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Microplastics in the environment are a relatively new form of anthropogenic contamination. Right now, the research focus is on the detection of microplastic accumulation in different environmental compartments and understanding the processes that have led to its transport. Detailed information on microplastics in floodplain areas and their distribution in depth are still missing to better understand accumulation points. Therefore, this study presents on the one hand microplastic detection in fluvial sediments from nine sampling sites along a river course. Polymers were determined with infrared spectroscopy and additional sedimentary analysis of the grain size and heavy metal concentration was performed. In total, there was less microplastic in the upper than in the lower river course and slip-off slopes were identified as accumulation hotspots also in deeper sediment layers. Mostly, microplastic particles were detected in fine sediment and heavy metal concentrations along the river were similar to those of microplastics. On the other hand, besides the spatial distribution of microplastics and accumulation in floodplain areas, microplastic analysis offered information in a sedimentary context. Sedimentation rates (0.29-4.00 cm a-1) and patterns between temporal deposition and microplastic polymers were identified. The basis for the development of a dating method by detection of MPs in sediments was thus established. Microplastics as a contaminant provide, in addition to the identification of deposition areas, further data in a temporal and sedimentary perspective.

Rivers are strongly influenced by humans. As the natural occurrence of trace elements (TEs) is controlled by the geological setting, elevated contents of TEs are caused by anthropogenic activities. TEs can be adsorbed at fine sediments and (re-)mobilized, transported and accumulated at the riverbed and as overbank deposits on the floodplains. Thus, rivers are the transition system for pollutants between their source areas and the depositional areas. To investigate the recent distribution of TEs related to different impact factors, suspendible riverbed sediments of three rivers with neighboring catchments (catchment size each ± 350 km2) within the International River Basin District Meuse (border triangle between Belgium, the Netherlands and Germany) were analyzed. The aim is to compare the variability of pollution profiles (longitudinal TE distribution of sediment samples along the river) of three rivers, that are representative for central European foothills to lowland rivers, with both similar natural settings and disparate human impact factors, and to identify and analyze the ‘fingerprint’ of each river. Hence, a characterization of the individual pollution characteristics of the rivers, with past and recent TE sources, is achieved, which is applicable to other rivers with a similar land use history. The suspendible riverbed sediments of all three rivers show high contents of Cr (71.3–846.7 mg kg−1), Ni (15.2–61.9 mg kg−1), Cu (10.7–357.8 mg kg−1), Zn (186.35–6,571 mg kg−1), As (3.05–25.25 mg kg−1), Cd (1.1–22.8 mg kg−1), Sn (0.325–36.1 mg kg−1), and Pb (16.6–1,116 mg kg−1). Most of the concentration values exceed European supraregional background levels. The three catchments are characterized by high geogenic background contents due to the occurrence of ore and coal deposits and urban sources. However, each river shows different characteristics, driven by the natural setting and the individual anthropogenic activities. The pollution profiles show heterogeneous patterns along the river, with both, increasing and decreasing TE values and pollution hotspots. The used sampling method after Lambert and Walling (1988) is very well suitable for comparable rivers with a heterogeneous riverbed composition and enables to analyze characteristics of longitudinal pollution profiles in different river catchments. The TEs contents of the suspendible riverbed sediments of the three catchments are anthropogenically elevated. While urbanization causes heterogeneous patterns and moderately elevated contents of TEs, concentrations caused by past exploitation and processing of ore and coal and other related industries exceed other possible pollution sources. Today, the historical pollution sources stored in the sediments still have a major impact on the river systems, while modern pollution sources contribute to a minor extent.

Environmental sciences Europe 30(1), 40 ([1]-21) (2018). doi:10.1186/s12302-018-0170-0, Published by Springer, Berlin