Ecological toxicity of the metabolites of chemical compounds produced in the sewage treatment systems

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Alkylphenol polyethoxylates (APnEO,n is the number of ethoxy units) are one of the nonionic surfactant widely used in the industrial fields. In this study we selected APnEO (especially, nonylphenol polyethoxylates (NPnEO)) as model chemical compounds which flow into the sewage treatment plant abundantly. Production of the metabolites of these compounds in ten sewage treatment plants in Japan was investigated. Nonylphenol ethoxylates with short EO chains (NPEO) and its carboxylates (NPEC) were detected in all of the treatment plants investigated here and its bromate in some of them. It is suggested that the biodegradation of NPnEO by the activated sludge process occured exclusively on the hydrophilic regiona of ethylene oxide (EO) chains and halogenated NPEO or NPEO were produced by chlorine disinfection process as by-products.Acute toxicity and mutagenicity of the metabolites detected in the sewage treatment system were investigated. Mutagenicity of the various metabolites were not detected at all. But acute toxicity test using Daphnia magna indicated the toxicity of the halogenated metabolites. And receltly, endocrine-disrupting activity of NPEO was also reported, so ecological impact of such metabolites discharged from sewage plant system is under the apprehension.These results indicated that various chemical compounds used in various fields with great quantities are flowing into the sewage treatment system and transformed to some metabolites which show ecological impacts and after that these metabolites are discharged into water environment.