NORDIC RADIOECOLOGY THE TRANSFER OF RADIONUCLIDES THROUGH NORDIC ECOSYSTEMS TO MAN potx

At the beginning of 1986 - a few months before the Chernobyl accident - general radioecology was removed from this collaboration', and from 1990 the NKS financing was transferred from th

NORDIC RADIOECOLOGY

NORDIC ECOSYSTEMS TO MAN

NORDIC RADIOECOLOGY

THE TRANSFER OF RADIONUCLIDES

THROUGH NORDIC ECOSYSTEMS

P.O B o x 21 1,1000 AE Amsterdam,The Netherlands

ISBN 1 0-444-8 16 17-8

0 1994 Elsevier Science B.V All rights reserved

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PREFACE

The present book is the final milestone in the radioecology programme, RAD, carried out from

1990 to 1993 under the Nordic Committee for Nuclear Safety Research, NKS This work was done

in parallel to three other NKS programmes: Reactor safety (SIK), Waste and decommissioning (KAN), and Emergency preparedness (BER) The NKS was established in 1966 and was financed

by the Nordic Council of Ministers from 1977 to 1989 It is now a joint Nordic committee financed by the Danish Emergency Management Agency, the Finnish Ministry of Trade and Industry, Iceland's National Institute of Radiation Protection, the Norwegian Radiation Protection Authority, and the Swedish Nuclear Power Inspectorate The NKS is further co-sponsored by a number of Finnish and Swedish companies working in the field of civil nuclear energy and protection of the population

The preparation of this book involved much painstaking effort by the authors, the participants

in the working groups and the four project leaders, Manuela Notter, Per Strand, Aino Rantavaara and Elis Holm I would like here to express my gratitude for their contribution The guidance and inspiration given by the RAD reference group is furthermore acknowledged Finally, it should be mentioned that there would have been no Nordic collaboration on Nuclear Safety without the energetic, persistent, diplomatic and occasionally maddening efforts of our travelling

"ambassador", Franz Marcus, executive secretary of the NKS from 1976 to 1994

Henning Dahlgaard

Co-ordinator of the RAD programme

1.1 The aims and justification of Nordic radioecology H Dahlgaard 3

1.2 General summary and conclusions H Dahlgaard, M Notter, J Brittain,

2.1 Introduction to aquatic ecosystems M Notter, J Brittain and

2.2 The characterization of radiocaesium transport and retention in Nordic

lakes H.E Bjernstad, J.E Brittain, R SaxBn and B Sundblad 29

2.3 The distribution and characterization of 137Cs in lake sediments

2.4 Transport of 137Cs in large Finnish drainage basins R Saxtn

2.5 The role of lake-specific abiotic and biotic factors for the transfer of

radiocaesium fallout to fish T Anderson and M Meili

2.6 Models for predicting radiocaesium levels in lake water and fish

U Bergstrom, B Sundblad and S Nordlinder

2.7 Radiocaesium in algae from Nordic coastal waters

L Carlson and P Snoeijs

2.8 Polonium-210 and radiocaesium in muscle tissue of fish from

different Nordic marine areas E Holm

2.9 Radiocaesium as ecological tracer in aquatic systems - a review

M Meili

Chapter 3 AGRICULTURAL ECOSYSTEMS

3.1 Introduction to radioecology of the agricultural ecosystem P Strand

3.2 Direct contamination - seasonality A Aarkrog

3.3 Influence of physico-chemical forms on transfer

D.H Oughton and B Salbu

3.4 Contamination of annual crops M Strandberg

3.5 Transfer of 137Cs to cows’ milk in the Nordic countries

H.S Hansen and LAndersson

3.6 Radiocaesium transfer to grazing sheep in Nordic environments

K Hove, H Lijnsjo et al

3.7 Dynamic model for the transfer of 137Cs through the

soil-grass-lamb foodchain S.P Nielsen

3.8 Studies on countermeasures after radioactive depositions

in Nordic agriculture K RosCn

229

239

4.1 Introduction to terrestrial seminatural ecosystems A Rantavaara 263

4.2 The transfer of radiocaesium from soil to plants and fungi

4.3 Radiocaesium in game animals in the Nordic countries K.J Johanson 287

4.4 Pathways of fallout radiocaesium via reindeer to man

4.5 The distribution of radioactive caesium in boreal forest ecosystems

Chapter 5 METHODOLOGY, QUALITY ASSURANCE AND DOSES

5.1 Introduction to intercalibration / analytical quality control

and doses E Holm

5.2 Intercomparison of large stationary air samplers I Vintersved

381

383

3 85

5.3 Intercalibration of whole-body counting systems

T Rahola, R Falk and M Tillander

5.4 Intercalibration of gamma-spectrometric equipment E Holm

5.5 Doses from the Chernobyl accident to the Nordic populations

via diet intake A Aarkrog

5.6 Internal radiation doses to the Nordic population based on

whole-body counting M Suomela and T Rahola

DEFINITIONS, TERMS AND UNITS

CONTRIBUTORS AND PARTICIPANTS

Hannele Aaltonen, STUK, P.O.Box 14, FIN 00881 Helsinki

Asker Aarkrog, ECO-Riss, Postboks 49, DK 4000 Roskilde

Magne Alpsten, Institut for Radiofysik, Sahlgrenska Sjukhuset, S 41345 Goteborg

Inger Andersson, Lantbruksuniversitetet, Box 59, S 23053 Alnarp

Tord Andersson, Naturgeografisk avd., Umel Universitet, S 90187 Umel

Ronny Bergmann, FOA-4, S 90182 Umel

Ulla Bergstrom, Studsvik Eco & Safety, S 61182 Nykoping

Torolf Bertelsen, Statens Strllevern, Postboks 55, N 1345 0sterh

Helge E Bjernstad, Agricultural University of Norway, N 1432 AS-NLH

Inggard Blakar, Agricultural University of Norway, N 1432 AS-NLH

John Brittain, Oslo Universitet, Sars Gate 1, N 0562 Oslo

Anders Broberg, Uppsala Universitet, Box 557, S 75122 Uppsala

Lena Carbon, Avd for Marinekologi, Box 124, S 22100 Lund

Gordon Christensen, IFE, Postboks 40, N 2007 Kjeller

Olof Eriksson, Lantbruksuniversitetet, Box 703 1, S 75007 Uppsala

Ake Eriksson, Lantbruksuniversitetet, Box 7031, S 75007 Uppsala

Sverker Evans, Statens Naturvbdsverk, Box 1302, S 17125 Solna

Rolf Falk, Swedish Radiation Protection Institute, Box 60204, S 10401 Stockholm

Torbjorn Forseth, Institut for Naturforskning, Tungasletta 2, N 7004 Trondheim

Lars Foyen, Havforskningsinstituttet, Box 1870, N 5024 Bergen

Torstein Garmo, Agricultural University of Norway, N 1432 AS-NLH

Eldar Gaare, Norwegian Institute for Nature Research, Tungasletta 2, N 7005 Trondheim

