Sorption of Plutonium-237 by Two Species of Marine Phytoplankton>-^

The adsorption of plutoniurn-23 7, added from an acid solution, by two species of marine phytoplankton, MOTIOchrysis luLheri Droop, a flagellated chrysomonad, and Phaeodactylutn tricornutum Bohlin, a diatom, is governed by a passive mechanism. This is clearly indicated by the observation that the rapid rates of sorption were not significantly different for live and heat-killed cells incubated at 24° C and 0° C. The Qjo values for the chrysomonad and the diatom of 0.95 and 1.18, respectively, are indicative of passive processes. The average ratio of (activity on algae/ activity infiltrate) per unit volume at 24 h, the time when maximum levels of algal radioactivity were attained, of (32 ±4) X 1(P was not significantly different for the diatom or the chrysomonad. On a per cell basis, maximum levels of radioactivity were attained within 2 h. Less than 20% ofthe adsorbed ^^^Pu clesorbed after 24 h. Key index words: adsorption factor; phytoplankton, marine; radionuclide; plutonium-237; sorption kinetics, pas-