [FI4, P12]. However, the relevant data are not avai.lable for wild animals in general.

86. In most cases, the activity concentrations of radio-nuclides in game are calculated in a simplified manner using aggregated transfer factors. This transfer factor neither takes into account the time-dependent intake rates nor can repro-duce the time-dependent activity concentrations in game.

Values for aggregated transfer factors for different species are compiled in table 6.

238 UNSCEAR 2008 REPORT: VOLUME II Table 6. Aggregated transfer factors (soil-ta-game) for mCs [A9, 116, J3, K8, S19, ZtJ Data tire given on H fresh mass oosis unless otherwise noted S""",", TF... (aq/kg organism (dry mass) per Bq/m' Wll (dry mass)} Default ViJlIJe Range of literature data Aices am (moose) Caproo/us caprooius (roo door) CefVIJS elaphus (rnd door) Lepus arr:ticus (arctic nam) lepus capensis (brown harol Lj'TIX lynx (lynx) Garno 9XCopt roo door il Data am givtln 00 a dry woight tJasis_

87. Table 7 summarizes the equilibrium concentration ratios for the reference organisms considered. The values are "order-oF-magnitude" estimates based on the compilation in reference [F4}. Some of the original values were given as aggregated transfcr factors and have been converted to con-centration ralios. At least in temperate environments, con-centration ratios are higher in forest and semi-natural ecosystems than in agricultural systems, because of their often lower nutrient supply and pH values. Furthennore, the high content of organic matter in forests is accompanied by high concentrations of fulvic and bumic acids, which act as AM 0.05 003 OOJ 0.004 0.3 002 OJXJ6--O.03 O.OOl-m 0_02--0_04 O.OOS--O.l OJXl2--O.05 O.Ol - 1()ii complexing agents and increase the mobility of cationic radionuclides in soil.

88. The nominal values of transfer factors provided ill table 7 have been suggested for use [E 10, F4 J. in the absence of site-specific infonnation, to estimate the exposure rates for biota after the release of radionuclides to atmosphere and their subsequent transfer to soil. As such, these transfer factors were intended to be applied for screening purposes to obtain an order of magnitude estimate, but they may not be appropriate for application to specific sites.

Table 7. Nominal values of transfer factors for reference organisms (adapted from [El0, F4]) EO_ Transfor factor.; (Bq/kg {fresh weight} per Bqfkg svil} H ISO ISO 150 0 01 7 7 S, 0.01 1 1 7, O' O' 0.' 1 01 O' 0.' C, 009 3 3 Np 0.1 0.04 0.04 om 0_02 0.02 Am 0.1 0~04 0.04 Ph OOJ 0.04 0.04 0.09 O~OJ O.OJ Th 0009 0.000 1 O.IXXII U 0.009 0.000 1 0000 1 C. Transfer to freshwater organisms

89. Radionuclides can enter water txxlies as a result of dis-charges to the aquatic environment (e.g. directly from a nuclear facility), by deposition of airborne radioactive mate-rial onto the water surface and by run-off of material 150 7

06 O' 04 08 004 0.02 004 006 004 0.1XXI4 0.000 5 hog Boo G,= Pirlf!uf!fJ ISO 150 150 150 7 0.3 10 1 1 006 01 0.5 O' O' 10 0.3 O' 0.3 0.1 0.1 0.6 006 07 01 004 0.1 om 0.3 om 0.06 om O.OJ 0.04 0.1 0.005 0.000 1 0.1 006 0.07 000 0.04 0.04 0.04 0.000 7 0.000 4 0.009 0.04 0.001 0.000 5 0009 0.02 0.007 deposited onto soil. For a point source of emission into a swiftly Howing stream. the flow rate of the stream can be divided by the flow rate of the effluent discharge to obtain the dilution factor. A certain mixing distance must be assumed, which could vary from a few tens of metres for a small stream to a few kilometres for a large river. Beyond the

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 239 mixing distance, a unifonn concentration of the radionuclide in water can be assumed. Suspended material may be depos-ited as sediment. The deposited material may become locked in the sediments and, over time, migrate to deeper sediments or be redissolved by physical and biological processes and re-enter the water column. Dissolved or finely suspended material may be transported over large distances, being pro-gressively diluted by water from other slreams and rivers, eventually reaching the oceans.

90. The movement of radionuclides in rivers is often model-led using the diffusion-lransport equation and the behaviour of radionuclides in the "water column-river bed sediment" system is often assessed using compartment models [M23].

At present, although the structures of the models have not been subjected to significant revisions, the scope of the trans-fers modelled (physical, chemical and biological) and of the associated radionuclide specific parameters has been consid-erably enlarged. For instance, the previous state-of-the-art publication of the IAEA, "Handbook of parameter values for the prediction of radionuclide transfer in temperate environ-ments" [I 16}, listed solely values of water-sediment partition coefficients and concentration factors for edible portions of fish. The most recent version also incorporated equations and parameters for representing lransfer by wash-off from water-sheds of deposited radionuclides. interaction between liquid and solid phases, migration to and from sediments, and transfers to freshwater biota [114J.

91. The mixing of radionuclides discharged into a lake or pond is much slower than is the case for rivers. As a first approximation, a unifonn radionuclide concenlration through-out the pond could be assumed, with a dilution factor equal to the pond outflow rate divided by the effluent input rate. In a large lake or coastal environment, a unifonn concentration would never be reached. Plume models have been developed for lake-shore environments analogous to atmospheric trans-port models. The lake-shore environment is often compli-cated by themlal layering within the water column, which impedes vertical mixing. Moreover, removal of material from the water column via sedimentation is an important long-leon process which results in an approximately exponential decline with time of the radionuclide concenlrations present in the water column.

92. Sedimentation and attachment to suspended particulates are the main processes influencing the residence times of radionuclides in freshwater. Fractions of dissolved and of particle-bound radionuclides are usually detemlined by the distribution coefficient, Kd> which is defined as the ratio of the radionuclide concenlration in water and the concentration of the radionuclide attached to particulate matter, under equilib-rium conditions. Values of Kdare element-dependent. Low Kd values and concenlrations of suspended matter indicate high dissolved fractions, whereas high Kd values and suspended load values indicate a considerable sorption of radionuclides by particles and favour sedimentation. Once deposited, radio-nuclides may migrate down within the sediment or may become involved in resuspension processes. These processes may create additional sources or sinks with potential impact on the long-term behaviour. The distribution coefficients for various elements in freshwater are given in table 8.

Table 8. Distribution coefficients Kd in freshwater ecosystems [114] [k,,_ K. (rrr'/kg) GeomeIIic mean GeometTic IMndard deviatioo B. 42 3.6 M" 130 11 C. 43 9.5 S, 0.t8 4.6 32 1.9 Ag B5 23 Sb 5 3.B I 4.4 14 C, B.5 6.7 2 3.6 C. 220 2.B Th IBO 21 7.4 3.1 fu 240 66 Am B50 3]

240 UNSCEAR 2008 REPORT: VOLUME II

93. Aquatic organisms may be directly irradiated by radionuclides present in their habitats (e.g. water, sedi-ment). They may also take up radionuclides from water and/or the food chain and incorporate them into their tissues. External irradiation of most aquatic organisms, with the exception of burrowing invertebrates and benthic organisms, is limited by the shielding provided by the surrounding water or sediment.

94. Considerable attention has been focused on fish because they are at a higher trophic level in aquatic food chains and serve as food for humans and predators. Polikarpov [P2] has given concentration ratios, CR, (CR here is the ratio of the activity concentration in fish expressed in units of Bqlkg and Table 9.

Concentration ratios for Illes in freshwater fish S"""'" NWr Lakes {L51 8"'001 OOIJ Lako whitefish 400--1 ()()() Aoood whitefish 1000-1800 Suckor 700 Ch"b AOwifu Bullhead Cisco 1600-5 000 Piko lako trout 3 om-;; 000 that in water expressed in units of BqlL, under equilibrium conditions) for Il1Cs ranging from SOO to 9,SOO l1kg for freshwater fish, compared to values of 3 to 2S l1kg for marine fish. The lower values for marine fish were thought to be as a result of the competition for uptake from potassium and other cations. Freshwater amphibians can also show high values of CR (1,000 to 8,000 l.1kg) in the aqueous environment. 9S. Table 9 gives values ofCR for 137Cs in fish in Canadian lakes in the Northwest Territories [1..5] and for the upper Great Lakes [TIS]. High trophic level fish such as trout. pike and cisco show an especially high accumulation of radiocaesium. Concoormtion ratXl (Ukg) GfINlI l.akes m 51 1500-2500 I "" 1800-2 300 2 300 2500-5 500 6100

96. Swanson [S20] has summarized concentration ratios for water to fish tissues for the naturally occurring radionuclides of uranium, 226Ra, 210Pb, and 22S"fh (table 10).

Table 10. Concentration ratios for natural radionuclides in freshwater fish [S20] Ek,,,,,,,. Concentration ratio (lfkg) radionuclide &00 '/ro' IN~ Kidooy S"'"" Sm U 21J-j\\1XJ 0.1-25 <004--0.5 01-{).5 0.01-{).35 0.05--0.5 m", 35-1 BOO 1-<0 1-45 3-30 5-115 7-45 "'I'b 100--2500 4-100 3-421l 6-7111l 10--150 11-206 "'Th 15-1 60 4-32 4-36 5-46 13-W 2Hill

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 241 D. Transfer of radionuclides to marine organisms

97. The main processes that modify the activity concentra-tions of radionuclides in marine water are (a) dilution due to convective and dispersive mixing during transport, driven by local, regional and global currents, (b) sedimentation after attachment to suspended particles and (c) radioactive decay.

98.

For a given continuous discharge rate into a specific sec-tion of the marine system, the steady-state concentration of a dissolved radionuclide in water, C.. (Bqlm3), can be calculated according to: A (2) where A is the activity of the radionuclide discharged per unit time to a specific part of the sea (Bq/a), V is the volume of this part (m3), T is the mean residence time (a), '\\, is the radioactive decay constant (a-I), Kd is the distri-bution coefficient (m3/kg), and S is the concentration of suspended particles (kg/m). T he steady-state activity concentration of the radionuclide in suspended particles, C, (Bq/kg), is then: C = A Kd V '(T 1+,\\,) I + Kd' S (3) The distribution coefficients for a number of elements in marine waters are summarized in table 11. Table 11. Distribution coefficients Kd for open ocean and ocean margins [120] K. lm'/l:g) Opoo-, Ocean margins H 0 S, T. I C, Ph Th U Np Am

99. A value of 3 years was given in reference [U3] for the mean residence time, I, in a specified part of the marine system.

for all radionuclides in coastal waters with the exception of 2J\\IPu, for which a value of 3.5 years was assumed. These values took accounl of radionuclide losses from water to sediment. 0_001 0_001 0.1 01 0.1 1 1 x to' 4 5 x 1lJ3 0.1 1 x 10" 2 x 1lJ3 2 x 1lJ3 0_001 0_1XXI3 0.008 01 0_07 4 1 x 10' 1 3 x 1(P 1 1 1 x 10' 2 x 1(}' From simulations of the transport of radionuclides discharged from the reprocessing plants at Sellaticld and La Hague through the North Atlantic and its marginal seas, the mean residence times given in table 12 were estimated using the North Atlantic-Arctic Ocean Sea Ice Model (NAOSIM) [121]. Table 12. Residence times in different parts of the North Atlantic according to the NAOSIM model Part flf ocean Volume (km') Moon residence time fa) North SIIiI 41000 2.5 +/- 0_36 NOfW!Igiall SIIiI 59000 0_37 +/- 0_11 Bamrrts Sea 111l 000 2.4 +/- 0.24 Karn Sea 38000 4_5 +/- 12 Cootral Nordic SIIiIS 44 000 0_52 +/- 0_18

242 UNSCEAR 2008 REPORT: VOLUME II 100. As for freshwater aquatic biota, activity concentra-tions of radionuclides in marine biota can be estimated using a concentration ratio approach. Concentration ratios for vari-ous elements in marine biota are compiled in table 13. For Table 13. Concentration ratios for marine biota (120] f""""" ' im H 1 0 0.06 S, 3 To 80 I 9 C, 100 Np 1 100 Am 100 Ph 100 100 Th 600 U 1 E. Evaluating doses to biota

1.

Fraction of radiation absorbed by organism 101. Radionucljdes distributed in the environment lead to external exposure of an organism living in or close to a medium thai contains radionuclides. The external exposure of biola is the result of complex and non-linear interactions of various factors: The geometrical relation between the source of the radiation and the target; The activity levels of the radionuclides in the environment; The materials in the environment and their shielding properties; The radionuclide-specific decay properties charac-terized by the radiation type, the energies emitted and their emission probabilities; and The habitat and size of the organism. 102. lbe geometric relationship between the radiation source and the exposed organism is an important factor in relation to the absorbed dose rate incurred. The intensity of the radiation field around a source decreases with distance and is influenced by the material between the radiat.ion source and the target. The number of possible source target configurations is infinite; therefore, a number of limited and representative situations need to be selected for detailed consideration. most elements, these data are based on concentrations in muscle (fish) and soft tissue (crustaceans). For the bone seek.ing elements such as strontium, however, the entries in table 13 are based on whole body concentrations. Coocentration factor.; fUkg fresh weight) Moaoo." Crustaceans 1 1 0.05 0.06 10 10 30000 1000 10000 100 50 30 50 100 4000 100 8000 400 1000 9000 100 100 100 1000 100 10 103. The exposure due to radionuclides incorporated into the organism is detennined by the activity concentrations in the organism, the size of the organism, and the type and the energy of the emitted radiation. A key quantity for estimat-ing internal doses is the absorbed fraction of energy, ¢(£). which is defined as the fraction of energy emitted by a radia-tion source thai is absorbed within the target tissue, organ or organism. In the simplest case, the organism is assumed to be in an infinite homogeneous medium and to have a uni-fonn activity concentration throughout its body. The densi-ties of the medium and the organism's body are assumed to be identical. Under these conditions, both internal (DIIIl) and external (D w) dose conversion coefficients (DCCs: the nec is defined as either the absorbed dose or the absorbed dose rate, according 10 the circumstances, per unit activity con-centration of the relevant radionuclide in the organism or medium) for monoenergetic radiation can be expressed as a function of the absorbed fraction [N I, V2]: (4) 104. Absorbed fractions for photon and electron sources unifonnly distributed in soft-tissue spherical bodies immersed in an infinite water medium have been systemati-cally calculated by Monle Carlo simulation [UI7]. The cal-culations covered a particle energy range of 10 ke V to 5 MeV, a range for the mass of the body from I O-t; to I ()3 kg. and shapes from spheres to ellipsoids with varying degrees of non-sphericity. Figures rn and IV show, respectively, the results for electrons and photons.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 243 Figure III. Absorbed fraction, ¢(£), for electrons of different energy uniformly distributed in spheres of different mass in a water medium Figure IV. Absorbed fraction, ¢ (E), for photons of different energy uniformly distributed in spheres of different mass in a water medium 105. For electron energies below 100 keV, the absorbed fraction is close to unity, even for very small organisms. The mean free path of electrons in living tissue increases from 160 flIn for 100 keVelectrons to 5 mm for I MeV electrons. Thus, even above 100 keY. the absorbed fraction is close to unity if the diameter of the target is much greater than the range of the electron. Only for very small targets and high energies does the absorbed fraclion become considerably smaller than 0.5. 106. The mean free path of photons is considerably longer than that of electrons. The absorbed fractions cover a range from nearly unity for low photon energies and large organ-isms to less than 0.0001 for small organisms and high photon energies. Absorption is a non-linear function of target size and energy. The main processes causing absorption of pho-ton energy are the Compton effect, the photoelectric effect and pair production; their contributions to absorption depend on the energy of the emitted photons. As a result, the absorbed fraction of photons in the energy range from 20 to 100 keY decreases by a factor of 10--15 for small organisms, but is relatively constant for photons with energies between 100 keV and I MeV. Beyond energies of I MeV, the absorbed fraction decreases steeply with energy. 107. The range of alpha particles in living tissue is very short, increasing from 16--130 flIn within the energy range of 3--10 MeV. Therefore, with the exception of bacteria, it is assumed for all organisms that all the energy emitted is absorbed. Since the dimensions of bacteria are well below the range of alpha particles, the absorbed fraction is assumed to be zero. 108. Re-scaling factors have been derived f.rom the com-puted absorbed fractions for spheres to detennine the dose coefficients for ellipsoidal shaped organisms, using the mass and proportions of the organism. The relationship between the re-scaling factors and the non-sphericity parameter of the organism's body are described analytically in reference [U 17]. Owing to the short range of alpha particles, the internal expo-sure due to incorporated alpha emitters is independent of the shape of the organism. 109. The approach was also applied to the calculation of the absorbed fractions for non-aquatic animals and their internal exposures. With the use of the absorbed fractions for spheres and the suggested re-scaling and interpolation tech-niques. a set of internal DCCs has been calculated for all reference animals and plants [U17]. 110. The estimation of external exposures of terrestrial ref-erence animals and plants is more complex than that of biota in the aquatic environment. The intrinsically different den-sity and composition of soil, air and organic matter cannot. in general, be adequately taken into account by the applica-tion of analytical solutions. Dosimetric models for estimat-ing external doses to biota in the terrestrial environment were developed within the FASSET project [F4, TID]. A key factor for detennining external exposure is the geometric

