Quantification Of Macroplastics Under Differing Weather Conditions Near A Japanese Farmland River

Abstract Plastics can long persist in nature to become an environmental issue if not taken care of properly. To understand factors affecting plastic pollution in Japan’s farmland Hamada River, this study examined quantification of macroplastics (those larger than 5 cm) during differing weather conditions. The average number of collected samples in unit area in unit amount of time during rainy days (after-rain period; 1.39 samples/hour.m2) almost doubled that of sunny days (0.87 samples/hour.m2). Sample density (g/m2) further revealed that rainfall increased the amount of plastic waste: the average plastic waste density in the Hamada River on sunny days was 2.04 g/m2, but rainy days’ samplings were 5.33 g/m2 downstream and 11.14 g/m2 upstream. Approximately 39% of samples during sunny days had an aspect ratio range of 2–5, whereas 38–46% of samples during after-rain periods had an aspect ratio range of 1–2. By more than half (53.6%), sunny days’ samplings were white; 25% were transparent, and the rest were black (7.1%), gray (3.6%), brown (3.6%), or green (7.1%). After-rain samplings showed a wider range of color variations including purple. An average of 92 pieces of macroplastic were found at each sampling, and polyethylene accounted for the majority, with an average of 70%. The majority of polyethylene samples were mulch films originating from the nearby tobacco farms.