Plastic pollution is an ever-growing problem in today's world, as most societies have become overly dependent on plastics for packaging, medical supplies, and general goods. Plastic litter accumulation in the ocean, either through deliberate dumping or by being transported from a river, poses significant environmental challenges. Additionally, this plastic eventually degrades into small fragments called microplastics, which then impact diverse marine and land ecosystems by working their way up the food chain and into most living organisms. Though their negative effects on cell health are still under study, many nations have taken a cautionary stance, increasing efforts to curb plastic usage and prevent pollution.
Because of its position in the North Pacific, Japan is a country that both greatly contributes to and is harshly impacted by plastic litter in the ocean and, therefore, needs proactive cleanup campaigns by the government and local communities to recover plastic litter from river basins. Unfortunately, very few studies have focused on the rate of plastic litter removal from Japanese river basins, which is essential for understanding plastic transport dynamics and taking more effective measures.
Against this backdrop, a research team led by Assistant Professor Mamoru Tanaka of Tokyo University of Science (TUS) decided to conduct the first nationwide-level analysis of plastic litter removal from rivers in Japan. As explained in their latest paper, which was published online in the Marine Pollution Bulletin on November 1st, 2024, the team quantified the annual recovery of plastic waste from river banks and water surfaces using a dataset provided by the Ministry of Land, Infrastructure, Transport and Tourism. Ms. Yumena Okada, who graduated from TUS in 2022, also participated in the study.
The dataset included the amount of plastic recovered from 109 river basins from 2016 to 2020. The researchers analyzed this information and also investigated potential correlations with other factors, such as basin population, the extent of nearby urban areas, and topographical characteristics. The total plastic recovery ranged from 763 to 1,177 tons/year, with an average of 938 tons/year. "Given the emission estimates from previous studies, Japan's annual plastic emissions are approximately 10,000–20,000 tons. The plastic recovery in river basins of approximately 1,000 tons/year estimated in this study represents approximately one-tenth to one-twentieth of this total. This is a non-negligible contribution toward reducing nationwide plastic emission, though not a decisive amount," highlights Tanaka.
According to the team's analysis, the top seven river systems by average plastic waste collection volume were the Yodo River system with 91.6 tons/year, the Yoshino River system with 85.8 tons/year, the Tone River system with 78.8 tons/year, the Tama River system with 72.0 tons/year, the Oto River system with 69.2 tons/year, and the Abukuma River system with 53.9 tons/year. These accounted for roughly 50% of Japan's total plastic collection volume.
By looking more closely at the data, the researchers noted that natural disasters and extreme weather events were closely related to spikes in the values of plastic litter collected from rivers. "The Ota and Kiso River systems saw a significant rise in plastic waste collected in 2018. Both systems were affected by heavy rains in western Japan that year," noted Tanaka, "Similarly, the Abukuma River system saw a rise in plastic collection in 2019, which can be attributed to the impact of Typhoon No. 19 in 2019, which caused substantial water damage." These results shed some light on potential links between climate change, which leads to more extreme weather events, and plastic pollution.
The team also identified other interesting correlations. For example, the Yodo and Tone River systems, which saw some of the highest recovery rates, also serve over 10 million people, but this also increases the amount of waste generated and leads to higher involvement from multiple municipalities. Therefore, there is a positive correlation between the basin population, plastic litter recovery, and the number of people participating in cleanup activities.
Taken together, the results of this nationwide analysis will be useful for authorities and volunteer-based organizations to plan future cleanup activities. "Currently, the Ministry of the Environment scientifically estimates plastic litter levels across various areas of Japan. Our estimates cover where and to what extent plastic waste is generated, how much is collected, how much is deposited in soil and riverbeds, and the amount discharged into the ocean, thereby providing key data to support these estimates," remarks Tanaka. With any luck, this study will pave the way to better measures to achieve sustainable plastic management, reducing the devastating effects of plastic pollution on wildlife and public health.
