SOLUBILITY OF PLUTONIUM AND AMERICIUM-241 FROM RUMEN CONTENTS OF CATTLE GRAZING ON PLUTONIUM-CONTAMINATED DESERT VEGETATION IN IN VITRO BOVINE GASTROINTESTINAL FLUIDS--NOVEMBER, 1974, TO MAY, 1975 Julius Barth Environmental Protection Agency Environmental Monitoring and Support Laboratory-Las Vegas ABSTRACT Rumen contents collected from cattle grazing at Area 13 of the Nevada Test Site were incubated in simulated bovine gastrointestinal fluids to study the alimentary solubility of plutonium and americium-241. The solubility of americium-241 was found to be similar to that of plutonium-239. In most cases, plutonium-238 was more soluble than plutonium-239. The solubility of plutonium-238, plutonium-239, and americium-241 was markedly greater when the rumen contents were collected from a cow which had grazed in a more intensively grazed enclosure located a greater distance downwind from ground zero. INTRODUCTION This is the second progress report of an ongoing study to determine factors affecting the solubility of selected field-ingested transuranics in an artificial rumen and simulated abomasal and intestinal fluids. An earlier report by Barth (1975) covered the period from the initiation of the study in November, 1973, through August, 1974, and was confined to plutonium-238 and plutonium-239. This report covers trials from November, 1974, through May, 1975, and includes plutonium-238, plutonium-239, and americium-241. The earlier report indicated that field-ingested plutonium-238 was generally more soluble than plutonium-239 in these fluids. The differences were, however, quite variable. During the late summer, fall, and winter trials, low plutonium solubilities were observed; these were accompanied by comparatively high concentrations of plutonium in the rumen contents. An analysis of the vegetal composition of the rumen contents indicated that these conditions were associ- ated with high levels of Furotta lanata (winterfat). In the simulated duodenal fluid, which is presently believed to be the most important digestive stage in 12]