244 UNSCEAR 2008 REPORT: VOLUME II relationship between the radiation source and the exposed organism. A number of limited and representative exposure situations were selected for detailed consideration. 111. Simple three-dimensional phantoms, i.e. ellipsoids and cylinders, were defined as model geometric equivalents of reference organisms based on their average mass and size characteristics. The dimensions ranged from a millimetre to a metre and the respective masses range from 0.2 g to 550 kg. The ellipsoids represented organisms such as wood-louse. earthwonn, mouse. mole, snake, fox. deer and cattle. Details of the assumed exposure conditions are given in ref-erence [T ID]. The fur and the outcr layers of skin consist of non-active tissue, and therefore shield the living organism. 112. Herbaceous vegetation, shrubs and trees were consid-ered as reference plants. Exposure of the meristem and buds was calculated because these organs are characterized by very intensive cell division, which may make them highly radiosensitive. 113. In order to take account of the distribution of radio-nuclides in the canopy, a distinction was made between alpha, beta and gamma radiation because of their different ranges. For gamma radiation, the whole canopy was consid-ered to have a homogeneous activity concentration. For high-energy beta radiation, the irradiation of the target was also assumed to result from a canopy with a homogeneous activity concentration. However, owing to the much shorter range of alpha and low-energy beta radiation, the irradiation resulting from external deposits on, or internal activity of, the target organ had to be considered explicitly. Because of the very short range of alpha particles in air, only the expo-sure due to the external deposits on, or internal exposure of, the target needed to be taken into account frIO], 114. The elemental composition and density of the materi-als involved have an important impact on the radiation trans-port calculation. All organisms were assumed to be composed of skeletal muscle alone wilh the characteristics/parameters given in reference [l15]. The DCCs were derived using Monte-Carlo techniques; all relevant processes of radiation transport and interaction with matter were included. For electrons, a thick-target bremsstrahlung model was used instead of an electron-transport simulation. For the calcula-tion of DCCs for a species in the soiL a volume source with unifonn activity concentration was assumed. For the calcu-lation of DCCs for a species on the ground, a planar radia-tion source on top of the soil with a surface roughness of 3 mm and a volume source with a depth of 10 cm were assumed. Calculations were made for monoenergetic gamma energies of 50 keY, 300 keY, 662 keY, I MeV and 3 MeV. Data for other energies were obtained by interpolation.

2.

Principal relationships for internal and external exposure (a) External exposure 115. Allhough the simulations cover only a limited number of possible exposure conditions, they allow the relationships between organism size, radiation energy and habitat to be deduced. The DCC (Gy per photon per kg) increases in pro-portion to the photon energy as illustrated in figure V for a volumetric source with a thickness of 0.5 m and target organ-isms that live at a depth of 0.25 m. Whereas the DCCs vary by a factor of 200 between photon energies of 50 keY 10 3 MeV, the variation between Ihe organisms does not exceed a factor of 2, even for low-energy photons (for high-energy photons, the difference is a factor of only 1.5). Figure V. Dose conversion coefficients for various soil organisms at a soil depth of 25 em, for monoenergetic photons from a uniformly distributed source in the upper 50 em of soil (soil density: 1,600 kg/ml) {F4] 10.11 c; /~ ~ 100lJ C B 0 ~ ~

8.

__ Woodlouse ~ ....... Earthworm ~ U 10-14 __ Mouse ~ -_. Mole ,_" Snake Rabbit - x-Fox 10-15 0.01 0.1 10 PHOTON SOURCE ENERGY (MeV)

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 245 116. The DCC CGy per photon per kg) for an earthwonn as a function of soil depth for monoenergetic photons is shown in figure VI. The upper 50 cm of the soil was assumed to have a homogeneous activity concentration. The maximum DCC was found to be at a depth of 25 cm and the lowest, at depths of 0 cm and 50 cm. The maximum DCC is a factor of 2 higher than the lowest. Figure VI. Dose conversion coefficients for an earthworm at various depths in soil. for monoenergetic photons from a uniformly distributed source in the upper 50 em of the soil (soil density: 1,600 kg/ml) [F4] 10*",--------------------------, ,p: . ~;, '//// .? Depth = OOOm ..--.¥, - Depth = 005m . /./...... / ¥ ...... Depth=0.25m ~r * - *"",,** Depth = 050m 10*"'---~-~~~~...w'---~-~~~~ ..... --~-~~~~"" 0.Q1 0.1 10 PHOTON SOURCE ENERGY (MeV) 117. The DCC at a depth of 5 cm is only about 20% lower than the maximum. This is because of the relatively short mean free path of photons in soil, which is about 0.2, 2 and 10 cm for photon energies of 20 keV, 100 keV and 3 MeV, respectively. Thus, an organism in soil would be irradiated by photons originating within a surrounding shell of, at most, 10 cm radius. 118. The DCCs (Gy per photon per m2) for different refer-ence organisms for a planar source on the soil surface are given in figure vn. The DCCs decrease as the photon energy increases from 10 to 100 keY by a factor of about 5 for small animals and 2 for large animals. Above 100 keY, the DCCs gradually increase by approximately two orders of magni-tude; the DCCs for small animals are greater than those for large animals owing to the more effective self-shielding in large organisms. Such differences are more pronounced at low energies; for example, the difference between the mouse and the cow is a factor of about 6 for 50 keV photons, whereas it is a factor of 3 for 3 MeV photons. Figure VII. Dose conversion coefficients as a function of the source energy for various reference organisms for a planar source on top of the soil [F4] 10.,4, ______________________ --, ~ Cow ....*.... Roe deer ~ Wolf Rabbit Mol. MOU5e 10*11 '-'-~ __ ~~~~~~_~~~~~~ ~~~~.....J 0.01 0.1 10 PHOTON SOURCE ENERGY (MeV)

24<1 UNSCEAR 2008 REPORT: VOLUME II 119. The DCCs for different animals as a function of the depth of a planar source in the soil are summarized in fig-ure VIII. The results show that the DCCs for low-energy photons for animals living on soil are low. Relatively shal-low depths of soil over the planar source suffice to attenuate the photons completely. Figure VIII. Dose conversion coefficients as a function of the source energy and depth of a planar source in the soil for fa} the mouse and (b) the cow living on the soil The source depth qUllntifies the amount of soil by which the photon source is covered (e.g. the source depth of 10 g.lcm2for soil densities of 1.0 Hnd 1.6 glcm2 are equivalent to 1.1 depth of the source in the soil of 10 Hnd 6.25 em, respectively) [F4] 10-" (a) Mouse 10-" ~, 10-" * . M I 10-" 0 ~ i v 10-" 'ioIJrce depth: ~

• Og/an' 10-"

, 1 g/an'

• 109/an' 0.01 PHOTON SOURCE ENERGY (MeV) 120. The data indicate that the relationship between the DCCs, the size and habitat of the organism and the energy and type of the radiation is complex. Nevertheless, these data provide an appropriate basis for deriving data, either by interpolation or by eXlrapolation, for other exposure condi-tions that were not explicitly considered. They were used to derive radionuclide-specific DCCs (JlGylh per Bqlkg) for internal and external exposure of a number of reference organisms, taking into account the type of radiation as well as the energy and intensity of the emission, as specified by the ICRP [113]. Table 14 summarizes the DCCs (f.1Gylhper Bqlkg) for external exposure. The data are provided accord-ing to the habitat of organisms considered. Animals living in soil were assumed to be at a depth of 25 cm in a soil layer that is homogeneously contaminated by radionuclides to a depth of 50 cm. Above ground organisms were assumed to be irradiated by a source homogeneously distributed in the soil layer to a depth of 10 cm. For the terreslrial organisms, only the contribution of photons was included, whereas for aquatic organisms, exposure due to electrons (including bremsstrahlung) was also implicitly taken into account.

This has the effect of causing the DCCs for lH, 90Sr and 10-",------------------, (b) Cow 10-" 10-" 10-" 'ioIJrce depth:

• og/cm' 1 g/cm'

.. 109/cm' 10*lD.L_~~---~-----~-----__j 0.01 PHOTON SOURCE ENERGY (MeV) I l~Cs to appear to be inconsistent: the DCCs for l H and Il~S for terrestrial organisms are zero, whereas the values for aquatic organisms are very small. Aquatic organisms are in direct contact with the contaminated medium, whereas elec-trons emitted from soil are attenuated by the surface rough-ness of the soil, the air and the fur of terrestrial organisms. So, this apparent inconsistency is of no significant practical consequence. (b) Internal exposure 121. The DCCs (flGylhper Bqlkg) for internal exposure are provided in table 15 [U 17]. The values are given in lenns of weighted absorbed dose rate per unit activity con-cenlration in the organism, assuming homogeneous distri-bution of the radionuclides. The DCCs have been weighted to take account of the different RBEs of the different quali-ties of radialion; a factor of 10 to reflect the RBE has been used for alpha radiation and a factor I to reflect that for gamma and beta radiation including that from triti um (see the next subsection).

o X ~ X ~ b X X - N " x X x ~ x X ANNEX E: EFFECTS OF ION IZ ING RADIATION ON NON-HUMAN BlarA x ~ x X X X X x x X X M b x x

• " x X

X x ~ b x x x - X X x ~ b X X x M M x X X X X ~ ~ x x X X ". M X x x X " x :; X x 1; x X X X X x ~ X X X X x X X X M X X ~ X ~ X X M x M X ~ X -"' X X x x x X.., x x x x 247

248 S N :> ~ ~ ~ 5 -" i ~ 0

• 0.e

.~ * ~ ~ * ~.. ~..

• j l

j,! ~ os ~ X ~ OS l ! X .0 OS ]~ X J~ OS - X ~ OS - ~ X OS ~ X '" -x OS .jl x OS r X OS il X <!l X X ~ X OS b b OS X X X X ~ '" ~ ~ <ci .n., - OS b b OS X X X X ~ ~ '" '" .n ~ - OS b b OS X X X X N.., ~ ~ - b b b OS X X X X ~ ~ - b b b OS X X X X .n ~ N b b b b X X X X .n ~ ~ - OS b b OS X X X X ~ ~ - ~.n M - b b b OS X X X X ~ N ~ ~ M - b b b b X X X X .n ~ - x x x x ~ ~ N X X X X N '" N ~., - X X X X ~ ~ ~ - r f! If, UNSCEAR 2008 REPORT: VOLUME II OS b OS OS b X X X X X ~ ~ ~ ~ ~ N oj - N - b b OS OS b X X X X X ~ ~ - N - OS b OS OS b X X X X X ~ '".,.., M - N - OS b OS OS b X X X X X ~ '" '"., N M - N - OS b b OS b X X X X X ~ ~ '"., M M N - b b b OS b X X X X X ~.,..,.., M - N - b b b b b b X X X X X X N b b b OS b N N N ~ ~ M X X X X X N., ~ ~ - N - OS b OS OS b X X X X X ~ '".,.., M - N - b b b b b X X x X X ~ '" '"., N M N N - X X X X X ~ ~ '"., M M N - x x X X X ~ '".,.., M - N - X X X X X ~ ~ '" M - N - f ~ * ~ f F '" ~.,., E i?,, ~ 0

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 249 (c) Relative biological effectiveness 122. The effects of radiation exposure on biota depend not only on the absorbed dose, but also on the type or quality of the radiation. For example, alpha particles and neutrons can produce observable damage at much lower absorbed doses than beta or gamma radiation. Thus, the absorbed dose (in gray) is often multiplied by a factor in order to account for the RBE of the quality of the radiation. 123. A number of authors have evaluated the data on the RBE of different types of radiation [A I, CI, E2. F4, 17. U4, U26]. Nominal values for the factor to reflect the RBE of alpha particles derived from these reviews are summarized in table 16. The experimental values of RBE are specific to the endpoint studied, the biological, environ-mental and exposure conditions (e.g. reference radiation, dose rate, and dose) amongst other factors. Thus. as noted in a FASSET report [F4], it is difficult to develop a gener-ally valid factor to reflect the RBE for different radiation qualities for use in an environmental risk assessment. The ACRP [AI] and FASSET [F4] have therefore proposed ranges of values for general application. Both selected a factor of 10 to reflect the RBE for alpha particles, the ACRP, citing references [K2, T7, U41, referring to it as a notional central value, and FASSET as a value "to illus-trate" the impact of the RBE for an internally deposited alpha emitter. Table 16. Modifying factors to reflect the RBE of alpha radiation for deterministic effects on non-human biota (relative to low-LET radiation) s~~ Nominal value INl] 1 BuH:-in consllMltism in dow modet 1\\41 20 Nurnorica!!y tho sarno as tho radiation Wllighting factor llSoo in tho praloctioo of humallS IBZ21 2-10 Nolt"slocMstic offoct of noutrons and Iloavy iollS ~" 5 Awrago for detorministic effects "7] 10 Delerministic population-rntllVilnt oodpoints lell 10 Likely to be COIlSOf\\IlItivO for deterministic effects [E31 40 tncludes studies with h91 RBE values [E121 <35 11<1800 on coocooirntions in lho whale body [Al] 5-20 (10) 5-10 detorministic effocls (eotl-killing. rnproductivol 10-20 C3rlCOr. ehromosDm!l ailnormatities 10 nominal contral value IF4! 5-50 110) 10 to ilIusl1ilto the effect of ttJe alpha RBE [K191 < 7 to < 35 Upper bound of estimato of ABE 124. Chambers et al. [01 reported a review of the litera-ture on experimentally detemlined RBEs for internally deposited alpha-emitting radionuclides. The relevance of each experimental result in selecting a factor to reflect the RBE for alpha particles was judged on the basis of pre-established criteria. They recommended a nominal factor of 5 to reflect the RBE for alpha particles for population-relevant detenninistic and stochastic endpoints but, to reflect the limitations in the experimental data, they also suggested uncertainty ranges of 1-10 and 1-20 for population-relevant detemlinistic and stochastic endpoints, respectively. The data developed by Chambers et al. [C51 after application of their evaluation criteria are summarized in figure IX. Three evaluation criteria were used in reference [C51. Criterion I required the dosimetric conditions to be sufficiently well defined and not peculiar to the source of radiation. Crite-rion 2 required the dose-effect relationships to be suffi-ciently well known so that the results from the dose rates used experimentally can be applied to effects that may occur with environmental dose rates. Criterion 3 required the experimental uncertainties to be discussed by the authors of the original studies.

