Abstract
Urban rivers remain the key conduits conveying land-sourced plastics into the ocean. However, detailed information is limited on the concurrent evaluation over a wide array of particle size-specific abundances, characteristics, and distribution patterns of plastics in riverine environments. Therefore, this study provides a comprehensive assessment of plastic pollution in an urban river network in Japan by analyzing mesoplastics (5000–25,000 μm), large microplastics (300–5000 μm), small microplastics (SMPs, 10–300 μm), and microplastic-fibers (MPFs, 10–5000 μm) concurrently, for the first time. Sampling was conducted at seven stations in the Kamo and Katsura Rivers flowing across metropolitan Kyoto City. The analytical procedures involved infrared spectroscopy and fluorescence-staining microscopy. The concentrations of plastics were moderate compared to the global reports and gradually increased along the river flow (3550–15,840 items/m3; 180–13,180 μg/m3), mostly due to urban discharges via non-point sources. The number concentrations increased with decreasing particle size, marking 99.94% of SMPs, including 50% smaller than 40 μm. Conversely, mass concentrations decreased, exhibiting 96% larger than 1000 μm (64% mesoplastics including 20% around 5000 μm), along with 2% SMPs. Polyethylene (PE) and polyvinyl alcohol were distinct among SMPs, with PE indicating higher susceptibility to fragmentation compared to polypropylene and other polymer types. MPF concentrations were homogeneous throughout the watershed (1470–3600 items/m3; 520–1060 μg/m3), with a higher proportion of fibers smaller than 1000 μm (86%), apparently originating from polyethylene terephthalate/nylon/acrylic-like textile fibers. The proportion of MPFs surpassed particles within 100–3000 μm and was considerably high around 300 μm (> 98%). The river network of Kyoto conveys billions of tiny microplastics to the Yodo River, the primary water resource downstream, within a dry day.
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The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
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Acknowledgements
We extend our sincere gratitude to all the students and the technical staff of “Environmentally Friendly Industries for Sustainable Development Laboratory” of the Graduate School of Global Environmental Studies (GSGES), Kyoto University who were involved in sampling and laboratory experiments. We also thank the members of the “Laboratory of Regional Planning,” GSGES for helping us with Geographic Information System (GIS) applications.
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This work was supported by Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research [JP19H00783] and [JP23H00194].
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Sachithra Imbulana: conceptualization, software, formal analysis, data curation, visualization, writing—original draft investigation; Shuhei Tanaka: conceptualization, methodology, investigation, resources, project administration, supervision, funding acquisition, writing—review and editing; Satoru Yukioka: methodology, investigation, project administration; Ibukun Oluwoye: writing—review and editing, supervision.
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Table S1. Details of the sampling stations. Table S2. Spectra of some polymers frequently tested with ATR-FTIR. Table S3. Spectra of some polymers frequently tested with μ-FTIR. Table S4. Microscopic observations of Nile red-stained MPFs of known polymers and non-plastic fibers (Scale in the images: 190 px represents 1 mm). Table S5. Proportions of mesoplastics (out of the total microplastics and mesoplastics) in river water. Fig. S1. Particle size distribution of plastics with respect to a) number concentrations; and b) mass concentrations, considering wide size intervals in the x-axis. Fig. S2. a) Distribution of the colors of plastics; b) Distribution of the shapes of plastics (In each figure, the distribution based on the number of plastic items is shown in the left side while the same based on mass of plastic items is shown in the right side. “MesoPs” refers to mesoplastics in the size range of 5–25 mm; “LMPs” refers to large microplastics in the size range of 300–5,000 μm; “SMPs” refers to small microplastics in the size range of 10–300 μm). Fig. S3. Distribution of the polymer types of MPFs, a) based on number; b) based on mass; c) based on fiber length (“MPFs” refers to microplastic fibers in the size range of 10–5,000 μm). Fig. S4. Correlations between the concentrations of different size categories of plastic particles (“MesoPs” refers to mesoplastics in the size range of 5–25 mm; “LMPs” refers to large microplastics in the size range of 300–5,000 μm; “SMPs” refers to small microplastics in the size range of 10–300 μm. Fig. S4-a shows that one MesoP particle corresponds to about 26 LMP particles) (DOCX 17460 kb)
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Imbulana, S., Tanaka, S., Yukioka, S. et al. Occurrence and distribution of plastic particles (10–25,000 μm) and microfibers in the surface water of an urban river network in Japan. Environ Monit Assess 196, 92 (2024). https://doi.org/10.1007/s10661-023-12221-6
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DOI: https://doi.org/10.1007/s10661-023-12221-6