AQUATIC TOXICOLOGY OF TRACE ELEMENTS 237 



formations. The chemical composition of bottom and fly ash is 

 highly variable, depending on the source of the coal used, combus- 

 tion conditions, and such factors as the efficiency of emission- 

 control equipment (Moulton, 1973; Chu, Nicholas, and Ruane, 1975; 

 Cooper, 1975). In addition to differences in ash composition, 

 numerous physical and chemical factors may affect the leaching of 

 trace elements and the final composition of ash-pond water. These 

 factors include the quantity of water used for sluicing; its tempera- 

 ture, pH, and hardness; and various performance characteristics of 

 the setthng pond. As noted by Chu, Nicholas, and Ruane (1975), the 

 effects of such variables on the quality of ash-pond effluents are not 

 sufficiently understood. It is knovm, however, that a number of 

 coal-derived inorganic elements reach appreciable concentrations in 

 ash-pond waters. Since 1973, TVA has analyzed for 17 trace 

 elements in quarterly grab samples from bottom ash, fly ash, and 

 combined ash ponds, and the results have been summarized by Chu 

 and co-workers (Chu, Nicholas, and Ruane, 1975; Chu, Krenkel, and 

 Ruane, 1976). Discharges from fly-ash ponds were reported to 

 contain up to 7.3 ppm Al, 0.3 ppm Ba, 0.04 ppm Cd, 0.1 ppm Cr, 

 0.3 ppm Cu, 0.08 ppm Pb, 13.4 ppm Mn, 1.1 ppm Ni, and 1.5 ppm 

 Zn. Ranges for a number of these metals are summarized in Table 4. 

 Other investigators also have considered various problems 

 associated with fly-ash disposal (Guthrie, Cherry, and Rodgers, 1974; 

 Theis, 1975; Holland et al., 1975). Theis (1975) indicated that the 

 production of metal leachates and alterations of pH and dissolved 

 oxygen may affect receiving waters. He also demonstrated significant 

 release rates for trace metals when fly ash was dispersed in distilled 

 water. Holland et al. (1975) investigated the environmental effects of 

 trace elements in the pond disposal of ash and flue-gas desulfuriza- 

 tion sludge. Samples of ash and sludge from five generating stations 

 were studied by simulated ponding. In general, concentrations of 

 aqueous leachates were low, but Ba, B, Cr, Hg, and Se exceeded EPA 

 guidelines for public water suppHes. However, these investigators did 

 not compare their findings with EPA standards for freshwater biota, 

 which generally are more stringent, and they did not consider the 

 combined toxic effects of the resulting metal mixtures. Guthrie, 

 Cherry, and Rodgers (1974) evaluated the impact on biota in 

 waters receiving ash-basin effluent from a coal-fired power plant. 

 Bacterial, plant, and animal diversities were reduced at sites affected 

 by ash effluents. Abiotic water parameters affected by ash-basin 

 effluents included temperature, turbidity, dissolved oxygen, and pH. 

 Concentrations of coal-ash leachates (e.g., Cd, Cr, Cu, Hg, and Zn) 

 were lowest in effluent water, somewhat greater in aquatic biota, and 



