Radioactive contamination of milk from the Nordic countries

For the NKS-B EcoDoses project 'Improving radiological assessment of doses to man from terrestrial ecosystems', data concerning 137Cs and 90Sr in cow's milk were collated from all Nordic countries for both the Nuclear Weapons Fallout and the post-Chernobyl periods. From the collated milk data, long and detailed data series with good consistency were selected for a more thorough study of time trends and effective ecological half lives emphasising regional variations. Unfortunately, the selected data series comprises only three of the Nordic countries, namely Denmark, Faroe Islands and Finland. Considerable variations in activity concentrations of 137Cs and 90Sr were observed between countries or regions due to factors such as different precipitation patterns, soil types and Chernobyl deposition. The observed time trends indicate that the factors influencing the ecological half-life for 90Sr are not entirely the same as for 137Cs in the pasture milk system. For 137Cs the effective ecological half-lives seem to be fairly equal for the different investigated regions. Slightly longer T2s were observed for the post-Chernobyl period for this radionuclide. For 90Sr the long component varies between 4 and 12 years. Finally, for some series (both 137Cs and 90Sr) a 'no decrease' in activity concentrations has been observed for recent years. (LN)