Halogenation and toxicity of the biodegradation products of a nonionic surfactant, nonylphenol ethoxylate

We simulated the formation of halogenated by-products of biodegradation products of a nonionic surfactant, nonylphenol ethoxylate (NPE), and evaluated the toxicity of these by-products. Most NPE derivatives bearing shortened ethylene oxide (EO) chains (abbreviated as NPnEO) and nonylphenol carboxylate (NPnEC) disappeared within 24 h. In both NPnEO and NPnEC, benzene rings are substituted by monobromine. In contrast, chlorine-substituted derivatives were scarcely detected. However, the stoichiometrical bromination of NPnEO and NPnEC was not found. Total amounts of NPnEO, NPnEC, and their bromine-substituted products (BrNPnEO and BrNPnEC, respectively) tended to diminish with increasing level of residual chlorine concentration. Hence, it was suggested that both NPnEO and NPnEC were transformed to unknown by-products. The optimum pH for the formation of both BrNPnEO and BrNPnEC was approximately 7, and these formations decreased remarkably at higher pH. The formation of both BrNPnEO and BrNPnEC was shown to be dependent on the bromide anion concentration but independent of the level of residual chlorine. In the umu assay, a mutagenicity test that uses genetically engineered Salmonella bacteria, neither BrNPnEO nor BrNPnEC showed significant mutagenicity irrespective of metabolic activation by S9-mix. However, both BrNPnEO and BrNPnEC showed higher acute toxicity to Daphnia magna than their nonbrominated precursors, NPnEO and NPnEC. The toxicity of BrNPnEO to Daphnia was higher than that of BrNPnEC.