Sediment-Water Interactions Affect Assessments of Metals Discharges at Electric Utilities

We present three examples to show the importance of sediment-water interactions to electric utilities: 1) Selenium (Se), in ash pond effluents, has caused declines in fish populations in North Carolina. A biogeochemistry model appears to explain Se dynamics for several reservoirs. However, further work on sediment water interactions is needed to predict the speed of reservoir Se declines following cessation of inputs; 2) Mercury (Hg), volatilized in stack gases from coal fired power plants, is a public and wildlife health concern. Sediments play a major role in the biogeochemistry of Hg as documented in the Mercury Cycling Model (MCM); As with Se, questions about sediment water interactions limit the confidence in predictions about dynamics and effects of Hg; and 3) One of the recommendations from a recent Pellston Conference was to evaluate the use of a new paradigm as a basis for metals regulations. Under this new paradigm, effects of surface active metals (Ag, Al, Cd, Cu, Ni and Zn) on fish can be viewed as dependent on competition between the gill, a 'biotic ligand', and other environmental ligands for metals in discharges. Under this new paradigm, then, the mechanics of toxicity can be viewed as analogous to interactions at the sediment-water interface. It is clear from these three examples that fostering discussion among chemists and toxicologists, through joint participation at meetings and publication in journals used by both fields, is critical for development of accurate assessment capabilities and support of cost effective decision making.