Transformation of diclofenac by the indigenous microflora of river sediments and identification of a major intermediate

Diclofienac is a non-steroidal anti-inflammatory drug, which tends to be relatively persistent in the environment. Now, a fixed-bed column bioreactor filled with sediment from the creek Munzbach (Freiberg/Saxony) under aerobic conditions showed rapid removal of diclofenac in a concentration range of 3-35 mu M without previous adaptation. The conversion of higher concentrations up to 260 mu M was accompanied by conspicuously decreased turnover rates indicating a toxic effect of this drug or its resulting metabolic burden on the indigenous microflora. A major metabolite occurred transiently and was identified by NMR and MS to be the p-benzoquinone imine of 5-hydroxydiclofenac. Abiotic adsorption to the biofilm was shown to determine the further fate of this reactive product of 5-hydroxydiclofienac (aut-)oxidation. The apparent lack of a degradative potential for this compound as well as the failure to detect an enrichment of diclofienac-depleting microbial activity both indicate a cometabolic nature of diclofienac transformation. 4'-Hydroxydiclofenac, the favoured transformation product of eucaryotic diclofienac metabolism, could not be identified. The ability to convert diclofenac was shown to be widespread among biofilms from different river sediments, but measured rates obviously do not correlate with the total microbial activity. In addition, application of sediments from locations exposed to communal waste water effluents did not indicate any form of adaptation measured as an increased specific diclofenae depletion rate. (C) 2007 Elsevier Ltd. All rights reserved.