Eva Hllkansson, Institut for Radiofysik, Sahlgrenska Sjukhuset, S 41345 Goteborg Lars EUkansson, Uppsala Universitet, Viistra Agatan 24, S 75220 Uppsala

Hanne S Hansen, Agricultural University of Norway, N 1432 AS-NLH

Lars Egil Haugen, Agricultural University of Norway, N 1432 AS-NLH

Knut Hove, Agricultural University of Norway, N 1432 AS-NLH

Erkki nus, STUK, P.O.Box 14, FIN 00881 Helsinki

Kki Indridason, Geislavarnir rikisins, Laugavegur 118d, Is 150 Reykjavik

Tim0 Jaakkola, Radiokemiska institutionen, Pb 5, FIN 00014 Helsingfors Universitet Hans Pauli Joensen, Academia Faroensis, Noatun, FR 100 Torshavn

Karl J Johanson, Lantbruksuniversitetet, Box 7031, S 75007 Uppsala

Bernt Jones, Lantbruksuniversitetet, Box 7038, S 75007 Uppsala

Pekka Kansanen, Helsingin kaupungin ymp., Helsinginkatv 24, FIN 00530 Helsinki Riitta Korhonen, VlT/YDI, Pb 208, FIN 02151 Espoo

Vappu Kossila, Lantbrukets forskningscentral, FIN 3 1600 Jokioinen

Andrew Liken, Agricultural University of Norway, N 1432 AS-NLH

Hans Liinsjo, Lantbruksuniversitetet, Box 7031, S 75007 Uppsala

Sigurdur Magnusson, Geislavarnir rikisins, Laugavegur 1 18d, Is 150 Reykjavik

Soren Mattsson, Inst for Radiofysik, Malmo Almanna Sjukhus, S 21401Malmo

Marcus Meili, Uppsala Universitet, Box 557, S 75122 Uppsala

Georg NeumaM, Lantbruksuniversitetet, Box 7031, S 75007 Uppsala

Sven P Nielsen, ECO-Riss, Postboks 49, DK 4000 Roskilde

Sture Nordlinder, Studsvik Eco & Safety, S 61 182 Nykoping

Tuire Nygren, Vilt- och Fiskeriforskningsinstitutet, Tutkimuslaitos, FIN 82950 Kuikkalampi

Elisabet D Olafsdijttir, Geislavarnir rikisins, Laugavegur 118d, Is 150 Reykjavik

Rolf A Olsen, Agricultural University of Norway, N 1432 AS-NLH

Deborah H Oughton, Agricultural University of Norway, N 1432 AS-NLH

Olli Paakkola, Torpantie 1 B, FIN 01650 Vanda

Arja Paasikallio, Lantbrukets forskningscentral, FIN 3 1600 Jokioinen

Sigurdur E Piilsson, Geislavarnir rikisins, Laugavegur 118d, Is 150 Reykjavik

Tua Rahola, STUK, P.O.Box 14, FIN 00881 Helsinki

Hannu Raitio, Skogforskningsinstitutet, FIN 39700 Parkano

Kristina Rissanen, STUK, Louhikkotie 28, FIN 96500 Rovaniemi

Klas Rosbn, Lantbruksuniversitetet, Box 7031, S 75007 Uppsala

Brit Salbu, Agricultural University of Norway, N 1432 AS-NLH

Chr Samuekson, Institutionen f Radiofysik, Lasarettet, S 22185 Lund

Ritva Saxbn, STUK, P.O.Box 14, FIN 00881 Helsinki

Tone Selnaes, IFE, Postboks 40, N 2007 Kjeller

Pauli Snoeijs, Uppsala Universitet, Box 559, S 75122 Uppsala

Riitta Sormunen-Christian, Lantbrukets forskningscentral, FIN 3 1600 Jokioinen

Hans Staaland, Agricultural University of Norway, N 1432 AS-NLH

Eiliv Steinnes, Universitetet, AVH, N 7055 Dragsvoll

Morten Strandberg, ECO-Riss, Postboks 49, DK 4000 Roskilde

Bjorn Sundblad, Studsvik Eco & Safety, S 61182 Nykoping

Matti Suomela, STUK, P.O.Box 14, FIN 00881 Helsinki

J6hann Thorsson, Agricultural Research Institute, Is 112 Reykjavik

Michael Tillander, Helsinki Universitet, Radiokemiska inst., FIN 00014 Helsinki

Ole Ugedal, Finmark Distrikth0yskole, Follumsvei, N 9500 Alta

Finn Ugletveit, Statens Strilevern, Postboks 55, N 1345 0sterh

Trygvi Vestergaard, Academia Faeroensis, Noatun, FR 100 Torshavn

Ingemar Vintersved, Forsvarets Forskningsanstalt, S 17290 Sundbyberg

PROJECT LEADERS

Elis Holm, Institutionen f Radiofysik, Lasarettet, S 22185 Lund

Manuela Notter, Statens NaturvArdsverk, Box 1302, S 17125 Solna

Per Strand, Statens Strhlevern, Postboks 55, N 1345 0steris

Aino Rantavaara, STUK, P.O.Box 14, FIN 00881 Helsinki

REFERENCE GROUP

Asker Aarkrog, Rise National Laboratory, Postboks 49, DK 4000 Roskilde

Henning Dahlgaard, Riss National Laboratory, Postboks 49, DK 4000 Roskilde (Co-ordinator)

Sigurdur Magnusson, Geislavarnir rikisins, Laugavegur 118d Is 150 Reykjavik

Franz Marcus, NKS, Postboks 49, DK 4000 Roskilde

Judith Melin, SSI, Box 60204, S 10401 Stockholm

Eiiiv Steinnes, Universitetet, AVH, N 7055 Dragsvoll

Matti Suomela, STUK, P.O.Box 14, FIN 00881 Helsinki

Seppo Vuori, VTT/YDI, Pb 208, FIN 02151 Espoo

Erik-Anders Westerlund, Statens StrAlevern, Postboks 55, N 1345 0sterh (Chairman)

