In-vivo estimates for the uptake of caesium-137 by cattle grazing contaminated pasture around the Esk and Irt estuaries,Cumbria, U.K.

Sea water contaminated with diluted radioactive effluent from the Windscale nuclear complex in Cumbria periodically floods low-lying grazing pasture around the estuaries of the rivers Esk, Irt and Mite near Ravenglass. During 1979, an experiment was carried out to measure the transfer of caesium-137 from grass to muscle in cows grazing these pastures. Grass samples were taken and in vivo external gamma-ray measurements were made on cattle. A very low transfer coefficient was found, less than 9 × 10^?4 days kg^?1 with a best estimate of 4 × 10^?4 days kg^?1, compared with a more usual value of around 3 × 10^?2 days kg^?1. The low transfer seems to occur because the bulk of the caesium-137 on the grass is bound to resuspended estuarine surface sediment deposited during flooding. In this form, the caesium-137 is only poorly absorbed across the gut of the grazing cattle.