Protective effects of water Cl- on physiological responses to waterborne silver in rainbow trout

The importance of water Cl- concentration in mitigating the effects of subl ethal waterborne AgNO3 exposure on rainbow trout was studied to test the re lationship between physiological response and concentration of ionic silver (Ag+). Trout were exposed to a total silver concentration of 30 nmol.L-1 ( as AgNO3) at a range of different water Cl- concentrations from 20 to 1500 mu mol.L-1. These levels were chosen by speciation modelling with MINEQL+ t o progressively reduce the concentration of Ag+ largely by replacement with dissolved AgClaq. Fish exposed to AgNO3 experienced a loss of Na+; increas ing the water Cl- concentration reduced these losses. In vitro measurements after 50 h of exposure showed that Na+ losses were related to Ag+-induced inhibition of gill Na+/K+ ATPase activity; increasing the concentration of Cl- in the water protected against the inhibition of Na+/K+ ATPase activity . The disruption of Na+ regulation in AgNO3-exposed fish was accompanied by increased plasma cortisol and total ammonia concentrations, but blood pH, plasma PCO2 and HCO3-, and hematocrit were, in general, unaltered. Gill sil ver content increased in all AgNO3-exposed trout and was not correlated wit h the disruption of Na+ balance. We conclude that physiological measurement s in combination with aquatic geochemical equilibrium modelling are useful in developing models to predict the acute toxicity of waterborne silver.