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

Long-lived radionuclides 137Cs and 90Sr 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 137Cs and 90Sr 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 137Cs deposition from nuclear weapon testings was approximately the same in all regions, 137Cs 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 137Cs 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 137Cs were higher in the regions with clayish soils. Half-lives of 90Sr for longer time intervals were considerably longer than those for 137Cs. The long-term data on behaviour of 137Cs and 90Sr in dairy milk can be utilized in testing food chain models.