SEASONAL EFFECTS ON THE SOLUBILITY IN ZN VITRO BOVINE GASTROINTESTINAL FLUIDS OF PLUTONIUM INGESTED BY GRAZING CATTLE Julius Barth National Environmental Research Center, Las Vegas* ABSTRACT In order to study the alimentary solubility of plutonium, plutoniumcontaminated rumen contents were collected from grazing cattle and were incubated in simulated bovine gastrointestinal fluids. During the spring and midsummer trials, a large increase in plutonium solubility and a marked reduction in the plutonium concentration of the rumen contents were observed concurrently with a reduction in intake of Eurotta lanata and an increase in the intake of Oryzopsts hymenoitdes or Sttanton jubatum. During the late summer, fall, and winter trials, comparatively high concentrations of plutonium, but low plutonium solubilities, were associated with high levels of Furotia lanata in the rumen contents. Plutonium-238 was generally more soluble than plutonium-239 in these in vitro bovine gastrointestinal fluids. INTRODUCTION ay. The primary purpose of this ongoing study is to determine the effects of grazing season, and the relative amounts of plant species ingested, on the solubility of plutonium-238 and plutonium-239 in an in vitro bovine digestive tract. Rumen contents, collected from grazing *Now designated as the Environmental Monitoring and Support Laboratory-Las Vegas (EMSL-LV). 35