title: Formation of toxic 2-nonyl-p-benzoquinones from α-tertiary 4-nonylphenol isomers during microbial metabolism of technical nonylphenol.
abstract: In many environmental compartments, microbial degradation of α-quaternary nonylphenols proceeds along an ipso-substitution pathway. It has been reported that technical nonylphenol contains, besides α-quaternary nonylphenols, minor amounts of various α-H, α-methyl substituted tertiary isomers. Here, we show that potentially toxic metabolites of such minor components are formed during ipso-degradation of technical nonylphenol by Sphingobium xenophagum Bayram, a strain isolated from activated sewage sludge. Small but significant amounts of nonylphenols were converted to the corresponding nonylhydroquinones, which in the presence of air oxygen oxidized to the corresponding nonyl-p-benzoquinones-yielding a complex mixture of potentially toxic metabolites. Through reduction with ascorbic acid and subsequent analysis by gas chromatography-mass spectrometry, we were able to characterize this unique metabolic fingerprint and to show that its components originated for the most part from α-tertiary nonylphenol isomers. Furthermore, our results indicate that the metabolites mixture also contained several α, β-dehydrogenated derivatives of nonyl-p-benzoquinones that originated by hydroxylation induced rearrangement, and subsequent ring and side chain oxidation from α-tertiary nonylphenol isomers. We predict that in nonylphenol polluted natural systems, in which microbial ipso-degradation is prominent, 2-alkylquinone metabolites will be produced and will contribute to the overall toxicity of the remaining material.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.
authors.forename: Frédéric L P
authors.initials: FL
authors.lastname: Gabriel
authors.forename: Mauricio Arrieta
authors.initials: MA
authors.lastname: Mora
authors.forename: Boris A
authors.initials: BA
authors.lastname: Kolvenbach
authors.forename: Philippe F X
authors.initials: PF
authors.lastname: Corvini
authors.forename: Hans-Peter E
authors.initials: HP
authors.lastname: Kohler
mesh_terms: D016227:Benzoquinones / Q000737:chemistry / Q000633:toxicity*; D001673:Biodegradation, Environmental; D008401:Gas Chromatography-Mass Spectrometry; D007220:Industrial Waste / Q000032:analysis*; D007536:Isomerism; D053858:Metabolic Networks and Pathways; D010636:Phenols / Q000737:chemistry* / Q000378:metabolism*; D045249:Sphingobacterium / Q000378:metabolism*
chemical_list: D016227:Benzoquinones; D007220:Industrial Waste; D010636:Phenols; C041594:4-nonylphenol