The joint toxicity of pesticide tank-mixes to rainbow trout

The joint toxicity to rainbow trout fingerlings (Salmo gairdneri Richardson) of eleven tank-mixes composed of pairs of six fungicides and herbicides (prochloraz, fenpropimorph, diclofop-methyl, tridemorph, benzoylprop-ethyl and propiconazole) was measured using 96 h LC₅₀ tests. The toxicity of the mixtures ranged from being half of that expected on the basis of additive toxicity of the components, to less than 1.4 times the expected value. In view of the degree of experimental error inherent in the LC₅₀ determinations, these data provide no evidence for the existence of synergistic (i.e. more-than-additive) toxicity of the respective tank-mixes.