Assessment of exposure of larval razorback sucker to selenium in natural waters.

This investigation evaluated effects of exposure of larval razorback sucker to waterborne and dietary selenium and other contaminants that occur in nursery habitats. Site waters were collected from three localities on the Colorado River near Grand Junction, CO; a total of five test waters (including control) were studied. Razorback sucker larvae were exposed to site-water contaminants via waterborne and dietary exposure using a laboratory food chain (algae, rotifer, razorback sucker). Fish were exposed for 28 days to site waters and food organisms cultured in site waters. Survival data were analyzed by inspection. Growth data were analyzed using analysis of variance to describe the response of fish in each site water and to describe the relative contribution of waterborne versus dietary exposure to constituents in site waters. Selenium concentrations in test-water treatments ranged from < 1 to 20.3 microg/L in water, < 0.702 to 21.8 microg/g in diet, and 2.34 to 42.0 microg/g in fish. Negative effects from dietary exposure to site-water constituents were detected, but the data suggest that they were caused by cocontaminants in the diet, not selenium exposure. Lack of detection of adverse effects from exposure does not imply that razorback sucker populations are not affected by increased environmental selenium concentrations. There are a variety of factors not included in this investigation that may influence sensitivity of razorback sucker populations to selenium.