Effect of Water Hardness on the Toxicity of Cobalt and Nickel to a Freshwater Fish, Capoeta fusca

Key words: 
• Acute toxicity /
• Hard water /
• Lethal concentration /
• Mortality /
• Very hard water

Abstract: Objective To determine the effects of water hardness on the toxicities of cobalt (Co) and nickel (Ni) to a freshwater fish,Capoeta fusca.Methods Toxicity was investigated by static bioassay.Fish were exposed to cobalt (as CoCl2) and nickel (as NiCl2) for 96 h in waters with two levels of hardness (“hard” and “very hard”,nominally 130 mg/L and 350 mg/L as CaCO3,respectively).Results Water hardness had a significant effect on the acute toxicity of both elements.The 96 h LC50 values for Co were 91.7 mg/L and 204.8 mg/L in hard and very hard waters,respectively,and for Ni the 96 h LC50 values were 78.0 mg/L and 127.2 mg/L,respectively.Conclusion The fish were more sensitive to Co and Ni toxicity in hard water than in very hard water;very hard water protects C.fusca against the toxicity of Co and Ni.