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Abstract Background The flood in July 2021 is considered one of the largest flood disasters in Western Europe in decades, with massive socio-economic consequences. The potential emission and remobilization of anthropogenic pollutants can lead to additional environmental consequences, which need to be addressed in long-term mitigation strategies. The Inde River and its tributary, the Vichtbach River, form a catchment located at the transition from the low mountain ranges of the Eifel to the lowlands of the Lower Rhine Embayment in Germany. The area has been an industrial and mining hotspot for centuries, making it a high-risk area for flood sediment pollution. The present study provides an ecotoxicological screening of flood sediments of the Vicht–Inde catchment to gain an impression of the degree of contamination by organic pollutants by means of in vitro effect-based method. Sediment samples were collected within days after the flood and fractionated prior to biotesting, and supportive instrumental geochemical analysis was performed. Results Flood sediments did not reveal estrogenic potential, which was included in the testing strategy as a relevant endpoint for industrial chemicals and untreated wastewater. In contrast, moderate-to-high dioxin-like activity was observed in 70% of the sediment samples with a peak dioxin-like potential at the restored section of the Inde. Overall, four hotspot samples were identified as at risk, which aligned mostly with the high concentration of organic pollutants including PAHs and PCBs. The fractionation allowed the identification of PAHs and their derivates as the most likely toxicity drivers for dioxin-like activity in the sediments of the Vicht–Inde catchment. Conclusion The results provide first information on the prioritization of hotspot locations at risk for a detailed ecotoxicological profiling and a post-flood monitoring of organic contamination. The identified sinks of contamination in the floodplain areas can be considered a source for remobilization of pollution in future flood events, which is highly relevant for the receiving Rur River.

Abstract Background The European flood that occurred between July 13th and 16th 2021, was a natural disaster that caused significant damage in Central European countries, including Germany, Netherlands, Belgium, and Luxembourg. This disaster resulted in the highest number of fatalities from a natural disaster in Germany during the twenty-first century, with over 180 people losing their lives and causing damages exceeding 30 bn€. The flood caused severe destruction in small mountainous river systems such as the Vicht and Inde rivers, particularly in the German state of North Rhine-Westphalia. In addition, the flood caused a significant release of pollutants, including old burdens from the former mining area of Stolberg. Results To assess the extent of pollution caused by the flood in the affected floodplains and urban areas, this study was conducted to inventorize organic contaminants identified through a non-target screening in water and sediment samples taken immediately after the disastrous flood event. In total, 56 individual contaminants were identified from the water samples, including substances derived from urban effluents, such as personal care products, cosmetics, odors, technical additives, pharmaceuticals and surfactants. The analysis of sediment samples revealed different types of environmentally hazardous contaminants, such as petrogenics, urban effluent and wastewater indicators, chlorinated industrial compounds, and pesticides. This diverse range of pollutants and their broad dispersion across various environments in the catchment is attributed to the dynamic nature of the flood. Conclusion The inventory of identified organic contaminants raises long-term environmental concerns and potential health implications for the flood-affected Vicht–Inde region.

Abstract Background In July 2021, destructive floods in Western Europe were triggered by enormous precipitation rates related to a low-pressure system named "Bernd." These catastrophic events led not only to major damage to infrastructure, severe economic losses, and the loss of lives but also to significant landscape changes and modifications. Here, we focus, as a case study, on the flood aftermath of the Ahr Valley in Rhineland-Palatinate state in western Germany, as it was one of the most affected and destroyed regions by the flood. We utilize high-resolution Digital Terrain Models (DTMs) based on airborne Light Detection and Ranging (LiDAR) that were taken shortly before and after the flood to investigate insights into geomorphic changes. Results By calculating Digital Terrain Models of Difference (DoD), we are able to quantify volumetric and areal changes caused by erosional and depositional processes for different sites in the Ahr Valley. Due to the morphology of the narrow Ahr Valley, most of the erosion and deposition is located within the deeply incised canyon of the Ahr River. The comprehensive analysis reveals notable morphological modifications throughout the study area, with a calculated erosion/deposition areal ratio of 0.46 and an erosion/deposition volumetric ratio of 0.63. Our findings indicate massive deposition regarding both areal and volumetric. We selected six different locations along the Ahr Valley that showcase distinct aspects of flood-induced fluvial morpho-dynamics. Deposition occurred mainly in point bars and downstream of destroyed artificial levees, in a braided river style. Conclusion Our investigations contribute to an overview and assessment of the morphological response to the destructive flood in the Ahr Valley. The results emphasize the necessity for implementing effective flood management strategies, as most of the urban areas in the Ahr Valley were flooded. Moreover, our results provide valuable insights into the impacted areas, highlighting vulnerable locations for flood-related erosion and deposition. This information could contribute to future mitigation and protection efforts, aiding in the development of comprehensive strategies to minimize the impact of similar events in the future.

Abstract Background Because of global climate change, extreme flood events are expected to increase in quantity and intensity in the upcoming decades. In catchments affected by ore mining, flooding leads to the deposition of fine sediments enriched in trace metal(loid)s. Depending on their concentration, trace metal(loid)s can be a health hazard. Therefore, exposure of the local population to flood sediments, either by ingestion (covering direct ingestion and consuming food grown on these sediments) or via inhalation of dried sediments contributing to atmospheric particulate matter, is of concern. Results The extreme flood of July 2021 deposited large amounts of sediment across the town of Eschweiler (western Germany), with the inundation area exceeding previously mapped extreme flood limits (HQextreme). These sediments are rich in fine material (with the Cu > Pb > Cd > Sn compared to local background concentrations. The concentrations of Zn, Pb, Cd, Cu, and As in flood sediments exceed international trigger action values. A simple assessment of inhalation and ingestion by humans reveals that the tolerable daily intake is exceeded for Pb. Despite the enrichment of other trace elements like Zn, Cu, Cd, and Sn, they presumably do not pose a risk to human well-being. However, exposure to high dust concentrations may be a health risk. Conclusions In conclusion, flood sediments, especially in catchments impacted by mining, may pose a risk to the affected public. Hence, we propose to (I) improve the flood mapping by incorporating potential pollution sources; (II) extend warning messages to incorporate specific guidance; (III) use appropriate clean-up strategies in the aftermath of such flooding events; (IV) provide medical support, and (V) clue the public and medical professionals in on this topic accordingly. Graphical Abstract