TRANSFER OF I-131 TO SHEEP MILK FROM VEGETATION CONTAMINATED BY CHERNOBYL FALLOUT

The transfer of I-131 to sheep milk was measured in a controlled feedi ng experiment using herbage recently contaminated by fallout from the Chernobyl accident. The transfer coefficient (F(m)) of I-131 from the Chernobyl-contaminated herbage was 0.29 +/- 0.017 day litre-1. The dai ly proportion of I-131 intake which was secreted in milk was 56 +/- 0. 035%. This is an order of magnitude higher than for cattle and agrees with the higher transfer of stable iodine from plasma to milk which oc curs in sheep and goats. At the same time the biological half-life of I-131 was measured in ewes which had been grazing outside during depos ition of the Chernobyl fallout and were then housed and fed an I-131 f ree diet. The loss of I-131 in sheep milk was described using a double exponential relationship. The calculated biological half-life for the first component in the milk was 1 day, accounting for 97.4% of the re duction in the concentration of I-131 activity in the milk. The I-131- free diet had a comparatively high stable iodine content since it was saltmarsh vegetation, however, the calculated half-life was similar to previously estimated values for goats. The transfer parameters presen ted here, which have been estimated using measured dietary intakes and milk outputs, appear to be the first such dates reported for sheep fo r an environmentally contaminated source.