Effects of Ionizing Radiation on Aquatic Organisms and Ecosystems

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TECHNICAL REPORTS SERIES No. 172

0 í J INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1 976 EFFECTS OF IONIZING RADIATION ON AQUATIC ORGANISMS AND ECOSYSTEMS The following States are Members of the International Atomic Energy Agency:

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Printed by the IAEA in Austria March 1976 TECHNICAL REPORTS SERIES No. 172

EFFECTS OF IONIZING RADIATION ON AQUATIC ORGANISMS AND ECOSYSTEMS

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1976 EFFECTS OF IONIZING RADIATION ON AQUATIC ORGANISMS AND ECOSYSTEMS IAEA, VIENNA, 1976 STI/DOC /10/172 ISBN 92-0-125076-2 FOREWORD

In recent years ecologists and environmentalists have shown a growing concern for conservation of ecosystems, especially marine ecosystems, in addition to the well established regard for the protection of human health. This concern was echoed at the UN Conference on the Human Environment in Stockholm, June 1972, which recognized that the over-all object of pollution control is to protect and enhance human well-being and that within this framework one of the principal objectives should be the protection of biotic populations other than man. As part of the IAEA's environmental protection programme, a panel was convened in Vienna in November 1970 to consider the principles for limiting the introduction of radioactive waste into the sea. The panel members noted that one important area in which research is required is the assessment of the effects of ionizing radiation on aquatic organisms, with special regard to effects at the genetic, population and ecosystem level. With this in mind, the IAEA assembled a group of experts from the fields of aquatic ecology and radiobiology to discuss the effects of ionizing radiation in the aquatic environment. At two panel meetings held in Vienna in November 1971 and April 1974, the experts assessed radiation exposure to aquatic organisms from a wide range of toxonomic groups and proposed models for calculating estimates.of dose rates which would be received by these organisms as a consequence of natural background radiation, fallout from nuclear tests and radioactive waste disposal practices. In addition, the panel reviewed existing literature dealing with the somatic and genetic effects of ionizing radiation on aquatic organisms from various toxonomic groups. As a third objective the panel reviewed and discussed scientific thought on the effects on aquatic populations and ecosystems resulting from radiation dose received by individuals. The present book contains the results of the deliberations of both panels. It is hoped that it will prove to be of general interest, especially to those groups involved with radioecological studies and environmental assessments of radioactive discharges. The views expressed represent the common opinions of the panel members acting in their capacity as individual scientists, and thus do not necessarily reflect the attitudes of any body or authority with which these scientists may normally be associated in the course of their employment.

CONTENTS

GENERAL SCOPE AND OUTLINE OF THE REPORT 1

CHAPTER 1. CONCENTRATIONS OF RADIONUCLIDES IN AQUATIC ENVIRONMENTS AND THE RESULTANT RADIATION DOSE RATES RECEIVED BY AQUATIC ORGANISMS 5

1.1. Concentrations of natural radionuclides in aquatic environments 5 1.1.1. Sea water 1.1.2. Seabed 1.1.3. Marine organisms 1.1.4. Fresh water 1.1.5. Fresh-water sediments 1.1.6. Fresh-water organisms 1.2. Concentrations of artificial radionuclides in aquatic environments 9 1.2.1. Concentrations of fallout radionuclides in aquatic environments 1.2.2. Concentrations of artificial radionuclides in aquatic environments from waste disposal operations 1.2.3. Considerations for the future 1.3. Radiation dose rates to aquatic organisms from environmental radioactivity 21 1.3.1. Dose rates from incorporated radionuclides 1.3.2. Dose rates from radionuclides in the water 1.3.3. Dose rates from radionuclides in the sediment 1.4. Discussion 31 1.5. Measurement of radiation dose rates in aquatic environments 36

1.6. Summary 41

Appendix A Alpha-particle energy deposition within a small spherical volume 46 Appendix B Beta-particle absorbed dose rate within a small spherical volume 49 Appendix C Beta-particle absorbed dose rate within a small cylindrical volume 50 Appendix D Example of a dose rate calculation 51

CHAPTER 2. EFFECTS OF IONIZING RADIATION ON AQUATIC ORGANISMS 57 2.1. Introduction 57 2.2. Somatic effects 57 2.2.1. Acute exposure 2.2.2. Chronic exposure 2.3. Genetic effects 74 2.4. Repair 79 2.5. Behaviour and metabolic stimulation 81 2.6. Influence of environmental factors on radiation effects 83 2.7. Summary 86 CHAPTER 3. EFFECTS OF IONIZING RADIATION ON AQUATIC POPULATIONS AND ECOSYSTEMS 89 3.1. Introduction 89 3.2. Somatic effects 90 3.2.1. Possible effects of irradiation on recruitment to marine fish populations 3.2.2. Possible effects of irradiation on the exploited part of fish stocks 3.2.3. Possible effects of irradiation on other species 3.2.4. Observations on irradiated populations 3.2.5. Stability of ecosystems 3.3. Genetic effects 97 3.3.1. Population genetics 3.3.2. Effects of increased mutation rates on populations 3.3.3. Radiation induced mutation rate in fish 3.3.4. Predicted effects

RECOMMENDATIONS FOR FUTURE RESEARCH 101 GENERAL CONCLUSIONS 103 REFERENCES 105 GLOSSARY 121 SECRETARIAT OF THE PANEL 127 PARTICIPANTS AND OBSERVERS OF THE PANELS IN 1971 AND 1974 128 GENERAL SCOPE AND OUTLINE OF THE REPORT

As outlined during the 1972 UN Conference on the Human Environment, the overall objective of pollution control is to protect and enhance human well-being; however, within this framework one prime objective should be the protection of organisms and populations other than man. The need for assessing criteria concerning the protection of biotic populations other than man and the conservation of aquatic ecosystems, especially those which are important to man, has also been stressed in several recent international meetings. In 1958 the UN Conference on the Law of the Sea recommended that the IAEA be given the responsibility of promulgating standards and drafting internationally acceptable regulations to prevent marine pollution by amounts of radioactive materials which could adversely affect man and his resources. Since that time the IAEA has sponsored a number of meetings on various matters related to the disposal of radioactive wastes into the sea as well as into rivers, lakes and estuaries. In November 1970 the IAEA convened a panel of experts to assess the principles for limiting the introduction of radioactive waste into the sea. This panel, in its conclusions, recommended pursuing some general areas of research, one of which was the study of the effects of ionizing radiation on organisms and their sensitive life stages with special regard to effects at the genetic, population and ecosystem level. From 15 to 19 November 1971 a panel of experts was convened by the IAEA to specifically consider the effects of ionizing radiation on aquatic organisms and ecosystems and to formulate more detailed suggestions for research in this area. The composition of the panel was not such that it could effectively evaluate radiation effects on population dynamics in ecosystems, so a supplementary panel meeting was held in October 1972 to review in depth several topics that would lead to an evaluation of possible effects of radiation exposure on population dynamics in ecosystems. Both panel meetings concluded that, on the basis of the present state of knowledge, it was impossible to demonstrate or predict radiation effects on populations and ecosystems at the low dose rates attributable to radioactive waste discharges. The difference between existing radiation levels and those levels that have been demonstrated to cause effects on organisms was felt to be so great that the control of discharges on the basis of the protection of man would usually also provide adequate protection for other organisms and populations. Nevertheless, the participants also felt that the effects of ionizing radiation on aquatic biota are certainly factors which must be taken into account when considering the disposal of radioactive wastes into the environment. Therefore a second panel meeting, from 22 to 26 April 1974, was held, in which experts on genetics and population dynamics took part, aiming at a clearer picture of the effects of ionizing radiation on aquatic organisms and ecosystems. The results of the work of the panels of November 1971 and April 1974 are presented in this report. The working papers and interim conclusions of the October 1972 supplementary meeting were studied by and used in the work of the April 1974 panel. The present report is divided up as follows. The first chapter discusses the concentrations of natural and artificial radionuclides in aquatic environments and the radiation dose rates received

1 GENERAL SCOPE AND OUTLINE OF THE REPORT by aquatic organisms. In particular, simple dosimetry models for phytoplankton, Zooplankton, mollusca, crustacea and fish are presented which permit the estimation of the dose rates from incorporated radionuclides and from radionuclides in the external environment. The second chapter reviews the somatic and genetic effects of ionizing radiation on aquatic organisms. Somatic effects are discussed separately as effects due to short-term exposure to near-lethal doses of radiation (acute exposure). Great attention is paid to the effects due to long-term exposure at lower dose rates (chronic exposure). Consideration is given to behaviour, repair mechanisms and metabolic stimulation after exposure, and also to the influence of environmental factors on radiation effects.

The third chapter considers the potential effects of low-level chronic irradiation on aquatic populations. The first part discusses the possible consequences of somatic effects on egg and larval mortality, stock- recruitment, fecundity and ecosystem stability. The second part deals with the assessment of genetic effects as they relate to population genetics and increased mutation rates.

2 Chapter 1

CONCENTRATIONS OF RADIONUCLIDES IN AQUATIC ENVIRONMENTS AND THE RESULTANT RADIATION DOSE RATES RECEIVED BY AQUATIC ORGANISMS Chairman: D.S. WOODHEAD, United Kingdom

Members of the Working Group: M. BEZZEGH-GALANTAI, IAEA S.W. FOWLER, IAEA A. FRANTZ, Austria M. IJUIN, OECD/NEA J. P. OLIVIER, OECD/NEA J. SAS-HUBICKI, Austria E. WANDERER, Austria CHAPTER 1 CONCENTRATIONS OF RADIONUCLIDES IN AQUATIC ENVIRONMENTS AND THE RESULTANT RADIATION DOSE RATES RECEIVED BY AQUATIC ORGANISMS

A knowledge of the radiation dose rate regimes experienced by aquatic organisms is an essential prerequisite for any attempt to assess the effects of radiation on aquatic ecosystems. A combination of this basic information together with the results obtained from relevant laboratory irradiation experiments allows predictions of possible effects to be made. It has been indicated for natural sources of radiation that the organisms occupying various parts of aquatic environments can experience widely differing radiation exposures [ 1 L and this is equally true for the artificial radionuclides introduced into the environment by man. The input of radioactivity is not uniform, even in the case of global fallout, and the activity is not dispersed to become uniformly distributed; the complex interactions of the chemical properties of the radioelements with the chemical, physical and biological processes of aquatic environments result in differential distributions. The data on the concentrations of radionuclides in the different components of aquatic ecosystems provide the basis for the estimation of radiation dose rates. Additional sources of variation in the dose rate experienced by an organism stem from the nature of the life-cycle (e.g. pelagic eggs and larvae and a benthic adult form) or temporal behaviour (e.g. diurnal, annual or longer period migrations between differing environments).

1.1. CONCENTRATIONS OF NATURAL RADIONUCLIDES IN AQUATIC ENVIRONMENTS

1.1.1. Sea water

The concentrations of naturally occurring radionuclides in surface sea water from open ocean environments are given in Table I. The values quoted are in broad agreement with previous summaries of earlier work [20, 21]. In coastal waters the concentrations of certain radionuclides may be higher than those quoted in Table I owing, presumably, to the input from land run-off. Both tritium and carbon-14 are produced in the atmosphere through the interaction of cosmic radiation with air nuclei. The variable concentration of tritium in sea water is a consequence of the non-uniform deposition pattern as tritiated water in rain coupled with a half-life for decay of 12.3 a, which is comparable with the time scales of oceanic mixing processes. The much longer half-life of carbon-14 at 5760 a results in the isotope being fairly uniformly distributed, in terms of specific activity, throughout the biosphere. Potassium-40, rubidium-87, uranium-235, uranium-238 and thorium-2 32 are very long-lived isotopes remaining from primordial nucleo- synthesis. The last three are the parent nuclides of radioactive decay series and the concentrations of practically all the longer-lived daughter radionuclides have also been measured in sea water. The departures from radioactive equilibrium apparent from the values given in Table I arise from the different geochemical and geophysical processes operating on the elements in the series. The concentrations of 40K and 87Rb have been calculated from the stable element values for sea water given by Goldberg etc. [22] and

5 CHAPTER 1

TABLE I. CONCENTRATIONS OF NATURAL RADIO- NUCLIDES IN SURFACE SEA WATER

Radionuclide Concentration, pCi-1 1 Reference

3H 0.6-3 2 14 C 0.2 3 40 K 320 87

Rb 2.9

238U 1.2 4, 5

234U 1.3 4, 5

230Th (0. 6-14) x lo"4 6, 7 226 -2 Ra (4-4. 5) x 10 8, 9, 10

222 -2 Rn « 2 x 10 8

210 -2 Pb (1-6.8) x 10 11, 12, 13, 14

210 -2 Po (0. 6-4.2) x 10 13, 14, 15, 16, 17 232 -4 Th (0.1-7.8) x 10 6, 7, 18

228 -2 Ra (0.1-10) x 10 19

228 - q Th (0.2-3.1) x 10 6, 7 235 -2 TU 5 x 10

isotopic abundance data [23]. Similarly, the concentration of 235U has been calculated from that of 238U assuming that the isotopic abundance in sea water is the same as that observed in terrestrial rocks. A few measurements have been made of the concentrations of thorium in coastal waters and have given values approximately ten times higher than those listed in Table I [ 6, 18, 24].

1.1.2. Seabed

The data on the levels of natural radioactivity in the sea bed are quite sparse and mainly refer to uranium and thorium determinations made in the course of geochemical and deep ocean sedimentation studies. The concentrations of uranium and thorium have been found to depend on the calcium CONCENTRATIONS OF RADIONUCLIDES 7 carbonate content of the sediment, and fall within the ranges 0.4- 3 ppm (0.13-1.0 pCi • g"1) and 0.4-18 ppm (0.04-2.0 pCi • g"1), respectively, with the lowest values associated with the highest carbonate content in each case [25]. It is found that there are varying degrees of disequilibrium between the longer-lived members of the uranium-238 decay series. The activity ratio 234u/238u depends on the carbonate content of the sediment since the mineral phase has an activity ratio of 0.94 [26], while the uranium in the carbonate fraction reflects the ratio in sea water, i.e. 1.13 [5]. The activity ratio 230Th/234U is considerably in excess of equilibrium due to the precipitation of the 230Th derived from the 234U in solution in the sea water, and ratios up to 94 have been measured [27]. The levels of 226Ra are like- wise in excess of equilibrium with respect to the 238U in the sediment, but the activity ratio 226Ra/230Th is less than unity due to the loss of radium through leaching; an average deficit of 40% was determined for the surface layers of four deep ocean cores studied by Ku [27]. Radium-226 levels in the range 1-46 pCi • g"1 have been reported [27 - 29]. The half-lives of the daughter radionuclides in the thorium decay series are sufficiently short for it to be reasonable to assume that radioactive equilibrium is maintained. In coastal waters it can be assumed that the mineral fraction of the sediment has uranium and thorium contents similar to those of terrestrial rocks for which typical values are given in Table II [ 30, 31]. A similar conclusion can be drawn in respect of the potassium levels in sediments although those with large feldspar or mica content (10-15% K) or a high clay content would be relatively richer in potassium [ 32].

1.1.3. Marine organisms

The concentrations of natural radionuclides have been measured in a great diversity of organisms; however, there is not a single instance in which a complete set of data is available for a single species, and indeed this is also true of groups of organisms. Therefore it has been found convenient to summarize the available data in terms of broad groups of organisms, and Table III gives the concentrations of natural radionuclides measured in phytoplankton, Zooplankton, mollusca, crustacea and fish. The values for tritium, carbon-14 and potassium-40 have been derived from the stable element compositions of the organisms given by Vinogradov [ 33] and the specific activity in water on the assumption that there is no isotopic fractionation between water and biota. The level of rubidium-87 in crustacea has been calculated from the value given in Table I for water and the concentration factor quoted by Lowman et al. [ 34]. The data for 234U in fish and 235U in fish, phytoplankton and Zooplankton have been calculated from that for 238U on the assumption that the isotopic abundance in the organisms parallels that observed in sea water.

1.1.4. Freshwater

The concentrations of most of the natural radionuclides in lakes and rivers are dependent on the rock and mineral deposits with which the water has been in contact and therefore reflect to varying degrees the geology of the watershed. The data are given in Table IV. The values for 234U have been calculated from those for 238U on the assumption that the activity ratio TABLE II. TYPICAL CONCENTRATIONS OF URANIUM THORIUM AND POTASSIUM IN BEACH SANDS, COMMON ROCK TYPES AND DEEP OCEAN SEDIMENTS!25, 30, 31J

Material U, ppm 238U(a), 235U(a\ Th, ppm 23Va>, K, % 4°K, pCi-g 1 pCi-g 1 pCi-g 1 pCi-g 1

Beach sands 3.0 1.0 0.05 6.4 0.69 0.33 2.7

Granite 5.0 1.7 0.08 18 2.0 3.8 32

Shale 3.7 1.2 0.06 12 1.3 1.7 14

Limestone 1.3 0.43 0.02 1.1 0.12 0.2 1.7

Sandstone 0.45 0.15 0.01 1.7 0.18 0.6 5.0

Basalt 0.50 0.17 0.01 2.0 0.22 0.5 4.2

Deep ocean sediments 0.4-3.0 0.13-1.0 0.01-0.05 0.4-18 0.04-2.0 NDA(b) NDA(b)

(a) In calculating the activity content it has been assumed that the original measurements detected only the long- lived uranium and thorium isotopes. C3)Here and in Tables HI, VI, VII, VIII, IX, XI, XIII, XIV, XV and XVI NDA indicates that no data appear to be available. Where NDA appears in Tables XVIII, XXIII, XXV, XXVI, XXVII, XXVIII, XXIX, XXX and XXXI it indicates that there are no data available which can be used to calculate the dose rate although the dose rate from the isotope is expected to be non-zero. CONCENTRATIONS OF RADIONUCLIDES 9

of two determined by Blanchard [26] is generally applicable, and it has also been assumed that the isotopic abundance of 235U relative to 238U in surface water is the same as that found in terrestrial rocks.

1.1.5. Fresh-water sediments

As for the marine sediments the concentrations of radionuclides in the mineral fractions will be similar to those found in terrestrial rocks and thus the values given in Table II will be applicable.

1.1.6. Fresh-water organisms

Table V gives the concentrations of natural radionuclides in fish, the only group of fresh-water organisms for which any significant data appear to be available. The values given for tritium, carbon-14 and potassium-40 have been derived from the stable element composition of the organisms and the known specific activity. As before the data for 234u and 235U have been derived from the value for 238U.

1.2. CONCENTRATIONS OF ARTIFICIAL RADIONUCLIDES IN AQUATIC ENVIRONMENTS

The various sources of artificial radionuclides in the aquatic environment have been comprehensively reviewed recently by Joseph et al. [21]. The two main sources are fallout from nuclear weapons tests and the operation of nuclear reactors including the concomitant processing of the spent fuel. If the input of large quantities of radioactivity in the immediate vicinity of nuclear explosions is ignored (on the basis that this type of local contamination has been almost completely eliminated with the partial implementation of the Test Ban Treaty), the two sources have different characteristics which have implications in respect of the resulting radiation exposure to aquatic organisms. Thus fallout represents an input of radioactivity to the marine environment which is extensive in time and space, but is at such a level that high concentrations of radioactivity do not occur. For example, the maximum rates of ®°Sr input occurred in 1963 between latitudes 40° N and 50° N and amounted to approximately 2 pCi • cm"2 - a"1 [21]. On the other hand, the inputs from reactor operation and fuel reprocessing are effectively point sources which can occasionally lead to relatively high concentrations of activity in localized environments. However, the overall extent of the contamination is fairly circumscribed and the activity is only rarely detectable or distinguishable from fallout at distances greater than a few hundred miles from the point of discharge. The continuous nature of the discharges permits the establishment of equilibrium situations in which the input is approximately balanced by the losses due to dispersion and decay.

1.2.1. Concentrations of fallout radionuclides in aquatic environments

1.2.1.1. Sea water. The data on the concentrations of fallout radionuclides in the oceans of the world have recently been reviewed by Volchok et al. [ 54]. Comprehensive data exist only for 90Sr, 137Cs [ 54], 3H [ 55, 56], 14C [ 57, 58], and 239Pu [ 59 - 61] and are summarized in Table VI. The levels of 137Cs TABLE ni. TYPICAL CONCENTRATIONS OF NATURAL RADIONUCLIDES IN MARINE ORGANISMS, pCi-g-! wet

Part 1

Isotope Phytoplankton Ref. Zooplankton Ref. Mollusca Ref.

3H (0.5-2.7) x 10~3 - (0. 5-2. 7) x 10~3 - (0.5-2.7) x 10~3 -

14C 0.3 - 0.3 - 0.5 40 K 2.5 - 2.5 - 2.9

87 —9 Rb NDA - NDA - 5x10 38 238 -2 —9 U (4-5) x 10 5 (1-2) x 10 5 NDA 2 34 -2 -2 U (4-5) x 10 5 (1-2) x 10 5 NDA

226 -2 -2 Ra 2 x 10 9 2 x 10 9 NDA 210 -1 -2 -3 Pb (1-7) x 10 14 (1.0-25) x 10 14, 15, 37 (5-10) x 10 13

21°Po (4-17) x 10-1 14, 35 (5-110) x lo"2 14, 15, 35, 37 (4-11) x lo"1 13 232 Th NDA - NDA - NDA 228 _ o _ o Th (7-54) x 10 36 (2-22) x 10 36 NDA 235 -3 -4 U 2x10 - 6x10 - NDA Part 2

Isotope Crustacea Ref. Fish Ref

3 3 3 H (0. 5-2. 7) x 10" - (0. 5-2. 7) x 10" -

14 c 0.6 - 0.4 - 40 K 2. 5 - 2. 5 -

87 2 2 Rb 4 x 10" - 2.5 x 10~ 40

238 3 u NDA - (0. 07-30) x 10" 41, 42

234u 3 NDA - (0. 08-35) x 10" 41, 42

226 4 Ra NDA - Soft tissue (2-51) x 10~ 37 210 Pb (4-7) x 10~2 13, 15 Flesh (2-23) x 10~4 13, 15, 37 Stomach (17-850) x 10"3 15 Liver (11-24) x 10~3 13, 15 Bone (9-130) x 10"3 13, 15 210 Po Whole animal (4-16) x 10_1 13, 15 Flesh (4-1400) x 10~4 13, 15, 17, 37 Lobster hepatopancreas 12 39 Stomach (2-26) x 10"1 15 Liver (2-9) x 10 13, 15, 39 Bone (2-22) x 10~2 13, 15 232 Th NDA - NDA -

228 Th NDA NDA -

235 3 u NDA - (0. 003-1.4) x 10~ - 12 CHAPTER 1

TABLE IV. CONCENTRATIONS OF NATURAL RADIO- NUCLIDES IN FRESH WATER

-1 Radionuclide Concentration, pCi-1 Reference

3H 5.4-16. 5 43, 44

40K 0.1-6.6 45, 46, 47

87Rb 2.4 x 10~2 47

238 u 5 x 10_3-1.7 3, 47, 48

234 -2 u 10 -3.4 - 226 Ra 0.01-3 2, 3, 37, 43, 48 222„ Rn 0.2-180 2, 3

Pb 0. 025-0. 36 2, 13, 49 210 Po 0.007-0.23 13

Th . (0.1-1.1) x 10~2 47, 48 235 -3 u (0. 2-70) x 10 -

have been calculated from those for 90Sr using the average observed activity- ratio of 1.6 for 137Cs/90Sr in sea water [54]. For the many other isotopes produced in nuclear explosions and therefore present in fallout, data on concentrations in sea water are few and in many cases their presence can only be inferred from the measured activities in biota or sediments [ 54]. 1.2.1.2. Marine organisms and sediments. The concentrations of fallout radionuclides have been measured in a variety of marine organisms but, as for the natural radionuclides, a complete set of data is not available for either a single species or even a group of organisms. The published data are summarized in Table VII; the measured concentrations of fallout radionuclides in marine sediments are also included. The data for marine organisms given in Table VII can only reflect the sea-water concentrations prevailing in the particular environment prior to the time of sampling and, because of the concentration variations consequent upon input fluctuations, decay, dilution and geochemical processes, are only rarely representative of an equilibrium situation. Thus, for those nuclides for which there are no measurements of sea-water concentrations, dose estimates can only be made on the basis of the measured concentrations in tissue giving values which are appropriate only to the particular organism CONCENTRATIONS OF RADIONUCLIDES 13

TABLE V. CONCENTRATIONS OF NATURAL RADIO- NUCLIDES IN FRESH-WATER FISH

Radionuclide Concentration, pCi-g ^ wet Reference

3 3 H (5-14) x 10~ -

14 C 0.4 -

40K 3. 5 46

87Rb (0.1-22) x 10"2 40, 50, 51

238 u (0.23-2. 3) x 10~3 51

234 -3 u (0.46-4. 5) x 10 - 226 Ra Whole fish 1. 0-3. 5 52 Flesh (2-20) x 10~4 37, 53 Bone (6 x 10~3)-2.1 37, 53 210„ Pb Flesh (0.1-4.7) x 10~3 13, 37 Bone (8-84) x 10~3 13, 37 Liver (0. 9-24) x 10~3 13 210„ PO Flesh (3. 7-110) x 10"3 13, 37 Bone (5-130) x 10"3 13, 37 Liver (7. 5-50) x 10"2 13

232Th (0.18-1. 3) x 10"3 51

235 4 u (0.1-1.0) x 10" -

at the specific time and place of sampling. It is not possible from the extremely limited data to extrapolate to either other types of organisms or the same organism at other times and locations. In the case of 90Sr, 137Cs, 3H, 14C or 239Pu for which there are more extensive data on the concentrations in sea water and which show much less variation with time, approximate tissue concentrations in organisms at any time and place can be derived using the appropriate concentration factors (if known). 1.2.1.3. Fresh water, fresh-water organisms and fresh-water sediments. There appear to be relatively few relevant data on the concentrations of fallout radionuclides in the fresh-water environment, and those available are summarized in Table VIII. The values for tritium have been derived TABLE VI. CONCENTRATIONS OF THE MAJOR FALLOUT RADIONUCLIDES IN SURFACE SEA WATERT 54-61 ]

Location Average concentration and/or range, pCi-1

14 239^ 90Sr 137Cs(a) 3H c Pu

-3 N Atlantic Ocean 0.13 (0.02-0.50) 0.21 (0.03-0.80) 48 (31-74) 0. 02 (0. 01-0. 04) (0.3-1.2) x 10' S Atlantic Ocean 0.07 (0.02-0.20) 0.11 (0. 03-0. 32) 19 (16-22) 0. 03 (0. 02-0. 04) 0. 2 x 10"3 Indian Ocean 0.10 (0.02-0.15) 0.16 (0.03-0.24) NDA NDA NDA NW Pacific Ocean 0. 54 (0. 07-3.1) 0.86 (0.11-5.0) 29 (6-70) 0.03 (0.02-0.03) (0.1-1.4) x 10--3 SW Pacific Ocean 0. 08 (0. 01-0. 20) 0.13 (0.02-0.32) 8 (0.7-22) NDA NDA NE Pacific Ocean 0.27 (0.05-0.58) 0.43 (0. 08-0. 93) 44 (10-240) 0. 03 (0. 00-0. 04) (0.1-1. 3) x 10_ -3 SE Pacific Ocean 0.09 (0.03-0. 33) 0.14 (0.05-0.53) 8 (0. 3-34) 0. 01 (0. 00-0. 03) NDA North Sea 0. 50 (0. 31-0. 97) 0.80 (0.50-1.55) NDA NDA NDA Baltic Sea 0.71 (0.36-1.0) 1.1 (0.56-1.6) NDA NDA NDA Black Sea 0.47 (0. 07-0.78) 0.75 (0.11-1.25) NDA NDA NDA Mediterranean Sea 0.23 (0.09-0. 38) 0. 37 (0.14-0. 61) NDA NDA NDA

Calculated from the 9°Sr values on the assumption that the activity ratio 137Cs/9°Sr = 1.6 CONCENTRATIONS OF RADIONUCLIDES 15 from the known stable element composition of the organisms and the specific activity in the external water; the values for 14C are based on the stable element composition of the organisms and the measured specific activity in terrestrial biota [104] on the assumption that the levels in the two different environments will be the same.

