Effect of mixtures of chlorophenols, surfactants, and aniline on growth of Pseudomonas fluorescens.

Industrial wastewater often contains a mixture of chemical substances and knowledge of joint action of toxicants is therefore important when the toxicity of an effluent is evaluated or reduction of the toxicity is needed. In this study, the joint action of three pairs of toxicants, selected on the basis of their expected different modes of toxic actions, was tested for inhibition of the growth of the bacteria Pseudomonas fluorescens: pentachlorophenol and aniline, the surfactants nonylphenolethoxylate and tetrapropylenebenzenesulfonate, and pentachlorophenol and 2, 4-dichlorophenol. The joint effect of pentachlorophenol and aniline did not differ significantly from additivity, whereas less than additive responses were observed for mixtures of nonylphenolethoxylate and tetrapropylenbenzenesulfonate. A more than additive response was observed for mixtures of pentachlorophenol and 2,4-dichlorophenol at some concentration levels, while at others additive responses were found. It was concluded that joint actions other than additivity may occur between commonly known toxic substances, and that the modes of toxic action of the substances studied can explain the different types of joint action observed in this study. Further, test strategy followed proved useful in the evaluation of the joint toxicity of binary mixtures.