UNSCEAR 2008 REPORT: VOLUME II Figure IX. Application of the criteria to the distribution of RBEs (all endpoints) [C5] 80 70 ~ 60 w => ~ ~ 50 w ~ ~ ~ 40 0 ~ w ~ " 30 => z 20 10 0 <5 125. Knowles [KI9] reported on experimental studies on groups of zebra fish that were exposed from an early age to different dose rates of gamma and alpha radiation (the laller was from 210PO). Among the gamma-irradiated fish, only those in the highest dose-rate group (7,400 mOyfh) showed radiation-related damage. No groups of alpha-irradiated fish showed evidence of radiation-induced reduction in egg pro-duction even though aUloradiographs showed concentrations of 21OpO in the testes and ovaries. Since the highest alpha dose rate (2 14 mOyfh) showed no effect, comparison with the gamma dose rate of 7.400 mOyfh, which caused egg pro-duction to cease, resulted in only upper limits to the RBE. These were calculated to be in the range of <7 to <20 based on ovary concentrations and <35 based on whole body con-centrations. The authors suggested that the RBEs derived from their work provide the best available (upper bound) estimates for a population-relevant effect for fish. 126. The ACRP [AI] considered tritium beta radiation because the low velocity of the beta particles (maximum energy = 18.6 keY) results in a relatively high LET over a short path length. It has an LET very similar to that of70 keY photons, which are representative of the X-rays used in radiobiological research and in diagnostic medicine rM6]. In their review of the effects of tritiated water (HTO) in mam-mals and fish, Environment Canada in their Priority Sub-stances List (PSL2) [E3] listed tritium RBE values ranging from 1.7 to 3.8, with gamma rays from c.oco or I37CS being used as the reference radiation. Based on this, they recom-mended a factor of 3 to reflect the RBE of beta radiation from tritium. Research conducted at Atomic Energy of Can-ada Ltd. on breast cancers in female rats [0 I] and on mye-loid leukaemia in male mice indicated an RBE value of 1.2 for trilium, with X-rays being used as the reference RBEs eliminated by criterion #3 only RBEs eliminated by criterion #2 only RBEs eliminated by criterion #1 only RBEs remaining after all criteria applied 41-80 81 - 160 >160 RBERANGE radiation. The difference between these values is largely the result of the choice of reference radiation. Sinclair [SS] has shown that, at low doses, X-rays are about twice as effective as gamma rays in producing damage. Hence, the radiation from tritium has an effectiveness for biological damage in the higher part of the range expected for the gamma and X-ray photon energies likely to be experienced in the envi-ronment. Citing Straume and Carsten [S9] amongst others, the ACRP concluded that for the dosimetry of non-human species. where the endpoints are usually detenninistic in nature, a reasonable average factor to reflect the RBE of beta particles may be 2 with a range of 1-3, depending on the endpoint being assessed [A 1]. 127. A number of studies suggested that beta radiation with energies below 10 keY has a higher RBE than electrons with energies above 10 keY [M 10. S9]. Straume and Carsten [S9] reviewed 33 studies of the RBE of tritium beta particles and found arithmetic means of I.S based on X-rays as the reference radiation, and 2.3 with I)1Cs or c.oco gamma rays as the reference radiation. Most of these studies related to detenninistic effects. Moiseenko et al. [M 10] considered an appropriate factor to reflect the RBE of beta particles from tritium (mean beta energy <10 keY) to be between 2 and 3. The UK Health Protection Agency (HPA) [H2I] reviewed the RBE studies on tritium beta particles along with a wide variety of experimental studies using X-rays and gamma rays as reference radiations and noted that the RBEs gener-ally ranged f.rom I to 2 when compared to orthovoltage X-rays and from 2 to 3 when compared to gamma rays [H2 1]. Little and Lambert [1.9] also reviewed the experimen-tal studies of cancer induction, chromosomal aberration, cell death and various other endpoints and arrived at similar conclusions for the RBE of tritium in water.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 251 128. In order to illustrate the effect of the radiation quality of emissions from internally deposited radionuclides, the FASSET programme recommended the use of a factor of 10 to reflect the RBE of alpha radiation, 3 for low-energy beta radiation (E < 10 keY), and I for both beta radiation with energies greater than 10 keY and for gamma radiation [F4, LA]. 129. The Committee, in its UNSCEAR 1996 Report [U4J, recommended a nominal factor of 5 to reflect the RBE for internally deposited alpha emitters. The Committee now recommends a nominal (generic) factor of 10 to reflect the RBE for internally deposited alpba radiation. For beta and gamma radiation, the Committee recommends a nominal (generic) factor of I to reflect the RBE. However. it should be understood that the most appropriate factor to reflect the RBE for low-energy <<10 keY) beta radiation remains an open question and ought to be the subject of future research. These reconllllended values to reflect the RBE are intended to apply on a generic basis across all organisms and endpoints. Where appropriate scientific infonuation specific to a particular organism and endpoint exists, such infonnation is preferred. (d) Dose rates for internal exposure 130. The dose from unit exposure of the selected reference organisms is estimated from the weighted absorbed dose rate due to external exposure arising from deposits in the ground and that due to internal exposure. Weighted absorbed dose rates to the reference organisms nonnalized for con-tinuous exposure to I Bq/ml in air for each radionudide are given in table 17. These weighted absorbed dose rates were calculated assuming the factors to reflect the RBE recom-mended by the Commillee. Table 18 summarizes the ratios of weighted to non-weighted nonnalized total doses. The results are particularly sensitive to the choice of factor, especially for radiation from the actinides and tritium. The contributions of weighted internal doses to the total nonnal-ized doses are close to or above 90%, which indicates that internal exposure is the dominant pathway. 131. These annual doses took account of external exposure as well as internal exposure via inhalation and ingestion. They are compared with the weighted absorbed doses to biota in table 19. The ranges given in the table for biota reflect the variations between the different reference organisms consid-ered. This comparison has however some inherent limita-tions. The values for humans are expressed in temlS of annual effective dose, whereas the values for biota are in tenus of weighted absorbed dose and were estimated assuming a homogeneous distribution of the radionuclide in the organ-ism. Furthennore, the annual effective doses per unit deposi-tion to humans were based on a radiation weighting factor of 20 for alpha particles, whereas the weighted absorbed doses to biota were based on a factor of 10 to reflect the RBE for alpha particles. Further still, the values for humans reflect largely the transfer of radionuclides through agricultural eco-systems, whereas the values for biota are more typical of the transfer in forests and semi-natural ecosystems. 132. Despite these differences, the estimated normalized effective doses to humans and the weighted absorbed doses to biota are about the same order of magnitude, except in the cases of 1191 and 131 1. These exceptions are probably due to the special importance of radiation exposure of the human thy-roid in evaluating effective dose, which has no counterpart in the dosimetry for biota. Thus, apart from these exceptions, the comparison indicates that for similar levels of radio-nuclides in the environment, the effective doses to humans and the weighted absorbed doses to biota are comparable. Table 17. Normalized weighted absorbed dose rates per unit activity concentration to various biota from internal exposure Radionnclide Weighted dase rare per UIlit activity concenlTatian {pGy/h per Bqfm'} f,,,,",,,,,, 0-D~* Frog G~, Pine tree ~ Ux to-" 1.7 x 10-" 1.7 x 10-" 1_7 x 10-" U x 10-" 17 x 10-" 1.7 x 10-" U x 10-" 5_6 x 10-" J_J x 10-" J.3 x 10-" J_J x 10-" J_J x 10-" 9.J x 10-" 5.4 x 10-" 5_5 x 10-" "S, 6.1 x 10-" L2 x 10-" l.Jx1o-" 7_J x 10-" 7_5 x 10-" 5.1 x 10-" I.B x 10-" 4.3 x 10-" "To 4.4 x 10-" 4_4 x 10-" 4.4 x 10-" 4_4 x 10-" 4.4 x 10-" 4_4 x 10-" 2A x 10-" 4_B x 10-" 2.3 x 10-" 4_B x 10-" 4_9 x 10-" 4_5 x 10-" 4.0 x 10-" 2_9 x 10-" L7 x 10-" 2_1 x 10-" 1 4.6 x 10-" 1.J x 10-" I.B x 10-" 42 x 10-" JA x 10-" 1.9 x 10-" 1.6 x 10-" 2.B x 10-" C, U x 10-" 2_7 x 10-" 4_5 x 10-" 9_7 x 10-" B_1 x 10-" 6.6 x 10-" 8.7 x 10-" 1.2 x 10-" 'Cs B.3 x 10-" 2_7 x 10-" 2_7 x 10-" 7_1 x 10-" 5.4 x 10-" 5.0 x 10-" 6_7 x 10-" 1.7 x 10-" "'Cs 4] x 10-" 4_4 x 10-" 1.1 x 10-" 1.9 x 10-" 2_0 x 10-" 2_0 x 10-" 1.9 x 10-" 2.3 x 10-" 2.9 x 10-" 9.4 x 10-" 9.2 x 10-" 12 x 10-" 1.2 x 10-" 1.1 x 10-" 1.J x 10-" 8.7 x 10-" 5.0 x 10-" 2_1 x 10-" 4_7 x 10-" B_9 x 10-" 9.J x 10-" J] x 10-" 1.5 x 10-" 1.J x 10-" "'Th 4.9 x 10-" 6_4 x 10-" 5_6 x 10-" 2_8 x 10-" 2_8 x 10-" 4_9 x 10-" 8.4 x 10-" 4_0 x 10-" "'IJ 5_B x 10-" 2_4 x 10-" 2.4 x 10-" 2_4 x 10-" 2.4 x 10-" 7_5 x 10-" 9_9 x 10-" 1.8 x 10-"

ruN, 1.9 X 10-"

1.5 x 10-" 1.5 x 10-" 1.5 x 10-" 1_5 x 10-" 4_0 x 10-" 4_1 x 10-" 4.9 x 10-" 2_1 x 10-" 1.7 x 10-" 1.7 x 10-" 1_7 x 10-" 1.7 x 10-" 4.4 x 10-" 4_5 x 10-" 5.4 x 10-" 72 x 10-" 2_9 x 10-" 2_9 x 10-" 2_9 x 10-" 2_9 x 10-" 9.3 x 10-" J_9 x 10-" J_l x 10-" "'11m B.B x 10-" 8.6 x 10-" 7_6 x 10-" 7_9 x 10-" B_O x 10-" 8_0 x 10-" J_7 x 10-" J_J x 10-"

252 UNSCEAR 2008 REPORT: VOLUME II Table 18. Ratio of weighted and unweighted doses RadiotJuclide Ratio of weighted dose/unweighted doseil Earthworm /Joo, F"" Grass -- ~ 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 "S, 10 10 10 10 10 10 10 10 ,,[, 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 1 10 10 10 10 10 10 10 10 C, 10 10 10 10 10 10 10 10 '"Co 10 10 10 10 10 10 10 10 mCo 10 10 10 10 10 10 10 10 "'I'b 10 10 10 10 10 10 10 10 ~"' 2.0 10 1.1 12 1.1 3.3 7 2 9.9 7.1 9.5 9.7 9.7 10 10 10 "'U 10 10 10 10 10 10 10 10

ruN, 9.1 8.9 9.6 9.'

9.3 9.6 9.6 9.7 "Th 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 "'Am '.1 '.3 7.9 6.1 5.9 5.9 10 10 a FacIOfs 10 reflocllha RBE: alpha radiation. 10; bola 3nd gamma radiation. 1_ Table 19. Comparison of doses to biota and humans, normalized for unit deposition to terrestrial ecosystems Radiooudide Biota {range(i Normalized weighted absotbed dose rate {Gy i£' per Bq rrr' g'l Minimum "S, 6_2 x 10"' ,,[, 4.4 x 10-' 1.7xl~ "'I 2_0 x 10",0 Co 6_7 x lIP Co 5_1 x 10-' 137Cs L1 x 10-' m,. 8_9 X 10-" ~"' 4_B x 10-' "'Th 5_6 x 10"' "'U 1.0 x 10"

ruN, 1.5 x 10" 1.7 x 10" 3_0 x I ~

"'Am n x 10' a IliHlQO roproooois tho minimum 300 maximum amoog tho OfQilflisms considoroo_ b CaK:datod according 10 0111_ Maximum 1_3 x 10" 2_5 X 10"' 5_0 x I~ 2_8 x 10-' 4_6 x 10-' 2_B x 10"' 4_8 x 10-' 2_9 x 10' 1.5 x ID-' 8_5 x 10"' 1.8 x ID-' 5_0 x 10" 5_5 x 10" 9_5 x 10" 3_8 x 10" HumandJ Normalized effective dase mte (Sv iT' per Bq rrr' iT') 4] x 10"' 1.8 x I~ 6.3 x 10"' 1.0 x 10"' 1.3 x 10-' 1.2 x 10-' 1.3 x 10-' 2.5x 1~ 1.6 x 10" 1.2 x 1~ 6_0 x 10-' 4_9 x 10"' 6_8 x 10-' 6_8 x 10"' 5_8 x 10-'

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA

3.

