EFFECT OF NATURALLY OCCURRING ORGANICS ON PLUTONIUM~237 UPTAKE BY ALGAE AND BACTERIA John P. Giesy, Jr. Savannah River Ecology Laboratory Aiken, South Carolina Donald Paine Battelle, Pacific Northwest Laboratories Richland, Washington and Lyda W. Hersloff Department of Radiology and Radiation Biology Colorado State University, Fort Collins, Colorado ABSTRACT Naturally occurring organics were concentrated from Skinface Pond, Aiken, South Carolina and separated into four nominal diameter size near fractions (F I > 6.0183; 0.0183 > F II > 9.0032; 0.0032 > F TIT > 0.009; F Iv < 0.009 um) by membrane ultrafiltration. Each fraction was introduced into Scenedesmus obliquus and Aeromonas hydrophila cultures at concentrations equal to those found in nature to determine their effects on 237pu uptake. Plutonium-237 uptake was determined in log phase cultures after 6 hr incubations. initial plutonium concentration in each flask was 1.1 x 10-4 uCi/ml 237put4(no4) 4. Fractions I and II significantly reduced 237pu uptake by S. obliguus, while F IV increased uptake and F ITI had no effect. uptake by A. The hydrophila was not significantly different in Plutonium-237 the presence of FoI, F Il or F III than tryptic broth medium alone, while F Iv significantly increased 237py uptake. INTRODUCTION While plutonium presently exists at very low concentrations in the biosphere, trophic biomagnification and possible localized contaminations may result in increased plutonium concentrations in organisms of higher trophic levels. Algae and bacteria form the base of aquatic food webs and concentrate plutonium greatly over water concentrations -(Noshkin, 531 1972; Folsom et al., 1975; Gromov