NAEG studies to gain information concerning the influence of soil microbial activities on the bioavailability and biotransport of transuranics in desert environments continue. Au and Beckert suggest that the biomass figure for fungal and bacterial biomasses should provide some understanding of potential microbial activities in Nevada Test Site soils. Of In fact, the course, many variables enter into such determinations. been observed have soils desert of soil fungal and bacterial populations to be very high and diversified, even in locations without plants. Experiments using Aspergillus ntger are under way to determine whether the availability and transfer of plutonium are increased during successive generations of soil microbial growth. G.I. tract studies with fistulated steers grazing in Area 13 continue. The relative solubility and concentrations of plutonium and americium in rumen samples collected under field conditions in Area 13 vary, depending on several factors discussed by Barth: season, predominant species ingested, vegetative stage of growth, presence of fruiting involucres on Eurotta lanata, grazing intensity, and distance of grazing area from ground zero. Future plans include combined studies with microorganisms and artificial rumen systems. Investigation of differences between biological availability of biologically incorporated plutonium and nonbiologically available plutonium, and study of whether biological organic binding protects plutonium from being removed from solution by competing chemical reactions are among studies planned. A comparison was made of data from cattle grazing in Area 13, NTS (a plutonium-contaminated safety-shot area), with data from cattle grazed in the area of the Rocky Flats Plant in Jefferson County, Colorado. Smith reported on Area 13 cattle, reflecting gonad concentrations equal to that of femurs and significantly higher than muscle. Similar relative tissue concentrations were found in the Rocky Flats cattle data, although generally the concentrations were less than those reported for Area 13 cattle. Smith also reported that concentrations of plutonium in the femurs of young animals were slightly higher than concentrations in adult animals. Holstein dairy cows were used to measure rate of passage of sand particles tagged with L4lce, 85sr, °4Mn, or 46so, through the G.I. tract. Patzer, Sutton, and Potter performed the study to determine whether passage rate of particles through the bovine G.I. tract is related to size. Results indicated significant variance with particle size, with measurements of up to 12 days for passage of 90% of the particles in feces. Comparisons between the biological transport of plutonium and curium in dairy goats were studied by Sutton et aZ. Intravenous or oral doses of curium-243 chloride were administered to 6 lactating goats, followed by milk, urine, fecal, and blood sampling for 6 days. Approximately 2% of the IV dose was transferred to milk during the 6-day period. Urine and feces averaged more than 4% of the administered IV dose. The oral dose results indicated excretion in feces of all but less than 1% of the administered dose, and nondetectable quantities in milk, urine, and blood. Compared with plutonium previously administered (IV) to a single 319