Behaviour of acidic pharmaceuticals in rivers: determination of elimination characteristics in a sediment-water test system
Christine Pechmann (01/2008)
Support: Michael Radke
The elimination of the acidic pharmaceuticals bezafibrate, diclofenac, ibuprofen and ketoprofen by biodegradation has been investigated using a sedimentwater test system. Additionally the kind of microbial biodegradation pathway for bezafibrate and diclofenac was determined. Sediment and water were sampled at a small river near Bayreuth where contamination with pharmaceuticals was negligible. The batch experiments were carried out with a small water-sediment ratio. Initial compound concentration was 2.5 μg L-1, a concentration at which these pharmaceuticals can occur in rivers behind the effluent of waste water treatment plants. Test bottles were incubated up to 54 days in the dark to exclude photochemical transformation. Each pharmaceutical was investigated separately. Different approaches and controls for the determination of the elimination kinetics were performed. Pharmaceutical- and DOC content were varied to investigate metabolic or cometabolic degradation. The analytical procedure included solid phase extraction, high pressure liquid chromatographic separation and detection by tandem mass spectrometry. All pharmaceuticals were eliminated from the system within 36 days with 50% dissipation time (DT50) of 0.5 d for ibuprofen, 2.1 and 4.8 d for bezafibrate and ketoprofen, respectively. The highest DT50 was observed for diclofenac with 8.0 d. In sterile controls the final pharmaceutical concentration was lower than the calculated equilibrium concentration for bezafibrate, ibuprofen and ketoprofen. This indicated sorption of these compounds to the sediment. Therefore distribution coefficients KD were determined with the program HYDRUS-1D. KD ranged from 0.19 for bezafibrate to 0.26 for ibuprofen. In approaches without sediment only diclofenac and ibuprofen were degraded at a slow rate, so for all compounds microbial degradation mainly took place in the sediment. For bezafibrate a clearly cometabolic biodegradation pathway was determined. Degradation was accelerated with increased DOC content and no change in time trend was observed with raised pharmaceutical content. For diclofenac a metabolic degradation can be assumed due to an initial lag-phase prior to degradation and the typical time trend for metabolic degradation in all approaches.