Soil-to-fungi transfer of 90Sr, 239+240Pu, and 241Am

Fungi have up to now generally been used as bioindicators of radiocaesium in terrestrial ecosystems. However there is little knowledge about the behaviour of other man-made radionuclides. In the present work, we analyzed the soil-to-fungi transfer of 90Sr, 239+240Pu, and 241Am by collecting several species of fungi and the corresponding surface soil (0−5 cm) of a selected semi-natural ecosystem. The transfer of these radionuclides was then quantified by means of the traditional transfer factor, TF, defined as the ratio between the content in the fruiting bodies and in the total fraction of soil. As a general rule, the 90Sr TF values were higher than those of 239+240Pu and 241Am. This definition of the transfer factor can underestimate the transfer of radionuclides of which a large percentage are bound to soil particles. We therefore also used a definition based on the amount of radionuclide available to be transferred instead of the total content of the soil — the available transfer factor, ATF — which would be closer to the actual process of transfer. Hebeloma cylindrosporumand Lycoperdon perlatumpresented 239+240Pu and 241Am ATF values that were greater than or similar to those of 90Sr. These species may thus be used as bioindicators for 239+240Pu and 241Am in a forest ecosystem.