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The objective of this investigation is to analyse the variations of xenobiotic concentrations and the fluxes of dissolved xenobiotics during runoff events in the small rural Mess catchment (35 km 2 ) in the Southwestern part of Luxembourg. Sulfonamides, tetracyclines, analgesics and hormones, dissolved nutrients, sulphate and chloride were measured to gather information about runoff generation. Typically, the highest values can be found during the first flush mainly in the rising limb of the flood hydrographs. The highest concentrations in eleven flood events are measured for ibuprofen (2,383 ng l -1 ), estrone (27 ng l -1 ) and diclofenac (20 ng l -1 ). From the tetracycline group tetracycline (9 ng l -1 ) itself is of relevance, while the sulfonamides are mainly represented by sulfamethoxazole (5 ng l -1 ). The variable patterns of chemographs are attributed to the heterogeneous runoff generation characterised by different reactions of storm overflows from the combined sewer systems. During single flood events, the fluxes of ibuprofen (maximum 24,000 mg), 17α-ethinylestradiol (122 mg), 17β-estradiol (32 mg) or estrone (274 mg) are rather low.

Urban and agricultural areas affect the hydraulic patterns as well as the water quality of receiving drainage systems, especially of catchments smaller than 50 km(2). Urban runoff is prone to contamination due to pollutants like pesticides or pharmaceuticals. Agricultural areas are possible sources of nutrient and herbicide contamination for receiving water bodies. The pollution is derived from leaching by subsurface flow, as well as wash-off and erosion caused by surface runoff. In the Luxembourgish Mess River catchment, the pharmaceutical and pesticide concentrations are comparable with those detected by other authors in different river systems worldwide. Some investigated pesticide concentrations infringe current regulations. The maximum allowable concentration for diuron of 1.8 μg l( - 1) is exceeded fourfold by measured 7.41 μg l( - 1) in a flood event. The load of dissolved pesticides reaching the stream gauge is primarily determined by the amount applied to the surfaces within the catchment area. Storm water runoff from urban areas causes short-lived but high-pollutant concentrations and moderate loads, whereas moderate concentrations and high loads are representative for agricultural inputs to the drainage system. Dissolved herbicides, sulfonamides, tetracyclines, analgesics and hormones can be used as indicators to investigate runoff generation processes, including inputs from anthropogenic sources. The measurements prove that the influence of kinematic wave effects on the relationship between hydrograph and chemographs should not be neglected in smaller basins. The time lag shows that it is not possible to connect analysed substances of defined samples to the corresponding section of the hydrograph.

Abstract:The investigation focuses on the analysis of dissolved sulfonamides, tetracyclines, analgesics, anticonvulsants and hormones in surface water. Runoff event and baseflow samples were analysed in two small river catchments of different land use in Luxembourg. For most of the flood events, similar pollutant loads to those transported during 1 day with average baseflow discharge were observed. The maximum contents during flood events and the event mean concentrations are controlled by preevent hydro-climatological conditions. For all substances under investigation, maximum concentrations and event mean concentrations show a decrease with raising antecedent rainfall. In addition, the interstorm and intrastorm variability of the pollutant transport was determined. Runoff generation and corresponding transport of xenobiotic compounds show a complex pattern with many interrelated processes, taking place within bedrock, soil, anthropogenic facilities and channel and in different parts of the basins under investigation. Different sources of pollutants can be identified and related to particular locations in the basin. The influence of the sewer systems is obvious. In the agricultural Mess basin, higher rainfall amounts lead to greater quantities of laterally inflowing soil water with higher concentrations of dissolved oxytetracycline. This originates from veterinary medicines administered to livestock and enters the environment through the application of organic fertilisers, especially by slurry that is applied to the fields.

In many cases, only selected well-known target chemicals are analysed and used for a comparison with biological effects. Predicting the environmental impact of different chemical compounds does often fail. Effects are the result of mixture toxicity of single chemicals and their degraded products, which can have different biological potency and bioavailability. In vitro toxicity or mechanism-based assays are used as screening tools, prior to extended evaluation in animals or natural populations, or even prior to chemical monitoring. This study illustrates the use of the yeast bioassay to investigate the presence of compounds or chemicals with estrogenic activity in wastewater and surface water in Luxembourg and compares results with chemical measurements. Although the approach described in this paper has already been published in many case studies before, it confirms earlier findings and it delivers results for Luxembourg where similar analyses have not been documented so far. By comparison of the biological signal in the yeast assay, expressed as estrogen equivalents, with available results by liquid chromatography-mass spectrometry for steroid hormones we could only obtain a similar ranking for the majority of samples with low or high estrogenic activity. Measurements can therefore only be used as a screening tool for estrogenic activity. Seasonal changes as apparent for chemical results in surface waters were confirmed in the yeast assay. Dissolved estrone is diluted by higher discharge in the rivers during winter containing larger amounts of unpolluted soil water and groundwater runoff.

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