|
The occurrence of 90Sr and 137Cs in the total Danish diet has been investigated since the early 1960’s. The dietary composition assumed over all the years has been based on the same estimate, which was made in 1962. The assessments thus reflect the changes in radionuclide content of a consistent set of dietary components, rather than taking into account the changes that have occurred over the years in the average Danish dietary composition. The dietary content of both 90Sr and 137Cs decreased markedly since the atmospheric nuclear tests ceased in 1963. The Chernobyl accident was clearly visible in the 137Cs content for both 1986 and 1987 (since some of the food items produced in 1986 were consumed in 1987), whereas the 90Sr contamination from Chernobyl was too low to be distinct.
Strontium has chemical similarities to calcium, and is therefore transferred to the bones of the human body. 90Sr levels are measured in bone samples collected from the institutes of forensic medicine in Copenhagen and Århus. The biological half-life (excretion from the body) of strontium is of the order of 50 years. Combined with 90Sr’s physical (decay) half-life of 28 years, this gives an effective half-life in the body of about 18 years, so even an instantaneous intake of 90Sr will result in increased bone content for decades.
Caesium has chemical similarities to potassium. This means that caesium, like potassium, is distributed in human muscle tissue. Gamma spectrometric whole-body 137Cs measurements and measurements of 137Cs in human urine have been made for decades for selected Risø staff members. The radiocaesium content in urine reflects the body content.
The variation in external exposure rates in open terrain has also been followed in 4 groups of Danish locations (averages for each group shown below). Also here, the Chernobyl contribution is distinct. The shifting in 1976 and 2000 is due to re-calibrations of the measurement equipment.
|