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Properties of radiocesium

Radiocesium in the environm.

Abstract of research results

Cs-137 in forest soils

Cs-137 in plants

Cs-137 in mushrooms

Cs-137 in deer truffle

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               Modelling the migration and accumulation of radiocesium (Cs-137) in
               soil, plants and wildlife of forest ecosystems
                                   

Radioecological modeling: introduction and research goals

An essential aim of the research project was the development of a dynamic radioecological model, which describes the time course of the contamination of roe deer, red deer and wild boar and which forecasts the future time course. The model should consider the dynamical processes of 137Cs in the soil, in plants and mushrooms and the food ingestion by the game.

Radioecological models, which describe the processes of 137Cs in forest ecosystems mathematically, have already been developed before the Chernobyl accident. OLSON (1965) has set up a system of equations to describe the transfer of 137Cs in different compartments of poplars in a test area, on which radio-cesium has been placed intentionally. Other models have been created to describe the radioactive contamination in oak forests caused by the global fallout (CROOM and RAGSDALE, 1980) and to describe the consequences of an accident in Kyshtym 1957 in the Ural Mountains (PROHOROV and GINZBURG, 1973).

Due to the radioecological importance of the Chernobyl fallout and basing on extensive data material the behavior of radio-cesium has been modeled for undisturbed ecosystems, particularly for forest ecosystems in the framework of different international research projects from 1996 to 2002 (e.g. BELLI, 2002). An overview of the different models is given in IAEA (2000).

In radioecological models, forest ecosystems are in general subdivided into different subsystems (compartments) with equal functionality, e.g. trees or animals. The compartments itself are subdivided into components (e.g. species). In these models 137Cs can be exchanged between the compartments and components (“fluxes”).

The Forest Working Group of IAEA (2002) concluded, that with regard to the long-term prognosis of the 137Cs activity for biological endpoints, such as mushrooms, berries and game the hitherto existing models led to very different results. Game was included only in few models. The seasonal course of 137Cs for roe deer has been described in models by AVILA (1998) and by ZIBOLD et al. (2001). In both models the increase of the 137Cs activity is explained by ingestion of mushrooms.

Figure 4 shows schematically the radioecological model, which has been developed in the present project. It bases on the model ECOSYS-87 of the GSF-National Research Center for Environment and Health, Neuherberg (MĂśLLER and PRĂ–HL, 1993). An essential feature of ECOSYS-87 is the comprehensive treatment of the radioactive contamination in the early phase after a deposition of radionuclides. It thus became part of decision support systems for nuclear emergencies, for example in the European decision support system RODOS (EHRHARDT, 2000).

Fig. 4: Scheme of the transfer of radionuclides in the radioecological model for game

 

However, since in the present research project the long-term effects of the Chernobyl accident had to be investigated, a modeling of processes, which are important only in the first weeks or months after the deposition of 137Cs, was not carried out. The model puts emphasis on the description of long-term processes, which affect plants and animals in forests and other undisturbed ecosystems. It contains a detailed description of the dynamics of 137Cs in the compartments soil and plants and a modeling of the qualitative and quantitative ingestion habits of roe deer, red deer and wild boar. The fluxes between the compartments are described by differential equations, mainly in the soil model.

 

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References:

Avila R.; 1998: Radiocaesium transfer to roe deer and moose. Acta Universitatis Aggriculturae Sueciae, Agraria 136. Diss..

Belli M., Zori P.; 2001: Assessment of uncertainty associated with soil sampling in agricultural, semi-natural, urban and contaminated einvironments. In: IUR Newsletter Nr. 37. International Union of Radioecology.

Croom J. M.; Ragsdale H. L.; 1980: A model of radiocaesium cycling in a sand hills-turkey oak ecosystem. Ecological Modelling. 11: 55-65.

Ehrhardt J.; 2000: RODOS – Decision Support System for Off-site Emergency Management in Europe. European Commission, EUR-Report 19144  EN.

IAEA-BIOMASS-1; 2002: Modelling the migration and accumulation of radionuclides in forest ecosystems. Report of the forest working group of the BIOsphe Modelling and ASSessment (BIOMASS) programm, theme 3.

Müller H. and Pröhl, G.; 1993: ECOSYS-87: A Dynamic Model for Assessing Radio-logical Consequences of Nuclear Accidents. Health Physics. 64 (3): 232-252.

Olson J.S.; 1965: Equations for Cesium Transfer in a Liriodendron Forest. Health Physics. 11 (12):1385-1392.

Prokhorov V. M.; Ginzburg L. R.; 1973: Modelling the process of migration of radionuclides in forest ecosystem and description of the model. Soviet. J. Ecology. 2: 396-402.

Zibold G., Drissner J., Kaminski S., Klemt E., Miller R.; 2001: Time-dependence of the radiocaesium contamination of roe deer: measurement and modelling. J. Environ. Radioact. 55 (1):5-27.

 

 

This research was conducted  with funds of the

Federal Ministry for Environmental, Nature Protection and Reactor Safety.

This report reflects the views and opinions of the contractor and need not necessarily correspond to those of the sponsor.

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