Marine Radioecology, Volume 6 E-Book

Jean-Claude Amiard

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2022

Seitenzahl: 600

Beschreibung

The marine environment, in addition to a not insignificant background of "natural" radioactivity, has continued to receive inputs of radionuclides directly or indirectly through atomic fallout, discharges from the nuclear industry or from nuclear accidents. After their introduction, the fate of these radionuclides is complex with modifications of physicochemical forms, dispersion in marine water masses and adsorption onto sedimentary particles. Marine organisms then bioaccumulate these radionuclides to a greater or lesser extent, dispersing them via their burrowing activities, horizontal and vertical migrations or through food webs. All of these phenomena lead to very variable radioactive contamination, depending on location and the nature of the marine environments concerned, and consequently, to very different doses of irradiation to marine organisms. The harmful effects of ionizing radiation on living marine organisms are felt at varying levels of biological organization from the molecule to the ecosystem, passing through the cell, the organ, the individual and the population. In the end, the radioactive risk for marine organisms can decline according to several situations, which can be normal, programmed or accidental.

Leseprobe

Radioactive Risk Set

coordinated byJean-Claude Amiard

Volume 6

Marine Radioecology

Jean-Claude Amiard

First published 2022 in Great Britain and the United States by ISTE Ltd and John Wiley &; Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

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© ISTE Ltd 2022The rights of Jean-Claude Amiard to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.

Library of Congress Control Number: 2022941924

British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78630-779-8

Preface

The marine environment is home to a large number of marine species. Moreover, as the marine environment is the domain where life on planet earth appeared, the number of taxonomic classes present is considerably greater than in others. This considerable marine biodiversity, associated with numerous ecosystems and the complexity of food webs, explains the great stability of this environment. It is also a current and future source for humans, both from the point of view of food and from the point of view of biomolecules of various interests (nutritional, therapeutic, diagnostic, anti-cancer and anti-viral, antioxidants, etc.).

However, the marine environment is the final repository of a large number of forms of physical, chemical and biological pollution that negatively affect marine life. The chemical pollution of rivers and oceans has become for the public an unavoidable subject, because it is measured in thousands of tons discharged per day. It overshadows all other forms of pollution which are more modest, but which also raise questions of concern. Among the latter, radioactive pollution is not negligible.

Radioecology, a scientific discipline born in the middle of the 20th century, has two objectives, the estimation of the fate of radionuclides in the environment and the evaluation of their radioactive risk for living organisms. This discipline is relevant to all the earth’s environments.

The design of this book follows the classical approach to risk estimation, which is divided into four steps: hazard identification, hazard exposure assessment, hazard characterization or effects assessment and risk characterization.

Chapter 1 is devoted to the objectives of radioecology and the approach to estimating radioactive risk. The assurances given by the ICRP (International Commission on Radiological Protection) until 2000 that “if Man is adequately protected then other living things are also likely to be sufficiently protected” were not at all well founded.

Chapter 2 identifies radioactive hazards. They are mainly due to the double origin of radionuclides in the marine environment. Their natural origin is essentially to the contribution of the lithosphere caused by the leaching of primeval rocks or the upwelling of magma. The unnatural origin of radionuclides is due to anthropogenic activities in the nuclear field, both military and industrial or medical, both during programmed activities and those resulting from accidents. The dominant source is however that of nuclear fallout.

Chapter 3 deals with the fate of radionuclides, which are never fixed, in the major marine compartments, i.e. water and sediments, with case studies of the impacts due to the nuclear facilities at La Hague and Sellafield.

Chapter 4 presents the fate of radionuclides in marine organisms. In particular, this chapter reports on the various routes of penetration, the modes of contamination by adsorption and absorption and the mechanisms of bioaccumulation of radionuclides in cells, their distribution into the bodies of organisms as well as their elimination. The factors influencing bioaccumulation and trophic transfers are also detailed.