Doses to non-human biota fa) Calculation of doses to biota 133. In terrestrial environments, the most important source of radiation exposure as a consequence of discharges of radionuclides to the environment is due to deposition on soil. Radionuclides present in soil are generally a persistent radia-tion source for all terrestrial biota. Aquatic organisms are irradiated externally by the activity in water and, in the cases of bottom dwellers and benthic organisms, the activity in sediments, and internally by incorporated radionuclides. The dose rate, D. can be calculated according to: (5) where DCC~J1.' is the DCC for external exposure to radio-nuclide r (JlGylh per Bqlkg); C-....-r.r is the activity concen-tration of radionuclide r in soil or water (Bqlkg); DCCw., is the DCC for internal exposure to radionuclide r (]lGylh per Bqlkg); and C bio/tv is the internal activity concentration of radionuclide r in biota (flora or fauna) (Bqlkg). (b) Activities in environmental media 134. In the absence of measurements, in order to evaluate equation (5), the activity concentrations, C-.,_"" and C_-" have to be estimated. Assuming a constant discharge of radio-nuclides over a period of 50 years, the activity in soil for the last year of that period is calculated as indicated in reference nlll c.., DIOI., cc(,\\- +'",\\"')-."-, *[I - exp(- (.I, +,\\.)-I.)J (6) where C *., is the activity concentration in soil (Bqlkg); D'OI.r is the total (wet plus dry) deposition rate to soil (Bq m*l a*I) ;

m. is the mass of the upper soil layer (kg/ml); A, is the radio-active decay constant (a' 1); \\. is the loss rate from the upper soil layer (a-I); and t~ i s the discharge period (50 a).

135. The total deposition is calculated as the sum of dry (Ddry.,) and wet deposition (D....,.,). The activity concentration in flora, C}o"'-r> is estimated by taking into account direct deposition on the foliage and uptake from soil according to reference [III]: + C",. TF flonJJ (7) where!... is the interception fraction (dimensionless); b is the standing biomass (kglml); >.". is the activity loss rate from plants due to weathering (a*1); t", is the exposure time (a); and TFjJ<>r"a., is the transfer factor from soil to flora (Bqlkg flora per Bqlkg soil). 136. The activity concentration in reference fauna is esti-mated from the soil concentration and the soil-fauna transfer factor as follows: c ~ C *TF fauna., '.r 1-"",' (8) where TFf""",,., is the soil-fauna transfer factor (Bqlkg fauna per Bqlkg soil). 137. The habitats of the reference fauna are differentiated according to whether the organisms live in or above soil. DCCs for species living in soil are expressed in units of tJGylh per Bqlkg and are based on the assumption tbal the organism lives in the centre of a slab containing radio-nuclides unifonnly distributed to a depth of 50 cm. For organisms living on soil, it is assumed that radionuclides are homogeneously distributed to a depth of 10 cm; the DCCs in this case have units of ]lGylh per Bq/ml. 138. The estimation of the activity concentration of a radio-nuclide in aquatic biota (C"'l"" _) is usually oblained from the activity concentration in water (C""",) and tbe concentra-tion factor (CF~ *aIt, __ ) according to: (9) 139. As outlined above, the exposure due to incorporated radionuclides is detennined by the size and geometry of the organism, the radionuclide distribution, and the type and energy of the emitted radiation. Currently, DCCs are not available for specific target organs in the reference organ-isms; the DCCs for internal exposure are therefore based on the assumption that the radionuclides are homogeneously distributed throughout the organism [flO]. (c) Doses to marine organisms and to humans due to consumption of marine food 140. As an example of the calculations of exposures of aquatic organisms, the exposures to marine organisms are calculated assuming a radionuclide concentration in water of I Bq/ml and applying the appropriate concentration faclor for water-biota in table 13 and the appropriate oces given in tables 14 and 15. The weighted absorbed dose rates to flatfish, crab and brown seaweed are summarized in table 20. For all radionuclides considered, the dose rates to biota are almost completely a result of internal exposure. For com-parison, the effective dose rates to an adult human are given assuming an annual fish intake of 20 kg. In general. the effective dose rates to humans are much less than the weighted absorbed dose rates to biola for a unit activity concentration of a radionuclide in marine water.

254 UNSCEAR 2008 REPORT: VOLUME II Table 20. Comparison of doses to non-human biota and humans, normalized to an activity concentration in marine water of 1 8q/ml Radioouclide NoiH!uman biota ""~"'" Weighted afuoriJed dose mte {JlGy/h per Bq/rrr'J Narmalized effective dOSfJ ri1te {JlSv/h per Bq/rrr'J frob Macroa/gae 'H 3.3 x 10-' 3.3 x 10-' 3.3 x 10-' 4_1 x 10-" "CI 9_6 x 10-' 9.6 x 10-' 7_0 x 10-' 1.3 x 10-" "S, 1.8 x 1~ 6.3 x 1~ 4_5x 1~ 1.9 x 10-' ,,[, 4_6x 1~ 5_8 x 10-' 1.7 x 10-' 1.2 x 10-' 3_8 x 10"' 4.3 x 1~ 3_8 x 10-' 2_3 x 10-' 1 1.2 x 1~ 1.4 x 10-' 1.0 x 10-3 4_5 x 10-' 13'CS 1.9 x 10-' 6_9x 1~ 4_Sx 1~ 4_3x 1~ "Co 3_9 x 10-' L2 x 10-' 1.9 x 10-' 4_6 x 10-' me. 1.8 X 10"' 5] x 10-' 6_5 x 10-' lOx 10-' 4_8 x 10-' 2.3 x 10-> 8_0 X 10-' 32x 10-' mR. 1.J X 10"' 1.4 X 10-' 1.4 X 10--' 6.4 x 10-' "'Th 1.4 x 10-' 2.3 X 10--' 4.6 X 10-3 l2x 10-' "'U 2_4 X 10-' 2_4 X 10-' 2_4 X 10-> 1.0 X 10-' "'N, 2_7 x 1D" 2J X 10-_3 1.4 X 10-_3 2_5 x 10-' 3_0 x 1n-' 6.0 X In-' L2 X 10-' 5_7 x 10-' 3_0 X 10-> 6_0 X 10-> 1.2 X 10-' 5_7 X 10-' Am 3_2 X Hr' L3 X 10--' 2_5 X 10-' 4_6 X 10-' a For all inl:aw of marirla fish of 2tI kg/a_

4.

Conclusions 141. In this section, approaches have been described for the assessment of exposures of flora and fauna to radiation from natural background levels of radionuclides or regulated dis-charges of radionuclides to the environment. The models cover two major fields. One is concerned with the transport processes of radio nuclides from the source to plants and animals, to which approaches may be applied that are similar to those used to assess the exposures of humans. In the terreslrial enviroruncnt, these are mainly atmospheric dispersion. deposition, intercep-tion, weathering and uptake from soil. For discharges to aquatic systems, models can be used that describe dispersion, dilution, sedimentation and uptake by freshwater or marine organisms. 142. There are major differences in the dosimetry involved in the assessment of the exposures of humans and non-human biota. The current approaches for biola rely on the mean activity concentrations in the whole organism rather than on those in dis-tinct organs or tissues. Thus, the calculated absorbed doses are to the whole organism. There is an ongoing discussion about the appropriate factors to be applied in order to account for the dif-ferent RBEs of the different kinds of radiation involved. Exam-ple calculations in this annex show that the estimated weighted absorbed doses from exposure to alpha radiation are sensitive to the value of the factor used. This is relevant to the assessment of doses to biota both as a result of radioactive discharges from a nuclear site and as a result of exposure to radiation from radionuclides that are naturally present in the environment. 143. The estimated doses to biota are compared in this annex with those to humans in accordance with the approach given in reference [U3J. The comparison shows that the weighted absorbed doses to terrestrial non-human biota and the effective doses to humans are gencrally of a similar order of magnitude, for a given level of environmental contamina-tion by radionuclides. The weighted absorbed doses to marine biota are. in general, considerably higher than the effective doses to humans (for whom an annual consumption of marine fish of 20 kg is assumed for illustrative purposes). 144. The results of the dosimelric calculations presented in this annex are based on stylized models of ecosystems using average values for most of the model parameters. Thus, they do not accurately reflect the variability of ecosystems and the pro-cesses present in nature that control the envirorunental mobility of radionuclides. In addition, the exposures due to the various sources of natural background radiation and their variabilities would have to be included if the results presented in this annex were to be used in a sitc-specific assessment. As indicated ear-lier, there are substantial uncertainties associated with the esti-mation of dose rates to non-hwnan biota, including those associated with the environmental pathways (such as in the val-ues of the transfer factors) and those related to dosimelric issues.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA II.

SUMMARY

OF DOSE-EFFECTS DATA FROM THE UNSCEAR 1996 REPORT 145. In the absence of reports of obvious deleterious effects on other organisms from exposure to environmental radiation, whether of natural origi n or due to the controlled discharges of radionuclides to the environment, it had gen-erally been accepted that priority should be given to evaluat-ing the potential consequences for humans (which are among the most radiosensitive mammalian species) and to providing a sound basis for protecting human health. By 1996, this position had. however. been questioned [01. TI], and at least one situation (namely deep-sea sediments, an environment very remote from man) had been identified where the above accepted priority could be incorrect ((3]. In response to such concerns, the Committee noted that the impact of radiation exposure of non-human biota had been studied in a number of situations [12, 13, 14, M I, N 1. WI. W2J and considered that it was appropriate to conduct an independent review of the matter and to summarize the state of knowledge existing at that time. The UNSCEAR 1996 Report [U4J took account of the earlier reviews and studies and the Commiuee's summaries of the radiobiological work carried out over the previous 50 years. 146. In its 1996 report, the Committee noted that there was a fundamental difference in the approaches to the protection of humans and non-human biota from the effects of exposure to ionizing radiation. For humans, ethical considerations had made the individual the principal object of protection. This meant, in practice, that any incremental risk to the individual arising from increased radiation exposure was to be con-slrained below some level that society judged to be accepta-ble; this level of risk. although small, was not zero [15J. For non-human biota, the populations of the biota were consid-ered to be important and protection from a significantly increased risk to each population arising from radiation exposure might be the appropriate objective. Exceptions might be populations of small size (rare species) or those reproducing slowly (i.e. with long generation times and/or low fecundity) for which protective measures might be more appropriately targeted at the level of the individual organ-ism. The Committee noted that there could not be any effect at the population level (or at the higher levels of community and ecosystem) if there were no effects on the individual organisms constituting the different populations. It went on to suggest that radiation-induced effects on some members of a population would not necessarily have any significant consequences for the population as a whole. 147. The Conunittee noted that natural populations of organisms existed in a state of dynamic equilibrium within their communities and environments and that exposure to ionizing radiation was but one of the stresses that may affect this equilibrium. The incremental radiation exposure from human activities could not, therefore, be considered in isola-tion from other sources of stress, whether natural (e.g. cli-mate, altitude, or volcanic activity) or of human origin (e.g. synthetic chemical toxins, oil discharges, exploitation for food or sport, or habitat destruction). When (as is not uncom-mon) ionizing radiation and chemicals, both resulting from human activities, acted together on a population, the difficult problem arose of correctly attributing any observed response to a specific cause. 148. The objective of the UNSCEAR 1996 Report on the "Effects of radiation on the environment" rU4J was to summarize and review information on: The exposures (actual or potential) of organ-isms in their natural habitats to the natural back-ground radialion. to radionuclides discharged into the environment in a controlled manner from industrial activities, and to radionuclides released as a consequence of accidents; and The responses of plants and animals, both as indi-viduals and as populations, to acute and chronic irradiation. 149. The Committee hoped that its review would assist national and international bodies to select appropriate criteria for the radiological protection of natural populations, commu-nities and ecosystems. The following paragraphs recapitulate the infonnation available to the Committee in 1996. A. Dosimetry for environmental exposures 150. As discussed in the annex to the UNSCEAR 1996 Report [U4J, reliable detemlination of the dose rate to organ-isms is essential for assessing the potential or actual impacts of contaminant radionuclides in the environment. The Com-mittee noted that "this simple statement conceals a multitude of difficullies that prevent the easy achievement of that esti-mation". In practice, it is necessary to make simplifying assumptions, with the degree of simplification depending on lhe purpose of the assessment. For example, for the purpose of screening, the concept of a single generic biota that repre-sented all plants and animals had been used LA2]. More sophisticated models attempted to account for the dose dis-tributions within reference organisms of assumed shapes and sizes and the fraction of radiation being absorbed within the organism [W2J. The Committee's views on dosimetry for estimating the exposure of biota based on what was known in the UNSCEAR 1996 Report [U4J are summarized below. 151. A dosimetric model is essentially a mathematical con-struction that allows the energy deposition in a defined target to be estimated from a given radionuclide (source) distribu-tion. The model was often derived using theoretical or empirical functions that described the distribution of dose about a point source [B2, B3, LI, W2J. The dose at a point in the target was then obtained by integrating the point source dose distribution function over the defined radionuclide source, either internal or external to the organism. This

