title: Isomer-specific degradation and endocrine disrupting activity of nonylphenols.
abstract: Degradation of technical nonylphenol by Sphingobium xenophagum Bayram led to a significant shift in the isomers composition of the mixture. By means of gas chromatography-mass spectrometry, we could observe a strong correlation between transformation of individual isomers and their alpha-substitution pattern, as expressed by their assignment to one of six mass spectrometric groups. As a rule, isomers with less bulkiness at the alpha-carbon and those with an optimally sized main alkyl chain (4-6 carbon atoms) were degraded more efficiently. By mass spectrometric analysis, we identified the two most recalcitrant main isomers of the technical mixture (Group 4) as 4-(1,2-dimethyl-1-propylbutyl)phenols (NP193a and NP193b), which are diastereomers with a bulky alpha-CH3, alpha-CH(CH3)C2H5 substitution. Our experiments with strain Bayram show that the selective enrichment of isomers with bulky alpha-substitutions observed in nonylphenol fingerprints of natural systems can be caused by microbial ipso-hydroxylation. Based on the yeast estrogen assay (YES), we established an estrogenicity ranking with a variety of single isomers and compared it to rankings obtained with different reporter cell systems. Structure-activity relationships derived from these data suggest that Group 4 isomers have a high estrogenic potency. This indicates a substantial risk that enrichment of highly estrogenic isomers during microbial degradation by ipso-substitution will increase the specific estrogenicity of aging material.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Frédéric L P
authors.initials: FL
authors.lastname: Gabriel
authors.forename: Edwin J
authors.initials: EJ
authors.lastname: Routledge
authors.forename: Andy
authors.initials: A
authors.lastname: Heidlberger
authors.forename: Daniel
authors.initials: D
authors.lastname: Rentsch
authors.forename: Klaus
authors.initials: K
authors.lastname: Guenther
authors.forename: Walter
authors.initials: W
authors.lastname: Giger
authors.forename: John P
authors.initials: JP
authors.lastname: Sumpter
authors.forename: Hans-Peter E
authors.initials: HP
authors.lastname: Kohler
mesh_terms: D052244:Endocrine Disruptors / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D007536:Isomerism; D010636:Phenols / Q000378:metabolism*; D020560:Proteobacteria / Q000378:metabolism*; D015003:Yeasts / Q000235:genetics
chemical_list: D052244:Endocrine Disruptors; D010636:Phenols; C025256:nonylphenol