The relative importance of water hardness and chloride levels in modifying the acute toxicity of silver to rainbow trout (Oncorhynchus mykiss)
Static-renewal 7-d toxicity tests for silver nitrate (AgNO3) were performed with juvenile rainbow trout (Oncorhynchus mykiss Walbaum). The relative influences of calcium and chloride concentrations on median lethal time (LT50) were assessed. Calcium concentrations were controlled by adding either Ca(NO3)2 or CaSO4, whereas chloride concentrations were adjusted with either NaCl or KCl. For both calcium salts, a 100-fold elevation in concentration increased the LT50 approximately 10-fold. However, a 100-fold elevation in KCl ameliorated silver (Ag) toxicity at least 100-fold, while NaCl protected against Ag toxicity even more substantially, demonstrating the much greater protective effect of chloride relative to calcium. In a separate series of bioassays, fish were exposed to 0.92 μM Ag (100 μg/L as AgNO3) with varying amounts of NaCl tittered into each tank to alter the free [Ag+]. The 7-d LC50 occurred at a [NaCl] of 2,500 μM. Using MINEQL+ (a geochemical speciation program), the predicted free [Ag+] at this LC50 value is 0.0285 μM. Further bioassays were performed in which [chloride] was maintained at either 50 or 225 μM, while total [Ag] was independently varied from 0.0092 to 0.0694 μM (1.0-7.5 μg/L). The 7-d LC50 value was calculated at 0.0294 μM Ag (3.18 μg/L) at a chloride concentration of 50 μM, very similar to the free [Ag+] value of 0.031 μM calculated from an earlier LC50 test at a fixed [chloride] of 730 μM. According to MINEQL+, the estimated [Ag+] at this LC50 value is 0.0289 μM. Although a 7-d LC50 value could not be determined at 225 μM chloride, it was estimated at slightly above 0.0277 μM Ag+. Elevating chloride concentrations from 50 to 225 μM did not alter the accumulation of Ag in the liver. In addition, there were no significant differences in hepatic Ag accumulation between any of the Ag-exposed fish, irrespective of the total Ag concentration used during the exposure. Overall, Ag accumulated to approximately 185 μmol/kg wet weight in all Ag-exposed groups (approximately a 10-fold increase above controls). These results, together with a reanalysis of published data, suggest that Ag toxicity can be correlated with the free Ag ion [Ag+], and that any factors altering Ag+ availability (i.e., chloride) will be expected to modify acute Ag toxicity.
Publication Source (Journal or Book title)
Environmental Toxicology and Chemistry
Galvez, F., & Wood, C. (1997). The relative importance of water hardness and chloride levels in modifying the acute toxicity of silver to rainbow trout (Oncorhynchus mykiss). Environmental Toxicology and Chemistry, 16 (11), 2363-2368. https://doi.org/10.1897/1551-5028(1997)016<2363:TRIOWH>2.3.CO;2