SEMINAT: Long term dynamics of radionuclides in semi-natural environments: derivation of parameters and modelling

• Forschungsstelle: EU FRP
• Projektnummer: 95.0559
• Projekttitel Englisch: SEMINAT: Long term dynamics of radionuclides in semi-natural environments: derivation of parameters and modelling

Schlüsselwörter (Englisch)

Caesium; bioavailability; forest; fluxes;soil

Alternative Projektnummern (Englisch)

EU project number: FI4P-CT95-0022

Forschungsprogramme (Englisch)

EU-programme: 4. Frame Research Programme - 5.2 Nuclear fission safety

Kurzbeschreibung (Englisch)

See abstract

Partner und Internationale Organisationen (Englisch)

ANPA, ARCS, BfS, GSF, ICSTM, RPII, UCL
Coordinator: Agenzia Nazionale per la Protezione dell'Ambiente (I)

Abstract (Englisch)

The project was a fully integrated field, laboratory and modelling study of caesium fluxes and persistence in semi-natural ecosystems. The ultimate aim was to quantify the operative parameters that rule the persistence of radionuclides and their contribution to the dose to man and to provide a generic modelling capability for internal and external radiation exposure evaluation.
The tasks of PSI were to collect field data on the radiocaesium distribution in oak trees, on precipitation, throughfall, stemflow and litter fall, to participate at a litterbag trial and to investigate the interaction between caesium, clay minerals and fungal mycelium under in vitro conditions.
All field data were ascertained on a 'Long-Term Forest Ecosystem Research' plot which is maintained by the Swiss Federal Institute of Forest, Snow and Landscape Research at Novaggio. Results showed that litterfall is the most important pathway returning radiocaesium from the tree to the ground. Stem flow and throughfall were of minor importance. Of the whole 137Cs-inventory, 2.5 % were recovered in the tree biomass only. Within the tree, 70 % of the activity were in the bole wood and bark, 20 % in the branches and 10 % in twigs and leaves. The activity concentration was highest in leaves (264 Bq/kg dry weight) and lowest in bole wood and branches (86 and 78 Bq/kg, respectively). The whole data set was successfully used to calibrate the newly developed forest model RIFE II. RIFE II is the main deliverable to the EC and will be made available to all project partners. In another field experiment which lasted 2.5 years it could be shown that the 137Cs-activity in litter increased in winter and decreased in summer. The seasonal levels however were nearly stable, i.e. no leaching occurred. It is assumed that the presence or absence of fungal mycelium is responsible for these findings. At the end of the investigated period it could also be demonstrated that plant roots in the organic soil layer accumulate radiocaesium and contribute to the retention of caesium in the topmost soil layers too.
The laboratory investigations showed that caesium accumulation in fungi is highly species-specific. Caesium uptake by the mycorrhizal species was generally lower than by the saprophytic fungus; however, whether the extent of caesium accumulation is linked to the type of fungal nutrition is still to be studied. The pH dependence of the uptake process indicated an active transport mechanism energised by the proton motive force. The influence of potassium on the ability of fungi to accumulate caesium pointed to a participation of the potassium transport system in the uptake process where potassium acts as an inhibitor of caesium transport. The small positive effect of low ammonium concentrations on the initial uptake rate may be a consequence of a reduced ionic strength of the medium; monovalent cations may lower the negative surface potential of the cell membrane as they shield or bind to negative head groups.

Datenbankreferenzen (Englisch)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 95.0559