Selenium impacts on fish: An insidious time bomb

A selenium time bomb situation is developing in the United States and elsew here that may result in substantial impacts on fish populations. The seleni um time bomb has three components: (1) high food-chain bioaccumulation, (2) steep toxic response curve for fish, and (3) insidious mode of toxicity. I f the threshold for selenium toxicity is exceeded, the time bomb explodes a nd a cascade of events is set into motion that will result in major ecosyst em disruption. Several human-related factors are emerging that are capable of igniting the fuse of the time bomb by increasing waterborne concentratio ns of selenium and providing conditions favorable for bioaccumulation. Some of these factors are (1) mobilization of selenium due to open-pit phosphat e mining, (2) use of constructed wetlands to treat selenium-laden wastewate r from oil refineries and agricultural irrigation, (3) landfill disposal of seleniferous fly ash from coal-fired power plants, and (4) mobilization of selenium from animal feedlot wastes. Collectively, these threats may be su fficient to cause widespread, unanticipated toxic effects in fish populatio ns. Only environmentally sound risk assessments followed by prudent managem ent actions can defuse the selenium time bomb - once it explodes, it is too late to avoid significant impacts.