Year-round spatial and temporal distribution of microplastics in water and sediments of an urban freshwater system (Jungnang Stream, Korea)

Abstract

Streams and tributaries can play a significant role in the transport of inland microplastics to rivers and oceans; however, research on microplastics in these water bodies is limited compared to riverine and marine environments. Analyzing microplastic abundance at higher spatial and temporal resolutions is crucial to comprehend the dynamics of microplastics in these water bodies. Therefore, this study investigated year-round spatiotemporal variations of microplastics monthly in surface waters and sediments along the Jungnang Stream, one of the main tributaries to the Han River in South Korea. The mean concentration of microplastics in the stream was 9.8 ± 7.9 particles L−1 in water and 3640 ± 1620 particles kg−1 in sediment. Microplastic concentrations in surface waters during summer were significantly higher than in other seasons, positively linked to increased precipitation and river discharges. Polymer compositions mainly consisted of polyethylene, polypropylene, and polyethylene terephthalate, with the majority of microplastics detected smaller than 200 μm. Fragment-shaped microplastics were predominant over fibrous ones. The estimated annual input and output of microplastics through surface waters were 1.2–207 kg (2.7–150 billion particles) and 11.3–272 kg (17–769 billion particles), with the summer months contributing more than 70% of the total output. The greater microplastics output in the Jungnang Stream's waters compared to its receiving waters (Han River) indicates microplastics transport from water to other environmental compartments, such as sediments. These findings highlight the importance of investigating microplastic abundances in surface waters and sediments with temporal resolution, at least across different seasons. Such investigations offer valuable insights into the spatiotemporal occurrence and dynamic transport of microplastics, providing essential information for water management and the development of policies in freshwater ecosystems.