Toxicity of Interactions of Zinc —Nickel,Copper —Nickel and Zinc —Nickel —Copper to a Freshwater Teleost,Lebistes reticulatus (PETERS)1

The lethal toxicity of mixtures of Zn²⁺ —Ni²⁺, Cu²⁺ —Ni²⁺ and Zn²⁺ —Cu²⁺ —Ni²⁺ to common guppy at 21£C in hard water (total hardness = 260 mg/l as CaCO₃) was studied under static bioassays test conditions with renewal of the test solutions every 24 h. The heavy metals were tested separately and in mixtures. The 48 h median lethal concentrations (LC₅₀) for individual salts were 75 mg/l Zn²⁺, 37 mg/l for Ni²⁺ and 2.5 mg/l for Cu²⁺. Concentrations were expressed in “toxic units” by taking them as proportions of LC₅₀ values. Experiments showed that in the Zn²⁺-Ni²⁺ mixture, when Ni²⁺ was more in proportion, the toxicity was more than additive. The 48 h LC₅₀ value and 95% confidence limits in the Ni²⁺-Cu²⁺ mixture were 0.684 (0.484 … 0.807) toxic units and the mixture produced more than the additive toxicity (synergism.). The LC₅₀ value and its 95% confidence limits in a Zn²⁺?Cu²⁺?Ni²⁺ mixture also suggested that the mixture was again strictly additive. The results indicate that heavy metallic mixtures would pose a greater toxicological danger to fish than the respective individual metals.