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Sewage input into a karst aquifer via leaking sewers and cesspits was investigated over five years in an urbanized catchment. Of 66 samples, analyzed for 25 pharmaceuticals, 91% indicated detectable concentrations. The former standard iodinated X-ray contrast medium (ICM) diatrizoic acid was detected most frequently. Remarkably, it was found more frequently in groundwater (79%, median: 54 ng/l) than in wastewater (21%, 120 ng/l), which is supposed to be the only source in this area. In contrast, iopamidol, a possible substitute, spread over the aquifer during the investigation period whereas concentrations were two orders of magnitude higher in wastewater than in groundwater. Knowledge about changing application of pharmaceuticals thus is essential to assess urban impacts on aquifers, especially when applying mass balances. Since correlated concentrations provide conclusive evidence that, for this catchment, nitrate in groundwater rather comes from urban than from rural sources, ICM are considered useful tracers. (C) 2015 Elsevier Ltd. All rights reserved.