1.2.2. Concentrations of artificial radionuclides in aquatic environments from waste disposal operations

It is not necessary to consider all the sites in detail and four, two fresh- water and two marine, have been chosen as examples;

(a) The discharge to the Columbia River from the plutonium production reactors at the Hanford Plant. This situation is of historical interest only since seven of the reactors have been closed down and the remaining one does not use Columbia River water for single pass cooling. (b) The discharge to the River Danube from the nuclear power station at Gundremmingen. (c) The discharge to the Irish Sea from the fuel reprocessing factory operated at Windscale by British Nuclear Fuels Limited. (d) The discharge to the Blackwater estuary from the nuclear power station operated by the Central Electricity Generating Board at Bradwell, United Kingdom.

There are no data available on the annual discharges to the Columbia River from the Hanford site, but Table IX gives the annual rate of transport of selected nuclides past Richland and Pasco, 48 and 61 kilometres respec" tively, downstream of the reactor sites. At these points radioactive decay and retention by biota and sediments have reduced the quantities of activity to approximately 8 and 6%, respectively, of the levels originally present in the cooling water [115]. The annual discharges of activity at each of the other three sites are given in Tables X-XII. As a result of dispersion and decay the levels of activity in the environment generally fall with increasing distance from the discharge point. Thus some form of weighted average concentration would be the most appropriate parameter to describe the degree of contamination of a given component of the environment; however, there are usually too few data available to achieve this ideal. Therefore, the descriptions have been given, as far as possible, in terms of the mean values and ranges of values in the vicinity of the discharge point, since these are taken to be indicative of the highest degrees of contamination. The data are given in Tables XIII - XVI.

1.2.3. Considerations for the future

Some concern has been expressed that with the expansion of the nuclear power industry the consequent concentrations of 3H and 85Kr in aquatic environments might be a source of significant radiation exposure. It has been estimated [ 120] that by the year 2000 the installed nuclear generating capacity could be 4300 GW(e) and that the corresponding cumulative inventories of 3H and 85Kr in the environment would be 420 and 5500 MCi, respectively. TABLE VII. CONCENTRATIONS OF FALLOUT RADIONUCLIDES IN MARINE ORGANISMS AND SEDIMENTS, pCi-g"1 wet

Part 1

Isotope Phytoplankton Ref. Zooplankton Ref. Total Ref. Mollusca Ref. plankton

54, 0.1-0.4 62 0.02-0.1 62 5. 3 66 0.05-6 62, 70 55 0.5 63 0.16-1.5 63 NDA 0.4-140 63

Co NDA - NDA 2. 3 67 0.05-0.44 67

Co NDA - NDA 0. 32-16 67 0.03-0.71 67

63„. Nl NDA - NDA 0.1-0.4 68 Kidney 0.03-15 68 n NDA - NDA NDA 0.02-11.5 62, 71 >re

NDA - NDA 0.02-0.34 66 NDA s »

95Zr/95Nb NDA - 0.5-88 2-800 66, 67 0.1-25 67

103Ru, 106RU NDA - NDA 0.3-30 65, 67, 69 0.03-14 67 125, Sb NDA - NDA 0. 9 66 NDA 108m Ag NDA - NDA NDA Hepatopancreas 0.15 72 110m Ag NDA - NDA NDA Hepatopancreas 0.004-4.2 72, 73

Cs NDA - NDA 0.5-36 67 0.13-0.68 67 141 144 Ce, Ce NDA - .NDA 0.4-480 66, 67 0.14-49 67

Pm NDA - NDA 3. 3 66 NDA

Eu NDA - NDA 0.4 66 NDA 239. Pu (0. 3-83) x 10"3 60,64 l.lxlo"3 NDA (9-60) x 10~5 60, 64 CONCENTRATIONS OF RADIONUCLIDES 17

TABLE VII (continued)

Part 2

Isotope Crustacea Ref. Fish Ref. Sediment Ref.

0.06 62 0.002-0.05 62 0.2-0.3 70

Fe NDA - Muscle 0.1-106 63 NDA Liver 1620-1860 63

Gonad 220-280 63 57 Co NDA - NDA 2.8 67

Co 0.65 67 Muscle 0.04-0.14 67 NDA Liver 0.03-0. 37 67, 73

NDA - NDA NDA

65„ 0.07 62 0.05-0.2 NDA 90, Sr NDA - NDA 0.02-0.03 76, 77 95 ,95 , Zr / Nb NDA - Whole 0.25-0. 55 67 NDA Liver 0.04-7.5 67 Muscle 0.03-0.34 67 103 106 Ru, Ru NDA - Muscle 0.04-0.68 67 NDA Liver 0.04-6.6 67

125Sb NDA - NDA NDA 108m Ag Hepatopancreas 0.06 72 Liver 0.003-0.009 72 NDA

"Ag Hepatopancreas 1.0 72 Liver 0.05-0.08 72, 73 NDA

Cs NDA - Muscle 0.04-0.08 67, 74 NDA 141 144 Ce, Ce NDA - Whole 4.8-6.9 67 NDA Liver 0. 35-28 67 Muscle 0.05-1.3 67 147 „ NDA - NDA 1. 5 76 155. Eu NDA - NDA 0.15 76 239. -5 Pu NDA - Muscle (0.1-0. 3) x 10 75 NDA Liver (2-13) x 10" '75 18 CHAPTER 1

TABLE Vni. CONCENTRATIONS OF FALLOUT RADIONUCLIDES IN FRESH WATER AND FRESH-WATER ORGANISMS AND SEDIMENTS

Part 1

Isotope Water, pCi-1 1 Ref. Mollusca, pCi-g~* wet Ref.

3 3 H 3.6-4750 45, 78, 79, 80 3.2 x 10" -4. 3 -

14 c NDA - 0.1-0. 3 -

54Mn 0.01-1.3 81, 82 0.11-14 81, 92

Fe ' NDA - NDA - 85_, Sr NDA - NDA -

89 Sr 0.01-51 83, 84, 85 NDA -

90o Sr 0.02-18 78, 85, 86, 87, 88 NDA -

95 ,95x„_ Zr/ Nb 1.1-64 82, 86, 89 NDA - 103„ Ru 0. 5-7.0 83, 89 NDA -

106 RU 0.4-29 87, 89 NDA -

131 I 140 90 NDA - 137 Cs 0.02-4.8 85, 86, 91 NDA - 141 Ce 0.1-2. 3 89 NDA - 144 Ce 0.09-11 85, 87, 89 NDA -

The predicted quantity of tritium is some 4 to 6 times that present from natural sources (70- 100 MCi [ 121, 122]) and if it is assumed that most of it is contained in the hydrosphere of the northern hemisphere (on the grounds that the major part of the activity will have been discharged from the reprocessing plants in the northern hemisphere where it would be very rapidly involved in the hydrologie cycle), then the concentrations in aquatic organisms resulting from this source would be approximately 8 to 12 times those given for natural tritium in Tables III and V. Virtually all the 8SKr released will remain in the atmospheric reservoir and become uniformly distributed, giving a specific activity of 3.2 XI 05pCrg_1Kr. CONCENTRATIONS OF RADIONUCLIDES 19

TABLE VIII (continued)

Part 2

Isotope Fish, pCi-g 1 wet Ref. Sediment, pCi-g ^ wet Ref.

3 3 H 3.2 x 10" -4. 3 - NDA -

14 c 0.1-0.2 - NDA -

54 M„ 0. 31 82 NDA -

Fe 0.03-0.08 93, 94 NDA -

850 Sr 0.001-0.012 95 NDA - 89 Sr 0.005-1.1 86, 89 NDA - 90„ Sr 0. 001-4. 8 46, 96, 97, 98 NDA -

Zr/ Nb 0.06-0.07 82 NDA - 103_, Ru NDA - NDA - 106 Ru NDA - NDA -

131 I NDA - NDA -

137Cs 0.04-26.3 46, 88, 95, 96 0.5-18 102, 103 98, 99, 100, 101

Ce NDA - NDA - 144 Ce NDA - NDA -

Thus, on the assumption that there is equilibrium between the krypton in the atmosphere and that in the mixed layer of the oceans, the 85Kr concentration in sea water would be approximately 0.1 pCi • l"1. (These figures have been derived by assuming that the atmosphere contains 3.3 X10"4% by weight of krypton, uniformly distributed throughout and that the krypton concentration in sea water is 0.3 ßg • 1"1[23].) Since there are no data concerning the accumulation of krypton in aquatic animals, accurate assessment of the concentrations attained is not possible. However, it might reasonably be assumed that 8oKr would become uniformly distributed in body fluids at approximately the same level as in sea water, i.e. approximately 10"4pCi • g"1. TABLE IX. RADIONUCLIDE TRANSPORT RATES (Ci-a-1) PAST PASCO AND RICHLAND^105"114]

Year Site Isotope

24 32 51 64 _ 76 90 131 239AT Na p Cr Mn Cu Zn AS Sr I Rare Np earths + Y

Half-life

15 h 24. 3 d 27. 8 d 2. 58 h 12.8 h 245 d 26. 5 h 28 a 8. 0 d - 2. 3 d

1960 Pasco 164 000 17 600 483 000 NDA 237 000 28 200 138 000 70 NDA 64 100 283 000 1961 Pasco 199 000 22 300 487 000 NDA 265 000 33 600 114 000 55 NDA 43 800 209 000 1962 Pasco 158 000 15 000 357 000 NDA 195 000 21 900 47 500 66 548 36 500 86 100 1963 Pasco 163 000 16 400 560 000 NDA 242 000 20 400 68 600 99 657 44 200 125 000 1964 Pasco 193 000 20 900 599 000 NDA 300 000 22 300 76 900 161 915 44 300 149 000 1964 Richland 373 000 28 500 997 000 NDA 552 000 40 600 126 000 168 1 650 74 700 266 000 1965 Richland 328 000 30 700 681 000 NDA 283 000 20 400 98 900 179 949 110 000 168 000 1966 Richland 247 000 17 500 406 000 137 000 13 500 NDA 730 NDA NDA 29 900 70 400 1967 Richland 272 000 18 600 358 000 121 000 235 000 25 200 39 400 95 803 54 000 88 700 1968 Richland 218 000 20 100 177 000 28 500 125 000 12 800 31 100 NDA 1 100 28 900 97 400 1969 Richland 200 000 NDA 156 000 177 000 228 000 50 700 37 600 NDA NDA 105 000 139 000 CONCENTRATIONS OF RADIONUCLIDES 21

TABLE X. ANNUAL DISCHARGES OF RADIOACTIVITY (Ci) TO THE DANUBE FROM GUNDREMMINGENL 116 J

Year 90Sr 89Sr 131I 140Ba/ 137Cs 58Co 60Co 3H 140La

1967 0.09 1.30 0.70 0.40 0.60 0.30 0.07 26.0 1968 0.02 0.70 0.50 0.20 0.70 0.20 0.10 21.4 1969 0.09 1.60 0.70 0.18 0.22 0.18 0.09 17.8

1.3. RADIATION DOSE RATES TO AQUATIC ORGANISMS FROM ENVIRONMENTAL RADIOACTIVITY

The information on the concentrations of radionuclides in aquatic biota refer to organisms of widely differing geometries, and in most cases even the approximate geometry is unknown. Therefore, to estimate the magnitude of the absorbed dose rate from the data given in Tables I - VII and XIII - XVI use must be made of very much simplified, idealized models, despite their obvious limitations as descriptions of the real situation.

1.3.1. Dose rates from incorporated radionuclides

1.3.1.1. Phytoplankton. These organisms have been represented by a sphere of unit density tissue 50 Aim in diameter. This has been taken as typical of the size of the more common marine phytoplankton in the waters around the British Isles. Although the sizes of different species vary between a few microns and perhaps 200 /um and the shape is rarely spherical [123], the model adopted provides a basis for estimating the absorbed dose rate for organisms in this size range in a simple way. It has also been assumed that the model is appropriate for fresh-water phytoplankton although the typical size of these organisms appears to be somewhat smaller than their marine counterparts, and again the sizes and shapes of the different species show wide variations [ 124]. The radioactivity accumulated by these organisms has been assumed to be uniformly distributed throughout the volume. As a consequence of the limited size of the model in relation to the ranges of the radiations being considered, significant proportions of the total energy emitted by the incorporated radionuclides are dissipated in the surrounding water. For »-particles, if the average range is assumed to be 60 Mm (i.e. the range of a 6 MeV a-particle in water [ 125]) at constant linear energy transfer (LET), the distribution of available path lengths within the sphere is such that approximately 30% of the emitted »-particle energy is absorbed within the volume (see Appendix A). That is,

where D (») = 2.13 E C yrad-h 1 , TABLE XI. ANNUAL DISCHARGES OF RADIOACTIVITY (Ci) TO THE SEA FROM WINDS CA LE

3 89 90 95 95.^ 103^ 106^ 134^ 137,, 144_ 9!L Year HU Sr Sr Zr Nb Ru Ru Cs Cs Ce Y + rare earths

1960 NDA 980 520 2 400 6 300 11 600 39 600 NDA 910 890 1 000 1961 NDA 1 370 490 1 700 7 900 3 200 25 300 NDA 1 100 2 200 2 400 1962 NDA 500 1 020 940 4 300 1 800 23 000 NDA 1 100 2 400 1 500 1963 NDA 170 550 560 3 300 9 600 33 400 NDA 370 1 400 1 100 1964 NDA 190 970 21 600 20 800 1 200 23 100 NDA 1 300 3 200 1 100 1965 NDA 170 1 160 17 700 33 700 1 800 21 000 NDA 1 200 3 500 880 1966 NDA 90 910 14 100 23 400 2 500 24 900 NDA 1 200 6 900 900 1967 16 100 140 1 390 18 800 25 700 2 200 17 200 NDA 1 600 13 700 2 400 1968 20 300 40 1 370 28 100 37 100 1 800 24 200 NDA 1 500 10 000 NDA 1969 24 800 230 2 950 31 600 30 000 1 400 22 900 630 12 000 13 500 NDA 1970 32 000 470 6 000 9 100 9 900 890 27 600 7 010 30 100 12 400 3 000 1971 31 500 390 12 300 18 000 17 300 830 36 400 6 370 35 800 17 200 4 400 1972 33 600 1 080 15 200 25 600 23 500 1 160 30 500 5 820 34 800 13 700 14 200

These values are based on data supplied to the Fisheries Radiobiological Laboratory by the UKAEA and British Nuclear Fuels Limited. CONCENTRATIONS OF RADIONUCLIDES 23

TABLE XII. ANNUAL DISCHARGES OF RADIOACTIVITY (Ci) TO THE BLACKWATER ESTUARY FROM BRADWELL

65„ Year 3H Zn Total activity excluding tritium

1962 NDA 0.002 0. 006 1963 234 0.031 0.199 1964 37.4 0.191 4.1 1965 471 0.227 18. 9 1966 583 0.143 28. 7 1967 499 0. 329 99. 6 1968 362 0. 086 61.4 1969 183 0. 086 113 1970 95 0. 085 129 1971 102 0.065 82.9 1972 249 0.032 104

These values are based on data supplied to the Fisheries Radiobiological Laboratory by the CEGB.

the dose rate in an infinite volume uniformly contaminate^ with C pCi • g"1 of a radionuclide emitting a-particles of average energy Ea MeV per disintegration. For j3-radiation, with ranges in unit density tissue up to 2 cm, it is clear that, except at very low energies, a major fraction of the total energy emitted is deposited outside the organism. In Fig. 1 the average ß-radiation dose

rates within spheres of different radii, Dsph(r), are given as a function of the 00 maximum energy of the ß-particle spectrum, in terms of Dß ( ) (defined as for Da(°°) above). The derivation of the curves is given in Appendix B. The absorption coefficient for 7-radiation is so low that it canbe assumed that 7-ray emission from radionuclides within the organism makes a negligible contribution to the dose.rate received. However, in the exceptional case of very high phytoplankton densities (> 1 ng • g"1 water) and high concentration factors (> 2 X 104), the radioactivity associated with the plankton becomes a significant fraction of the total activity in the water volume and individual organisms then receive an absorbed dose rate from both the ß- and 7- radiation emanating from the activity on other organisms. For species of phytoplankton which have average dimensions less than or greater than the 50 /Jm adopted for the model the dose rates from internal a- and ß-radioactivity (assuming constant concentration of activity) will be less than or greater than the calculated values given by the dosimetry model. TABLE Xm. CONCENTRATIONS OF RADIONUCLIDES (pCi-g*1 wet) IN THE COLUMBIA RIVER^109'117'

32, 46 51 54, 60 65 131. Site Year Material Sc Cr Mn Co Zn

Av. Range Av. Range Av. Range Av. Range Av. Range

McNary 1964 Water 70 8.1-190 NDA 3 400 250-6 900 NDA 150 96-310 77 16-190 6.7 3.0-20 Reservoir Surface NDA NDA 130 1 900 NDA 59 62 NDA 2 100 NDA NDA NDA sediment Fish 58 3-280 NDA NDA NDA NDA NDA NDA 20 5-37 NDA NDA

32, 58 60 65 137 Co Co Zn Cs

Av. Range Av. Range Av. Range Av. Range Av. Range

Hanford 1964 Fish 290 4-1 700 1.3 0.7-3.4 2.4 0.6-6.1 34 7-190 1.0 0.7-1.9

32 46 51 _ 54 59^ 60„ 65„ 95„ ,95_ 140,. 140 239 , P Sc Cr Mn Fe Co Zn Zr/ Nb Ba TLa Np

Hanford 1966 Plankton NDA 5 690 12 600 791 1 250 41 4 580 953 1 910 4 630 3 010

Caddis fly 28 200 968 3 030 447 537 1 790 156 367 656 384 larvae Limpets 19 000 87 696 136 260 80 1 560 109 96 333 79 Water(a) NDA NDA 5 000 NDA NDA NDA 200 NDA NDA NDA NDA

Part 1

Material 9°Sr(b) 89Sr(b) 13lI 14°Ba/4°La

Water(a) 0.02 0.37 0.16 0.04 Fish flesh 0-4 x 10~4 0-1.5 x 10"2 NDA NDA Sediment 5 x 10"4-1. 5 x 10-3 10"2-4 x 10"2 7 x 10_2-8. 3 x 10"1 10_2-4. 6 x 10_1

Part 2

,»4. • , 137 ~ (b) 3 (b) Material Csv ' Cs Co Co TTHv '

(a) Water ' 0.05 0.01 0.04 0.02 4.0 Fish flesh 1.1 x 10"2-9.4 x 10~2 NDA 0-9 x 10"2 0-6 x 10"2 3.8xl0~3 Sediment 6.1xl0~^1.4 NDA 10"2-1.2 10"2-2.5 x 10"1 NDA

(a)pCi-l-l. '^Corrected for probable contribution from fallout. TABLE XV. CONCENTRATIONS OF RADIONUCLIDES (pCi-g wet) IN THE VICINITY OF THE WINDSCALE OUTFALL 1968^1® and unpublished data J

134„ 137„ 144„ 106„ 95„ .95 - Material Cs Cs Ce Ru Zr/ Nb

Av. Range Av. Range Av. Range Av. Range Av. Range

Water (a)' NDA NDA 58 14-120 27 15-57 87 23-228 351 49-1254

Sediment NDA NDA 14 4-29 440 59-1220 702 86-1990 2340 78-9510

Porphyra NDA NDA NDA NDA 17 1.9-73 154 34-403 108 4.3-717

Fucus vesiculosis NDA NDA 6.9 2.5-16 15 5.2-30 40 13-99 140 23-353

Plaice muscle 0.4 0. 2-0.7 1.2 0. 7-2. 0 NDA NDA NDA NDA NDA NDA

«"pen-1.

-1 TABLE XVI. CONCENTRATIONS OF RADIONUCLIDES (pCi-g * wet) IN THE BLACKWATER ESTUARY, 1968[1191

32. 65„ 55 60 110m 137 1 34„ Material Fe Co Ag Cs Cs

Av. Range Av. Range

Sediment NDA NDA NDA NDA NDA 0.1 NDA 2.2 1.0

Fucus vesiculosis NDA NDA NDA NDA 0.06 0.2 NDA 0.6 NDA

Oysters (Ostrea edulis) 0.2 5 0.1-0.3 7.6 5.4-12 0.28 0.28 0.38 1.4 0.6 CONCENTRATIONS OF RADIONUCLIDES 27

FIG.l. Mean ß-radiation dose rate in uniformly contaminated unit density spheres. The continuous curve corresponds to the model adopted.

FIG.2. ß-radiation dose rate at the centre of small uniformly contaminated unit density cylinders (L = length, D = diameter). The continuous curve corresponds to the model adopted. 28 CHAPTER 1

1.3.1.2. Zooplankton. These organisms have been represented by a cylinder of unit density tissue 0.5 cm long and 0.2 cm diameter. This has been taken to be typical of the size of the organisms making up the zooplankton in the waters around the British Isles. As was the case for the phytoplankton, the different zooplankton species show wide variations in size and shape [123] and the model adopted is merely used to provide a simple basis from which to derive estimates of the absorbed dose rates likely to be experienced by organisms in this size range from the available data on concentrations of radioactivity. The model has also been assumed to be an acceptable approximation to fresh-water zooplankton, although here again the typical size is probably somewhat smaller than for the marine zooplankton [ 126, 127]. The radioactivity has been assumed to be uniformly distributed throughout the volume. In the case of ö-radiation, the volume is sufficiently large relative to the particle range for it to be valid to assume that the mean absorbed dose rate closely approaches Da(°°). For ß-radiation the dimensions of the volume are of the same order or less than the ß-particle ranges and thus a variable proportion of the emitted energy escapes from the cylinder. The ß-radiation dose rate, Da(P), at the centre of a series of cylinders (with constant length to diameter ratio) is given in Fig.2 in terms of Dß(°°) as a function of the maximum ß-ray energy. The derivation of the curves is given in Appendix C. The calculation of the absorbed dose rate within a volume containing a distributed 7-ray source also requires consideration of geometrical factors [ 128], and the average dose rate is given by

Dy = rCpgx 10-J jjrad-h 1 ,

where F = the specific 7-ray constant in cm2-rad • h"1 • mCi~- C = the specific activity in pCi • g"1, p = the density of the organism in g • cm"' have a value of unity, g = the mean geometrical factor in cm and is unity for the geometry of the model adopted to represent zooplankton.

For species of zooplankton which have dimensions less than or greater than those of the model used in the calculations (i.e. 0.5 cm long and 0.2 cm diameter) the dose rates from internally distributed ß- and 7-ray emitters will be respectively less than or greater than those predicted by the model (assuming a constant concentration of radioactivity). 1.3.1.3. Mollusca, crustacea and fish. The models adopted to represent each of these groups of animals are of such dimensions that it can be assumed that the dose rates from a- and ß-radiation closely approach D,,!00) andDg(°°), respectively. The dimensions of the models and the geometrical factors appropriate to the calculation of the mean 7-ray dose rate are as follows:

Mollusca: flat cylinder 1 cm high and 4 cm diameter; g - 10 cm Crustacea: cylinder 15 cm long and 6 cm diameter; g = 25 cm Fish: cylinder 50 cm long and 10 cm diameter; g = 41 cm CONCENTRATIONS OF RADIONUCLIDES 29

In each case the tissue density has been assumed to be unity and the activity has been assumed to be uniformly distributed throughout the volume. For the fish, the largest animal considered, the mean 7-ray dose rate corresponds to the absorption within the animal of approximately 10% of the total 7-ray energy emitted.

1.3.2. Dose rates from radionuclides in the water

The estimation of the dose rate from radionuclides in the water also requires consideration of the geometry of the organism, more particularly in the case of a- and ß-radiation. 1.3.2.1. Phytoplankton. Since the dose rate from »-particles emitted within the organism is approximately 0.3 Da(°°), it follows that the dose rates from »-particles incident from outside is approximately 0.7 Da(°°), where

Da(°°) is calculated from the concentration of or-activity in the water. Similarly, for j8-radiation from sea water the mean dose rate is given by

D/5 = D/3<œ> - Üsph

where Dß(°°) and Dß(r = 25 jum) are calculated using the concentration of activity in sea water and the data in Fig.l. For 7-radiation the dose rate to the organism is effectively equal to D^i00) in sea water. 1.3.2.2. Zooplankton. It has been assumed that the dose rate from external ö-radiation is negligible. For external /3-radiation the dose rate is given by

Vß = Dß(») - DjS(P) , which is evaluated using the concentration of the radionuclides in sea water and the data in Fig. 2. The dose rate from 7-radiation from the sea water has been taken to be for sea water. 1.3.2.3. Mollusca, crustacea and fish. It has been assumed that external a- and ß-radiation from the sea water contribute negligible amounts to the average dose rates within the animals, and again the 7-ray dose rate has been taken to be D^i00) for sea water.

1.3.3. Dose rates from radionuclides in the sediment

For the natural radionuclides the sea bed has been assumed to be a plane, infinitely thick source of uniformly distributed activity. Each of the 238U and Z32Th decay series have been assumed to be in equilibrium, i.e. there is no depletion of the volatile or relatively more soluble elements among the daughter products. Thus, the dose rate at the sediment-water boundary is |Dg(°°) and £Dy(°°) [ 129] for the ß- and 7-radiation, respectively. Within the sediment the ß-radiation dose rate increases to Dß(°°) at approximately 1 cm depth. In calculating the dose rate from the sediment at Windscale, account has been taken of the finite thickness of the source and the variation of activity with depth in the sediment [ 130]. At the other three sites, for which no comparable data are available, it has been assumed that these two parameters 30 CHAPTER 1

TABLE XVII. DOSE RATES (firad-h TO MARINE ORGANISMS FROM NATURAL RADIONUCLIDES IN SEA WATER

Isotope (a) Phytoplankton Zooplankton Mollusca, crustacea and fish

3 7 H (1.5-7.7) x 10~ - -

14 5 c 1.5 x 10" - - 40 K 4.1 x lo"1 2.4 x 10 1 1.1 x 10_1

4 Rb 4. 9 x lo" - - 238 .234 234m u+ Th + pa 9.7 x 10~3 1.5 x 10-3 1. 3 x 10~4

234 3 u 9.2 x 10" - -

230_ 6 Th (0.4-9.7) x 10" - -

226 4 Ra (2.8-3.2) x 10~ - -

222 218 214 Rn + Po + Pb+ ^ I> 6.8x10 "4 9.3 x 10~5 7.9 x 10~5 214t,. ^ 214„ Bi + Po

210„ 210„. 5 5 Pb + Bi (0.8-5.6) x 10 (0. 3-2. 0) x 10~ - 210„ -4 Po (0. 5-3. 3) x 10 - -

232mv 7 Th (0.6-47) x 10~ - - 228„ 228 Ra + A c (0. 3-34) x 10~5 (0. 3-28) x 10~5 (0. 3-25) x 10~5 228Th + 224Ra + 220Rn + " ] 2 16 212 212 —fi po + pb + Bi + > (0.1-1.6) x 10 4 (0. 9-14) x 10 (0.8-12) x 10~6

212 208 Po+ Tl ) 235 -4 u 3. 5 x 10 2.0 x 10~5 2. Ox 10"5

(£0 Where more than one isotope is given it has been assumed that the relatively short- lived daughter nuclides are in equilibrium with the parent isotope. CONCENTRATIONS OF RADIONUCLIDES 31 produce a similar effect to that at Windscale and the 7-radiation dose rate above the sediment has accordingly been taken to be approximately equal to 0.25 Dr(°°). The dose rates to aquatic organisms calculated on the basis of these very simple models are given in Tables XVII - XXIX. (See Appendix D for a simple example.)

