Ecological half-lives of ¹³⁷Cs and ⁹⁰Sr in dairy milk in regions with different soil types

Radiation and Nuclear Safety Authority, Research and Environmental Surveillance,PO Box 14, 00881 Helsinki, Finland

Abstract

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.