HALOGENATION AND TOXICITY OF THE BIODEGRADATION PRODUCTS OF A NONIONIC SURFACTANT, NONYLPHENOL ETHOXYLATE

We simulated the formation of halogenated by-products of biodegradatio n products of a nonionic surfactant, nonylphenol ethoxylate (NPE), and evaluated the toxicity of these by-products. Most NPE derivatives bea ring shortened ethylene oxide (EO) chains (abbreviated as NPnEO) and n onylphenol 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 a mounts of NPnEO, NPnEC, and their bromine-substituted products (BrNPnE O 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 p H for the formation of both BrNPnEO and BrNPnEC was approximately 7, a nd these formations decreased remarkably at higher pH. The formation o f both BrNPnEO and BrNPnEC was shown to be dependent on the bromide an ion concentration but independent of the level of residual chlorine. I n the umu assay, a mutagenicity test that uses genetically engineered Salmonella bacteria, neither BrNPnEO nor BrNPnEC showed significant mu tagenicity irrespective of metabolic activation by S9-mix. However, bo th BrNPnEO and BrNPnEC showed higher acute toxicity to Daphnia magna t han their nonbrominated precursors, NPnEO and NPnEC. The toxicity of B rNPnEO to Daphnia was higher than that of BrNPnEC.