Aerobic biodegradation studies of nonylphenol ethoxylates in river water using liquid chromatography-electrospray tandem mass spectrometry

The aerobic biodegradation of nonylphenol ethoxylates (A(9)PEO) was kinetically investigated in a laboratory-scale bioreactor filled with river water, spiked at a concentration of 10 mg L-1 nonionic surfactants. Analyses of the samples applying liquid chromatography-electrospray mass spectrometry (LC-ES-MS) after solid-phase enrichment revealed a relatively fast primary degradation of A(9)PEO with >99% degradation observed after 4 days. Contrary to the generally proposed degradation pathway of EO chain shortening, it could be shown that the initiating step of the degradation is omega -carboxylation of the individual ethoxylate chains: metabolites with long carboxylated EO chains are identified (A(9)PEC). Further degradation proceeds gradually into short-chain carboxylated EO with the most abundant species being A(9)PE(2)C. The oxidation of the nonyl chain proceeds concomitantly with this degradation, leading to metabolites having both a carboxylated ethoxylate and an alkyl chain of varying lengths (CAPEC). The identity of the CAPEC metabolites was confirmed by the fragmentation pattern obtained with LC-ES-MS/MS. Both A(9)PEC and CAPEC metabolites are still present in the:bioreactor after 31 days. In the aerobic degradation pathway, A(9)PEO(2) is formed only to a minor extent: and is even further degraded in several days. The endocrine disruptor nonylphenol was not found as a metabolite in this study.