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 EC50 values for single compounds and EC50mix values for coexistent compounds were obtained. The n-octanol/water partition coefficient (logPmix) and the frontier orbital energy gap (ΔEmix) 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/EC50) = 0.445logP – 0.801ΔE + 9.501 (r2 = 0.876) and log (1/EC50mix) = 0.338logPmix – 0.492ΔEmix + 6.928 (r2 = 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/EC50mix) = 0.222logP – 0.277ΔE + 5.250 (r2 = 0.879) can be used successfully to predict the toxicity of a mixture.