LABORATORY COLUMN EXPERIMENT ON REDOX-SENSITIVITY AND TRANSPORT BEHAVIOUR OF SELECTED PHARMACEUTICAL COMPOUNDS

Laboratory column experiments are suitable to investigate the hydraulic properties of the used sediment and also to detect the transport behaviour of dissolved substances in these sediments, e.g. pharmaceuticals. Processes like retardation and degradation can be identified.

In the conducted experiment fine-grained natural sediment with a low hydraulic conductivity from a study site in the Grand Duchy of Luxembourg was used. The water used for the experiment was natural water taken from a small stream at the same fieldsite. It was spiked with four pharmaceutical compounds (carbamazepine, diclofenac, ibuprofen, sulfamethoxazole), which were also detected in groundwater and surface water samples at the study site. As some of the substances are known to be sensitive to the redox-conditions, the oxidation reduction potential (ORP) was varied throughout the experiment. A change of the ORP was realised by adding nitrate at the inflow of the column. During the experiment, which lasted for 2.5 months, four different nitrate concentrations were applied, beginning with the highest concentration. This should enhance the understanding of redox-dependent metabolism and degradation of the pharmaceuticals.

Water samples were taken daily from the reservoir tank to detect potential degradation of the pharmaceutical compounds before the water enters the column. The effluent water was sampled every three hours to realise a maximum resolution for the analysis of the pharmaceuticals where necessary. In addition major ions were analysed in the influent and effluent samples. Throughout the experiment physicochemical parameters (ORP, dissolved oxygen, electrical conductivity, and pH-value) were measured and logged at the outflow of the column.

First results show the influence of the added nitrate on the effluent water. The ORP starts with positive values and goes down to reducing conditions in the course of the experiment. The presented column experiment, which is closely connected to a field study in the Grand Duchy of Luxembourg, yields a better understanding of the processes influencing the occurrence and transport behaviour of the selected pharmaceuticals. In addition, some general findings on redox-dependent transport behaviour and metabolism of the chosen trace compounds for low permeable sediments are gained.