In an extensive monitoring programme, event mean concentrations of 12 heavy metals, 16 polycyclic aromatic hydrocarbons (PAH), nine pesticides/biocides, three pharmaceuticals, three benzotriazoles, acesulfame, and DEHP (di-(2-ethylhexyl)phthalate) were measured at 10 combined sewer overflow (CSO) facilities throughout Bavaria, Germany, for more than 110 overflow events. A harmonised approach with large volume samplers was used to produce volume-proportional event composite samples. A wide range of event durations and volumes was covered successfully. All substances analysed were detected in CSO samples and the majority were quantified in more than 80% of the samples. Our results confirm that CSOs need to be considered in the debate on micropollutant emissions, and knowledge regarding their concentrations at a regional level needs to be solidified. Distinct substance-specific patterns can be observed in the variability between events and sites as well as in a correlation analysis of substance concentrations. These trends underline the need for differentiation of the substances by their predominant sources, pathways, and transport behaviours. Compared to wastewater treatment plants, CSOs are an important pollution source especially for ubiquitous, primarily stormwater-transported pollutants, including substances causing failure to achieve good chemical status of surface waters, such as the uPBT (ubiquitous, persistent, bioaccumulative and toxic) substances Hg and PAH.

The assessment of pollution from sewer discharges requires flexible and reliable sampling methods. The characteristics of the sampling system must be known to allow comparison with other studies. Large volume samplers (LVS) are increasingly used for monitoring in sewer systems and surface waters. This article provides a comprehensive description of this widely applicable sampling system, gives insight into its comparability to standard methods, and provides recommendations for researchers and practitioners involved in water quality monitoring and urban water management. Two methods for subsampling from LVS are presented, i.e., collection of homogenized or sedimented samples. Results from a sampling campaign at combined sewer overflows (CSOs) were used to investigate the comparability of both subsampling methods and conventional autosamplers (AS). Event mean concentrations (EMC) of total suspended solids (TSS) derived from homogenized LVS samples and AS pollutographs were comparable. TSS-EMC of homogenized and sedimented LVS samples were also comparable. However, differences were found for particle size distribution and organic matter content. Consequently, sedimented LVS samples, which contained solids masses in the range of 3–70 g, are recommended to be used for particle characterization. The differences between homogenized and sedimented LVS samples, e.g., the quality of homogenization and the stability of samples during sedimentation in LVS, should be further investigated. Based on LVS results, average TSS concentrations of 50–60 mg/L were found for CSOs from centralized treatment facilities in Bavaria. With a median share of 84%, particles <63 µm were the dominant fraction.