The Toxicity of Dissolved Metallic Salts toPolycelis Nigra(Muller) andGammarus Pulex(L.)

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Abstract
1. A brief review is given of previous work on the toxic effect of aqueous solutions of metallic salts on living protoplasm and fresh-water animals. 2. The behaviour of Polycelis nigra in aqueous solutions of metallic salts is described, survival curves for this animal in some variety of salts are given, and the mode of toxic action of these salts is discussed. 3. It is shown that in the case of heavy metal salts the toxic effect at concentrations below isotonicity is due almost entirely to the cation, the toxicity of the anion being relatively small. At concentrations above isotonicity the anion and the osmotic pressure of the solution act as additional lethal factors. 4. Salts of the metals of the alkalis and alkaline earths are shown to be comparatively harmless below isotonicity, with the exception of salts with a toxic anion such as potassium chromate. This salt is highly toxic at low concentrations. 5. It is shown that in the case of the nitrates and sulphates of the heavy metals, the toxicity is determined by the product of the normality and the electrical conductance ratio at that normality. 6. Recovery experiments with Polycelis are described and it is shown that these illustrate the above relationship between toxicity and conductivity. 7. Survival curves for Gammarus pulex in salts of copper and zinc are described. Those for zinc exhibit the same relationship.