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 rad iocaesium in semi-natural environments is rather limited, the transfer of t his radionuclide and of natural K-40, from soil-to-plant as well as from pl ant-to-cow's milk was investigated for a typical alpine pasture (site P). F or comparison, a nearby alpine pasture (site K) not used for cattle grazing was also studied. Small seasonal effects were found for Cs-137 in the plan ts, 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 ver y large, and the seasonal effects were observable only because of the large number of samples (N approximate to 100) collected. The aggregated soil-to -plant transfer factor of Cs-137 was for site P, on average, 0.002 +/- 0.00 1 m(2) kg(-1). The plant-to-milk transfer coefficient was, on average, 0.02 day l(-1). The Cs-137 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 ma ximum in the beginning of August. As a result of soil adhesion due to cattl e trampling, significantly higher ash- and Cs-137 contents of the plants we re observed at site P as compared to site K. Possible consequences of the a bove observations with respect to a representative sampling design of veget ation and milk are discussed. (C) 2000 Elsevier Science Ltd. All rights res erved.