Chapter 5 summarizes the radioactive contamination of various marine sites. These are mainly the marine sites of the American, British, French and Soviet atomic bomb tests, the sites impacted by atmospheric fallout, the sites near reprocessing plants for radioactive nuclear fuel and the marine sites affected by civilian (Chernobyl, Fukushima) and military (Palomares, Thule) nuclear accidents and the dumping of solid radioactive waste. The various environmental monitoring networks are detailed.

Chapter 6 provides an inventory of radiation doses to marine organisms from nuclear accidents and releases from civil nuclear facilities and the main factors influencing these doses. The systematic underestimation of absorbed doses resulting from the poverty of the available calculation tools is underlined, a deficit that leads to the use of simplifying assumptions and to the neglect of radiation sources.

Chapter 7 details the harmful effects of ionizing radiation (mortality, alteration of reproduction, effect of age on irradiation effects) at the various levels of biological organization of marine organisms from the molecular to the ecosystem. It underlines the lack of knowledge about doses received at the organ level and the impacts on marine biodiversity.

Chapter 8 evaluates the radioactive risk to marine organisms with the significance of uncertainties that affect both the doses received and their effects.

The conclusion summarizes all the information in the book and discusses the main gaps in our knowledge of radioecology so that a more realistic assessment is possible.

Nuclear power is a complex scientific and technical field that has also been invited into the social debate, following the serious accidents at Chernobyl and Fukushima, as well as the environmental problems posed by the various links in the so-called “fuel cycle”, which ranges from uranium mining to the final storage of the various types of radioactive waste.

In order to remain within the scientific domain, and in keeping with the other volumes of the “radioactive risk” series, I have endeavored to adhere to the scientific truth as closely as possible. To do this, each statement is supported by at least one bibliographic reference to a scientific work published in an international peer-reviewed journal (i.e. where the texts are reviewed and corrected by peers) or by official national or international organizations working in the nuclear field.

August 2022

Acknowledgments

Jean-Claude Zerbib, former CEA Senior Expert and radiation protection engineer, had the difficult task of reviewing, annotating and criticizing this manuscript. He also provided me with precious documents to complete the abundant literature that was used in the writing of this work. I would like to thank him very much for this. Professor Philip Rainbow (former Keeper of Zoology, Natural History Museum, London, United Kingdom) has done the same for the English version. I warmly thank them both for their time and efforts.

Pierre Barbey, from the University of Caen, member of ACRO and expert to the Haut Comité pour la transparence et l’information sur la sécurité nucléaire (French Committee for Transparency and Information on Nuclear Safety, HCTSIN), was kind enough to proofread and correct the last two chapters of the French book. His contribution has been very useful. I also wish to thank Professor Philip Rainbow (former Keeper of Zoology, Natural History Museum, London, UK) who did the same for the English version. I warmly thank them both for their time and efforts.

Several colleagues answered my questions. They include Karine Beaugelin-Seiller (IRSN), Henri Métivier (former IRSN) and Scott Fowler (former IAEA researcher in Monaco).

I would also like to thank the members of the Scientific Council of the ANCCLI who helped me in the understanding of certain subjects. The same goes for all the members of the Groupe Radioécologie Nord Cotentin (North Cotentin Radioecology Group, GRNC), a pluralist group, for the remarkable work carried out together with every courtesy.

2The Origins of Radionuclides in Marine Environments

2.1. Natural or anthropogenic origins of radionuclides in the marine environment

The presence of radionuclides in the marine environment has a double origin: a natural origin and an artificial origin linked to human activities. The natural radioactivity of the environment results from two distinct sources of radionuclides: (i) radionuclides born from the interaction of matter with radiation of cosmic origin (3H, 7Be, 14C, 32Si, 36Cl, etc.) and (ii) the radionuclides present in the earth’s crust since the origin of the earth (40K, 87Rb, 115In, 138La, 147Sm, 176Lu, 187Re, etc.) and the descendants of the four radioactive families (238U, 235U, 232Th and 237Np) [EIS 73].

