Parallel pathways of ethoxylated alcohol biodegradation under aerobic conditions

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 C₁₂E₉ having 9 oxyethylene subunits, under aerobic conditions. Enterobacter strain Z3 bacteria were chosen as biodegrading organisms under conditions with C₁₂E₉ 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 C₁₂E₉ 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 C₁₂E₉, C₁₂E₈, C₁₂E₇ and C₁₂E₆. Apart from the substrate, the homologues C₁₂E₈, C₁₂E₇ and C₁₂E₆, being metabolites of C₁₂E₉ biodegradation by shortening of the oxyethylene chain, as well as intermediate metabolites having a carboxyl end group in the oxyethylene chain (C₁₂E₈COOH, C₁₂E₇COOH, C₁₂E₆COOH and C₁₂E₅COOH), were identified. Poly(ethylene glycols) (E) having 9, 8 and 7 oxyethylene subunits were also identified, indicating parallel central fission of C₁₂E₉ 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. - Highlights: • Two parallel biodegradation pathways of alcohol ethoxylates have been discovered. • Apart from central fission, oxyethylene chain shortening has been evidenced. • Both a single Enterobacter strain and raw river water cause the same two pathways. • Ω-carboxylated alcohol ethoxylates are intermediate metabolites for chain shortening. • Homogeneous alcohol ethoxylate C₁₂E₉ was the model used in this study.