CO-ORDINATOR

Henning Dahlgaard, Rise National Laboratory, Postboks 49, DK 4000 Roskilde

NORDIC RADIOECOLOGY 1990 - 1993

1.1 THE AIMS AND JUSTIFICATION OF NORDIC RADIOECOLOGY

BACKGROUND

The word RADIOECOLOGY came into being in the 1950's when it became evident that man-made radionuclides produced in atmospheric nuclear weapons tests had been spread globally and were transferred through various ecosystems to man From the very beginning the scientific study of radioecology was developed by scientists with an interest in ecology and genetics However, physicists, analytical chemists and engineers played an essential role because accurate measurements of the low levels of the relevant radionuclides - e.g %k, '37Cs and 239Pu - found

in the environment, required the elaborate analytical procedures and advanced electronic equipment that were gradually developed during the 1960's - the "Golden Age" of radioecology At most institutions radioecology became a branch of health physics ultimately aiming at studying and reducing the radiation dose to man Attempts were made at several institutions to incorporate the field in general ecology and to utilize the radionuclides as global-scale tracers for, e.g., studies of atmospheric pollutant transport and trace element turnover However interest in radioecology dwindled with the declining activity from atmospheric fallout, and by the mid-1980's work in radioecology had been reduced to a minimum, or was even non-existent in several countries Furthermore the integrity of radioecologists and health physicists had been challenged by

"environmentalist" groups fighting the peaceful utilization of nuclear energy on a non-scientific basis Several institutions thus reduced funding to radioecology to serve political ends

When the accident at the Chernobyl nuclear power station happened in April 1986

radioecology was reinvented throughout Europe and surviving centres of study were given an economic boost At several places ecologists of different backgrounds introduced new and fruitful concepts, using the Chernobyl radiocaesium for more than just radiation protection studies The Nordic countries, Denmark, Finland, Iceland, Norway and Sweden, have a long, historic tradition of cultural and scientific collaboration This has also applied to radioecology, where the Nordic Committee for Nuclear Safety Research (NKS), financed by the Nordic Council of Ministers, included this subject in their programmes from 1977 to 1985 At the beginning of 1986

- a few months before the Chernobyl accident - general radioecology was removed from this collaboration', and from 1990 the NKS financing was transferred from the Nordic Council of Ministers to the national authorities responsible for nuclear safety and radiation protection in the different countries The Nordic radioecology programme RAD, which is the subject of the present book, was run under the auspices of the new NKS from 1990 to 1993 Via the NKS, the RAD programme has had funding of around 6 million Danish kroner ( - 1 million US $) As the contents

of the present book will show, this is only a minor part of the total costs of the work described here However, without the catalytic support provided by the NKS much of the present work would not have taken place, and efforts in different Nordic countries would not have been co- ordinated

Plans for the Nordic Radioecology programme 1990-1993 were described in the Scandinavian languages in a publication issued by the Nordic Council of Ministers (NKS, 1989)

THE NORDIC RADIOECOLOGY PROGRAMME

The RAD programme consists of four projects As the largest doses to man immediately after the Chernobyl accident were derived from the consumption of terrestrial products and freshwater fish, the programme included 2 projects on terrestrial radioecology: RAD-3, Agricultural ecosystems (project leader: Per Strand) and RAD-4, Forest and alpine ecosystems (project leader: Aino Rantavaara), and one on aquatic radioecology: RAD-2, Aquatic ecosystems (project leader: Manuela Notter) that mainly dealt with Nordic lakes Finally, RAD-1 included training, methodology, quality assurance and doses to the Nordic population (project leader: Elis Holm) Results from the four projects are presented in detail in chapters 2-5, and are summed up in the following chapter 1.2

~

I: The AKTU program 1985 - 1989 did, however, include environmental radioactivity after the Chernobyl accident (Tveten, editor)

AIMS AND JUSTIFICATION

After the Chernobyl accident it became clear that the transfer of radionuclides via food to man could result in significant internal radiation doses to the Nordic population after nuclear accidents

In the long term the most significant internal doses from Chernobyl were expected to be related

to the contamination of specially sensitive Nordic environments leading to a high transfer of radiocaesium to man It was considered important for the authorities to have access to up-to-date knowledge of the spreading and turnover of radionuclides in different Nordic ecological systems

in order to be able to decide on the relevant countermeasures Furthermore, knowledge of the contamination levels of agricultural products was necessary to assure exports and avoid unnecessary loss of resources

There is an immense variation within the Nordic countries not only in the distribution of the Chernobyl deposition, but also in the transfer of radiocaesium to man The contamination of a highly productive agricultural area is expected to give relatively small individual doses to a large population during a short period, whereas the contamination of the lichen carpets utilized as winter- grazing for reindeer, or of the abundant oligotrophic lakes, will give a larger individual dose to

a small population for many years

The overall scientific aim of the Nordic Radioecology programme was to perform a quantitative comparative study of the pathways of selected radionuclides through different Nordic ecosystems Moreover the programme aims at helping a new generation of radioecologists to become acquainted with different Nordic ecosystems and to foster Nordic contacts The RAD programme has aimed at obtaining the widest possible coverage, i.e the inclusion of as many Nordic radioecological centres as possible This is not cost-effective with respect to research results, but it does promote Nordic radioecological contacts As a consequence, the programme

is to a large extent based on nationally-funded programmes

A general goal for the entire programme - and a justification for the funding of the programme by the nuclear safety authorities - is its benefits in respect of preparedness for nuclear accidents On first thoughts this goal may seem remote from a scientific field programme on the cycling of caesium in the environment However, one benefit of keeping radioecological centres alive is that the necessary measuring equipment is ready for use, and that competent staff are available to take suitable samples and carry out reliable radionuclide analyses the very day an accident happens In addition, knowledge of the pathways of radionuclides through ecosystems to

man will be available A nuclear preparedness plan without working scientific projects is like an

airforce without trained fighter pilots

Maybe the most important justification of such programmes is not the production of final reports, but rather the less definable benefits such as inspiration and collaboration based on the

close personal relations among individual scientists from different Nordic countries and institutions

having common interests A further aspect of the personal contact between Nordic radioecologists

and radiation protection officials is that it will facilitate information exchange between the different countries in any future nuclear emergency

REFERENCES

NKS (1989) Plan for Nordisk Kjernesikkerhetsprogram 1990-1993 Nordisk Md, Nordisk Ministerriid, NU 19895 (in the Scandinavian languages)

Tveten, U (editor) Environmental consequences of releases from nuclear accidents Final report

of the NKA project AKTU-200 IFE, P.O Box 40, N - 2007 Kjeller, 1990 261 pp

1.2 GENERAL SUMMARY AND CONCLUSIONS

HENNING DAHLGAARD', MANUELA NOTTER', JOHN E BRITTAIN3, PER STRAND4, AINO RANTAVAARA' AND ELIS HOLM6

'Riss National Laboratory, DK - 4000 Roskilde, Denmark

2Swedish Environmental Protection Agency, S - 171 85 Solna, Sweden

3Freshwater Ecology and Inland Fisheries Laboratory (LFI), University of Oslo, Sars gate 1, 0562