The anthropogenic origins of radioactive pollutants in the marine environment are various and varied. It is common to separate the intended releases of radionuclides into the environment (fallout from nuclear explosions and discharges of radioactive liquid and gaseous effluents into various environments) and the unintended origins of these pollutants (linked to incidents or accidents). Artificial radionuclides are mainly fission products and activation products as well as transuranics produced by neutron capture.

Some radionuclides have a dual origin, natural and anthropogenic. This is the case for tritium, which is produced by the interaction of cosmic rays with the atmosphere, and also by military nuclear tests and the civilian use of nuclear energy, and in the medium term even more so with the use of nuclear fusion (ITER). This is also the case for uranium and its descendants, especially during the first stages of its exploitation (mines).

Figure 2.1.The radioactive family of uranium-238 and its descendants.

Natural radionuclides are introduced into the hydrosphere primarily by leaching from the earth’s crust. According to Arnold and Martell (1973 in [AMI 80]), in the ocean, 232Th and 230Th (which is a descendant of 238U) precipitate very rapidly, uranium-238 a little less rapidly, while radium-226 (formed by decay of 230Th, whose physical half-life is 1,600 years) can be resolubilized in waters close to the bottom. Some human activities will reintroduce into the environment various natural radionuclides present in the lithosphere. These will be, for example, phosphate plants, coal-fired power plants, oil exploitation or the first stages of the nuclear fuel cycle (mines, mills, etc.). Thus, a coal-fired power plant releases into the atmosphere 122.103 Bq.h-1 of 226Ra, 77.103 Bq.h-1 of 228Ra, 122.103 Bq.h-1 of 232Th, 298.103 Bq.h-1 of 210Pb and 298.103 Bq.h-1 of 210Po [KIR 77]. The offshore oil and gas industry is the largest non-nuclear sector contributor of radioactive substances to the marine environment. Almost all of the radionuclides released from this sector come from produced water (water extracted from the reservoir along with the oil and gas) and pipe descaling. A less significant source is the use of radioactive substances (e.g. tritium) as markers. Naturally occurring radionuclides in produced water include lead-210 (210Pb), polonium-210 (210Po) and radium-226 and 228 (226Ra and 228Ra) [PSP 09].

The fate of natural radionuclides that are descendants of uranium-238 involves various compartments of the environment according to their nature (gaseous, solid) and according to their speciation. Thus, radon is mainly in the atmosphere and polonium-210 in the hydrosphere (Figure 2.1).

There are seven major sources of anthropogenic radionuclides in the marine environment. These are military nuclear weapons programs, nuclear weapons testing, uranium mining and processing, nuclear power plants, commercial fuel reprocessing, ocean dumping of radioactive waste and nuclear accidents involving nuclear facilities or nuclear powered vessels [HU 10].

2.2. The natural origins of radionuclides

More than 60 radionuclides are known to occur naturally in the environment. These are the terrigenous radionuclides (40K, 87Rb) and those descending from the thorium series (228Ra, 228Th, 232Th), actinium (227Ac, 231Pa, 235U), uranium (210Pb, 210Po, 222Rn, 226Ra, 230Th, 234Th, 234U, 238U), as well as cosmogenic radionuclides (3H, 7Be, 10Be, 14C, 26Al, 32Si) [FUK 82]. Cosmic rays are 89% protons (hydrogen), 10% helium and 1% heavy elements [LAI 99]. The most abundant natural radionuclides in the ocean are potassium-40 with 15,000,000 PBq and uranium-238, 37,000 PBq [BUE 14].

The main characteristics of naturally occurring radionuclides in marine environments are listed in Tables 2.1 and 2.2.

Water produced by the offshore oil industry contains naturally occurring radionuclides [HOS 12]. As a result, high levels of radionuclides (mainly 226Ra and 228Ra) are discharged into the sea in connection with oil and gas production on the Norwegian continental shelf. The presence of added chemicals such as scale inhibitors in produced water has a marked influence on radium speciation [ERI 09].

