Factors affecting the transfer of radiocaesium from soil to roe deer in forest ecosystems of southern Germany

Since 1987, in Southern Germany, as a consequence of the Chernobyl accident, the Cs-137 activity concentration in roe deer (Capreolus capreolus) has been intensively monitored. A large data set is now available with approximately 5000 samples, with information about the location of the animal, the time of slaughtering, soil characteristics and distance to intensively managed agricultural land. Both the roe deer Cs-137 activity concentrations and aggregated transfer coefficients soil-roe deer (T-ag,T-r) show a considerable variability with geometric mean and geometric standard deviation in meat of 270 . 3.5(+/-1) Bq . kg(-1) and 0.01 . 3.5(+/-1) m(2) . kg(-1), respectively. From 1987 to 1991, T-ag,T-r values exhibited a decline with an ecological half-life of about 3 years. Since 1991, no further decrease of the roe deer contamination level was observed. This general trend is superimposed by an increase in T-ag,T-r in autumn that has occurred in almost every year, which is probably due to consumption of mushrooms. This hypothesis is supported by a significant positive correlation between the precipitation during July and August, stimulating the fungi's growth and the height of the maximum in T-ag,T-r in autumn. Animals are less contaminated when living in parts of the forest from where they have access to intensively managed agricultural land. A small, but significant correlation is observed between the T-ag,T-r and soil parameters; the total potassium content of the soil and the pH of the organic soil layer. The highest transfer coefficients soil-roe deer were found on a peat bog, where most values ranged from 0.01-0.1 m(2) . kg(-1), and neither a pronounced seasonal variation, nor a long-term decrease was observed. On sites with coniferous forests, most T-ag,T-r, values range from 0.005 to 0.05 m(2) . kg(-1), on sites with a mixture of coniferous and deciduous trees, the transfer coefficients range mostly from 0.002 to 0.02 m(2) . kg(-1). This is a further indication of the importance of the uppermost soil layers and the biological processes therein with respect to the bioavailability of caesium. On the two sites, the values at the lower boundary are more typical for animals that have access to agricultural areas, whereas the higher values were observed in autumn and for animals grazing distant from agricultural areas.