Oslo, Norway

4Norwegian Radiation Protection Authority, P.O.Box 55, N - 1340 0sterA.9, Norway

5Finnish Centre for Radiation and Nuclear Safety, P.O.Box 14, FIN - 00881 Helsinki, Finland 6Department of Radiation Physics, Lund University, Sweden

INTRODUCTION

On Monday, 28th April, 1986, most Nordic radioecologists and health physicists realized the area was being contaminated by debris from a serious nuclear accident The cloud from Chernobyl had already reached the Nordic countries on Sunday, 27th April, and contamination was to continue during May Figure 1.2.1 shows the resulting ground deposition of 137Cs in kBq m-2 in the Nordic countries Denmark, Finland, Norway and Sweden Off the map, the Chernobyl contamination on Iceland and Greenland was very low, whereas the deposition on the Faroe Islands was 0.6-4.5 kBq

1 3 7 ~ ~ m-2

The Nordic post-Chernobyl radioecology programme, RAD, consisted of four projects The main radionuclides chosen for study were the two radiocaesium nuclides, 137Cs and 134Cs, because they appeared to be the most important contributors to doses to man after the Chernobyl accident, and because they are relatively simple to measure However, a few results for %rand 210Po were also reported The present chapter is intended to give an overview of the results from the RAD programme

RAD-1 (project leader Elis Holm) had a multiple purpose: methodology, training, quality assurance and doses Initially, a major task was to conduct a two-week post-graduate training course in various aspects of radioecology The course included 20 lectures by various Nordic radioecologists These are published elsewhere (Holm, editor) An exchange programme permitting, preferentially, young scientists to stay for one or two weeks at another Nordic laboratory, e.g to adopt a new radiochemical method, was also conducted by RAD-1 Three

separate programmes on quality assurance were carried out Of these, the intercomparison of nine large, stationary air samplers and the intercalibration of 20 Nordic whole-body counting systems are especially remarkable Finally, RAD-1 was responsible for dose assessments based partly on the results produced in the three other RAD projects The results from RAD-1 are given in chapter

5 and in Holm (editor)

RAD-2: Aquatic ecosystems (project leader: Manuela Notter) mainly concerned Nordic lakes,

as the major problems in aquatic environments after the Chernobyl accident appeared in fresh- water systems However, two minor projects were run in the marine environment The results from RAD-2 are described in detail in chapter 2

RAD-3: Agricultural ecosystems (project leader: Per Strand) focused on various aspects of Nordic agriculture in relation to nuclear contamination: annual crops, cows’ milk, grazing sheep

and on countermeasures RAD-3 also included a study of physico-chemical forms and a model

study The results are given in chapter 3

Finally RAD-4: Forest and alpine ecosystems (project leader: Aino Rantavaara) concerned the natural terrestrial environment which, like the freshwater environment, appeared to surprise the authorities with high and variable radionuclide levels after the Chernobyl accident RAD-4 studied radiocaesium transfer from soil to plants and fungi, game animals, the reindeer foodchain and boreal forests in general The results are reported in chapter 4

AQUATIC ECOSYSTEMS

With respect to Nordic aquatic ecosystems, the main exposure pathway of 137Cs to man after the Chernobyl accident has been through the consumption of freshwater fish Caesium accumulates in fish muscle due to its chemical similarity to potassium and the accumulation of 137Cs is of particular importance in the Nordic countries where ionic concentrations in freshwaters are generally low Chapter 2 identifies the important parameters determining radionuclide concentrations in fish, thereby permitting the development and assessment of potential remedial

measures Since the Chernobyl accident in 1986, there has been an intensive research effort in the

Nordic countries aimed at obtaining reliable input data for prediction models and determining the important driving forces and parameters for such models

Lakes received radionuclides from Chernobyl fallout via two sources: direct fallout on the lake surface and leakage from the catchment Chapter 2.2 describes fractionation techniques used

in a study of the input of radiocaesium to three widely different Nordic lakes, Hillesjon in Sweden,

!&re Heimdalsvatn in Norway and Saarisjawi in Finland Using hydrological data, the degree of

retention of 137Cs in these three lake systems was estimated Transport of 137Cs in plant material (Coarse Particulate Organic Material, CPOM) is considerable in Nordic lakes Through its rapid

resulting from the Chernobyl accident

assimilation into the invertebrate foodchain, it is potentially a major source of 137Cs for lake ecosystems CPOM transport is higher in mountain and forest lakes than in lowland lakes in agricultural areas However, in all lakes almost all such plant material is retained in the lake The Nordic lakes studied differed in the concentration of 137Cs in the various molecular weight fractions

in the water phase Free ions may easily cross biological membranes and the low molecular weight fraction is assumed to have a high degree of bioavailability However, both organic and inorganic substances in the water phase may affect the biological uptake of a given element In fact, the low molecular weight fraction showed no retention in the three study lakes and was exported downstream In contrast, half the colloidal (pseudocolloidal) fraction was retained during passage through both &re Heimdalsvatn and Saarisjarvi In Hillesjon, ten times more 137Cs flowed out than flowed in, due to resuspension of 137Cs-ri~h sediments

Although some of the radiocaesium from Chernobyl has been transported out of lakes because of the high flows associated with the spring snowmelt at the time of deposition, most of

it still remains in lake sediments Chapter 2.3 describes a study of the distribution, physico- chemical forms and concentration of radiocaesium in lake sediments In 1987, 137Cs was to a large extent bound to chemically labile fractions, but it has subsequently been transformed to less available fractions, thus reducing the tendency for resuspension The horizontal distribution of 137Cs in the sediments is affected by the shape of the lake basin, steep-sloping bottoms tending to focus the radiocaesium towards the deeper parts The degree of bioturbation, diffusion and the rate

of sedimentation determine the vertical distribution of 137Cs in lake sediments A strong tendency for resuspension was found in shallow lakes Although this may transport 137Cs to deeper areas where it is less available, it also increases its availability to the biota, delaying recovery in shallow lakes

The importance of leakage from catchment areas has been studied on a large scale in Finland, where the whole country has been divided into seven different catchments, each with its own

characteristics with regard to fallout, soil type and topography (chapter 2.4) However, during the

first year after the fallout the activity concentrations in lake waters and fish could be estimated using simple relationships to the deposition In subsequent years catchment characteristics played

an increasing role, leading to differences between lakes in the different catchment areas For example, a high incidence of bogs prolonged the decrease of 137Cs in lake waters and in fish, whereas a predominance of clay soils reduced the transfer to aquatic systems

