Radionuclide migration in forest ecosystems--results of a model validation study

The primary objective of the IAEA's BIOMASS Forest Working Group (FWG) was to bring together experimental radioecologists and modellers to facilitate the exchange of information which could be used to improve our ability to understand and forecast radionuclide transfers within forests. This paper describes a blind model validation exercise which was conducted by the FWG to test nine models which members of the group had developed in response to the need to predict the fate of radiocaesium in forests in Europe after the Chernobyl accident. The outcomes and conclusions of this exercise are summarised. It was concluded that, as a group, the models are capable of providing an envelope of predictions which can be expected to enclose experimental data for radiocaesium contamination in forests over the time scale tested. However, the models are subject to varying degrees of conceptual uncertainty which gives rise to a very high degree of divergence between individual model predictions, particularly when forecasting edible mushroom contamination. Furthermore, the forecasting capability of the models over future decades currently remains untested.     

Generic values for soil-to-plant transfer factors of radiocesium

There is a need for soil-to-plant transfer factors of radionuclides that take into account all possible crops on all soil varieties to support dose assessment studies. Because only limited experimental data exist for worldwide soil systems, such values should necessarily have a generic character. This paper describes a generic system for 137Cs, mainly based on a reference soil-to-plant transfer factor which depends solely on soil properties such as nutrient status, exchangeable K-content, pH and moisture content. Crops are divided into crop groups, cereals serving as reference group. The transfer of other crop groups can be calculated by multiplying data for cereals by a conversion factor. Existing data present in the IUR (International Union of Radioecologists) databank and in large part the work of a FAO (Food and Agriculture Organisation)/IAEA(International Atomic Energy Agency)/IUR project on tropical systems provided the basis for the derivation of the conversion factors and reference values.