'56 UNSCEAR 2008 REPORT: VOLUME II procedure was frequently simplified by using ideal geometries (spheres, ellipsoids, etc.) of appropriate size to represent the target and by assuming that the radionuclide distribution was unifonn (over a surface or lhrough a vol-ume) or varied in a way that could be described by a simple mathematical expression (e.g. an exponential decline in radi-onuclide concentration with depth in soil or sediment). Alternatively, Monte-Carlo calculations had been used to delennine the absorbed fractions of energy for a variety of source and target geometries IB4, E2l These data could be used, either directly or with interpolation (or, to a lesser extenl, with extrapolation) for geometries that could repre-sent targets of environmental concern. In principle, these pro-cedures could be adapted for use in estimating doses to terrestrial and aquatic organisms, from both the plant and ani-mal kingdoms, for both internal and external sources of radiation. 152. Dosimetric models had been developed to take account of the radiation type; the specific geometry of the target (e.g. the whole body. the gonads, the developing embryo or the plant meristem); and the source of exposure (e.g. radionuclides accumulated in body tissues, adsorbed onto the body surface or distributed in the underlying soil). Clearly, it was not possible to consider all organisms. and there were limitations in the basic data that were available as input to the models (e.g. the spatial and temporal distribu-tions of radionuclides both within the organism and in the external environment). Additional sources of complexity arose from the behaviour of mobile organisms, particularly some aquatic organisms and many insects, which inhabit dif-ferent environmental niches at different stages of their life cycles. Thus, the models had to be simplified and general-ized without undue loss of the realism that is essential for a valid estimation of dose. 153. The presence of an alpha particle component in the total absorbed dose rate to a tissue in a plant or animal raised the question of how to take account of the probably greater effectiveness of this type (quality) of radiation in producing biological damage. The RBEs of different qualities of radia-tion had been very critically examined for the purposes of human radiation protection. Each component of the absorbed dose to a tissue or organ was weighted by a factor which took account of the RBE of the radiation involved [IS]. It seemed reasonable to apply a similar approach to the radia-tion dosimetry for organisms other than man. In practice, however, there were circumstances that altered the detailed application of this approach. In the human case, the major concern had been with the induction of stochastic effects (principally cancer) at low doses and dose rates. For alpha radiation, experimental detemlinations ofthe RBE had led to a recommended radiation weighting factor of 20 for the pur-pose of human radiation protection. In the case of wild ani-mals. however, the Committee assumed that it was likely that detenninistic effects were of greater significance. For alpha radiation, the experimental data for animals indicated that a lower factor to reflect the RBE would be more appropriate; the factor to reflect the RBE of beta and gamma radiations would however be numerically the same as the radiation weighting factor used in human radiation protection. On the assumption that mammals are the most sensitive species, these values could be applied to other taxonomic groups. 154. In its 1996 UNSCEAR Report [U4], the Committee assumed that these factors would also apply to effects on plants, although there were no definitive experimental data to support this. In the absence of protection quantities (equivalent and effective dose) for non-human organisms. the absorbed doses from low-LET radiation (beta particles. X-rays and gamma rays) and from high-LET radiation (alpha particles) were assessed and specified separately in the UNSCEAR 1996 Report [U4]. The absorbed doses retained the unit, joule per kilogram (J/kg), with the special name grny (Gy). 155. An IAEA technical report [14J provided estimates of the dose rates to terrestrial plants due to radionuclides depos-ited following discharges to the atmosphere. The model, PATHWAY [W3], developed to eslimate doses to humans, had been used to derive the equilibrium concentrations of radionuclides in plants and animals for the limiting case in which humans, while living on the land, breathing the air over it and eating the food produced from it, would receive an annual effective dose of I mSv. To estimate the dose to plants from internal sources, it was assumed that the energy of alpha and beta particles would be totally absorbed (except for emissions from 32p, which would be 50% absorbed) and that 10% of the gamma-ray energy would be absorbed. An additional degree of conservatism was provided by using estimates of the radionuclide concentrations in plant tissue on a dry weight basis (which are 5-10 times higher than on a wet weight basis) to calculate the absorbed dose rates to living (i.e. "wet") plant tissue. The results are given in table 21. As these estimates had been made using a radio-ecological model and a scenario designed for calculating exposures to humans, the calculated exposures of non-human species should be interpreted cautiously. 156. The annex of the UNSCEAR 1996 Report [U4] noted that there have been fewer estimates of the potential expo-sures of fully terrestrial animals than of animals occupying semi or fully aquatic niches. This was thought to be a reflec-tion of the greater use that had been made of aquatic systems for the discharge of radioactive waste. 157. The annex of the UNSCEAR 1996 Report [U4J sug-gested that naturally occurring alpha-emitling radionuclides appeared to be the most significant sources of background radiation exposure for the majority of wild organisms. 158. In its 1996 report, the Committee considered that the data on the radiation exposures of non-human biota due to both natural background radiation and contaminant radio-nuclides were incomplete, more in some areas than in others. The Committee also noted that the aquatic environment was probably the most thoroughly studied environment up to that lime [12, 13, 17, NI, N2, WI], even with the substantial

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BillA generalizations that had had to be made, particularly with respect to the range of organisms that could reasonably be considered [13]. As had been emphasized elsewhere [13, 16}, the limiting factor was not the development of an appropri-ate dosimetric model for a particular organism but rather the acquisition of essential input data on the temporal and spa-tial distributions of the radionuclides both external to and within the organism. Although dynamic mooels had been employed to describe the dispersion and dilution of radio-nuclides in a water body, related phenomena (e.g. transfers to sediments and biological tissues) were almost always modelled as equilibrium processes, i.e. using simple distri-bution coefficients and (whole-body) concentration factors. This simplification largely neglected the temporal variations in dose rate due, for example, to short-tenn fluctuations in discharge rate, differing stages in the life cycle, and behav-ioural and short-tenn environmental processes (e.g. season-ality). As a consequence, while the estimated absorbed dose rate might be a reasonable indication of the general magni-tude of the actual environmental value, the Committee con-sidered that it did not provide a very secure basis for evaluating total doses over time. Table 21. Estimated dose rates to organisms from controlled discharges of radionuclides that would each result in an annual dose of 1 mSv to humans residing in the same environment Table 6 of UNSCEAR 1996 Report [U4J; based on [14. N1J RiJdionuclide 'H "C "P

• Co "S,

'il "f, "'I "'Cs ~"" ~"' ~"' "'Arrfl iJ Dischargos to atmosphoro. b DOIllIlstic shoop. e Discnargos to wator (IamsL d High-LET radiation. 5.B 1B 3Z 1.0 3B 1.1 5.4 0.013 159. The Committee also noted that accident situations were by nature quite different from routine situations, par-ticularly in their potential to produce high dose rates and doses to the environment. It concluded that generalization is difficult because the actual exposure regime depends on the types and quantities of radionuclides released, their initial dispersal and deposition patterns, and their redistribution over time in the environmenl. Following the accident at the Chernobyl nuclear power plant. large quantities of short-lived radionuclides were released, leading to high dose rates in the local area. Total doses up to 100 Gy were delivered to trees (and, by inference, to most other organisms in the local-ity) over a period of a few days [KII. This radiation regime might have been characterized as "acute" in that the doses were delivered in perioos that were shorter than or compara-ble to the time taken for severe damage to become apparent. During this initial (acute) phase, the dose rates declined rap-idly as the very short-lived radionuclides decayed. The release following the accident in 1957 in the south-eastern Urals was dominated by '-<<Ce-'<<Pr (approximately 66%: Dose mtrJ (IlGylh) AnimaJsil.b Fislf 5.B 0.59 11 1B 4.B 0.53 0.041 67 1.0 3.B 0.058 3.1. 0.7Z 3.6 1.6 4.7 O.lJOO 55 0.49 0.71 t.", = 285 d) and ~_9Wb (approximately 25%; Iv. = 65 d). In that case, the dose rates locally were also relatively high dur-ing the initial phase (more than 4 mGylh) but declined more slowly, such that high total doses (causing severe effects, including mortality) could still be accumulated from essen-tially chronic exposure. Close to the release point, total doses up to 2,000 Gy were experienced [T4]. In the longer tenn. the exposure regime for the Chemobyl release was domi-nated by mCs (tv, = 30 a) and 'JOSr (t\\> = 28.6 a), and that for the south-eastern Urals accident area by 'JOSr. In both cases, the exposures were chronic and moderately high, with responses other than mortality becoming significant. 160. Radioactive waste discharges to atmosphere, landfills or aquatic systems from man-made practices entail increased radiation exposure of wild organisms. The incremental radiation exposures are chronic (i.e. continuing) at absorbed dose rates of generally no more than 100 flGylh, but, very exceptionally, they may reach several thousand microgray per hour. The Committee [U4} noted that these additional

'58 UNSCEAR 2008 REPORT: VOLUME II radiation exposures may be greater than the nonnal range of natural background exposures but generally are within the extreme range of background exposures, if the exceptional cases of areas of uranium and thorium mineralization are included. Given that radioactive wasle discharged to the environment will nonnally be dispersed and diluted. dose rates higher than those due to nonnal natural background exposure are likely to apply to only a small proportion of the individual organisms in any population and the average dose rate to the population would probably be much lower [W8, W9j. B. Effects of radiation exposure on plants and animals 161. Studies of the effects of ionizing radiation exposure on plants and animals were started immediately following the discovery of X-rays and radioactivity (see, for example, reference [A4J). Since 1945, when the first nuclear detona-tions were conducted, there was widespread concern about the impact of environmental radiation exposures and interest in the environmental behaviour of radioactive materials. As a result, studies using a wide variety of plant and animal species were perfonned [A4, 8 5, C3, PIJ. 162. The Committee, in its 1996 report [U4}, noted that the responses of organisms to radiation exposure were varied and may become manifest at all levels of organization. from individual biomolecules to ecosystems. The significance of a given response depended on the crilerion of damage adopted, and it was not to be concluded that a response at one level of organization would necessarily produce a consequential, detectable response at a higher level of organization. 163. The Committee also noted lIlat a population might be defined as all members of a population species [U4J. Alterna-tively, a population might be considered as an aggregate of inter-breeding individuals of a species occupying a specific location in space and time [S5J, The laller definition is per-haps more useful given the Committee's observation that radiation fields, such as those arising from radioactive waste discharges, generally show large spatial variability, not least because of the often discrete nature of the source, and there-fore many members of a population might not receive any significant exposure from a particular source. The natural dis-tributions of most species are inhomogeneous because of the variations in physical, chemical and biological conditions under which the individuals of the species are able to survive, i.e. species are geographically restricted. Thus, it is probable that a more limited, and relevant, definition of a population could be developed for the purposes of environmental impact assessment. 164. The following definition (developed for use in popula-tion ecology) has been suggested as a useful basis for discus-sion and progress [l4J: "A population is a biological unit for study, with a number of varying statistics (e.g. number, den-sity, birth rate, death rate, sex ratio, age distribution), and which derives a biological meaning from the fact that some direct or indirect interactions among its members are more important than those between its members and members of other populations" [B6J, Notwithstanding this definition, it has to be understood that a population of a particular species is always linked to its environment. Such a population would (or could) be a self-sustaining unit, independent of other, geographically separate populations of the same species. However, protection of this population would require that increased radiation exposure did not significantly affect the attributes mentioned in the definition on which the popula-tion depended for its maintenance within the nonnal dynamic range of variation dictated by the interactions of natural physical, chemical and biological factors. 165. These attributes, which could be defined only for populations of organisms and might be taken to be indicators of their health, are nevertheless amalgamations of properties that relate to individuals (in no sense was this meant to imply simple addition). The Committee concluded. in effect, that for a response to radiation exposure at the population level (or, indeed, at any higher level of organization) some clearly detectable effect in individual organisms (i.e. at lower levels of organization) would be expected. This clearly implied that the protection of the population (as the ultimate objective) might be achieved by restricting the exposure of individual organisms to the extent that there are no significant radiation effects on those processes necessary for the maintenance of the population. It is therefore necessary to consider the avaiJ-able infonnation on the effects of radiation exposure (mainly at chronic low dose rates) on the relevant processes in indi-vidual organisms, to consider how these responses might translate to an impact on the population, and to examine the results of studies of population responses to deliberate experimental irradiation or to exposure in the environment due to controlled or accidental releases of radionuclides. 166. Examination of the population attributes indicated that the individual responses to radiation exposure likely to be significant at the population level are mortality (affecting age distribution, death rate and density), fertility (birth rate), fecundity (birth rate, age distribution, number and density) and the induction of mutations (birth rate and death rate). These individual responses can be traced to events at the cellular level in specific tissues or organs. An extended sum-mary discussing the processes involved was provided in annex J, "Non-stochastic effects of irradiation", of the UNSCEAR 1982 Report [U9}. There was a substantial body of evidence indicating that the most radiosensitive sites are associated with the cell nucleus, specifically the chromo-somes, and that, to a lesser extent, damage to intracellular membranes is additionally involved. The end result is that the cells lose their reproductive potential. For most cell types, at moderate doses, death occurs when the cell attempts to divide; death does not, however, always occur at the first post-exposure division: at doses of a few gray, seve-ral division cycles might be successfully completed before death eventually occurs. It was also well known that radio-sensitivity varies within the cell cycle, with the greatest sen-sitivities being apparent at mitosis and the commencement

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 25' of DNA synthesis [U9]. It followed that the greatest radio-sensitivity is likely to be found in cell systems undergoing rapid cell division for either renewal (e.g. spermatogonia) or growth (e.g. plant meristems and the developing embryo); these examples clearly underlie the processes in individual organisms that are important for the maintenance of the population. 167. Fractionation or protraction of exposure to low-LET radiation increases the total dose required to produce a given degree of damage since at low dose rates. the factors respon-sible for mitigating the response come into play. These include the repair of sublethal damage, the repair of poten-tially lethal damage, the replacement of killed cells through proliferation of survivors, and other slow repair processes not related to cell repopulation [U9]. Although it was clear to the Committee that repair. in the general sense, is possible. the existence and extent of residual injury was less clear. While such an outcome might be demonstrated for moder-ate, acute doses, it was not possible to extrapolate these results in order to predict the likely response to low-level exposures extending over a significant fraction of the life-time of an organism. However, given that genetic mutations might be passed from generation to generation, it was rea-sonable to suppose that somatic mutations individually con-sistent with cell survival could occur and accumulate over time until the combined impact might reduce cell viability.

1.

Terrestrial plants 168. Radiation injury in plants expresses itself as abnornlal shape or appearance, reduced growth or yield, loss of repro-ductive capacity, wilting and (at high exposures) death lSI]. Acute lethal doses 10 higher plants ranged from 10 to about 1.000 Gy (approximate mean absorbed doses averaged over the whole plant). The Committee concluded that plants such as mosses, lichens and unicellular species are at one extreme of radiosensitivity being highly resistant to radiation expo-sure; woody species are at the other extreme being the most sensitive. In 12 species of woody plants assessed 10--14 months after exposure, the lethal doses were found to be in the range of S-96 Gy [S2]. The pine tree was the most sensitive, experi-encing mortality following short-ternl absorbed doses of about 10 Gy [W5]; growth was severely inhibited at 50--60% of the lethal dose. Roral inhibition was observed at 40--50% of the lethal dose, and fail ure to set seed at 25--35%. Thus, the capacity of the plant population to maintain itself could be damaged at acute doses lower than those required to cause mortality. Below 10% of the lethal dose, effects were not so apparent and the plants maintained a normal appearance. These general observations for several herbaceous plant spe-cies are illustrated in figure X [S3]. Another general relation-ship was that the dose that reduced survival by 10% (LD)o) was roughly equivalent to the dose that reduced the yield by 50% (YD~)[S 1 J. Figure X. General ranges of response to radiation exposure by herbaceous plants as a percentage of the lethal dose (lD,OII) [S3] Mortality in 50% of plants ---+- Severe growth inhibition Floral inhibition Pollen sterility Mortality in 10% of plants Yield reduced by 50% Failure to set ---+- Yield reduced by 10% Normal appearance o 10 20 30 40 50 60 70 80 PERCENTAGE OF LETHAL DOSE 169. The Committee, in the UN5CEAR 1996 Report [U4]. noted that protraction of radiation exposures increased the total doses required to kiU plants [54]. 170. A range of sensitivities to radiation exposure was exhibited by the components of plants, ranging from dry seed (least sensitive) to apical meristems (most sensitive). Various crop plants showed different reductions in yield following radiation exposures, with further modifications being caused by external factors (e.g. temperature and humidity). 171. Plant species also varied in their tolerance to chronic radiation exposures. For the more sensitive pine species, dose rates of more than 3 mGyfll over 3-4 years reduced needle growth; in one-year-old saplings, needle length was substan-tially reduced when subjected to a dose rate of7 mGylh over a single growing season. Trunk growth was reduced in mature pine trees by dose rates in the range 0.4-2 mGyfll over a 9-year period. Delayed bud burst and an extended period of leafing out was demonstrated in white oaks chronically exposed to gamma radiation. At dose rates greater than 4 mGylh, the trees were more susceptible to aphid infestation.

