LONG-TERM ENVIRONMENTAL BEHAVIOUR OF RADIONUCLIDES
François Bréchignac, Leif Moberg, Matti Suomela RECENT ADVANCES IN EUROPE

CEC-IPSN Association Final ReportIn December 1996, the Institut de Protection et de Sûreté Nucléaire
(IPSN) signed an Association contract (F14P-CT96-0039) with theEuropean Commission (EC), Directorate General Research.

Within the framework of the Association Contract, research in radiation
protection was carried out in the fields covered by the Fourth Framework
Programme on Nuclear Fission Safety. The contract running over a period of
36 months from January 1, 1997 to December 31, 1999, contained 3 projects, which were executed by a total of 18 partners from all over Europe
including Norway as a non EU member state funded by its own government.
The contract value amounted to 4,2 MECU, with the contribution from thecommission of up to 2,3 MECU.
IPSN has born the overall responsibility for coordination of the workwithin three multinational projects. Each project was managed by a scientificproject leader coordinating the scientific work ; Dr François Bréchignac,
IPSN, FR, for the PEACE project, Dr Leif Moberg, SSI, SE, for the
LANDSCAPE project and Dr Matti Suomela, STUK, SF, for the EPORA
project. The implementation of the association contract was supervised bya steering committee consisting of EC and IPSN representatives. IPSN wasproviding the secretariat and administrative support to the committee.
Chairmanship was assumed by Mr. Ezio Andreta, then Mr. Hans Forsström
for EC and Pr. Henri Métivier for IPSN.
The association contract covered the following topic "Evaluation ofradiation risks: quantification of parameters which determine the fluxesof radionuclides in ecosystems, and long-term consequences of accidental
contamination in semi-natural environments".
The overall objectives of the PEACE project aimed at assessing the impactof the radioactive contamination on agricultural environments by accidental
releases of caesium and strontium radioisotopes from a nuclear power plant.
Research efforts focused on studies of the soil-to-plant interface processes
with special emphasis on the quantification of key parameters which influence and govern the fate of Cs and Sr in soils and their transfer to plant crops.
The objectives of the LANDSCAPE project were to obtain a basis forreliable assessments of the radiation exposure to man from radionuclides inplant and animal systems of semi-natural (forest) ecosystems in Europe under
different time scales. The work included studies of the seasonal and annual
variations of the radionuclide content in the main above-ground biological

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1components of different representative forest ecosystems, the estimation ofradioactive caesium flow between these biological components and the soil,and quantification of the impact of classical forest management on the radionuclide contents and fluxes within the vegetation.
The objective of the EPORA project was to evaluate the potential effectof industrial pollution on migration of radionuclides in soil, on radionuclides
association in different soil constituents and on transfer of radionuclides fromsoil to plants. The potential impact of industrial pollution on runoff of radionuclides as well as radiation doses has also been studied. Therefore, an assessment was made of the current pollution status in the Kola peninsula withparticular emphasis on the Monchegorsk area in Northern Fennoscandia.
The integration of these three projects within this association created aunique opportunity to link research efforts together, by bringing about experimental data under laboratory conditions and research concerned with the
production of field data bases, therefore allowing for a confrontation between
the different approaches with their underlying concepts for modelling. This
report shows the permanent effort of integration of the three projects and provides a good illustration of the european synergy. In this report an overview
of the output results from this synergy is given. For more information on thethree projects readers should refer to the final project reports listed at the endof this document.
The success of this integration is mainly due to the constant efforts of thethree projects leaders, François Bréchignac, Leif Moberg and Matti Suomela.
Working with them was a constant pleasure and a permanent enrichment.We
wish to thank them for their European spirit along the three years and thanks
to such scientists we can be confident in the future of the scientific Europe.
The association chairmen wish to gratefully acknowledge the three project
leaders but also, the members of the association, Jean-Claude Barescut,
Martine Contini, Gilbert Desmet, Laurent Le Yanc, Jack Sinnaeve, Martine
Wauters, Ernst H. Schulte, Remi Seydoux, and more especially our secretary
Stéphane Lorthioir and Martine Jacquard who prepared all the association
meetings with her usual efficacy.
Pr. Henri MÉTIVIER
Director of Research IPSN

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Mr Hans FORSSTRÖMHead of Unit DG RTD-DII-3 EC

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R E P O R TWhat have we learnt?
■ It is of paramount importance to know the soil solution composition in order to under-

stand radionuclide transfer to plants.
■ On untilled mineral agricultural soils, the migration of 137 Cs and of 90 Sr remain simi-lar, and the depth profiles are established early on, with very slow further evolution.
■ On the forest podzolic soils studied, migration of 137 Cs is pronounced, with increased

amounts in the mineral layer ten years after an aerial deposition.
■ The classically used K D , as determined in vitro , does not allow an acceptable predictionof migration. The initial soil structure and hydric conditions upon contamination areimportant.
■ During the past decade, there is a general decrease of 60-80 % in 137 Cs concentrations

in ground vegetation, fungi, mosses and lichens at both temperate and boreal forestsites studied.
■ More than a decade after Chernobyl, the total inventory of 137 Cs is still rising in pinetrees of boreal forests.
■ The forest models currently developed yield agreeing estimates of the 137 Cs concen-

trations in the different compartments of the ecosystem, taking natural variability into
account.
■ An increasing load of heavy-metal pollution in boreal forests modifies the radionuclides

status in podzolic soils and their subsequent transfer to plants.
■ Fertilisation can be a beneficial tool for restoring contaminated forests, as well as forthe remediation of the state of agricultural lands in severe fallout situations.
■ There is almost no 137 Cs loss via runoff water from boreal forest ecosystems except

from the wetter portions of bogs.
■ Spatial variations in radionuclide deposition are dominant and largely cancel out evo-lution over time and the influence of climatic intermittence.
■ Variability of 137 Cs uptake by moose is caused more by spatial variation in deposition

and the normal movements of the animal than by variations in diet selection or intake.
■ The 90 Sr contamination of plant food products is important for internal dose assess-ment and may be affected by additional non-radioactive pollution.

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EPORA
NorwayPEACELANDSCAPE
UnitedKingdom

PEACE

EPORA

LANDSCAPE

Germany

Belgium

France

Spain

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PEACE

PEACE

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R E P O R TKola Peninsula

LANDSCAPE
PEACE

EPORA

LANDSCAPE

Finland

EPORA
SwedenEPORA
RussiaLANDSCAPEPEACELANDSCAPE

Italy

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5François Bréchignac: Institut de Protection et de Sûreté Nucléaire, IPSN, France.
Leif Moberg: Swedish Radiation Protection Institute, SSI, Sweden.
Matti Suomela: Radiation and Nuclear Safety Authority, STUK, Finland.
Moose photo on cover page: Per Claesson, Bildhuset
Copyright 2000 - Mission communication IPSN
Conception: Penez Communication - Tel: (33) 01 48 78 07 70

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SUMMARY

8 |

■

■

Introduction

■

10 |

Redistribution in the soil-plant system

■

29 |

Modelling■

38 |Countermeasures (fertilisation)

■

44 |

Runoff■49 |Spatial variations

■

56 |

Dose assessment implications

60 |I P S N - C E C«What is still needed ?»A S S O C I AT I O N

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INTRODUCTIONT

he widespread radioactive environmental pollution which resulted from atmospheric nuclear weapons testing during the mid-years of this century prompted
the first concern among the scientific community about its potential impact onhuman health. Although the development of the civilian nuclear industry has evolved with a parallel effort of mastering the associated risks, the Chernobyl accident
in 1986 revealed, on a global scale, the radiological impact of radioactive pollutionof the environment. Assessing the resulting radiation doses that humans might receive, either by exposure from radionuclides on the ground or by internal ingestion (via
food), requires a good understanding of the long-term behaviour of radionuclides inthe environment. This knowledge constitutes a basis for the prevention goals ofradiation protection.

This document reports on a joint European effort to advance this understanding,placing particular emphasis on the soil-plant system of semi-natural ecosystems andagricultural land. The problem has been tackled through various converging andinnovative approaches to the long-term behaviour of the radionuclides 137Cs, 90Srand 239/240Pu. The approaches range from in situ experiments, designed to exploit
past contamination events, to laboratory simulations in controlled conditions ofaccidental contamination, in view of mastering the wide variability of the naturalenvironment. Particular attention has been devoted to the philosophy of experimental data acquisition in order to secure the various modelling developments
undertaken with appropriate validations. A broad scope of different ecosystems,
ranging from arctic and boreal regions down to Mediterranean ones, has been considered, with emphasis on forests and agricultural land, where food production takes
place. Up to 22 different site locations scattered throughout this territory have been
investigated, reflecting a wide, and representative, variety of European soils and climatic conditions. A brief description of the various ecosystems and soils considered
Table 1is given in Table 1.
Long-term behaviour of radionuclides in these ecosystems are most susceptible totheir vertical distribution and migration in the soils, as well as to their availability
and uptake by plants and animals, processes which have been examined particularly
closely, within time-frames ranging between a few years to several decades. Finally,
the occurrence of additional non-radioactive pollutants in many ecosystems, which
could invalidate our current prediction pertinence, has been questioned for the firsttime with respect to their potential influence on radionuclide movements.
This report is focused on six different themes, each of which having been studied at least in two of the three projects: redistribution in the soil-plant system,
modelling, countermeasures, runoff, spatial variations, and dose assessment.
More extensive information on the project results can be found in the final
reports of the individual projects (see short reference list).
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INTRODUCTION■◗ Table 1 : Main soil characteristics of the various ecosystem/site locations investigated.

Geographical
Site

Ecosystem
Type

Soil type
Soil texture

Mol (Belgium)

Agricultural

Jülich (Germany)

AgriculturalBarcelona (Spain)

Agricultural

PodzolSand
Luvisol
Silt loam
Luvisol

Agricultural

Loam calc.
Fluvisol

Belleville (France)
Wellesbourne (U.K.)