Table 2.1.Concentrations in marine waters and sediments of some naturally occurring radionuclides (from [SZY 12, NIE 18a])

Radionuclide

Physical half-life (years)

Concentrationsurface waterin (Bq.m

-3

)

Concentrationsediments in (Bq.kg

-1

)

Cosmogenic origin

3

H

12.3

20–100

–

7

Be

0.146

1.1–3.4

–

14

C

5,730

5.5–6.7

–

32

If

172

0.2–3.3.10

-3

–

Land origin

40

K

1.28.10

9

11,800–12,300

2–1,000

87

Rb

4.8.10

10

100

–

232

Th

1.34.10

10

0.4–29;10

3

12–50

228

Ra

5.76

0.8–8

–

228

Th

1.91

0.004–0.3

–

235

U

7.04.10

8

1.9

–

238

U

4.47.10

9

40–44

2.5–150

234

Th

0.066

0.6–6.8

–

234

U

2.45.10

5

47

–

230

Th

9.0.10

4

2–52.10

-3

–

226

Ra

1,617

0.8–8

10–100

210

Pb

22.3

1–4.5

100–280

210

Po

0.378

0.5–1.9

100–280

Table 2.2.Characteristics of the main radionuclides introduced into the marine environment by human activities (from [NIE 18a])

Radionuclide

Physicalperiod (year)

Distribution factor (Kd) between water and sediment

Bioconcentration factor (BCF)

Effective dose coefficient for adult ingestion (Sv.Bq

-1

)

3

H

12.3

1.0

1.0

1.8.10

-11

14

C

5,700

1.10

3

2.10

4

5.8.10

-10

60

Co

5.27

1.10

5

7.10

2

3.4.10

-9

90

Sr

28.64

8.10

0

3.10

0

2.8.10

-8

99

Tc

213,000

1.10

2

8.10

1

6.4.10

-10

106

Ru

1.02

4.10

4

2.10

1

7.0.10

-9

125

Sb

2.77

2.10

3

6.10

2

1.1.10

-9

129

I

1.57.107

7.10

1

9.10

0

1.1.10

-7

131

I

0.0219

2.2.10

-8

134

Cs

2.06

4.10

3

1.10

2

1.9.10

-8

137

Cs

30.17

1.3.10

-8

238

Pu

87.74

1.10

5

1.10

2

2.3.10

-7

239

Pu

24,110

2.5.10

-7

241

Pu

14.35

4.8.10

-9

241

Am

432.2

2.10

6

1.10

2

2.0.10

-7

2.3. The military origins of anthropogenic radionuclides

Since World War II and the military use of nuclear energy, direct and indirect releases of radionuclides into the marine environment have been particularly significant, especially between 1945 and 1990. The impact on the marine environment is considerable due to the atmospheric fallout from the aerial testing of atomic bombs. Direct releases of radionuclides are also significant from military research and manufacturing centers for nuclear weapons, from poorly controlled military radioactive waste, and from releases related to the nuclear propulsion of ships and submarines.

2.3.1. Radionuclides due to atmospheric fallout from atomic device explosions

The input of long-lived radionuclides into the oceans was considerable, especially from 1945 to 1980 [EDG 80]. Between 1945 and 1965, 520 atomic bombs were tested, more than 100 of which were tested on islands or over/in large bodies of water. For the United States, these were the islands of Bikini, Eniwetok and Johnston; for the United Kingdom, Montebello Islands; for the United States and the United Kingdom, Christmas Island; for the USSR, the island of Novaya Zemlya; for France, the islands of Fangataufa and Mururoa; and for China, Lake Lob-Nor.

The principal sites of atomic bomb tests were located for the Americans in the coral atolls of the Marshall Islands at 110°N and 160–165 E. The result was a strong contamination of the marine environment [CAR 97]. The inventory of the quantities of radionuclides involved in the tests in French Polynesia (Mururoa and Fangataufa) is 1.7.105 TBq [HU 10].

