Effects of altering freshwater chemistry on physiological responses of rainbow trout to silver exposure

The influence of different water Cl- (50-600 mu M), Ca2+ (50-1,500 mu M), Na+ (50-1,500 mu M), or dissolved organic carbon (DOC, 0.31-5 mg/L) levels on silver-induced physiological and biochemical perturbations of rainbow trout were investigated. Fish were acclimated to soft water (50 mu M; Cl-, Ca2+, and Na+), then exposed to 3.7 mu g/L Ag (as AgNO3) for 6 h, which resulted in a reduction in Na+ influx from the water, an inhibition of gill sodium- and potassium-activated adenosine triphosphatase (Na+/K+-ATPase) activity, and an accumulation of silver on the gills. Increasing the water Cl- or DOC levels ameliorated the silver toxicity. However, increasing water Ca2+ or Na+ concentration did not reduce the silver-induced physiological and biochemical perturbations. The free silver ion (Ag+) concentrations (calculated from MINEQL+, a geochemical speciation computer program) showed a negative correlation with the Na+ influx rates and gill Na+/K+-ATPase activity. However, gill silver levels did not correlate to Ag+ concentrations and no correlation was found between gill silver levels and either Na+ influx rates or gill Na+/K+-ATPase activity. These results support the notion that the [Ag+] concentration is of major importance when assessing silver toxicity in fish, and that this should be taken into account in regulatory strategies for silver in the natural environment.