Ozonation of oxytetracycline and toxicological assessment of its oxidation by-products Kuixiao Li a,b , Ayfer Yediler b, * , Min Yang a , Sigurd Schulte-Hostede b , Ming Hung Wong c a Research Center for Eco-Environmental Sciences, State Key Laboratory of Environmental Aquatic Chemistry, Chinese Academy of Sciences, Beijing 100085, PR China b Helmholtz Zentrum Mu ¨ nchen, Research Center for Environmental Health (GmbH), Institute of Ecological Chemistry, Ingolstaedter Landstrasse 1, 85764 Neuherberg, Germany c Croucher Institute for Environmental Sciences and Biology Department, Hong Kong Baptist University, Hong Kong SAR, PR China Received 20 November 2007; received in revised form 4 February 2008; accepted 6 February 2008 Available online 19 March 2008 Abstract Antibiotic formulation effluents are well known for their difficult elimination by traditional bio-treatment methods and their impor- tant contribution to environmental pollution due to its fluctuating and recalcitrant nature. In the present study the effect of ozonation on the degradation of oxytetracycline (OTC) aqueous solution (100 mg l 1 ) at different pH values (3, 7 and 11) was investigated. Ozone (11 mg l 1 corresponds the concentration of ozone in gas phase) was chosen considering its rapid reaction and decomposition rate. The concentration of oxytetracycline, chemical oxygen demand (COD), biochemical oxygen demand (BOD) and BOD 5 /COD ratio were the parameters to evaluate the efficiency of the ozonation process. In addition, the toxic potential of the OTC degradation was investi- gated by the bioluminescence test using the LUMIStox 300 instrument and results were expressed as the percentage inhibition of the luminescence of the marine bacteria Vibrio fischeri. The results demonstrate that ozonation as a partial step of a combined treatment concept is a potential technique for biodegradability enhancement of effluents from pharmaceutical industries containing high concen- tration of oxytetracycline provided that the appropriate ozonation period is selected. At pH 11 and after 60 min of ozonation of oxy- tetracycline aqueous solutions (100 and 200 mg l 1 ) the BOD 5 /COD ratios were 0.69 and 0.52, respectively. It was also shown that COD removal rates increase with increasing pH as a consequence of enhanced ozone decomposition rates at elevated pH values. The results of bioluminescence data indicate that first by-products after partial ozonation (5–30 min) of OTC were more toxic than the parent compound. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Oxytetracycline; Ozonation; Biodegradability; COD; Bioluminescence test; Vibrio fischeri 1. Introduction Oxytetracycline (OTC), a member of tetracyclines, is one of the widely used pharmaceuticals in today’s human and veterinary medicine (Zhu et al., 2001; Kim et al., 2005; Sar- mah et al., 2006). Residues of antibiotics have been detected in surface water resources that receive effluents of municipal wastewater treatment plants (WWTPs), agricultural runoff and discharges of pharmaceutical manufacturers (Kolpin et al., 2002, 2004; Miao et al., 2004; Simon, 2005). The pres- ence of low levels of antibiotics and their transformation products in the environment is suspected to provide condi- tions for the transfer and spread of antibiotic resistance bac- teria and it clearly shows that elimination in municipal sewage treatment plants is often incomplete (Boxall et al., 2003). The immediate concern is the potential toxicity of these compounds to aquatic organisms and humans through drinking water or the consumption of vegetables and crops irrigated by polluted water. Data on the occur- rence of pharmaceuticals as contaminants in wastewater effluents and in the aquatic environment in China is scarce. 0045-6535/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2008.02.008 * Corresponding author. Tel.: +49 89 3187 2777; fax: +49 89 3187 3371. E-mail address: yediler@gsf.de (A. Yediler). www.elsevier.com/locate/chemosphere Available online at www.sciencedirect.com Chemosphere 72 (2008) 473–478