Radiocaesium variability within sheep flocks: determination of 137Cs intake in free-ranging sheep

摘要

A study is described in which 137Cs intake by free-ranging sheep was estimated at two farms in the area of west Cumbria (northwest England) which received some of the highest amounts of fallout from the Chernobyl accident within the United Kigdom. The faecal excretion of ~137Cs was estimated from faecal ~137Cs activity concentrations and the use of intraruminal controlled release devices containing Cr_2O_3 to determine faecal dry matter output. The intake of ~137Cs was estimated by assuming an apparent absorption coefficient appropriate to the herbage grazed. The methodology has the advantage that sampling of herbage representative of that ingested by study animals is not required. Caesium-137 dietary intake explained >60% of the observed variability in the ~137Cs activity concentration determined in the muscle of sheep. Resultant transfer coefficient (F_f) values to describe the transfer of 137~Cs from the diet to muscle were in agreement with previously reported value. At one farm, there was a positive correlation between the ~137Cs activity concentration in muscle and F_f whilst at the other farm there was a negative correlation between F_f and ~137Cs dietary intake. Potential reasons for these observations are discussed.