There are two main types of bombs, A-bombs or fission bombs and H-bombs or thermonuclear bombs (fission–fusion–fission).

2.3.1.1. Atomic A-bombs

The “classic” atomic (A) bombs involve the fission of a charge of uranium-235 or plutonium-239. The power of these bombs, which were very weak at the beginning (Hiroshima 16 ± 2 kilotons of TNT), now reaches more than 100 times a “unit bomb” (corresponding to 20 kt of the explosion of TNT or trinitrotoluene). The explosion of these A-bombs releases into the environment a large sum: the unreacted fuel (235U or 239Pu) (about 90%, or 10 kg or 222.1011 Bq for a unit bomb) and fission products (10%). The neutrons emitted during the explosion induce a significant radioactivity in the surrounding environment (activation products).

A “unit bomb” of 1 Mt releases about 1 kg of fission products, a complex mixture of about two hundred radionuclides corresponding to 35 different elements. The fission of heavy nuclei of 235U or 239Pu most frequently gives rise to two lighter nuclei with masses oscillating around two values: 90 and 140. The main fission products are 89Sr, 90Sr, 95Zr, 103Ru, 131I, 137Cs, 141Ce, 144Ba-La, 144Ce and 144Pr. One minute after the explosion, the radioactivity due to fission products and activation products is 3.03.1022 Bq for a “unit bomb”. The decay of the radioactivity is rapid, but after one year, the residual radioactivity is still 4.1.1015 Bq.

Activation products typically account for only 25% of the radioactivity from fission products. The activation products formed will vary depending on the location of the explosion. In the case of an airborne explosion, there is formation of 3H (< 37.109 Bq.Mt-1), 41A, 16N, 19O and especially 14C (1.26.1015 Bq.Mt-1). If the explosion is underwater, it will be mainly 35S, 38Cl and 24Na that will be produced and to a lesser degree 32P, 51Cr, 59Ni, 64Cu, 65Zn, 99Mo and 113Sn. When the explosion is terrestrial or underground, one generally notes the formation of 45Ca as well as 14C, 24Na, 28Al, 31Si, 32P, 35S, 38Cl, 42K, 54Mn, 55Fe, 65Zn and 89Sr (in [FON 60]).

2.3.1.2. Atomic H-bombs

H-bombs are composed of a nucleus of uranium-235 or plutonium-239 surrounded by a mass of lithium-deuterium or tritium, itself often contained in a uranium-238 envelope (3F bomb). During explosion, the fission–fusion–fission reactions follow one another extremely rapidly. The quantity of fission products formed is certainly proportional to the power of the device; on the contrary, the quantity of activation products must be much greater. The quantity of fissioned material is greater than for A-bombs.

Eight days after the explosion of an enriched uranium thermonuclear bomb (March 18, 1954), Kimura et al. (cited by [FLA 63]) estimated the following composition of the fallout: 237U (20%), 144Ce (16%), 106Rh, 103Ru, 129Te,131 I, 132Te (15%), 147Pm (9%), 147Ne (9%), 91Y (8%), 141Ce (7%), 140Ba (5%) and 95Zr (5%). This composition, due to the large differences in the physical half-lives of the radionuclides, varies considerably over time. Thus, after four years, the main radionuclides are 144Ce (28%), 147Pm (24%), 90Sr (19.6%) and 137Cs (19.2%) (according to Siegel in [FLA 63]).