1.4. DISCUSSION

Within the limitations imposed by the data and the idealized models employed in the dose calculations, it is now possible to make some comparisons. In the marine environment the greater proportion of the background dose rate to phytoplankton, Zooplankton and pelagic fish arises from incorporated activity, »-emitting isotopes (principally 21&Po) being the main source and 40K contributing most of the remainder; for benthic mollusca and crustacea and demersal fish the 7-radiation from the sea bed is an equally important source of radiation exposure. Given the importance of »-emitting nuclides as a source of exposure, it is clear that the assumption of a uniform distribution of activity within these organisms can lead to underestimates of the dose rates to particular tissues if the observed whole body concentrations of a nuclide are due, in part, to higher levels of accumulation in these tissues, e.g. 210Po in the lobster hepatopancreas or the fish liver. Of the radionuclides present in sea water only 40K makes a significant contribution to the overall dose rate. The dose rate from cosmic radiation is of importance for organisms in the surface layers of the sea, but declines from 4 Mrad • h"1 at the surface to 0.5 Mr ad • h"1 at 20 cm depth and becomes negligible at depths greater than 100 m [1]. In the freshwater environment a similar general pattern is apparent, although in water containing appreciable levels of 222Rn and daughter radionuclides these are also a significant source of external exposure, particularly for phytoplankton. As can be seen from Tables XXX and XXXI, which summarize the ranges of dose rates received by aquatic organisms from the various sources in different environments, the background dose rates to each group of organisms are of comparable magnitude in both the fresh- water and marine situations. The dose rates from fallout radionuclides are very variable, reflecting the variation in the concentrations of activity in the organisms due to spot sampling. In the marine environment, incorporated activity appears to be the only significant source of exposure, although there are insufficient data available to make a realistic assessment of the possible importance of activity in sediments. In the past 95Zr and 9oNb appear to have been the principal sources of exposure for phytoplankton, Zooplankton and mollusca and in the medium term radionuclides of the transition elements have made significant contributions to the total dose rate received by all groups of organisms. In the long term, however, 137Cs is the major contributor to the dose rate for all groups of organisms, with 239Pu and 90Sr/90Y being of some significance for phytoplankton and for Zooplankton and crustacea, respectively. In the fresh-water environment the data are insufficient to support detailed conclusions, although it appears that 90Sr/90Y and 13ts are likely to be the major contributors to the overall dose rate in the long term. 32 CHAPTER 1

TABLE XVIII. DOSE RATES (pxad-h X) TO MARINE ORGANISMS FROM INTERNAL NATURAL RADIONUCLIDES

Part 1

Isotopr * e (A) Phytoplankton Zooplankton Mollusca

5 5 5 3H (0.6-3.4) x 10" (0.6-3. 5) x 10" (0. 6-3. 5) x 10" -2 -2 14c 1.1 x 10 3.4x 10"2 5. 6 x 10 40 K 2.4 x 10"2 1.4 2.8

Rb NDA ÑDA 9.8 x 10"3 238 U 1.2 x 10_1 (0.9-1.8) x 10_1 NDA 234 U 1.4 x lo"1 (1. 0-2. 0) x 10_1 NDA 226„ Ra 6.1 x 10~2 2. 0 x 10_1 NDA 210 , 210 Pb + Bi (2.6-18) x 10"3 (0.6-14) x 10~2 (4.2-8.5) x 10"3 210 Po 1.4-5.8 0.6-12 4.5-12 228 -2 -2 Th (2.4-19) x 10 (2. 3-25) x 10 NDA

228 224 220 Th + Ra + Rn + ' ) 216 212 212 po + pb + Bi + > (1.4-11) x 10 1 (1.4-15) x lo"1 NDA 212po + 208T1 J

235u 5. 6 x 10~3 5.6 x 10"3 NDA

In each of the four environments receiving radioactive waste which has been considered, the dose rate from activity in the water is small compared with that from either absorbed radioactivity or from activity incorporated into the sediment. In the Columbia River activity absorbed by the organisms was the most important source of exposure, 32P being the principal radionuclide involved. The dose rates from contaminant activity in the River Danube are low with activity in the sediment being the main source of increased exposure. At Windscale the estimated dose rates received by phytoplankton and zooplankton must be treated with some reservation, since they are based on the levels of activity in the water and concentration factors. The values given are maxima and are overestimates to an extent which depends on the fraction of the equilibrium level, implied by the concentration factor, which CONCENTRATIONS OF RADIONUCLIDES 33

TABLE XVIII (continued) Part 2

TIsotop * e (A) Crustacea Fish

3H (0. 6-3. 5) x 10~5 (0.6-3.5) x 10 5

14 -2 c 6.8 x 10~2 4. 5 x 10 40 K 2. 5 2.5

8 V 7.8 x10~3 4. 9 x 10"3

238 u NDA (0.6-270) x 10"3

234 u NDA (0.8-350) x 10~3 226 -2 Ra NDA (0.2-5.2) x 10 210 , 210 -2 -4 Pb + Bi (3.4-5. 9) x 10 (1. 7-20) x 10 210 Po Whole animal 4.5-18 Flesh 5xl0"3-1.5 Hepatopancreas 140 Stomach 2.2-29 Liver 2.2-10 Bone 0.2-2.5

228Th NDA NDA

228 224 220 Th + Ra + Rn+]

216 212 212 • Po + Pb + Bi + NDA NDA 212po + 208T1 J 235 u NDA (0. 03-13) x 10~3

/a\ Where more than one isotope is given it has been assumed that the relatively short-lived daughter nuclides are in equilibrium with the parent isotope.

can be reached before dilution and dispersion of the activity occurs. For benthic organisms the most important source of exposure is the under- lying sediment. At Bradwell the levels of effluent radioactivity in the water are below the limits of detection, and dose rate estimates are possible only for the oyster, an organism in which significant accumulation of activity occurs, and for benthic organisms for the exposure from the activity in the sediment. The projected environmental inventories of 3H and 85Kr do not appear likely to pose any problems from the standpoint of radiation exposure of aquatic organisms, since the maximum estimated absorbed dose rates from the two radionuclides are 2.2 X 10"3 and 5.3 X 10"5 Mrad • h"1, respectively. 34 CHAPTER 1

TABLE XIX. DOSE RATES (firad-h*1) FROM NATURAL RADIOACTIVITY IN SEDIMENTS

Isotope Gamma-ray dose Beta-ray dose Beta-ray dose rate at sediment rate at sediment rate in the surface surface sediment

238 U + daughters 0. 3-4 0.3-4 0.6-7 in equilibrium 232 Th + daughters 0.7-6 0. 3-2 0.5-5 in equilibrium 40, K 0.5-6 1-15 3-30

TABLE XX. DOSE RATES (urad-h-1) TO FRESH-WATER ORGANISMS FROM NATURAL RADIONUCLIDES IN THE WATER

Isotope (a) Phytoplankton Zooplankton Mollusca, crustacea and fish

3 6 H (1.4-4. 3) x 10" - - -3 -4 -4 40K (0.1-8. 5) x 10 (0. 7-49) x 10 (0. 3-22) x 10

87 6 Rb 4.1 x 10" - -

238 234 234m 4 5 6 U + Th + Pa (0.4-140) x 10~ (0.6-200) x 10" (0. 3-85) x 10"

234 -4 u (0. 7-240) r. 10 - - 226_ -4 Ra (0.7-210) x 10 - -

222 218 214 Rn + Po + Pb + "1 (0.7-610) x 10~2 (0.9-840) x 10"3 (0.8-700) x 10"3 214 214 Bi + Po J

210 21 5 5 Pb + °Bi (2.1-30) x 10~ (0.7-10) x 10~ - 210 -4 Po (0.6-18) x 10 - -

232 5 Th (0.6-6.6) x 10" - -

235 6 -6 u (0.1-46) x 10"5 (0.08-28) x 10" (0. 08-28) x 10

^ Where more than one isotope is given it has been assumed that the relatively short- lived daughter nuclides are in equilibrium with the parent isotope. CONCENTRATIONS OF RADIONUCLIDES 337

TABLE XXI. DOSE RATES (^rad-h_1) TO FRESH-WATER FISH FROM INTERNAL NATURAL RADIONUCLIDES

Isotope Fish

3H (6.4-18) x 10"5 14 c 0. 04 40 K 3. 5

87Rb (0. 2-43) x 10~3

238u (0.21-2.1) x 10"2 -2 234u (0.47-4.7) x 10 226 -2 Ra Flesh (0. 2-2) x 10 Bone (0. 6-210) x 10_1 -4 Pb/ Bi Flesh (0. 8-40) x 10 Liver (0. 8-20) x 10"3 210„ Po Flesh (0.4-12) x 10_1 Bone (0. 6-15) x 10"1 Liver 0.9-5.7

232Th (0.2-1.1) x 10~2 -4 235u (0. 9-9.4) x 10

TABLE XXII. DOSE RATES (^rad-h 1) TO MARINE ORGANISMS FROM FALLOUT RADIONUCLIDES IN SEA WATER

Isotope Phytoplankton Zooplankton Mollusca, crustacea and fish

3H (0.8-610) x 10"7 - 14 -6 C (0.8-3. 1) x 10 - 90 90 -4 -4 Sr/ Y (0.2-72) x 10 (0.1-43) x 10 137 -4 -4 -4 Cs (0. 3-83) x 10 (0. 3-66) x 10 (0. 3-65) x 10 239 -6 Pu (0.8-11) x 10 36 CHAPTER 1

1.5. MEASUREMENT OF RADIATION DOSE RATES IN AQUATIC ENVIRONMENTS

Thermoluminescent dosimeters provide a neat and practical method of assessing the radiation dose rate actually received by organisms in contaminated environments and provide an experimental check on the estimates derived on the basis of the measured concentrations of radionuclides and simple dosimetry models. At Windscale in situ measurements with thermoluminescent dosimeters attached to plaice (Pleuronectes platessa), a demersal fish, have largely confirmed the estimates obtained from the dosimetry calculations, although the results indicate that the natural behaviour of the fish tends to reduce considerably the average dose rate received. It is

TABLE XXIII. DOSE RATES (fjrad-lT1) TO MARINE ORGANISMS FROM INTERNAL FALLOUT RADIONUCLIDES

Isotope Phytoplankton Zooplankton Mollusca

3H (0. 3-270) x 10~5 (0. 3-280) x 10~5 (0. 3-280) x 10"5

14c (0. 6-2. 6) x 10"3 (1. 9-8. 0) x 10~3 (0. 3-1. 3) x 10"2

90Sr/9°Y (0.5-8.8) x 10"3 (0.2-3. 3) x 10 1 (0.2-73) x 10"4(a) -2 137Cs (0.8-60) x 10 0.2-13 (0. 6-2. 9) x 10 1 239 -2 -2 Pu (0. 1-27) x 10 1.2 x 10 (1. 0-6.6) x 10"3

54 -4 2 Mn - (0. 9-4. 5) x 10 (0.2-27) x 10"

55Fe 6.4 x 10"3 (2. 0-19) x 10 3 (0. 5-180) x 10"2

57Co 3.4 x 10"2 4.2 x 10~2 (1. 3-12) x 10"3 60„ Co (0. 7-37) x 10"2 (0.7-36) x 10_1 (0.1-2.4) x 10_1 -2 Ni (0.4-1. 5) x 10~2 (0. 5-1. 9) x 10"2 Kidney (0.1-70) x 10 65_ Zn NDA NDA 6 x 10"4-0. 35 95 .95 Zr/ Nb (0. 6-240) x 10 1 0. 3-130 (0.2-50) x 10 1 -2 Sb 2.7 x 10 0.20 NDA 147 „ Pm 9.7 x 10"2 0. 53 NDA 155„ Eu 1.5 x 10"2 4.8 x 10"2 NDA CONCENTRATIONS OF RADIONUCLIDES 339

TABLE XXIII (continued)

Isotope Crustacea Fish

-5 5 3h (0. 3-280) x 10 (0. 3-280) x 10~

14 -2 c (0.4-1.6) x 10 (0. 3-1.1) x lo"2 3(a) 90Sr/9°Y (0.1-22) x 10" (0.2-73) x 10"5(a) 137 3(a) Cs (0. 2-56) x 10~ (0. 2-0.41) x 10_1 239 6(a) Pu (3. 3-46) x 10 Muscle (1.1-3. 3) x 10"5

Liver (2. 2-14) x 10~4

54 -3 ™M n 6.9 x 10 (0.4-9. 3) x 10~3 55 -2 Fe NDA Muscle (0. 1-140) x 10 Liver 21-24 Gonad 2.8-3.6 Co NDA NDA 60 Co 3. 5 x 10"1 (0. 3-1. 0) x 10_1

Ni NDA NDA 65 -3 -2 Zn 4. 9 x 10 (0. 6-2. 3) x 10 -2 95Zr/95Nb NDA (8-18) x 10

125 sb NDA NDA 147 Pm NDA NDA 155 Eu NDA NDA

These values were calculated from the water concentrations given in Table VI and the concentration factors given in Ref. [34], 340 CHAPTER 1

TABLE XXIV. DOSE RATES (jirad-h-1) TO FRESH-WATER ORGANISMS FROM FALLOUT RADIONUCLIDES IN THE WATER

Isotope Phytoplankton Zooplankton Mollusca, crustacea and fish

3 7 3 H 9 x 10" -1.2 x 10~ - -

54M„ (0. 2-24) x 10~4 (0.2-24) x 10~4 (0. 2-24) x 10~'

89 4 -4 Sr (0.1-530) x 10" (0.05-260) x 10 -

90 9 4 4 Sr/ °Y (0. 5-420) x 10" (0. 3-250) X 10~ - 95 ,95 Zr/ Nb (0.2-11) x 10~2 (2-110) x LO"3 (2-110) x 10"3 103 Ru (0.6-8.8) x 10~3 (0.6-7.9) x LO"3 (0.6-7.9) x 10'

106RU (1. 3-95) x 10"3 (1.1-81) x 10"3 (0.2-13) x 10~"

131I 0.18 0.13 0.12 137 „ -4 Cs (0. 3-80) x 10 (0. 3-63) x 10~4 (0. 3-62) x 10~' -4 Ce (0. 5-11) x 10 (0.2-3.4) x 10~4 (0.1-3.2) x 10' 144 -3 Ce (0. 3-30) x 10 (0.2-23) x 10"3 (0.1-11) x 10~'

TABLE XXV. DOSE RATES (urad-lT1) TO FRESH- WATER ORGANISMS FROM INTERNAL FALLOUT RADIONUCLIDES

Isotope Mollusca Fish

-4 -4 3H (0.4-550) x 10 (0.4-550) x lo" -2 -2 14c (1.1-3.4) x 10' (1.1-2. 3) x 10 -2 -2 54Mn (0. 5-6. 3) x 10 5.8 x 10 -3 55Fe NDA (0.4-1.0) x 10 85„ -3 Sr NDA (0.1-1.4) x 10"

89Sr NDA 5 x 10~3-1.2

9°Sr/9°Y NDA 2 x 10"3-11 95„ ,95 , -2 Zr/ Nb NDA (2. 0-2. 3) x 10 137„ Cs NDA 2 x 10~2-14 CONCENTRATIONS OF RADIONUCLIDES 39

TABLE XXVI. DOSE RATES (^rad-lT1) TO AQUATIC ORGANISMS FROM WASTE DISPOSAL RADIONUCLIDES IN THE COLUMBIA RIVER

Year Isotope Phytoplankton Zooplankton

External Internal External Internal External

McNary 0.01-0.23 NDA 0.01-0.13 NDA NDA Reservoir NDA NDA NDA NDA NDA NDA

0.02-0.43 NDA 0.02-0.43 NDA 0.02-0.43 NDA

NDA NDA NDA NDA NDA NDA

0.5-1.7 NDA 0.5-1.6 NDA 0.5-1.6 NDA

Zn 0.02-0.2 NDA 0.02-0.2 NDA 0. 02-0.2 NDA 131. (0.4-2. 5) x 10 ' NDA (0.3-1.8) X 10~ NDA (0. 3-1.8) x 10" NDA

NDA NDA NDA NDA NDA NDA

Zn NDA NDA NDA NDA NDA NDA 137_ NDA NDA NDA NBA NDA NDA

P NDA NDA NDA 14 000 NDA 23 000 6 Sc Mas. 1Q NDA 260 NBA 32

0. 3 0.3 0.5 0. 3 1.0

NDA NDA 2.0 NDA 6.1

NDA 27 NDA 140 NDA 85

NDA 0.9 NDA 1.6 NDA 27 0.2 2.1 0.2 13 0.2 48 95 .95 Zr/ Nb NDA 29 NDA 26 NDA 22

NDA 43 NDA 170 NDA 58

NDA 26 NDA 350 NDA 350

Np NDA 55 NDA 120 NDA 27 342 CHAPTER 1

TABLE XXVI (continued)

Year Isotope

External Internal y-radiation ß-radiation

McNary 3.6-340 NDA NDA Reservoir NDA NDA 150 17

0.02-0.43 NDA 30

NDA NDA 28

0. 5-1. 6 NDA 81 7

Zn 0.02-0.2 0.6-4.2 570 5

131. -2 (0. 3-1. 8) x 10 NDA NDA NDA

NDA 5-2 100 NDA NDA

NDA 0.2-0.8 NDA NDA

NDA 0.3-3.2 NDA NDA

Zn NDA 0.8-20 NDA NDA 137„ NDA 0.1-0.2 NDA NDA

0.2 NDA NDA NDA 95, ,95 „ Zr/ Nb NDA NDA NDA NDA 140„ Ba NDA NDA NDA NDA 140 La NDA NDA NDA NDA 239„ Np NDA NDA NDA NDA CONCENTRATIONS OF RADIONUCLIDES 41

TABLE XXVII. DOSE RATES (jjrad-h TO FISH FROM WASTE DIS- POSAL RADIONUCLIDES IN THE RIVER DANUBE

Isotope Source

Internal External: water External: sediment y-radiation only y-radiation only

-5 H 5 x 10

58. -2 -5 -2 Co 0-2. 5 x 10 9 x 10

60 (0.6-68) x 10 Co 0-4.4 x 10~ 1.0 x 10 (1. 3-33) x 10"2 Sr 0-1. 6 x lO"

90Sr/9°Y 0-9.4 x lO" 131. -4 NDA 1.4 x 10 (2. 9-35) x 10~2 134 -5 Cs NDA 3 x 10 NDA

137 -2 "5 Cs (0. 6-4. 9) x 10 6x10 (2. 0-45) x 10~2 140 ,140_ La/ Ba NDA 2.1 x 10 (1. 3-59) x 10"2

also found that (3-radiation from the sediment is a significant component of the overall exposure of the gonad of the fish [131, 132]. Thermoluminescent dosimeters have also been used in the Columbia River to measure the absorbed dose rate to periphyton from the reactor effluents [133]. In these instances it appeared that the activity in the water or more probably on suspended sediment was at least as important a source of exposure as incorporated nuclides.

1.6. SUMMARY

Despite the limitations of the very simple models and the data on the concentrations of radionuclides in aquatic organisms, the results of the calculations given in the preceding sections provide an indication of the magnitude of the radiation exposures experienced by aquatic organisms in varied environments. As was to be expected, there are large variations between organisms and between environments for the different sources of radiation (i.e. natural, fallout or waste). The estimated dose rates in aquatic environments from the natural background range up to approximately 40 Mrad • h"1, and are of the same order as those found in the majority of terrestrial TABLE XXVm. DOSE RATES (jirad-h"1) TO MARINE ORGANISMS FROM WASTE DISPOSAL RADIONUCLIDES AT WINDSCALE

Part 1

Isotope Phytoplankton Zooplankton Mollusca

Internal External Internal External Internal External

95„ ,95 -2 (1.1-11) x 10"2 l34 c. NDA NDA NDA NDA NDA NDA -2 137Cs NDA (2.3-20) x 10 NDA (1.9-16) xio"2 (9.4-81) xl0"2{a) (1.8-16) xio"2

144Ce/144Pr 41-160

Part 2

Isotope Crustacea Fish Sediment

Internal External Internal External y-radiation 0-radiation

•2(a) 2 2 ^Zr/95^ (3. 3-84) X lO" (8-210) x 10" NDA (8-210) x 10" 25-3100 6.3-770

-2 2 106Ru/°6Rh 6.7-66(a' (1.1-11) x 10 NDA (1.1-11) x 10 " 8. 8-200 120-2900 134 Cs NDA NDA 0.14-0.49 NDA NDA NDA

•2(a) -2 2 l37Cs (8. 5-73) X 10 (1.8-16) x 10 0.36-1.0 (1.8-16)x lo" 1.4-10 0.8-5.6

-2(a) -3 3 Vpr (8.1-31) x 10 (1.4-5.5) X 10 NDA (1.4-5.5) x 10~ 1.2-25 80-1700

^These values were calculated from the water concentrations given In Table XV and the concentration factors given in Ref. [34], CONCENTRATIONS OF RADIONUCLIDES 43

TABLE XXIX. DOSE RATES (¿¿rad-h-1) TO MARINE ORGANISMS FROM WASTE DISPOSAL RADIONUC- LIDES AT BRADWELL

Isotope Mollusca Sediment

Internal •y-radiation ß-radiation

32. 0.12-0.36 NDA NDA 55. -3 Fe 3.6 x 10 NDA NDA

60 -2 Co 9. 5 x 10 0. 12 0.01 65 Zn 0.17-0. 37 NDA NDA 110m Ag 0.14 NDA NDA 134 Cs 0.26 0.81 0. 18 137 Cs 0.59 0.76 0.43

environments. The estimated dose rates from global fallout, although initially somewhat higher than the natural background in some cases, are now declining to be in the same range as natural dose rates. The estimated dose rates in environments receiving radioactive waste have a much greater range and the actual values are determined primarily by the character of the discharge. It appears that the dose rates to aquatic organisms from the discharged waste in the vicinity of a nuclear power station will not significantly exceed natural background values under normal operating conditions. In the Columbia River the dose rates were, and in the north-east Irish Sea the dose rates are, substantially higher in the vicinity of the discharge points than the natural background values with a maximum value of perhaps 25 mrad • h"1. It seems unlikely that dose rates greater than this will occur in environments receiving waste where the discharge is controlled on public health criteria. The accuracy of these estimates of the dose rates received by aquatic organisms could undoubtedly be improved by refining the models and improving the data on the concentration and distribution of radionuclides in the environment and within the organisms. However, the estimates are sufficiently realistic to provide a basis for assessing the possible effects of irradiation in contaminated environments. TABLE XXX. SUMMARY OF DOSE RATES ((jrad-h-1) TO MARINE ORGANISMS FROM ENVIRONMENTAL RADIOACTIVITY

Source Phytoplankton Zooplankton Mollusca Crustacea Fish

20 m depth, remote 20 m depth, remote 20 m depth, on 20 m depth, on 20 m depth, remote 20 m depth, on from sea bed from sea bed the sea bed the sea bed from sea bed the sea bed

NATURAL BACKGROUND Cosmic radiation 0.5 0. 5 0. 5 0. 5 0.5 0.5 Internal activity 1.9-7.3 2.6-15.7 7.4-14.9 7.9-21.4 2.7-4.2 2.7-4.2 Water activity 0.4 0.2 0.1 0.1 0. 1 0.1 Sediment activity, y 1. 5-16.0 1. 5-16.0 1.5-16.0 8 1.6-21. 0 1.6-21.0 1.6-21.0 Total(a) 2. 8-8.2 3. 3-16.4 9. 5-31. 5 10.0-38.0 3. 3-4.8 4.8-20. 8

FALLOUT n Internal activity, Ç 3H, 14C, 90Sr, 137Cs, 239Pu 0.01-0.88 0.23-13.4 0.06-0.32 0.004-0.097 0.02-0.06 0.02-0.06 Other nuclides 0.25-24.6 1.2-134 0.04-7.7 0.36 0.12-1.7 0. 12-1,7 ä Water activity 5xl0"5-0.016 4xl0"5-0.011 (0.2-32) x 10"4 (0. 2-32) x 10~4 (0. 3-65) x 10~4 (0.2-32) x 10~4 * Total,a) 0.26-25.5 1.4-147 0.10-8.0 0.36-0.46 0. 14-1.8 0. 14-1.8

WASTE DISPOSAL Windscale Internal activity 200-2100 530-6900 15.3-58.9 6.9-67.9 0.5-1.5 0.5-1.5 Water activity 0.2-3. 3 0.2-3.0 0.05-1.2 0.05-1.2 0.09-2.4 0.05-1.2 Sediment activity, y 36.4-3340 36.4-3340 36.4-3340 ß 207-5380 207-5380 207-5380 Total

Internal activity NDA 1.37-1.81 NDA NDA Sediment activity, y 1. 69 1. 69 1.69 B 1.32 1. 32 1. 32 Total 3.1 -3. 5 1.7 1.7

^Excluding the contribution due to ß-radiation from the sediment. TABLE XXXI. SUMMARY OF DOSE RATES (jirad-lT1) TO FRESH-WATER ORGANISMS FROM ENVIRONMENTAL RADIOACTIVITY

Phytoplankton Zooplankton Mollusca Fish

1 m depth, and > 1 m 1 m depth, and > 1 m 2 m depth on 2 m depth on 1 m depth, and > 1 m 2 m depth on from river bed from river bed river bed river bed from river bed river bed

NATURAL BACKGROUND Cosmic radiation 2.7 2.7 2.2 2.2 2.7 2.2 Internal activity NDA NDA NDA NDA 3.6-4.8 3.6-4.8 Water activity 7.4 x 10~3-' 9.8 x 10~4-0.85 4.2 x 10~4-0. 35 4.2 x 10~4-0. 35 8. 3 x 10"4-0.70 4. 2 x 10-4-0. 35 Sediment activity, y 1.5-16.0 1.5-16.0 1.5-16.0 O 1.6-21.0 1. 6-21.0 1.6-21.0 § (a) mo Total 2.7-8.9 3.7-18.6 3.7-18.6 7.3-23.4 Z H

FALLOUT O Internal activity NDA NDA 1.6 x 10 -0.15 NDA 0.12-26.4 0.12-26.4 2» Water activity 0.18-0. 53 0.13-0.40 6.2 x 10"2-0.13 6.2 x 10"2-0.13 0.12-0.26 6.2 x 10~2-0.13 Sediment activity, y 0.16-5.8 0.16-5.8 9.8 x 10 -3. 5 9.8 x 10"2-3. 5 9.8 x10-2-3.5 Total (a) 0.18-0.53 0.22-5.9 0.24-26.7 0.34-32.3 S H WASTE DISPOSAL Columbia River 4 3 3 Internal activity 195 1.5 x104 2.4 x10 4.8-2.1 x10 4.8-2.1x10 Water activity 0.55-2.6 0.55-2.4 0.27-1.1 0.27- 0.54-2.3 0.27-1.1 Sediment activity, y 860 860 860 ß 29 29 29 3 Total(a) 2. 5 x 104 860 . 3-2.1 xlO3 870-3. 0 x 10

