DEGRADATION PATHWAY OF QUINOLINES IN A BIOFILM SYSTEM UNDER DENITRIFYING CONDITIONS

This article reports for the first time the degradation pathways of qu inoline, isoquinoline, and methylquinolines by a mixed culture in a bi ofilm under nitrate-reducing conditions. A simple reverse-phase high-p erformance liquid chromatography method using ultraviolet detection at 223 nm for determination of seven quinoline analogues and 15 metaboli tes was developed, and gas chromatography-mass spectrometry and thin-l ayer chromatography analyses were used for identification. The inhibit ion of nitrification by the parent compounds and their degradation pro ducts was assessed by a nitrification toxicity test called MINNTOX. Qu inoline and 3-, 4-, 6-, and 8-methylquinoline were all transformed by hydroxylation into their 2-hydroxyquinoline analogues (2-quinolinones) , and isoquinoline was transformed into 1-hydroxyisoquinoline. 2-Methy lquinoline was not transformed by this microcosm, likely due to the bl ockage at position 2 by the methyl group. The hydroxylated metabolites of isoquinoline and quinolines methylated at the heterocyclic ring we re not transformed further, whereas metabolites of quinoline and quino lines methylated at the homocyclic ring were hydrogenated at position 3 and 3, and the resulting 3,4-dihydro-2-quinolinone analogues accumul ated. Of these metabolites, only 3,4-dihydro-2-quinolinone from the de gradation of quinoline was further transformed into unidentified produ cts. All quinolines and their metabolites had inhibiting effects on th e nitrifying bacteria at the same level (ppm) in the applied bioassay, indicating that the inhibition of the compounds was not influenced by the initial transformation reactions.