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Four kinds of widely used synthetic surfactants and polyethylene glycol (PEG) which corresponds to the hydrophilic moieties of polyoxyethylene-type nonionic surfactants were subjected to a complete biodegradation test using microorganisms from relatively unpolluted river waters (the TOC-Handai method). Sodium dodecyl sulfate (SDS), alcohol ethoxylate (AE) and PEG were mineralized by most of the microorganisms used as inocula, irrespective of differences in their degradation rates, which is in agreement with their biodegradabilities confirmed so far by other tests.These degradable surfactants were, however, not completely degraded by some river microorganisms. Among the surfactants tested, SDS was degraded most rapidly by microorganisms of each river in the same manner but the degradation rates of AE and PEG differed considerably according to the inoculum sampling station. Sodium linear alkylbenzensulfonate (LAS) and nonylphenol ethoxylate (NPE). which are known to be recalcitrant molecules, were not degraded completely by microorganisms of any of the river waters within the testing period; degradation of the former rarely proceeded , while that of the latter ceased leaving the well-known intermediates. The residual metabolites of NPE generated by biodegradation, which were analyzed by high-performance liquid chromatography and gas chromatography/mass spectrometry, revealed that this surfactant was transformed to carboxylated metabolites, nonylphenoxy acetic acid (NP1EC)and [(nonylphenoxy)ethoxy] acetic acid (NP2EC) exclusively.
