The transfer of 239/240Pu to cow milk

In summer 1993 we measured the transfer of 239/240Pu to milk from herbage from a pasture located 5 km from the Chernobyl nuclear power plant. In one treatment cows were allowed to graze freely on the pasture. In a second treatment, cows were fed herbage collected from the pasture in stalls. The milk transfer coefficient; Fm did not vary significantly between treatments and the mean value of 7.5 × 10−6 d l−1 was higher than previously reported values. Despite many values of Fm for Pu in the literature we identified few relevant original data sets. Transfer coefficient values for Pu are only appropriate when used in conjunction with a specified time period or an appropriate model which allows for the biological half-life. We recommend for screening purposes an Fm value of 1 × 10−5 d l−1 for Pu, with an order of magnitude lower value being appropriate for cows which are only exposed for one grazing season.