5:15 PM - 7:15 PM
[MIS21-P01] Characteristics and deposition systems of microplastics in the downstream areas of rivers discharging into Tokyo Bay
Keywords:Microplastics, Debris particles, Downstream and inner bay area, Brackish water, Aggregation, Principal component analysis
Plastic, due to its light weight, plasticity, and chemical stability, is used in a wide range of applications. Reflecting human industrial activities, plastic is a symbolic deposit of the Anthropocene. These plastics become microplastics (MPs) due to physical and chemical impacts when released into the environment. In recent years, MPs have been discussed including synthetic rubber called elastomers in addition to conventional plastics. These MPs are pointed out as factors of ecosystem destruction and environmental pollution, and countermeasures are urgently needed. Since many MPs are transported from their sources to the ocean via rivers, it has become clear that riverbed sediments can also serve as storage sites. In particular, the lower reaches of rivers, as points connecting terrestrial and marine environments, are crucial locations for understanding the continuous dynamics of MPs.
In this study, sediments were collected from the estuarine areas of the Tamagawa River, Edogawa River, Hanamigawa River, Yorogawa River, and the downstream area of the Arakawa River, which flow into Tokyo Bay. Through the analysis of MPs and clastic particles, the study aimed to determine the characteristics of MPs and to clarify the factors that regulate the distribution of MPs in the sediments.
MPs were found in the sediments collected from all rivers. The confirmed MPs were classified into five shapes (fragment, plate, film, column, and bead), and fragment-shaped MPs were particularly dominant. From the morphological characteristics, it was clarified that these are derived from artificial turf, vinyl products, plastic parts, tire pieces, etc. As for the types of MPs, in addition to high-density polyethylene terephthalate and acrylic rubber, low-density polyethylene and polypropylene were also confirmed, and relatively low-density MPs were also deposited. The depth distribution of MPs was not dependent on the depth, and many MPs were contained in the sediments, and the MP concentration in the estuarine area tended to be higher than the MP concentration offshore of Tokyo Bay shown in previous studies. This is likely due to the estuarine environment near the river mouth, where flocculation causes rapid compaction and sedimentation of clastic particles, preventing MPs from resuspending and being re-transported, thus becoming trapped and preserved within the sediment. In addition, principal component analysis of 4 parameters obtained from MPs and 3 parameters obtained from sediments showed that the particle size and roundness of the sediments have a large effect on MPs deposition.
In this study, sediments were collected from the estuarine areas of the Tamagawa River, Edogawa River, Hanamigawa River, Yorogawa River, and the downstream area of the Arakawa River, which flow into Tokyo Bay. Through the analysis of MPs and clastic particles, the study aimed to determine the characteristics of MPs and to clarify the factors that regulate the distribution of MPs in the sediments.
MPs were found in the sediments collected from all rivers. The confirmed MPs were classified into five shapes (fragment, plate, film, column, and bead), and fragment-shaped MPs were particularly dominant. From the morphological characteristics, it was clarified that these are derived from artificial turf, vinyl products, plastic parts, tire pieces, etc. As for the types of MPs, in addition to high-density polyethylene terephthalate and acrylic rubber, low-density polyethylene and polypropylene were also confirmed, and relatively low-density MPs were also deposited. The depth distribution of MPs was not dependent on the depth, and many MPs were contained in the sediments, and the MP concentration in the estuarine area tended to be higher than the MP concentration offshore of Tokyo Bay shown in previous studies. This is likely due to the estuarine environment near the river mouth, where flocculation causes rapid compaction and sedimentation of clastic particles, preventing MPs from resuspending and being re-transported, thus becoming trapped and preserved within the sediment. In addition, principal component analysis of 4 parameters obtained from MPs and 3 parameters obtained from sediments showed that the particle size and roundness of the sediments have a large effect on MPs deposition.