A number of lake-specific factors, both abiotic and biotic, have been put forward as determining the concentration of radiocaesium in fish Chapter 2.5 describes a major study encompassing a large number of Swedish lakes, and assesses the importance of a wide range of such factors The maximum activity concentration in fish was reached within three years in most

reflecting their trophic level However, the transfer to fish varied by up to an order of magnitude between lakes Variation in the expected transfer to pike can be explained by differences in the theoretical residence time of 137Cs, determined from the mean hydraulic residence time and the scavenging capacity of the lakes, which in turn is well indicated by the concentration of base cations in lake waters

The model assessment in chapter 2.6 is based on three Nordic lakes for which extensive data are available, both in terms of the radiocaesium inventory and in terms of ecosystem characteristics This allows an evaluation of the precision of the model predictions and an assessment of the parameters contributing to their uncertainty The latter is particularly important

in the long term when factors other than the primary load become important in determining radiocaesium concentrations in lake water and in fish The compartment model gave satisfactory predictions for concentrations in fish and lake waters during the first five years after Chernobyl However, the results were sensitive to appropriate parameter values such as the K, and the biological half-life in fish Uncertainty analyses demonstrated that leakage from the drainage area

is important for mountain lakes, while resuspension is of significance in lowland lakes

As indicated by the model uncertainty analyses in chapter 2.6 and the sediment studies in

chapter 2.3, the behaviour of Chernobyl caesium is now entering a new phase as different processes, insignificant in the short term, begin to increase in importance It is therefore essential

that the research effort initiated after the Chernobyl accident is maintained This is necessary in

order to understand the long-term consequences of fallout from Chernobyl and other similar events, especially in systems with long half-lives It will also provide a different set of dynamics, which will increase our knowledge and experience, thus forming a broader base for prediction and remedial measures should there be future and perhaps even more serious nuclear accidents

As mentioned in chapter 1.1, the main emphasis in the aquatic radioecology programme was put on fresh-water radioecology However, chapters 2.7 and 2.8 deal with marine and brackish water environments Chapter 2.7 describes a project where the brown alga Fucus vesiculosus was used to monitor the level of radiocaesium in the coastal waters of all the Nordic countries, Denmark, Finland, Iceland, Norway and Sweden, in 1991 The Chernobyl fallout pattern appeared clearly with highest concentrations in the southern Bothnian Sea Fucus vesiculosus occurs along most Nordic coasts except in the northern parts of the Baltic Sea, where it becomes scarce because

of the low salinity Epilithic diatom communities proved useful as an alternative bioindicator for radiocaesium in these waters

Whereas the main work in the present programme was centred on radiocaesium, chapter 2.8

reports concentrations of the natural a-emitting radionuclide 2'oPo as well as radiocaesium in fish

muscle from different Nordic marine areas, the Baltic Sea, the Norwegian Sea and Icelandic waters A dose assessment after the Chernobyl accident showed that the population received similar doses from *loPo and radiocaesium via fish caught in the Baltic, whereas from other locations the

dose from 210Po was the most important from the marine environment

In addition to the importance of radiocaesium in the aquatic foodchain in terms of dose to man, fallout from Chernobyl has enormous potential as an ecological tracer Chernobyl caesium has been and will indeed continue to be used as a tracer to monitor and elucidate basic ecological processes, as reviewed in chapter 2.9

AGRICULTURAL ECOSYSTEMS

Nordic agriculture is highly variable because of differences in climate, latitude, altitude and soil types It includes a wide spectrum of farming, ranging from highly intensive grain, meat and dairy centres in Denmark and part of Sweden, southern Finland and south-east Norway, to free-range goat and sheep grazing in natural environments in Iceland and the Norwegian mountains Direct contamination of agricultural plants immediately after a nuclear accident is the fastest

and most direct route to the human foodchain Chapter 3.2 deals with the direct contamination of agricultural products including secondary direct deposition, i.e rain splash and resuspension The chapter focuses on seasonality, i.e the varying response to contamination of crops according to the time of year when contamination occurs The effect of seasonality is largest for short-lived radionuclides (such as I 3 l I ) and for elements that mainly enter the foodchain by direct contamination (e.g 137Cs) As a result of seasonality, the transfer of radiocaesium to man from the Chernobyl accident was higher in southern than in northern Europe normalized to the same deposition density

The effects of the physico-chemical forms of the deposited radionuclides on transfer and

mobility in the environment are dealt with in chapter 3.3 The activity levels of radionuclides (Bq

m-2) deposited in the Nordic countries showed considerable variation, even within a single m2 Activities in vegetation and transfer factors also show variations between sites, within sites, with

time and between the different radionuclides In 1989 studies on the mobility of radionuclides

(137Cs and %Sr) in Norwegian soil-plant systems indicated that the fraction of radionuclides

deposited as fuel particles was not having any significant effect on the transfer of 137Cs or %Sr

Apparently the lability of 137Cs and depends more heavily on the physical and chemical properties of the soil and on the chemical properties of the element, than on the fallout speciation Hence, the particle form of deposition from Chernobyl is not expected to be important for future transfer of radionuclides in the Nordic countries In contrast, studies on soils collected from the

30 km zone around Chernobyl suggest that the lability (or rather "non-lability") of wSr is largely

determined by the fraction associated with fuel particles Studies on Norwegian soils suggest that both transfer factors and mobility factors are needed for a full understanding of the processes involved and for future predictions of radionuclides in the other parts of the ecosystem

In chapter 3.4 special emphasis is laid on annual crops as a vector for the transfer of

radiocaesium to man Barley, potato, cabbage, carrot and pea are used as examples After a nuclear accident, a common trend is that contamination levels in annual crops decrease rapidly

from the first to the second year Thereafter the rate of decrease is more variable and it seems that long ecological half-lives are possible in some agricultural ecosystems.The uptake of radiocaesium

from soil through roots to edible parts of annual crops is generally very low in Scandinavian agricultural ecosystems, except on peaty organic or sandy soils that are often used for other purposes such as livestock or forage production The most important pathway for the transfer of radiocaesium from annual crops to man is through direct contamination, because of the low uptake from soil Therefore the season of the year is the most important factor determining the transfer

to man after a nuclear accident, as mentioned above and in chapter 3.2 On the Faroe Islands the uptake is generally between one or two orders of magnitude higher than in the other Nordic countries The high content of organic matter and sand may be part of the explanation An effective half-life for radiocaesium content in barley of between 5 and 10 years seems reasonable

on common Nordic arable land soil types in the first years after an accident In potatoes a similar

value of 6 years was calculated for Denmark

Following the Chernobyl nuclear accident in 1986 several studies were made in Denmark, the Faroe Islands, Finland, Iceland, Norway and Sweden on the transfer of 137Cs from feed to

cows’ milk The present review (chapter 3.5) shows that the transfer of 137Cs to cows’ milk related

to ground deposition was highest in the Faroe Islands, Iceland and Norway and lowest in Denmark,

