Acute Toxicity to Fish of Solutions Containing Complex Metal Cyanides, in Relation to Concentrations of Molecular Hydrocyanic Acid

Publisher Website
Google Scholar
Abstract
Published indirect evidence indicating that the toxicity of solutions of complex metal cyanides to fish is a function of the concentration of molecular (not ionized) HCN is reviewed. The striking influence of pH on the toxicity of the nickelocyanide complex could be explained only by assuming that HCN is the toxic factor. Recent re‐evaluation of the dissociation constant of the tetracyanonickelate (II) ion, which showed previously accepted values to be grossly inaccurate and the true value to be in close agreement with an estimate based on toxicological data and theory, has confirmed the above interpretation of toxicity test results. By means of a recently published method for determination of molecular HCN by gas‐liquid chromatography, it was possible to demonstrate conclusively that this factor virtually alone determined the acute toxicity to bluegills of various solutions of simple and complex cyanides. Median immobilization times for bluegills in the solutions varied independently of total cyanide concentrations but were clearly related to molecular HCN levels. Two of three tested solutions containing the silver‐cyanide complex proved exceptional; their toxicity produced symptoms strongly suggestive of heavy‐metal poisoning and was deemed referable to toxicity of the complex anions or of silver cations. The presence of representative water pollutants tested did not impair the precision and accuracy of the HCN determinations. Changes in CO2 content and pH of the medium occurring at gill surfaces had no appreciable influence on the toxicity of the nickelocyanide complex, presumably because dissociation is not very rapid. Thus, the analytical method used for determination of HCN was shown to be useful in waste disposal control. Its practical application in connection with water pollution problems is discussed.