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

Abstract

Abstract-Toxicity bioassays were conducted to quantify water quality conditions under which silver, as silver nitrate, is toxic to Oncorhynchus mykiss, Pimephales promelas, and Daphnia magna. Bioassays for P. promelas and D. magna were conducted as static replacement tests, whereas a flow-through bioassay system was modified and used for O. mykiss. Results from 96-h toxicity bioassays for O. mykiss indicated that chloride, hardness, and dissolved organic carbon (DOC) protected against silver toxicosis, with DOC affording the highest protective effects. For P. promelas and D. magna, little protection was provided by increased CaCO 3 alone, whereas DOC had a major ameliorating influence on measured silver toxicity. Lower concentrations of chloride (Ͻ20 mg/L) had little effect on reducing silver nitrate toxicity. Dissolved organic carbon was more important than hardness for predicting the toxicity of ionic silver in natural waters to O. mykiss, P. promelas, and D. magna. Similarly, DOC significantly reduced silver nitrate toxicity to trout, whereas Cl Ϫ and hardness had only a minor protective effect. However, Cl Ϫ /DOC mixtures showed a greaterthan-additive protective effect. Thus, we suggest that incorporating an organic carbon coefficient into the silver criterion equation will enhance the criterion values for site specificity.

Is Cl− protection against silver toxicity due to chemical speciation?

“…Additionally, in at least one study reporting the protective effects of Cl − against silver toxicity in rainbow trout, Cl − was added as NaCl and protection may have been the result of increased ambient Na + and/or Cl − (Bury et al, 1999). Increased ambient Cl − was also not protective against silver toxicity to P. promelas, which is consistent with the majority of existing literature (Table 1; Bury et al, 1999;Karen et al, 1999). The 96-h LC50s were 2.3 and 2.7 g/L Ag for P. promelas exposed to silver in soft water and 1 mM KCl, respectively (Fig.…”

“…Of the fishes tested to date, only O. mykiss conclusively displays Cl − -induced protection against Ag + toxicity and at least four other fish species do not get protection from ambient Cl − alone, at the concentrations tested (Bury et al, 1999;Karen et al, 1999;Grosell et al, 2000-summarized in Table 1). …”

“…While external Cl − has been demonstrated to reduce silver toxicity to O. mykiss, discrepancies in the literature exist, because the formation of AgCl does not appear to substantially influence silver sensitivity for any other fish species tested (Erickson et al, 1998;Bury et al, 1999;Karen et al, 1999;Grosell et al, 2000). Additionally, Wood et al (2002) demonstrated that unlike silver toxicity, branchial silver accumulation was not reduced in rainbow trout exposed to AgCl as compared to those exposed to the silver ion.…”

Effects of sodium chloride on chronic silver toxicity to early life stages of rainbow trout (Oncorhynchus mykiss)

“…It can be ascertained from the data that if any protective effect exists, it is modest and would result in an increase in the LOEC of less than a factor of two. Previous studies of acute silver toxicity and chloride using rainbow trout [1,2,6,41] have reported a significant protective effect of chloride and linked it to alterations in the speciation of silver, with increased chloride resulting in a decrease in Ag ϩ . In the only previous chronic study of silver and chloride using rainbow trout ELS [10], chloride offered little protection against silver-induced mortality.…”

“…Data resulting in this conclusion have been generated primarily in laboratory tests of acute silver toxicity [1][2][3] that used AgNO 3 , a freely soluble salt that dissociates completely to yield high proportions of free ionic silver. It is recognized, however, that most natural waters contain ligands, such as chloride, dissolved organic carbon (DOC), and sulfide, that bind silver, and recent research has focused on characterizing the role of such ligands in mitigating acute silver toxicity in waterways [1,[4][5][6].…”