Occurrence and concentration of a broad spectrum of micropollutants are investigated in Austrian river catchments, namely polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), organotin compounds, perfluoroalkyl acids (PFAAs) and metals. The parallel analysis across multiple environmental and engineered compartments sheds light on the ratio of dissolved and particulate transport and on differences in concentration levels between point and diffuse emission pathways. It is found that some PAHs and organotins are present in rivers, groundwater and bulk deposition at higher concentrations than in municipal wastewater effluents. Among PFAAs and metals, highest concentrations were recorded either in atmospheric deposition or in discharges from wastewater treatment plants. The relevance of the analysis across compartments is best shown by the case of perfluorooctanesulfonic acid (PFOS). Despite municipal wastewater effluents being the emission pathway with highest concentrations, this study reveals that not only rivers, but also atmospheric deposition and groundwater sometimes exceed the environmental quality standard for surface waters. Moreover, this work reveals partially counterintuitive patterns. In rivers with treated wastewater discharges, increasing levels of dissolved compounds were measured at rising flow conditions, whereas the opposite would be expected owing to the dilution effect. This might derive from the mobilisation from soil or suspended particulate matter or rather find its explanation in high concentrations in atmospheric deposition. These hypotheses require however being tested through targeted studies. Additional future research includes the analysis of how regional or catchment specific characteristics might alter the relative importance of different emission pathways, and the modelling of emission and river loads to assess their relative contribution to river pollution.

An accurate budget of substance emissions is fundamental for protecting freshwater resources. In this context, the European Union asks all member states to report an emission inventory of substances for river basins. The river basin management system MoRE (Modeling of Regionalized Emissions) was developed as a flexible open-source instrument which is able to model pathway-specific emissions and river loads on a catchment scale. As the reporting tool for the Federal Republic of Germany, MoRE is used to model annual emissions of nutrients, heavy metals, micropollutants like polycyclic aromatic hydrocarbons (PAH), Bis(2-ethylhexyl)phthalate (DEHP), and certain pharmaceuticals. Observed loads at gauging stations are used to validate the calculated emissions. In addition to its balancing capabilities, MoRE can consider different variants of input data and quantification approaches, in order to improve the robustness of different modeling approaches and to evaluate the quality of different input data. No programming skills are required to set up and run the model. Due to its flexible modeling base, the effect of reduction measures can be assessed. Within strategic planning processes, this is relevant for the allocation of investments or the implementation of specific measures to reduce the overall pollutant emissions into surface water bodies and therefore to meet the requirements of water policy.

Surface water pollution with poly- and perfluorinated compounds (PFAS) is a well-recognized problem, but knowledge about contribution of different emission pathways, especially diffuse ones, is very limited. This study investigates the potential of the pathway oriented MoRE model in shedding light on the relevance of different emission pathways on regional scale and in predicting concentrations and loads in unmonitored rivers. Modelling was supported with a tailor-made monitoring programme aimed to fill gaps on PFAS concentration in different environmental compartments. The study area covers the whole Austrian territory including some additional transboundary catchments and it focuses on perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). These two PFAS are regulated and therefore their production and use in Europe are currently decreasing. Nevertheless, these compounds are still emitted into the environment via legacy pollution and as transformation products from other PFAS. These two compounds were selected for this study in view of the larger information availability compared to other PFAS. Despite considerable uncertainties in the input data, model validations show that this approach performs significantly better than previous modelling frameworks based on population-specific emission factors, population density and wastewater treatment plant information. The study reveals the predominance of emissions via municipal wastewater treatment plants for PFOS and a relevant role of diffuse emission pathways for PFOA. Results suggest that unpaved areas contribute the biggest share to total diffuse emissions, but the estimation of these pathways is affected by the highest uncertainty in the input data and requires better input data from monitoring. Once the currently growing substance-specific data sets on the concentration of PFAS, others than PFOS and PFOA, in different environmental compartments, will reach an adequate quality, the model presented here will be easily applicable to them.

