AQUATIC TOXICOLOGY OF TRACE ELEMENTS 233 



100 



80 



< 60 



> 



Z) 

 00 



>? 40 



20 



 , Goldfish 

 • , Trout 

 ▲ , Toad 



OU L_J L_^ I t ^•^f 



0.0001 0.001 0.01 0.1 1.0 



SILVER CONCENTRATION, ppm 



Fig. 3 Effects of silver on embryo — larval stages. 



Several patterns of response were discernible concerning the 

 differential sensitivity of the three test organisms. Highest uniformity 

 was obtained for silver, which gave an exceptionally narrow range of 

 LC50 values (0.01 to 0.03 ppm). As seen in Fig. 3, this relationship 

 held for the full range of exposure concentrations. Germanium 

 produced similar effects on the two most sensitive test animals, trout 

 and toads, but was substantially less toxic to the goldfish (Fig. 4). 

 This same pattern was given by Cu, Mo, Ni, Sb, Sr, Tl, and V. A still 

 more heterogeneous response occurred for Pb (Fig. 5), Hg, and 

 certain other elements (e.g.. La, Sn, and W). Considering the response 

 patterns summarized in Figs. 3 to 5, it is probable that the diversity of 

 aquatic species affected by pollution would increase in the order of 

 Pb, Ge, and Ag. Although elements such as Pb and Ge hkely 

 would affect fewer species, these toxicants probably would con- 

 tribute to an ecological imbalance of aquatic biota. As noted, Se, 

 Zn, and certain other elements (e.g.. As and Co) were more selective 

 for the toad, and, on the basis of LCg o values, the toad was the most 

 sensitive species for 17 of the 22 elements. This suggests that 

 amphibians may constitute particularly sensitive target sites for coal 

 contaminants. For example, goldfish LCj o determinations for 

 selenium and zinc exceeded those for the toad about 100 and 250 

 times, respectively. 



