By T. G. Miller, W. C. Mackay
Water Research, Volume 14, Issue 2, 1980, Pages 129-133, ISSN 0043-1354, DOI: 10.1016/0043-1354(80)90228-6.

1. 1. Rainbow trout were used to determine the effects of water alkalinity and hardness on the incipient lethal concentration (ILC) of copper.
2. 2. At low water hardness (12 ppm) the ILC of copper was not affected by a five-fold change in medium alkalinity (10-50 ppm); however in hardwater (98 ppm) the same change in alkalinity caused the ILC to increase by 1.8 times.
3. 3. The ILC for copper increased as hardness increased regardless of alkalinity.
4. 4. At pHs of less than 5.4 the toxicity of various combinations of copper and hydrogen ion were antagonistic but at pH 5.4 there appeared to be some synergism between pH and Cu toxicity.

More details...