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

ObjectiveTo determine the effects of water hardness on the toxicities of cobalt (Co) and nickel (Ni) to a freshwater fish, Capoeta fusca.MethodsToxicity 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).ResultsWater 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.ConclusionThe 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.