Uptake of natural and man-made radionuclides by lichens and mushrooms.

Due to the large absorbing surface of the mycelium that grows in the upper parts of the soil mushrooms take up higher amounts of 137Cs and 40K than lichens. Besides these nuclides only the long-lived radionuclides 125Sb and 60Co could be measured; but not the short-lived fission-products 144Ce, 95Zr and 95Nb which probably decayed before absorption into the mycelium. These nuclides, however, are present in lichens because of their surface structures which enable high foliar deposition. The 137Cs-content of lichens is probably due to absorption by the mycobiont and seems to be used to satisfy their potassium-requirements. Mushrooms on the other hand are characterized by a relatively stable potassium-content and a wide ranging 137Cs-content which depends on the availability in different substrates. Occasionally the natural radionuclides 238U and 226Ra could be detected in mushroom and lichen samples, showing no correlation with the natural radionuclide content of the soil.