Toxicity of paired mixtures of candidate forest insecticides to rainbow trout

The toxicities of Zectran, Dylox, Volaton, Guthion, pyrethrum extract, and the synthetic pyrethroids SBP-1382, and RU-11679 were determined individually and in paired mixtures against rainbow trout. The carbamate Zectran was the least toxic, and the synthetic pyrethroids were the most toxic. Nine of the mixtures produced less than additive toxicity (antagonism), nine produced additive toxicity, and two produced greater than additive toxicity (synergism). None of the mixture toxicities deviated markedly from additive,and only two pairs of mixtures would pose a greater toxicological hazard to fish than the respective individual chemicals.