River Danube Internal activity 6 x 10~3-0.13 6 X 10~3-0.13 Water activity 6. 3 x 10~4 3.2 x 10"4 Sediment activity, y 6.7 x 10~2--2.23

Total (a) 7 x 10 -0-13 7. 3 x 10 -2. 36

(a)Excludin g the contribution due to ^-radiation from the sediment. 46

APPENDIX A

ALPHA-PARTICLE ENERGY DEPOSITION WITHIN A SMALL SPHERICAL VOLUME

The calculation of the energy deposition within a small sphere containing a uniform distribution of an »-emitting radionuclide requires a knowledge of the distribution of ranges available to the »-particles within the sphere. The assumption of uniform radionuclide distribution and isotropic »-particle emission simplifies the problem, since the particle flux is then independent of direction, and the equivalent case of a parallel flux can be considered. The necessary range distribution has been derived by Caswell [134] as follows. Using the geometry and notation given in Fig. 3, the probability of a range within the sphere greater than, or equal to L for uniform, parallel radiation is given by 2

FIG.3. Geometry for the derivation of the range distribution within a sphere. APPENDIX A 47

Also the probability of a range in L to L + dL is given by

P,L>dL - I dL

- » - D

An «-particle emitted at point A on a given chord of length L and moving along it has a path length St within the sphere, and a fraction (L - i)/L of all the particles emitted on this chord and travelling along it will have a range greater than or equal to £. Thus the probability that any »-particle emitted within the sphere will have a range greater than, or equal to i is given by D D 2L XLX^dL \ ? L J 1) l P(>JÍ) = D ~ X L dL 0

= J_ ,2D + 2D < 3 3D2 '> and the probability of a range in & to i + di> is

P(i)di = I ^ I di

3 I2 = â«1-^»«"

The mean range within the sphere of »-particles emitted at any point within the sphere is given by

D 3 t2

o D o „2 48 CHAPTER 1

Then, given the simplifying assumptions that the average total range of «-particles in water is 60 um at constant linear energy transfer, the mean energy deposited in a sphere 50 Mm diameter of unit density tissue uniformly contaminated with an «-emitting radionuclide is given by

BETA-PARTICLE ABSORBED DOSE RATE WITHIN A SMALL SPHERICAL VOLUME

It has been shown that the ß-radiation dose rate at the centre of a sphere of radius r and density p, uniformly contaminated with activity, can be represented by the expression

D 0 2 + (1 + 3 sPh<' * = v>{° «[*f T>-T> - ]

+ 1 - a(l + vpr) exp (1 - vpr) j ,

where

+ (l+^)exp(l Mfbrr^ L C c c J pu and

. [135]. 3c" - e(c" - 1)

The energy-dependent parameters v and c have been derived from the following expressions:

-1 70 2-1 v = 15.0 E cm -g for E = 0. 5 MeV[136] 8 ß

1 37 2 _1 v = 18.6[Eo - 0.036]" ' cm -g for E > 0.5 MeV[135] 8 8

c = 3.11 for E S0.1 MeV, 8 -0.364 c = 1. 35 E . for 0.1

c = 1.00 for E. >2.25 MeV, P where Eg is the maximum ß-ray energy in the spectrum being considered. The expression for c in the middle energy range is a smoothed interpolation for the data given in Ref. [ 135]. The range of validity of the dose expression given above was stated to be 0.167 to 2.24 MeV but it has been assumed that it can be extrapolated to maximum ß-particle energies outside these limits without incurring large errors. The average dose rate within the sphere can be obtained from the expressions given above using the data given in Ref. [135] (Fig.25, p.735), and the resultant curves are given in Fig.l for unit density spheres with radii of 3, 10, 25 and 60 Mm. 50

APPENDIX A

BETA-PARTICLE ABSORBED DOSE RATE WITHIN A SMALL CYLINDRICAL VOLUME

An estimate of the ß-radiation dose rate at a point P within a non- spherical volume can be obtained by breaking the volume down into an approximately equivalent series of spherically symmetric elements (a sphere and one or more partial, spherical shells) centred on P and using the expression

given in Appendix B for the ß-ray dose rate (Dsph(0, pr)) at the centre of a sphere of radius r and density p uniformly contaminated with activity [ 135].

If the partial spherical shell has inner and outer radii r¡j and r0j, respectively, and subtends a solid angle Wj at P, then it produces a contribution to the dose rate at P of

^ r i D„(p)- = D JO, r .) -D , (0, r..) 1 8k '] 4n L sph oj sph ij' J and the total dose at P is to- D (P) = f ~~ [~D .(0, r.)-D (0, r..) 1 ß0 J 4ir L sph oj sph lj J

The geometry appropriate to the estimation of the /3-radiation dose rate at the centre of the small cylinder representing Zooplankton is given in Fig.4 and the parameters are as follows:

sphere: radius = 0.1cm, solid angle = 4Tt.

1st partial spherical shell: inner radius = 0.1cm, solid angle = 1.44 IT, outer radius = 0.175 cm.

2nd partial spherical shell: inner radius = 0.175 cm, solid angle = 0.52ir, outer radius = 0.26 cm.

Using this approach the curve showing the dependence of Dg(P) (in terms of Dg(°°)) on maximum ß-ray energy has been obtained and is given in Fig.2. Also given in Fig.2 are the results obtained in an identical way for similar cylinders with dimensions both less than and greater than those adopted for the model. 51

APPENDIX A

EXAMPLE OF A DOSE RATE CALCULATION

As an example of the way in which the results obtained using the dosimetry models can be applied in practice the case of 238U in sea water can be considered. The concentration of 238U in sea water is 1.2 pCi • l"1 and as a consequence of the relatively short half-lives of the daughter radionuclides, namely, 234Th (24.1 d),234mPa(l.2 min) and 234Pa (6.7 h), these can be reasonably assumed to be in equilibrium with the parent. The radiation characteristics of the nuclides are given in Table XXXII fl37] (234Pa has been excluded as it is the product of a low probability (0.13%) isomeric transition and has been neglected in the calculations).

TABLE XXXII. RADIATION CHARACTERISTICS OF 238Uj 234Th AND 234mpa

Isotope Radiation Frequency, % Energy, MeV type

238 U a 100 4.2 234 Th ß 65 0.191 ß 35 0.100 y 35 0.093

234mPa 8 98 2.29 g 1 1.53 ß 1 1.25 y 0.81 1.001 y 0.74 0.810 y 0.03 0.786 y 0.38 0.767 y 0.04 0.743 y 0.07 0.255 y 0.12 0.236 y 1.23 0.044

A-D-l. Dose rate to phytoplankton. For a-radiation incident on the organism from the surrounding water the dose rate is given by

D = 0.7D (•) (see section 1. 3.2.1) a ' In the present case 238U is the only source and 100% of the decays produce a-particles with an energy of 4.2 MeV. Thus

Ë = 4. 2 MeV a 52 CHAPTER 1 and since D (») = 2.13 C E urad-h"1 a oi ^

D = 0.7 X2.13X1.2X10_3X4.2

= 7. 51 X 10"3 fjrad-h-1

For /3-radiation incident on the organism from the surrounding water the dose rate is given by

D = D^™) - D (r = 25 ßm) (see section 1. 3. 2.1)

where Dsph(r = 25 um) = (Eßmax) Dß(°°) and Fsph (Eßmax) is obtained from the appropriate curve in Fig. 1. Therefore

D = DJ») |~1 - F , (E ) 1 L sph ßmax' J

234 In the present case both Th and 234mpa emj-t ß-particles and each spectrum is complex, i.e. it results from the sum of several alternative transitions having characteristic maximum ß-ray energies (see Table XXXII), thus

D = ? D„.(») [~1 - F (E )1 1 ßi L sph Smax. i. J

where Dßi (») is the dose rate in an infinite volume from the (3-radiation from the ith transition with maximum energy Eßmax L. Therefore

D(234Th) = 2.13C [0.65 X 0. 064 X (1-0. 24)+0. 35x0. 033X(l-0. 63)] -5 -1 = 9.17 X 10 (¿rad-h

and D(234mPa) = 2.13C [ 0.98 X 0.763 X (1-0.004) +0. 01 X 0. 510 X (1-0. 008) +0.01 X 0.417 X (1-0. 011)1 -3 -1 = 1.93X10 fjrad-h

In the calculations the average /3-ray energy resulting from a transition

has been taken to be one-third of Eßmax[135]. For a distributed 7-ray source in the water the dose rate to the organism 234 234m has been taken to be Dr(°°) (see section 1.3.2.1). Again, both Th and Pa emit 7-rays. Therefore

D(234Th) = 2.13 CE y

= 2.13 C X 0. 35 x 0. 093

= 8.32 xio"5 yrad-h*1 APPENDIX A 53 and

2.13C (0. 0081 X 1.001) + (0. 0074 X 0.810) +(0. 0003 X 0. 786) + (0. 0038 x 0. 767) +(0. 0004 X 0. 743) + (0. 0007 x 0. 255) +(0. 0012 X 0. 236) + (0. 0123 X 0. 044)

The total dose rate to the phytoplankton from 238U plus its two short-lived daughter isotopes in sea water is therefore

-1 9.7 X 10 3 urad-h 1.

A-D-2. Dose rate to zooplankton. For «-radiation incident on zooplankton from the surrounding water, the contribution to the mean dose rate within the organisms has been assumed to be negligible. For external ß-radiation the dose rate to the animal is given by

D = D„(<=)-D (P) (see section 1. 3. 2. 2)

where D (P) = F , (E ) D „(») cyl v jSmax^ 8

and Fcvl (Eßmax) is obtained from the appropriate curve in Fig. 2. Therefore

and for complex ß-ray spectra

Thus

D(234Th) = 2.13C [ 0.65 X 0.64 x (1-1) + 0. 35 X.O. 033 X (1-1)1

= 0 and

D(234mpa) = 2.13C [ 0.98 X 0.763 X (1-0.288) + 0.01 X 0.510 X (1-0.482) + 0.01 X 0.417 X (1-0.610)] -1 = 1. 37 X 10 3 urad-h 1 54 CHAPTER 1

The dose rate from 7- rays incident on the animal from the water is taken to be and is therefore the same as for phytoplankton. Thus

D(234Th) = 8. 32 X lo"5 ^rad-h"1 and

5 1 D(234mpa) = 4. 74 X lo" urad-h"

The resultant total dose rate to the Zooplankton from 238U and the daughter nuclides in sea water is therefore -3 -1 1. 5X 10 jjrad-h

A-D-3. Dose rate to mollusca, crustacea and fish. The contribution to the mean dose rate within these organisms from external a-and ß-radiation has been assumed to be negligible. For external 7-radiation the dose rate has been assumed to be Dy(°°), therefore

D(234Th) = 8. 32 X 10"5 ^rad-h"1

and

5 1 D(234mPa) = 4. 74 xl0~ fjrad-h"

and the total dose rate to these animals from 238U and its short-lived daughter nuclides in the surrounding water is

1. 3X 10"4 (jrad-lT1 Chapter 2

EFFECTS OF IONIZING RADIATION ON AQUATIC ORGANISMS Chairman: I.L. OPHEL, Canada

Members of the Working Group-. M. HOPPENHEIT, Federal Republic of Germany R. ICHIKAWA, Japan A.G. KLIMOV, IAEA S. KOBAYASHI, IAEA Y. NISHIWAKI, IAEA M. SAIKI, Japan CHAPTER 2 EFFECTS OF IONIZING RADIATION ON AQUATIC ORGANISMS 2.1. INTRODUCTION

Our survey of the published literature dealing with radiation effects on aquatic organisms reveals that the majority of papers deal with acute exposures of the organisms to ionizing radiation. Less than 10% refer to conditions of continuous or chronic — and consequently, low-level — exposure. After considering the information on dose rates in the first chapter of this Report it is obvious that any effects due to chronic, low- level exposure are of greatest interest in considering possible ecological effects of man-made radiation. Surprisingly, despite the suspected dose- effect relationships, only 6% of the publications deal with genetic effects. Again, it is here that any effects, particularly population consequences, are of most interest to this Panel. Consequently, in the following pages the authors have devoted more relative space to the few papers which are relevant to radioecological effects and have dealt much less exhaustively with those many publications in which acute exposures or gross somatic effects (due to high doses) were investigated. The task of the Panel has been considerably lightened by two recent reviews of the literature of radiation effects on marine organisms by Templeton et al. [ 138] and by Chipman [ 139] . Publications up to and including some of those from the year 1969 were considered by these authors. Our review included many of the same papers plus many additional publications that have appeared since that time.

2.2. SOMATIC EFFECTS

Ionizing radiation produces effects on both adult and young individual organisms (somatic effects) and on the progeny of irradiated individuals (genetic or hereditary effects). For convenience, in this review we will discuss separately those studies of somatic effects due to short-term exposure to high doses of radiation (acute exposure), and those due to long- term continuous or fractionated exposure at lower dose rates (chronic exposure).

2.2.1. Acute exposure

A large number of publications deal with the survival of adult and young organisms after a single irradiation with relatively high doses. These papers normally contain information on the median lethal dose whereby the

LD50/30 (which is the lethal dose killing 50% of the organisms within 30 days) has a surprising popularity. The period of 30 days was probably chosen because of the fact that small mammals, which are frequently used in laboratory studies, have a good chance of continuing survival if they do not die within this period [ 140] . As experiments are carried out under different conditions and the median lethal doses are given for different periods of time, it is very often impossible to compare the published results. For

57 58 CHAPTER 2

TABLE XXXIII. RANGES OF ACUTE LETHAL RADIATION DOSES3 FOR ADULTS OF VARIOUS GROUPS (krad)

Bacteria 4.5 - 735 (LD90)

Blue green algae <400 ->1200 (LD90)

Other algae 3 - 120 (LDS0)

Protozoa ? - 600 (LDS0)

Molluscs 20 - 109 (LD50/3O)

Crustaceans 1.5- 56.6 (LDs0/30)

Fish 1.1- 5.6 (LDs0/30)

aMostly derived from Ref. [139].

TABLE XXXIV.3 ACUTE BETA DOSE ALLOWING ULTIMATE SURVIVAL OF ALGAE (krad)

Chlorella pyrenoidosa 1000 Anabaena sp. 100-200 Chaetomorpha melagonium (zoospores} 100 Spirogvra subechinata 40 Mougeotia sp. 20-50 Zygnema cvlindricum 20-50 Cosmarium subtumidum 20-50 Eudorina elegans 20-50 Spirogvra crassa 15 Chaetomorpha melagonium 10

aAfter Godward [141],

that reason, lists of the median lethal doses of different animal and plant groups are of limited value. Because of this we will not give long lists of lethal doses for many species, but indicate ranges of tolerance (Table XXXIII).

In an effort to avoid the problems of using the LD60 concept Godward [ 141] determined the ß-irradiation doses allowing 'ultimate survival' of cultures for a number of different algae (Table XXXIV). The term 'ultimate survival' was used in referring to cultures which, after receiving a nearly lethal dose, contain at least one cell which retained the ability to multiply at a normal rate when returned to conditions favourable for growth. However, the author points out that, while this concept has some empirical use, it lacks absolute significance because the chance of one or more cells surviving in an irradiated culture is a function of the size of the initial population. AQUATIC ORGANISMS 59

Special attention should be paid to observations continued for a long time after irradiation with lower doses of radiation. Late damage is the kind of somatic radiation effect on the individuals that is potentially of some concern for the population dynamics of the full ecosystem, both after acute and during continuous exposures. Consider, for example, the case of those invertebrates that continue to reproduce as long as they live: a life-span- shortening effect may directly influence the population structure by means of a reduced total average productivity of the affected individuals. The observations of Shechmeister et al. [ 142] are of great interest in this respect. They irradiated goldfish (Carassius auratus) with X-ray doses ranging from 100 to 10 000 R and observed them for the following year. At 3 6 days after irradiation all fish receiving more than 3000 R were dead, but only 2.5% of the fish exposed to 100 R had died. At 363 days after irradiation all of the 100 R group were dead but none of the unirradiated control group had died. Other observations in the same paper on the effects of parasitic trematodes on irradiated and control fish show that irradiated fish are more susceptible to infection. Thirty days after irradiation mortality of parasitized control fish had reached 2 8%, whereas in the groups which had received 100 R and 1000 R the cumulative mortalities were 75% and 100%, respectively.

Angelovic et al. [ 143] determined the median lethal dose (LD50) of gamma radiation for an estuarine fish (Fundulus heteroclitus) at different salinities, temperatures and periods of time after irradiation. They continued their observations of the fish for 60 days after irradiation. At low salinity (5%O)

and high temperature (27°C) the LD50 calculated after 20 days of observation was 2450 rad but if the LD50 is based on fish deaths during 60 days of observation it becomes only 350 rad. Similarly, at high salinities (25%O)

and high temperature the LD50 is 890 rad based on 20 days of observations and 300 rad for 60 days. There is evidence to suggest that an even lower

LD5O might have been obtained if the observations had been continued for a larger period of time. Today we know that several lethal doses for one species can be obtained according to culture conditions and developmental states. For several developmental stages of the rainbow trout (Salmo gairdneri) different dose- effect curves can be found [ 144] . Bonham and Welander [ 145] have shown the most radiation-sensitive period of silver salmon (Oncorhynchus kisutch) egg development to be a particular stage during the mitosis of the single

cell. They calculated an LD50/150 of approximately 16 R. For the rainbow trout, Welander [146] calculated an LD60 for the eggs at hatching of 78 R and at the end of the yolk stage of 58 R. Feldt and Bühringer [ 147], however, found no effects of irradiation of the one-cell stage in the eggs of Salmo gairdneri with doses as high as 88 R. Testing the effect of X-rays and temperature on the one-cell, 32-cell, epiboly and eyed stage of the Chinook salmon (Oncorhynchus tshawytscha), Wadley and Welander [ 148] found the most sensitive stage to be the 32-cell stage.

At 11,3°C they estimated an LD50/IO7 of about 300 R and at 13.3°C an LD50/107 of about 100 R. After irradiation of the eggs with X-rays at 24 hours after fertilization (approximately 5% of incubation), larvae of the plaice

(Pleuronectes platessa) were found to have an LD50 for survival to meta- morphosis of 90 rad [ 149 ]. Periods of high radiosensitivity have been found by Kulikov [ 150] in pike (Esox lucius L. ) roe during fertilization and early cleavage after 60 CHAPTER 1 irradiation with 200 R of 7-rays. The first period of increased radiosensitivity was found to be the stage of convergence of the male and female pronuclei. Later periods of increased radiosensitivity are the interkinetic stages of the nucleus between divisions of cleavage. When eggs of carp (Cyprinus carpió) were exposed to acute 7-radiation [151], radiosensitivity decreased äs development increased, except for an increase in radiosensitivity during late cleavage. Stages in order of decreasing radiosensitivity were: zygote, late cleavage, early cleavage and post-organogenesis. Hatchability of eggs irradiated after organogenesis was not affected by any of the doses (500 to 16 000 rad). Belyaeva and Pokrovskaya [152] determined changes in radiosensitivity during the course of first embryonic mitosis in loach (Misgurnus) eggs. An experiment was carried out to test the radiosensitivitity from the time when the furrow of the first cleavage was formed up to the time when all the ova had reached the four blastomere stage. Portions of the eggs were irradiated with 500 or 50 R every six minutes. In another experiment, the developing eggs were irradiated during the second and third mitotic cycles and the irradiation was given every seven minutes as a dose of 500 R. The percentage of disrupted mitosis at the gastrula stage, the percentage of eggs which died between the period of irradiation and hatching, and the percentage of malformations in the total number of hatched embryos were used as indices of radiosensitivity. The greatest radiosensitivitity was found when the irradiation was applied at anaphase and telophase, at a time when furrows were appearing in the developing ova. Even 50 R administered at that time cause 30% mortality and produce a considerable number of deformed offspring at hatching.

Kobayashi and Hirata [153] irradiated trout fry of a length of 37 to 72 mm with doses from 100 to 1200 R. There was no indication of lower survival in the 1200 R group over a period of 115 days. However, even in the 300 R group some distant effects were found in the reproductive organs, kidney tubules, intestinal epithelium and blood cell constituents. A temporary depression of feeding activity was found even in the 100 R group. In a long- term study with offspring of a cross between a rainbow and a steelhead trout Welander et al. [ 154] found that irradiation up to 200 R applied during the eyed-egg stage had no effect on fecundity. A useful summary and discussion of earlier studies on relative sensitivity of different life stages of fish (mostly salmonids) is found in Donaldson and Foster [ 155] . Of great interest are so-called 'negative' results from experiments or situations where no lethal or visible harmful effects of known doses of radiation were observed. For example, Hoppenheit [156-158] has found in females of Gammarus duebeni (which has an LD50/30 of 3500 R) that the highest dose that does not affect survival time is about 1000 R and the highest dose that does not influence fertility after irradiation of the females is about 170 R.

2.2.2. Chronic exposure

If organisms are irradiated continuously at low dose rates there is an increase in the total dose necessary for death (or some other injury) as compared with a sinlge large dose [ 159] . At low dose rates there is a competition between injury and repair (for a discussion of relevant experi- AQUATIC ORGANISMS 61 ments on repair see section 2.4). Under such conditions there should exist a dose rate (at least for somatic effects) at which repair processes keep pace with injuries and the chronic exposure produces no obvious ill-effects.

2.2.2.1. Irradiation from external sources

Irradiation due to penetrating radiation from outside the body of an organism is referred to as external radiation. Such penetrating radiation would usually be X- and 7-rays which are both very short wavelength electromagnetic radiations; but neutrons, which are uncharged particles, can also penetrate considerable distances into living tissues. There are a number of ways in which electromagnetic radiation may interact with matter. However, the energy of X- and 7-ray photons which are of interest for biological experiments, is mostly absorbed by the ejection of electrons from the atoms of the material which they traverse. The ejected electrons produce ionization in the atoms or molecules through which they pass. Consequently the ions will be produced along the track of the ejected electron in the tissue. Neutrons do not produce ionization directly, but the energy of fast neutrons is deposited by nuclei recoiling after a collision with the neutron or by the various secondary particles and photons, (protons, o-particles, photons) produced by an interaction of the neutron with a nucleus of the medium. In the hydrogenous material such as tissues, fast neutrons knock out protons which are hydrogen nuclei and are therefore positively charged. When the charged particle moves in the tissue, a dense ionization will be produced along its track. The primary effects of fast neutrons are therefore mostly due to the ionization produced by protons in the tissue. Slow neutrons do not eject protons but are captured by nuclei in the tissues of the irradiated organism, thereby producing a new nucleus which may be radioactive and will emit ß- or 7-rays. During the process of neutron capture the nucleus may emit a 7-ray. Donaldson and Bonham [ 160, 161], Bonham and Donaldson [ 162] and Donaldson [ 163] have taken advantage of the migratory habit and the fecundity of Chinook salmon to make a continuing long-term study of the effect on a population of chronic low-level 7-irradiation from a 60Co source during embryonic development. Eggs were first irradiated at dose rates ranging from 0.5 R -d"1 to 20 R -d"1 from shortly after fertilization until feeding commenced. The fingerlings were reared and then allowed to migrate to sea; those that returned to the hatchery during the second year were precocious males; and during the third and fourth years following irradiation both male and female adults returned. Various crosses were made and some of the eggs and larvae obtained from irradiated fish were re-irradiated. These series of long-term experiments involving large numbers of fish (96 000 to 256 000 fingerlings were released per experiment) indicate that irradiation at rates between 0.5 R -d"1 and 5.0 R d"1 (total of 355 R) from the fertilization stage to the feeding stage produced no damage to the stock sufficient to reduce the reproductive capability over a period of several generations. Although abnormalities in young fish were increased by all dose rates, the number of adults returning was not affected. On the contrary, the low-dose irradiated stock returned in greater numbers and 62 CHAPTER 1 produced a greater total of viable eggs than the control stock. At dose rates of 10 R • d"1 (total of 810 R during incubation period) and above, measurable radiation damage was evident and the growth rate of the irradiated fingerlings was significantly less than that of the controls [ 163]. Brown and Templeton [164] and Templeton [ 165] report on a series of experiments in which the eggs of plaice were irradiated with a 137Cs source. Total y-doses ranging from 0.6 to 500 R were used, at rates of 10 mR • h"1 to 1 R • h"1 from fertilization until hatching. No significant differences at hatching were observed in the survival or in the number of abnormal larvae produced. Adult fish (Oryzias latipes) exposed to chronic y-irradiation over a period of 79 days showed little effect of the radiation stress [ 166] . The doses received by the fish ranged from 2.2 X 102 to 1.65 X 104 rad. A small decrease in percentage of body water was observed with increasing radiation. This effect is attributed to hastened ageing and/or failure of the fish to maintain the normal proportion of soft tissue to skeletal material. An investigation on the effect of chronic irradiation in the reproductive performance of the fish Lebistes reticulatus by Purdom and Woodhead [ 167] showed a reduction of fecundity by about 50% over a two-year period in pairs irradiated at dose rates of 0.25 and 0.5 rad • h"1. At a dose rate of 1.7 rad -h"1 fish were sterile within four months. Engel [ 168] reports on studies of the effects of chronic low-level irradiation on the growth and survival of young blue crabs (Callinectes sapidus). Single acute exposures had indicated that the sensitivity of these crabs is similar to that observed for other marine invertebrates. In the chronic irradiation experiment, the crabs received a total radiation dose over 70 days of 5105, 11 502 and 45 693 rad. A significant number of deaths due to radiation occurred only among the crabs that received the highest radiation dose. Laboratory populations of the aquatic snail Physa heterostropha were exposed to chronic y-irradiation during their life-span (approximately 24 weeks) at dose rates of 1, 10 and 25 rad • h"1 [ 169] . All of these dose rates caused a decrease in the fecundity of the snails although the effect at 1 rad • h"1 was not significant. A dose rate of 25 rad • h"1 eliminated reproduction and led to extinction of the population. The reduction in fecundity at 10 rad -h"1 would cause rapid elimination of the population. Dose rates of 10 and 2 5 rad -h"1 significantly increased growth (size of adult snails). The life-span of snails was shortened by all dose rates except 1 rad • h"1.

