Transfer of 131I to sheep milk from vegetation contaminated by chernobyl fallout

Abstract

The transfer of 131I to sheep milk was measured in a controlled feeding experiment using herbage recently contaminated by fallout from the Chernobyl accident. The transfer coefficient (fm) of 131I from the Chernobyl-contaminated herbage was 0·29±0·017 day litre −1. The daily proportion of 131I 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 occurs in sheep and goats. At the same time the biological half-life of 131I was measured in ewes which had been grazing outside during deposition of the Chernobyl fallout and were then housed and fed an 131I-free diet. The loss of 131I 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 reduction in the concentration of 131I activity in the milk. The 131I-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 presented here, which have been estimated using measured dietary intakes and milk outputs, appear to be the first such dates reported for sheep for an environmentally contaminated source.