AQUATIC TOXICOLOGY OF TRACE ELEMENTS 235 



The heterogeneity of response observed for the three animal 

 species somewhat comphcates application of the bioassay data on 

 coal elements to impact assessment and pollution-abatement tech- 

 nology. Therefore, the mean LC50 and sensitive species indexes 

 (Table 3) w^ere developed to provide a simplified data base for energy 

 and environmental engineers. The sensitive-species ranking for coal 

 elements was used to delineate upper limits of toxicity observed for 

 the 66 independent bioassays, and the mean index summarized 

 average test responses. Despite some notable exceptions (e.g., Al and 

 La), the toxicological orders given in the two indexes were generally 

 similar. Principal differences in relative order were attributed to 

 elements exhibiting disproportionate selective toxicity for a particu- 

 lar animal species. The only extreme disparity involved lanthanum, 

 for which mean and sensitive species LC50 values differed by three 

 orders of magnitude. We should note that several recent publications 

 review additional bioassay data for some of the trace metals found in 

 coal (National Academy of Sciences— National Academy of Engineer- 

 ing, Committee, 1973; Vaughan et al., 1975; Environmental Protec- 

 tion Agency, 1976). 



In the fly-ash leaching study, characteristics of the simulated 

 effluent were compared with those recorded for 14 TVA ash ponds. 

 As seen in Table 4, good agreement was obtained for all test 

 parameters except aluminum and cadmium, but concentrations for 

 these metals were within TVA ranges early in the third elution 

 interval. The high initial values for aluminum and cadmium may have 

 resulted from use of distilled influent water, which contributed to 

 low pH in the simulated ash pond. These and other results indicate 

 that the quality of effluent water may be improved somewhat by 

 regulating certain parameters (e.g., pH and alkalinity) of influent 

 water used for ash sluicing. 



Appreciable metal leaching continued, however, even after 770 

 hr, when the change was made in influent water (Table 5). The 

 resulting suite of toxic metals produced lethality of test organisms 

 through 1775 to 1847 hr of continuous elution time (Table 6). 

 Effluent metal concentrations (Table 5) were compared to fresh- 

 water guidelines (National Academy of Sciences— National Academy 

 of Engineering, Committee, 1973; Environmental Protection Agency, 

 1976) to further evaluate potential effects of fly-ash leaching on 

 aquatic biota. Through 1775 hr, mercury remained well above the 

 limit of 0.05 ppb, and aluminum exceeded the 100-ppb level 

 considered deleterious to growth and survival of fish. Cadmium was 

 over the trout standard of 0.4 to 1.2 ppb for 1775 hr and exceeded 

 the maximum limit for other aquatic species (4 to 12 ppb) for 1050 



