Parallel pathways of ethoxylated alcohol biodegradation under aerobic conditions

摘要

Non-ionic surfactants (NS) are a major component of the surfactant flux discharged into surface water, and alcohol ethoxylates (AE) are the major component of this flux. Therefore, biodegradation pathways of AE deserve more thorough investigation. The aim of this work was to investigate the stages of biodegradation of homogeneous oxyethylated dodecanol C_(12)E_9 having 9 oxyethylene subunits, under aerobic conditions. Enterobacter strain Z3 bacteria were chosen as biodegrading organisms under conditions with C_(12)E_9 as the sole source of organic carbon. Bacterial consortia of river water were used in a parallel test as an inoculum for comparison. The LC-MS technique was used to identify the products of biodegradation. Liquid-liquid extraction with ethyl acetate was selected for the isolation of C_(12)E_9 and metabolites from the biodegradation broth. The LC-MS/MS technique operating in the multiple reaction monitoring (MRM) mode was used for quantitative determination of C_(12)E_9, C_(12)E_8, C_(12)E_7 and C_(12)E_6. Apart from the substrate, the homologues C_(12)E_8, C_(12)E_7 and C_(12)E_6, being metabolites of C_(12)E_9 biodegradation by shortening of the oxyethylene chain, as well as intermediate metabolites having a carboxyl end group in the oxyethylene chain (C_(12)E_8COOH, C_(12)E_7COOH, C_(12)E_6COOH and C_(12)E_5COOH), were identified. Polyethylene glycols) (E) having 9, 8 and 7 oxyethylene subunits were also identified, indicating parallel central fission of C_(12)E_9 and its metabolites. Similar results were obtained with river water as inoculum. It is concluded that AE, under aerobic conditions, are biodegraded via two parallel pathways: by central fission with the formation of PEG, and by Ω-oxidation of the oxyethylene chain with the formation of carboxylated AE and subsequent shortening of the oxyethylene chain by a single unit.