AQUATIC TOXICOLOGY OF TRACE ELEMENTS 229 



TABLE 4 

 CHARACTERISTICS OF SIMULATED ASH-POND EFFLUENT 



*Mean ± standard error for initial 500 hr of continuous operation. 

 tRange of mean values for 14 TVA ash ponds (Chu, Ruane, and Steiner, 



1976). 



t Alkalinity determined for the third 500-hr elution interval. 



effluent water did not differ substantially in pH, alkalinity, conduc- 

 tivity, or total dissolved solids. 



Effluent concentrations for the seven selected metals monitored 

 through 1500 hr are summarized in Table 5. Maximum concentra- 

 tions, which in most instances were observed during the first 100 hr 

 of elution time, were 126 ppm Al, 766 ppb Zn, 518 ppb Cu, 500 ppb 

 Cd, 370 ppb Ni, 87 ppb Hg, and 8 ppb Ag. Mean concentrations for 

 the first 500 hours were 32.6 ppm Al, 350 ppb Zn, 156 ppb Cd, 155 

 ppb Ni, 110 ppb Cu, 2.1 ppb Ag, and 1.8 ppb Hg. The 500-hr elution 

 patterns for Al, Cu, Ni, and Zn are illustrated in Fig. 2. Elevated 

 concentrations observed at about 300 hr correlated with mechanical 

 disturbances that temporarily facilitated water filtration through the 

 fly-ash bed. Concentrations for all metals except mercury continued 

 to decline progressively with further leaching time, resulting in mean 

 values for the third elution interval of 540 ppb Al, 61.4 ppb Zn, 33.6 

 ppb Ni, 25.7 ppb Cd, 4.1 ppb Cu, and 0.2 ppb Ag (Table 5). Mercury 

 fluctuated from 0.3 to 7.4 ppb during the first 500 hr but increased 

 substantially thereafter, with mean values of 27.4 and 14.9 ppb for 

 the second and third elution intervals. However, the mercury level 

 dropped markedly toward the end of the third elution period, 

 averaging 2.6 ± 0.7 ppb after 1360 hr. Metals were not detected in 