2.2.2.2. Irradiation from radionuclides present in the water

Radionuclides in the medium represent only one radiation source to which aquatic organisms are exposed in the environment. A high degree of sorption of radionuclides into or on the egg, for example, could give rise to a radiation dose within, or in the immediate vicinity of, the developing embryo that would be greater than that arising from the medium alone [164, 170-173], In addition, radiation from incorporated radionuclides in the developing tissues of an embryo may also be more effective in causing damage than external radiation alone [ 173]. Polikarpov and his co-workers, who pioneered the studies in this field, have reported on extensive studies with eggs of a number of marine and AQUATIC ORGANISMS 63 fresh-water species over the concentration range 10'14 to 10"4 Ci -l"1 of

90Sr _90y [ 170, 171, 173, 174] . Reduced hatching of the larvae and early mortality were seen at concentrations of 10"7 Ci • l"1 and above, and the number of abnormalities increased significantly and with remarkable consistency at concentrations of 10"10 Ci -l"1 and above. Kosheleva [ 175] observed death during the entire embryonic development in the Atlantic salmon (Salmo salar) and found a considerable number of deaths when the eggs were exposed to a mixture of nuclear fission products with a concentration of 1 X lO"10 Ci • l"1. A high number of deaths were also observed in water containing 137Cs with a concentration of 1 X 10"8 Ci -l"1. Fifty per cent mortality of eggs occurred in water with 144Ce at a level of about 3 X 10"9 Ci-1"1. For 90 Sr-90 Y at concentrations of 5 X 10"6, 5X 10"8 and 5X 10"10 Ci -l'1 egg mortality during the time of incubation was at the control level. In the same species contamination of water by 144Ce in the range of 3 X 10"6 to 3 X 10"9 Ci-1"1 results in an increase in the rate of development of eggs in the period from onset of segmentation to onset of gastrulation [ 176]. The duration in hatching of larvae is prolonged at concentrations of 90Sr -90Y in the range of 5X 10"6 to 5 X 10"10 and of 144Ce in the range of 3 X 10"6 to 3 XIO"9. In another paper, Migalovskij [177] showed that hatching begins earlier at 90Sr -90Y concentrations of 2 X 10"5, 0.7 X 10"6 and 0.6 X 10"7 Ci -l"1. Egg mortality was greater in all experimental variants. The process of formation of primary S6x c©lls wsts d6pr©ss6d a.t th© cone6ntra/tion of 2 X 10"6 Ci-l"1. At a concentration of 0.7 X 10"6 Ci-l"1 their number approached the control, but at 0.6 X 10"7 Ci -l"1 it increases somewhat. Kasatkina [ 178] showed that the action of 90Sr -90Y at concentrations of 2 XIO*5, 0.7 X10"6 and 0.6 X 10"7 Ci-l"1 causes a more intensive enzyme accumulation by the hatching glands. Oganesyan [179] observed degenerative changes in the thyroid gland of larvae from chronic exposure during embryonic development to radiation from 90Sr-90Y. These changes were most clearly expressed at 2 X 10"6 Ci -l"1. Clearly expressed changes of a degenerative character have also been found by Kosheleva [ 180] in erythropoiesis of fish larvae at a 90Sr-90Y concentration of 2 X 10"5 Ci -l"1. Brown [172], Brown and Templeton [164] and Templeton [165] conducted similar experiments using eggs of the brown trout (Salmo trutta) and of plaice maintained from immediately after fertilization until hatching in water contaminated with 90Sr-90Y over the concentration.range 10"lc Ci-1"1 to 10"4 Ci • l"1. They did not observe any significant increase in mortality or in the production of abnormal larvae. Shekhanova and Pechkurenkov [181] incubated developing eggs of the loach in solutions with activities of 90Sr-90Y from 10"10 to 10"4 Ci -l"1. Significant increase of numbers of larvae with skeletal malformations was observed in solutions with activities of 3.1 XIO"10 and 1.5 XIO"8 Ci-1"1. A higher amount of non-developing larvae appeared in the 3.1 X 10"10 and 1.8 X 10"6 solutions but there was no similar effect with solutions having activities of 1.5 X 10"8 and 1.5 X 10"4 Ci -l"1. It could not be established that the chosen specific activities of 90Sr-90Y have a detrimental influence on the mortality rate of the eggs. On the contrary, a lower rate of mortality for the entire period of incubation has been observed in solutions of 1.5 X 10"4 Ci -l"1. From their findings the authors have postulated the possible existence of a protective mechanism which comes into operation at moderate radionuclide concentrations. 64 CHAPTER 1

Shekhanova and Voronina [ 182] investigated the effects of 90Sr-90Y in solutions of 3.IX lO"10 , 1.5X10"8 and 1.3 X 10"6 Ci-1"1 on the formation and functional activity of gonads of loach and Tilapia mossambica in an experiment lasting eight months. In Tilapia, spawning occurred earlier at a concentration of 10"8 Ci-1"1 than in control fish and in fish held at concentrations of 10'6 and lO"10 Ci-1"1. The weight of fishes from this group was lower than in the other groups. The frequency of spawning and the number of eggs produced was increased. At 10"6 Ci-1"1 a decreased fecundity was observed in the female loach and the male Tilapia became sterile. Shekhanova et al. [183] found no functional or histological response of gonads in the adult loach kept in solutions having an activity of 3.11 X 10"10, 1.5 X 10"8 and 1.32 X 10"6 Ci-1"1 for 115 days. Mashneva [184] performed experiments to assess the effects of mixtures containing rare earth isotopes, alkaline earth isotopes and other isotopes on developing eggs of carp and Coregonus peled in relation to the radionuclide concentration and the stage of embryogenesis at the beginning of exposure. Several criteria such as embryo mortality, time of hatching, number of prehatched larvae and morphological anomalies were used to detect harmful effects of the irradiation. Damage was found at early stages of development at a concentration of 10"5 Ci-1"1 . Concentrations of 2 X 10 4 to 1 X 10"3 Ci-1"1 were required to affect later stages. Concentrations of 1X10"7 Ci/l"1 had no effects, irrespective of stage and species. Fedorova [185] found an increase of malformed larvae of Coregonus peled in a 5 1 14 concentration of 2 X 10" Ci-1" (NaH CC>3) of about 5.5% when compared 14 with control. The NaH COs was added to the water seven days after fertilization (gastrula stage). Later stages were less radiosensitive. Inspired by the contradictory data, Tsytsugina [ 186, 187] studied the cytogenetic effects of radiation in the developing egg of the ruff, Scorpaena porcus, and the turbot, Scophthalmus maeoticus. The fertilized eggs of these fish were placed in solutions of 90Sr-a0Y, 91Y, 89Sr and 14C in sea water. Significant increase of chromosomal breakages was found at 1X10"9 Ci-1"1 of 90Sr-90Y, 2 X 10"8 Ci-1"1 of 89Sr and 1.8 X 10"7 Ci-1"1 of 14C in the ruff. A considerably greater number of cells with chromosome breakages was found in tissues of the externally normal one-day old prolarvae of the turbot after a three-day stay in a solution of 3 X 10"10 Ci-l"1 91Y. A cytological analysis of the tissues in the prolarvae with varying morphological anomalies, revealed a higher level of radiation injury to the chromosome apparatus as compared with the externally normal prolarvae. An increase in the dose by several orders of magnitude resulted in a slight increase (if at all) in the number of aberrant mitosis. These findings are in agreement with those of Polikarpov and Ivanov [170, 171] who observed a disproportion between dose and occurrence of major morphological abnormalities. In this connection Tsytsugina [186] draws attention to the fact that cells with non-viable chromosome aberrations, the number of which is higher at higher concentration of radionuclides, are eliminated. However, not all the cells with rearrangements of the chromosomes are eliminated because of genetic unbalance. Part of the dicentric chromosomes may be preserved in the form of a stabilized cycle of chromosome and chromatid bridges over many cellular generations. In experiments by Migalovskaya [188] with salmon embryos, three levels of contamination with 9°Sr-90Y (2X10'15, 0.7X10"6 and 0.6 X10"7 Ci-1"1) were used. Mitotic index and frequency of chromosome disturbances were AQUATIC ORGANISMS 65 checked in stages of blastomeric and epithelial blastula, gastrula, and one- day old larvae. A decrease in mitotic activity was not observed at any concentration. An increase in mitotic activity was found in the embryonic 'ligula' stage (half gastrulation). A distinct increase in frequency of chromosome disturbances beginning with the stage of the epithelial blastula was observed at the 2X 10"5 Ci-1"1 level only. Pechkurenkov et al. [ 189] stated that conflicting results on the radiosensitivitity are the consequence of application of different experimental methods as well as different statistical criteria. In experiments with developing embryos of the fishes, Misgurnus fossilis (loach), Salmo salar (salmon) and Esox lucius (pike), the authors appraised the degree of genetic heterogeneity among offspring from one pair of spawners and among offspring of several pairs of spawners, and checked the validity of different statistical criteria. The critical evaluation of data failed to indicate any effect on the number of deaths as well as on the number of malformed larvae in solutions of 90Sr-90Y ranging from 2X 10"10 to 1.5 X 10~4 Ci-l"1 and of 239Pu ranging from the order of 10"nto 10"7 Ci-1"1 in the loach, and of 137Cs ranging from 10"10 to 1CT6 Ci-l"1 on salmon and pike. Fedorov et al. [190] reported that the eggs of plaice from the Barents Sea were sensitive to low concentrations of 90Sr-90Y in sea water. They reported an increase in malformations at hatching over a range of concentrations from 10"11 to 10"6 Ci-l"1 . White and Angelovic [191] report on the effects of chronic exposure to low levels of 137Cs on the developing eggs and larvae of the fish, Fundulus heteroclitus. The concentrations of 137Cs used, 3 X 1CT7 , 3 X 10"6 and 3 X 10"5 Ci-l"1, produced no visible abnormalities. Neustroev and Podymakhin [192], in similar studies with the eggs of the Atlantic salmon, Salmo salar, found that at 10"10 Ci-1"1, 90Sr-90Y, the rate of development of the egg was the same as the control up to the stage of 1/3 development of the yolk sac. Subsequently, the rate of development in the contaminated aquaria was more rapid than in the control. However, the mortality and number of deformities did not differ from those of the controls. At 10"8 and 10"6 Ci-l"1 , the rate of development was the same as that observed in the 10"10 Ci-l"1 experiment. Mortality and deformities were increased only at the higher levels of radioactivity. Hiyama, Shimizu and Suyama [193] have also studied the effect of various 90Sr-9<)Y concentrations on the hatching and malformation rates of the eggs of two species of marine fish (Mylio macrocephalus and Rudarius ercodes). They found no effects on either of these characteristics at any of the concentrations between 10"12 Ci-l"1 and 10"3 Ci-l"1. Similar studies on the eggs of fish (Oryzias latipes) were carried out by Egami and co-workers [ 194, 195] . The eggs were hatched in 90Sr-90Y concentrations of 1CT6, 10"5 and 5 X 10"5 Ci •l"1. No effects on mortality rate or abnormalities were found during this period (approximately 14 days). However, when the fish were kept in the two higher concentrations of contaminated water after hatching, there were observable histological effects on the gonads after 30 days of exposure. After 70 days there was some interference with growth, abnormalities in ovaries and significant disturbance of germ-cell production. When adult fish were exposed to the same radionuclide pair at concentrations between 10"7 and 10"6 Ci-l"1 there was almost complete destruction of 'seminal glands' after 30 days at 10"5 Ci-l"1. No effects were observed at 10"7 Ci-l"1. It was estimated that the total radiation dose to the whole-body of Oryzias exposed at 10"5 Ci-l"1 was 970 rad. Much 66 CHAPTER 1 of this dose was, of course, due to 90Sr-90Y taken up by the fish from the water. Studies of the effects of 8-rays from 90Sr-90Y on the ovary of the marine goby, Chasmichthys glosus, by Hyodo-Taguchi et al. [ 196] showed degener- ation of oocytes in the fish kept in water containing 10"6 CM"1 of 90Sr after exposure of 10 days only. Several reports have been published on the effects of weapons fallout residues on the development of fish eggs [ 197, 198] . Effects were found at radioactivity levels of 4 X 10"10 CM"1 of mixed fission products. However, the interpretation of these results is complicated by the lack of information on radionuclide composition and the chemical effect of the residues. In experiments with sea-urchins Akita and Shiroya [199] observed developing eggs of Pseudocentrotus depressus and Anthocidaris crassispina in various concentrations of 90Sr-90Y in sea water ranging from 10"12 to 10"3 CM"1. At the highest concentration of the radionuclides (10"3 Ci-1"1) they found a sharp decrease in the rate that eggs of both species reached the pluteus stage. Using the same two organisms Akita and Shiroya [ 199] found a surprising difference in the response of their eggs to ß-radiation from tritium (as tritiated water) in the medium. Both were exposed to various concentrations of 3H between 1.8 X 10"7 and 1.8 X 101 Ci l"1. For Anthocidaris the tritium concentration reducing the percentage of eggs reaching the pluteus stage to 50% was 1.8X 10"1 Ci-1"1 whereas for Pseudo- centrotus the corresponding concentration was 2.5X 10"5 Ci-1"1 . Nelson [200] studied the effects of radionuclides on larvae of Pacific oyster, Crassostrea gigas. The larvae were reared for 48 hours following spawning in sea water containing either 6oZn, 51Cr or 90Sr-90Y. The concentrations of each radionuclide ranged from 10"2 Ci-1"1 to 10"8 Ci-1"1. Significant increases in abnormal larvae were detectable at the following minimal concentrations: 65Zn, lO^Ci-l"1; 51Cr, 10"4 Ci-1"1; 90Sr-90Y, 10"3 Ci-1-1. The effects of chronic irradiation on the hatching of eggs of the gastropod mollusc Limnea stagnalis L. were studied by Kulikov et al. [201] using aqueous solutions of 90Sr-90Y. They found that the first appearance of disturbances in embryogenesis occurred at 10"4 Ci-1"1. Lebedeva and Sinevid [202] using the cladoceran, Daphnia magna, investigated the effect of 90Sr-90Y in concentrations between 3 .4 X 10"10 and 3 .4 X 10"3 Ci-1"1. They found that a concentration of 3.4 X 10"5 Ci-1"1 shortened the life-span of adult individuals, and a concentration of 3.4 X 10"3 Ci-1"1 led to death of all offspring within one week. Experiments performed by Telichenko [203] on the effects of 238U, 232Th and 90 + 89Sr in Paphnia magna resulted in a decrease of rate of reproduction at concentrations of 1 mg uranium/litre as uranyl nitrate, 0.5 mg thorium/litre as thorium nitrate and IX 10"5 Ci radiostrontium/litre of water. The effects of uranium and thorium at these concentrations would probably be chemical rather than due to radiation. Williams and Murdoch [204] found no influence on population density in a population of a copepod (Tigriopus californicus) kept in water contaminated by 4.5 X 10"6 Ci 131Cs/litre for several years. Hallopeau [205] studied the effect of 137Cs (4 X 10"5 Ci-1"1) and a mixture of fission products (2X 10"6 Ci-1"1) on the reproduction of Artemia salina. At the chosen concentrations no differences were found between controls and irradiated specimens. Table XXXV summarizes in graphical form the results discussed above. It can be seen that a considerable number of experiments following those of AQUATIC ORGANISMS 67

Polikarpov and Ivanov have failed to confirm the extreme sensitivity of fish eggs to low concentrations of radionuclides in water that was found by those workers.

2.2.2.3. Irradiation from incorporated radionuclides

The literature on the somatic effects of incorporated (metabolized) radionuclides on individuals and populations of aquatic organisms is very sparse. This is probably due to early studies with X-rays and other external radiation sources which showed that (with the exception of early fish embryos) rather large doses were needed to produce visible effects. However, the magnitude of concentration factors which are now known for some artificial radionuclides in fresh-water and marine organisms indicates that some tissues of organisms living in contaminated environments could receive biologically significant beta doses. Radioisotope decay generally produces a number of local (at the site of the atom) and distant physical and chemical effects. Research has particularly centred on the effects of decay when isotopes are localized in molecules of DNA, which carry the genetic information of the cell. The most widely studied effects have been cellular death and genetic mutation. Both of these are generally believed to be mediated by damage to the DNA of the cellular chromosomes. There is excellent evidence that a single chemical lesion in a DNA molecule can cause either cell death or a detectable mutation [ 220, 221] . In 3 -decay the atom undergoes a chemical transformation due to the change in atomic number, generally accompanied by a change in valence. The electronic structure of the atom is left in an excited state. This excitation is sometimes great enough to cause ejection of an orbital electron. Beta decay by electron capture usually causes the ejection of large numbers of orbital electrons. The atomic nucleus may recoil with enough kinetic energy to rupture chemical bonds. In addition to these local effects, an emitted electron may produce distant radiation effects. In ß-decay by electron capture there is no emitted ß-electron but distant effects may result from the emission of X-rays (K radiation), or orbital electrons when the vacancy created by the capture is filled [222] . The cascade of electrons which fall to replace those lost in shells closer to the nucleus and the ensuing emission of electrons from the atom without X-ray emission is known as the 'Auger effect'. By this process the atom may have a large number of vacancies in the outer shell which are filled from other atoms in the molecule resulting in positive charges being distributed throughout that molecule. The positively charged atoms strongly repel each other by coulombic repulsion and the molecule virtually explodes. In addition the emitted Auger electrons are of extremely short range producing an enormous energy density over a very small volume and producing great differences in dose distribution within the cell. Although studies are incomplete there is evidence that when an isotope that decays by electron capture (such as 125I) is attached to DNA it may produce a biological effect far in excess of that predicted on the basis of absorbed dose; and the factor involved may be between 10 and 20 [223] , Alpha particles are given off by a few radioactive nuclides. Because of their high charge and low velocities they are readily stopped by matter. o> 00

TABLE XXXV. SUMMARY OF EXPERIMENTAL STUDIES ON THE EFFECTS OF RADIONUCLIDES IN WATER ON AQUATIC ORGANISMS

(POSITIVE EFFECT: • or I (NEGATIVE EFFECT: O or

Concentration of radionuclides * (Ci" Types of effects

10-i2 10-io 10-8 ,0-6 10-4 ,0-2 J

Shortened the life-span of adult individuals of Daphnia magna 90Sr- 90y

Delay in embryonic development of fish eggs (anchovy)

n Increase in the mortality rate of embryo of fish eggs and >X tendency to be smaller in size of young fish was observed Decrease in cell division in gastrula stage and chromosome aberration of fish eggs (anchovy, stone perch)

Increase in malformation rate of fish eggs (anchovy, mullet, green wrasse, horse mackerel) Increase in malformation rate of fish eggs (plaice, Pleuronectes platessa) No significant increase in mortality or in the production of abnormal larvae (brown trout, Salmo trutta). (plaice, Pleuronectes platessa) The rate of development of the egg was the same as the control up to the stage of one-third development of the yolk sac (atlantic salmon, Salino salar) Morphological abnormalities, delay in development, and mortality (eggs of the fresh water mollusc, Limnaea stagnalis) 10*12 lO"10 10"8 10"6 10"4 10"2 1

Shekhanova, Non-developing larvae appeared in developing eggs of the loacli 90Sr- • ó • ó Pechkurenkov 90y [181] Hiyama, Sharp decrease of the rate on attaining to pluteus stage (see Shimizu, c urchins, Pscudocentrotus depressus, Anthoeidaris crassispina Suyama [193]

Normal rate of hatching and malformation of eggs (Mvlio c macroeephalus and Rudaris ere o des in sea water) Egami et a I, Normal rate of mortality and abnormality of the embryo [194] o (fresh water killifish, Oryzias latipes) Effect on gonad was found in fish, exposed in contaminated water, continuously 70 days after hatching (fresh water killifish, Qryzias latipes) Damage on seminal glands in fish, exposed 15-30 days (fresh water kiliifish, Qryzias latipes) Kosheleva Egg mortality during the time of incubation was at the control [175, 180] c± level in the Atlantic salmon (Salmo salar) Nelson Significant increases in abnormal larvae (pacific oyster, [200] c Crassostrea gigas) Tsytsugina Significant increase of chromosomal breakages was found in [186, 187] the ruff (Seorpaena p o reus) Guthrie and The testes and ovaries of adults were atrophied when larvae Brust of Aedes aegypti and A. atropalpus were reared in radioactive [206, 207] water. Scott [208]

Strand et al. No significant differences on rainbow trout during [209, 210] o embryogenesis TABLE XXXV (continued)

(POSITIVE EFFECT: »or (NEGATIVE EFFECT: O or )

1 Investigators Concentration ^f radionuclides * (Ci ' JT ) Types of effects 10"10 10"s 10"' 1CT4 10"2 1

90Sr- No decrease in the percentage of dividing cells was detected 90y in the investigated development stages. In variants with 2 X 10~5 Ci - l"1, there was a reliable increase in the frequency of chromosomal aberrations, beginning with the epithelial blastula stage (Salrno salar)

137Cs No influence on population density in a population of a copepoda (Tigriopus californicus) kept in radioactive water for several years. No visible abnormalities on the developing eggs and larvae (mummichogs, Fundulus heteroclitus) F.P., o No effect on the reproduction of Artemia salina 137Cs Considerable number of deaths were observed in the Atlantic F.P., salmon (salmo salar) when the eggs were exposed to radio- 137Cs, active water 144Ce

F. P. Damage at early stages of developing eggs of carp and 3 Coregonus peled 51Cr o T Significant increases in abnormal larvae (Pacific oyster, 65Zn Crassostrea gigas) 226Ra Photosynthetic oxygen production in fresh-water phytoplankton was sharply reduced by 24 hours exposure to > 226 8 a Ra concentration of 3 X 10" Ci • 1 HTO 50% attainment to pluteus (red sea urchin, (tritiated Pseudocentrotus depressus) water) 50% attainment to pluteus (violet sea urchin,

Büggeln, Held HTO I Reduced percentage of germination of the asexually produced [215] (tritiated water) spores (Padina japónica) Blaylock et al. F

Note: * It is important to realise that the quoted concentrations do not indicate directly the dose, received by organisms and/or organs. TABLE XXXVI. EFFECT OF CHRONIC INGESTION OF "P, 90Sr - 90Y, or 65Zn ON YEARLING RAINBOW TROUT, salmo gairdneri (After Refs [224 - 226])

Concentration at end of feeding (/xCi • g"1 wet)

Treatment Duration of Growth Significant Gut Leucopenia Bone Muscle piCi-g"1 fish (day) feeding (weeks) depression mortality damage

32p 0.006 25 no no no no _ _ 0.06 25 wk 17 no 4 months no 1.8 0.23

0.60 25 wk U yes 17 days yes - -

90Sr _ 90y 0.005 21 no no no no 2.1 0.002 0.05 21 no no no no 28 0.078 0.50 21 wk 12 wk 15 wk 15 yes 248 0.27

65 Zn 0.01 17 no no no no - - 0.10 17 no no no no - - 1.0 17 no no 110 no 4.0 0.35

10.0 10 no no wk 10 no - - AQUATIC ORGANISMS 73

In water or tissue the range of particles given off by most «-emitting radionuclides is less than 100 /urn and the ionization density along its track is very high. The effects of ingestion of some biologically important radionuclides on rainbow trout have been studied. In a series of feeding experiments, either 32P, 90Sr-90Y, or 65Zn was fed daily to rainbow trout at levels from 0.005 ßCi' g"1 per fish to high levels of about 10 ¡jCi-g"1 per fish [224-226] . These experiments used very high levels of radionuclides, which would not normally be experienced in a contaminated aquatic environment as the controlled disposal of radionuclides is limited to lower levels by man's use of the environment. However, the data from these ingestion experiments help to keep observations of the body burdens of radioactivity in field- contaminated fish in proper perspective with respect to potential radiation damage in fish in general. Table XXXVI summarizes the results. Leucopenia was an early indicator of radiation damage following the ingestion of ,6-emitting 32P or 90Sr and 7-emitting 65Zn. Depression of growth also indicated radiation damage for the rapidly growing yearling trout. The radiation syndrome, including leucopenia, anorexia, loss of scales, lethargy and growth depression was very pronounced for fish fed 32P at the higher levels and to a lesser extent for fish fed 90Sr-90Y. Because much of the energy from the 7-emitting 65Zn is not absorbed, trout were able to ingest without observable effect much higher levels of 65Zn, on a ¡uCi-g""1 per fish basis, than either 32P or 90Sr-90Y. In addition to the differences in the radiation characteristics of the isotopes, the rates at which the fish metabolize and the deposition sites for each radionuclide also differ, although all three are so-called 'bone-seekers'. Srivastava and Ram [ 22 7] studied the effects of large amounts of injected 60Co (5 - 30 /uCi) on adult catfish (Heteropneustes fossilis Bloch). They found the liver of the fish had the same degree of radiosensitivity as the intestine. The 20 ,uCi and 30 pCi doses cause hepatic degradation and ultimate death whereas the fish recover from the hepatic damage caused by the 5 /uCi and 10 ßCi amounts. Injection of 10 ^iCi of 32P per fish [ 228] resulted in lesions in the ovaries observed 10 days after injection. Studies by Ophel and Judd [229] were aimed at finding radiation effects, from relatively large amounts of internally deposited 90Sr and 131I, on heat regulating mechanisms in fish. Significant increases in survival times of irradiated fish at lethal temperatures were found in many experiments. It is postulated that radiation damage to gill tissue could produce this result. A number of recent papers have dealt with the effects of tritiated water on the development, growth and behaviour of fish. The radionuclide is present in the external medium but because of the low energy of the tritium ß-particles it is not until the tritiated water mixes internally with the tissue water that most of the radiation dose is delivered. Blaylock et al. [216] used eggs of Cyprinus carpió and Waiden [217] studied eggs of Gasterosteus aculeatus during hatching in various concentrations of tritiated water. They found no effects on embryo development until concentrations of greater than 0.5 Ci-1"1 of tritium were reached. Erickson [218] studied the effects of tritiated water on mortality growth, male characters, behaviour and thermal death of the guppy fish, Lebistes reticulata. Again, no significant effects were found until tritium concentrations reached 0.5 Ci-1*1. (A tritium concentration of 0.5 Ci-1"1 if present in the tissue water would deliver approximately 150 rad-d"1 to that tissue. ) The eggs 74 CHAPTER 3 of two species of marine fish (Paralichthys olivaceus and Fugu niphobles) were hatched in tritiated sea waters ranging from 10"8 to 10 Ci-1"1 [219] . No effects were found until the tritium concentration reached 10"2Ci-l"1. At 1 and 10 Ci-1"1 decreases in hatchability were observed and at 10 Ci-1"1 effects were noted on body shape and eye diameter of larvae. Suppression of Chondrococcus columnaris immune response in rainbow trout sublethally exposed to tritiated water concentrations of 1 X 10~6 and 1 X 10~5 Ci-r1 during embryogenesis has been studied by Strand et al. [209] . The results show a significantly lowered antibody synthesis in tritium-exposed fish. No significant differences were found between the 1X10"6 and 1X10"5 Ci-1"1 groups. Other studies [210] assessed the effects of four concentrations of tritium (10"6 to 10"2 Ci-1"1) on the hatching success and numbers of abnormal larvae produced by the eggs of the same species. Selected behavioural and physiological tests were applied to detect any sublethal effects of the tritium exposure on the juvenile fish. No significant effect could be detected at any of the levels used. Recent work by Guthrie and Brust [ 206, 207] with young mosquitoes suggested that significant effects can be observed at total beta doses (from 90Sr-90Y) of approximately 100 rad to larvae. However, later dose estimates, which take biological concentration into account, suggest that this estimate is low by a factor of approximately 10 [208] . These workers reared larvae of Aedes aegypti and A_. atropalpus in water containing various concentrations 4 1 2 1 of 9oSr_9oY between IX 10" Ci-1" to 2 X 10" CM" . All of these concentrations produced some effects. In many individuals (even at the lowest doses) the testes and ovaries of the adults were atrophied. In others (at higher doses) the production of viable sperms and their transfer to the spermathecae were affected and the oocytes did not mature. Females in the higher dose categories that received viable sperm laid non-viable eggs. Some results of research on the effects of incorporated (absorbed and adsorbed) radium on several species of fresh-water phytoplankton have recently been given by Havlik and Robertson [ 213 ]. A description of the experimental arrangements and a tabulation of 226Ra concentration factors found in seven species of phytoplankton can be found in another publication [230] . They studied the effects of radium in the culture medium on growth, protein content andphotosynthetic oxygen production. A wide range of radium concentrations were tested (from 10"11 Ci-1"1 to 10"6 Ci-1"1). The most interesting results were those which showed that photosynthetic oxygen production in all four species of algae was sharply reduced by 24 hours exposure to a 226Ra concentration of 3 X 10"8 Ci-1"1. Studies of radionuclide effects on aquatic organisms in their natural environment (field studies) have been almost entirely confined to genetic effects (section 2.3.). Apart from a pioneering study by Krumholz [231] of fish mortality in a contaminated lake, which produced no conclusive results, there has been no publication of similar aquatic studies elsewhere.

