A novel metabolic pathway for degradation of 4-nonylphenol environmental contaminants by Sphingomonas xenophaga Bayram - ipso-hydroxylation and intramolecular rearrangement*
ABSTRACT Several nonylphenol isomers with alpha-quaternary carbon atoms serve as growth substrates for Sphingomonas xenophaga Bayram, whereas isomers containing hydrogen atoms at the alpha-carbon do not. Three metabolites of 4-(1-methyloctyl)-phenol were isolated in mg quantities from cultures of strain Bayram supplemented with the growth substrate isomer 4-(1-ethyl-1,4-dimethyl-pentyl)-phenol. They were unequivocally identified as 4-hydroxy-4-(1-methyl-octyl)-cyclohexa-2,5-dienone, 4-hydroxy-4-(1-methyl-octyl)-cyclohex-2-enone, and 2-(1-methyl-octyl)-benzene-1,4-diol by high pressure liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy. Furthermore, two metabolites originating from 4-n-nonylphenol were identified as 4-hydroxy-4-nonyl-cyclohexa-2,5-dienone and 4-hydroxy-4-nonyl-cyclohex-2-enone by high pressure liquid chromatography-mass spectrometry. We conclude that nonylphenols were initially hydroxylated at the ipso-position forming 4-alkyl-4-hydroxy-cyclohexa-2,5-dienones. Dienones originating from growth substrate nonylphenol isomers underwent a rearrangement that involved a 1,2-C,O shift of the alkyl moiety as a cation to the oxygen atom of the geminal hydroxy group yielding 4-alkoxyphenols, from which the alkyl moieties can be easily detached as alcohols by known mechanisms. Dienones originating from nongrowth substrates did not undergo such a rearrangement because the missing alkyl substituents at the alpha-carbon atom prevented stabilization of the putative alpha-carbocation. Instead they accumulated and subsequently underwent side reactions, such as 1,2-C,C shifts and dihydrogenations. The ipso-hydroxylation and the proposed 1,2-C,O shift constitute key steps in a novel pathway that enables bacteria to detach alpha-branched alkyl moieties of alkylphenols for utilization of the aromatic part as a carbon and energy source.
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ABSTRACT: Contamination by tetrabromobisphenol A (TBBPA), the most widely used brominated flame retardant, is a matter of environmental concern. Here, we investigated the fate and metabolites of 14C-TBBPA in a submerged soil with an anoxic-oxic interface and planted or not with rice (Oryza sativa) and reed (Phragmites australis) seedlings. In unplanted soil, TBBPA dissipation (half-life 20.8 days) was accompanied by mineralization (11.5% of initial TBBPA) and the substantial formation (60.7%) of bound residues. Twelve metabolites (10 in unplanted soil and 7 in planted soil) were formed via four inter-connected pathways: oxidative skeletal cleavage, O-methylation, type II ipso-substitution, and reductive debromination. The presence of the seedlings strongly reduced 14C-TBBPA mineralization and bound-residue formation and stimulated debromination and O-methylation. Considerable radioactivity accumulated in rice (21.3%) and reed (33.1%) seedlings, mainly on or in the roots. While TBBPA dissipation was hardly affected by the rice seedlings, it was strongly enhanced by the reed seedlings, greatly reducing the half-life (11.4 days) and increasing monomethyl TBBPA formation (11.3%). The impact of the inter-connected aerobic and anaerobic transformation of TBBPA and wetland plants on the profile and dynamics of the metabolites should be considered in phytoremediation strategies and environmental risk assessments of TBBPA in submerged soils.Environmental Science and Technology 11/2014; 48(24). DOI:10.1021/es503383h · 5.48 Impact Factor
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ABSTRACT: Over the last two decades, nonylphenols (NPs) have become to be known as a priority hazardous substance due primarily to its estrogenicity and ubiquitous occurrence in the environment. Nonylphenols are commonly treated as a single compound in the evaluation of their environmental occurrence, fate and transport, treatment or toxicity. However, technical nonylphenols (tNPs) are in fact a mixture of more than 100 isomers and congeners. Recent studies showed that some of these isomers behaved significantly differently in occurrence, estrogenicity and biodegradability. The most estrogenic isomer was about 2 to 4 times more active than tNP. Moreover, the half lives of the most recalcitrant isomers were about 3 to 4 times as long as those of readily-biodegradable isomers. Negligence of NP's isomer specificity may result in inaccurate assessment of its ecological and health effects. In this review, we summarized the recent publications on the analysis, occurrence, toxicity and biodegradation of NP at the isomer level and highlighted future research needs to improve our understanding of isomer-specificity of NP.Environment International 09/2014; 73C:334-345. DOI:10.1016/j.envint.2014.08.017 · 5.66 Impact Factor
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ABSTRACT: The paper describes the studies on the photodecomposition of 4-n-nonylphenol (NP), a widely used pesticide and endocrine disrupting agent. For this purpose a new hybrid photosensitizer (RB-HNT) was obtained composed of Rose Bengal (RB) incorporated into the halloysite nanotubes (HNT). The photosensitizer was characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), confocal microscopy, as well as UV-Vis and fluorescence spectroscopies. The results confirmed that the crystalline structure of HNTs was preserved-after modification with RB. The obtained hybrid material efficiently adsorbs hydrophobic compounds. It was also found to be an efficient photosensitizer for singlet oxygen generation. RB-HNT combines the advantages of both of its components, i.e., the ability to adsorb hydrophobic pollutants, which is characteristic for HNT, and photocatalytic properties of RB. Photooxidation kinetics of n-nonylphenol in the presence of RB-HNT and in the aqueous solution of RB were followed spectrophotometrically and compared. The photooxidation in the presence of Bengal Rose followed the first order kinetics, while in the presence of sensitizer (RB-HNT) observed zero-order kinetics. Furthermore the pesticide oxidation by the hybrid catalyst was found to be more efficient. The products formed after various irradiation times were identified by the GCMS analysis and the photodegradation pathway has been proposed.Chemical Engineering Journal 02/2015; 262:125–132. DOI:10.1016/j.cej.2014.09.081 · 4.06 Impact Factor