Improvement in Understanding of Plastic Cycle in Japanese Urban Regions

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Abstract
Plastic contamination has been receiving considerable attention during the last few decades. In the present study, the authors extended process‐based eco‐hydrology models, NICE (National Integrated Catchment‐based Eco‐hydrology) and NICE‐BGC (BioGeochemical Cycle), to link them with a plastic debris model, and applied it to all of the 109 first‐class (Class A) river basins throughout Japan. The model included advection, dispersion, diffusion, settling, dissolution, and deterioration due to light and temperature, interaction with suspended matter (heteroaggregation), resuspension and biofouling. These processes could help to evaluate the effect of mismanaged plastic waste (MPW) and point sources (tyres, personal care products, dust and laundry) on the spatio‐temporal dynamics of macro‐ and micro‐plastics there. The result clarified the finer resolution promoted more settlement during the runoff process to slightly decrease the flux of macro‐plastics, particularly in urban regions. The model also revealed that the amount of micro‐plastic flux calculated by accumulating point information at sewage treatment plants could be replaced by analysis using grid data categorised for treatment methods (sewage, septic tank, untreated) in each grid instead of global data of per capita emission and treatment rates. The result also clarified that the plastic cycle, particularly micro‐plastic, in rivers flowing through urban areas has been significantly altered. Finally, the authors evaluated the method to improve the plastic cycle in urban regions towards understanding the urban plastic cycle with fewer inventory data. These results help to quantify the impacts of plastic waste on the biosphere in urban systems and may aid the development of solutions and measures to reduce plastic input to the ocean.
Funding Information
  • Environmental Restoration and Conservation Agency (JPMEERF21S11900)

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