Main pathways for microplastics in freshwater systems: A review on potential sources and drivers of microplastic pollution in rivers

Microplastic Source Land-use Freshwater River

Authors

  • Amir Hossein Hamidian Department of Environmental Science and Engineering, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
  • Mahdieh Dalvand Department of Environmental Science and Engineering, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
December 25, 2023

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Microplastics are ubiquitous in surface waters and sediments of freshwater systems. Reports of MP presence in high concentrations, even in remote regions, indicated that this emerging pollutant can be a serious problem for environmental health. Because of their diverse sources, tracking and identification of all entry routes of MPs into freshwater rivers remain unknown. Investigation of drivers of MP concentration and distribution in these systems can help reach a point of view about the potential sources of these particles. In this review, more than 100 documented papers about MP particles and their presence in surface waters and sediments of different freshwater systems (with a focus on rivers) were investigated. MP pollution in a river can be due to anthropogenic factors including point and non-point (diffuse) sources of MPs. In this regard, waste­water treatment plants are the most investigated point source of MPs. However, there is much less investigation on other point sources such as industrial wastewater. The most important diffuse sources of microplastics are urban land-use, which consists of various sources such as domestic sewage (point) and road runoff (non-point). Agricultural land-use as a diffuse and important source of MPs is also less studied in the literature. Water hydro dynamic (e.g. surface currents and stagnant water zones) and seasonal variability (e.g. rainfall) are important factors in MP distribution in rivers. Physio-chemical characteristics of MPs (including shape, size, color, and chemical composition) can serve as indicators of potential sources of particles; and are effective in MP distribution in riverine systems. It should be noted that freshwater rivers can be considered as both sink and source for MPs.