A comparison of the absorption and retention by rabbits of strontium-90 incorporated into plant material and of added strontium chloride in the diet.

A large part of the strontium-go from fallout that reaches man is from fallout on vegetation, and any process affecting its absorption by animals affects its transfer to man. The 90Sr content of vegetation comes from two sources, that in the soil from previous fallout which is incorporated through the roots into the plant tissue, and that from current fallout producing a surface contamination of the plant (Russell, 1959). This surface contamination may in turn also be incorporated into the plant tissue (Middleton, 1958; Morgan, 1959). It is known that several organic substances present in plants, e.g. phytic acid, can affect calcium and strontium absorption from the gut of animals (Nicolaysen, ErgLarsen & Malm, 1953; Irving, 1957). It was not obvious whether such an effect would be found equally for Sr incorporated in grass tissues and strontium chloride added to the same diet. Conflicting evidence on this problem has been produced by other workers (Gross, Taylor, Lee & Watson, 1953 ; Horstman, Selders, Nicholson, Hungate & Bustad, 1957). Sr in world-wide fallout has been shown to be as readily absorbed from the gut of animals as a solution of its chloride when added to the diet (Carr, Harrison & Sutton, 1959) and so is similar in availability to surface contamination of grass. Samples of grass hay containing incorporated gOSr were available from the Agricultural Research Council Radiobiological Laboratory at Compton from experiments on the uptake of 90Sr from the soil by grass. Perennial rye-grass was grown on a soil profile taken fromvarious localities and contained in a concrete cylinder, the 9OSr being added at or just below the surface. Various cuts of the grass were made during the growing season and dried for storage and assay. The samples consequently contained rather more of the young leaves than in normal hay cuts from the field and were similar to the intake of a grazing animal. An experiment with bulked samples of this dried grass from several cylinders was carried out to check the relative absorption from the diet, simultaneously in the same animal, of this incorporated 90Sr and added strontium chloride.