Testing selected micro-contaminants for their applicability as water quality indicators

Abstract

The use of anthropogenic micro-contaminants such as pharmaceuticals, lifestyle products, biocides, and pesticides as water quality indicators has aroused great interest in the scientific community and there is a high potential of using these compounds as indicators for process optimization, source delineation, and to evaluate the extent of a contamination (e.g. the amount of wastewater in surface- and groundwater). The presented work is the successful and consequent continuation of ongoing research activities on the evaluation of selected micro-contaminants as water quality indicators, their occurrence and fate in the environment, and their redox-dependent transformation. In order to use a compound as an indicator the availability of sensitive and selective analytical methods is essential. In this thesis, the development of a multi-residue analytical method based on high-performance liquid chromatographic separation and electrospray ionization with tandem mass spectrometric detection (HPLC-ESI-MS/MS) for the simultaneous analysis of 46 basic, neutral, and acidic compounds covering a wide range of polarity (log Kow <0–5.9) and potential contamination sources is described. The main feature of the method is the simultaneous solid phase extraction (SPE) of all analytes followed by the simultaneous separation and detection by HPLC-MS/MS with electrospray ionization in both positive and negative polarization within the same chromatogram. Method quantitation limits (MQL) for river- and seawater are in the low ng/L range. Furthermore, the high flexibility of the method (inserting additional analytes and adaptation to other water types) is demonstrated. The following part of the thesis presents the results from extensive river monitoring with focus on the correlation of 41 micro-contaminants with potassium (K+) and its temporal and spatial variation. Depending on the (geogenic) K+ background concentration, urine can be a significant source of K+ for surface waters. Accordingly, a positive correlation of concentrations of wastewater-related micro-contaminants and K+ is to be expected in receiving waters of wastewater treatment plant (WWTP) effluents. This correlation was found for compounds, which meet the following criteria: 1) WWTP effluent is the dominating source of the compound; 2) Variability of its mass flux in the WWTP is negligible; and 3) The compound is persistent in WWTPs and in the environment. Among other compounds, carbamazepine, sulfamethoxazole, and tolyltriazole demonstrate the best correlations. K+-equivalents of the individual micro-contaminants obviously depends on land use and population structure of the investigated river section. A correlation with K+ indicates that the concentration of the respective micro-contaminant depends only on river discharge. Following this assumption, the prediction of micro-contaminant concentrations at certain river locations could be substantially simplified. Regarding bank filtration and the interaction of surface water and groundwater in general, it may be possible to derive input functions of the correlating micro-contaminants. This would allow for a better evaluation of the attenuation potential at individual filtration sites. Furthermore, the approach can be used for contamination source delineation. Additionally, an approach to estimate the volume of untreated wastewater entering karst aquifers through rapid recharge is presented. Contamination from untreated wastewater leakage and related bacterial contamination poses a serious threat to drinking water quality and public health. However, a quantification of the magnitude of leakage is difficult. For this purpose a balance approach was adapted. It is based on the mass flow of caffeine in spring water, the load of caffeine in untreated wastewater, and the daily water consumption per person in a spring catchment area. The methodology was applied to estimate the amount of leaking and infiltrating wastewater to a well-investigated karst aquifer (Gallusquelle, Germany) on a daily basis. Also presented is a microcosm study on the transformation of the antibiotic sulfamethoxazole (SMX) under denitrifying conditions. A selective reaction pathway with the under denitrifying conditions produced nitrogen species nitrogen oxide (NO) and nitrite (NO2−) was suspected and the evaluation of two hypothesized transformation products (TP) 4-nitro-N-(5-methylisoxazol-3-yl)-benzenesulfonamide (4-nitro-SMX) and N-(5-methylisoxazol-3-yl)-benzenesulfonamide (desamino-SMX) was confirmed in a denitrifying water/sediment batch experiment. Furthermore, the compound 4-nitro-SMX has the potential to retransform to its parent compound SMX. The TPs were also detected in environmental samples demonstrating the high relevance of this study regarding the occurrence and fate of SMX in the environment and for water quality monitoring. Furthermore, TPs, which are specific for certain redox conditions, could be potentially used as redox indicators regarding reactive transport.