Abstract
Microplastics have been detected in lake environments globally, including in remote regions. Agricultural and populated areas are known to congregate several inputs and release pathways for microplastic. This study investigated microplastic (50–5000 µm) contamination in five Danish freshwater lakes with catchments dominated by arable land use. The concentrations in sediments (n = 3/site) and the zebra mussel, Dreissena polymorpha (n = 30/site), were calculated and compared with catchment characteristics and environmental parameters. Microplastic concentrations in sediment were relatively low (average 0.028 ± 0.017 items/g dry weight sediment) whilst only a single microplastic was found in the mussels (average 0.067 ± 0.249 items/10 individual). Hence, no relationship between the number of observed microplastics in sediment and mussels could be identified, nor could a relationship between concentration in sediment and environmental parameters. As all lakes studied received their water from moderate to heavily anthropogenically impacted catchments, it was expected that they would be sinks for microplastic with high bioavailability. Based on the results of the present study, D. polymorpha were found to not be contaminated by microplastics in the five study lakes. Thus, our results suggest that these mussels do not interact with microplastics at low concentrations. We speculate that the results on sediment and biota could be explained by several factors related to regional differences in plastic use, species characteristics, sampling size, and the fact that finding no microplastic is not always reported in the scientific literature. Thus, the paper provides insight into the dynamics between the catchment, lake, and biota in systems with low microplastic concentration.
Highlights
Research increasingly indicates the significant role of freshwater systems in relation to microplastic pollution (Li et al 2020)
No relationships were found between sediment microplastic concentrations and a series of environmental parameters nor between environmental data (e.g. total nitrogen (TN), total phosphorous (TP), chemical oxygen demand (COD) discharge to lake and catchment, application of sludge, potential plastic cover) and polymer types in the sediment, except for plastic cover, which was in turn not supported by the qualitative data of microplastic characteristics
This sheds a light on the difficulties associated with identifying and apportioning microplastic sources in catchments, where many of the actual inputs are expected to be spatially and temporally dynamic, and may be diffuse in nature
Summary
Research increasingly indicates the significant role of freshwater systems in relation to microplastic pollution (Li et al 2020) This in part refers to their capacity as a vector between terrestrial and marine environments, and— and importantly—as vital ecological systems which can be affected by the potential impacts of microplastic contamination, following accumulation of particles and exposure in freshwater ecosystems (Horton et al 2017b; Wagner and Lambert 2017). Research points towards the role floodplain and freshwater sediments have as accumulation zones for microplastic, in lakes, but more research is needed to assess and describe the sources of microplastic to the freshwater environment (Clayer et al 2021, Hurley et al 2018a; Rodrigues et al 2018; Turner et al 2019; Xu et al 2020). It is necessary to investigate different matrices to establish a baseline for the presence of microplastics across freshwater systems and assess the contribution from different sources
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