The risk may not be limited to flooding: polluted flood sediments pose a human health threat to the unaware public

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 < 63 µm fraction making up 32% to 96%), which either can stick to the skin and be ingested or 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 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

Impacts of metal mining on river systems: a global assessment

“…The increasing frequency of river flooding associated with anthropogenic global climate warming ( 50 ) can result in augmented erosion and sediment-associated metal remobilization from recently and historically contaminated floodplains ( 10 , 24 , 51 ), which now in many parts of the world constitute the principal source of metal contaminants in rivers. In addition, because of rapid urbanization and increasing settlement in floodplains worldwide (notably in sub-Saharan Africa and Southeast Asia), the proportion of the population exposed to flooding and contaminated flood waters has risen by 20 to 24% from 2000 to 2025 ( 52 ).…”

Mixed response of trace element concentrations in fluvial sediments to a flash flood in a former mining area

“…In the immediate aftermath of the flooding, when the extensive deposition of flood sediments became apparent, concerns arose due to the possible contamination of the sediments [108]. The exceptionally high water levels caused overflowing in areas usually unaffected by flooding, which activated additional pollution sources, as shown by enhanced pollutant levels in the exceptionally widespread deposited sediments [109,110].…”

“…By far, the most intense event was the flood in July 2021, which has already been described in detail. The extremely high water levels led to the widespread deposition of fine flood sediments [110].…”

“…Included elements were limited to trace metal(oid)s with a signal-to-noise ratio (S/N) of S/N > 2 (calculated following [89]). Exceptions were made for Cd (S/N = 1) and Sb (S/N = 0.9) because they are relevant pollutants in the Inde catchment [110,136]. To account for their low S/N, their uncertainty was tripled [89].…”

“…Ciszewski & Grygar [14] argue that this process is only of minor importance for trace metal transfer from the floodplain to the channel compared to input via eroded bank sediments. However, erosion processes are restricted due to river engineering measures in the lower Inde catchment (i.e., by the trapezoidal cross-section of the river from Stolberg down to the "Neue Inde") [110]. Under high antecedent soil moisture, interflow was shown to be of particular relevance during flood events in Central European low mountain ranges [191].…”