Accumulation of microplastic in a Lower Rhine alluvial floodplain in Germany

, Rolf Markus, Laermanns Hannes, Steininger Florian, Löder Martin, Möller Julia, Bogner Christina.

River systems are major pathways for the transport of microplastics (MPs). The Rhine River is among the biggest rivers with respect to basin size and discharge in northwestern Europe. It is highly impacted by human activities with a multitude of different land use forms in its basin. Studies have documented the presence of MPs in the Rhine, along its course through Germany, as well as in several of its tributaries. However, the highly dynamic and ecologically sensitive alluvial floodplains of the Rhine River have not been investigated in detail so far. Knowledge on the state of MP contamination and on potential entry pathways of MP into meadows of the Rhine is essentially important for an ecological risk assessment. In this study we analysed the contamination level and distribution of MPs in the meadow soils of the Rhine. We investigated a study site in the northern periphery of Cologne in the nature reserve Merkenich-Langel. We hypothesize that the main entrance pathway of MPs into the meadow soil is via fluvial transport and flooding. Indeed, the site was regularly flooded in the past and agricultural fields, which could be another major source of MP input via surface runoff, are not present in the vicinity of the sampling site. We chose three sampling transects with increasing distance to the river water level located within the past flooded area. Three mixed samples from those transects were taken and analysed for MP concentrations via ATR-FTIR and µ-FPA-FTIR spectroscopy after density separation and enzymatic-oxidative purification. We found an increase of MP concentration per kg of dry soil in the depth 5-20 cm with increasing distance to the river (ML1: 25.612 particles/kg, ML2: 50.776 particles/kg & ML3: 85.076 particles/kg). We attribute this increase to differences in intensity and frequency of flooding.

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