Agricultural

Hille (Sweden)

ForestLångsjön (Sweden)

ForestLoamy sandFluvisol
Sandy loam
PodzolFerricPodzolPrylen (Sweden)

ForestPodzolVindeln (Sweden)

ForestRegosolLiesineva (Finland)

ForestPeatlandSiikakangas (Finland) Forest
ForestPodzolFerricPodzolMonchegorsk (Russia) Forest

PodzolLapland (Finland)

1 Tilled layer

a pH (KCl)

2 Organic layerb pH (CaCl )2n.d. Not determined

3 Mineral layer

Soil
Particle size
layer % clay % silt % sandpH

CEC
Organic(cmol/kg) matter %

P1

4.1

14.6

78.3

4.6a

11.7

3

P1

11.2

78.8

8.4

7.1a

13.4

1.5

P1

13.9

28.8

47.7

7.3a

16.4

2.3

P1

5.8

13.7

79.0

4.1a

5.8

1.5

P1

9.5

19.7

66.9

6.3a

17.8

3.9

O2
M3
O2
M3
O2
M3
O2
M3
O2
M3
O2
M3
O2
M3
O2
M3

n.d.
1.9
n.d.
3.7
n.d.
3.4
n.d.
<11
n.d.

n.d.
8.9
n.d.
28.1
n.d.
17.1
n.d.
26.1
n.d.

n.d.
89.2
n.d.
67.5
n.d.
79.5
n.d.
69.7
n.d.

3.5b
4.2b
3.6b
4.1b
3.7b
3.9b
3.4b
4.4b
3.2b

n.d.

58.2
2.0
43.8
5.0
53.6
5.1
66.8
5.2
95.2

n.d.
2.6
n.d.
2.4
n.d.
1.3

n.d.
17.5
n.d.
7.5
n.d.
8.2

n.d.
66.3
n.d.
90.1
n.d.
90.5

3.1b
4.1b
3.0b
3.7b
3.0b
3.8b

n.d.

n.d.
n.d.
n.d.
n.d.

193
24
206
30

59.1
6.8
79
3.2
76
8.6

It should be borne in mind that forest podzols are fundamentally different fromagricultural soils. Forest podzols present a clear multilayered vertical structure
characterised mainly by a clay-poor mineral layer (sand) which supports anorganic layer rich in organic matter (>50 %). In contrast, agricultural soils present reduced amounts of organic matter (a few %) associated with higher clay
contents.

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1 REDISTRIBUTION IN THE SOIL-PLANT SYSTEM●

Agricultural ecosystems●

Forest ecosystems (podzols)●

Forest ecosystems submitted
to additional pollution by heavy metals

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A G R I C U LT U R A L E C O S Y S T E M S| Redistribution in the soil-plant system

Agricultural ecosystems

These data have been obtained fromlong-term experiments carried out in a
dedicated facility designed for simulating, in fully controlled conditions, anaccidental deposition of radioactive
aerosol contaminants. The facility
hosts various soil monoliths sampledthroughout Europe, which are monitored in lysimeters with advanced
control over hydrological fluxes, andconducted under artificially reconstructed and computer-controlled climatic conditions.

On a contaminated soil, the long-term
pollution of plant food products occurs
via root uptake. Prediction models
have first tackled this problem byapplying a “transfer factor” coefficientdefined as the ratio between the specific activity in the plant and the specificactivity in the soil. This empiricalapproach, however, suffers from highand poorly documented variabilities,
which can largely be accounted for by
the plant species considered, but also
by the complexity and diversity of thesoil compartment. This is illustrated by
the 137Cs and 90Sr transfer factors
which have been measured simultaneously on five distinct soil types, withvariable respective contents of clay,
loam and sand, for three different plant
consumables: barley grains, bean pods
and lettuce.
figure 1

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The classification of the observed
transfer factors does not always agreewith soil physico-chemical characteristics alone. For 137Cs in particular, thisis due to complex variations of the soil
solution composition, which is a function, not only of soil type, but also of
a number of other parameters such as
soil moisture, climate, fertilisation androot uptake activity. The “soil solution” composition is of paramountimportance, since this is the very place
where roots absorb radionuclides
along with dissolved mineral
nutrients. Predictions have been refined by introducing the “KD” concept,
defined as the radionuclide partition
coefficient between the soil liquid andsolid phases, reflecting either theimmobilization potential of a given
soil for a radionuclide (retention on
the solid matrix), or its availability toplants (presence as solute in the liquid

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Redistribution in the soil-plant system | A G R I C U L T U R A L E C O S Y S T E M S

137Cs Root Transfer (Concentration Ratio)

CR (Bq/kg) / (Bq/kg)■◗ figure 1
137Cs and 90Sr root transfer(as concentration ratios,
Bq.kg-1 in plants /Bq.kg-1 insoil) obtained on five distinct
agricultural soils for lettuce,bean pods and barley grains.
PEACE

Soils types

CR (Bq/kg) / (Bq/kg)

90Sr Root Transfer (Concentration Ratio)

KD 134Cs (% change with respect to saturation)

Soils types■◗ figure 2
Influence of soil moisture
on KDCs.
PEACE

Soil water content (% with respect to saturation)
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A G R I C U LT U R A L E C O S Y S T E M S

phase). This approach has made it
possible to take into account the wellknown competition occurring between Cs and K for fixation on clays,
or between Sr and Ca for adsorption
on the argilo-humic complex, which
both influence the soil solution
content. Limits are imposed on thisconcept by the equilibrium nature of
the KD coefficient, which is further
often determined in water-saturated
conditions. Such conditions are rarely
actually encountered in nature, due forexample to the continuous pumping
activity of the roots or climate-driven
variations in soil moisture.
Based on a series of in vitro experiments, soil moisture is indeed
demonstrated to have a marked
influence on the radionuclides concentration in the soil solution. ForI P S N - C E C| Redistribution in the soil-plant system

example, reducing soil moisture promotes an increase in Cs concentration,
thereby reducing its KD, tending tofigure 2favour root uptake.
In parallel, the K concentration is also
increased, to an extent proportionallyeven greater than for Cs (Cs/K lower
for
reducedsoil
moisture).
Furthermore, considering the root
uptake, it has been confirmed that
increasing K in the soil solution
reduces 137Cs uptake due to competition for the transport systems. The
ultimate 137Cs root uptake, and subsequent plant contamination rate,
results from a combination of theseeffects. This demonstrates the central
role played by the soil solution composition as a key element contributing
to the variability of transfer factors.
This is further supported by modelling

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Redistribution in the soil-plant system | A G R I C U L T U R A L E C O S Y S T E M S

137Cs Vertical Migration

90Sr Vertical Migration■◗ figure 3
137Cs and 90Sr migration

profiles observed 4 years
after contamination onvarious agricultural soils.

Depth (cm)Depth (cm)PEACE■◗ figure 4
137Cs Migration Evolution

90Sr Migration Evolution

137Cs and 90Sr migration evolution

during three successive years on an«Silt loam» soil depth (cm)«Silt loam» soil depth (cm)untilled silt loam soil installed in anadvanced lysimeter facility withhydrological and climatic control.
Experimental contamination by
aerosols was performed in 1994.
PEACE

Silwood Caesum and Strontium Activity Profiles
Activity concentration (Bq/g)■◗ figure 5
Cs and Sr profiles observed

Depth (cm)after 1, 3.5 and 8 months following contamination in an
undisturbed soil driven incolumns submitted to a highhydrological flux.
PEACE

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developments of root uptake, which
reveal that soil type and climaticconditions act on the soil-to-planttransfer essentially via the chemicalcomposition of the soil solution andthe physiological features of theplant: K and plant growth for 137Cs
transfer, Ca and transpiration for 90Sr
transfer.
When attempting to understandmigration patterns, the first elements
are furnished by chemistry, whichindicates that the high potential
mobility of 137Cs, due to its significant solubility, is counteracted by itsvery specific and efficient capture
within clay particles (illite, in particular). Conversely, the lower potential
mobility of 90Sr, due to its lower solubility, is not counteracted to the same
extent by specific fixation sites on thesoil matrix. This results in clearly distinct KD values for the two radionuclides, as determined in vitro, fromwhich a higher migration rate is
expected for 90Sr than for 137Cs after
several years. However, experimental
observations do not fit this theoretical approach.
On the one hand, the two radionuclides developed migration profiles,
on a given agricultural soil (untilledplots), which still show similar shapes
four years after the contamination

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deposition. Even the soil type, which
is traditionally characterized by aradionuclide-specific KD coefficient,does not significantly alter the obserfigure 3
ved profiles.
On the other hand, the low rates of
migration observed in the long term(around 1 cm/year in the years following contamination) cannot explain
figure 4
the shape of the profiles.
In the shorter term, when experimentally forcing migration on soilcolumns with a high hydrologicalflux, the two radionuclides exhibit
profiles which are established within
one month, with very limited further
figure 5
evolution.
Altogether, these observations strongly suggest that the migration profiles
are established very early after contamination, under the influence of initial processes that do not depend primarily on the soils’ KD coefficients, as
determined in vitro. Their evolution issubsequently very slow. This indicatesthe importance of the early conditions
prevailing immediately after contamination, such as soil moisture and firstrain events, which may be paramountin determining the extent to whichradionuclides will penetrate in depth.
This aspect particularly deserves further consideration.

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Redistribution in the soil-plant system | F O R E S T E C O S Y S T E M S ( P O D Z O L S )a) Hille Cs-137 (%)b) Langsjön Cs-137 (%)c) Prylen Cs-137 (%)d) Siikakangas Cs-137 (%)e) Vindeln Cs-137 (%)■◗ figure 1
The vertical distributionof 137Cs (%) in the various
horizons of forest soils in
Fennoscandia:a) Hille, b) Långsjön,c) Prylen, d) Siikakangas ande) Vindeln.
LANDSCAPE

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F O R E ST E C O S YST E M S ( P O D Z O L S )| Redistribution in the soil-plant system

Fo r e s t e c o s y s t e m s ( p o d z o l s )In contrast to agricultural soils, theforest podzol soils are characterized
by a multi-layer structure, or horizons: organic horizons (Ol=non-fragmented litter, Of=fragmented organic
matter, Oh=humified organic matterand the OAh and Ah horizons which
are organic-rich mineral horizons),
and mineral horizons (A and B).
From studies after the Chernobyl accident, it is known that most of the caesium during the first years was locatedin the raw humus layers. The vertical
distributions of 137Cs in podzol soils
in the regions of this study show atrend towards redistribution from thevegetation and raw humus layers
figure 1
down to the mineral layer.
By 1995 to 1998 after deposition,
between 20 and 40% of the original
deposit had reached the mineral layer.
Although there is a general trend to
downward migration, the depth distribution varies between different locations. The soil particle distribution
affects the hydraulic conductivity andcapillarity. Dense soil with low hydraulic conductivity and high capillarity
will probably be more effective in retaining caesium in shallow layers due toslow percolation, high ion-exchange
capacity and an upward water flow
during warm periods. Biotic factors
may also lead to variations in soil
microflora which may influence thecaesium distribution. The depth distribution is further affected by differences

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in clay content in the mineral layer
which, in areas with high contents, may
trap caesium in the mineral fraction.