2.3. GENETIC EFFECTS

Our present knowledge on the effects of radiation and of radioactive contaminants on the hereditary material of aquatic organisms is not sufficient to draw any general conclusions. Of the information available, only very few papers on direct genetic effects have appeared in the open AQUATIC ORGANISMS 75 literature. A few more observations, however, are available from experiments in which either repeated or chronic exposures were used, and data were collected over several generations, so that if any genetic effects were present in the organisms under consideration, they should have contributed to, or have been included in the overall observational data. This kind of information will also be reviewed here, because such effects seem to be as relevant to population dynamics as the clearly defined genetic effects. Classical concepts of radiation genetics have been firstly, the lack of apparent threshold in the dose-response relationship, and secondly, a simple accumulation of genetic damage with successive dose increments. We now know that radiation damage to genetic material is potentially repairable at the cellular level and that it depends on both biological and environmental variables (e.g. stages in the cell cycle, oxygen availability etc.). Further- more, the mutation rate does not depend on dose in any simple way if energy deposition rate is fractionated, protracted, or chronic. The latter cases are those most likely to be of concern, if they do occur in practice, because they are likely to produce some measurable effects. Their relevance to aquatic ecosystems should therefore be considered. Circumstances in which massive doses of localized irradiation released in a short time result in a sudden destructive effect on a limited portion of an ecosystem are not relevant here, because of the predominance of lethal effects. The new genetic burden would be soon diluted in the gene pool of the survivors. Because of the extreme diversity of aquatic forms, the very long time required and technical difficulties in handling millions of individuals [ 232], an enormous effort is likely to be needed to obtain meaningful results on the effects of small doses on the genetic structure of any population, unless some experimental models can be utilized. These may allow some reasonable degrees of useful generalization for higher organisms, as was the case with Drosophila [233], and the mouse [ 234, 235]. However, there is no apparent reason to support that aquatic organisms should react differently from other species to the induction of genetic damage by radiation (see Chapter 3). As far as is known at present, scoring of inherited changes that can be classified as true mutations has been carried out only in fish (Lebistes reticulatus) by Purdom [ 236] and Purdom and Woodhead [ 167] after irradiation of mature spermatozoa, and by Schröder [237] after irradiation of various stages of both male and female gametogenesis. Purdom observed changes in the colour patterns at the first post-irradiation generation, interpreted as dominant mutations at loci on the sex chromosomes. Schroder scored either recessive visible or specific locus mutations. The estimates of mutation rate (per gamete per R) are in the range 0.4 to 11 X 10"s for recessive visibles (number of loci not known) and 2.5 X 10"7 per locus in the case of specific loci. Schroder makes straightforward comparisons with the rates of mutations that had been much more accurately determined both in Drosophila and in the mouse. Such comparison may be questionable at present, but the conclusion is that Lebistes germ cells do not seem to be more sensitive than those of flies and mice, and perhaps they are less sensitive by a factor of about 4-5, in agreement with Purdom's conclusions. Blaylock [ 23 8] also studied the fecundity of a natural population of fish, Gambusia affinis that had been exposed to chronic irradiation in White Oak Creek for many generations, compared with a control population. The calculated dose rate from the bottom sediments was 10.9 rad-d"1 . 76 CHAPTER 3

A significantly larger brood size occurred in the irradiated than in the non-irradiated population, although significantly more dead embryos and abnormalities were observed in the irradiated broods. He suggests that an increased fecundity is a means by which a natural population having a . relatively short life cycle and producing a large number of progeny, can adjust rapidly to an increased environmental stress caused by radiation. Gunstrom [239] found no significant differences in gross physical anomalies, lengths and weights at various growth stages, and in mortality in the Fj generation eggs and fry of irradiated and non-irradiated Coho salmon. Doses of 0.44 R-d"1, resulting in a total dose of 40 R, were administered to the parental generation during the egg and yolk absorption stage. Newcombe and McGregor [240] and McGregor and Newcombe [241] were concerned with embryonic malformations in rainbow trout due to radiation-induced gross chromosomal changes in gamma irradiation sperm and eggs; and with the shape of the dose-response curve for such malformations [242] . The dose-response curve for eye malformations (due to chromosome aberrations) found in rainbow trout embryos, after doses to sperm ranging from 25 -400 rad, was determined. It was found that the frequencies, at various doses, fitted a linear regression curve. Schroder [237, 243, 244] irradiated neonatal guppies (Lebistes) with relatively high doses of 500 and 1000 R. Brood size, number of still-births, postnatal mortality, sex ratio and development of abnormalities were used as criteria of mutagenic effects of radiation. A hybrid and an inbred line were chosen as experimental material. In both hybrid and inbred lines brood size increased in the progeny of irradiated parents in the generations following irradiation. In inbreeding experiments there was a lower number of still-births and a lower post-natal mortality in the progeny of irradiated specimens than in controls. Sex ratio was little affected. The number of abnormal fish was higher in the post-irradiation generations. About 90% of all fish with abnormalities showed curvature of the spine. ' The frequency of this morphological malformation increased among offspring of parental fish which had curvature of the spine under inbreeding conditions. Studies on variability of number of vertebrae and proportions of body shape [ 245, 246] showed an increased number of vertebrae in the Fj - and the F2 -males and lower number in F2-females after ancestral irradiation of females or males with 1000 R. The variability coefficient for the female in the irradiated series was predominantly higher than that of the control females, whereas this value was reduced in the post-irradiated male offspring. Schröder assumes that these changes in variability can be attributed to radiation induced micromutations. Holzberg and Schröder [247] compared males from sham-treated parents with males from parents irradiated with 2 X 500 R (24 hours apart, both to oogonia and spermatogonia) and found a reduction of agressiveness in the first post-irradiation generation of the cichlid fish, Cichlasoma nigrofasciatum, which did not seem to be associated with a general lowering of activity. Anders et al. [248, 249] found in the fish Platypoecilus maculatus that functional females with heterosomal male constitution XY appear after irradiation (1000 - 2500 R) of embryos with X-rays. All of these XY females are outwardly normal individuals, displaying normal sex characteristics and functions. Schröder [250] showed that irradiation of male . germ stem cells in neonate guppies causes an increase of the exchange AQUATIC ORGANISMS 77 frequency between X and Y chromosomes among the offspring of irradiated males. Recently the so-called 'Hertwig effect1 — fertilization of unirradiated eggs with heavily irradiated sperm permitting parthenogenetic development of a haploid embryo without the deleterious effects of radiation-damaged chromosomes because of their complete destruction and inactivation — has been successfully used in fish (together with temperature shocks) to obtain diploid embryos. Theoretically, this effect can be used to increase the rate of inbreeding and to obtain inbred lines for commercial breeding, without having to carry out many generations of inbreeding [ 251, 252] . For further information on the published literature on radiation genetics and radiation-induced mutations in fish the reader is referred to a recently published review article by Schröder [253] . Cooley and Nelson [254] and Cooley [255] examined a natural population of an aquatic snail (Physa heterostropha) living in an area where it was exposed to chronic environmental radiation 0.65 rad-d"1. When compared to a control population, the frequency of capsule production in the exposed population was reduced. A reduction in total egg production did not occur because each capsule contained an increased number of eggs. It was suggested that the compensation for the reduced capsule production by increased number of eggs per capsule was brought about by natural selection. A study of the effect of acute gamma radiation on the irradiated population indicated that this population had not developed any increased resistance to radiation. The aquatic larvae of an insect Chironomus tentans, which inhabit the contaminated bottom sediments of White Oak Creek and White Oak Lake, at Oak Ridge National Laboratory, were examined for five years for chromosomal aberrations [256] . Calculations and measurements of the absorbed dose for the larvae living in the sediments gave values of 230 - 240 R-a"1, or 1000 times background for that area. More than 130 generations have been exposed to this or greater dose rates over the previous 22 years. He concluded that the ionizing radiation from the contaminated environment was increasing the frequency of new chromosomal aberrations in the irradiated population, but that the new aberrations were eliminated by natural selection. The level of chronic irradiation did not affect the frequency of endemic inversions. Blaylock [257] reared another species of Chironomus (C. riparius) in different concentrations of tritiated water and examined the progeny for chromosome aberrations. The concentration of tritium ranged from 1X10"5 Ci-1"1 to 5 X 10"1 Ci-1"1 . Chromosome aberrations were observed in larvae which had developed in 1.25 X 10"1 Ci-1"1 and higher concentrations; however, no aberrations were detected at concentrations of lX10"4Ci-l"1 or lower. The response curve relating the frequency of chromosome aberrations to the concentration of tritiated water was similar to a two-hit dose-response for aberrations produced by X- or y-radiation. Squire [ 258] found no effect on male Fj reproductive performance of Artemia salina following paternal irradiation of mature sperm with 1000 and 2000 R. A paternal dose of 3.5 kR resulted in a 44% decrease in the number of fertile males. Data for survival to adulthood, adult mortality and reproductive patterns indicate that genetic damage is present in the Fx generation after treatment of parental females with 2 or 5 kR [ 259] . Performing experiments with populations of Artemia salina living in water 78 CHAPTER 3 contaminated by 32P, Grosch [260, 261] found that when there are the same numbers of adults in irradiated and unirradiated cultures sub-populations of irradiated cultures react differently to addition of radioactive material than sub-populations of unirradiated cultures. Descendants of specimens which were living in contaminated water do not necessarily survive a new addition of 32P, even when the total dose is lower than a single dose which resulted in extinction of a population. By observation of isolated pairs it was found that descendants from irradiated populations have a lower life expectancy and produce fewer eggs per brood. Ballardin and Metalli [ 262], working with laboratory strains of parthenogenic Artemia salina, established lines that were exposed at each generation to relatively low doses of external radiation. Fecundity, fertility and survival rate to reproductive age decreased after 6-7 generations, the degree of damage being roughly dependent on dose. Mortality and infertility after irradiation in this species appeared to be much more affected through damage accumulated in their genome (i.e. appearing in subsequent generations) than by direct somatic damage [263], These results are essen- tially in line with those of Marshall discussed below, with the only difference that in the case of Artemia the life-span of adults is also shortened by radiation, which may further contribute to the decreased productivity. Radiation sensitivity of populations of this species should then be due to the combined effects of damage to several measurable components of Darwinian fitness rather than to one critically sensitive stage in the life cycle. Although there is clear evidence for cytogenetic and genetic segregation in parthenogenetic Artemia, obligate parthenogenesis results in a somewhat more rigid genetic system, where radiation-induced mutations may have quite different fate than in the more common bisexual species. The relevance of these data should therefore be carefully considered before generalizations can be made. The effect of a single irradiation on the reproductive performance in Artemia has been described by Holton et al. [264, 265] . They found that both the number of broods per pair, and consequently the number of nauplii produced per pair, as well as the percentage of young reaching maturity were influenced. Paired specimens whose ancestors had been exposed to doses of 1500 and 3000 rad 20 weeks before, showed a distinct reduction of the reproduction rate, but no differences were found in population densities of irradiated and unirradiated populations. The experiments are of special interest because they show that under optimal conditions in the laboratory even a considerable reduction of the reproduction rate does not result in extinction of a population. In his study of parthenogenic Daphnia populations exposed to chronic gamma irradiation at high dose rates (25 - 75 R-h"1), Marshall [266] found there was a decrease of the 'intrinsic rate of increase' as a non-linear function of the dose rate. The decreased rate of population increase was attributed to direct effects of radiation on the ovaries. Self-regulating populations with a limited amount of food and limited space showed a lower tolerance against chronic irradiation than unlimited populations [267] . Experiments with exploited population have been performed by Marshall [ 268]. He exposed populations of Daphnia pulex to chronic irradiation and exploitation rates of 0.15, 0.40, 0.65 and 0.90 per week. The biomass yield decreased with increasing dose rate. However, it was found that exploited populations - if the exploitation rate does not exceed AQUATIC ORGANISMS 79 a certain limit — tolerate higher dose rates than unexploited populations. Marshall assumes that the higher resistance may be due to higher turnover and consequently to a reduction in the accumulated dose per generation. When natural populations of the alga Chlorella vulgaris were exposed to 90Sr-90Y [269], an increased mutation rate was found and strains isolated from the populations showed an increased resistance to X-rays. The LD50 of irradiated strains was 1.5 to 2 times greater than the controls. Growth rate and productivity of the radioresistant strains were also greater than control strain. Radioresistant strains were more thermorésistant.

2.4. REPAIR

Organisms often show greater resistance to radiation damage when exposed to fractionated (i.e. chronic) doses. Splitting the dose allows repair processes in the intervals to compensate for the damage. With very low dose rates repair processes may keep pace with injury and consequently no detrimental effect of the radiation will be observed. There are sufficient indications now to assume that repair mechanisms are widely distributed in organisms and that they are of major significance for survival. Moreover, Newcombe [252] considers it unlikely that they exist solely to protect living matter against damage from ionizing radiation. Associations with such normal cell functions as genetic recombination and spontaneous mutation indicate a much more general and presumably necessary role which they play in normal functioning of the cell. Egami [270] analysed the repair process after whole-body irradiation with two fractions of X-rays in the fish Oryzias latipes. Taking into account histological studies on the intestine and haematopoietic organs of irradiated fish [271-276], he formulates and explains three phases in the recovery process in Oryzias latipes as follows: (1) A decrease in residual injury taking place within three hours after irradiation corresponds to an initial rapid recovery phase as reported by several other workers. This probably reflects intracellular repair processes in critical organs. The duration of this phase is temperature-dependent1. (2) The second phase, starting at about three hours and lasting up to 48 hours after irradiation, is subject to considerable variation. These differences might be attributed to difference in radiosensitivity among cells involved. (3) In the third phase, recovery from radiation injury was evident three days or more after the first irradiation. In critical organs, damaged cells might be replaced by newly divided cells from undamaged cell clusters during this period. Recovery processes during this phase may be interpreted on the basis of cell population kinetics in critical organs. In fish eggs both irreversible and reversible (repairable) damage has been found and it has been established that the reversibility depends not only on the magnitude of the dose but also on the stage of development at which radiation is administered. It was also found that if the damage was reversible it disappeared in all specimens; although recovery times may vary between individuals [277] (and personal communication). Irradiation of fertilized eggs of tench (Tinca tinea) .with gamma radiation doses of

1 The effect of temperature on repair processes is discussed in section 2. 6. 80 CHAPTER 3

25-100 R increases the survival rate of the pre-larvae that hatch (in comparison with the control) and also increases their resistance to large supplementary radiation doses (4000 R) given at a later stage of development [278] . Other experiments [ 279] show that irradiation of pre-larvae with 250 R causes increased mortality but produces a radioprotective effect on the survivors with respect to subsequent irradiation at a dose of 1500 R. These experiments offer evidence of a 'triggered' repair system and it has been proposed by Kulikov et al. [278] that the effects of radiostimulation (see section 2.5) and increase in radioresistance, as a result of preliminary irradiation with small doses, are regulated by a single mechanism. Studies by McGregor and Newcombe [280], Newcombe [281] and Newcombe and McGregor [282] show that low doses to sperm in the rainbow trout have the unexpected effects of increasing both the production of visible embryos in the fertilized eggs and also the viability of the embryos once they are formed. The embryo production following fertilization with irradiated sperm exceeded that in the unirradiated controls, for gamma radiation doses of 25 and 50 rad by factors of 1.34, 1.40, respectively. A higher dose of 400 rad was unconditionally harmful/and the corresponding factor was 0.2 8 for this dose. A similar trend has been observed by Meyer and Abrahamson [283] in the frequency of sex-linked recessive lethal mutations following irradiation of immature germ cells of adult Drosophila females with doses of 20, 100 and 500 R of X-rays. At the lower doses the frequencies were below the controls and even for the 500-R experiment the induced frequency was much below that to be expected on a linear model. A possible interpretation, which has been advanced by Abrahamson (see Ref. [281]), might be that lower doses of radiation serve to stimulate repair mechanisms, which then proceed to over-compensate by repairing part of the naturally-occurring damage as well as much of that produced by the radiation. Migalovskaya [211] found that irradiation of sperm of the Atlantic salmon (Salmo salar) with 50, 150 and 350 R did not cause a change in the fertilization capacity. Iwasaki [284] and others have performed experiments on changes of hatchability of Artemia eggs caused by prolonging the time interval between fractionated irradiations and varying the dose ratio of the fractionated irradiations. No indication of recovery from radiation damage was found. This lack of evidence for repair in these experiments can be explained by: (1) Artemia eggs are, in fact, diapause embryos irradiated in a dry dormant state; (2) The effects looked for do not depend on cell division between irradiation and hatching; (3) There is a 'storage effect' known for Artemia eggs, i.e. hatching rates decrease as the time between irradiation and hydration increases. The latter effect would tend to compensate for any event that might have taken place after the first dose fraction [263] . A rather complex situation in the response to radiation was found by Calkins [ 285] in Tetrahymena. Experiments suggest the existence of two interacting repair systems, induced and constitutive. Induction of repair seems limited to certain times in the growth cycle, and it appears that repair is then induced when the proper trigger conditions are fulfilled. Other experiments in Tetrahymena performed by Pittock and Calkins [286] have shown that post-irradiation treatment with u.V. light after irradiation with americium a-particles results in a significant increase in survival. The experiments offer evidence that a 'triggered', or activated, repair system is present and is capable of repairing the damage. In the green AQUATIC ORGANISMS 81

alga Chlorella pyrenoidosa a high capacity for repair of DNA strand scissions has been found by Cabela et al. [287] . Using the green alga Oedogonium cardiacum, Horsley and Laszlo [288] and Laszlo and Horsley [289, 290] found an enhanced capacity for repair of X-ray induced sublethal damage in two-dose fractionated exposures. It is suggested that an efficient recovery mechanism is activated by the first dose of radiation because of the higher percentage survival than was expected from values calculated. As the additional capacity for recovery is suppressed by cycloheximide and not influenced by inhibition of DNA and RNA synthesis, the authors postulate the existence of a recovery mechanism which would be dependent on protein synthesis.

2.5. BEHAVIOUR AND METABOLIC STIMULATION

Scattered reports describe the use of behavioural criteria to determine the effects of radiation on aquatic organisms. These studies suggest that aquatic organisms apparently detect ionizing radiation, although the receptors have not been identified. In experiments with fish, particularly for high levels of external radiation, it has not been established whether the fish are responding directly to a radiation source or indirectly to radiolysis products. Metabolic activity of salmon (Salmo salar) eggs and fry was increased by the presence of 137Cs at a concentration of 1 /uCi-1"1. Upon hatching the eggs, the oxygen consumption increased by 50% in the control and 200% in the treated aquaria [192] . Field, Lichtenheld and Kilambi [291] noticed higher swimming activity of rainbow trout tagged with 16 |uCi 60Co wire tags. The response persisted for at least 26 hours after removal of the tag. Hyperactivity in irradiated fish has been reported by Scarborough and Addison [292] and Tsypin and Kholodov [ 293] . Pora et al. [294] found a stimulating effect of a very low dose of gamma radiation on the tissue respiration of the liver in Rana esculenta. A cumulative dose of 1.44 R applied during 10 days (144 mR-d"1) resulted in an increase of oxygen consumption of 10%. In land and water snails Hug [ 295] observed reflex retraction of the feelers under exposure to rather low doses of X-rays and a-particles. Dose rates of 1.5 to 15 R- s"1 and exposure times of 5 to 15 seconds were necessary for releasing the withdrawal of the feelers. In addition, further studies by Born [296] showed the contraction of the mantle cavity of pulmonate snails occurred under the influence of X-rays and a -particles. Engel [168] reports that exposure of young blue crabs, Callinectes sapidus, to radiation resulted in significantly more rapid growth than of control crabs. Since molting is associated with growth, the percentage increase in molted carapaces was monitored; it was found to be related to the radiation dose rate. In the fiddler crab, Uca pugnax, Brown et al. [ 297] found a significant response of the chromatophore system to increase in showers of cosmic-ray origin obtained through the interpolation of lead screens. Jordan and Kimelçiorf [298] detected electroretinographic (ERG) responses to ionizing radiation in the purple shore crab, Hemigrapsus nudus. Their findings indicate some rhodopsin excitation process after stimulation with visual light and X-irradiation. In the case of 8-radiation 82 CHAPTER 3 they assume that the Cerenkov and induced fluorescence radiation play a significant role in the ERG response. Baylor and Smith [299] observed negative phototactic and positive geotactic response in Daphnia magna when irradiated with X-rays. Threshold (air dose) was found to lie between 160 and 180 R-min-i. From their findings they conclude that radiation- induced fluorescence cannot be accepted as an explanation of the effect observed. Eugster [300] stored Artemia eggs for five months in a Simplón metal bunker in the absence of penetrating cosmic radiation and y-radiation from the rock and found a hatching rate of zero, while that of the controls amounted to about 80% [301] . A weak stimulating effect was found by Holton et al. [ 264] in Artemia. A single irradiation with 300 rad increases the mean number of offspring produced per pair. Telichenko [203] reports that the interval between broods in Daphnia magna is increased by small amounts of uranyl nitrate and thorium nitrate. He also found an earlier beginning of maturity and a higher production of young. Investigations in the same object by Lebedeva and Sinevid [202] with 90Sr-90Y showed a slight increase of reproduction rate at a concentration of 3.4 X 10"10 CM"1 and a temporary but distinct increase in the parental generation as well as in the filial generation at concentrations of 3.4 X 10"7 and 3.4X 10"6 Ci-1"1. In the third and fourth generation the number of offspring was smaller than in the control experiment. Even at a concentration of 3 .4 X 10"3 Ci-1"1 an increase of the number of offspring was observed in the parental generation at the fourth and fifth day after the start of the experiment. White et al. [212] have found a higher rate of growth in Artemia salina after irradiations with 2500 and 500 R. Hoppenheit [ 157, 158] has found a stimulating effect of radiation doses of 220 R or lower in females of the amphipod Gammarus duebeni. A higher survival rate of irradiated specimens has the consequence of a significant larger total amount of eggs and young produced, whereby the reduced production rate of eggs and young after irradiation with 220 R is more than compensated. A modification of the locomotor orientation of the planarian Dugesia dorotocephala has been reported under low-level chronic irradiation in the range 26 /uR- h"1 to 240/nR-h"1 [302,303], Kimeldorf and Fortner [304] studied the response of the green anemone, Anthopleura xanthogrammica, to X-irradiation. They chose the anemone because of the coelenterates1 relatively elementary nervous system. They found that the anemone responds with withdrawal of its tentacles at an exposure to 20 R or more. At higher exposures tentacle withdrawal -was followed by a sequence of oral disc and column reactions leading to complete closure of the oral disc. Planel and co-workers [ 305 - 313] and Tixador et al. [314] have performed many experiments to show that the natural background of ionizing radiation has a stimulating effect on growth of cultures of Paramecium aurelia and P. caudatum. They found a depression in growth of the cultures in a shielded environment. Daniel and Park [315] found a stimulating effect of administered ß-radiation (0.77 to 3.13 rep-h"1) or reproduction in Paramecium caudatum. The effect disappeared immediately on removal from the influence of the radiation so that a mutational effect must be excluded. Komala [316] irradiated conjugating Paramecium with a single dose of 9 R in the prophase AQUATIC ORGANISMS 83 stage and found a stimulating effect on growth and reproduction of ex- conjugants in the Fj -generation. Observations carried out on the - generation showed that this stimulating effect is ephemeral. Experiments with another protozoan (Colpoda sp. ) under chronic irradiation with doses of some 10 prad-h"1 have shown a decrease of the period between cell divisions, and permit the assumption that the division process can be triggered by high energy particles [317] . Rogatykh [318] found an acceleration in growth and an increase in the number of auto-spores in Chlorella vulgaris when irradiated at the Gj stage. The acceleration in growth is the consequence of a contraction of the Gj stage. Experiments by Gileva et al. [319] have shown that increase in biomass of fresh-water algal periphyton is optimal at a dose rate of 5 R-d"1. After irradiation with 1 and 5 kR a stimulation of cell reproduction was found by Sagromsky [320] in the green algae Ankistrodesmus braunii and Chlorella vulgaris. Apparent stimulation of growth by radiation in aquatic organisms is reported for algae, periphyton, certain marine invertebrates and rainbow trout, salmon and frog [ 148, 173, 321 - 323] . Other examples of possible stimulation of organisms by low or moderate doses of radiation can be found (see, for example, Ref. [324]). However, only little knowledge exists about either the mechanisms involved or the significance of ionizing radiation as a 'beneficial' or 'harmful' stimulus to individuals, populations, or ecosystems.

