Toxicity of Ferro- and Ferricyanide Solutions to Fish, and Determination of the Cause of Mortality

The investigation of the causes of a fish kill in waters containing ferro- and ferricyanide at concentrations far under those generally accepted as non-lethal have shown these low concentrations to be lethal due to photo-decomposition and release of the cyanide ion. Experimental data place the toxic level of these compounds, under similar conditions of light intensity, at a concentration between 1 and 2 p.p.m. This level is assumed to vary slightly under natural conditions with latitude, period of the year, temperature, water turbulence, and interferences. Rapid development of toxicity has been demonstrated at a concentration of 2 p.p.m. of either potassium ferro- or ferricyanide.