The vertical redistribution of radiocaesium in podzol soils is also reflected asa decreasing rate in photon fluence asmeasured by in situ gamma spectrometry. Between 1986 and the late 1990´s,
the photon fluency at 662 keV decreased faster by a factor of at least two
than what would have been expectedfrom the physical half life of 137Cs.
Except for the exponential decrease,temporal fluctuations up to a factor of
two were observed. These are due tovariations in soil moisture and lead tolower external doses during winter,spring and autumn compared to thesummer.

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Redistribution in the soil-plant system | F O R E S T E C O S Y S T E M S ( P O D Z O L S )■◗ figure 2
Tag (Bq/kg) / (kBq/m2)

Temporal changes of 137Cs (Tag)in green parts of heather andcurrent shoots of young Scots
pine for three regions:Saint-Léger, Belgium (red);
Hille, Sweden (blue) and
Vindeln, Sweden (green).
LANDSCAPE

Tag (Bq/kg) / (kBq/m2)

Time (years after the Chernobyl accident)

Time (years after the Chernobyl accident)

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F O R E ST E C O S YST E M S ( P O D Z O L S )The changes in the vertical distributionof 137Cs in soil have implications forplant root uptake, which, depending on
species, can cause either an increase ora decrease in the uptake of caesium. At
both boreal (Hille) and temperate sites(Belgium and Luxembourg), plants on
average lost 70% of their activity overthe past decade. In relative terms,
however, major differences were observed in connection with this loss, whichsurprisingly tallied with the taxonomic
families. For instance, most of theplants in the Asteraceae, Fabaceae andLiliaceae families were characterised bya loss exceeding 70%. In contrast, theloss in most of the grasses and Rubus
species was considerably less than
70%. The loss in Ericales and ferns wasin the middle range.
The relationship between rooting depth
and radiocaesium migration may
partly explain the differences in thecontamination trends of plants. This isundoubtedly the most likely explanation in the case of the shallow-rooting
Oxalis acetosella and in pine, which
has a deep tap root. Furthermore, thecontribution of successive cohorts ofever deeper-rooting mycorrhizal fungiin this species cannot be excluded.
Most of the radiocaesium stored in the
Liliaceae runners has probably been lostto the soil surface horizon, in which
there has been a general decrease of
137Cs due to migration. On the otherI P S N - C E C| Redistribution in the soil-plant system

hand, the fibrous rootsystem of grasses
enables them to maintain firm anchorage in deeper humiferous horizons thatare still relatively heavily contaminated.
Ericales and ferns often have runningroots. However, they also produce
numerous, more or less fibrous, adventitious roots that explore deep soil
layers. One should also bear in mind
that these plants are mycotrophic, andtherefore the buffer role of mycorrhizal
fungi in the decontamination of these
species cannot be precluded.
Aggregated transfer factors, Tag(Bq.kg-1 per kBq.m-2) can be used tocompare data from different sites.
Such a comparison shows that the Tagvalues in vegetation ranged from 0.2
to 241 (10-3 m2.kg-1). The lowest
values were found in young plants ofdeciduous trees and in herbs, while thehighest values were found in dwarf
shrubs. On average, the general trend
for 137Cs in the vascular plants investigated from seven studied sites was:
Salix spp < Betula spp < Epilobium
angustifolium < Deschampsia flexuosa< Pinus sylvestris < Vaccinium spp <Calluna vulgaris, with the same variations between the sites.
A comparison of the long-term annualchanges in aggregated transfer factors
shows that the activity in heather(Calluna vulgaris) changed in a very
similar way over time for the sites
figure 2
studied.

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Redistribution in the soil-plant system | F O R E S T E C O S Y S T E M S ( P O D Z O L S )For Scots pine (Pinus sylvestris), the Tagvalues have increased dramaticallysince a few years after the deposit.
Although the Tag amplitudes are different, the rate of increase is equal between the sites, indicating (as in the caseof Calluna vulgaris) that a general process is at work. This can be a protracted
redistribution of Cs in the forest floor
from the mosses and litter layers down
to the humus and mineral soil, wherepine roots are found. The monotonously increasing Tag values in young pinesneed further investigation, since thismay be of significance for external
doses, internal doses via meat frommoose and gallinaceous birds, for forestry in general (biofuels) and the steadystate levels for the different compounds
in the forest ecosystem.
Mushrooms are the most heavily

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contaminated organisms in forest ecosystems and many of them play a direct
and significant role in the contamination of food chains by radioactivity.
The contamination and decontamination curves of mushrooms reflect theevolution of the activities in the various
soil horizons. This characteristic has tobe considered in the light of the specificuse of soil horizons by the mycelium ofthese organisms. The data available
indicate an overall reduction of 137Csconcentrations in mushrooms between
1991 and 1998. When comparing the
average activity, during this period, ofobligate mycorrhizal species (usuallycharacterised by a deep mycelium)with that of facultative mycorrhizal
species (which have a more superficial
mycelium), a reduction of 60% and
80% is observed, respectively.

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F O R E ST E C O S YST E M S ( P O D Z O L S )A rough assessment of the proportionof caesium retained in fruitbodies intheir growing area shows that the average value in Cortinarius alboviolaceusis was about 5% of the deposition,
whereas it varied from 1.3 to 1.7% inother mushrooms. In mushrooms thathave lost 70% of their contamination
over the past seven years, one can estimate that at least 5% of the total
deposition had been retained at thetime of maximum fruitbody contamination. There is a need for continuing
the investigations on the role ofmycorrhizae in the active radiocaesium transfer from the soil to hostplants.
Trees are often the most significant
component in a forest ecosystem froman economical point of view.
Concentrations of radiocaesium in different parts of trees vary, and are changing with time. The use of trees inforest industry and the question ofaccess of people to heavily contaminated forests motivate analysing the distribution of man-made radionuclides
in trees in the short and long term.
Root uptake adds to the radionuclide
content of the tree roughly in proportion to growth intensity and thusincreases the radiocaesium content of
the tree which originates from metabolised, initially deposited, radiocaesium.

I P S N - C E C| Redistribution in the soil-plant system

This caesium will be found in bothabove-ground parts and in roots, andvaries with the season of the year.
Growth dynamics cause fluctuation inradiocaesium contents in conifer
needles of different ages during the
growth period. Different growth
conditions add to the variation between sites.
There is an overall increase in 137Csconcentration in the stem wood of pine
between 1991 and 1997. The concentration of 137Cs in the new growth oftwigs and needles of these trees figure 2
has also increased during the period between the two samplings, due to root
uptake. The caesium concentrations arehighest in the youngest twigs, which isconsistent with other measurements.
The total activity, in percentage of theground deposition, stored in the aboveground parts of the trees of the older
stand has increased from 1.1% in 1991
to 2.0% in 1997.

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Redistribution in the soil-plant system | FOREST ECOSYSTEMS SUBMITTED TO ADDITIONAL POLLUTION BY HEAVY METALS

Soils■◗ figure 1
Characterisation of the(mg.kg-1)

heavy metal pollution
gradient generated aroundthe smelter. Illustration of
the soil contents in Cu andexchangeable K observed at
7 up to 152 km from thesmelter, and the corresponding plant content in Cu andK as measured within 4
understorey plant species.

(mg.kg-1)

EPORA(mg.kg-1)(mg.kg-1)

PlantsDistance from smelter (km)22

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FOREST ECOSYSTEMS SUBMITTED TO ADDITIONAL POLLUTION BY HEAVY METALS | Redistribution in the soil-plant system

Fo r e s t e c o s y s t e m s s u b m i t t e d t o a d d i t i o n a lpollution by heavy met als

The Severonikel smelter atMonchegorsk, Kola Peninsula, has
released huge amounts of SO2, Ni and
Cu into the atmosphere since its
construction in 1938. As an example
the annual emissions released in 1984
amounted to about 270,000 tons for
SO2, 3,200 tons for Ni and 2,400 tons
for Cu. Annual emissions had been
reduced by about one half in 1994 but
although decreasing, considerable pollution of the surrounding environmenthas been going on. This pollution has
caused a dramatic alteration in thevegetation status as observed in thevicinity of the plant.
A strong pollution gradient has been
generated around the smelter, as illustrated in figure 1 . The concentrations

was located 152 km from the smelter).
The total concentrations of Ni and Cu
in the organic layer increase regularly,
from about 10 mg.kg-1 at the referencesite up to about 5,000 mg.kg-1 at themost polluted site. Near the smelter (7 km),concentrations in the underlying mineral horizons are also higher, indicatingsome vertical migration from the surface
layers, but the trends observed indicatethat only a very small fraction of themetals has leached to levels lower thanthe maximum sampling depth. The
total amounts of nickel or copper at agiven site may therefore be used torepresent the integrated pollution effectat that site, which can be compared tothe other sites. Only minor changes areobserved in soil pH and cationexchange capacity with distance fromof heavy metals in the upper soil horizons(litter and O horizons) show a very
sharp increase as distance from thesmelter decreases (the reference site

the smelter, their respective vertical
distribution being usual for such
podzols. The heavy-metal accumulationin plants displays a similar trend, withI P S N - C E C

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Redistribution in the soil-plant system | FOREST ECOSYSTEMS SUBMITTED TO ADDITIONAL POLLUTION BY HEAVY METALS

Litter% activity withrespect to total■◗ figure 2
Influence of heavy metal loads
on the distribution of 137Cs, 90Srand 239+240Pu in the litter, theroot zone (O and E horizons)and below the root zone, expressedas percentages relative to thetotal inventories in the overallsoil profile.

