The comparison of generic model predictions with chernobyl fallout data on the transfer of radioiodine over the air-pasture-cow-milk pathway

Data have been collected on concentrations of 131I in air, vegetation and milk from numerous locations receiving Chernobyl fallout. Time-integrated concentrations derived from these data are used to compare predictions from generic models used for routine environmental radiological assessments. In general, the models markedly overestimated the transfer of 131I over the air-grass-cow-milk pathway. The reasons for this overestimate appear to be related to a combination of different factors, among which overestimation of the dry deposition velocity assumed for elemental 131I, overestimation of the interception and retention of wet-deposited 131I by pasture vegetation and overestimation of the cow's diet-to-milk transfer coefficient appear to be most important. The low transfer of Chernobyl 131I from air to milk indicates that the direct inhalation of contaminated air by humans may be more important in determining the 131I exposure to large populations than the consumption of contaminated cow's milk. Radiological assessments conducted prior to the Chernobyl accident have typically assumed that 131I exposure would be dominated by the consumption of milk. The consumption of milk, however, is still of dominant importance for the exposure of critical population subgroups composed of infants and small children.