Influence of Water Hardness, pH, and Alkalinity on the Mechanisms of Copper Toxicity in Juvenile Rainbow Trout,Salmo gairdneri

Juvenile rainbow trout were exposed to 25–400 μg copper∙L−1for 24 h. Water hardness, pH, and alkalinity were varied independently at a constant [Na+]. Net and unidirectional sodium fluxes were measured in hard and soft, low-alkalinity water and in hard, high-alkalinity water at neutral pH and pH 5.0. In low alkalinity water, Na+uptake (Jin) was inhibited at copper concentrations as low as 25 μg∙L−1, and sodium efflux (Jout) was stimulated above 100 μg∙L−1. High-alkalinity water significantly reduced the effects of copper on Jinand Jout, but there was no significant effect of increasing water hardness. The effects of pH 5.0 and copper were additive from 25 to 100 μg∙L−1, but a pure copper effect was found from 200 to 400 μg∙L−1. Fish died when they had lost about 50–55% of their exchangeable Na+pool. Water hardness and alkalinity had no effect on the apparent uptake of copper, but copper uptake was reduced by about 50% at pH 5.0.