260 UNSCEAR 2008 REPORT: VOLUME II 172. Ln view of the effects on the most sensitive plants evi-dent with chronic exposure at dose rates of 1-3 mGylh and of some specific changes noted at dose rales of 0.4--2 mOylh, the Committee [U4J suggested that chronic dose rates at or below 400 )JGylh (10 mGy/d) should have only slight effects on sensitive plants but would be unlikely to produce any sig-nificant deleterious effects on the wider range of plants present in natural plant communities.

2.

Terrestrial animals 173. TIle effects of radiation exposure on mammals had been extensively studied in radiobiological experiments using labo-ratory animals (mice, rats, dogs and monkeys) and domestic livestock (pigs, sheep, goats, burros and cattle) [87, 88]. Except in the case of exposure involving unusually high doses, radiation damage or lethality in mammals results from distur-bances in the haematopoietic system and the gastrointestinal mucosa. These cell self-renewal systems contain stem cells, differentiating cells and functional end cells, with the stem cells being the most radiosensitive and thus having the pre-dominant influence on the radiation response. Symptoms become apparent when end cells are not replaced. 174. Protraction ofa given total exposure generally reduces the extent of injury, as it allowed two distinct processes to intervene. First, sublethal danlage is reparable at the cellular level, which is particularly important for exposures to low-LET radiation. Secondly, cell proliferation could replace lethally damaged cells and maintain the cell population at a new level, which is detennined by the dynamic interaction between the dose rate and the rate of cell death, and by the total reserve proliferative capacity. 175. The Commillee noted that at reduced dose rates (pro-traction of a given total dose) of low-LIT radiation, all species showed a gradual increase in LD):,l> i.e. higher total doses were tolerated. This changing response was attributed to the increas-ingly effective influence of cellular repair of sublethal damage at the lower dose rates. As the dose rate was further reduced, a sharply increasing trend in the val.ues for the median lethal dose was apparent for mice, pigs. dogs. goats and sheep; the approximate threshold dose rates for this change in response corresponded to the accumulation of an LD~ dose within peri-ods ranging from 0.2 days (mouse) to 9 days (goat). This rapid change in LD~ with dose rate was interpreted as being the consequence of a shifting balance in the dynamic interaction between the dose-rate-dependent cell loss and the cell prolif-eration and maturation kinetics in the haematopoietic system; the latter processes are under homeostatic control, i.e. their rate constants can alter in response to radiation-induced cell loss. The data for the burro (donkey) and primates did not show any sharp increase in the median lethal dose at dose rates down to 8.3 mGylh(LD~ in 18 days) and 5.4 mGylh (LOX) in 60 days), respectively. There did not appear to be any data for LO~ values at dose rates of less than 4 mGylh or for exposure periods exceeding 60 days, although studies had been made outside these levels for other purposes. 176. While acknowledging that the numbers of mamma-lian species that had been (or indeed were likely to be) studied were extremely limited and probably atypical, the Committee noted [U4] that, even taking account of substan-tial interspecific variability, the available data provided very little evidence that chronic dose rates below 400 IlGylh (approximately 10 mGy/d) to the most exposed members of the population would seriously affect their mortality (and, thus, the death rate in populations of these species) from either detemlinistic or stochastic responses. 177. The effects of radiation exposure on reproduction had also been much studied, with most of the results suggesting that nataHty is a more radiosensitive parameter than mortal-ity in species other than man and therefore of more relevance in an environmental context. The Committee considered that the minimum dose required to depress reproduction rates might be less than 10% of the dose required 10 produce direct mortality [W6]. 178. The Committee suggested that damage to the develop-ing mammalian embryo appeared to be a potentially signifi-cant criterion for assessing the impact of contaminant radionudides in the natural environment. Dose rates of 420 f-LGylh throughout gestation produced readily detectable reductions in the populations of gemI cel.ls in the developing gonads of a number of mammalian species. and the lowest dose rate at which damage had been seen was 10 IlGylh from lritium (as HTO in drinking water) incorporated in female mouse embryos. In addition, dose rates of the order of 420 IlGylh induced reductions in neonatal brain weight, although the significance of this deficit was unknown in functional or behavioural teons. The wider significance of these responses at the population level had not been investi-gated. Even recognizing that only very limited data were available, the Committee concluded that maximum dose rates of 100 IlGylh (2.4 mGy/d) Lo pregnant members of a mammalian population were unlikely to have any conse-quences for the population as a whole from the induction of damage in the developing embryos. 179. The Committee noted Ihat the data on the radiosensi-tivity of terrestrial animals were dominated by data on mam-mals, the most sensitive class of organisms. Acute lethal doses (LO~) were 6-10 Gy for small mammals and 1.5-2.5 Gy for larger animals and domestic livestock. When a toLal dose of magnitude similar to the LOW)O was delivered over a lifetime-for example. 7 Gy to the mouse (420 IlGylh. or \\0 mGy/d}-the average loss of lifespan had been esti-mated to be about 5% and resulted from the induction of neoplastic disease [U9]. There was substantial inter-species variability, but, in general, little indication that dose rates below about 400 IlGylh to the most exposed individual would seriously affect mortality in the population. 180. The Committee noted that reproductive capacity was more sensitive to the effects of radiation exposure than life expectancy (mortality) and felt that the reproductive rates of mammals might be depressed at doses that were 10% of

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 261 those leading to mortality. It also felt that some loss of oocytes might occur at I % of the lethal dose, but because of excess oocyte production, fecundity should be affected to a lesser extent. Mice, exposed from conception to a dose rate of 800 )lGylh, could be made sterile at 25 weeks. In the most sensitive mammal studied, the beagle dog, a dose rate of 180 IJGylh caused progressive cell depletion and sterility within a few months, but a dose rate of 36 IJGylh over the whole life produced no damaging response. The Committee concluded that a radiation dose rate of less than 40 )lGylh to the most exposed individual in a population (and most prob-ably, therefore a lower mean dose rate to individuals in the population as a whole) would be unlikely Lo have an impact on the overall reproductive capacity of a mammalian popula-tion as a consequence of the effects of radiation exposure on fertility. fecundity or the production of viable offspring. 181. The effects of radiation exposure on birds had been shown to be similar to those on smal.1 mammals. Reptiles and invertebrates were less radiosensitive, although physio-logical differences began to make direct comparisons with other species less appropriate. The chronic exposure of one short-lived species of lizard in enclosures had shown no evident effects when exposed over 5 years at a dose rate of 830 IJGylh. In two longer-lived species of lizard. some indi-viduals had been made sterile after 3.5 years at a dose rate of 630 fJGyfh in one species and after 5.5 years at a dose rate of 210 )lGyfh in another species. Adult invertebrates were seemingly quite insensitive to the effects of radiation exposure in tenns of induced mortality. but the process of gametogenesis, developing eggs and juvenile stages were more sensitive.

3.

Aquatic organisms 182. A number of reviews of the studies of the effects of exposure to ionizing radiation on aquatic organisms were available to the Committee [A3, B9, C3, E2, 12, 13, NI, N2, Pl, T5, W9] during the preparation of the annex of the UNSCEAR 1996 Report [U4]. Some of these had been pre-pared speci fically to provide a basis for assessing the poten-tial effects of discharges of liquid radioactive effluents on aquatic organisms in their natural environment [12, 13, NI, N2, WI J. 183. Among aquatic organisms. fish were the most sensi-tive to the effects of radiation exposure; the developing fish embryos were particularly sensitive. The LD.,., for acute irra-diation of marine fish was in the range 10--25 Gy for assess-ment perioos of up to 60 days following exposure. The upper end of the range of LD:;o for marine invertebrates had been found to be several hundred grays. Embryos, on the other hand, were affected at much lower doses, for example, the LD~ for salmon embryos was O. 16 Gy [B I 0]. 184. Chronic exposures at dose rates of 10--30 mGyfh had no effect on the mortality of snails. marine scallops, clams and blue crabs. Dose rates somewhat above this range had some effects on food-limited populations of Daphnia pulex. Short-tenn (40 days) exposure of mosquito fish at dose rates in the range 14--54 mGylh showed no radiation-induced mortality, but. for the closely related guppy, there was some indication that long-lenn exposure (>470 days) at dose rates above 1.7 mGyth reduced the nonnal lifespan, particularly for males. 185. Reproductive effects are a more sensitive indicator of radiation response for aquatic organisms. Chronic dose rates in the range 3.2-17 mGyfh reduced the reproductive capa-city in the freshwater snail, Pliysa lieterostroplia, and in the marine polychaete wonns, Opliriotrocha diadema and Neall-tlies arenaceodentata. Exposure at a dose rate of 7.3 mGyth rendered male freshwater fish (Ameca splendens) effectively sterile after 50 days, and exposure at a dose rate of 1.7 mGyth over the lifespan of pairs of guppies (the freshwater fish. Poecilia reticulata) significantly reduced the lifetime pro-duction of offspring [W7]. It had been concluded that sig-nificant effects on fish gonads from chronic radialion exposure would be unlikely at dose rates less than I mGyth [13, WI]. Overall consideration of the data available led to the conclusion that chronic irradiation at dose rates up to 400 IJGyfh to a small proportion of the individuals in an aquatic population (and, therefore, with correspondingly lower average dose rates to the whole population) would not have any detrimental effects at the population level [14, N I].

c. Effects of radiation exposure on populations of plants and animals 186. The Committee noted in the annex of the UNSCEAR 1996 Report [U4] that one of the difficulties in evaluating the effects of radiation exposure on populations and ecosystems was the determination of the parameters to measure. Typi-cally measured attri bules at the population level included numbers of individuals, mortality rate, reproduction rate and mean growth rate. The Committee also noted that measura-ble changes in populations and communities required rather severe effects to be induced at the cellular and individual organism levels [e.g. W8]. The Committee also noted that genetic or somatic mutations that could be produced by rela-tively low levels of exposure might have little or no impact on population or community perfomlance because of natural selection [8 10, C4, M2, P3. T5] and the convergence of genetic infonnation among adjacent populations [R I, T5].

187. The Committee also noted that the effects of radialion exposure at the population and community levels were mani-fest as a combination of direct changes due to radiation dam-age and indirect responses to the direct changes. This seriously complicated the interpretation of the effects of radiation exposure on organisms in the natural environment. The wide range of radiosensitivities of the organisms that make up most natural communities creates a situation where, if doses are such that the sensitive species, but not the more resistant ones, are affected, the latter might gain a signi ficant competitive advantage and increase in abundance or vigour.

262 UNSCEAR 2008 REPORT: VOLUME II This could erroneously be interpreted as a honnetic response; such a response might not however be produced if the resist-ant species alone were irradiated. This is but one of many examples of indirect response to the direct effects of radiation exposure. 188. Because of the compensation and adjustment possible in animal species, the Committee considered that it is unlikely that radiation exposures causing only minor effects on the most exposed individual would have significant effects on the population. Reproductive changes are a more sensitive indicator of the effects of radiation exposure than mortality, and mammals are the most sensitive animal organ-isms. On this basis. chronic dose rates of less than 100 IlGylh to the most highly exposed individuals would be unlikely to have significant effects on most terrestrial animal communi-ties. The Committee also concluded that maximum dose rales of 400 IJGylh to a small proportion of the individuals in aquatic populations of organisms would not have any detri-mental effect at the population level. These conclusions referred to the effects of low-LET radiation exposure. Where a significant part of the incremental radiation exposure comes from high-LET radiation (alpha particles), the Com-mittee considered that it is necessary to take account of the different RBEs. D. Effects of major accidents 189. The UNSCEAR 19% Report [lJ4] discusses the effects of two accidents in the fornler Soviet Union (at Chemobyl and at Mayak in the south-eastern Urals) leading to major releases of radioactive material into the environ-ment [A28, GI9, 123.124, KI, K22, K23, N9, 529, S34. S40, T4, 1'27]. These accidents provided opportunities to observe radiation-related changes in plant and animal communities. The Committee noted however that any major accident is likely io be unique in tenns of the quantity and composition of the radioactive material released, the time course of the release, the dispersal and deposition patterns, which are gov-erned by local and regional meteorological or hydrological conditions, and the biochemical and geochemical character of the areas subject to contamination. Where long-lived radionuclides are released, biochemical and geochemical processes would detennine the long-ternl behaviour and redistribution of the radionuclides in the environment. Given this multiplicity of factors, any major nuclear accident would be expected to yield new radioecological infonnation. How-ever, the primary concern following an accidental release of radionuclides is to ensure that the radiation risks to human populations are controlled and minimized. Consequently, the only environmental infonnation likely to be collected is that which is immediately necessary to meet this objective. Such infonnation is unlikely to be sufficient for the purposes of developing a complete radioecological description of the situation. The larger the incident and the greater its potential human impact, the more limited would be the resources available to collect radioecological infonnation, particularly in the early phase following the accident. 190. In particular, the data required to develop estimates of the radiation exposure of wild organisms (i.e. the space and time-dependent variations of the radionuclide concen-trations, especially of the short-lived radionuclides both within the organisms and in their external environment immediately following an accident) would not be known. These variations would result in substantial intra-species and inter-species inhomogeneities in exposure and would pose considerable difficulties for establishing a clear and reliable relationship between cause (the accumulated radia-tion dose) and any observed effect. In practice, it is likely that estimates of the dose rates in the early period following the release would be calculated subsequently from the observed distribution of deposition densities of the longer-lived radionuclides, from a knowledge of the relative quan-tities of the radionuclides released, and using models of radionuclide behaviour in the environment. Such dose-rate estimates are inevitably imprecise and could be subject to significant systematic error. 191. The highly variable habits and target geometries of the wild organisms are additional complicating factors. These range, for example, from soil bacteria to single-celled algae and protozoa, and include a wide variety of terrestrial and aquatic invertebrates, mammals (ranging from shrews to deer) and large deciduous or evergreen trees. Plants provide a very high surface area to mass ratio (compared with ani-mals) for deposition/adsorption of a radioactive aerosol. Because the leaves, flowers and lerminal buds of plants are responsible for energy absorption, growth and reproduction, a coincidence arises between radionuclide accumulation (and hence radiation dose) and potential radiosensitivity. Other examples of coincidence are the surface litter layer and its populations of invertebrate decomposers in terrestrial environments, and surface sediments and benthic organisms in aquatic systems. 192. Depending on the quantities of specific radio-nuclides released following an accident. the radiation exposures might range from low (a few multiples of the natural background) to high (absorbed doses greater than lOy). Different phases of biological response to the higher total doses might be distinguished. Initially, and, in particular if short-lived radionuclides made up a signifi-cant proportion of the release, there might be an acute phase in which total doses sufficient to produce immediate or relatively early detectable biological responses are accumulated. In the intermediate phase, dose rates would decrease owing to the decay of the short-lived radio-nuclides and possibly, but not necessarily, owing to the redistribution of the longer-lived radionuclides by natural processes. Even in this phase, the slower accumulation of radiation dose might still result in total integrated doses sufficient to prevent recovery of organisms damaged in the initial phase or lead to the appearance of medium-term damage. In the long-tenn phase, post-irradiation recovery (and adaptation) becomes apparent, provided that the ini-tial and medium-tenn damage had not been large enough to radically alter the population or community structure.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 263 III.

