Abstract The three metabolites hydroxyibuprofen (OH- Ibu), carboxyibuprofen (CA-Ibu), and carboxyhydratropic acid (CA-HA), also known from human metabolism of ibuprofen, could be identified in biodegradation experi- ments. Identification was based on EI mass spectra and comparison with literature data. Detection was performed by selective MS–MS measurements by GC–ion-trap MS and online methylation. Ibuprofen (Ibu), OH-Ibu, and CA-Ibu could be detected with a signal-to-noise ratio of 10:1 at a concentration of 2 nmol L –1 , CA-HA at 0.5 nmol L –1 . Degradation experiments in both biofilm reactors (BFR) and batch experiments with activated sludge (BAS) reveal OH-Ibu as the major metabolite under oxic conditions, and CA-HA under anoxic conditions. CA-Ibu was found under oxic and anoxic conditions almost only in the BAS. The metabolites together do not account for more than 10% of the initial concentration of Ibu. Keywords Biodegradation · Pharmaceutical residues · Ibuprofen · Biofilm reactors · Sewage sludge Introduction Ibuprofen (Ibu) is a non-prescription drug used widely as an anti-inflammatory, analgesic, and antipyretic pharma- ceutical compound in the treatment of fever and pain. Be- cause of the large amount produced (estimated to be sev- eral kilotons per year world-wide and 100 t year –1 in Ger- many) and used (dosage 600–1200 mg day –1 ) Ibu is an en- vironmentally relevant compound [1]. After application a large proportion of the active compound is excreted by the patient as the parent compound and in form of its metabolites hydroxyibuprofen (OH-Ibu), carboxyibupro- fen (CA-Ibu), and carboxyhydratropic acid (CA-HA; Fig. 1) [2, 3]. In excretion from man the parent drug and the metabolites were found to be conjugated to glucuronic acid (so-called phase-II metabolites) [3, 4, 5]. In sewage water, sewage effluents, and surface water Ibu was de- tected among other pharmaceutical residues in the low μg L –1 -range [1, 6, 7, 8]. These findings in sewage and surface water indicate the diffuse sources of Ibu as a result of excretion and incomplete degradation during sewage treatment. Influent concentrations of Ibu are also in good agreement with overall consumption of the pharmaceuti- cal [1]. In particular, OH-Ibu was detected in the influents of sewage treatment plants and in even higher concentra- tions in the effluents [6]. Starting from these data the question remained whether the elevated OH-Ibu concen- trations are because of formation of this compound or be- cause of the cleavage of the glucuronides of OH-Ibu dur- ing biodegradation in activated sludge treatment. In this study we report metabolite formation from Ibu during oxic and anoxic biodegradation. Laboratory-scale biofilm reactors (BFR) [9] were employed as model sys- tems for sewage treatment and the results were compared C. Zwiener · S. Seeger · T. Glauner · F. H. Frimmel Metabolites from the biodegradation of pharmaceutical residues of ibuprofen in biofilm reactors and batch experiments Anal Bioanal Chem (2002) 372 : 569–575 DOI 10.1007/s00216-001-1210-x Received: 7 August 2001 / Revised: 16 October 2001 / Accepted: 23 October 2001 / Published online: 21 December 2001 ORIGINAL PAPER C. Zwiener (✉) · S. Seeger · T. Glauner · F.H. Frimmel Engler-Bunte-Institut, Water Chemistry, Universität Karlsruhe (TH), 76131 Karlsruhe, Germany e-mail: christian.zwiener@ciw.uni-karlsruhe.de © Springer-Verlag 2001 Fig. 1 The structures of Ibu and its metabolites