Root zone% activity withrespect to total

EPORA% activity withrespect to total

Below root zone

Distance from smelter (km)Cs sequential extractions% of total Cs in
the organic layer■◗ figure 3
Influence of heavy metal loads
in the soil organic layer on
the 137Cs exchangeable andpersistently bound fractions as
determined through sequential
extractions.
EPORA

Distance from smelter (km)24

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FOREST ECOSYSTEMS SUBMITTED TO ADDITIONAL POLLUTION BY HEAVY METALS | Redistribution in the soil-plant systemhigher concentrations in the vicinity ofthe smelter.
In view of this pollution gradient, it isof great interest to examine how thepresence of heavy metals is affecting
the soil nutrients status and their
uptake by plants. Concentrationsof exchangeable K, Mg, and Ca all
exhibit a strong depletion in the O-layer(organic) with increasing pollution

centage of the total inventory in theoverall soil profile) increases withdecreasing distance from the smelter(higher load of heavy-metal pollution).
This increase is especially sharp for
239+240Pu, which rises from 1% at thereference site up to 56% at the mostpolluted site. Conversely, in the root zone
(O and E horizons), the radionuclide
content decreases versus decreasinglevels, whereas there is an increase in thelower horizons (E and B).
The corresponding contents of thesenutrients within plants follow a trend
similar to that observed for the exchangeable fraction in the O horizon, withhighly depleted concentrations near the
figure 1
smelter.

figure 2
distance from the smelter.
These observations most likely result
from an increased thickness of the litter
layer at the most polluted sites (vicinityof the smelter), with a parallel thickness
reduction in the organic layers (rootzone), both being promoted by an
inhibition (by heavy metals) of the
microbial activity which converts litter
into humic substances. Below the root
zone, 90Sr and 137Cs are also affected.
This is most evident for 90Sr, thecontent of which increases in the B-layerfrom about 10 % at the reference site(152 km from the smelter) up to 50 %The additional pollution by heavy
metals (Cu and Ni) clearly affects the
distribution of radionuclides (137Cs,
90Sr and 239+240Pu) in the various soil
horizons. In the litter layer, the radionuclide content (expressed as a per-I P S N - C E C

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Tag (m2.kg-1)

Tag (m2.kg-1)(Bq.kg-1)

Redistribution in the soil-plant system | FOREST ECOSYSTEMS SUBMITTED TO ADDITIONAL POLLUTION BY HEAVY METALS■◗ figure 4
Tag (m2.kg-1)

Concentrations of 137Cs (Bq.kg-1
dry weight) and aggregated transfer factors (Tag, m2.kg-1) of 137Cs,
90Sr and 239+240Pu from the global

fall-out for four plant species
as affected by the heavy metal
pollution load at various distancesfrom the Cu-Ni smelter.
EPORA

Distance from smelter (km)26

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FOREST ECOSYSTEMS SUBMITTED TO ADDITIONAL POLLUTION BY HEAVY METALS | Redistribution in the soil-plant systemat the most contaminated site. No
effect, however, can be observed for
239+240Pu. It is to be stressed thatthese results are also due to differencesin the solubility of the radionuclides inthe soils studied.
A clear influence of this additional pollution by heavy metals has also been
observed on the availability of radionuclides in the soil’s organic layer (O horizons), as examined through sequential
extractions of radionuclides from thesoils. The effect is most marked for
137Cs, the exchangeable fraction ofwhich is significantly reduced for
figure 3increased heavy-metal loads.
90
239+240
Pu, theAlso, for Sr andexchangeable fractions were lower at
the most polluted site (35 % and 1 %,respectively) as compared to thosefound at the other sites (46 % and4-6 %, respectively). At each site, 90Sr
was essentially distributed between theexchangeable, bound-to-oxides andbound-to-organic matter fractions,with only 1-2 % persistently bound,whilst 85-90 % of 239+240Pu wasbound to the organic fraction.
Radionuclide behaviour in plants along
the heavy-metal pollution gradient wasobserved by measuring the 137Cs, 90Srand 239+240Pu content of four understorey species at the five sites, ranging
from 7 up to 152 km from the smelter,each site consisting of five distinct
plots. The plant activity concentrations

I P S N - C E C

ranged from 10 to 100 Bq.kg-1(dry weight) for 137Cs, from 1 to
17 Bq.kg-1 for 90Sr and from 0.001 to
0.019 Bq.kg-1 for 239+240Pu, withconsiderable intra-site variability.
Vaccinium myrtillus, Empetrum
nigrum and Vaccinium vitis-idaea (to alesser extent) all displayed reduced
137Cs contamination levels at higher
pollution loads, whereas Deschampsia
flexuosa, the only grass-like species,
exhibited higher contamination levels.
figure 4

Except for Vaccinium vitis-idaea,
which tended to remain unaffected, the90Sr activity concentration also decreased
in all plants at higher pollution loads incontrast to 239+240Pu, which increased.
When taking into account the total
radionuclide inventory in the soil profile
considered, the aggregated transfer
factors can be calculated for each plant(Tag, m2.kg-1) (Figure 4). Ranging
from 0.01 to 0.11 m2.kg-1, the 137Cs
Tag values agreed with the relatively
large range reported in the literaturefor understorey forest vegetation.
Except for Deschampsia flexuosa
again, the median Tag values for 137Cs
were observed to decrease at higher
pollution loads (reduced distancesfrom the smelter). When excluding thereference site and only considering thefour polluted sites, the effect was statistically significant, except for
Vaccinium vitis-idaea. These results

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Redistribution in the soil-plant system | FOREST ECOSYSTEMS SUBMITTED TO ADDITIONAL POLLUTION BY HEAVY METALS

agree with the data on the easily
exchangeable 137Cs fractions in theroot zone, previously described, which
also decrease at higher pollution loads(Figure 3). It is interesting to point out
that this is quite similar to the K
behaviour.
In contrast, transfer factors ofDeschampsia flexuosa tended toincrease at higher pollution loads, but
it is important to note that this plant
exhibited considerably clearer physiological alterations than did the others,
especially at the most polluted site. The
aggregated 90Sr transfer factors do notappear to be as sensitive to the pollution load as 137Cs is. Only Vaccinium
myrtillus and Empetrum nigrum fromthe two most polluted sites show atrend similar to that observed for
137Cs. These results broadly agree withthe easily exchangeable 90Sr fractionsin the organic horizon, as reported
above. In contrast to the general trends
observed for 137Cs and 90Sr, the aggregated 239+240Pu transfer factors increased significantly at higher pollution
loads. This seems particularly clear for
Vaccinium myrtillus, Empetrum
nigrum, and Deschampsia flexuosa, noeffect being detectable for Vaccinium
vitis-idaea. However, it should be stressed that this could be an artefact resulting from the higher amounts of28

I P S N - C E C

239+240Pu in the litter layer at the mostpolluted sites, which might have led tosuperficial contamination of the plants.
(Due to its extremely small soil-toplant transfer, the Tag values for Pu areespecially sensitive to superficial contamination of plants by soil).
It is of great interest to compare thetrends observed for radionuclide
behaviour along the pollution gradientwith those observed for the distributionof nutrients and heavy metals in thesoil-plant system. It appears thathigher inputs of additional pollutants
promote a reduction of 137Cs and
90Sr transfer factors (at least forsome plants), which parallels aconcomitant decrease in nutrient
cations, such as K, Ca, and Mg, inthe organic horizon. Conversely, themost polluted sites also exhibit
higher contents in exchangeable
metallic cations (Al, Fe, Ni, Cu) in
the organic layer, where root colonisation is most pronounced. However, it
should be stressed that the effects
observed are not similar for all plants
and all radionuclides considered,demonstrating that some specificplant and radionuclide features are
involved which are still unresolved.

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2MODELLING●

Root uptake in mineralagricultural soils●

Migration within mineralagricultural soils●

Redistribution of radiocaesiumin forest ecosystems

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29Accumulated K (g.m-2)

Accumulated Cs (kBq.m-2)[K] at root surface (mM)[Cs] at root surface (Bq.l-1)

Modelling | R O O T U P T A K E I N M I N E R A L A G R I C U L T U R A L S O I L S

Time (days)■◗ figure 1
Soil solution 137Cs and K
evolution in the root vicinity
during a barley crop, andtheir observed/predictedaccumulation in plants.
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30

I IPPSS NN -- CC CE EC AA SS SS OO C I A T I O N

FF II NN AA LL RR EE PP OO RRTTR O OT U P T A K E I N M I N E R A L A G R I C U LT U R A L S O I L S

Assessment models currently used forprediction of radionuclide behaviour
have generally been derived empiricallyfrom given contamination situations
against which they have been calibrated. Largely ignoring the actual processes involved, they often lack a moregeneric nature, which would allow
their broader and more secure application. This is where analytical model| Modellingdevelopment can provide substantial
improvements, since they provide a
better understanding of what is actually occurring. This strategy is illustrated
by model-based clarification of therelevant mechanisms involved in plantcontamination via root uptake andmigration through confrontation withexperimental observations.

Root uptake in mineral agricultural soils

If the soil solution composition isaffected by soil parameters (such as
texture, moisture content, counterions availability, etc…), it is also
influenced by the root uptake activity
itself, which is primarily designed tosupply such nutrients as K and Ca to
the plant in amounts suitable to support appropriate growth. Based on thefinding, derived from recent advancesin plant biology, that 137Cs and 90Sr
are withdrawn respectively by theK- and Ca-transport mechanisms, theanalytical model developed (RUR:
Root Uptake of Radionuclides) takes
the physiology of plant growth into
account in that it reproduces theplant’s ability to adjust the rate of supply to its demand. By this means, thedominant process leading to 137Cs
accumulation in plants can vary according to soil type, and even change
during crop growth on certain soils.
Large temporal variations of radionuclide accumulation in plants haveI P S N - C E C

indeed been observed during growth,and these are accurately predicted by
figure 1
the model.
But also, in the event of drastic K
depletion that roots may promote intheir vicinity under certain soil conditions, plants can regulate the efficiencyof their transport systems in such a
way that soils with high initial 137Cs
and K concentrations in the solution
may lead to 137Cs accumulations inplants that are similar to those foundin soils with lower 137Cs and K. The
empirical relationship, often reported,
between the uptake of a radionuclide
and its nutrient analogue concentration is now reaching an appropriate
resolution, which clarifies the influence of soil type, agricultural practices
and time. The main conclusion towhich the RUR model leads is thatradionuclide bioavailability is not a
constant for a given soil, but rather isvariable depending on crop type andon time.