2.6. INFLUENCE OF ENVIRONMENTAL FACTORS ON RADIATION EFFECTS

We know that the open ocean is the most constant aquatic milieu known; but organisms of coastal waters, estuaries and fresh-waters are exposed much more to changing environmental conditions. When these changes are severe they exert stresses on the organisms in such ecosystems often with disastrous effects; such as the loss of most of the benthic organisms in the German Bay of the North Sea during the severe winter 1962/63 [325, 326]2. Many other reports of mass kills of estuarine and fresh-water organisms due to sudden changes in environmental factors such as salinity, dissolved oxygen, temperature and algal blooms can be found in the literature. For example: extensive mortalities of blue crabs in Chesapeake Bay, USA [327]; mass mortality of marine animals on the west coast of Florida [32 8]; fish kills in the Great Lakes [329] . Brongersma-Sanders [330] has reviewed a number of recorded mass mortalities of organisms in estuaries and coastal waters caused by natural phenomena. When radiation is present it represents one of many physical and chemical factors influencing the biota. At the moment we do not know to what extent the effects of industrial wastes, radioactive wastes, sewage and thermal pollution will interact and result in damage to the essential biota of lakes, rivers and coastal waters. Unfortunately, to date is has not been possible to breed ecologically and economically important species in the laboratory. Therefore, for the most part, easy-to-breed organisms are studied, which are often the most tolerant species and less vulnerable to pollution. Biihringer [331] irradiated carp (Cyprinus carpió) with doses in the range from 2000 to 6000 R. He found prolonged survival times at low temperature. However, after raising the temperature in the course of an

2 See also contributions to the Fourth Marine Biological Symposium, Helgoländer wiss. Meeresunters. 10 (1964) 246. 84 CHAPTER 3 experiment the carp died within a short period of time, in the same pattern as those kept at high temperature. Etoh and Egami [332] have shown in the fish Oryzias latipes that a decrease of lethal effect by dose fractionation does not take place if temperature during the interval period is low. They conclude, that the repair processes are slowed down under low temperature conditions. In other experiments [ 333] they irradiated Oryzias, adapted to different temperatures, with different doses of X-rays. At the chosen post-irradiation holding temperature of 23°C they found no significant influence of adaptation temperature on survival time. At unchanged low temperature (6°C) the majority survived for more than 120 days. However, if irradiated fish were subsequently transferred to 23°C after having been maintained at 6°C for 21 days, the survival time after the transfer was approximately the same as that of irradiated fish continuously kept at 23°C. In the goldfish, Carassius auratus, a majority of the fish survived for more than 100 days if they were kept at 4°C after they had been exposed to 8 kR whole-body irradiation, whereas most of the similarly irradiated fish die within 10 days at 22°C. Low temperature inhibited the development of damage of the intestinal epithelium. Those irradiated fishes which were kept continuously at 4°C showed marked histological damage of the intestinal epithelium at more than 100 days after irradiation (about 75% of the fish died between 150 and 200 days after irradiation). If irradiated fish maintained at 4°C for different times are then transferred to 22°C they die within about 10 days, exhibiting similar damage of the intestinal epithelium [ 271, 272] . Hyodo [334] also examined the alkaline and acid phosphatase enzyme activity in goldfish after irradiation with 8 kR followed by maintenance of fish at 25 and 4°C. At 4°C the activity of the enzymes was not affected for a period of 100 days after irradiation. Aoki [ 335] found no damage in the haematopoietic tissue of goldfish, kept at 4°C and exposed to 8 kR, at 40 days after irradiation. Etoh [336] showed that the rate of development of radiation injury in the haematopoietic tissue is slowed down at lower temperatures. Gros et al. [33 7] conclude from their findings that irradiation has a protective effect against cold by lowering the thermal tolerance in the crucian carp (Carassius carassius). They too observe that a rise in temperature leads to death in irradiated specimens which have been adapted to cold. In irradiated dry eggs of Artemia salina the hatchability is temperature dependent [33 8] . Irradiated dry eggs kept at dry ice temperature show no decrease in hatchability — a result that could be interpreted as an effect of low temperature in pre- venting the amplification of the damage due to the 'storage effect' [ 339] . Angelovic et al. [340] found that the fish Fundulus heteroclitus, and the grass shrimp, Palaemonetes pugio, typical estuarine species, were more resistant to radiation at lower salinities. However, the radiation resistance of the brine shrimp (Artemia) (which is normally found in highly saline waters) is not reduced by lower salinities but this genus is known to have unique capabilities for osmotic and ionic regulation [341] . Hyodo- Taguchi et al. [342] have shown that in specimens living at 23°C the radiosensitivity of the oocytes of the marine goby (Chasmichthys glosus) is higher than that of the fresh-water medaka (Oryzias latipes). The ovary in Chasmichthys is definitely affected by irradiation with 0.5 and 1 kR of X-rays, whereas the same doses produce very little or no damage to the ovary in Oryzias. Angelovic et al. [ 143] report on the combined effects of ionizing AQUATIC ORGANISMS 85 radiation, salinity and temperature on Fundulus heteroclitus. In a factorial experiment, fish were subjected to four levels of acute radiation (500, 1000, 2000 and 2500 rad); three levels of salinity (5, 15 and 25%o); and four levels of temperature (12, 17, 22 and 27°C). They found that different combinations of levels of temperature and salinity yield different LD50 values. The estimated LD50 values for different experimental conditions ranged from 300 to 350 rad to more than 2500 rad. The fish tolerated more radiation in low salinity at the upper end of the temperature range. At the lower end of the temperature range, tolerance was reversed. As irradiated fish generally lose sodium more rapidly than unirradiated fish, one can assume that some of the lethal effects of radiation may stem from damage to osmoregulatory capabilities. This was certainly true in the case of irradiated salmon (Oncorhynchus kisutch) which were exposed to 1000 rad or more by Conte [343] and then transferred from fresh to saline water. Approximately 50% of the transferred fish died in 60 days whereas the fish remaining in fresh water (and therefore not subjected to osmotic stress) were unaffected. A striking example of the influence of bad environmental conditions is given by Engel et al. [344] . They tested the effect of sublethal doses of X-rays on juvenile striped'mullet, Mugil cephalus, in flowing sea water in the laboratory. Sudden and extensive mortalities occurred in all groups of irradiated fish after a severe storm which caused a drastic reduction in salinity and lowering of temperature. None of the control fishes died. Angelovic and Engel [345] measured the respiration rate of irradiated brine shrimp nauplii at salinities from 5 to 200%o. Respiration rates of irradiated nauplii were found to be lower at 5, 10 and 200%o but higher at 100 and 150%'o. The highest levels of radiation and salinity acted synergisti- cally and depressed the respiration rate to the lowest point. Marshall [267] maintained a series of chronically irradiated Daphnia pulex populations each supplied with a fixed quantity of food regardless of the total number of individuals. Under these conditions each population was experiencing a second stress (other than radiation) in the form of intra- specific competition for food. He found that the maximum indefinitely tolerable dose rate was 24 R-h"1, a value that was much lower than that obtained in an earlier set of experiments [266] where the extra stress on the populations was absent. Also, in contrast to the result obtained in the first series of experiments, it was found that the birth rate increased with increasing dose rate. It was concluded that the expected reduction in fecundity due to irradiation was more than compensated for by the higher per capita food supply at the higher dose rates where the mean population size was lower. The most remarkable result obtained related to the net biomass production which was found to be independent of radiation dose rate in all of the populations that did not become extinct (i.e. at all dose rates up to 24 R-h"1). Hoppenheit [ 156] found that of the three gammarid species — G. duebeni, G. zaddachi, G. salinus — G. duebeni is twice as resistant to ionizing radiation than the other two species. Experiments on the culture of the three species have shown that G^ duebeni is much easier to rear than G_. zaddachi and G_. salinus. Experiments on resistance to desiccation and changes of temperatures [346] have shown that G_. duebeni is more resistant and can withstand poor conditions much better than G. zaddachi and G. salinus. 86 CHAPTER 3

By multifactorial experiments, Styron [347J compared a population of the isopod Lirceus fontinalis living in small temporary pools on granite gneiss rock with a population living in a spring-fed stream with tempered environmental conditions. The comparison of the reactions of the two populations to stresses of acute gamma radiation, temperature and drought showed a significantly higher resistance of the population living under rigorous environmental conditions in the pools. In experiments studying the differential sensitivity of 12 species of salt-marsh epiphytic algae to ultra-violet, thermal stress and 7-radiation, Saks and Lee [348] found rough correlations between radiation sensitivity, ultra-violet radiation and thermal shock. Those species are more resistant which are adapted to exposure to higher temperatures and light intensities in shallow pools or in interstitial waters in the tidal zone. The significance of these and other experiments [l59, 349- 353] is the demonstration of the importance of the environmental factors on the radiosensitivity of aquatic organisms. In other words, the effects of radiation on aquatic organisms can only be evaluated along with the effects of other major environmental factors. It would seem that organisms which are exposed to variable physical conditions are less radiosensitive than those living in buffered environments. This may be due to a higher degree of genetic polymorphism in those species living in a fluctuating environment [354 - 357] . However, the possible alteration of the balance of adaptive value of genetic polymorphism by increase of segregational genetic load must be taken into consideration as a problem in adapting to pollution [358] .

2.7. SUMMARY

There is now an extensive body of literature dealing with the effects of ionizing radiation on aquatic organisms. Unfortunately the majority of this work has been carried out at doses and/or dose rates which bear little relevance to the doses and dose rates discussed in Chapter 1. Doses used in many experimental studies are commonly hundreds or thousands of rads delivered at high dose rates. The most sensitive aquatic organisms now known are teleost fish, particularly the developing eggs and young of some species. Some mortality has been observed at acute doses in the order of 100 rad. With regard to chronic exposure some minor effects on physiology or metabolism have been observed at dose rates in the order of 1 rad-d"1. A number of aquatic organisms have been used as experimental material for genetic studies. However, the prediction or observation of consequences of any observed mutations on populations of such organisms is a difficult matter. At the present time it would appear that no deleterious effects on populations would be expected at the doses calculated in Chapter 1. Chapter 3

EFFECTS OF IONIZING RADIATION ON AQUATIC POPULATIONS AND ECOSYSTEMS Chairman: W. L. TEMPLETON, United States of America

Members of the Working Group: M. BERNHARD, Italy B. G. BLAYLOCK, United States of America C. FISHER, IAEA M.J. HOLDEN, United Kingdom A. G. K LI MOV, IAEA P, METALLI, Italy R. MUKHERJEE, IAEA O. RA VERA, Euratom L. SZTANYIK, IAEA F. VAN HOECK. CEC CHAPTER 3 EFFECTS OF IONIZING RADIATION ON AQUATIC POPULATIONS AND ECOSYSTEMS

3.1. INTRODUCTION

The objective of this section of the report is to discuss the effects of ionizing radiation that might occur in aquatic populations and ecosystems if they were exposed to low-level chronic irradiation. We have only considered exposure at dose rates within the ranges which either exist or may potentially exist in the aquatic environment as a result of the expansion of the use of nuclear energy (Chapter 1), and have not concerned ourselves with the possible damage or impacts that could occur as the result of acute and chronic exposures under accident or emergency conditions. In general, we are faced, however, with the difficulty of extrapolating from those effects demonstrated in controlled laboratory experiments at high dose rates to those effects that could occur in populations and communities of aquatic organisms in the natural state. In the first place, there is a serious lack of any data concerning the radiosensitivity of aquatic populations, communities, or ecosystems as compared to that of the individuals within them. Secondly, the experimental dose rates at which responses by individuals have been determined (Chapter 2) are usually orders of magnitude higher than those experienced by natural populations, even in those areas where controlled radioactive disposal is practised. Thirdly, the assumption is made that the dose-response curve is linear. Although it has not been shown unequivocally that the commonly used biological endpoints for somatic effects, such as fecundity, growth, development, and mortality are altered at low doses and dose rates, at these low levels there is some evidence that repair and stimulation processes may compensate for detrimental effects. The available data on effects of ionizing radiation on individuals have been reviewed in Chapter 2. From this review one may generalize that it requires, as the lower limit, an acute dose of about 100 rad to produce some mortality in a number of organisms but not in all, and that depending on the biological end point the effects at higher levels are proportional to dose. Under conditions of chronic exposure the effects, in most cases, are less marked, though with this type of exposure the selection of the biological end point is more critical. When experimental and field dose- rates are less than one rad per day it becomes very difficult to observe effects which can be used as indicators of damage that are not within the inherent variation that is already present. Even when it can be demonstrated that changes at the cellular level occur, be they altered biochemical/ metabolic functions or chromosomal damage, it is nearly impossible to predict the ultimate consequences to either the individual or the population in question. It may appear that we have given insufficient attention in this report to the basic ecological considerations. However, we feel that these are adequately explored in Chapters 5 through 8 in Ref.[359], We would draw particular attention in that report to the discussion on ecological interactions, understanding that the hypotheses and arguments presented there

89 90 CHAPTER 3 are not predicted upon existing or even potential dose rates in the aquatic environm ent. Despite the paucity of experimental and field data on populations and ecosystems, we feel that we should discuss some of the potential problems by drawing on the knowledge that has been developed in related fields of population dynamics in order to place radiation-related effects in better perspective. Our conclusions are in no way definitive, but this chapter should provide an improved basis for the assessment and understanding of the degree of risk that aquatic populations are exposed to from the introduction of radionuclides into the aquatic environment.

3.2. SOMATIC EFFECTS

The prediction of the somatic effects of low-level, chronic irradiation on aquatic ecosystems is hampered not only by lack of knowledge about the effects of such irradiation upon both individuals and populations, but also by lack of knowledge about the mechanisms by which the numbers of organisms inhabiting these ecosystems are regulated. Although there are many studies of experimental populations of various species, most of the studies of regulatory mechanisms in natural populations have been undertaken on commercially exploited populations of marine organisms. In an attempt to predict the possible effects of irradiation upon the aquatic ecosystem the known regulatory mechanisms of these populations will be considered in detail and the principles then applied, insofar as this is possible, to other members of the ecosystem.

3.2.1. Possible effects of irradiation on recruitment to marine fish populations

3.2.1.1. Species with high fecundity

There is some experimental evidence, discussed in Chapter 2, that fish eggs are very sensitive to low levels of irradiation [170, 171, 174] and from these observations it has been argued that the yield from commercial fisheries will be adversely affected by radionuclides in the sea, even at extremely low concentrations [173], These authors conclude that radiation must be limited to a level at which no more than 10% of the eggs produced by a fish stock will be damaged, although even at this' level they state that catches will be perceptibly reduced. This argument overlooks the nature of the stock and recruitment relationship of highly fecund fish, on which most marine fisheries are based. In this section only stocks of such species will be considered. The number of young recruiting to a population is theoretically dependent upon: (a) The number of eggs laid. (b) The mortality rate operating on the eggs and larvae prior to recruitment, recruitment being the stage at which the fish become available for capture by fishing. The number of eggs produced by one mature female at a single spawning is very large and a female will spawn on average more than once (Table XXXVII). AQUATIC POPULATIONS AND ECOSYSTEMS 91

TABLE XXXVII. NUMBER OF EGGS PRODUCED BY VARIOUS MARINE TELEOSTS

Species Weight (kg) No. of eggs

Lins» (Molva molva) 24.1 28 X 106 Conger eel (Conger conger) 12.7 15 X 106 Turbot (Psetta maxima) 7.7 90 X 10s Cod (Gadus morhua) 9.8 67 X 10s Haddock (Melanogrammus aeclefinus) 4.1 30 X 10s Haddock 0.7 30 X 104 Plaice (Pleuronectes platessa) 2.0 59 X 104 Plaice 0.4 85 X 103

AGE (a) FIG. 5. Typical survival curve of an unexploited plaice stock.

Assuming a sex ratio of unity and no differential mortality between the sexes only two of these eggs have to survive, on average, to maintain the stock in equilibrium. Most of the mortality occurs within the first 6 months of life in the larval stage, and only 1 in 10 000 eggs survives, on the average, to produce a fish aged 1 year (Fig.5). Many attempts have been made to derive a relationship between the size of the spawning stock and subsequent recruitment, with little success [360]. The types of relationship that is found is shown in Fig.6, which is for the north-east Arctic stock of cod (Gadus morhua), one of the best documented [361]. 92 CHAPTER 3

t Î 1963 1950 24.29 23.39 20

1970 1948

1958 1942 1962 1943 • J971 .1954 1947 1959 .1957

* 1956 .'«I

1960 . 1955 .1953 .1961

1969 .1952

20 25

FIG. 6. Relationship between mature stock and number of recruits for the north-east Arctic cod stock (modified from Ref. [361]).

The most notable features of this relationship are that: (a) Very low recruitment and the highest level of recruitment (24.29 X 10s recruits in 196 3) have been produced at low levels of spawning stock. (b) The level of recruitment was the same in 1953, 1955, and 1960 as that in 1944-46, even though the size of the spawning stock in these years was only 25% of that in 1944-46. From this it may be deduced that recruitment is not related to spawning stock size and that the mortality rate operating on the eggs and larvae varies considerably from year to year. Although the mechanisms controlling the survival of eggs and larvae are not fully understood, it is now generally accepted that survival of fish larvae depends to a great degree upon the availability of phytoplankton and Zooplankton, the food of larval fish [362], except at the extremes of the range of a species, where hydrological conditions become of major importance. The spawning time of fish in temperate waters is fixed but the production cycle of plankton is not, because its timing is largely dependent upon the amount of solar radiation. Therefore, the hatching of fish eggs may or may not coincide with availability of food: in years when the plankton production cycle coincides with the hatching of the eggs, food will be plentiful and above average numbers of larvae will survive; in AQUATIC POPULATIONS AND ECOSYSTEMS 93 years in which the production cycle and hatching do not match, food for the larvae will be less abundant and below average numbers of larvae will survive. Density-dependent mortality reduces the population of fish larvae to that level which can be supported by the available food supply [363]. Similar mechanisms operate in tropical waters, although in such areas the plankton production cycle and spawning are more or less continuous. Thus, if the numbers of eggs which hatch were reduced as a result of irradiation, there would be fewer larvae competing for food, density-dependent mortality would be decreased, and there would be no obvious effect on the number of recruits until egg and larval survival were reduced to very low levels. What the minimum egg production must be to produce a stock which can replace itself is uncertain. Some fish stocks have been almost eliminated by heavy fishing, reducing their spawning potential to nearly zero, though the north-east Arctic cod stock proved to be viable even when the spawning potential was reduced to approximately 5% of its maximum recorded level (Fig.6). However, there was serious concern among fisheries scientists about the state of this stock from 1965 onward, and it was probably only favourable climatic conditions, not food supply, that led to enhanced survival of the larvae from 1969 onward, and saved the stock from possible extinction. It may be concluded that if mortality is being enhanced by the low levels of irradiation presently existing in the marine environment, then recruitment to the stocks of highly fecund marine species of fish is unlikely to be adversely affected unless those stocks are already at risk because of severe over-exploitation. Studies of irradiation laboratory populations of the cladoceran, Daphnia pulex, which were exploited at various rates [268] support this conclusion. Only one extinction out of a total of 47 occurred at the lowest level of irradiation (3.7-5.1 R • d"1), and that was in a population exploited at the highest rate (90% a day). Less is known about the mechanisms controlling recruitment in commercially exploited populations of invertebrates; the available data have been reviewed by Hancock [364]. He shows that recruitment of cockle (Cardium edule) is inversely proportional to parental stock. He also con- cludes that recruitment is probably also inversely proportional to parental stock for the Pacific razor clam (Siliqua patula) but that for the majority of molluscs any relationship which might exist is obscured by the effect of environmental factors. There are too few data for crustaceans from which to draw any conclusions. Therefore the mechanisms controlling recruitment in molluscs are similar to these for marine fishes, except that environmental factors probably play a more important role for invertebrates.

3.2.1.2. Species with low fecundity

It is not possible to be so categorical about species with low fecundity, which include most of the elasmobranch stocks (rays, sharks and dogfish) as well as the marine mammals. The majority of these species produce live young, the major exception being the rays which produce small numbers of large egg capsules attached to the substrate, from which fully developed young hatch after a period of 6-15 months, depending upon species. Stocks of rays might be affected if their spawning grounds coincided with an area of discharge of radioactive material but, as far as is known, the spawning areas of rays are not discrete and so only part of the egg production would 94 CHAPTER 3 be at risk. (The sensitivity of ray eggs to irradiation is unknown; nor is it known whether any area of radioactive discharge coincides with a spawning area for rays.) For this group of species recruitment is closely related to parent stock size and for the least fecund species the relationship must be almost direct. Although the fecundity of baleen whales has increased as a result of exploitation [365] and there is some evidence that the same is true for elasmobranch stocks [366], there is an upper limit to fecundity set by the minimum age at maturity, the duration of pregnancy and the number of young produced each pregnancy, which in turn is limited by the size of the maternal body cavity. The available data suggest that this upper limit has been reached by the exploited stocks of low fecund marine mammals and elasmobranchs [365,366]. In these circumstances any further stress on the stocks would decrease their chances of survival. In the absence of any data on the somatic effects of irradiation it is not possible to make any definitive predictions on what the effect of irradiation on these groups of animals might be. However, at the low dose rates existing in marine environments at present it is reasonable to assume that any effect is likely to be very small in comparison with fishing, which is the major stress on the stocks.

3.2.2. Possible effects of irradiation on the exploited part of fish stocks

Irradiation can also affect fish stocks by altering fecundity, growth rates and mortality rates. Fecundity is another aspect of the stock and recruitment relationship; it varies under natural conditions forming another density-dependent population regulatory mechanism [367], If fecundity of the highly fecund fish species were reduced by irradiation the density-dependent larval survival mechanism would compensate within the levels already described. A similar case could be argued for decreases in fecundity related to reductions in growth rates. Possible increases in mortality rates must be considered in terms of the rates already experienced in the exploited part of fish stocks. Rates of exploitation of 50% a year on all year-classes recruited to the fishery are common in commercially exploited stocks. In addition the stocks are subject to deaths from natural causes so that a heavily exploited fish stock may be experiencing total mortality rates of 60-70% a year and the stocks have survived, with few exceptions. Any increase in the total mortality rate would reduce the numbers in a stock, but this would not affect the ability of a stock to replace itself unless the rate was so high as to reduce it to below the 'critical size', whatever size that might be. Any mortality caused by low levels of irradiation would probably not be detectable as such and would appear as 'natural' mortality. Additional natural mortality would affect management of the stocks; the level of fishing mortality rate at which the optimum yield is taken increases as the natural mortality rate increases, up to the level at which recruitment is affected [368] (Figs 17 and 18, p.321). However, it is not possible to estimate natural mortality rates accurately and 95% confidence limits which are equal to/or greater than the estimate of the rate are often the best that can be derived from the available data. (The estimates of the instantaneous natural mortality rates for the majority of marine fish lie within the range 0.1 to 0,3.) In stock assessments it is usual to take a set of instantaneous natural mortality rates, ranging from 0.1 to 0.3 depending upon species. Given AQUATIC POPULATIONS AND ECOSYSTEMS 95 that the level of mortality from irradiation did not increase the natural mortality rate markedly beyond the upper limits used in assessment calculation, no effects in stock management would be detectable.

3.2.3. Possible effects of irradiation on other species

The population dynamics of most other aquatic species have not been studied in the same detail as those which are commercially exploited. The median life expectancy of Daphnia pulicaria increased with exploitation [369] ; so did the maximum dose rate which D. pulex could tolerate [268], Studies on a marine copepod, Tisbe holothuriae (Hoppenheit, personal communication), show that populations of these animals exploited under laboratory conditions do respond in much the same way as fish populations; the frequency of production of egg-sacs, the number of eggs produced in a brood, the development rate of the young and number of viable young all increase as exploitation increases. It is logical to assume that all organisms have such density-dependent regulatory mechanisms which enable the numbers in their populations to respond to changes in their environment. This being so it can be concluded that no effects of low- level, chronic irradiation are likely to be shown by populations of any other aquatic species, particularly as the experimental evidence, discussed in Chapter 2, indicates that fish eggs are one of the most sensitive parts of the aquatic system [170, 171], To the extent that many commercially exploited fish populations are being so heavily exploited that there is some doubt about their ability to replace themselves and others have been almost totally eliminated by fishing it can be argued that commercially unexploited organisms should be able to withstand the effects of irradiation better because they have not reached the limits of their density-dependent response mechanisms.

3.2.4. Observations on irradiated populations

There are few recorded studies of populations which are subject to low-level irradiation. The fecundity of populations of the fish, Gambusia af finis, subject to chronic irradiation in White Oak Creek, USA, was higher than that of control populations [238], while 'beneficial effects' have been observed in populations of chinook salmon, Oncorhynchus tshawystcha, as described in Chapter 2. The fish stocks in the North Irish Sea have been subject to low-level irradiation now for 20 years, the source being the Windscale discharge. The'plaice stock which inhabits this area has been routinely monitored as part of the routine programme of monitoring of fish stocks by the Fisheries Laboratory, Lowestoft, since 1968 and the results are given in Table XXXVIII together with the data from two other areas, the Bristol Channel and the North Sea. The numbers in each length group for each port are comparable between years, because they are expressed as numbers caught for a standard period of fishing (100 h), but not between ports because the fishing powers of the vessels at the three ports are different. Furthermore, the Lowestoft trawlers fish offshore fishing grounds on which small plaice are not abundant. Although there are differences between the three areas in catch-rates by both numbers and weight there is no trend in the pattern of landings at Whitehaven which is obviously different 96 CHAPTER 3

TABLE XXXVIII. COMPARISON OF THE NUMBER OF PLAICE CAUGHT PER 100 HOURS' FISHING BY SEINERS FISHING THE IRISH SEA AND LANDING AT WHITEHAVEN, TRAWLERS FISHING THE BRISTOL CHANNEL AND LANDING AT MILFORD HAVEN AND TRAWLERS FISHING THE NORTH SEA AND LANDING AT LOWESTOFT

cm 1968 1969 1970 1971 1972 1973

Landings at Whitehaven from the North Irish Sea 20-24 3 75 79 457 136 849 25-29 10 689 10314 12 401 15 894 18 268 14854 30-34 8 704 5 283 5 845 4618 6 556 3 702 35-39 501 1 613 590 1 076 645 853 40-44 101 217 115 228 133 192 45 + 22 94 42 87 85 69 Total no./100 h 20 020 17 596 19 072 22 360 25 823 20519 Tons/100 h 4.44 4.81 4.62 5.44 6.40 4.61

Landings at Milford Haven from the Bristol Channel

20-24 0 0 12 33 11 39 25-29 1 393 1 434 2 525 3 148 1 682 2771 30-34 2 480 1 835 2 022 1 941 1 964 2 544 35-39 394 350 281 239 533 431 40-44 69 88 58 50 78 118 45 + 10 18 9 8 22 51 Total no./100 h 4 346 3 725 4 907 5419 4 290 5 954 Tons/100 h 1.47 1.14 1.41 1.50 1.16 0.94

Landings at Lowestoft from the North Sea

20-24 3 4 0 3 1 4 25-29 1 430 947 1 029 483 345 910 30-34 5 163 5515 5 651 3 624 3 565 5217 35-39 3 050 4 308 6 007 5 821 5 196 6 527 40-44 1 239 1 601 1 806 2 533 1 931 2 330 45 + 580 788 700 895 721 898 Total no./100 h 11 465 13 163 15 193 13359 11 759 15 886 Tons/100 h 4.74 5.75 6.95 6.75 6.15 7.39

from that at either of the other two ports, except that the catch-rates of plaice less than 30 cm long in both the North Irish Sea and the Bristol Channel increased from 1968 to 1971 while those in the North Sea fell. These data, and in particular the increase in recruitment to the North Irish Sea stock of plaice, which continued into 1972, provide no evidence that the low levels of irradiation there have any adverse effect on this stock. AQUATIC POPULATIONS AND ECOSYSTEMS 97

3.2.5. Stability of ecosystems

The available data indicate that at low levels of irradiation most components of aquatic ecosystems will be unaffected (there appear to be no data for plants, but these are less sensitive to irradiation than animals). This is not surprising because ecosystems are subject to various natural stresses, and yet they remain inherently stable. The numbers of individuals in the populations of each species may alter with environmental conditions but there are few recorded examples of complete changes due to natural causes in marine ecosystems. The reason for the stability of the marine ecosystem may lie in the complexity of the food web which enables considerable modification of the pathways along which energy is channelled through the ecosystem, without there being any visible effects on those species which are monitored by man. Thus, events happening at the base of the food web are less likely to have apparent effects than those happening near its apex, particularly in complex webs. As the food web becomes smaller and the number of species in it decreases, the chances of events causing apparent changes become greater. For this reason fresh water ecosystems may be more at risk from irradiation effects than marine ecosystems because the number of species in fresh water is in general fewer than in the sea. Another factor that favours marine ecosystems is that they are generally larger than fresh-water ecosystems. It is more difficult to build up high levels of any type of pollutant because they are flushed by currents, except for almost closed seas such as the Baltic and Mediterranean. Furthermore, there is a greater chance of repair of any damage done to the system by immigration of individuals into the affected area from unaffected areas. The differing susceptibility of these parts of aquatic ecosystems has already been shown by their reactions to chemical pollution. As yet the open sea has been unaffected by this type of pollution and the large changes which have occurred are attributable only to climatic changes. However, in an ecosystem into which radioactive material is discharged all members would be affected and it is difficult to state what might be the results of irradiating all species rather than one, but such evidence as we have does not indicate that present levels of radioactivity in marine environments give cause for concern.

3.3. GENETIC EFFECTS

Most systematic studies on population genetics have been conducted on the fruitfly genus Drosophila, and it is from these studies that we must take our general knowledge until other data are available. Although most aquatic species may be far removed from the genus Drosophila, undoubtedly some of the basic principles of population biology are expected to apply to all organisms.

