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The impact of flood events on the spatio-temporal variability of microplastics in the river sediments of two contrasting streams discharging towards the southern Caspian Sea
Summary
Microplastic concentrations in two Iranian rivers flowing into the Caspian Sea were monitored before and after a major 2019 flood, revealing that flood events temporarily flush microplastics downstream and redistribute them. Polystyrene fragments dominated the samples, and concentrations were highest at downstream stations influenced by urban areas. The findings show that extreme rainfall events play a key role in mobilizing and spreading microplastic pollution through river networks.
Microplastics (MPs), as global emerging pollutants, have received significant attention worldwide due to their wide spread presence in aquatic and terrestrial ecosystems. However, the mechanisms controlling their fate and transport through river networks remains poorly understood. This study investigates the spatio-temporal distribution of MPs in two contrasting rivers (Tajan and Talar) discharging to southern coasts of the Caspian Sea, Iran and identifies pollution sources and their activation. In both rivers, MPs were dominated by black-gray larger-sized (1000-5000 μm) Polystyrene (PS)particles. Spatially, MPs concentrations in both rivers differ from upstream to downstream and showed uneven distribution. The March 2019 flood event affected on the concentration and patterns of MPs in river sediments. The total MPs concentration in both river sediments in all stations significantly decreased from pre to post-flood time (p-value