Toxic European Summer Flood – Dispersion of organic pollutants along the Vicht and Inde rivers, Germany

The 2021 European floods (July 13^th–16^th, 2021) marked Germany’s deadliest (>180 fatalities) and most costly (>€ 30 billion) natural disaster of the 21^st century. In North Rhine-Westphalia (Germany) the floods have caused drastic scenes of destruction along small mountainous river systems, such as the Vicht and Inde rivers. Alongside this destruction stands the release of organic pollutants and the remobilization of sediment-associated old burdens in the former mining area of Stolberg. In a preliminary study 10 samples along the floodplains and urban areas of Vicht and the successive Inde rivers have been collected directly after the flood to determine the pollution concentration, dispersion and potential sources. With this information an assessment of the short-term and long-term environmental risks can be evaluated.

First results show acute enrichment of organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs – petrogenic pollutants), polychlorinated biphenlys (PCBs – old burdens/plasticizers) and linear alkylbenzenes (LABs – sewage). The sewage indicators show their highest release and accumulation in samples taken in the urban areas, and subsequently dilute along the natural floodplain segments. This repeats for at least for Stolberg and Eschweiler, which were flooded by the Vicht and Inde, respectively. Old burdens, such as represented by PCBs, related to historical and present heavy industry in the vicinity to the rivers. The flood caused the remobilization of respective old burdens from contaminated plains and urban sources. Petrogenic markers, especially those of PAHs, have been measured in concentrations of mg/kg, vastly exceeding all environmental guidelines and restrictions. These can also be linked to the flooding of industrial and urban sites (e.g., household oil heating tanks, vehicles).

The wide range of observed pollution and fast dispersion of sediment-associated pollutants can be linked to the highly dynamic nature of this flood. In addition, the multitude of historical (mining, heavy industry) and present sources (e.g., fuels, oil, factory effluents, wastewater), sediment-associated pollutants have been remobilized or acutely released with the flood. This unprecedented 2021 European floods may allow insights into the relationships and interactions between hydrodynamics, sedimentology and pollution during such events.