SUMMARY

OF OOSE-EFFECTS OATA FROM THE CHERNOBYl ACCIDENT 193. A great deal of scientific infonnation concerning the effects of exposure to ionizing radiation has been developed from studies of non-human biota in the area surrounding the site of the Chemobyl accident. The follow-up studies pro-vided the main source of new infonnation on the effects of radiation exposure on non-human biota since the UNSCEAR 1996 Report [U4]. This area has a temperate climate and flourishing flora and fauna. Much of the new infonnation, originally reported in Russian. has been summarized in a report prepared for the Committee [A5.l and by the work of the Chemobyl Forum [E8]. The following discussion of radiation levels and effects on biota observed in the region around Ihe Chemobyl nuclear power plant is based on infomJation presented in reference fE8] and in other recent reviews {G26]. A. Radiation exposure 194. The Chernobyl Forum Expert Group on Environment (EGE) [E8] noted that the effects of the Chemobyl accident should be studied within specific time periods. Three distinct phases of radiation exposure have been identified in the area local to the accident [U4]. In the first 20 days, radiation exposures were essentially acute because of the large quanti-ties of short-lived radionuclides present in the passing cloud (",Mo, lJ"-Tell, I33Xe, 131 1 and I40BaILa). Most of these short-lived, highly radioactive nuclides deposited onto plant and ground surfaces, resulting in gamma radiation dose rates of up to about 20 Gy/d. However, for surface tissues and small biological targets (e.g. mature needles and the growing buds of pine trees) there was a considerable additional dose rate due to the beta radiation from the deposited radionuclides. High doses to the thyroids of vertebrate animals also occurred during the first days/weeks following the accident owing to the inhalation and ingestion of radioactive isotopes of iodine and their radioactive precursors. 195. The second phase of radiation exposure extended through the summer and autumn of 1986, during which time the short-lived radionuclides decayed and the longer-lived radionuclides were transported to different components of the environment by physical, chemical and biological pro-cesses. Dominant transportation processes included rain-induced transfer of radionuclides from plant surfaces onto soiL and bioaccumulalion through plant tissues. Dose rates at the soil surface declined to much less than 10% of the initial values owing to radioactive decay of the short-lived radionuclides, but damaging total doses were still accumu-lated. Approximately 80% of the total radiation dose accu-mulated by plants and animals was received within 3 months of the accident, and over 95% of this was due to beta radia-tion exposure [E8]. Measurements made with thennolumi-nescent dosimeters on the soil surface at sites within the 30-km exclusion zone indicated that the ratio of beta to gamma dose was about 26: I, (i.e. % % of the total dose was due to beta radiation exposure) [P18]. 196. The EGE fE8] also defined a third (and continuing) phase of radiation exposure with chronic dose rates less than 1% of the initial values and derived mainly from I37Cs. With time, the decay of the short-lived radionuclides and the migration of much of the remaining mCs into the soil meant that the contributions to the total radiation exposure from the beta and gamma radiations tended to become more compara-ble. Reference [E8] noted that the balance depended on the degree of bioaccumulation of mCs in organisms and the behaviour of the organism in relation to the main source of external exposure resulting from the mCs in the soil. B. Effects of radiation exposure on plants 197. The report of the EGE was a great advance on previ-ous publications describing the follow-up work on the effects of the Chemobyl accident. In particular, the report gave considerable attention to evaluating the dosimetry of, and consolidating the infonnation on the effects on non-human biota. Thus, given both the greatly improved quality of the data and the comprehensive nature of the evaluation provided by the EGE, much of the following discussion is adapted from reference [ES]. 198. Doses received by plants arising from the deposited radionuclides resulting from the Chemobyl accident were influenced by the physical properties of the various radio-nuclides (i.e. their half-lives, radiation emissions, etc.), the physiological stage of the plant species at the time of the accident. and the different species-dependent propensities to take up radionuclides into critical plant tissues [E8]. The occurrence of the accident in late April 1986 was thought to have enhanced the damaging effects of the deposition because it coincided with the period of accelerated growth and reproduction of plants. 199. The deposition of beta-emitting radionuclides onto critical plant tissues resulted in their having received a sig-nificantly larger dose than animals living in the same envi-ronment [p18, P19]. According to reference [G9]. large apparent inconsistencies in the dose-response observations occurred when the beta-irradiation component was not appropriately taken into account. 200. Within the 30-km zone around the Chemobyl plant, the doses to plants associated with the deposition of total beta activity (0.7-3.9 GBq/m2) were sufficient to cause short-tenn sterility and reduction in productivity of some species [PI9]. By August 1986, crops that had been sown prior to the acci-dent began to emerge. Growth and development problems were observed in plants in fields with deposition densities of 0.1 - 2.6 GBq/m2 of total beta activity, and with estimated dose rates initially received by the plants having reached 300 mGy/d. Spot necroses on leaves, withered tips of leaves, inhibilion of photosynthesis, transpiration and metabolite

264 UNSCEAR 2008 REPORT: VOLUME II synthesis were detected. as well as an increased incidence of chromosome aberrations in merislem cells [S22]. The fre-quency of various anomalies in winter wheat exceeded 40% in 1986--1987, with some abnonnaHties apparent for several years afterwards [GI2]. 201. Coniferous trees were already known to be among the more radiosensitive plants, and the pine forests, 1.5---2 km west of the Chemobyl nuclear power plant, received suffi-cient doses, more than 80 Gy, at dose rates thaI exceeded 20 Gy/d, to cause mortality [TIS]. The first signs of radiation injury were yellowing and needle death in pine trees in close proximity to the nuclear power plant and appeared during the summer of 1986. The colour of the dead pine stands resulted in the forest being referred to as the "red forest". 202. Tikhomirov and Shcheglov [T I8] and Arkhipov et aL [A II] found that mortality rate, reproduction anomalies, stand viability, and re-establishment of pine-tree canopies were dependent on absorbed dose. Acute irradiation of Pinus silves-Iris at dose.s of 0.5 Gy caused detectable cytogenetic damage; at doses of more than I Gy, growth rates were reduced and morphological damage occurred; and, at more than 2 Gy. the reproductive abilitie.s of trees were altered. Doses of less than 0.1 Gy did not cause any visible damage to the trees. Table 23 shows the variation in activity concentration and dose among pine trees within the 3D-km zone. 1be radiosensitivity of spruce trees was observed to be greater than that of pines. At absorbed doses as low as 0.7-1 Gy, spruce trees had malfonned needles, buds and shoot growth [K I]. 203. About 90% of the absorbed dose to critical parts of the trees was due to beta irradiation from the deposited radio-nuclides with the remaining 10% from gamma irradiation. Table 22 summarize.s the external gamma dose rates and the internal radionuclide concentrations in the conifers around the Chernobyl plant. By 1987, recovery proce.sses were evident in the surviving tree canopies and the forests were re-establishing themselve.s where the trees had perished {All]. In the deci-mated pine stands, a sudden invasion of pests occurred that later spread to adjoining areas. Grassland. with a slow inva-sion of self-seeding deciduous trees, has now replaced the deceased pine stands. Four distinct zones of radiation-induced damage to conifers were discemable (table 23). Table 22. Activity concentration in needles of coniferous trees and estimated external gamma dose rates in October 1987 as a function of distance from the Chernobyl nuclear power plant For Hzimuth 205 to 260 degrees (adHpted from reference [K12J) Distance from NPP ExtemaJ exposure rate Accumulated external dose Activity concentration in noodles (kBq/kg) 1""1 {/1Gv/hjiJ {mGyfl Ce ~R" Oil ON' "e. me. 1 1500 126000 13400 4100 BOO 1500 1500 4100 110 5 "" ISO 60 B 15 17 71 16 0.' 14 1.5 0.6 0.1 0.17 0.18 0.55 ~ Basod on gamma rildiation IllVllIs all m ooight aoo.e the so~ SOOaG1l. The valoos given in tho origiMI relofllllC6 WGfe in mR/11 and IIave boon converted assuming 1 mR/11 is oquivalenl to 10 flliy/h. Table 23. Zones and corresponding damage to coniferous forest in the area around the Chernobyl nuclear power plant (from reference [K1 ]) lone and classification External gamma dose bposuroratf! Intemal dose ro needles (GyJ (/1Gv/hjil (GyJ Conifor death 14 km'l Complete dealh of pines over 80---1 DO ovor 5 000 _100 Partial damage 10 deciduous troos Subkrthall38 km') Death of mosl growth points 10---20 1 1XXl-5 "" 51)-100 Partial death of coniferous trees Morphological cllangos to deciduous trees Modium damage 11 ZO km'l Supprossod ropmducliw ability H 500-1 "" N-50 Dried noodlos. moIpoologicai changos MiflOfdamage Disturbances in !1Owth. roproduction and morphology 0.5--1.2 < 100 < 10 of coniferous treos ~ The ~a/uos given in tho original reference were in mR/11 and have boon converted assinling 1 mR/11 is equivalent to 10 ~Gv/h.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 265 C. Effects of radiation exposure on soil invertebrates 204. Between 60% and 90% of the initial fallout of radio-nucl.ides was captured by the forest canopy and other plants [£8]; however, within weeks to a few months, the processes of wash-off by rain and leaf fall removed most of the initial deposition to the litter and soil layers, where soil and litter invertebrates were exposed to high radiation levels for pro-tracted time periods. The timing of the accident coincided with the most radiosensitive life stages of the soil inverte-brates: reproduction and moulting following their winter dormancy [Tl8]. Within two months after the accident, the numbers of invertebrates in the litter layer of forests 3-7 km from the nuclear power plant were reduced by a factor of 30 [Kill. and reproduction was strongly impacted (larvae and nymphs were absent). These effects corresponded to doses of approximately 30 Gy (estimated from TLDs placed in the soil) resulting in mortality of eggs and early-life stages. as well as reproductive failure in adults. However, within a year of the accident, reproduction of invertebrates in the forest litter resumed, due, in part, to the migration of invertebrates from less contaminated sites. After 2-3 years, the ratio of young to adult invertebrates in the litter layer, as well as the total mass of invertebrates per unit area, were no different from those in control sites; however, species diversity remained markedly lower [KII]. As noted in the report of the EG E [E8], this is important since the diversity of invertebrate species within the soil faci litates an analysis of the community-level effects of radiation exposure (i.e. changes in species composition and abundance). For example, only five species of invertebrates were found in 10 soil cores taken from pine stands in July 1986, 3 km from the Chemobyl nuclear power plant, com-pared to 23 species at a control site 70 km away. The mean density of litter fauna was reduced from 104 individuals per 225 cm1 core at the control location to 2.2 at the 3-km site. Six species were found in all 10 cores taken from the control site, whereas no one species was found in all 10 cores from the 3-km location [K 13]. The number of invertebrate species found in the heavily contaminated sites was only half that of controls in 1993, and complete spe-cies diversity did not recover until 1995, almost 10 years after the accident LX II]. 205. A fourfold reduction in earthwoml numbers was found in arable soils, but no catastrophic mortality in any group of soil invertebrates was observed. The dose to inver-tebrates in forest litter was 3--10 fold higher than that to those residing in unploughed surface soil since the radio-nuclides deposited on the surface had not migrated down-wards. The result was no reduction in the numbers of soil invertebrates below a depth of 5 cm in the soil as they were shielded by the overlying soil [K II]. 206. Although, the researchers were unclear if sterility of invertebrates occurred in the heavily contaminated sites around the Chernobyl nuclear power plant [K II], the 30 Gy cumula-tive dose reported in the field studies was within the range of experimental doses used to control pest insects by external irra-diation. A recent review indicated that most insect, mite and tick fa.milies require a sterilization dose of less than 200 Gy [B4O], although the sterilization dose for some insects and related arthropods is much lower than this and varies widely. As was found for plants [S2], the radiosensitivity of insects is related to the average interphase nuclear volume [840]. D. Effects of radiation exposure on farm animals 207. Ruminants. both domestic (cattle, goats and sheep) and wild (elk and deer), generally receive relatively high doses in radioactively contaminated environments, because they consume large amounts of vegetation, and many radio-nuclides accumulate in their bodies. For example, a single cow consumes about 75 kg of fresh grass each day. 208. In the period shortly after the accident, domestic live-stock within the 3D-kIn zone were exposed to high levels of radioactive iodine e"l and 113I with half-lives of 8 days and 21 hours, respectively). This resulted in significant internal and external doses due to beta and gamma radiation expo-sure (table 24). A dose of about 76 Gy is sufficient to cause hann to the thyroid gland [B23]. Soils of Ukraine and Belarus are naturally low in stable iodine, cobalt and man-ganese. in conditions of endemic deficiency of stable iodine. the transfer of radioactive iodine from blood to the thyroid gland may be 2-3 times greater than nonnal [P19]. These conditions accentuated the consequences of the accident. Table 24. Doses to cattle that stayed in the 30-km zone around the Chernobvl plant from 26 April to 3 May 1986 [Kl 2] Di::taree from nuclear Surface activity Absorbed dose (Gy} power plant {kIn} (10' lktlm') Thyroid G/ """ Vv1IoIe body internal 3 84 300 1.5 14 10 6.1 130 1.8 1.0 14 3.5 160 1.0 0.6 11 14 180 0.7 0.' 35 1.1 !lO 04 01