Finland and Sweden The effective ecological half-life for Chernobyl I3’Cs ranged from 1-2 years for all the Nordic countries and was 18.4 years for global 137Cs fallout in Iceland

Radiocaesium transfer in the soil-herbage-lamb foodchain was assessed in a four-year trial

conducted in sheep production locations of the Nordic countries (chapter 3.6) Radiocaesium contamination of the topsoil ranged from 3 to 30 kI3q m-’ and was predominantly of Chernobyl

origin in Finland, Norway, and Sweden, whereas in Iceland 137Cs was primarily of nuclear weapons test origin, and in Denmark and the Faroe Islands contamination was derived from both sources Soil-to-herbage radiocaesium transfer factors were high on the organic and acidic soils

of the Faroe Islands, Iceland, Norway, and Sweden, averaging 18-82 Bq 137Cs kg-I herbage on a soil deposition of 1 kBq 137Cs m-’, and much lower on the sandy soils of Denmark and clay soils

in Finland (0.4-0.8) Herbage-to-lamb concentration factors were generally more homogeneous,

indicating that the absorption of radiocaesium from herbage was similar in each of the countries

A I3'Cs deposition of 1 kBq m-' soil gave rise to much lower meat radiocaesium concentrations

at the sites in Denmark, the Faroe Islands, and Finland (0.5-3.0 Bq kg-I) than in Iceland, Norway,

and Sweden (20-47 Bq kg-') It is concluded that among the Nordic countries the soil-herbage-lamb

pathway is clearly of greatest importance in Iceland and Norway, intermediate in the Faroe Islands, and of comparatively lesser importance in Denmark and Sweden The data were further utilized

in a dynamic radioecological model describing the transfer of radiocaesium through the soil-grass-

lamb foodchain (chapter 3.7)

Finally, chapter 3.8 reviews experiments on countermeasures after radioactive deposition in

Nordic agricultural systems carried out since the sixties Experiments have mainly concerned two strategies: ploughing and fertilization It was found that efficient placement below root depth can

be achieved by means of two-layer ploughs and by deep-ploughing equipment However, soil type and moisture conditions in the soil during ploughing will influence the quality of the work Loose, sandy soils and heavy clays are more difficult to handle than other soil types On soils with low

clay content such as sandy soils and peat soils, fertilization with up to 200 kg potassium per

hectare can efficiently reduce caesium uptake by both grass and arable crops These soils have low potassium reserves and need new potassium dressings during crop rotation Heavy clays generally need no extra potassium dressings to reduce crop uptake of caesium

FOREST AND ALPINE ECOSYSTEMS

There is an area of overlap between the agricultural and the natural ecosystems in the Nordic

countries Some of the results described under the agricultural ecosystems (chapter 3) relate to the

utilization of more or less natural ecosystems, e.g sheep production in part, whereas reindeer herding is treated in chapter 4 alongside forest ecosystems and game animals In the early sixties

during the major atmospheric nuclear tests, the transfer of radiocaesium in the lichen - reindeer -

man foodchain was a major radioecological factor in Scandinavia It was therefore more of a political difficulty than a scientific puzzle when, after Chernobyl, the natural ecosystems gave rise

to relatively high individual doses However, the actual transfer of radiocaesium through natural terrestrial ecosystems, and in particular the role of fungi in this transfer, gave new results

Chapter 4.2 deals with the transfer of radiocaesium from soil to plants and especially to fungi

in seminatural ecosystems The radiocaesium concentration in fungal fruit bodies is often more than

50 times higher than in plants growing at the same location, and whereas the radiocaesium content

in higher plants has decreased since 1988, in fungi it has tended to be stable or even increasing Comparisons with measurements of old global fallout radiocaesium make it possible to predict that the content of Chernobyl radiocaesium in fungi will be high for many years in several Nordic ecosystems This has implications for the radiocaesium content of wild as well as domestic animals

grazing in seminatural and forest ecosystems

Furthermore chapter 4.2 reports on studies of horizontal and vertical redistribution of

Chernobyl radiocaesium after deposition In the mostly acid seminatural and forest soils in the Nordic countries, practically no vertical transport of radiocaesium has occurred More than 90%

is still bound in the top 3-4 cm organic layer In areas covered with snow during the deposition,

a horizontal redistribution took place during snowmelt giving rise to much higher variation in the area content than in nearby sites not covered in snow during deposition This may in part explain

the patchiness mentioned elsewhere, e.g in chapter 3.3

One of the main pathways for the transfer of radiocaesium from natural ecosystems to man

is via game animals (chapter 4.3) Roe deer consume large quantities of fungi in autumn, resulting

in a high and very variable content of radiocaesium Normally, the radiocaesium concentration in roe deer peaks in August to October The transfer per kg of moose is lower and not as variable, partly because of the smaller consumption of fungi However because of the importance of this supply of meat in Sweden, Norway and Finland, the transfer of radiocaesium to man via moose

is much higher than that via roe deer There has been no significant decrease in the radiocaesium content of moose or roe deer after Chernobyl, implying that the effective ecological half-lives for

the forest ecosystems are very long It is suggested that the physical half-life of 137Cs and 134Cs

may be the best estimate

As mentioned above, the lichen - reindeer - man foodchain was studied in Scandinavia in the early days of radioecology, and the Chernobyl accident put new life into these studies (chapter

4.4) The reason for the importance of reindeer as a vector for radiocaesium is its choice of food,

which consists of 70-80% lichen in winter and 10-20% in summer Coupled with the short biological half-life of caesium in reindeer, 10-20 days, this leads to a strong seasonal variation of radiocaesium in reindeer meat: a late winter high that is about five times higher than the late summer low In contrast to results from the game animals above, an effective ecological half-life

of radiocaesium in reindeer meat after Chernobyl could be estimated to 3-4 years For the lichen

species serving as winter forage, effective ecological half-lives of 5-7 years on ridges and 6-11 years in more sheltered habitats were observed

Finally, chapter 4.5 reviews the distribution of radiocaesium in boreal forest ecosystems based on Chernobyl as well as global fallout results The review thus focuses on data of relevance for both the early and the later phases after nuclear fallout over forest areas In boreal forests the humus layer usually retains a major fraction of the deposited radiocaesium even decades after deposition This feature, as well as a persistent high availability in important foodchains, may explain the long effective ecological half-lives, approaching the physical half-life of the radionuclides, observed for radiocaesium in forest ecosystems This is in contrast to the intensive

significant decrease in concentrations with time is observed

METHODOLOGY, QUALITY ASSURANCE AND TRAINING

For all environmental measurements, quality assurance of the analyzed values is of central importance In the present programme, the concept of quality assurance has included quality- promoting activities such as the exchange of analytical methodology, short exchange programmes for scientists wanting to acquire knowledge of an analytical method from one of the other Nordic laboratories, and a two-week postgraduate training course including 20 lectures on several aspects

of radioecology from sampling and radiochemistry to statistical analysis The course included a

series of practical laboratory exercises The 20 lectures are being published in book form (Holm,

editor)

