SEDIMENT-WATER INTERACTIONS AFFECT ASSESSMENTS OF METALS DISCHARGES AT ELECTRIC UTILITIES

We present three examples to show the importance of sediment-water int eractions to electric utilities: 1) Selenium (Se), in ash pond effluen ts, has caused declines in fish populations in North Carolina. A bioge ochemistry model appears to explain Se dynamics for several reservoirs . However, further work on sediment water interactions is needed to pr edict the speed of reservoir Se declines following cessation of inputs ; 2) Mercury (Hg), volatilized in stack gases from coal fired power pl ants, 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 wa s to evaluate the use of a new paradigm as a basis for metals regulati ons. 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 sedimen t-water interface. It is clear from these three examples that fosterin g discussion among chemists and toxicologists, through joint participa tion at meetings and publication in journals used by both fields, is c ritical for development of accurate assessment capabilities and suppor t of cost effective decision making.