A category approach to characterize river sites based on non-target screening and target analysis

The objective of this study was to characterize monitoring sites with regard to their contaminating sources and to identify potential pollution hotspots as well as previously unknown compounds. Several evaluation methodologies were combined via a category approach consisting of site-specific detections using a combination of an extended target analysis via GC/MS and LC/MS/MS, NTS using LC-reversed phase high resolution MS, and suspect screening via spectral libraries. Furthermore, we considered the fraction of treated wastewater, the agricultural land use, and industry located in the vicinity. In order to evaluate our concept, more than 520 water samples of rivers from 79 locations throughout Saxony were analyzed by target analysis and NTS. Overall, a very good comparability between the results of target analysis and NTS was observed for pharmaceuticals and pesticides. In a first step, NTS data were used to identify hotspots of pollution with organic micropollutants. By this approach, 13 of 79 sites were characterized as "anomalous" as defined by empirical thresholds. More than 350 compounds could be identified using our spectral data library. In a second step, features of two sampling sites, which were likely contaminated by treated industrial wastewater, were investigated in detail, leading to the identification of four currently unknown compounds. These were cyclohexyldiethanolamine (CDA), 2,4,6-tri-(6-amino-hexanoic acid)-1,3,5-triazine (THAT), 2-(dibutylamino)ethanol, and 3,6,9-trioxaundecanedioic with estimated concentrations of up to 100 µg/L in rivers and streams using a semi-quantitative approach. However, based on the NTS database obtained, the identification of further currently unknown compounds can be easily done. The suggested category approach was also suitable to identify pollution hotspots of organic chemicals.