Quantification of riverine macroplastics in a farmland area in Japan

Plastic pollution has become a major environmental threat, with extensive research focusing on the transfer of plastic waste from urban areas to oceans. However, limited attention has been given to the role of agricultural areas in plastic emissions to rivers. Rivers play a crucial role in transporting plastics to the ocean. This study investigates plastic waste pollution in the Hamada River, which drains into Mikawa Bay, with a particular focus on how agricultural activities and weather conditions affect plastic distribution. We collected macroplastics from both the river and its banks under sunny and rainy conditions. On sunny days, lightweight plastics, especially film-shaped items, dominated the river's waste. In contrast, rainy weather led to greater accumulation of plastics along the riverbank, with a broader diversity of shapes and colors. Plastic mulch was the predominant type of waste found in both the river and along the banks, with polyethylene as the most common polymer, followed by polypropylene. Notably, no PET plastics were detected in the river, contrasting with marine environments. These findings suggest that weather patterns and the proximity of agricultural sources significantly influence plastic distribution in rivers. Future research should explore the long-term dynamics of plastic transport, especially during high-flow events, to better understand the impact of plastic pollution on river ecosystems and the wider environment.