3.3.1. Population genetics

Natural populations of sexually reproducing organisms harbour large stores of genetic variability concealed in the heterozygous condition. It is generally accepted that some of these variants are detrimental or even 98 CHAPTER 3 lethal in the homozygous and hemizygous conditions. Genetic variability, or a variety of genotypes, is found in all natural bisexual populations. The degree of variability differs from population to population and is influenced by population size, ecological diversity of the environment, habitat and other factors. The wide variety of genotypes characteristic of outbreeding species imparts adaptive advantage to its carrier in nature and enables the carrier population to occupy a diversity of habitats with greater efficiency and presumably on the whole, greater biomass. Selection pressure on the variety of genotypes as exerted by environmental conditions is a major driving force in the evolutionary process [370]. Recent biochemical studies of specific loci in Drosophila and other organisms seem to indicate that the degree of intrinsic genetic variability in natural populations has been greatly underestimated [371]. The fitness of an individual within a population reflects its ability to survive and reproduce (i.e. transmit its genetic endowment to successive generations) relative to the corresponding abilities of all other individuals comprising the population. Experimentally, a multitude of parameters such as fertility, fecundity, longevity, variability, competitive ability, biomass, etc., have been used to measure the components of fitness [372-375] — all testifying to the fact that fitness is a multi-dimensional entity.

3.3.2. Effects of increased mutation rates on populations

It is generally accepted that radiation (and other mutagens) exert their long-term effects on the fitness of population through the artificial induction of mutations. The term 'genetic load' was coined by Muller [376] to describe the resultant depression in average fitness of a population as a result of mutagens. The concern over the prospects of an increase in mutation rate stems, on the one hand, from belief that the genetic variability of a species should be close to optimum for that species, and on the other hand, that most mutations have deleterious effects on the biological processes of their carriers. Most deleterious alleles are maintained at equilibrium in a population by the opposing forces of mutation and selection, which means that they normally exist at very low frequencies. Favourable or over- dominant alleles exist at high frequencies. Radiation by virtue of its mutagenic properties increases the mutation rate. Theoretically the consequences of increasing the frequency of mutation of existing genes to alleles with non-neutral adaptive values is expected to decrease the fitness of the population by increasing the frequency of alleles with detrimental effects. Short-term genetic effects will be expressed in one generation as detrimental dominant mutations, i.e. sterility and dominant lethal mutations. Long-term effects resulting from an increase of deleterious recessive mutations will become apparent as the recessive alleles gradually increase over many generations and are expressed in homozygotes as malformations or 'genetic diseases'. The consensus still favours this general point of view; however, a number of recent developments has tempered its significance in respect of the long-term fate of the population concerned. It can be argued, and has been shown experimentally under certain conditions, that a modest increase in mutation rates with the concomitant enhancement in the genetic variability may even lead to an improved fitness of the population [377-330]. AQUATIC POPULATIONS AND ECOSYSTEMS 99

The large amount of previously concealed variability recently revealed by biochemical techniques challenges the assumption that mutations are generally of a detrimental nature. Thus 'new' alleles resulting from radiation-induced mutation might possibly be neutral in their effects with respect to the pressures of selection (and therefore could be retained in the gene pool of the populations). Experiments with mice receiving relatively large doses of radiation over a series of generations do not appear to show a net increase in inherited deleterious effects [381]. This suggests either that an unexpected efficient process exists for the elimination of newly induced mutations or that estimates of induced mutation rates are too high or that estimates of the average heterozygous deleterious effects of induced mutations in Drosophila are not directly applicable to mammals. This does not contravene the principle that induced mutations are in general deleterious, but rather emphasizes the importance of understanding the selective process and the dynamics of the newly introduced mutants in the existing gene pool. These developments have increased the difficulty of predicting the potential long-term genetic impact on populations of radiation exposure. Since quantitative data on radiation-induced deleterious genetic changes in aquatic populations are presently lacking, our predictions of the potential effect have to be indirectly estimated from experiments with other organisms, such as Drosophila and mice.

3.3.3. Radiation induced mutation rate in fish

Another major difficulty in estimating the genetic effect of radiation on populations of aquatic organisms is a lack of mutation rate data. The only mutation rate data revealed by an extensive review of the literature was that for the guppy, Lebistes reticulatus [236, 237], Values of (0.4 - 11) X 10"5/rad per gamete and 2.5 X 10~7/rad per locus for the radiation induced mutation rate have been determined [236], and Purdom has indicated that the specific locus mutation rate in the guppy is probably not greater than 2 X 10"7/rad per locus [167, 236], Although these data on the guppy are not extensive, we can evaluate them in the light between a recently demonstrated relationship of DNA content and induced mutation rate in a wide range of organisms [382], The radiation-induced specific locus mutation rate appears to be directly proportional to the haploid DNA content of the nucleus [382], Measurement of the nuclear DNA content of 275 species of fish (not including the guppy, for which no information appears to be currently available) has given values in the range of 0.4-4.4 pg per haploid genome with a modal value of 1 pg [383]. Based on these data the modal value of 1 pg implies a specific locus mutation rate of 7 X 10"8 per rad per locus (Fig.7). This estimate agrees moderately well with the observed mutation rate in the guppy and provides grounds for some confidence in the use of the data to estimate the genetic effects of environmental irradiation in fish. If it is assumed that the number of loci coding for functional genes is about 104 [384], then the mutation rate would be in the order of 7 X 10"4 per rad per zygote. Conservatively, if it is assumed that all mutations are dominant lethals resulting in non-viable zygotes, then less than 1 of every 1000 embryos would be eliminated as the result of accumulation of an integrated dose of 0.5 rad by each of the parents. 100 CHAPTER 3

DNA PER HAPLOID GENOME Ipg)

FIG.7. Relation between mutation rate per locus per rad and the DNA content per haploid genome (modified from Ref. [382]).

3.3.4. Predicted effects

Any prediction of the effects of an increased mutation rate on fish and other aquatic organisms resulting from an increase in the levels of environmental radiation must be made within the perspectives of the reproductive rate of the species and the value of one individual to the population. The same criteria cannot be used to assess and evaluate the consequences of an increased mutation rate for aquatic populations as are used for human populations. For humans, a great value is placed on the individual members and many with relatively low adaptive values are maintained in the population. On the contrary, for aquatic organisms whose reproductive rates are generally very high and on which the selective pressures are strong, the value of one or even thousands of individual organisms to the population is rather insignificant insofar as the long-term structure and fate of the population are concerned. In such populations often much less than 1% of the viable zygotes are normally expected to mature to adulthood and to reproduce, i.e. to comprise the effective gene-pool. Even if we make the most conservative assumption that all induced mutations are harmful to the population, we would predict that, even so, no significant deleterious effects are likely to be produced in populations of aquatic organisms at the dose rates estimated in Chapter 1. Species such as whales and sharks must be discussed separately since these are less fecund, and therefore the reproductive success of the individual is much more important to the overall success of the population. In the absence of any data on the somatic and mutagenic effects of irradiation on these organisms, it is impossible to make any definitive predictions. However, it should be noted that the estimates of the dose rates likely to be received are rarely of the same order as, and generally less than, the limits recommended by ICRP as permissible for humans; therefore, a significant detrimental effect resulting from the increased mutation rate at these low dose rates would not be expected. RECOMMENDATIONS FOR FUTURE RESEARCH

1. There is a real need for more data on the concentrations of natural radionuclides in representative organisms, including detailed tissue distributions, and also in the different external environments, i.e. fresh, estuarine, coastal and open ocean waters and sediments. In most instances similar data are also required for the artificial radionuclides. 2. Dosimetry models need to be refined, particularly with respect to a more realistic geometry of the organism including the consequences of non- uniform distribution of activity within tissues. One should also consider the variation in relative biological effectiveness (RBE) between «-radiation and ß- and -y-radiation in order to allow a more realistic assessment of the biologically effective doses and dose rates of the radiation involved. 3. It is important that experimental work to assess the possible effects of irradiation in contaminated environments should be performed at the lowest dose rates practicable in order to minimize the extent of extrapolation of effects from high to low dose rates. 4. When performing experiments concerning the biological effects of radionuclides in solution, it is essential to make an estimate of the dose rates received by the organisms from the radi'onuclides in the water and from those which have been accumulated by the organism. 5. Better methods must be developed to permit the recognition of radiation effects in individual organisms, populations, communities and ecosystems so that in the future it will be possible to develop sound criteria for the conservation of ecosystems. 6. Parallel experiments between individuals and populations of the same species should be considered in order to provide information on the degree of correlation between their responses and to assess the possible interaction of radiation effects and other environmental stresses which might not be apparent when studying individuals or populations separately. 7. Research should continue on the effects of low concentrations of radionuclides in water on both developing eggs and gonadal tissues of fishes. Great differences exist among the effects reported in the literature; however, unfortunately different fish species, radionuclides and experimental conditions were used in the various studies. Efforts should be made to adopt similar experimental designs in order to achieve comparability of results. 8. Coastal regions and inland waters generally show the highest degree of contamination in aquatic ecosystems. As these areas are of well-known importance to man, and the populations of aquatic organisms residing there, are exposed to rapidly fluctuating environmental conditions, priority should be given to research on radiation effects on organisms and populations from such areas. 9. In most cases organisms, which are easy to culture and which have little ecological significance, have been used in laboratory studies on radiation effects. More attention should be paid to species which, although more difficult to culture, may have more important ecological roles in nature or may be unexpectedly sensitive to radiation. These organisms may prove to be sensitive 'indicators' of radiation effects. 10. It is recommended that aquatic communities, especially as regards their stability, be studied at every trophic level. Comprehensive studies should cover the impact of all pollutants, as well as radiation, on populations, communities and ecosystems and could effectively be carried out on a

101 102 RECOMMENDATIONS collaborative basis among various institutes. Basic studies should consider the following: (a) Comprehensive census of both numbers and relative proportions of marine organisms on a spatial, temporal and financial scale in order that significant alterations in ecosystem structure due to pollution can be recognized. (b) The study of experimental communities in order to approach specific problems such as: (i) Stability of artificial communities of two or more species under 'control conditions'. (ii) Stability of artificial communities in the face of various insults — radiation, heavy metals, pesticides, oil etc. — either singly or in combination. To the extent that is feasible, the above studies should be performed with the view of understanding the role of genetic variation (expressed as discrete polymorphisms and quantitative variations) of individual species in the establishment and maintenance of marine communities. 11. It is recommended that comparative studies of mutation rates induced by radiation and/or conventional pollutants be undertaken on a wide range of aquatic organisms including species which possess both high and low reproductive capacities. One important area of investigation is the study of the genetic effects of low-level radiation, singly or in combination with other stresses, with respect to both genetic damage (gene mutation, chromosomal aberrations, recombination, etc.) and population damage (population size, biomass, fecundity, fitness components, etc.). 12. Surveys of the extent of genetic polymorphisms in marine species, e.g. gene-enzyme polymorphisms, should be carried out. To be most useful, the experimental design should be orthogonal with respect to species and enzymes. In order to understand the significance of polymorphisms, the response of these polymorphisms to varying physical (both mutagenic and non-mutagenic) and biological environments should be studied in both the laboratory and in the field. It would be of particular interest to study the effects of acute as well as chronic exposure on such systems. 13. It is recommended that the IAEA convene a panel to consider the methodology for the study of the effects of radiation on aquatic species, populations, communities and ecosystems. This would be an important step towards achieving comparable results among laboratories undertaking these types of studies. GENERAL CONCLUSIONS

1. The data and models presented in Chapter 1 indicate that it is possible within certain limitations to make estimates of the radiation regimes existing within aquatic environments. The estimated dose rates experienced by aquatic organisms are relatively low even in those environments which are contaminated with radioactive waste. These estimates, which could clearly be improved in specific instances if additional information were available, are however sufficiently realistic to provide a basis for assessing the effects of irradiation in contaminated environments. 2. The results of radiobiological studies indicate that the most radiosensitive aquatic organisms presently known are teleost fish, particularly the developing eggs and young of some species. 3. Doses used in many experimental studies are commonly hundreds or thousands of rads delivered at high dose rates. Unfortunately the majority of the experimental work on radiation effects has been carried out at doses and/or dose rates which bear little relevance to those doses and dose rates that exist in the marine environment (see Chapter 1). 4. There are a numbçr of restraints in extrapolating the data on effects of ionizing radiations at high dose rates derived from controlled laboratory experiments to effects which potentially might occur in populations and ecosystems exposed to low levels in natural waters. 5. When considering the possible effects of ionizing radiation on aquatic organisms and ecosystems, the relative importance of radiation can be kept in perspective by a comparison with known effects of conventional pollutants and from losses due to natural mortality. 6. When considering ecosystems, populations are of more interest than individuals. The most important effects are those that operate at the population level, particularly effects on development, fertility, fecundity and genetic material. Effects on individuals (e.g. late somatic effects of low doses such as life-shortening) which could affect the entire ecosystem by influencing population structure and total productivity of the system, are also of interest. 7. At the present time it would appear that no deleterious effects on populations would be expected at the doses and dose rates estimated in Chapter 1. 8. From studies of the mechanisms of recruitment to exploited aquatic populations, in particular fish populations, it is concluded that any effects caused by low-level chronic exposure to ionizing radiation would be compensated by density-dependent responses in highly fecund species. Thus, it is improbable that any effects due to radiation will be detectable when considering the natural fluctuations in aquatic populations. 9. Few quantitative population genetic studies have been conducted on aquatic populations. Using predicted mutation rates and considering the chronic low-level dose rates present in the environment, it is concluded that significant deleterious genetic effects would not be produced in the types of aquatic populations considered.

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GLOSSARY

Allele: one of a group of alternate genes which may occur at a given locus on a chromosome

Ancestral irradiation: radiation received by previous generations Anorexia: absence of appetite Auger effect: the electronic rearrangement (after production of an electron vacancy in an inner shell of an atom) following electron capture accompanied by weak electron emission Benthic: pertaining to organisms living in or on fresh water or marine sediments Biomass: a measure of the quantity of organisms Blastula: a hollow sphere of cells formed at the termination of cleavage in many animal eggs Centromere: a localized region in each chromosome to which the spindle fibre appears to be attached during cell division Chromatid bridge: an abnormal connection between the separating halves of a chromosome during meiosis Cladoceran: small planktonic crustacea — 'water fleas' Copepod: small planktonic crustacea Darwinian fitness: the reproductive capability of an organism (genotype) as compared with another genotype Diapause embryo: an embryo in a resting or arrested state Dicentric chromosome: an abnormal chromosome containing two centromeres Diploid: having a double set of chromosomes DNA: deoxyribonucleic acid; an essential con- stituent of chromosomes Ecosystem: a community of organisms interacting with the physical environment so that a flow of energy leads to a trophic structure and an exchange of materials within the system Electroretinographic response: an electrical signal produced by the retina in response to radiation stimulation Embryogenesis: the development of an embryo Endemic inversion: a chromosome aberration which is maintained in a fraction of a population

121 122 GLOSSARY

Epiphyte: a (non-parasitic) plant which grows on other plants

Erythropoiesis: the production of red blood cells Exploitation: removal of individuals from a population Exposure: subjecting an organism to an agent such as radiation Fecundity: a measure of the production of viable eggs Fertility: a measure of the production of living offspring Food web: the diagram which describes the energy flow through an ecosystem. For each species all those other species which eat it and all those species which are eaten by it are shown by a series of arrows pointing in the direction in which the energy flows (from prey to predator). These links are then described for all other species until no more paths of energy flow can be described

Gamete: a germ cell which unites with another in sexual reproduction of organisms Gametogenesis: the process which results in gamete production Gastrula: an early embryonic stage in which the embryo forms a hollow sphere by invagina- tion of the blastula (q.v.) Gastrulation: the formation of a gastrula from a blastula Genetic burden (load): the proportion of harmful mutations in the gene pool of a population Genetic polymorphism: ,the regular and simultaneous occurrence of two or more genetically determined forms of a species in the same population Genetic recombination: the rearrangement of linked genes due to crossing-over Genome: the chromosome complement of a cell

Haematopoietic tissue: a tissue in which blood cells are formed Haploid: having a single set of chromosomes Hemizygous: a gene present in a single dose. It may be a gene in a haploid organism, or a sex-linked gene in the heterogametic sex

Hepatopancreas: a digestive gland found in some invertebrates GLOSSARY 123

Heterosomal: involving chromosomes distinguished from each other by differences in form or size

Heterozygous: having two different alleles at one locus Homozygosity: the state of having a gene or genes in the double condition so that the organism is pure-breeding Homozygous: having identical rather than different alleles in the corresponding loci of a pair of chromosomes Hybrid: the product of a cross between individuals of unlike genetic constitution Inbred line: organisms with a great degree of homozygosity due to continued inbreeding and selection Interstitial water: water present in spaces between particles Intrinsic rate of increase the factor by which a population multiplies per unit time interval

LDS0 (Median lethal dose) the amount of an agent which results in the death of 50% of a group of experimental organisms Leucopenia: a reduction in the number of white cells in the blood Locus: the position of a gene on a chromosome Mitosis (and stages): the process of nuclear division in which daughter nuclei are formed each having a chromosome complement the same as the original nucleus. The following stages are recognized (i) prophase (ii) metaphase (iii) anaphase and (iv) telophase Mitotic index: the fraction of a cell population under- going mitosis at the time of examination Natural mortality rate: the rate at which fish die from all causes except fishing Nauplius: a free-swimming larva of crustaceans

Neonate: the new-born of live-bearing fish Oocyte: the egg mother-cell Oogonia: the cells from which the ovarian eggs arise Osmoregulation: the maintenance of normal osmotic pressure of the body fluids Parthenogenesis: the development of an organism from a gamete without fertilization 124 GLOSSARY

Periphyton: algae which grow attached to surfaces Phytoplankton: free-floating microscopic algae Pluteus: a free-swimming larval form of some Echinodermata (starfish, sea urchins, etc..)

Poikilotherm: an organism which is incapable of regulating its body temperature Population: an interbreeding group of individuals which share a common gene pool Protozoa: single-celled, usually microscopic animals R: the roentgen; a quantity of X- or 7-radiation (such that the associated corpuscular emission per 0.001293 g of air produces, in air, ions carrying one electrostatic unit of electricity of either sign) Rad: one hundred ergs of absorbed energy per gram of absorbing material

Radiolysis: the breakdown of a compound due to radiation Recruitment: process by which fish become available for capture either by growing large enough to be caught by the gear in use by the fishermen or by migration into the area where the fishery operates or by a combination of both

Rep: roentgen equivalent, physical; a unit of absorbed dose of radiation with a magnitude of 93 ergs per gram of absorbing material (usually soft tissue)

Selection pressure: the effectiveness of natural selection in altering the genetic composition of a population over a series of generations

Sham-treated: control organism treated in exactly the same way as an experimental organism except for switching on the irradiation device Spermatheca: a sac for storing spermatozoa Spe r matogonia: the cells from which spermatozoa arise Spermatozoa: a free-swimming male gamete Stock (= unit stock): a self-contained and self-sustaining population of one spe.cies of fish, based on a single spawning group, from which there is little or no emigration and into which there is little or no immigration 125

Trematode: a class of parasitic flat-worms Year- class: all the fish of one stock born in the same calendar year Zooplankton: small animals which drift with the surrounding water

SECRETARIAT OF THE PANEL

Chairman: C. POLVANI Comitato Nazionale per l'Energia Nucleare, Rome

Scientific S.W. FOWLER International Laboratory Secretaries: of Marine Radioactivity, Monaco

A. G. KLIMOV Division of Nuclear Safety and Environmental Protection, IAEA, Vienna

Y. NISHIWAKI Division of Nuclear Safety and Environmental Protection, IAEA, Vienna

Editor: Brigitte KAUFMANN Division of Publications, IAEA, Vienna

127 PARTICIPANTS AND OBSERVERS OF THE PANELS IN 1971 AND 1974

AUSTRIA

A. Frantz Bundesanstalt für Wasserbiologie und (1971, 1974) Abwasserforschung, Schiffmühlenstrasse 120, A-1223 Vienna

J. Sas-Hubicki Bundesanstalt für Wasserbiologie und (1971, 1974) Abwasserforschung, Schiffmühlenstrasse 120, A-1223 Vienna

E. Wanderer Gemeinschaftskernkraftwerke Tullnerfeld GmbH, (1971, 1974) Marc Aurelstrasse 4, A-1010 Vienna

CANADA

I. L. Ophel Environmental Research Branch, (1971, 1974) Atomic Energy of Canada Ltd. , Chalk River Nuclear Laboratories, Ontario

FEDERAL REPUBLIC OF GERMANY

M. Hoppenheit Biologische Anstalt Helgoland, (1971, 1974) Laboratorium Sülldorf, 2 Hamburg 55, Wüstland 2

ITALY

M. Bernhard Laboratorio per lo Studio délia Contaminazione (1971, 1974) Radioattiva del Mare, Comitato Nazionale per l'Energia Nucleare, 1-19030 Fiascherino, La Spezia

P. Metalli Laboratory of Animal Radiation Biology, (1971) C.S.N. Casaccia, 1-00060 S. Maria di Galeria, Rome

C. Polvani Comitato Nazionale per l'Energia Nucleare, (1971, 1974) Viale Regina Margherita 125, 1-00198 Rome

128 PARTICIPANTS AND OBSERVERS 129

JAPAN

R. Ichikawa National Institute of Radiological Sciences, (1974) Chiba City, Chiba

M. Saiki Marine Radioecological Research Station, (1971, 1974) National Institute of Radiological Sciences, 9-1-4 chôme, Anagawa, Chiba Citv

UNITED KINGDOM

M.J. Holden Fisheries Laboratory, (1974) Lowestoft, Suffolk

D.S. Woodhead Fisheries Radiobiological Laboratory, (1971, 1974) Hamilton Dock, Lowesoft, Suffolk

UNITED STATES OF AMERICA

B. G. Blaylock Environmental Sciences Division, (1974) Oak Ridge National Laboratory, P. O. Box X, Oak Ridge, Tennessee 3 7830

W. L. Templeton Pacific Northwest Laboratories, (1971, 1974) Battelle Memorial Institute, Richland, Washington 99352

ORGANIZATIONS

COMMISSION OF THE EUROPEAN COMMUNITIES (CEC)

F. Van Hoeck 200, rue de la Loi, (1971) B-1040 Brussels, Belgium

EURATOM

O. Ravera Research Centre, (1974) Ispra (Várese), Italy 130 PARTICIPANTS AND OBSERVERS 130

INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)

M. Bezzegh-Galantai Division of Nuclear Safety and (1974) Environmental Protection, Kärntner Ring 11, A-1011 Vienna, Austria

C. Fisher Division of Life Sciences, (1971) Kärntner Ring 11, A-1011 Vienna, Austria

S.W. Fowler International Laboratory (1971, 1974) of Marine Radioactivity, Oceanographic Museum, Monaco

E, Harvey Division of Life Sciences, (1971) Kärntner Ring 11, A-1011 Vienna, Austria

D.G. Jacobs Division of Nuclear Safety and (1971) Environmental Protection, Kärntner Ring 11, A-1011 Vienna, Austria

A.G. Klimov Division of Nuclear Safety and (1971) Environmental Protection, Kärntner Ring 11, A-1011 Vienna, Austria

S. Kobayashi Division of Life Sciences, (1971) Kärntner Ring 11, A-1011 Vienna, Austria

H. Marchart Joint F AO/IAEA Division of Atomic Energy (1971) in Food and Agriculture, Kärntner Ring 11, A-1011 Vienna, Austria

R. Mukherjee Division of Life Sciences, (1974) Kärntner Ring 11, A-1011 Vienna, Austria

Y. Nishiwaki Division of Nuclear Safety and (1974) Environmental Protection, Kärntner Ring 11, A-1011 Vienna, Austria

L. Sztanyik Division of Life Sciences, (1974) Kärntner Ring 11, A-1011 Vienna, Austria PARTICIPANTS AND OBSERVERS 131

F.P.W. Winteringham Joint FAO/IAEA Division of Atomic Energy (1974) in Food and Agriculture, Kärntner Ring 11', A-1011 Vienna, Austria

ORGANIZATION FOR ECONOMIC CO-OPERATION AND DEVELOPMENT/NUCLEAR ENERGY AGENCY (OECD/NEA)

M. Ijuin 38, Boulevard Suchet, (1974) F-75016 Paris, France

J. P. Olivier 38, Boulevard Suchet, (1971, 1974) F-75016 Paris, France

WORLD HEALTH ORGANIZATION (WHO)

M. Sentici WHO Liaison Officer,

(1974) International Atomic Energy Agency, Kärntner Ring 11, A-1011 Vienna, Austria

E. Shalmon Avenue Appia, (1971) Geneva, Switzerland HOW TO ORDER IAEA PUBLICATIONS

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UNITED KINGDOM Her Majesty's Stationery Office, P.O. Box 569, London SE 1 9NH UNITED STATES OF AMERICA UNIPUB, P.O. Box 433, Murray Hill Station, New York, N.Y. 10016

In the following countries IAEA publications may be purchased from the sales agents or booksellers listed or through your major local booksellers. Payment can be made in local currency or with UNESCO coupons.

ARGENTINA Comisión Nacional de Energía Atómica, Avenida del Libertador 8250, Buenos Aires AUSTRALIA Hunter Publications, 58 A Gipps Street, Collingwood, Victoria 3066 BELGIUM Service du Courrier de l'UNESCO, 112, Rue du Trône, B-1050 Brussels CANADA I nformation Canada, 171 Slater Street, Ottawa, Ont. K 1 A OS 9 C.S.S.R. S.N.T.L., Spálená 51, CS-110 00 Prague Alfa, Publishers, Hurbanovo némestie 6, CS-800 00 Bratislava FRANCE Office International de Documentation et Librairie, 48, rue Gay-Lussac, F-75005 Paris HUNGARY Kultura, Hungarian Trading Company for Books and Newspapers, P.O. Box 149, H-1011 Budapest 62 INDIA Oxford Book and Stationery Comp., 17, Park Street, Calcutta 16; Oxford Book and Stationery Comp., Scindia House, New Delhi-110001 ISRAEL Heiliger and Co., 3, Nathan Strauss Str., Jerusalem ITALY Libreria Scientifica, Dott. de Biasio Lucio "aeiou", Via Meravigli 16, 1-20123 Milan JAPAN Maruzen Company, Ltd., P.O.Box 5050, 100-31 Tokyo International NETHERLANDS Marinus Nijhoff N.V., Lange Voorhout 9-11, P.O. Box 269, The Hague PAKISTAN Mirza Book Agency, 65, The Mall. P.O.Box 729, Lahore-3 POLAND Ars Polona, Céntrala Handlu Zagraniçznego, Krakowskie Przedmiescie 7, Warsaw ROMANIA Cartimex. 3-5 13 DecembrieStreet, P.O.Box 134-135, Bucarest SOUTH AFRICA Van Schaik's Bookstore, P.O.Box 724, Pretoria Universitas Books (Pty) Ltd., P.O.Box 1557, Pretoria SPAIN Diaz de Santos, Lagasca 95, Madrid-6 Nautrónica, S.A., Pérez Ayuso 16, Madrid-2 SWEDEN C.E. Fritzes Kungl. Hovbokhandel, Fredsgatan 2, S-103 07 Stockholm U.S.S.R. Mezhdunarodnaya Kniga, Smolenskaya-Sennaya 32-34, Moscow G-200 YUGOSLAVIA Jugoslovenska Knjiga, Terazije 27, YU-11000 Belgrade

Orders from countries where sales agents have not yet been appointed and requests for information should be addressed directly to: Polishing Section, § Ci^V 'ntemat'ona' Atomic Energy Agency, s ^^ Kärntner Ring 11, P.OBox 590, A-1011 Vienna, Austria

INTERNATIONAL SUBJECT GROUP: II ATOMIC ENERGY AGENCY Nuclear Safety and VIENNA, 1976 Environmental Protection/All