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137Cs activity (% of total deposition)

Modelling | M I G R A T I O N W I T H I N M I N E R A L A G R I C U L T U R A L S O I L S

90Sr activity (% of total deposition)

Depth (cm)Depth (cm)■◗ figure 2
Model-based predictions of
137Cs and 90Sr migration against

experimental data obtainedin a «silt loam» agricultural soil
(three replicates).
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M I G R A T I O N W I T H I N M I N E R A L A G R I C U LT U R A L S O I L S| Modelling

Migration within mineral agricultural soils

The simulation of the hourly-to-yearlyvertical migration of 137Cs and 90Sr ina saturated/unsaturated soil column
with vegetation is undertaken based ona one-dimensional, dynamic physically-based model formulation (TRANSSOL model). The major processes
involved in water flow and transfer ofradionuclides have been taken into
account. Mechanisms such as downward migration enhancement due tomacropores, water exchanges with surface atmospheric layer and time-dependent sorption of radionuclides onto thesoil matrix are accounted for, as well as
the slow initial dissolution of aerosols
and the influence of soil moisture on
the radionuclide concentrations in thesoil solution. Despite this accurate description effort, introducing the radionuclides’ respective KD coefficients, asderived from in vitro sorption/desorption experiments, shows migration
profiles which are underestimated for
137Cs, and overestimated for 90Sr.

appropriate overall “global retention
coefficient”. In addition to soil type, as
described by the respective KD valuesof the radionuclides, migration also
probably depends on the soil structure(particle aggregation) and the associatedbiological activity of the soil (microbial
and root activity), which can be
accounted for by a “global retention
coefficient”.

figure 2

However, the model also demonstrates
that prediction of the observed profiles
is improved within the first 15 cm soil
layer for both radionuclides when apartition coefficient of about 600 is
introduced. This suggests that migration is governed not only by physicochemical features accounted for by thein vitro radionuclide KD, but also byadditional soil properties which, whentaken into account, result in a more

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33Modelling | R E D I S T R I B U T I O N O F R A D I O C A E S I U M I N F O R E S T E C O S Y S T E M S

Variables
All variables
LitterLitter/Soil
Needles
Tree
Wood
Berries
Moose

Km-m
1.9
1.9
2.2
1.9
2.9
1.6
1.4

■◗ Table 1

Km-d
2.1
1.15
1.8
3.0
3.2
1.5
-

Reliability Indices (RI),
showing the level of agreement between the model
predictions themselves(Km-m) and between themodels predictions and theexperimental data (Km-d).
A RI of 2 corresponds to anagreement within a factorof 2. The smaller the RI,
the better the agreement.
LANDSCAPE

1- Swedish Defence Research Establishment
2 - University of Trieste
3 - Swedish Radiation Protection Institute. The development of FORESTLAND was performed in close co-operation with the Russian Institute of Agricultural
Radiology and Agroecology, Obninsk, Russia (SSI Project RYS 6.15).
4 - It should be noted that part of the data used for parameterisation of FORESTLAND was collected in experimental plots located in the Bryansk area.

34

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R E D I ST R I B U T I O N O F R A D I O C A E S I UM I N F O R E ST E C O S YST E M S| Modelling

Redistribution of radiocaesium in forest ecosystems

The modelling of radionuclide migration and transfer in forest ecosystems
has been an area of scientific investigation since the advent of radioecology inthe late 1950’s and early 1960’s. The
Chernobyl accident led to radioactive
contamination of vast forested areas.
The knowledge obtained from studies
carried out in these forests has beenused in the development of several newmodels.
Based on a general conceptual modeland the results of a review of existingmodels, three models were developed:
the FOA model 1, the LOGNAT model 2(LGN) and FORESTLAND 3 (FRLD).
These three models are based on thecompartment model principles andfirst-order kinetics for the turnover of
caesium in the boreal forest. However,owing to the individual strategies chosen for describing and structuring theecosystem and the different emphasis
put on certain transfer and turnoverprocesses, the resulting models exhibit,
in essence, different characteristics.
The three models are also based on
experimental data obtained in different
geographical areas. This has resulted indifferences in the model structures andin the values assigned to different
model parameters. To what extent dothese differences lead to disagreementin the predictions made with themodels? To what degree would modelI P S N - C E C

predictions agree with experimental
observations made independently inother areas, i.e. not used for calibrating
the models? To answer these questions,a two-step inter-comparison exercise
was carried out with the following specific objectives:
1. To determine the level of agreement
between the predictions of radiocaesium
levels in different forest components
after an aerial deposition (model-modelcomparison).
2. To assess the agreement of the model
predictions with experimental dataobtained in field studies (model-datacomparison).
The experimental data for step 2 wereobtained from pine forests in the
Bryansk 4 region of Russia that were
contaminated by the Chernobyl accident, and these data were collectedindependently from 1986 to 1994. The
experimental values were not disclosed
until after the results of the calculations
had been submitted.
The model predictions were made on a
yearly basis for the first 50 years following the contamination event. The
results were presented for thevariables/endpoints: Litter, Litter/soil,
Needles, Tree, Wood, Berries, Moose.
Table 1 shows the level of agreement
between the predictions for both steps 1
and 2 of the inter-comparison. Table 1

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35Model predictions

Modelling | R E D I S T R I B U T I O N O F R A D I O C A E S I U M I N F O R E S T E C O S Y S T E M S(Bq.kg-1 / kBq.m-2)

137Cs concentration

Experimental data■◗ figure 1
Experimental values versus model
predictions for the variables
Needles, Wood, Tree and Berries
and for all three models (up).
Model predictions and observed
values of the radiocaesium
concentration in needles (down).
The dotted lines correspondYears

to the interval of variationof the experimental values.
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R E D I ST R I B U T I O N O F R A D I O C A E S I UM I N F O R E ST E C O S YST E M S

Model predictions for all three models
versus the experimental data forneedles, wood, tree and berries, areshown in Figure 1 (up). Figure 1 (down)
also shows the results for needles including the 50-year predictions, the experimental values and the natural variabilifigure 1
ty in the experimental data.
The predictions made with the models
for the scenario studied were in relatively good agreement (within a factor of
1.4 to 2.9) for all the variables considered. There was also good agreement
between the model predictions and theexperimental data (within a factor of
1.15 to 3.2). There were no significant
differences between the models studied
as to how they reproduced the experimental data. This suggests that, at least
for the scenario concerned and for the
first ten years after the deposition, allthree models are equally serviceable if
the final aim is to estimate absoluteconcentrations in different forest com-

I P S N - C E C| Modelling

ponents. The agreement between themodels, however, decreases with time,
and there were differences in the formof the time dependencies predicted by
the models, especially for wood. This
may lead to larger differences,although probably within a factor of
10, between the model predictions andthe experimental data for time intervals
in excess of the period for which data
were available for comparison. Fromthe experimental data (due to the highvariability) it was not possible to discern which model predicts best the
kinetics.
The comparison with the experimental
data confirms the fact that a major
question remaining to be solved is whether the models correctly predict the
kinetics of radiocaesium levels in different forest components. The experimental data used in the comparison did
not allow this question to be answered
due to the high spatial variability ascompared to the observed time variations.
Any similar data set collected for validation purposes will probably encounter the same problem. To answer thisquestion, longer time series need to be
used. Alternatively, field or laboratory
experiments can be carried out to test
the hypothesis underlying the models,and from them conclusions drawn
about the accuracy of the time dynamics predicted.

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3

38

COUNTERMEASURES (FERTILISATION)●

On agricultural soils●

On forest soils

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O N A G R I C U LT U R A L S O I L S| Countermeasures (fertilisation)

On agricultural soils

Fertilisation of agricultural crops hasoften been reported as a potential
means for reducing the contaminationof plant food products. From initial,
sometimes confusing, experimental
results, a consensus has evolved that
this can be expected to be most effective in soils with low retention capacity(low KD or CEC) and reduced fertility(especially, low K and Ca concentrations in the soil solution). Focusing on
the soil solution composition provides
an efficient approach to understanding
this feature. The 137Cs and 90Sr
concentration factors in lettuce andbeans (CF, expressed with respect to thesoil solution) decrease logarithmicallywith increasing concentration of theirrespective analogue ions, K and Ca+Mg.
figure 1

figure 2

The influence of analogue ions is therefore stronger in the low range ofconcentrations-most likely in soils with
reduced fertility. Measured on various
soil types, the degree of correlation between CF and the concentration in ana-

I P S N - C E C

logues remains high, suggesting thatplant contamination is primarily susceptible to the status of analogues inthe soil solution, irrespective of the soil
type. This agrees with the principle ofradionuclide competition with its analogue ion occurring at the root level for
membrane-based ionic transport systems.
It is of interest to note that concurrent
with this competition effect at the rootlevel where plant radionuclide uptake(CF) is reduced by increasing concentrations of analogue ions, the radionuclide
availability at the soil matrix/liquidinterface (KD) is increased. The resulting
plant contamination is therefore a combination of both effects, CF being moresensitive to analogues than KD, especiallyin the low concentration range. This is
why the fertilisation effect on CR(expressed with respect to the bulk soil)
is most often limited on traditionallyfigure 3
fertilized agricultural soils.

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39Countermeasures (fertilisation) | O N A G R I C U L T U R A L S O I L S■◗ figure 1
137Cs CF (l/kg)

Influence of the Kconcentration on the 137Cs
plant contamination(CF: concentration factor,
Bq.kg-1 in plants / Bq.l-1 in soil
solution) for lettuce and beans.
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K (mM)

90Sr CF (l/kg)■◗ figure 2
Influence of the Ca+Mg
concentration on the 90Sr
plant contamination(CF: concentration factor, Bq.kg-1
in plants / Bq.l-1 in soil solution)
for lettuce and beans.
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Ca + Mg (mM)■◗ figure 3
137Cs CR or
K (mMx10-1)

Fertilisation effect on the
137Cs Concentration Ratio (CR,

Bq.kg-1 in plants / Bq.kg -1 in soil)in lettuce observed on various soils.
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Soil type40

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O N F O R E ST S O I L S| Countermeasures (fertilisation)

On forest soils

When assessing the influence of the different forest ecosystems on the exposure of man to radiation, it is also necessary to understand how radionuclides
circulate in forest ecosystems that havebeen subjected to various management
measures. The most common management measures are fertilisation, liming
and site preparation. Potassium is probably the most interesting fertiliser
affecting the distribution of radiocaesium in forest ecosystems. Generally,
peat soils contain quite small amountsof potassium compared to the othermain nutrients and compared to theamounts bound in the tree stands.
Mineral soils, on the other hand, normally contain enough potassium forthe tree growth. Instead, nitrogen isquite often a growth-limiting factor on
podzol soils.
It is therefore of interest to investigate
the effects of potassium fertilisation on
the radiocaesium distribution in Scots
pine stands on peat and mineral soils
and to assess whether fertilisation can bea possible countermeasure or restoration technique in a radioactive fallout
situation. Such fertilisation experiments
were located in western Finland, where
the radioactive fallout resulting from the
Chernobyl accident was relatively high.
The 137Cs concentrations in bark,wood and needles of Scots pine, as
well as in many samples of branches of

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different ages, were found to be lower
in the fertilised plots than in thecontrol plots, both on mineral soil andon peat-land. For dead branches anddead portions of living branches, somesamples of branches of different ages
and of needles more than four years
old, 137Cs concentrations did not
differ between treatments.
On the mineral soil site, the 137Csconcentration
was
lower
in
Deschampsia flexuosa and Vaccinium
myrtillus on the fertilised plots compared to the control plots. For grasses,
herbs, lichens, mosses and other dwarf
shrubs (Empetrum nigrum and
Calluna vulgaris) no statistically significant difference in the 137Cs concentration was observed between the treatments. However, at the fertilised plots,
the concentrations were only 15-50 %of those at the control plots in these
species.
On the peat-land site, Vaccinium myrtillus, tree seedlings, lichens, mosses
and other dwarf shrubs (Empetrum
nigrum and Calluna vulgaris) had
lower concentrations of 137Cs than on
fertilised plots. In herbs, grasses, deadvegetation, Dryopteris carthusiana
and Vaccinium vitis-idaea, theconcentrations at fertilised plots were
38–68 % of those at control plots,
although the differences were not statistically significant.

