Concentration and vertical distribution of plutonium and americium in Italian mosses and lichens

Abstract

The plutonium and americium concentration and vertical distribution in some Italian mosses and lichens have been determined. The^239,240Pu,²³⁸Pu and²⁴¹Am concentration ranges in tree trunk lichens 0.83–1.87, 0.052–0.154 and 0.180–0.770 Bq/kg, respectively. The corresponding values in tree mosses are higher and more scattered ranging from 0.321 to 4.96, from 0.029 to 0.171 and from 0.200 to 1.93 Bq/kg. The mean²³⁸Pu/^239,240Pu and²⁴¹Am/^239,240Pu ratios are 0.088±0.037 and 0.38±0.13 in lichens and 0.091±0.072 and 0.54±0.16 in tree mosses. The Pu and Am concentrations are relatively low in terrestrial mosses. The^239,240Pu,²³⁸Pu and²⁴¹Am vertical distributions in a terrestrial moss core (Neckera Crispa) collected near Urbino (central Italy) show an exponential decrease with the height. On the contrary the²⁴¹Am vertical distribution in another terrestrial moss core (Sphagnum Compactum) collected in the Alps (northern Italy) shows an interesting peak at 16 cm which corresponds to the deposition of fallout from the nuclear weapon tests in 1960's. The²⁴¹Am movement upward and downward in the moss core is also studied. The results show once again that both mosses and lichens are very effective accumulators of Pu and Am and that they can be used as good biological indicators of the radionuclide airbome pollution from nuclear facilities and nuclear weapon tests. They can play a very impotant role in cycling naturally or artificially enhanced radionuclides in the atmosphere over long time scales.