266 UNSCEAR 2008 REPORT: VOLUME II 209. Depressed thyroid function in cattle was related to the dose received (69% and 82% reductions in function with thyroid doses of 50 Oy and 280 Oy, respectively). The con-centration of thyroid honnones in the blood of animals was lower than the physiological nonn during the whole lactation period. Radiation damage to the thyroid gland was con-fimlcd by histological studies (i.e. hyperplasia of connective tissue and sometimes adipose tissue, vascular hyperaemia and necrosis of epithelium). Animals with practically no thy-roid tissue were observed in Ukraine. Disruptions of the hor-monal status in calves born to cows with irradiated thyroid glands were especially pronounced [AI2I. Similar effects were observed in cattle evacuated from the Belarusian portion of the 30-km zone [118]. 210. Although most livestock were evacuated from the area after the accident, several hundred cattle were main-tained in the more contaminated areas for a 2-4 month period. By autumn 1986, some of these animals had died; others showed impaired immune responses, lowered body temperatures and cardiovascular disorders. Hypothyroidism lasted until 1989, and may have been responsible for repro-ductive failures in animals that received thyroid doses of more than 180 Oy [118]. Offspring of highly exposed cows had reduced weight, reduced daily weight gains, and signs of dwarfism. Reproduction returned to nonnal in the spring of 1989. Haematological parameters were nonnal for ani-mals kept in areas with 137CS deposition densities of 0.2-1.4 MBq/ml (5-40 Cilkml) [A 12]. 211. No increase in the rates of birth defects were detected above background levels at annual doses below about 0.05 Oy [PI7]. E. Effects of radiation exposure on other terrestrial animals 212. Surveys and autopsies of wildlife and of abandoned domestic animals that remained within 10 km of the Chernobyl nuclear power plant were conducted four months after the accident. [K 11]. Fifty species of birds were identi-fied, including some rare ones; all appeared nonnal in appearance and behaviour. No dead birds were found. Swal-lows and house sparrows were found to be producing prog-eny that also appeared nonnal. Forty-five species of mammals from six orders were observed and no unusual appearances or behaviours were noted. 213. in a review of thirty-three studies of the biological consequences of the Chernobyl accident, M~ller and Mousseau [M 19] commented on various increases in muta-tions and cytogenetic abnonnalities attributed to elevated radiation levels. They noted that the fitness consequences of such increases were largely unknown and cited a study of differences in phenotypes in bam swallows from near Chernobyl and those from relatively uncontaminated con-trol areas [M 18]. The authors suggested that mutations with slightly negative fitness effects could have been exported from the contaminated zones and potentially affected unexposed populations. In an exchange of views, M011er et al. 1M 17, M20] challenged the hypothesis of Smith [S26] that the impacts on bam swallows arose from factors other than radiation exposure, namely the change in habitat and wildlife community arising from changes in agricultural practices resulting from efforts to reduce the spread of radioactively contaminated food. Smith however noted that tbe most contaminated sites were located within abandoned lands, which had large differences in both land use and ecology from the control sites. 2 14. Some wildlife and domestic animals were shot and autopsied in August and September 1986. Dogs and chickens showed signs of chronic radiation syndrome (reduced body mass; reduced fat reserves; increased mass of lymph nodes, liver and spleen; haematomas present i.n liver and spleen; and thickening of the lining of the lower intestine). No eggs were found in the nests of chickens. nor in their ovaries. 215. During the autumn of 1986, the number of small rodents on highly contaminated research plots decreased by a factor of2-IO. Estimates of absorbed doses during the first five months after the accident ranged from 12-110 Oy for gamma and 580-4,500 Oy for bela irradiation. By the spring of 1987, the numbers of animals were recovering, mainly due to immigration From less affected areas. In 1986 and 1987, the percentage of pre-implantation deaths in rodents in the highly contaminated areas was 2-3 fold greater than that in the controls. Resorption of embryos also increased mark-edly in rodents from the impacted areas; however, the number of progeny per female did not differ from that of the controls [TI6]. F. Effects of radiation exposure on aq uatic organisms 216. Cooling water for the Chernobyl nuclear power plant was obtained from a 21.7 kru1 man-made reservoir located to the south-east of the plant site. The cooling reservoir became heavily contaminated following the accident with a total activity of over 6.5 +/- 2.7 PBq of a mixture of radionuclides (alpha and beta emitters) in the water and sediments [KI4]. Aquatic organisms were exposed to external radiation from the radionuclides in the water, contaminated bottom sedi-ments, and aquatic plants. Internal irradiation occurred as organisms took up radionuclides in their food and water or inadvertently consumed contaminated sediments. The result-ant doses to aquatic biota over the first 60 days following the accident are depicted in figure XI.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA 267 Figure XI. The dynamics of absorbed dose rate to organisms within the Chernobyl nuclear power plant cooling pond during the first 60 days following the accident Data are model results based on concentrations of rHdionudides in the water column and lake sediments (adapted from reference (K12]) 10c0.-~--,------,-----,----~-----,-----, Benthic organisms Ma roalgae l00 +-~)( ,~/~ "" ~ '~ ''~- --~--~---+--~ ... 1 ~~ "" "'r=- ""'" +'~ ""'" ".-J 10 t--+' --. +~_._+ ___ I::-:=::-:C+/-=,-,F:oi5h",="",_~_=_~_~.cl i /,

l *

11 it,*

f, Phytopla kton......... Z plankton /. o 10 20 30 40 50 60 DAYS POST ACCtDENT 217. The maximum dose rates to aquatic organisms (excluding fish) were reported in the fi rst two weeks after the accident, when short-lived radionucUdes (primarily 1111) contributed 60-80% of the dose. During the second week, the contribution of short-l.ived radionucl.ides to the doses of aquatic organisms decreased by a factor of two. Maximum dose rates to fish were delayed (see figure XI) owing to the time required for their food webs to become contaminated with longer-lived radionuclides (largely u.*1J7Cs, 144CefPr, 11l6RulRh and 9OSr/Y). The dose rates to fish depended on their trophic positions. Non-predatory fish (carp, goldfish and bleak) incurred estimated peak dose rates of 3 mGy/d due to internal exposure in 1986, followed by significant reductions in 1987. Dose rates to predatory fish (perch), however, increased in 1987 and did not start to decline until 1988 [KI2]. Accumulated doses were greatest for the fi rst generation of fish born in 1986 and 1987. Bottom-dwelling fish (goldfish, silver bream, bream and carp) that were significantly irradiated by the bottom sediments accumulated total doses of approximately lOGy. 218. The reproductive capacity of young silver carp was analysed in 1990 [R 10]. The fish were in live boxes within the cooling pond at the time of the accident. By 1988, the fish had reached sexual maturity. Over the entire post-accident period, they received a dose of 7---8 Gy. Biochemical analyses of muscles, liver and gonads indicated no difference from the controls. The amount of fertilized spawn was 94%; II % of the developing spawn was abnonnal. Female fertility was 40% higher than that of the controls. but 8% of the irradiated sires were sterile. The level of fluctuating asymmetry in off-spring did not differ from that of the controls, although the level of cytogenetic damage (22.7%) significantly exceeded that of controls (5-7%). In contrast, Pechkurenkov [P20] reported that the number of cells with chromosome aberra-tions in 1986---1987 in carp. bream Hat and silver carp was within the nonn. It is worth noting that the cooling pond was subjected not only to radioactive contamination. but also to chemical pollution. Table 25 provides a summary of the recent reviews of the chronic effects of ionizing radiation exposure on the reproduction in fish. The Chemobyl accident data are included. Table 25. Chronic effects of exposure to ionizing radiation on reproduction in fish Derived from the FASSET database [el l] 0"" "" Dosemlfl Reproductive effect:: (pGylh) (mGyld) 0-99 0--2.4 Bactgrumd doSlI group. IlOfITIaI C9n typ9S, normal damago and r.ormat mortatity obsorved 100-199 2.4-4.6 No data aVililab10

268 UNSCEAR 2008 REPORT: VOLUME II Dosemte DfJIlf! rate Repmductivo effects IpGylh) (mGy/d) 100-499 U - 12 Aodocod spormatogonia and sporm inlissoos 500-999 12-24 Olllaylid spawnirlQ, roouction ill tootis mass 1 000--1 999 Z4-4ll M9il1l I~atiroo focundity dacmasad. QilrIy onwt of mfortilrty RadWld numbor of viablo offspring IfIcmaood rumbor of ombryos with aooormalitiGs 2000--4999 48--1z{) IrlCmaood rumbor of smoIts in which sox was undiffomntiatod lncmaood brood silo roportlld locIWsoo mortafrty of ombryos 5000--9999 lZ0--240 Aoouction in numoor of yoong fish surviYing 10 1 month 01 ago Incmaood VilrtGbrai aboormalities Inter-brood limo teoos to docmaso with iflGfllilsing doso IlIID S~rificant r9duction in IlilOfli!tlIl survival StGrility in adult fish > 10000 > Z4ll Oootruction m gmm colis within 50 days in roodaka fdl High mortality of fry, gorm wlls oot IlYidanl Sigrificant docmaso in rombor of mali! satmoo mtuming to spawn; aft9r 4 yoars, fomalo salmon had signifrcantly rodlk:lld focuooity G. Genetic effects in animals and plants 219. High quality data on the incidence of radiogenic mutations in plants and animals as a result of the accident are relatively sparse. An increased mutation level was apparent in 1987 in the form of various morphological abnormalities in Canada fleabane, common yarrow and mouse millet. Examples of abnormalities included: unusual branching of stems; doubling the number of racemes; abnormal colour and size of leaves and flowers ; and development of "witch's broom" in pine trees. Similar effects within 5 km of the nuclear power plant also appeared in deciduous trees (leaf gigantism, and changes in leaf shapes). Morphological changes were observed at an initial gamma dose rate of 4.2-6.3 mGy/d. At a dose rate of 15.8-3 1.5 mGy/d, enhancement of vegetative reproduction (in heather) and gigantism of some plant species were observed [A II, K 10. Tl7, TIS]. 220. Cytogenetic analysis of cells from the root meristem of winter rye and wheat genn of the 1986 harvest demon-slrated a dose dependency in the number of aberrant cells. A significant excess over the control level of aberrations was observed at an absorbed dose of3.] Gy. Inhibition of mitotic activity occurred at a dose of 1.3 Gy, and germination was reduced at a dose of 12 Gy [G I OJ. The analysis of three suc-cessive generations of winter rye and wheat on the most con-taminated plots revealed that the rates of aberrant cells in the intercalary meristem in the second and third generations were higher than in the first. 221. From 1986-1992. mutation dynamics were studied in populations of Arabidopsis thaliana Heynh. (L.) within the 30-km zone [A 10]. On all study plots during the first 2-3 years after the accident, Arabidopsis populations exhib-ited an increased mutation burden. In later years, tbe level of lethal mutations declined; nevertheless the mutation rate in 1992 was still 4-8 times higher than the spontaneous level. The dose dependence of the mutation rate was best approxi-mated by a power function with an exponent value of less than one. 222. Zainullin et aI. [Z2} observed elevated levels of sex-linked recessive lethal mutations in natural Drosophila mel-anogaster populations living under conditions of increased chronic exposure to radiation resulting from the Chemobyl accident. The mutation levels were increased during 1986-1987 in flies inhabiting the more contaminated areas with initial exposure rates of 2 mGylh (expressed as 200 mRlh in the original text) and more. During the subsequent two years. mutation frequencies gradually returned to normal. 223. Shevchenko et aI. [S2 1} and Pomerantseva et al. [P16} reported studies of adverse genetic effects in wild mice. These involved mice caught during 1986-1991 within a 30-km radius of the Chemobyl nuclear power plant with dif-ferent levels of gamma radiation exposure and, during 1992-1993, on a site in the Bryansk Oblast, Russia. The estimated total doses of gamma and beta radiation varied widely; the dose rates reached 3-4 Gy per month in 1986-1987. One endpoint was dominant lethality, measured by embryo mor-tality in the offspring of wild male mice mated with unex-posed female laboratory mice. The dominant lethality rate was elevated for a period of a few weeks following capture in mice sampled at the most contaminated site. At dose rates

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BlarA of about 2 mGylh, 2 of 122 captured males produced no off-spring and were assumed to be sterile. The remainder showed a period of temporary infertility and reduced testis mass. Fertility and testis mass. however, recovered with time after capture. 224. The frequencies of reciprocal translocations in mouse spennatocytes were consistent with previous studies. A dose-rate-dependent incidence of i.ncreased reciprocal trans-locations (scored in spennatocytes at meiotic metaphase I) was observed in all collected mice. The frequency of mice harbouring recessive lethal mutations decreased with time after the accident [PI6]. Radiation-related gene mutation is unlikely to have any adverse effect on populations, at the dose rates that prevail now. 225. Increasing sophistication in the technologies for the detection of molecular and chromosomal damage have allowed researchers on the genetic consequences of the Chemobyl accident to examine endpoints not previously considered [E8]. Most prominent, and controversial, is the technique involving the measurement of mutation frequen-cies in repeat DNA sequences tenned hminisatellite loci" or "expanded simple tandem repeats" (ESTR). These are repeat DNA sequences that are distributed throughout the gennline and have a high background (spontaneous) mutation rate. Presently. ESTRs are considered to have no function, although this is a matter of much interest and discussion [B33, ClO, 19]. MinisateUite mutations have only rarely been associated with recognizable genetic disease. 226. Although laboratory examination of mutations in mouse ESTR loci show clear evidence of a mutational dose response [04. FI6], the EGE was not aware of any convin-cing data on elevated levels of minisatellite mutations in plants or animals residing in the contaminated areas having been published in peer-reviewed scientific literature [E8]. In general, quantitative interpretation of the ESTR data is dif-ficult because of conflicting findings, their weak association with genetic disease, dosimetric uncertainties and methodo-logical problems [ClO]. This is an area of science that requires additional research. H. Overall observations on the effects of the Chernobyl accident 227. According to the EGE [E8], prior to the accident, much of the area around the Chemobyl nuclear power plant was covered by 30--40 year old pine stands that, from a suc-cessional standpoint, represented mature, stable ecosystems. The high dose rates due to ionizing radiation exposure dur-ing the first few weeks following the accident altered the bal-ance in the community and opened niches for immigration of new individuals. 228. The ecological conditions within the 30-km Chemobyl exclusion zone arose from the complex interaction of a nwnber of factors. The highest level of contamination occurred within this zone. As a result of the elevated radiation doses associated with the contamination, human activities such as agriculture, forestry, hunting and fishing within the exclusion zone were stopped [E8]. After the accident, the fields continued to yield agricultural produce for a number of years and, in the absence of active management in the areas that had been evacuated, many animal species, especially rodents and wild boars, consumed the abandoned cereal crops, potatoes and grasses as an additional source of forage [E8]. This was advantageous to these animal species and, along with the special reserve regulations established in the exclusion zone (e.g. a ban on hunting), tended to compensate for the adverse biological effects of radiation exposure and promoted an increase in the populations of wild animals, including game mammals (wild boars. roe deer, red deer, elk, wolves, foxes, hares, beaver, ele.) and bird species (black grouse. ducks, etc.) [G8, S23]. In addition. the Chemobyl exclusion zone has become a breeding area of white-tailed eagles. spotted eagles. eagle owls, cranes and black storks [09]. 229. The high dose rates from ionizing radiation during the first few weeks following the Chemobyl accident affected the balanced community by killing sensitive individuals, altering reproduction rates, destroying some resources (e.g. pine stands), making other resources more available (e.g. soil water), and opening niches for immigration of new and sometimes negative organisms (e.g. negative entofauna). These components and more, were interwoven in a complex web of action and reaction that altered populations and communities of organisms [E8]. 230. Overall, the EGE [E8, H25] arrived at a number of general observations from their evaluation of the Chemobyl data, namely that: Radiation from radionuclides released as a result of the Chemobyl accident caused numerous acute adverse effects on the biota located in the areas of highest exposure (i.e. up to a distance of a few tens of kilometres from the release point). Beyond the exclusion zone, no acute radiation-induced effects on biota have been reported; The environmental response to the increased radia-tion exposure incurred as a result of the Chemobyl accident was a complex interaction among radia-tion dose, dose rate and its temporal and spatial variations, as well as the radiosensitivities of the different taxons. Both individual and population effects caused by radiation-induced cell death were observed in plants and animals and included increased mortality of coniferous plants, soil inver-tebrates and mammals; reproductive losses in plants and animals; and chronic radiation sickness in animals (mammals, birds, etc.); No adverse radiation-induced effects were reported in plants and animals exposed to a cumulative dose of less than 0.3 Gy during the first month after the accident (i.e. <10 mGy/d, on average); and}}