CONCENTRATION AND VERTICAL-DISTRIBUTION OF PLUTONIUM AND AMERICIUM INITALIAN MOSSES AND LICHENS

The plutonium and americium concentration and vertical distribution in some Italian mosses and lichens have been determined. The Pu-239,Pu-2 40, Pu-238 and Am-241 concentration ranges in tree trunk lichens 0.83- 1.87, 0.052-0.154 and 0.180-0.770 Bq/kg, respectively. The correspondi ng 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. ?he mea n Pu-238/Pu-239,Pu-240 and Am-241/Pu-239,Pu-240 ratios art: 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 Pu-239,Pu-240,Pu-238 and Am-241 vertical distr ibutions in a terrestrial moss core (Neckera Crispa) collected near Ur bino (central Italy) show an exponential decrease with the height. On the contrary the Am-241 vertical distribution in another terrestrial m oss con: (Sphagnun Compactum) collected in the Alps (northern Italy) s hows an interesting peak at 16 an which corresponds to the deposition of fallout from the nuclear weapon tests in 1960's. The Am-241 movemen t upward and downward in the moss core is also studied. The results sh ow once again that both mosses and lichens are very effective accumula tors of Pu and Am and that they can be used as good biological indicat ors of the radionuclide airborne pollution from nuclear facilities and nuclear weapon tests. They can play a very important role in cycling naturally or artificially enhanced radionuclides in the atmosphere ove rlong time scales.