The radionuclides present in the fallout in significant quantities and dangerous because of a long or medium physical half-life, easy incorporation into the food chain, or significant retention in the human body, are 90Sr (28.8 years – 37.1014 Bq.Mt-1), 137Cs (30.05 years – 37.1014 Bq.Mt-1), 14C (5,700 years – 81.1012 Bq.Mt-1), as well as actinides

2.3.1.3. The case of the Nagasaki explosion

The explosion of a plutonium atomic bomb (10–15 kg) in Nagasaki, Japan, on August 9, 1945, led to the worldwide release of man-made radionuclides. This was a historic event. Part of the bomb was split, 1.2 kg of 239Pu, releasing 21 kt of TNT energy with various fission products. The rest of the unspent fissile material, 13.8 kg (3.49.1013 Bq) of 239,240Pu, was released into the atmosphere with the fission product, 137Cs, 23.4 g (7.44.1013 Bq). The fates of 239,240Pu and 137Cs were studied by analyzing local and global fallout. The highest concentration of 239,240Pu was 64.5 mBq.g-1 (181 mBq.cm-2) while it was 188 mBq.g-1 (526 mBq.cm-2) for 137Cs, both 2.8 km east of the hypocenter. The total amount of deposition in the local fallout region of 264 km2 was 37.5 g (9.48.1010 Bq) for 239,240Pu and 3.14 mg (5.88.1010 Bq) for 137Cs. The Nagasaki explosion resulted in atmospheric fallout as far away as the Arctic, where deposition was about 0.16 µBq.cm-2 for 239,240Pu and 20 µBq.cm-2 for 137Cs in 1994 (Kudo et al. pp. 233–250 in [KUD 00]).

2.3.1.4. The distribution of deposition between the northern and southern hemispheres

From 1945 to 1980, there were 423 atmospheric tests1 of atomic bombs (about 217 MT) releasing numerous radionuclides into the atmosphere (Hamilton et al. pp. 29–58 in [GUÉ 03]). These tests resulted in significant deposits to the oceans. Thus, for 90Sr, the maximum cumulative deposits were 355 PBq in the Northern Hemisphere in 1966 and 107.3 PBq in 1972, 1973 and 1974 in the Southern Hemisphere (Hamilton et al. pp. 29–58 in [GUÉ 03]).

Figure 2.2.Integrated 1995 deposits of strontium-90 corrected for radioactive decay (modified from [UNS 93]).

Because the currents that affect the stratosphere are mostly east-west and very weak in the latitudinal direction, the northern hemisphere, where most of the nuclear tests have taken place, is significantly more contaminated than the southern hemisphere. In each hemisphere, radioactive pollution is most intense between 25 degrees and 50 degrees of latitude. This is verified by the results of atmospheric fallout of most radionuclides. This is, for example, the case of the global deposition of strontium-90 (Figure 2.2) [NAS 71, UNS 93]. It is easy to find the atmospheric fallout of other radionuclides since the ratios between them remain fairly constant. These ratios are 1.5 between 137Cs and 90Sr, 9.4 between 55Fe and 90Sr, 0.017 between 239Pu and 90Sr, and 0.33 between 60Co and 90Sr [NAS 71].

Deposition of 137Cs and 239,240Pu into the Pacific Ocean from atomic bomb testing has been significantly greater in the Northern Hemisphere than in the Southern Hemisphere (Table 2.3) [HAM 03]. As a result, Pacific water concentrations are slightly higher in the Northern Hemisphere than in the South. In the South Pacific Ocean around the French Polynesian islands, the concentrations decreased from 1979 (about 6 Bq.m-3) to 1994 (2.7 Bq.m-3), with a turnover rate of 14 years for cesium-137 ([BOU 92]; Bourlat et al. pp. 75–93 in [GUÉ 03]), as well as for 39,240Pu (0.62–0.32 Bq.m-3) [BOU 95].

Similarly, atmospheric deposition of 210Pb has been higher in the northern hemisphere than in the southern hemisphere. Moreover, deposition at the equator (10–15 mBq.cm-2.yr-1) is significantly higher than at the poles (< 5 mBq.cm-2.yr-1) [BAS 11].

The dispersion of radioactive aerosols will vary according to the power of the nuclear device, the location of the explosion, the weather conditions, and the nature and size of the debris.

