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into beakers containing 0.50 L dilution water. Test solutions were stirred and transferred to <br />exposure beakers within 30 minutes of preparation. <br />Analytical procedures <br />Dissolved selenium concentrations in the ELS test were measured weekly (four <br />occasions). Concentrations in acute tests were measured on one occasion at the beginning of the <br />exposure period. Dissolved selenium concentrations in algae and rotifer batch cultures were <br />measured on one occasion. On each sampling occasion, three 250-m1 samples were collected. <br />Unfiltered samples were placed in acid-washed polyethylene bottles, acidified to pH < 2 with <br />analytical-grade nitric acid, and held at 4°C until analyzed by Paragon Analytics, Inc. (Fort <br />Collins, Colorado). Measured concentrations were adjusted for recovery of selenium in spiked <br />samples (99.2%, SE = 1.65). <br />Selenium concentrations in algae, rotifer, razorback sucker, and flannelmouth sucker <br />were also determined for the ELS test. Duplicate samples of algae and rotifer were collected <br />weekly (four occasions). Fish within an exposure beaker were pooled and collected at the end of <br />the exposure period. Samples were placed in acid-washed polyethylene vials, and held at -4°C <br />until analyzed. Algae and rotifer samples were analyzed at Colorado State University <br />(Department of Environmental Health, Fort Collins, Colorado). Fish larvae were analyzed at <br />North Carolina State University (Nuclear Services, Department of Nuclear Engineering, Raleigh, <br />North Carolina). All tissue concentrations are based on dry-weight determinations. Average <br />water content of algae, rotifer, and fish was 70.5% (SE = 1.69, n = 10), 92.3% (SE = 0.474, <br />n = 10), and 83.0% (SE = 0.0736, n = 5), respectively. Tissue concentrations were adjusted for <br />9 <br />