Baseline assessment of riverbank macroplastic pollution in downstream areas flowing into mikawa bay, japan

Abstract

Abstract Macroplastic pollution is a growing environmental concern, especially in rivers which it serves as pathways for land-based plastics entering marine ecosystems. This study establishes a baseline of the macroplastic debris along the banks of eight selected rivers that drain into Mikawa Bay, Japan. A single field Survey for this study was conducted in April 2025. It was based on standardized 10 m × 2.5 m transects, though area size was modified according to site conditions. Plastics were visually categorized and measured, and for the type of polymer composition was evaluated using portable ATR-FTIR. Highest abundance observed at Yagyu River with 1.9 items/m 2 , while the highest density by weight was recorded at Asakura River with 7.073 g/m 2 . Polyethylene (PE) dominated by abundance, however heavier polymers PET and PVC contributed more by weight. Spatial differences regarding plastics were associated with surrounding land use where urban rivers were characterized by more packaging waste compared to agricultural rivers. Our results emphasize riverbanks as important macroplastic accumulation zones and served as baseline data for overarching monitoring of pollution, both gross and otherwise, in coastal river systems.

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