17:15 〜 18:45
[AHW25-P05] Microplastics Generation in the Sediment Cascade: Experimental Analysis from the Sumiyoshi River Urban Catchment, Kobe City, Japan
★Invited Papers
キーワード：microplastic, Sumiyoshigawa River, sediment transport, river sediments
Microplastic has unfortunately become an ubiquitous component of the environment, with adverse effects on both flora and fauna, beyond simplistic toxicological guidelines. If mechanical abrasion and grinding of microplastic have been discarded in numerous researches, it is arguably because investigation has occurred in static environments. In the present contribution, the authors hypothesized that rivers and torrents are not solely transporting microplastics, but they can also generate them from larger plastic debris, due to the interaction with sediments in motion in torrents and rivers.
In Kobe City, Japan, the Sumiyoshigawa River flows from the Rokko Mountains, through the urban area and down to Osaka Bay. In the river, microplastic has been found in sediments and confirmed with FTIR. Thus, using a rotating tumbler, and P.E.T. pellets and strips < 5 mm in size and width, mixed with grinding marbles, then calibrated silicated of 0.5 mm and finally sediments from the Sumiyoshigawa inside a water mixture, the change of mass and surface characteristics of the plastic debris was measured by a high-precision balance and both a polarizing microscope and an engineer-microscope.
Results reveal that against commonly accepted ideas, the surface of the P.E.T. is showing several impacts, striations, and the originally shiny surface becomes matte. Moreover, tears extending > 1 mm were also recorded. Under the microscope, the edges of the flat pellets and strips also display micrometer-sized tear and shards. Finally, these abrasion forms are confirmed by a mass reduction of the original debris used in the experiment.
The level of tearing and abrasion has been found to be higher with the 2.5 cm diameter grinding marbles as well as the Sumiyoshigawa sediments (which include small gravels and coarse sand) compared to calibrated fine sands.
These results have confirmed (a) the role of mechanical abrasion in the generation of microplastics, and (b) the control sediment grain-size distribution and shape exerts over microplastic generation in rivers.
These results entail that different rivers will generate different volumes of microplastic, even for similar source debris, according to hydraulic and sediment properties.
In Kobe City, Japan, the Sumiyoshigawa River flows from the Rokko Mountains, through the urban area and down to Osaka Bay. In the river, microplastic has been found in sediments and confirmed with FTIR. Thus, using a rotating tumbler, and P.E.T. pellets and strips < 5 mm in size and width, mixed with grinding marbles, then calibrated silicated of 0.5 mm and finally sediments from the Sumiyoshigawa inside a water mixture, the change of mass and surface characteristics of the plastic debris was measured by a high-precision balance and both a polarizing microscope and an engineer-microscope.
Results reveal that against commonly accepted ideas, the surface of the P.E.T. is showing several impacts, striations, and the originally shiny surface becomes matte. Moreover, tears extending > 1 mm were also recorded. Under the microscope, the edges of the flat pellets and strips also display micrometer-sized tear and shards. Finally, these abrasion forms are confirmed by a mass reduction of the original debris used in the experiment.
The level of tearing and abrasion has been found to be higher with the 2.5 cm diameter grinding marbles as well as the Sumiyoshigawa sediments (which include small gravels and coarse sand) compared to calibrated fine sands.
These results have confirmed (a) the role of mechanical abrasion in the generation of microplastics, and (b) the control sediment grain-size distribution and shape exerts over microplastic generation in rivers.
These results entail that different rivers will generate different volumes of microplastic, even for similar source debris, according to hydraulic and sediment properties.