An evaluation of selenium concentrations in water, sediment, invertebrates, and fish from the Republican River Basin: 1997-1999

The Republican River Basin of Colorado, Nebraska, and Kansas lies in a vall ey which contains Pierre Shale as part of its geological substrata. Seleniu m is an indigenous constituent in the shale and is readily leached into sur rounding groundwater. The Basin is heavily irrigated through the pumping of groundwater, some of which is selenium-contaminated, onto fields in agricu ltural production. Water, sediment, benthic invertebrates, and/or fish were collected from 46 sites in the Basin and were analyzed for selenium to det ermine the potential for food-chain bioaccumulation, dietary toxicity, and reproductive effects of selenium in biota. Resulting selenium concentration s were compared to published guidelines or biological effects thresholds. W ater from 38% of the sites (n = 18) contained selenium concentrations excee ding 5 mug L-1, which is reported to be a high hazard for selenium accumula tion into the planktonic food chain. An additional 12 sites (26% of the sit es) contained selenium in water between 3-5 mug L-1, constituting a moderat e hazard. Selenium concentrations in sediment indicated little to no hazard for selenium accumulation from sediments into the benthic food chain. Nine ty-five percent of benthic invertebrates collected exhibited selenium conce ntrations exceeding 3 mug g(-1), a level reported as potentially lethal to fish and birds that consume them. Seventy-five percent of fish collected in 1997, 90% in 1998, and 64% in 1999 exceeded 4 mug g(-1) selenium, indicati ng a high potential for toxicity and reproductive effects. However, examina tion of weight profiles of various species of collected individual fish sug gested successful recruitment in spite of selenium concentrations that exce eded published biological effects thresholds for health and reproductive su ccess. This finding suggested that universal application of published guide lines for selenium may be inappropriate or at least may need refinement for systems similar to the Republican River Basin. Additional research is need ed to determine the true impact of selenium on fish and wildlife resources in the Basin.