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Dsn?uno?son, M7 Arch. Environ. Contam. Toxicol. 38, 479-485 (2000) DOI: 10.1007/s002449910063 7AP A R C H I V E S O F Environmental Contamination a n d Toxicology © 2000 Springer-Vertag New York Inc. r Selenium Concentrations in the Colorado Pikeminnow (Ptychocheilus lucius): Relationship with Flows in the Upper Colorado River B. C. Osmundson,l T. W. May,2 D. B. Osmundson3 1 U.S. Fish and Wildlife Service, Ecological Services, 764 Horizon Drive, Bldg B, Grand Junction, Colorado 81506-3946, USA 2 U.S. Geological Survey, Columbia Environmental Research Center, 4200 New Haven Road, Columbia, Missouri 65201, USA 3 U.S. Fish and Wildlife Service, Colorado River Fishery Project, 764 Horizon Drive, Bldg B, Grand Junction, Colorado 81506-3946, USA Received: 21 June 1999/Accepted: 10 November 1999 Abstract. A Department of the Interior (DOI) irrigation drain- water study of the Uncompahgre Project area and the rand Valley in western Colorado revealed high selenium concentra- tions in water, sediment, and biota ales.wer ni- son Riw and the AColamd9 River in the study area are designated critical habitat for the endangered Coloradn?nikP- _minnow (Ptychocheilus lucius) and razorback sucker (Xyrauchen texanus). Because of the endangered status of these fish, sacrificing individuals for tissue residue analysis has been avoided; consequently, little information existed regarding selenium tissue residues. In 1994, muscle plugs were collected from a total of 39 Colorado pikeminnow captured at various Colorado River sites in the Grand Valley for selenium residue analysis. The muscle plugs collected from 16 Colorado pike- minnow captured at Walter Walker State Wildlife Area (WWSWA) contained a mean selenium concentration of 17 pg/g dry weight, which was over twice the recommended toxic threshold guideline concentration of 8 pg/g dry weight in muscle tissue for freshwater fish. Because of elevated selenium concentrations in muscle plugs in 1994, a total of 52 muscle plugs were taken during 1995 from Colorado pikeminnow staging at WWSWA. Eleven 'of these plugs were from fish previously sampled in 1994. Selenium concentrations in 9 of the 11 recaptured fish were significantly lower in 1995 than in 1994. Reduced selenium in fish may in part be attributed to higher instream flows in 1995 and lower water selenium concentrations in the Colorado River in the Grand Valley. In 1996, muscle plugs were taken from 35 Colorado squawfish captured at WWSWA, and no difference in mean selenium concentrations were detected from those sampled in 1995. Colorado River flows during 1996 were intermediate to those measured in 1994 and 1995. source of salinity and selenium problems documented in the western United States (Seiler and Skorupa 1995). A study of contaminant concentrations in fish and wildlife at sites that received irrigation drainwater associated with the Uncompah- gre Project area and the Grand Valley in western Colorado was conducted during 1991-1993, because much of the irrigated area consists of Mancos shale. This study revealed high selenium concentrations in water, sediment, and biota samples (Butler et al., 1994, 1996). Selenium concentrations in water samples collected from the lower Gunnison River and the Colorado River near the Colorado-Utah State line often ex- ceeded the U.S. Environmental Protection Agency criterion of 5 µg/L for the protection of aquatic life (US EPA 1987). Selenium concentrations in biota often exceeded toxic threshold guide- lines proposed by Lemly (1996), i.e., 8 gg/g in muscle tissue. Because the lower Gunnison and Colorado Rivers were within "critical habitat" designated for the endangered Colorado pikeminnow (Ptychocheilus lucius) and razorback sucker (Xyrauchen texanus) (USFWS 1994), we were concerned about potential adverse effects to these endangered fish from sele- nium. Because of the endangered status of the razorback sucker and Colorado pikeminnow, tissue sampling using lethal procedures has not been conducted, and therefore little information exists regarding tissue residues of selenium. To determine selenium residues in Colorado pikeminnow in the Grand Valley and assess the potential hazard, we selected a nonlethal sampling procedure developed and described by Waddell and May (1995). They took muscle plugs from razorback suckers using a 5-mm biopsy punch, and then analyzed the plugs for selenium residues using neutron activation. They demonstrated that the method was accurate and a good substitute for whole-body sampling when sacrifice of rare fish is prohibited. In 1985, the U.S. Department of the Interior initiated a program to assess water-quality problems associated with federal irriga- tion projects in the western United States (Feltz et al., 1991). Mancos shale, a marine shale, was identified as the primary Correspondence to: B. C. Osmundson Materials and Methods Study Area The Grand Valley, one of the largest agricultural and urban areas in western Colorado, is located along the Colorado River (Figure 1). Locations along the Colorado River are expressed in river kilometers