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Background Because of global climate change, extreme flood events will 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, the 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 enormous 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 < 63 µm fraction making up 32% to 96%), which either can stick to the skin and be ingested or be inhaled. They are moderately to heavily enriched in Zn>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 uptake 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.

Extreme precipitation and resulting extraordinary discharge on July 15th 2021 caused serious flooding and erosion in the northern foreland of the Eifel Mountains, western Germany. We provide two examples of strong backward erosion and sedimentation events from two open cast mining areas in North Rhine-Westphalia (NRW). The first one from the catchment of the Inde River close to Lamersdorf and the lignite open cast mining Inden; the second one from the catchment area of the Erft River near the village of Blessem and the local gravel mining. On-site fieldwork was supported by surveys of unoccupied aerial systems (UAS). Subsequent structure-from-motion (SfM) analyses were compared with the 1 m digital elevation model of the state NRW to estimate size and volume of the erosion and to provide the basis for a geomorphological mapping approach.At the Inde River between 1998 and 2005 a new river course was created due to the eastward extension of the lignite mining Inden. The 4 km long course of the Inde River was abandoned and today the river relocation, “new Inde River”, passes the mining area in a ~12 km long river bend to the west. At the junction of the new and old river course a flood protection dam was constructed to avoid the flooding of the lignite mining. After heavy rainfall on July 15th bankfull discharge of the Inde River resulted in a spill over at the junction and the reoccupation of parts of the old river channel. As the lignite mining is more than 200 m below the surface, rapid erosion of the old channel and fast backward erosion creates a 540 m long gorge which was about 5 m deep. More than 500.000 m³ of material were eroded and subsequently accumulated in the lignite mining area.At the Erft River flooding of a 60 m deep gravel pit occurred and backward erosion quickly reaches the nearby settlement Blessem resulting in the destruction and damage of several houses. In Blessem, first the settling basin of the gravel pit was flooded on July 15th 2021, resulting in backward erosion of the flood protection dams and finally in a large canyon. An area of more than 7 ha eroded until a depth of 8 m to max. 14m and more than 530,000 m³ sediment were transported into the nearby gravel pit. The new erosion level of the Erft River was about 3 m below its previous base. The original 60 m deep gravel pit was filled with water and about 30 meters of sediments. The digital elevation model and the aerial images indicate three morphdynamic phases of this flood event, with different direction of backward erosion and sediment transport.Both areas show semi-circle like structures caused by the backward erosion at the headwalls. Immediately deposited material in the headwalls during the event slowed down the erosion processes. Both examples show the high risk and strong geomorphological processes in flooded open-cast mining areas with large base-level changes on short distances.

Microplastic research has experienced almost exponential growth in publications and proceeded faster than ever throughout the last years. This increase comes with a downside in terms of missing standardizations and definitions especially concerning experiments. Furthermore, incomparability and lacking transferability of fragmentation studies onto the marine environment still hinder more realistic extrapolations and accurate numerical models. This review offers a first approach to tackle this problem by converting studies into comparable dimensions by rating their experimental settings and comparing them to in-situ values, thus, assisting future research with an unbiased and fast tool to assess the applicability of studies for their calculations. For this purpose, the main influencing factors for the environmental fragmentation of plastics were identified, ranked in terms of their impact, and, subsequently, applied to 49 setups of peer-reviewed studies. The average transferability into nature of the considered laboratory studies is 41%. Unconsidered implementation of proper mechanical wear by water and sediment movement into the test setups of around 80% of all reviewed studies explains this value. However, other parameters like UV radiation implementation, also pose an obstacle in about 50% of the laboratory studies. Nevertheless, even the reviewed in-situ fragmentation studies revealed problems in transferability in some of the weathering components caused by the fixation of the samples. This review indicates that the current database on plastic fragmentation is most likely not reliable enough for robust extrapolations or numerical models. A set of recommendations for test settings is proposed to improve upcoming experiments' quality and comparability.

s & presentations / EGU General Assembly 2021 EGU General Assembly 2021, vEGU21, online, 19 Apr 2021 - 30 Apr 2021; G��ttingen : Copernicus Gesellschaft mbH EGU21-7513, 1 Seite (2021). doi:10.5194/egusphere-egu21-7513, Published by Copernicus Gesellschaft mbH, G��ttingen