The contents of ${}^(239,240)Pu$ and ${}^(238)Pu$ in piankton and sea water samples collected in some zones of Italian coasts were determined. Through other authors' data on samples collected in oceans and in the Great Lakes of Northern America we can make some interesting considerations. The values chiefly refer to the plutonium of the radioactive fallout whose amount is the same in the whole latitudinal band of the northern hemisphere between the 40th and the 60th parallel. The concentrations of ${}^(239,240)Pu$ in pCi/Kg of wet Mediterranean plankton are close to the lowest values found for the plankton of Lakes Erie and Michigan. The same considerations are valid for the values of the concentration factors that, for the Mediterranean samples, are between 50 and 250. The concentration factors of the mixed plankton from the Atlantic and Pacific Oceans are about 2500, whereas those of the Lake Michigan plankton range from about 100 to 15,000 according to the increase of the phytoplankton contents in the sample. This would lead us to think that the real value of the concentration factor for the zooplankton, both of sea water and of fresh water, is of some hundreds.
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Con il contributo del Ministero per i Beni e le Attività Culturali