In the field of radioecology, international intercomparisons of low-level radionuclide concentrations, measured in thoroughly homogenized samples, are organized routinely by the International Atomic Energy Agency (IAEA) in Vienna and Monaco Under the present Nordic programme, most of the old-established laboratories were already participants in the IAEA intercomparisons, and it was decided to urge the remaining laboratories to join However, two types of equipment of central importance for the surveillance of nuclear fallout, and for dose assessment, are normally not quality-assured on an international scale: large stationary air samplers and whole-body counters The reports in chapters 5.2 and 5.3 are therefore internationally unique The intercomparison of large stationary air samplers (chapter 5.2) was performed by

circulating two high-volume air samplers between the nine participating laboratories and operating them for two - six months parallel with the local air sampler The intercomparison included several types of filter material, including glass fibre as well as organic filter media During part of the test

period (1990-1993), air concentrations of 137Cs were too low for high-quality measurements The

natural radionuclide 7Be was therefore used as the main basis for the comparisons showing a difference of up to 15% when using one type of glass-fibre filters and no significant difference using another type of glass fibre This indicates that the quality of the data on radionuclides in air from the Nordic countries is surprisingly good

Whole-body counting is used for the determination of X- and y-emitting radionuclides in the human body Its use includes the surveillance of selected groups of the general public and of radiation workers for dosimetric purposes The intercalibration of 20 Nordic whole-body counting

systems (chapter 5.3) was performed by circulating a modular phantom system filled with

calibrated solutions of radiocaesium The modular phantom could simulate all varieties of whole- body geometries in use The observed quotient between measured and expected activity was 0.9 -

1.1 for most systems, i.e *lo% This is better than previously expected

Finally, two sets of homogenized samples intended for y-spectrometric analysis were distributed as a supplement to the above-mentioned IAEA sources The results from 26 laboratories given in chapter 5.4 are generally satisfactory, although there were a few unexplained outliers

INTERNAL DOSES TO THE NORDIC POPULATION

One of the aims of the RAD programme was to produce a good data background for the estimation

of doses to the Nordic population after the Chernobyl accident Furthermore this was a good basis

on which to make better predictions of population doses after any future nuclear contamination of various Nordic environments Two main approaches were used for the dose estimates: food intake (chapter 5.5) and whole-body counting (chapter 5.6)

The individual mean doses from radiocaesium intake with diet since the Chernobyl accident

in 1986 were determined for Denmark, Finland, Iceland, Norway and Sweden (chapter 5.5) The estimates were obtained by two methods The first used consumption data, i.e information on the amounts of food eaten by an average individual in each of the five countries The other method applied food production in the Nordic countries, ignoring the export and import of food but taking into account the amounts actually eaten The consumption method gave an individual mean dose

commitment of 1.3 mSv and the production method gave 1.0 mSv In comparison the external

mean dose, i.e the dose received from penetrating radiation emitted by radionuclides outside the body, was 0.8 mSv for the Nordic countries Figure 1.2.2 shows the relative intake of 137Cs from different diet groups in % since the Chernobyl accident by an average person in Denmark, Finland, Norway and Sweden The study emphasizes the importance of wild produce for the internal doses from radiocaesium More than 50% of the total 137Cs intake with the Nordic diet came from natural and seminatural ecosystems In this context it is unfortunate that information on the consumption of and radiocaesium concentration in wild produce is relatively scarce It is believed that the dose based on consumption data is an overestimate because of the lack of reliable information especially on wild produce, both with regard to amounts actually eaten and because the exact effective half-lives are not known Nordic critical groups with high consumptions of fungi, wild berries, reindeer, freshwater fish, elk, lamb and goat products may receive dose commitments from dietary intake that are 1-2 orders of magnitude higher than those of the general population Such groups are found in Norway, Sweden and Finland, in particular among the Lapp population It should, however, be kept in mind that remedial measures introduced in the Nordic countries after Chernobyl significantly reduced the exposure of these population groups After the Chernobyl accident whole-body measurements on selected population groups were performed in Denmark, Finland, Norway and Sweden Chapter 5.6 presents the mean internal

Table 1.2.1 A comparison between the Nordic countries of radioecological sensitivities in total diet for Chernobyl 137Cs

be that the biological half-life of radiocaesium in the Nordic countries is shorter than the internationally accepted values used in the calculation based on the food consumption data If so,

the whole-body content and the estimated dose would be lower than reported in Chapter 5.5 Other explanations could be that the selected whole-body groups were not representative enough, poor representativeness of the radionuclide concentration in samples used to estimate the radiocaesium content of the diet, or limited knowledge of the amounts of wild produce actually consumed These last explanations might further explain the large discrepancy found in Sweden, where the contamination level was extremely variable resulting in almost unattainable representativeness, and the better correlation in Denmark, where fallout was lower and much more homogeneously distributed

The introduction of the term radioecological sensitivity reveals that, on average, the Chernobyl-derived radiocaesium concentration in a diet produced in Norway would be 7 times higher than that of a diet produced in Denmark for the same ground surface deposition (Table 1.2.1) The radioecological sensitivity for 137Cs in diet is defined as the infinite time-integrated

Figure 1.2.2 Relative intake by an average person in Denmark (DK), Finland (SF), Norway (NO) and Sweden (SW) of 13'Cs from different diet groups in % since Chernobyl

concentration of 137Cs in the diet arising from a given deposition, Bq kg-' * yr / kBq m-* (Aarkrog,

1979) Table 1.2.1 also shows that, on average, a unit deposition in Finland would result in 3

times higher, and in Sweden and the Faroe Island 5 times higher diet concentrations than in Denmark However, as food production in Denmark is much greater than in the other Nordic countries, contarnination in Denmark might give rise to a larger population dose if no countermeasures were introduced By comparing the radioecological sensitivity for Chernobyl 137Cs

in a diet produced in Denmark with comparable values found earlier for global fallout (Aarkrog,

1979), it is seen that the transfer of global fallout was transferred 2.5 times more efficiently to man

than the Chernobyl debris* The primary reason for this is seasonality (chapter 3.2), which

resulted in lower 137Cs concentrations in the production of especially grain and milk during the first year after the Chernobyl accident than seen for similar depositions of global fallout

REFERENCES

Aarkrog, A (1979) Environmental Studies on Radioecological Sensitivity and Variability with Special Emphasis on the Fallout Nuclides ?Sr and I3'Cs Rise-R-437

Holm, E (editor) Radioecology Lecture Notes in Environmental Radioactivity World Scientific

