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

Diclofenac 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 Münzbach (Freiberg/Saxony) under aerobic conditions showed rapid removal of diclofenac in a concentration range of 3–35 μM without previous adaptation. The conversion of higher concentrations up to 260 μM 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-hydroxydiclofenac (aut-)oxidation. The apparent lack of a degradative potential for this compound as well as the failure to detect an enrichment of diclofenac-depleting microbial activity both indicate a cometabolic nature of diclofenac transformation. 4′-Hydroxy-diclofenac, the favoured transformation product of eucaryotic diclofenac metabolism, could not be identified.