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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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               Abstract of the research project: “Evaluation of ecosystems following
               Chernobyl concerning the radiation dose of human populations”
 

Abstract
Since 1988, within the scope of several research projects, in 7,000 samples of soil, plants, mushrooms and game from forest ecosystems, the Cs-137 activity concentration was measured, in order to investigate the dynamics of the nuclide. The investigation sites are a spruce mountain forest near the village Bodenmais (Bavaria) and an oak forest close to  Fuhrberg (Lower Saxony). In both forests, unfavourable location conditions cause a relativ high transfer of Cs-137 into plants and game. At Bodenmais, the mean Cs-137 inventory was 53,690 Bqm-2 (corrected to 1 May 1986, n=59), in Germany this site belongs to the highest contaminated areas by the Chernobyl accident. 1999, a different investigation site, a beech forest close to Göttingen with favourable location conditions and resulting low Cs-137 transfers was included in the study. All soil and plant samples were taken exclusively from 100x100 m permanent study plots. The location of the investigation sites are shown in figure 1.

Fig. 1: Location of the investigation sites in Germany

Typifying for the 3 forest sites was the high intra- and interspecies variability of the Cs-137 activity concentration. Even 14 years after the Chernobyl-fallout at the 3 investigation sites, the average Cs-137 inventory, contained in the top 10 cm of soil was 56% and 93% in the top 20 cm. A typical distribution of Cs-137 in the forest soil profile is presented in figure 2.
 

Abb. 2: Cs-137 activity concentration (in percent per cm) versus depth of soil profile, permanent study plot B1, Bavaria, Germany  2001

 

From 1987 till 1994, in the leaves of the investigated plant species the Cs-137 activity concentration decreased significant, during the following years there was little change. The effective half life of Cs-137 varies between –3 years for raspberry and –24 years for the fern Pteridium aquillinum, whereas most of the plant species show half lifes of about -5 years.

In 2000, as usual mushrooms from the Bodenmais investigation site showed the highest Cs-137 contaminations: Xerocomus subtomentosus and Armillaria mellea had about 400 Bq/kg, Cantharellus cibarius, Boletus edulis and Xerocomus chrysenteron about 1,000 Bq/kg, Xerocomus badius 3,030 Bq/kg, and Cortinarius hercynicus 6,750 Bq/kg, in fresh weight. The Cs-137 activity concentration of the underground growing Elaphomyces granulatus (figure 3) had 25,660 Bq Cs-137/kg and exceeded all overground fructifying mushrooms.
 

 

 

Fig. 3: Elaphomyces granulatus on moss

 

 

 

 

 

 

 

 

The aggregated transfer factors (Tagg) for soil → plant and soil → flesh varied with several orders of magnitude. Tagg values for soilautotroph plant species reached from 0,0001 m2/kg to 0,41 m2/kg. While at the permanent study plots in Bodenmais and Fuhrberg the Tagg values were of comparable quantity, at Göttingen, they were lower than two orders of magnitude. For example Tagg for Cs-137 in wild boar from Bodenmais was 392 times higher than for wild boar from Göttingen.

From 1987 till 2000, the Cs-137 activity in roe-deer from Bodenmais varied according to the seasons, with highest values in autumn, and lowest values in spring (figure 4).

 

Fig. 4: Activity concentration of Cs-137 in roe deer at Bodenmais (monthly medians, n=1557), Germany from 1987-2003

In consequence of the decrease of the Cs-137 activity concentration in grazing plants, from 1987 until 1995, the Cs-137 contamination in roe deer (n=1.429) declined, but from 1996 till 2000 it stagnated. The effective half-life of Cs-137 in roe deer was 6 years. In 2000, the median of the Cs-137 values in roe deer from Bodenmais was 776 Bq/kg, for wild boar 7,890 Bq/kg. There was no significant change in the Cs-137 contaminantion of wild boar, from 1987 till 2000.

This research was conducted  with funds of the Federal Ministery for Environment. 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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