Abstract
Floodplain soilscapes act as temporary sinks in the environment and are nowadays affected by multiple contaminant accumulations and exposures, including heavy metals and (micro-)plastics. Despite increasing knowledge of the occurrence and behaviour of (micro-)plastics at the interface between aquatic and terrestrial systems, there are still major uncertainties about the spatial distribution of plastics, their sources and deposition, as well as spatial relationships with other contaminants. Our recent case study addresses these questions, using the example of a river system ranging from rural to urban areas. Based on a geospatial sampling approach we obtained data about soil properties, heavy metal contents via ICP-MS analyses, and particle-based (171 µm–52 mm) plastic contents, analysed using sodium chloride density separation, visual fluorescence identification and ATR-FTIR analysis. We found plastic contents of 0.00–35.82 p kg−1 and heavy metal enrichment (Enrichment factor 1.1–5.9). Levels of both contaminations occur in the lower range of known concentrations and show a different spatial distribution along the river course and in the floodplain cross-section. Furthermore, we found that plastic enrichment occurs in the uppermost soil layers, while heavy metal enrichment is located at greater depths, indicating different sources and deposition periods. Finally, direct short to long-term anthropogenic impacts, like floodplain restoration or tillage may affect plastic enrichments, raising questions for future floodplain management.
Highlights
After an initial half-decade of investigating plastic contamination in terrestrial environments, and with increasing progress in the development of suitable analytical methods, it has become clear that our soils contain far more plastics than perhaps previously assumed (Möller et al, 2020; Qi et al, 2020; Zhang et al, 2020; Braun et al, 2021)
The question now is about where, and to what extent, high concentrations of plastics can be found, what spatial differences exist and what the reasons are for different susceptibility levels of soils to plastics? When talking about plastics in soilscapes, there are various definitions and size classifications resulting from the different 35 research disciplines dealing with plastic contaminations in the environment (Hartmann et al, 2019)
3.1 Plastic loads and features In the floodplain soils along the Nidda River, plastic particles were found at each transect site and sampling point, resulting in a positive rate of 73 % of all samples (n = 100) which contain plastics
Summary
After an initial half-decade of investigating plastic contamination in terrestrial environments, and with increasing progress in the development of suitable analytical methods, it has become clear that our soils contain far more plastics than perhaps previously assumed (Möller et al, 2020; Qi et al, 2020; Zhang et al, 2020; Braun et al, 2021). After plastics were detected 30 in soils of different soilscapes, from highly cultivated to semi-natural scapes (Huerta Lwanga et al, 2017; Zhang and Liu, 2018; Liu et al, 2018; Corradini et al, 2019; Piehl et al, 2018), whether microplastics can be found in soils, appears no longer to be the major question. When talking about plastics in soilscapes, there are various definitions and size classifications resulting from the different 35 research disciplines dealing with plastic contaminations in the environment (Hartmann et al, 2019). Plastics in the environment can be defined as solid and insoluble, polymeric or co-polymeric, human-made particles that are produced (primary form) or fragmented by biogeochemical and physical processes (secondary form) to a certain size range (Bancone et al, 2020; Andrady, 2017). Plastics as environmental contaminants can be distinguished from other contaminants, like heavy metals, through their recent occurrence (exponential increase in production of plastics since the 1950s) and the absence of geogenic background levels, due to the purely anthropogenic 45 production of the materials (Zalasiewicz et al, 2016; Dong et al, 2020)
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