Abstract: The toxicities of each and their binary mixtures of 2 ,4-DNT and five derivatives of nitro benzenes to vibrio fischeri were determined respectively. Toxicity unit ( TU ) , additive index ( AI ) , similarity parameter (λ) and mixture toxicity index( MTI ) were used to evaluate the joint toxicity. The results show that the five binary mixtures showed all synergistic action. The abilities of synergistic action of the five mixtures were compared. The result by MTI was a little different from those by other three methods , but in general , when mixed with 2 ,4-DNT , p-chloronitrobenzene had the weakest synergistic action.

Key words: derivatives of nitro benzenes, joint toxicity, synergistic action, vibrio fischeri