UPTAKE OF RADIOCESIUM BY DIFFERENT SPECIES OF MUSHROOMS

Since summer 1987, the distribution of radiocaesium in three different coniferous forest soils in South Bavaria and the radiocaesium concentration in mushrooms has been investigated A total of 364 samples from 83 different fungal species, distinguishable according to their living habits into the three groups of symbionts, saprophytes and parasites were taken and analyzed. The Cs-137 activity concentration in the fruiting bodies ranges between 2 and 15 000 Bq/kg fresh weight, depending on the living habits and the species of mushroom, indicating a species-specific accumulation rate. Therefore, Xerocomus badius, which is the most frequent species on the authors' sampling sites, was taken as a standard, and the radiocaesium content of the other species relative to this mushroom was calculated. Most fungi show a stable ratio, independent of the year and location of sampling. To describe these uptake rates, a transfer factor soil-fungi, defined as caesium activity concentration in the fruiting body of fungi to that in the organic soil horizon, is suggested. This is because mushrooms take up most of their nutrients from these layers and most of the radiocaesium from the Chernobyl accident is still present in the organic horizons. Also the Cs-137/Cs-134 ratio in mushrooms and O-horizons is very similar. During the last five years, no significant decrease of the Cs-137 activity in the fruiting bodies studied has been observed.