The Lethal Action of Soluble Metallic Salts on Fishes

Abstract

A. Introduction and detailed investigation of the action of lead-salts. A study of pollution of Welsh rivers by lead-mine-effluents revealed the fact that fishes were killed by the action of soluble salts of lead, which proved lethal at concentrations so low as Pb I: 3,000,000. A physiological investigation of the action of lead-salts revealed the following facts: 1. The action does not correspond to the normal toxic type established by Powers (4, 5). 2. The graph of survival-times in different concentrations closely follows the equation K = I / t log I / conc. 3. The speed of the reaction is dependent upon the total quantity of metallic ion present, as well as upon the actual concentrations. 4. The speed of the reaction varies in inverse relation to the size and weight of fishes employed. 5. The most marked symptom is the formation of a film over gills and skin, by interaction of the metallic ion with a mucus-constituent. Death by suffocation is the final result. Where insufficient lead ion is present, the film is shed off, and complete recovery takes place. 6. The speed of the reaction varies in direct relation to the temperature consistently with Van't Hoff's Rule. 7. Chemical analysis of residues shows that no trace of metallic ion penetrates into the body itself. The action is thus held to be purely external in process, chemical in type, and mechanical in effect; i.e. it is not a "toxic" action in the ordinary sense of the term. B. Action of other metallic salts. The action of soluble salts of zinc, iron, copper, cadmium and mercury is shown to follow the same law as that of lead. Attention is directed to the economic importance of the facts, in connection with the pollution of rivers.