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Assessment of the sources and inflow processes of microplastics in the river environments of Japan
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Researchers mapped microplastic concentrations across 29 Japanese rivers and found plastic particles present at 31 of 36 sampling sites. The concentrations were strongly linked to urbanization and population density, confirming that human activities in river basins are a major driver of freshwater microplastic pollution. The findings demonstrate that significant plastic fragmentation occurs before debris reaches the ocean, making rivers an important area for pollution monitoring.
The numerical and mass concentrations of microplastics collected at 36 sites on the surfaces of 29 Japanese rivers were mapped and compared with four basin characteristics (basin area, population density, and urban and agricultural ratios) and six water quality parameters (pH, biochemical oxygen demand (BOD), suspended solids (SS), dissolved oxygen (DO), total nitrogen (T-N), and total phosphorus (T-P)) in each river basin. Microplastics were found in 31 of the 36 sites, indicating that some plastics fragment into small pieces before reaching the ocean. The microplastic concentrations are significantly correlated with urbanisation and population density, indicating that the microplastic concentrations in the river depend on human activities in the river basin. Furthermore, we found a significant relationship between the numerical and mass concentrations and BOD, which is an environmental indicator of river pollution. This result demonstrates that microplastic pollution in river environments has progressed more in polluted rivers with poor water quality than in rivers with good water quality, leading to the conclusion that the sources and inflow processes of microplastics in river environments are similar to those of other pollutants. Our findings can help identify potential sources (i.e., point and non-point sources) of fragmented microplastics to improve waste management in Japan and model the transport fluxes of fragmented microplastics in Japanese rivers using water quality parameters and basin characteristics.
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Research digests by email
When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.