Ecological half-lives of137Cs and90Sr in dairy milk in regions with different soil types

Abstract

Long-lived radionuclides 137 Cs and 90 Sr have been regularly monitored since the 1960's in dairy milk in Finland. The aim of this work was to study regional differences in long-term behaviour of 137 Cs and 90 Sr in dairy milk including the nuclear weapons tests period and the period after the Chernobyl fallout. In the milk production areas in Finland soil types vary from clayish to humus and peat soils. Although total 137 Cs deposition from nuclear weapon testings was approximately the same in all regions, 137 Cs concentrations in dairy milk during the 1960s ranged between 5 and 35 Bq/l being highest in regions with high proportion of peat soils. The uneven deposition after the Chernobyl accident before the start of the growing season gave rise to 137 Cs concentrations in dairy milk ranging from 3 Bq/l to 60 Bq/l. In the milk production areas dominated by organic soils the ecological half-lives for decrease of 137 Cs were higher in the regions with clayish soils. Half-lives of 90 Sr for longer time intervals were considerably longer than those for 137 Cs. The long-term data on behaviour of 137 Cs and 90 Sr in dairy milk can be utilized in testing food chain models.