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41

Countermeasures (fertilisation) | O N F O R E S T S O I L S■◗ figure 1
The relative distribution of
137Cs in pine-dominated137Cs distribution (%)

forests on mineral soil andon peat-land (up), and the
distribution of 137Cs invegetation (down) as apercent of the 137Cs
budget of pine-dominatedforests on mineral soil andon peat-land.

137Cs distribution (%)

LANDSCAPE

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O N F O R E ST S O I L S

The 137Cs distributions on fertilised
and control plots on the mineral soil
site and on the peat-land site (Figure 1)
show significant changes due to thetreatments. The activity fraction invegetation decreased and the activity inthe soil increased on fertilised plots. On
the mineral soil, fertilised vegetation
contained less than 20 % of the 137Cs
activity found in vegetation on control
plots; on peat-land, the corresponding
figure was 60 %. In above-groundparts of vegetation the reduction in
137Cs activity in vegetation was slightly more than when roots and stumps
figure 1
were included in vegetation.
In general the results show that radiocaesium uptake in vegetation can be
reduced by site-specific nutrient fertilisation on nutrient-poor sites. The more
efficient reduction of 137Cs content invegetation on fertilised mineral soil
compared to peat-land may reflect theexcess of nutrients. On peat-land, thedose of K-fertiliser was less abundantin relation to the prevailing nutrient
status of the stand. Dry-mass accumulation can be increased by fertilisation,
especially in stem-wood. The results onmineral soil site show clearly that the
reduction in Cs uptake cannot be
explained by growth response alone,
but that is also related to root uptake.
The growth response of trees to fertilisation is normally observed in the
I P S N - C E C| Countermeasures (fertilisation)

growing season immediately followingthat of the treatment. As to the timingof treatments in relation to Chernobyl
fallout, the observed reduction in
uptake of 137Cs on the mineral soil site
may represent nearly the maximum
reduction that can be achieved withthe amounts of fertiliser used.
However, the effect of fertilisation on
the dry-mass accumulation of vegetation will last only a few years on subdry mineral soil sites, and 15-20 years
on peat-land sites poor in mineral
nutrients.
In summary, the results indicate thebenefits of fertilisation for restoring
contaminated forests in a severe fallout
situation. The availability of timber tothe forest industry can be increased
considerably by long-term treatmentsof forests. Through multiple use offorests, wild berry and mushroom
gatherers, as well as hunters, receive
less radiocaesium through foodstuffs
from fertilised forests than from unfertilised ones.
The results of the study motivate further research on the applicability offorest management methods as countermeasures in a fallout situation.
Such methods offer possibilities forrespecting the principles of sustainable forestry, as the treatments do
not radically alter the ecosystem.

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43

RUNOFF

4●

From forest ecosystems●

From forest ecosystems submitted
to additional pollution by heavy metals

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F R O M F O R E ST E C O S YST E M S| Runoff

Fr o m fo r e s t e c o s y s t e m s

In northern Sweden, snowmelt andrunoff had achieved their maximum
annual intensity at the time of the main
caesium deposition of Chernobyl,
which occurred on April 29, 1986. The
amount of 137Cs discharged during
this period from a 0.5 km catchmentthat was studied was about 600 MBq,
corresponding to 5 % of the total
deposition in the area. In the following
years only relatively low levels of radioactive caesium were detected in thestream water, and in total about 10 %has been lost over the period 1986figure 1
1994.
New and more detailed calculations
show that the initial loss during snowmelt in 1986 essentially occurred fromthe peat areas and amounted to about

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40 % of the total deposition in theseareas. No significant loss from the pineand spruce forests occurred during thesame period. From autumn 1986
onwards, the annual loss amounted to
30% from the “wetter” part of the peatbog-i.e., the part often contributing to
the surface runoff-while it is about 2%
from the “drier” part of the peat area.
The loss from areas of unsaturated
mineral soil type is less than 0.03%.
The corresponding ecological half-life(Teco, not taking into account radioactive decay) for the boreal type ecosystem was estimated from measurements
on groundwater and exceeded 4000
years (Teff = 30 years, including decay),while the Teco for the drier fractions ofbogs was about 34 years (Teff = 16
years). On the wet fractions of bogs,

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45Cumulative Discharge (%)

Runoff | F R O M F O R E S T E C O S Y S T E M STime after 29 april 1986 (years)■◗ figure 1
The cumulative amount (%)
of 137Cs in stream water
discharged froma catchment.

137Cs (Bq/l)

LANDSCAPE

Aquifer■◗ figure 2
The activity concentration (Bq/l)of 137Cs in stream- and groundwater (GW) in January 1999 at
the Vindeln site (the error bars
represent 1 σ).
LANDSCAPE

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F R O M F O R E ST E C O S YST E M S S UB M I T T E D TO A D D I T I O N A L P O LL U T I O N B Y H E AV Y M E TA L S | Runoff

which often contribute to saturated surface discharge, Teco, was about two to
three years.
The measurements on surface andgroundwater show that a small fractionof the 137Cs deposition has reached thegroundwater at a depth of about 1 m.
Assuming that the total annual discharge of 330 mm exceeds this depth, witha constant activity of 0.0018 Bq.l-1(Figure 2), the corresponding discharge
via groundwater would be 6 x 10-5%

per year, which can be neglected compared to the discharge from the bog,
which on average has been 1-2% per
figure 2
year over a ten-year period.
In conclusion, more than a decade after
the Chernobyl deposition, the amountof 137Cs leaving the forest ecosystem
via runoff is negligible except from thewetter fraction of bogs. The caesium
has now reached the groundwater at a
depth of 1 m, but the discharge fromthe system remains negligible.

Fr o m fo r e s t e c o s y s t e m s s u b m i t t e d t o a d d i t i o n a l
p o l l u t i o n b y h e av y m e t a l s

In addition to soil type, vegetation,
geography and climate, a chemicalindustrial pollution of the catchment
area may also affect the runoff process. This question has been addressed through investigations on two
catchment areas located at 7 km
(heavily pollution load) and 21 km(moderately pollution load) from theMonchegorsk Cu-Ni smelter. The
reference catchment area was selectedin northern Finland, about 137 km
from the smelter.
Of the total 90Sr deposition, only
about one half is still present in theorganic horizons and the upper 15 cm

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47Runoff | F R O M F O R E ST E C O S YST E M S S UB M I T T E D TO A D D I T I O N A L P O LL U T I O N B Y H E AV Y M E TA L S

of the underlying mineral soil, both at
the reference and moderately-polluted catchments.
Conversely, at the most polluted
catchment, close to Monchegorsk,
only 15 % of the estimated total
deposition of 90Sr remains in soil atthese depths. Yet, the fraction in theorganic horizon of the total in thesampled soil is very similar at all threesites, indicating that loss from theorganic fraction probably governs theresidence time and distribution between organic and mineral fractions of
the sampled soil.
The activity concentrations of 137Cs
in stream water correlate well with arelationship based on the fraction of
the upstream catchment area containing deep organic soil found to bevalid at several Scandinavian sites
free of notable impact from regionalsources of chemical pollution. Thus,
no significant influence of chemical
pollution on the loss of 137Cs by
runoff can be seen. In contrast, theactivity concentration of 90Sr in thestream water at the most polluted
catchment is about twice as high as
expected from the 90Sr/137Cs activity
ratios at the two other catchment
areas (reference and moderately-polluted). This coincides, moreover, with48

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a loss of about 85 % of the initialdeposit from the sampled soilcolumns at the most polluted catchment (i.e., a much greater loss thanfrom the others).
Severe wind erosion of the organic
soil is obvious at the most polluted
catchment, giving rise to an airborne
transfer to the stream water.
However, the loss of 137Cs in thiscatchment does not agree, apart fromthat likely to be related to a verysmall peat area. This indicates thatthe contributions of 137Cs and 90Sr to
the transfer of organic matter fromthe atmosphere to the stream water
are not the major cause of the notablychanged 90Sr/137Cs ratio in water. A
more probable explanation for the
relatively high loss of 90Sr from themost polluted catchment is therefore
transfer by shallow groundwater inthe steep slopes of the stream.
The increased rate of 90Sr transfer tostream water in the heavily polluted
catchment emphasises the importanceof considering concomitant input todownstream aquatic recipients inlandscapes affected by chemical pollution, and the potentially increased
contamination in freshwater foodchains leading to man.

