Influence of water quality on silver toxicity to rainbow trout (Oncorhynchus mykiss), fathead minnows (Pimephales promelas), and water fleas (Daphniamagna)

Toxicity bioassays were conducted to quantify water quality conditions unde r which silver, as silver nitrate, is toxic to Oncorhynchus mykiss, Pimepha les promelas, and Daphnia magna. Bioassays for P. promelas and D. magna wer e conducted as static replacement tests, whereas a flow-through bioassay sy stem was modified and used for O. mykiss. Results from 96-h toxicity bioass ays for O. mykiss indicated that chloride, hardness, and dissolved organic carbon (DOC) protected against silver toxicosis, with DOC affording the hig hest protective effects. For P. promelas and D. magna, little protection wa s provided by increased CaCO3 alone, whereas DOC had a major ameliorating i nfluence on measured silver toxicity. Lower concentrations of chloride (<20 mg/L) had little effect on reducing silver nitrate toxicity. Dissolved org anic carbon was more important than hardness for predicting the toxicity of ionic silver in natural waters to O. mykiss, P. promelas, and D. magna. Si milarly, DOC significantly reduced silver nitrate toxicity to trout, wherea s Cl- and hardness had only a minor protective effect. However, Cl-/DOC mix tures showed a greater-than-additive protective effect. Thus, we suggest th at incorporating an organic carbon coefficient into the silver criterion eq uation will enhance the criterion values for site specificity.