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EXECUTIVE SUMMARY This project examined the hypothesis that selenium contamination is not the principal cause of the decline of endemic fish species in the Upper Colorado Basin. Activities employed to test this hypothesis included a reconnaissance of locations altered by recent road construction, a re- interpretation of available literature regarding selenium toxicity, and the interpretation of unpublished data obtained from the Upper Colorado Basin Fish Recovery Program. The project demonstrates that most of the evidence implicating selenium is circumstantial. Specifically, this research demonstrates that neither the historical record nor the technical literature consistently supports the emphasis given selenium toxicity. For example, many locations in the intermountain region have elevated selenium in water and sediments without obvious consequences for wildlife. Consequently, biological and geochemical studies are required to understand the cycling, relative abundance, and bioavailability of selenium and other constituents so that causal agents in the Upper Colorado Basin can be identified with greater certainty. The project also demonstrates the need for subcellular indicators of selenium poisoning. Unfortunately, most potential biomarkers are not specific for selenium. A potential candidate based on the mammalian literature is glutathione peroxidase (GPx) activity and/or the cellular levels of reduced glutathione and hydrogen selenide (Greeley, M.S., Oak Ridge National Laboratory, personal communication, Jan. 22, 1999). Evidence of increased lipid peroxidation and related glutathione peroxidase activity has been found in aquatic birds at sites such as Kesterson (Hoffman and Heinz 1988, Ohlendorf et al. 1988). Selenium has an antimutagenic effect so genomic research is not feasible. However, the activity of the GPx gene could be explored as a potential selenium biomarker. Little is known regarding the mechanistic relationships between GPx and selenium, which of itself is an area where additional research would provide important information. Studies also are needed with the endangered fish and other species to develop predictive tools regarding the manner in which selenium cycles geochemically and biologically in riverine and backwater environments. Finally, hydrological investigations and modeling are needed to further examine the coordination of dam operation and water diversions to determine whether modifications can provide the habitat necessary to ensure survival of the endangered species. The performance of this project has developed the relationships and knowledge required to advance proposals in the specific areas just described. Within the Environmental Sciences Division (ESD), a seminar and several group discussions were held to identify team members for proposals. Potential funding sources within and outside of the U.S. Department of Energy (DOE) have been identified, and ESD staff members are approaching these informally. The preparation of one or two proposals is anticipated during FY 2000. Finally, the journals Bioscience and Reviews in Fisheries Science were selected as appropriate venues for publishing this work, and a manuscript is in preparation. ix