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

Abstract

Transfer / Fungi / 90 Sr / 239+240 Pu / 241 Am Summary. 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 90 Sr, 239+240 Pu, and 241 Am 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 90 Sr TF values were higher than those of 239+240 Pu and 241 Am. 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 soilthe available transfer factor, ATF -which would be closer to the actual process of transfer. Hebeloma cylindrosporum and Lycoperdon perlatum presented 239+240 Pu and 241 Am ATF values that were greater than or similar to those of 90 Sr. These species may thus be used as bioindicators for 239+240 Pu and 241 Am in a forest ecosystem.

A Review of the Occurrence of Alpha-Emitting Radionuclides in Wild Mushrooms

“…Plutonium is not effectively accumulated by mushrooms and shows a similar distribution in fruiting bodies to that of thorium and uranium (stem > cap > gills) [40]. Baeza et al studied 239+240 Pu accumulation in the saprophytic fungus Pleurotus eryngii cultivated under laboratory conditions and its occurrence in wild-growing mycorrhizal mushroom species (Tricholoma equestre), and concluded that its distribution seemed to be species-dependent, but were not able to confirm whether saprophytic fungi presented a lower content of this radionuclide than mycorrhizal fungi, as was observed in the case of 137 Cs [40,115]. The highest activity concentrations of Pu isotopes have been determined in mushrooms collected at sites in the Ukraine that were associated with indirect contamination from the Chernobyl incident fallout in 1986 [83,108,112].…”

“…Nevertheless, the presence of man-made nuclides in mushrooms and plant-based foods depends on local radioactive pollution conditions (nuclear test sites, facilities, accidents and distance from these sites) and is influenced by global atmospheric fallout [9,12,108,109]. Due to analytical difficulties, very few studies have dealt with anthropogenic alpha emitters released into the environment, and have instead focused on the most common radioactive elements, namely plutonium and americium, as well as uranium 236 U [83][84][85][86]92,108,[110][111][112][113][114][115][116][117][118].…”

“…[113,117,118] The element americium may originate from global atmospheric fallout connected to nuclear weapon testing or as a decay product of its parent nuclide, 241 Pu, which was identified in Chernobyl fallout [103]. So far, its presence has been measured and reported only in mushrooms sampled in European countries such as Finland, Slovakia, Spain and the UK, and the activity concentrations were the lowest of all the alpha emitters, i.e., in the range from 0.003 to 1.01 Bq/kg dw [86,[113][114][115][116][117][118] (Table 2).…”