The mass production and wide usage of surfactants and aromatic compounds disturb seriously the natural ecosystem of physical,chemical and biological processes.The study on the mechanisms of joint toxicity can indicate the characterization of real environmental behavior and assessment of joint ecological effect.The toxicity to Photobacterium phosphoreum of different mixture systems of cationic surfactant of dodecyl dimethyl benzyl ammonium chloride (DDBAC) and three substituted aromatic compounds according to equi-concentration ratio of 1∶1,as well as individual toxicity,were determined respectively.They were evaluated by toxicity unit (TU),additive index (AI),similarity parameter (λ),and mixtures toxicity index (MTI).Four evaluating methods were compared and the modes of joint action of different systems were analyzed.It was shown that coherent results were obtained by four different evaluating methods in most situations.Conclusions can be drawn that the joint effects of different mixture systems were synergistic.Mechanisms of joint toxicity action could be discussed according to luminescence principle of Photobacterium phosphoreum and molecule structures of the mixture components.
There is little information about the influence of organic solvents for low water-solubility organic compounds on Photobacterium phosphoreum toxicity test,though it appears likely that much of data were obtained by using solutions prepared with cosolvents or surfactants.In this study the influence of five stock solvents,including dimethyl sulphoxide（DMSO）,acetone,aether,ethanol,tetrahydrofuran,on Photobacterium phosphoreum toxicity test was measured and different effective concentration values were obtained.DMSO was selected as the most suitable solvent for organic compounds with low water-solubility according to its good characteristics and less toxicity effect on Photobacterium phospherum.Chlorobenzene and nitrobenzene with proper solubility were selected to verify the effect of DMSO on Photobacterium phosphoreum toxicity.It was demonstrated that DMSO(concentration no higher than 0.20 mol·L-1) had little effect on the toxicity of organic chemicals with relative error no more than 10%.The successful application of DMSO as cosolvent provided a good example and a good idea to improve traditional acute toxicity test of Photobacterium phosphoreum,and broadened the application to identifying the toxicity of low water-solubility organic compounds.
