In this study a laboratory column experiment under water saturated conditions was conducted to investigate the transport behaviour of the pharmaceutical compounds sulfamethoxazole, carbamazepine, diclofenac, and ibuprofen under varying nitrate concentrations. Organic rich sediment (f(OC)=0.01) and surface water from a formerly investigated field site were used. The water was spiked with the four compounds and the specific redox conditions in the column (0.351 m height) were varied throughout the experiment by adding nitrate in the influent water. Stepwise controlled decreasing influent nitrate concentrations between 131 and 20 mg L(-1) were applied in the course of the experiment which lasted 71 days. This established temporarily denitrifying conditions in the column during the reduction of nitrate. Sulfamethoxazole was severely influenced by this process. During denitrification sulfamethoxazole concentrations in the effluent water decreased rapidly and significantly. This experiment demonstrates the strong dependency of sulfamethoxazole transformation specifically on nitrate reducing redox conditions and therefore may help to explain the wide ranges of reported degradability for this compound. Ibuprofen was more stable under denitrifying redox conditions. Both for carbamazepine and diclofenac apparent retardation was observed. For carbamazepine this was attributed to sorption and also to degradation. For diclofenac nitrate controlled degradation seems the dominating process for the apparent retardation of this compound.
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