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5SPATIAL VARIATIONS●

On agricultural soils●

In forest ecosystems-radiocaesium in moose

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49

Lysimeter west side (cm)Spatial variations | O N A G R I C U L T U R A L S O I L S

Lysimeter south side (cm)■◗ figure 1
Gamma emission mapping(103 counts/s) over alysimeter soil surface twoyears after contamination.
PEACE

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O N A G R I C U LT U R A L S O I L| Spatial variations

On agricultural soils

After the Chernobyl accidental releasein the atmosphere, large spatial variations in radionuclide deposition wereobserved due to rain events over certain
areas, that washed the radioactive
cloud to a varying extent. On a smallerscale, large spatial variations resulted
from the deposition of hot particles(essentially in the vicinity of the plant),
and also, in the longer term, from horizontal redistribution by runoff. It
should be noted that large spatial variations are still present on a small scale.
For example, records show the metric
to decimetric surface deposition of calibrated aerosols (3 µm on average)
simulated under controlled conditions(no wind, no rain) to be heterogeneous.
The subsequent influence of rain in

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washing off the radionuclides intercepted by the canopies further contributes
to this heterogeneity, as illustrated by
gamma emission mapping of the lysifigure 1
meter soils’ surface.
Large spatial variations in radionuclide
migration have also been observed in
the soil profiles, which may evenexceed that caused by soil type or climatic intermittence. The soil structure(particle aggregation resulting from thesoil’s biological activity), already cited
to explain the patterns of migration
observed, most likely contributes to thisvariability. Soil microfauna (earthworms, in particular) and microflora(decomposition and turnover of organic matter) are key elements governing
the soil structure.

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Spatial variations | I N F O R E S T E C O S Y S T E M S — R A D I O C A E S I U M I N M O O S E

In forest ecosystems-radiocaesium in moose

The semi-natural ecosystems of northern Europe have abundant large
wild herbivores that are a significant
food source for man. After the
Chernobyl accident, large variations inradiocaesium levels were found in thetissues of free-ranging herbivores culled from the affected areas. Although
in herbivores there is relatively little
scope for variation in the degree ofabsorption and metabolism of pollutant radionuclides, the ability to predict the intake of radionuclides by herbivores living in heterogeneous environments has been poor. The radionuclide intake by herbivores was expected to depend critically on diet composition, in terms of plant parts and plant
species, and the overall levels of environmental contamination, as it varies
over a range of spatial scales. The
need to quantify diet composition isespecially acute where herbivores
ingest fungal fruiting bodies, which
can contain very high concentrationsof radiocaesium and other pollutants.
These are most abundant and may beingested in late summer and autumn,
prior to the culling seasons for large
ruminants, whose radionuclide contamination levels may hence be strongly
affected. In this project, methods weredeveloped and applied (i) to measure
the intake and diet composition ofmoose in the Boreal forest, and (ii) toassess the use of space by moose, andto consider these in relation to likely

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patterns of deposition and distributionof radionuclides in vegetation. Thisfacilitates examination of the likely
contributions of these factors to variability in radionuclide intake and contamination levels in moose, against thewider background of variability due todeposition pattern.
A method had been previously developed to quantify diet composition
and intake by domestic ruminantsgrazing on temperate grassland. This
non-invasive technique relies on comparing faecal concentrations of natural plant hydrocarbons with the similar compounds-usually long-chain nalkanes which are orally dosed at
known rates. The method had notheretofore been applied to wild ruminants because of the requirement toadminister a daily oral dose, nor had
it been applied to ruminants foraging
on diets of woody browse or mixturesof woody and non-woody plants,
typical of wild boreal herbivores. The
availability of intra-ruminal, controlled release devices (CRD’s), which
release the n-alkane marker over a
period of several weeks, provided theopportunity to apply the method towild herbivores. Experiments wereconducted to test and validate themethod using CRD’s under conditions
relevant to foraging by boreal forest
ruminants before it was applied towild moose.

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I N F O R E ST E C O S YST E M S — R A D I O C A E S I UM I N M O O S EPrevious results had suggested that the behaviourof the dosed hydrocarbons
in the digestive tract is similar for all species of ruminant, and is similar to thatof natural plant wax
constituents. The expectation that the method would
apply equally well to bothmoose (Alces alces) anddomestic ruminants wasborne out in the experiment, but further work isneeded on the quantification of the exact faecal
recoveries of all the markers used, in order to obtain accurate
measurements of food intake.
Validation experiments conductedwith red deer (Cervus elaphus) andcaptive moose suggested that themethodology is equally applicable toruminants ingesting diets of woodybrowse plants, in both summer andwinter seasons. There was good quantitative agreement between the resultsof the hydrocarbon marker method
and measurements of diet composition by weighing, in the case ofmoose. There was also good agreement between the hydrocarbon marker method of intake estimation withdetailed calibration of mass intake via
browsing damage, in the case of red
deer.

I P S N - C E C| Spatial variations

The experiments further showed thatn-alkanes are suitable dietary markers
for birch in leaf, and, although theconcentrations in twig material are
low, they are sufficient to be used as
markers in winter, when leaves areabsent. Scots pine did not containsignificant amounts of n-alkanes.
Hence the use of long-chain fatty alcohols is suggested when this is a likely
dietary constituent. In a separate experiment, using housed goats, the common fungal sterol, ergosterol, was tested as a potential faecal marker for dietary fungi. Because of the negligible
recovery of ergosterol itself in the
faeces of goats, it is unlikely that it canbe used as a suitable marker for dietary fungi in ruminants.

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53Spatial variations | I N F O R E S T E C O S Y S T E M S — R A D I O C A E S I U M I N M O O S E■◗ figure 1
Trajectories of two female
moose in mid-March 1997.
LANDSCAPE■◗ figure 2
Home ranges for five moose
for the period late April
to late June 1998.
LANDSCAPE

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I N F O R E ST E C O S YST E M S — R A D I O C A E S I UM I N M O O S E

The plant hydrocarbon marker
method was applied to wild moose innorthern Sweden, with the objective of
estimating the intake and diet composition of moose in two seasons, winterand summer. The moose were locatedfrom helicopter and shot with ananaesthetic dart. The immobilization,
the CRD insertion and the attachment
of GPS (Geographical Position
System) collars were carried out in1997 and 1998. Inall, CRD’s wereinserted into eight animals and 20 animals were equipped with GPS-collars.
Location of the alkane-dosed moose
was carried out using the radio telemetry facility of the GPS collars in thewinter of 1997, whereas in winter andsummer 1998, the GPS system wascalled on to locate the dosed moose forthe collection of faeces.
Samples of the vegetation available tothe moose were collected in all threeseasons in order to provide information on the range of hydrocarbons andlong-chain fatty alcohols likely to beingested by moose.
The conclusion on the basis of theresults for the intensively studiedmoose in northern Sweden is that the
winter diet of both moose bulls andI P S N - C E C| Spatial variations

cows was dominated by Scots pine. In
contrast the summer diet was dominated by broad-leaved tree species, primarily birch (Betula spp.). Somesamples showed evidence that heather(Calluna vulgaris) was present in thediet, but the levels were such that it
was unlikely to have significant
radioecological consequences at the
population level.
Overall, however, it is unlikely thatvariation in diet composition of moose
in late summer and autumn, prior toand during the hunting season, is amajor determinant of variation inradionuclide uptake. The exception tothis remains the ingestion of fungal
fruiting bodies, which can lead to significant uptake of radionuclides, but theingestion of which is unpredictable dueto their ephemeral temporal and spatial
distribution.
It seems likely that the greatest variability in radionuclide uptake by moose isbrought about by spatial variation in
deposition, in conjunction with normal
movements of the animals, rather thanbeing due to variations in diet selection
figure 2
figure 1
or intake per se.

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6

DOSE ASSESSMENT IMPLICATIONS●Forest ecosystems●

Forest ecosystems submitted
to additional pollution by heavy metals●

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Agricultural lands

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F O R E ST E C O S YST E M S| Dose assessment implications

Fo r e s t e c o s y s t e m s

Semi-natural ecosystems can makesubstantial contributions to the radiation exposure of man. This fact became
known among radioecologists as aresult of research performed following

the atmospheric nuclear weapons tests
in the 1950’s and 1960’s. This knowledge was broadened after the
Chernobyl accident, and today it is also
well known to the general public living
in contaminated regions. In particular,
it has been shown that forests can deliver large radiation doses through theconsumption of berries, mushrooms
and game, but also through the industrial use of forest products. The
LANDSCAPE project focussed on
creating a basis for reliable assessmentsof the radiation exposure of humans.
Knowledge about the distribution andconcentrations of radionuclides(137Cs) in the forest ecosystem andchanges taking place over time is necessary for estimating the doses. However,in addition, assumptions also have to

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be made concerning consumption
habits and time spent in the contaminated environment in order to calculate the internal and external doses.
The results of the project give 137Cs
evolution over time in important compartments of the forest, as well as thechange in the radiation field expressedas photon fluence, and necessary
migration models have been tested.
One particular exposure case wasinvestigated: the radiological consequences following energy production
using radioactively contaminated biofuels from forests in Sweden. The dose
estimates used the available data
concerning the transfer of 137Cs fromsoil to forest flora and fauna. Several
exposure pathways were considered,including the enrichment of 137Cs in
the waste products and their recycling
back to the forest as fertilizer. With anactivity concentration of 5 kBq.kg-1
137Cs in the ashes, which is the recommended limit for ash recycling in
Sweden, the highest doses among the
public, about 0.02 mSv.y-1, are received
by a critical group composed of huntersand gatherers in forests. The average
Swedish population in the same forest
conditions receives a tenth of that dose.
Considering the occupational doses, thehighest doses-on the order of 0.1 to 0.5
mSv.y-1-are received by persons working on an ash deposit.

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Dose assessment implications | FOREST ECOSYSTEMS SUBMITTED TO ADDITIONAL POLLUTION BY HEAVY METALSFo r e s t e c o s y s t e m s s u b m i t t e d t o a d d i t i o n a l
p o l l u t i o n b y h e av y m e t a l s

The extensive data generated on 137Cs
redistribution in the podzolic soils of
boreal forest ecosystems have been
exploited to assess the potential
influence of heavy-metal pollution on
external radiation doses. The external
gamma radiation due to 137Cs in thesoil depends on the vertical distributionof this radionuclide as well as on the
wet-bulk density of the various soil
layers. The gamma dose rates were calculated at all plots from each site along
the pollution gradient.
The contributions of 137Cs from
nuclear bomb and Chernobyl fallouts
to the external dose rate are different.
When normalising the data on a deposition of 1 kBq.m-2, the 137Cs-generated external dose rate from Chernobyl
is about 1.6 times higher than thatfrom the global fallout. In these podzolic soils, it is true, the Chernobyl-derived 137Cs remains closer to the soil
surface than that from the global fallout. However, since total deposition ofChernobyl 137Cs is only about 10 % of
the total inventory in the soil, the total
external dose rate from 137Cs in soils is
mainly due to the global fallout.
Although the pollution load was clearly affecting the vertical 137Cs distribution in the soils, the total external dose
rate was not affected, with an estimated amount of about 1.5 nGy.h-1. Thismight be due to the very low wet bulk
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densities of the litter and the organic
horizons of these podzolic soils (0.1g.cm-3). As a consequence, the attenuation of the gamma rays is quite small,and different depth profiles of 137Cs in
the soil produce very small changes inthe dose rates at a height of 1 m above
the ground.
It must be stressed, however, thatconsidering the influence of heavy
metals on the radionuclide uptake offour understorey plant species, a pioneer aspect examined in EPORA, an
influence of the pollution load on
external and internal dose rates fromthe vegetation is not at all precluded.
This is a question which particularly
deserves further attention.