The contamination of the ocean environment will be directly influenced by underwater explosions (< 0.1% of all explosions) and by explosions on the surface of islands (firing on barges). The distribution of radioactivity following an underwater explosion depends on the power of the device and the depth at which the explosion occurs. For explosions that take place at shallow depths, generally one-third to two-thirds of the debris is mixed near the explosion site (within a few hundred meters) and at the thermocline when it exists [NAS 71]. This distribution will be influenced by currents, turbulent diffusion and radioactive decay. As a 10 kt bomb volatilizes 7.106 kg of seawater (1.3.105 kg of chlorine, 7.7.104 kg of sodium and potassium, etc.), the percentages of soluble and insoluble forms of radionuclides will vary according to the position of the explosion, underwater or on the surface [NAS 71].

Avargues [AVA 71] reports that in 1968, the total deposition of strontium-90 on the globe was 481.1015 Bq, of which 355.1015 was for the Northern Hemisphere (73.8%), or an average of 2,405.106 Bq.km-2. Estimating that the ratio 137Cs/90Sr is 1.6 in fallout, the cumulative global deposition of cesium-137 was about 740.1015 Bq in 1968, of which 555.1015 Bq was for the Northern Hemisphere. Similarly, the deposition of 55Fe would have been 2,366.1015 Bq from 1962 to 1966 (including 1,900.1015 Bq for the Northern Hemisphere) [NAS 71].

Table 2.3.Deposits and inventories of 137Cs and 239,240Pu in the Pacific Ocean due to fallout from atomic bomb tests (modified from Hamilton et al. pp. 29–58 in [GUÉ 03])

Latitude (°)

Area (thousand km

2

)

Deposit of

137

Cs (GBq.km

-2

)

Deposit of

239,240

Pu (GBq.km

-2

)

137

Cs inventory

239,240

Pu inventory

60–90 N

749

0.94

0.037

0.70

0.03

30–60 N

25,976

2.16

0.067

56

1.9

0–30 N

54,665

0.92

0.016

50

0.93

Subtotal

107

2.83

0–30 S

50,760

0.39

0.011

20

0.58

30–60 S

30,355

0.60

0.012

18

0.40

60–90 S

9,203

0.23

0.0024

2.1

0.024

Subtotal

40

1.00

Total

147

3.83

The difference in radionuclide concentrations between the northern and southern hemispheres is illustrated by two oceanographic expeditions carried out in 1988/1989 and 1991 by the Swedes (Holm et al. pp. 59–74 in [GUÉ 03]). Thus, for 137Cs, surface waters had concentrations lower than 5 Bq.m-3 for the Southern Hemisphere and between 5 and 23 Bq.m-3 for the Northern Hemisphere. Similarly, for 239,240Pu, concentrations in the Southern Hemisphere were less than 10 µBq.L-1 and often less than 5 µBq.L-1, while in the Northern Hemisphere, they were often greater than 5 µBq.L-1 up to more than 15 µBq.L-1. These authors estimate that the residence time in surface waters of plutonium is 8 years and about 100 years for cesium.

Before the use of nuclear energy, natural carbon-14 was in equilibrium in the biosphere at a concentration of 277.5 ± 99.9 mBq.g-1 C. The excess of carbon-14 due to thermonuclear bombs was estimated in January 1964 to be 63.4.1027 atoms or 155.1014 Bq (UNSCEAR, 1964 in [EIS 73]). The circulation of 14C in the stratosphere, the troposphere, the biosphere and at the surface of the hydrosphere takes place in a few years but more slowly in the deep ocean. Thus, by the end of 1967, the tropospheric 14C content had increased by 510% in the Northern Hemisphere and 390% in the Southern Hemisphere, resulting in a rapid increase in carbon-14 in the biosphere (Nydal, 1968 in [EIS 73]).

Taking the average production of 2,368.1015 Bq of iodine-131 per Mt of fission, the world production of iodine-131 due to nuclear explosions can be estimated in 1963 at 44.1018 Bq [EIS 73]. Iodine-131 from a bomb explosion of less than 100 kt will be distributed in the troposphere and will necessarily contaminate the aquatic environment.