Distribution, remobilization and accumulation of organic contaminants by flood events in a meso-scaled catchment system

Abstract

Background Extreme weather events and natural disasters such as floods can cause severe damage and impacts on catchment systems covering natural as well as urban, industrial or agricultural areas. Thus, floods often lead to the acute and unusual release of organic pollutants, as well as the remobilization of legacy contaminations or old burdens. Floodplains are then of major relevance for the accumulation of pollutants. Accordingly, various floodplains distributed throughout the course of the Rur River were sampled immediately after two flood events in January/February and July 2021. The main objective was to address the general lack of knowledge on indirect effects of flooding and the corresponding distribution and accumulation of organic pollutants regarding different dimensions and dynamics of flood events. Results Gas Chromatography/Mass Spectrometry (GC/MS) based non-target screenings revealed the presence of several lipophilic to moderate polar organic pollutant groups, including PAHs (polycyclic aromatic hydrocarbons), hopanes, PCBs (polychlorinated biphenyls), LABs (linear alkylbenzenes) and various other industrial substances. These substances are indicators of petrogenic pollution, historical and current industry in the catchment area, and of wastewater and urban pollution, respectively. In general, concentrations detected after the extreme summer flood were higher than in winter. This points to additional emission sources due to substantially higher discharges and consequently more severe flooding in July. The main tributaries also had a major influence on the input and concentrations of organic pollutants at the receiving Rur River. Further on, structural features such as dams and reservoirs, but also (re)naturalized areas were clearly recognizable in the flood-related dispersion of organic pollutants. Interestingly, LAB contamination was similar after both flood events regardless of the specific dimension. Conclusions Flood dimension and frequency are of great relevance for the distribution, remobilization and accumulation of organic contaminants. However, special attention should be given to the introduction of wastewater pollutants for any flood extent. Overall, organic indicators are therefore very useful to obtain information on specific distribution patterns and the influence of tributaries or structural measures, providing an important basis for the assessment of short- and long-term environmental risks and hazards.

Inventory of aqueous and sediment-associated organic pollutants released by the 2021 flood in the Vicht–Inde catchment, Germany

“…The vast destruction in the study area, the flooding of industrial sites, and flushing out of sewage systems all contribute to the release and distribution of DIPNs throughout the river catchments. This is further supported, as Schwanen et al [92]-this issue, have also identified DIPNs in the Rur river into which the Vicht and Inde rivers flow. These downstream observations are likely linked to industrial emission sources along the Vicht and Inde catchments where most of the destructive flood-impacts took place.…”

“…Through the past two decades, few studies provided evidence for the widespread distribution of Mesamoll ® in the environment, as well as the ability to adsorb and accumulate in sediments (e.g., [7,34,36,83,94]). Mesamoll ® pollution in the Rur catchment, to which the Vicht-Inde catchment contributes, has previously been documented by Schwanen et al [92].…”

“…The hydrophobic characteristics and persistency of LABs favor their accumulation in river and floodplain sediments (e.g., [46,50,104]). Previously to the 2021 flood, LAS have been detected in the surface waters of the Rur catchment [89], and LABs were detected in the floodplains of the Rur River [92], in which the Vicht-Inde catchment flows into. In the case of the 2021 flood, damages to infrastructure, breakage, leakage, and flushing of sewers and pipes (Fig.…”

“…Well-documented examples of smaller rivers with a long history of mining-related and industrial pollution that were also affected by the 2021 floods are the Inde and the Vicht (e.g., [110]-this issue). In particular, man-made heavy metal contamination since the Medieval times has been known to pollute the Vicht and Inde catchments (e.g., [28,87,92]). The 2021 flood provided unpredictable forces and prompted the remobilization of old burdens and the distribution of heavy metals (Zn, Pb, Cd, Cu, and As) across the inundated floodplains and urban areas of the catchment (e.g., [62,110]-this issue).…”

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].…”