Transfer of organically bound radionuclides through foodchains to man: Model - example with radiocobalt and vitamin B12

Radiocobalt in the form of long-lived aerosol is often emitted among the effluents from nuclear power plants. In most of the radioecological model calculations assumptions are primarily based on the inorganic form of cobalt. However, considerable amounts of inorganic cobalt are known to be complexed into organic forms, such as vitamin B12 in the foodchain grass-livestock-milk-meat-man. Because of the high resorption rate of vitamin B12 in the GI-tract, its specific accumulation in the liver and its long biological half-life, the uptake of organic forms of radiocobalt may lead to a relatively high liver dose rate. The relevance of these considerations has been shown in a revised radioecological model calculation based upon a comparison with the conventional assumptions and the available values in the literature. The revised calculation shows that the values for the 60Co-fodder-milk pathway may involve underestimations by a factor ranging from 280 to 2300. In the revised radioecological model calculation non-mean values have been chosen for the parameters to illustrate a potential example of worst-case estimate. More investigations in this field are necessary. (author)