Background: The European Water Framework Directive foresees the establishment of emission inventories for micropollutants (MP) to facilitate an evidence-based development of mitigation measures. Regionalized pathway analysis constitutes a moderately data-intensive approach to quantify the contribution of different pathways to the total pollution of surface waters. So far, only few European member states have created an inventory that includes diffuse pathways. The fundamental basis to enable it is an accessible, well-structured and harmonized database with data on the concentration of MPs in multiple compartments, such as soils, groundwater, atmospheric deposition and urban systems. Combined with the water and suspended substance balance in river basins, such data enables the estimation of emission loads via specific pathways. In the Danube River Basin, but in general in Europe, a public data management platform with such scope and criteria is still lacking. Results: We collected and harmonized MP measurements across multiple compartments and countries together with key metadata, harmonized and combined them into a new database. The resulting tool, available for download, facilitates the assessment of current data availability, in terms of quantity and quality. For example, while the majority of available data stems from groundwater and surface water, other highly relevant compartments are scarcely represented. By examining differences in MP concentration level across compartments, the database can lead to understand the relevance of specific emission pathways and thus to prioritize data-retrieval and calculation efforts in modelling applications. Selected examples show how to exploit the metadata associated to the measurements to extrapolate the results to regions not covered by specific monitoring programmes. For example, PFAS concentrations in treated wastewater show significant dependence on the design capacity of the treatment plant. Conclusions: This study showcases how such database can support the setup of emission inventories, guide data providers and national authorities in prioritizing the allocation of resources for new surveys and in optimizing their national data collection and management systems. The process tested showed a great need for enhanced data literacy across countries and institutions to increase data availability and quality to secure the exploitation of the full information potential generated via monitoring programmes.

This study investigates the concentration dynamics of potentially toxic elements (PTE) during flow events to improve process understanding of the transport dynamics and derive conclusions for monitoring and management. The case study is a medium-sized lowland river catchment (387 km²) with mainly agricultural and urban land use. Three-to-four events were sampled at three monitoring sites in sub-catchments with different characteristics, with one-to-six samples taken per event. Total and dissolved concentrations of 29 major and trace elements were analysed, and concentrations in suspended particulate matter (SPM) derived by calculation. This was complemented by 10 riverbed sediment sample and 10 soil composite samples collected through a land-use stratified sampling design, ensuring high representativeness of soil across the entire catchment. The results confirm that PTE transport is primarily driven by the transport of SPM, but the PTE content in SPM exhibits distinct and systematic dynamics. Higher content of road traffic related elements (e.g. Sb) at earlier stages of the event indicates street runoff inputs, which has important implications for selecting effective emissions mitigation measures. Variability in both SPM transport and its quality has major implications for designing fit-for-purpose monitoring, for example for the accurate estimation of river loads or at the identification of contamination sources. The investigation of the dissolved fraction of the PTE concentrations shows significant differences between some events and therefore offers high potential to discriminate between different event types. Furthermore, we were able to identify the duration of the pre-event low-flow period as a possible driver for differences in events. The contamination level found in the catchment is low to moderate, with no exceedance of environmental quality standards. The calculation of enrichment factors identifies elements impacted by anthropogenic emissions, indicating important pollution sources and pathways. This is key to effective management.

This study aimed to investigate the occurrence and concentration patterns of three groups of trace contaminants—potentially toxic elements (PTEs), polycyclic aromatic hydrocarbons (PAHs), and per‐ and polyfluoroalkyl substances (PFASs)—in river catchments with contrasting land use and landscape characteristics. A second objective was to relate the concentrations in suspended particulate matter (SPM) to those in soils and to catchment attributes in order to identify dominant transport processes and contaminant sources. A spatially explicit monitoring campaign was conducted in three river catchments of the central Danube River Basin: Zagyva and Koppány in Hungary and Wulka in Austria. Composite soil samples (∼10 per catchment, totaling ∼200 subsamples) were collected from forest, pasture, and cropland areas. SPM was collected using both passive and active samplers under base‐flow and high‐flow conditions. The results revealed strong spatial variability in concentrations for five of seven PTEs, all PAHs, and eight of 10 PFASs. Substances predominantly deposited atmospherically—such as PAHs and several PFASs—were more concentrated in forest soils compared to pasture and cropland. Base‐flow SPM samples were often more contaminated than high‐flow samples, especially for PAHs and some PTEs. Concentrations in SPM were generally correlated with soil concentrations, suggesting that erosion‐related transport of these chemicals may be significant in rural catchments. However, enrichment patterns and correlation strength varied by substance group and land use type. These findings support the use of parallel SPM and soil sampling for improving empirical emission modeling and source identification in catchments with mixed land use.