Transport of 131I and 137Cs from air to cows' milk produced in North-Western Italian farms following the Chernobyl accident

Abstract

After the Chernobyl accident, the levels of 131I and 137Cs were measured in surface air, pasture grass and milk produced by cows fed exclusively on fresh grass. The observed values of the vegetation-to-air, milk-to-vegetation and milk-to-air concentration ratios were compared with the values predicted by an internationally recognized assessment model for the transfer of radionuclides through terrestrial food chains. Predicted values were higher than the observed results by factors of 2·6, 2·1 and 5·6 for 131I and 4·3, 3·7 and 16 for 137Cs, for the vegetation-to-air, milk-to-vegetation and milk-to-air ratios, respectively. A better agreement between prediction and observation was achieved by using experimental values of the following parameters; the mass interception factor ( R/Y), the effective decay constants on vegetation ( λ v ) and the milk transfer coefficients ( F m ), these being lower than the model default values. Milk produced by dairy cows fed on a mixed diet showed a different behaviour with regard to excretion of 137Cs.