Hard water reduces heavy metal toxicity of fish

The aim of this study was to utilize static test for examining the acute toxicity of two essential elements, Cu and Zn, to a native fish, Capoeta fusca, by static bioassay. The acute toxicity of two heavy metals to C. fusca was determined in the soft, hard and very hard water (40, 150 and 380 mg/L as CaCO3). Results showed that toxicity of Cu and Zn decreased with increasing water hardness, so that water hardness had a significant effect on Cu and Zn toxicity on fish. Copper and Zn were more toxic in the soft water than in the hard water. The 96-hour lethal concentration for 50% (LC50) values for C. fusca were lower in the soft water compared with the hard and very hard water. The 96-hour LC50 for Cu at the soft, hard and very hard water was found to be 1.1, 5.4 and 7.5 mg/L, respectively, while the 96-hour LC50 for Zn at the soft, hard and very hard water was found to be 13.7, 74.4 and 102.9 mg/L, respectively.