Why analysing microplastics in floodplain sediments is beneficial

, Lechthaler Simone.

Microplastics has already been detected in every environmental area and were thus defined as omnipresent anthropogenic contaminant. The current research focuses on understanding transport and sedimentation processes and detection of sinks. Thereby, fluvial systems are the predominant transport path for microplastic from land-based sources. Due to numerous sources along a river course, a continuous entry of microplastics is possible. If microplastics are transported in the river, floods can lead to sedimentation on the floodplains. Thus, they act as storage for microplastics which is why the analysis of floodplain sediments offers many information on flood related deposition and indicates a chronological context. So far, there are hardly any studies on microplastics in floodplains. Therefore, this study sampled at nine river sites (Inde River, Germany) depth profiles in floodplain areas which were examined for microplastics, grain size and heavy metals. In addition, composite samples from the riverbed and surface samples outside the flooding area were taken. An increase of microplastics [n/kg] from source to mouth was recorded and slip-off slopes showed higher microplastic abundance than cut-off slopes. Microplastics accumulated predominantly in fine grain sediments and the distribution along the river was similar to lead, which was exemplarily considered as one of the analysed heavy metals. As a new method, sedimentation rates of floodplains were determined based on microplastic detection. Furthermore, the temporal deposition of sediments was linked to the identified polymers where older polymers, such as polyethylene, were found in all layers and younger polymers, such as polyethylene terephthalate, only in the upper layers. The maximum time of deposition can be identified with the year of polymer development and therefore be used as a new dating method in the future. Overall, this study provides not only information on concentration of microplastics in floodplains but also on time related sediment deposition.

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