Publishing Co., Singapore (1994, in press)

NKS (1991) Radioecology in Nordic Limnic Systems - Present Knowledge and Future Prospects SNV Report 3949

* For total Danish diet 1963 - 1976, the radioecological sensitivity was 4.2 Bq 137Cs (g K)-'

per kBq 137Cs m-2 or 1 1 Bq 137Cs kg-I per kBq '37Cs m-2 (Aarkrog, 1979)

AQUATIC ECOSYSTEMS

2.1 INTRODUCTION TO AQUATIC ECOSYSTEMS

MANUELA NOTTER', JOHN E BRITTAIN' & ULLA BERGSTROM'

'Swedish Environmental Protection Agency, 171 85 Solna, Sweden

'Freshwater Ecology and Inland Fisheries Laboratory (LFI), University of Oslo, Sars gate 1,0562 Oslo, Norway

3Studsvik Eco and Safety, 61 1 82 Nykoping, Sweden

SUMMARY

This paper summarizes the background, objectives and major results of the NKS programme on aquatic radioecology and serves as an introduction to the more detailed research papers The programme included both marine and freshwater studies

INTRODUCTION

The NKS RAD-2 programme on aquatic radioecology continues a long Nordic tradition in co-

operative work concerning the behaviour of radionuclides in aquatic ecosystems In a previous

Nordic project (Nilsson et al., 1981) the environmental status with regard to radioactive pollution

in the seas surrounding the Nordic countries was studied using the seaweed, Fucus vesiculosus Fucus samples were analyzed for their content of radionuclides and distribution patterns and turnover times were obtained More recently there has been a need to verify previous models and compare the behaviour of Chernobyl caesium with earlier results

From studies of fallout in the 1960's (Kolehmainen et al., 1966; 1967; 1986; Hasanen et al., 1963; 1967; 1968) it was known that predatory fish in oligotrophic lakes reach high concentration levels of caesium It was also known that different fish species reach varying caesium levels depending on feeding habits (Hannertz, 1966; 1968)

The Chernobyl accident took place four years prior to the start of the present programme Oligotrophic lakes predominate in northern Scandinavia and fish from these lakes rapidly reached high concentrations of caesium in areas with high fallout rates There was a considerable interest from the authorities for models to predict caesium concentrations in fish as the consumption of freshwater fish is the major source of the dose to the Nordic populations received via the aquatic food web Model development and validation were also given high priority internationally Several international studies were initiated to create and verify radioecological fish models

OBJECTnTES

The three main objectives of the RAD-2 project were to:

- collect data for developing and evaluating models for the prediction of caesium concentration in fish for different types of Nordic lakes,

- earlier studies of the concentration of radionuclides in the bladderwrack Fucus

vesiculosus and to compare the uptake in Fucus with the accumulation rates in other algae,

- secure data for a relevant calculation of the dose to the Nordic population from the aquatic environment and to compare the dose contributed by Chernobyl with the dose received by radiation from natural sources,

Numerous participants from all the Nordic countries have worked on the programme,

although in most cases RAD-2 has only given limited financial support However, it has made it possible for Nordic scientists in the field of aquatic radioecology to meet in small groups to discuss mutual problems and to co-operate Six seminars/workshops were held under the auspices of the programme RAD-2 has had a total budget of Dkr 1.2 million, but the participants and their institutions have contributed substantially both in terms of funding and in personal involvement Their joint efforts have also permitted the presentation of ongoing research projects outside RAD-

2, thereby contributing to the success of this work

BACKGROUND AND MAIN RESULTS

Carlsson et al (1994) report the results from the efforts that were put into repeated Fucus

investigations in 1991 in order to provide a picture of caesium distribution in the Nordic sea basins

after Chernobyl The accumulation rates and biological half-lives in Fucus are compared with those

of other algal species, particularly benthic diatoms A summary of the results was presented at the Nordic Radioecology Seminar in June 1992 (Carlsson et al., 1992)

Resources were also directed towards assessing the radiation dose that can be received by the population through fish consumption Several radionuclides were measured in herring, cod, perch and char Fish also contain certain amounts of natural radionuclides, including 2'%, which

will contribute to the dose As very few data are available, this programme has encouraged analyses providing improved dose calculations for 2"%'o in fish from Nordic waters (Holm et al., 1994)

In addition to the importance of radiocaesium in the aquatic food chain in terms of dose

to man, fallout from Chernobyl has an enormous potential as an ecological tracer Radionuclides

in general, and certainly Chemobyl caesium, have been and will indeed continue to be used as tracers to monitor and elucidate basic ecological processes Meili (1994) provides a review of such studies

One of the main concerns after the Chernobyl accident was the concentration of I3’Cs in the aquatic food chain and particularly in freshwater fish In lakes the main exposure pathway of I3’Cs to man is through the consumption of freshwater fish Highest priority and considerable RAD-2 resources were given to studies of the behaviour and bioavailibility of caesium in freshwater systems The main part of this chaper gives the results of these studies

Largely through co-ordinating of results from ongoing work in the Nordic countries, it was possible to study the influence of lake morphology and hydrology on caesium concentrations in fish

and also within the relevant food webs It was possible to elucidate the major factors determining

concentrations in freshwater fish and in freshwater ecosystems in general, thereby contributing to dose assessment studies The identification of the important parameters determining radionuclide concentrations in fish also permits the development and assessment of potential remedial measures

in aquatic ecosystems

As a result of processes associated with the last Ice Age, lakes are a typical feature of the landscape in the Nordic countries This is especially striking in Finland, although there is also a high incidence of lakes both in Norway and Sweden In the Nordic countries, freshwater fishing

is therefore widespread, both as a leisure activity and a commercial undertaking Sports fishing

is also an integral part of the tourism associated with the unspoilt countryside and pristine environments typical of the Nordic countries In many areas freshwater fish also form an important part of people’s diet and there are several traditional methods of preparation

Caesium accumulates in fish muscle because of its chemical similarity to potassium This accumulation is most pronounced in freshwater and is of particular importance in the Nordic

countries where ionic concentrations in freshwaters are generally low However, Nordic lakes differ widely in many other characteristics For instance there are wide differences between lowland, coastal lakes and high altitude, mountain fresh waters in terms of, for example, temperature and fish species Winter ice cover is also a feature of importance for many lakes, especially as much of the Nordic countries was still covered in ice and snow at the time of the Chernobyl accident

The environmental impact of radionuclide releases from nuclear installations can be predicted using assessment models However, many of the models were developed and tested on the basis of the fallout from nuclear weapons testing in the 1950s and 1960s, or from laboratory experiments In contrast, fallout from Chernobyl constituted a single mdionuclide pulse which entered natural, agricultural and urban ecosystems at the end of April 1986 The fallout was also