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A G R I C U LT U R A L L A N D S| Dose assessment implications

Agricultural lands

Agricultural lands, which support
human food production, are central
for assessing the potential radiological impact to humans of radioactive
contaminants. The improved understanding of their behaviour in the soilplant system, as derived from the
PEACE project achievements, is suchas to contribute to refining radiation
protection issues, with a particular
contribution made to improving prediction performances. As an example,
in-depth soil migration profiles ofboth 137Cs and 90Sr appear to be
most strongly influenced by the initialclimatic conditions prevailing upon
contamination-such as soil humidity
and the first rain events. 90Sr does not
penetrate in depth as fast and deeply

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as existing prediction models would
indicate; it therefore remains in theroot zone of most crops, with potential impact on their further contamination. Indeed, 90Sr is shown to betransferred to food crops in higher
amounts than 137Cs, irrespective of
the plants considered or of soil type.
Such features illustrate how the better
understanding of radionuclide movements thus procured is conducive tothe improvement of assessment
models, whilst providing useful information for optimising the current
philosophy on post-accidental intervention.

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59What is still needed?
■ Reaching a better understanding of the concept of “bioavailability” and its applicability

in different ecosystems.
■ Clarifying the importance of climatic conditions immediately after radioactive

deposition.
■ Identifying what is needed for the assessment of radiation doses and where basic

research can afford support.
■ Investigating the scientific pertinence of dose to ecosystems.
■ Distinguishing dose distribution over time from different ecosystems.
■ Unravelling the influence of chemical industrial pollutants on the behaviour ofradionuclides in the environment.
■ Further model development and testing, including other lines of enquiry related towaste repositories and other radionuclides, for example.
■ Practical countermeasures in different time perspectives and different terrestrial

ecosystems.
■ Clarifying current knowledge and identifying research needs through a systematic

expert evaluation of all experimental data.
■ Collection of strategic data series for model validation.

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S H O RT R E F ER E N C E L I ST

Bréchignac F. et al. 1999 PEACE Final Report. Programme for Evaluating the impact ofAccidents Contaminating the Environment – Soil-radionuclides processes of interaction andmodelling of their impact on contamination of plant food products. CEC-IPSN Association
contract n° F14P-CT96-0039a within the 4th EURATOM Framework Programme on Nuclear
Fission Safety. IPSN Report Series DPRE/SERLAB/99-017(P), Paris, France.
Moberg L. et al. 1999 LANDSCAPE Final Report. An integrated approach to radionuclide
flow in semi-natural ecosystems underlying exposure pathways to man. CEC-IPSN Association
contract n° F14P-CT96-0039b within the 4th EURATOM Framework Programme on Nuclear
Fission Safety. SSI Report 99:19, Stockholm, Sweden. ISSN 0282-4434.
Suomela M. et al. 1999 EPORA Final Report. Effect of industrial pollution on the dynamics ofradionuclides in boreal understorey ecosystems. CEC-IPSN Association contract n° F14PCT96-0039c within the 4th EURATOM Framework Programme on Nuclear Fission Safety.
STUK Report Series A168, Helsinki, Finland. ISSN 0781-1705

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A B ST R A C T

T

his document provides an overview on the recent advances in Europe concerning
the long-term environmental behaviour of radionuclides. It describes and illustrates the most significant scientific achievements gathered through three European
projects, PEACE, LANDSCAPE and EPORA, which have been co-funded by theEuropean Commission (DGXII) under the Nuclear Fission Safety Programme.
The improvement of radiation protection issues requires an accurate understanding of
the radionuclide contaminants behaviour within ecosystems. The three projects havetherefore been focused on the soil-plant system of agricultural lands and semi-naturalforest ecosystems based on both, experimental approaches in controlled conditions andin the field. A particular emphasis is devoted to unravelling intra-compartments loads
and inter-compartments movements of 137Cs, 90Sr and 239+240Pu, addressing also for
the first time the potential influence of non-radioactive additional pollutants (heavy
metals). The variety of conditions encountered in Europe is emcompassed through awide selection of experimental sites ranging from Mediterranean up to Boreal ecosystems. Experimental data acquisition and mechanistic modelling are synergisticallydeveloped in order to promote access to improved assessment predictions in an accidental situation.
The knowledge generated first includes the redistribution of radionuclides in the soilplant system with emphasis on vertical migration in soils and root uptake by plants. It
provides next recent advances into the mechanistic modelling of these features. From
the new data gathered through three years of investigations, essential conclusions on
contamination discharge via run-off water are drawn, and insights discussed with respect to counter-measure, and spatial variations. Preliminary conclusions are finallyderived in the perspective of dose assessment, and areas deserving further research
identified.

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EPORARADIATION AND NUCLEAR

TUA RAHOLASAFETY AUTHORITY, HELSINKI, FINLAND :KRISTINA RISSANEN
MARKETTA PUHAKAINENTARJA HEIKKINEN

COORDINATOR :MATTI SUOMELANATIONAL DEFENCE RESEARCHRONNY BERGMANESTABLISHMENT, UMEÅ, SWEDEN :THORBJÖRN NYLÉNNATIONAL RESEARCH CENTER

KURT BUNZLFOR ENVIRONMENTAL HEALTH,WOLFGANG SCHIMMACKNEUHERBERG, GERMANY :UNIVERSITY OF HELSINKI,

TIMO JAAKKOLAFINLAND :LISA RIEKKINENMICHAEL TILLANDERNORWEGIAN UNIVERSITY OF SCIENCE

EILIV STEINNESAND TECHNOLOGY, TRONDHEIM, NORWAY :TORIL HAUGLAND
HÅVARD THØRRINGI P S N - C E C

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LANDSCAPESWEDISH RADIATIONRODOLFO AVILAPROTECTION INSTITUTE,

LYNN HUBBARDSTOCKHOLM, SWEDEN :LENA WALLBERG

COORDINATOR :LEIF MOBERG

UNIVERSITY OF TRIESTE, ITALY :ENRICO FEOLIMAURO SCIMONECHRISTINA MILESIMACAULAY LAND USE RESEARCHBOB MAYESINSTITUTE, ABERDEEN, U.K. :GLENN IASONRADIATION AND NUCLEAR SAFETYAINO RANTAVAARAAUTHORITY, HELSINKI, FINLAND :VIRVE VETIKKONATIONAL DEFENCE RESEARCHRONNY BERGMANESTABLISHMENT, UMEÅ, SWEDEN :TORBJÖRN NYLÈNSWEDISH UNIVERSITY OF AGRICULTURAL

THOMAS PALOSCIENCES, UMEÅ, SWEDEN :NEIL WHITE

THE FINNISH FOREST RESEARCHHANNU RAITIOINSTITUTE, PARKANO, FINLAND :LASSE AROSEPPO KAUNISTOFACULTÉ UNIVERSITAIRE DES SCIENCES

OLIVIER GUILLITTEAGRONOMIQUES, GEMBLOUX, BELGIUM :64

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PEACEINSTITUTE FOR NUCLEAR PROTECTIONCHANTAL MADOZ-ESCANDEAND SAFETY, DEPARTEMENT FOR

CLAUDE COLLEENVIRONMENTAL PROTECTION,

MARC-ANDRÉ GONZESERLAB, CADARACHE, FRANCE :THOMAS PERRIERCHRISTIAN TAMPONNETVIRGINIE CAMILLERI
HÉLÈNE JUHANERIC DUBOISCOORDINATOR :FRANÇOIS BRECHIGNAC

SCK-CENTRE D’ÉTUDES NUCLÉAIRES

NADIA WAEGENEERS

DE MOL, BELGIUM :YVES THIRYCHRISTIAN VANDECASTEELE

UNIVERSITY OF BARCELONA, SPAIN :RAMON VALLEJOJAUME CASADESUSCINTA ROCATERESA SAURASSWEDISH UNIVERSITY OF AGRICULTURAL

K.J. JOHANSONSCIENCES, UPPSALA, SWEDEN :KLAS ROSENSVERKER FORSBERG

IMPERIAL COLLEGE OF SCIENCEGEORGE SHAWTECHNOLOGY AND MEDICINE,

JOANNA MARCHANTLONDON, U.K.:

ADRIAN BUTLER
JOHN TOMPKINSCEC-DGXII, BRUSSELS, BELGUIMERNST-HERMANN SCHULTE(DETACHED TO CADARACHE) :I P S N - C E C

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I n fo r m a t i o n c e n t e r o n n u c l e a r s a fe t y
7 7 - 8 3 , av e n u e d u G é n é r a l - d e - G a u l l e
9 2 1 4 0 C l a m a r t , Fr a n c e
Mailing address:
B P 6 – 9 2 2 6 5 Fo n t e n a y - a u x - R o s e s C e d ex
Te l . : ( 3 3 ) 0 1 4 6 5 4 8 0 0 7
Fa x : ( 3 3 ) 0 1 4 6 5 4 7 9 4 9© Édition 2000 / Mission communication IPSN - Dépôt légal Avril 2000

The Institut de protection et de sûreté nucléaire (French institute forprotection and nuclear safety) is assigned the task of conducting researchand expert appraisals in all disciplines implicated in the control of nuclear
risks and of their impact on man and the environment. Its field of concern
primarily addresses the safety of installations, the study and prevention of
accidents, the protection of human health, transport safety, the inspectionof nuclear materials, and organization and training in crisis management.
Under the joint authority of the Ministries of Industry and of theEnvironment, IPSN has, since 1990, been granted a specific status as wellas its own budget. IPSN’s staff numbers about 1300, two-thirds of whomare engineers and research personnel specialized in a variety of branches(physics, chemistry, biology, medicine, agronomy, etc.). Within the framework of an ongoing reflection concerning the French nuclear inspection
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