Toxicity, silver accumulation and metallothionein induction in freshwater rainbow trout during exposure to different silver salts
Static-renewal 168-h toxicity tests of silver nitrate (AgNO3), silver chloride (AgCl(n)), and silver thiosulfate (Ag(S2O3)(n)) with juvenile rainbow trout (Oncorhyncus mykiss) were performed by standard methods. Because of low solubility of AgCl(s), bioassays for AgCl(n) were performed in two separate ways. In one test series, AgCl(s) was added to freshwater and in another. AgCl(n)(aq) was generated by adding AgNO3 to freshwater supplemented with 50 mM NaCl. Concentrations of Ag and metallothionein (MT) were analyzed in gills and livers of fish that survived the exposures. Although Ag added as AgNO3 was found to be highly toxic to rainbow trout (168-h LC50 = 9.1 μg Ag L-1), the toxicities of the other Ag salts were low. The 168-h LC50 for Ag(S2O3)(n) was 137,000 μg Ag L-1 and no mortality was observed in AgCl(n) (100,000 μg Ag L-1). Exposure to AgNO3, Ag(S2O3)(n), or AgCl(n) caused accumulation of Ag and induction of MT. Highest Ag levels were found in livers of trout exposed to 164,000 μg Ag L-1 as Ag(S2O3)(n). In these fish, the hepatic Ag concentration was increased 335 times from the control value. The MT levels in gills and liver increased with the water Ag concentration and the highest level of MT was found in liver of fish exposed to Ag(S2O3)(n).