Radionuclide transfer in forest ecosystems

The behaviour of radionuclides in forest ecosystems differs substantially from the other ecosystems. The contamination of various forest products is commonly quantified using the Aggregated Transfer Factor (Tag in m2 kg-1) which integrates various environmental parameters including soil and plant type, root distribution as well as nature and vertical distribution of the deposits. This review aims at compiling the most relevant quantitative information on radionuclide transfers to forest biota including trees, understorey vegetation, mushrooms, berries and game animals. For both radiocaesium and radiostrontium in trees, the order of magnitude of mean Tag values is 10-3 m2.kg-1 (dry weight). The transfer of radionuclides to mushrooms and berries is high, in comparison with foodstuffs grown in agricultural systems. Concerning caesium uptake by mushrooms, the transfer is characterized by a very large variability of Tag, from 10-3 to 101 m2.kg-1 (dry weight). For berries, typical values are around 0.01 to 0.1 m2.kg-1 (dry weight). Transfer of radioactive caesium to game animals and reindeer and the rate of activity reduction, quantified as an ecological half-life, reflect the soil and pasture conditions at individual locations. Even if, the importance of radioactive contamination of forests as a significant source of the population exposure is recognized, most of the data refer to caesium and to a lesser extent, strontium. Data for other radionuclides are rather limited. (author)