Quantitative structure-activity relationships for joint toxicity of substituted phenols and anilines to Scenedesmus obliquus

There are often many chemicals coexisting in aquatic ecosystems, and few information on the joint toxicity of a mixture of organic pollutants is available at present. The 48-h toxicity of substituted phenols and anilines and their binary mixtures to Scenedesmus obliquus was determined by the algae inhibition test. The median effective inhibition concentration EC;values for single compounds and EC;values for coexistent compounds were obtained. The n-octanol/water partition coefficient (logP;and the frontier orbital energy gap (ΔE;) for mixtures were calculated. The following two-descriptor quantitative structure-activity relationships （QSARs） models were developed to predict single toxicity and joint toxicity respectively: log(1/EC;)=0.445logP-0.801ΔE+9.501（r;= 0.876） and log (1/EC;)=0.338logP;-0.492ΔE;+6.928 （r;=0.831）. The two equations were found to fit well. In addition, the model derived from the structural parameters of single components in binary mixtures log(1/EC;)=0.222logP-0.277ΔE+ 5.250（r;=0.879） can be used successfully to predict the toxicity of a mixture.