Experimental determination of transfer coefficients of 137Cs and 131I from fodder into milk of cows and sheep after the Chernobyl accident.

Following the Chernobyl accident in April 1986, the transfer of 131I and 137Cs from feed to milk was studied under experimental and common agricultural conditions. From measurements in different dairy farms in Southern Bavaria, equilibrium transfer coefficients for cow's milk were calculated to be 0.003 d L-1 (range 0.0015 to 0.005) for 131I and 0.003 d L-1 (range 0.0025 to 0.004) for 137Cs. In feeding experiments with cows and sheep under more controlled conditions, milk transfer coefficients of 0.007 d L-1 (range 0.0055 to 0.0081) for 131I and 0.003 d L-1 (range 0.0023 to 0.0053) for 137Cs were obtained for cows, while for sheep the 137Cs transfer coefficient was higher: 0.06 d L-1. The kinetics of the Cs transfer from fodder to cow's milk can be described by two exponential terms assuming biological half-lives in milk of 1-2 d and 10-20 d. The use of a fast component with 1.5 d and a fraction of 0.8, and a slow component with 15 d, gives a good approximation to the kinetics for all cows in this experiment.