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<br />Field: <br /> <br />A total offour localities on the Colorado and Gunnison rivers where site water <br />will be obtained. <br /> <br />VI. Study Methods/Approach: <br /> <br />The basic methodology of this experiment is based on the ongoing study entitled <br />"Assessment and Prediction of Effects of Selenium Exposure to Larval Razorback Sucker" <br />in which rotifers are cultured in selenium-contaminated water and fed to razorback sucker <br />larvae. The strength of this approach is that the food for larvae is allowed to accumulate <br />selenium naturally. In contrast to the previous study, the proposed research will expose <br />razorback larvae and rotifers to site waters that contain selenium as well as <br />co-contaminants. The potential influence of co-contaminants is of interest because they <br />may interact with selenium and increase or decrease its toxicity. The advantages of <br />studying the effects of exposure to site waters within a laboratory environment are <br />increased environmental realism while minimizing the potential for confounding <br />influences. Consequently, a strong case for cause and effect can be made, and a better <br />assessment of the accuracy of the predictive equations can be conducted. <br /> <br />Site waters will be obtained weekly from four localities in the 16- and 18-mile reaches on <br />the Colorado River and from the Gunnison River. Unfiltered water will be collected in <br />plastic barrels and transported to laboratory facilities at Colorado State University. Site <br />waters will be pasteurized by heating to 500C for 2 hours to destroy microbes and algae <br />that could contaminate laboratory cultures. Pasteurizing can be used to sterilize culture <br />media, but does not change the chemical composition of treated water (Hoff and <br />Snell 1989). Preliminary studies will be conducted during 1998 to confirm that the <br />pasteurizing process does not influence the concentration of selenium in water. Two <br />replicate samples will be collected from each site-water batch for 'chemical analysis. <br />Analysis will include: selenium, calcium, magnesium, sodium, potassium, carbonate, <br />bicarbonate, sulfate, nitrate, chloride, boron, total dissolved solids, phosphorus, aluminum, <br />iron, manganese, copper, zinc, nickel, molybdenum, cadmium, chromium, barium, lead, <br />alkalinity, hardness, pH, and specific conductance. <br /> <br />Rotifers and algae (food source for rotifers) will be allowed to accumulate selenium and <br />co-contaminants naturally by culturing them in four different site waters or control water <br />obtained from the well-water supply on the Colorado State University campus. The well <br />water has the following characteristics: pH, 8.0; alkalinity, 250 mglL; hardness, 360 mglL; <br />and specific conductance, 730 f.lS/cm. These levels are similar to water quality of the <br />Colorado River near the Colorado-Utah state line based on USGS records (gage <br />09163500). <br /> <br />Toxicity tests will be conducted using methods prescribed by the American Society for <br />Testing and Materials (1990a) for early life-stage toxicity tests. A replicated (n=4), <br />balanced 5x2 factorial design with five test waters and contaminated or uncontaminated <br /> <br />Selenium 4 <br />