Soil-to-plant and plant-to-cow's milk transfer of radiocaesium in alpine pastures: significance of seasonal variability

Because our present knowledge on the environmental behaviour of fallout radiocaesium in semi-natural environments is rather limited, the transfer of this radionuclide and of natural 40K, from soil-to-plant as well as from plant-to-cow's milk was investigated for a typical alpine pasture (site P). For comparison, a nearby alpine pasture (site K) not used for cattle grazing was also studied. Small seasonal effects were found for 137Cs in the plants, but they were different for the two pastures. Due to the presence of a large variety of different plant species on the pastures and soil adhesion on the vegetation from trampling cattle, the scattering of the data was very large, and the seasonal effects were observable only because of the large number of samples (N approximately 100) collected. The aggregated soil-to-plant transfer factor of 137Cs was for site P, on average, 0.002 +/- 0.001 m2 kg(-1). The plant-to-milk transfer coefficient was, on average, 0.02 day l(-1). The 137Cs concentration in the milk of the cows varied within the grazing period only between 1.4 and 2.9 Bq l(-1), with a significant maximum in the beginning of August. As a result of soil adhesion due to cattle trampling, significantly higher ash- and 137Cs contents of the plants were observed at site P as compared to site K. Possible consequences of the above observations with respect to a representative sampling design of vegetation and milk are discussed.