The toxicity to fish of mixtures of poisons

Abstract

SUMMARY Experiments have been made with rainbow trout in solutions of ammonium chloride and zinc sulphate to examine the empirical rule that a mixture of two poisons, P and Q , should be at the threshold concentration for acute toxicity when PS/PT + Q S /Q T = I, where the suffix S stands for the concentration in solution and T for the threshold concentration of a poison when tested by itself. The most detailed experiment, with a hard dilution water in which the dissolved‐oxygen concentration was at the air‐saturation value, gave results within 4% of those expected from the hypothesis. Agreement was not so close in a soft dilution water, nor in a hard dilution water containing a reduced concentration of dissolved oxygen, but in these two cases the threshold concentrations for the mixtures were within 26 and 17% of the expected value of unity. In every case the rule under examination provided a better description of the data than models based on the hypothesis of independent joint action.