Abstract
The geographical environment fundamentally influences the transport and deposition of sediments, including microplastics. In addition, the socioeconomic differences inherent in transboundary catchments result in various waste management strategies among the different countries influencing the input of microplastics into rivers. The catchment of the Tisza River in Central Europe is shared by five countries with different economic statuses and wastewater treatment practices. The aim of this research is to study the spatial changes in microplastic debris deposition along the Tisza and its main tributaries. The mean number of microplastic particles in the sediments of the Tisza was 3177 ± 1970 items/kg, while 3808 ± 1605 items/kg were counted in the sediments of the tributaries. Most of the particles were fibres, indicating the dominance of municipal wastewater input; this is especially the case in the upstream sub-catchments, where there are low degrees of wastewater management. The highest amount of microplastics was found in the sediments of the most-upstream section, where a low number of households are connected to wastewater treatment plants. Thus, it is hypothesized that suburban areas where high population densities and improper waste management co-exist may contribute to the direct input of microplastics into river systems and the development of local microplastic contamination hotspots. In addition, a high microplastic concentration was measured at the furthest downstream section, resulting from the decreased flow velocity related to impoundment by a dam. The efficiency of the microplastic trapping of the various depositionary forms varies along the river, suggesting various influencing factors and the complexity of the process. The higher concentration of microplastics observed in the tributaries compared to that observed in sediments of the main stream may reflect the importance of local sources and the complexity of source-to-sink relations for microplastic routes through the fluvial system; these processes do not always reflect progressive downstream increases.
Highlights
Plastics are widely used in every field of our lives; after a while, plastics can move into the air, onto the lands, and into surface and subsurface waters
The sediments collected at the sampling sites in Ukraine (No 1–14) contained much higher numbers of microplastics (3810 ± 1826 items/kg) than the Hungarian Upper Tisza (No 15–18: 2004 ± 1084 items/kg) samples or the samples collected from the entire Hungarian section of the Tisza (No 15–41: 2825 ± 1991 items/kg)
8067 items/kg, while in the sediments of the 10 tributaries, 900–7115 items/kg were counted. These data suggest that in this part of Central Europe, the fluvial sediments are slightly more contaminated by microplastics than those in Western Europe; this matches the results of Bordós et al (2019), who measured higher numbers of microplastics in the water (23.12 items/m3) of the Tisza than the values published for other European rivers
Summary
Plastics are widely used in every field of our lives; after a while, plastics can move into the air, onto the lands, and into surface and subsurface waters. Plastic pollution can enter freshwater systems via surface runoff (He et al, 2018), wind transport or direct human deposition, and, plastics can reach the seas and oceans (Horton et al, 2017; van Emmerik and Schwarz, 2020). During their route, plastics degrade, and this degradation is driven by sunlight (ultraviolet radiation), pH, temperature, physical weathering caused by friction, oxidative weathering, and biodegradation by microorganisms (Li et al, 2020, Huang et al, 2021a, 2021b). Microplastics (grain size: ≤5 mm) can be divided into two classes (Ballent et al, 2016; Horton et al, 2017): primary microplastics are manufactured at the microscale (e.g., for cosmetics, industrial abrasion processes and synthetic fabrics), while secondary microplastics are the result of the natural degradation of larger plastic products (e.g., the washing of artificial textiles creates fibres)
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