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

Abstract

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 (J_in) was inhibited at copper concentrations as low as 25 μg∙L⁻¹, and sodium efflux (J_out) was stimulated above 100 μg∙L⁻¹. High-alkalinity water significantly reduced the effects of copper on J_inand J_out, 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.