Researchers reveal key factors behind Japan’s plastic waste removal rates in rivers
Their findings will help shape cleanup efforts and minimize the amount of plastic litter that makes it to the sea
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Plastic litter recovery from rivers is a rather understudied topic in Japan. To tackle this knowledge gap, researchers conducted an in-depth analysis of plastic removal from over 100 important river basins. Their findings reveal important correlations between plastic litter recovery and demographic and natural factors, which could help improve organized cleanup efforts.
view moreCredit: Mamoru Tanaka from Tokyo University of Science, Japan
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.
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Reference
Title of original paper: Country-wide assessment of plastic removal rates on riverbanks and water surfaces
Journal: Marine Pollution Bulletin
DOI: https://doi.org/10.1016/j.marpolbul.2024.117218
About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of “Creating science and technology for the harmonious development of nature, human beings, and society," TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
Website: https://www.tus.ac.jp/en/mediarelations/
About Assistant Professor Mamoru Tanaka from Tokyo University of Science
Mamoru Tanaka obtained a PhD in Applied Marine Environmental Studies from the Tokyo University of Marine Science and Technology in 2019. He currently serves as an Associate Professor at the Tokyo University of Science, focusing on observational physical oceanography, microplastics, hydraulic engineering, and turbulence. He has 15 refereed papers published under his name.
Funding information
This study was supported by the Environment Research and Technology Development Fund [JPMEERF21S11900] from the Environmental Restoration and Conservation Agency of Japan. Partial funding was provided by The River Foundation, Japan [2022-5211-028] and [2024-5211-060].
Journal
Marine Pollution Bulletin
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Country-wide assessment of plastic removal rates on riverbanks and water surfaces
A first step towards integrating marine plastics into urban recycling
A study by the University of the Basque Country (UPV/EHU) has assessed the technical feasibility of automatically separating marine plastic waste
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From left to right Amaia Mendoza, Galder Kortaberria and Cristina Peña
view moreCredit: Gorka Estrada. UPV/EHU.
In response to the millions of tonnes of marine litter, mostly plastics, floating on the oceans, the need to manage this waste effectively is more urgent than ever. Faced with this reality, the UPV/EHU’s Materials + Technologies research group decided to take a first step. “We assessed a practical approach: the possibility of integrating plastics collected from the sea into the urban waste system. This pioneering study, which is part of a PhD thesis, explores the possibility of managing this waste efficiently in current urban recycling infrastructures,” explained Cristina Peña, lecturer in the Department of Chemical and Environmental Engineering at the Faculty of Engineering, Gipuzkoa (UPV/EHU) and author of the work.
Unlike municipal solid waste, marine litter does not yet have a systematised management system; it is managed on a very ad hoc basis and within the framework of very specific projects. “It is important to bear in mind that this waste, having been at sea, has a level of degradation that is significantly different from, for example, a bottle deposited in a yellow container under normal conditions. So our starting point and key question was precisely this: Does the level of degradation of marine waste prevent it from being classified in an urban waste management process?” as Amaia Mendoza, a researcher in the UPV/EHU’s Materials + Technologies research group, pointed out.
PET plastic bottles
“In this work,” Amaia Mendoza went on, “we used identical PET plastic water bottles of the same brand to assess the effects of various environmental conditions. We divided the bottles into two batches: the first batch was left in the open air for nine months, simulating exposure on a beach or rocky coast, and the second batch was submerged in the sea for the same period. We saw that the submerged bottles underwent increased chemical degradation, while those exposed to the open air on the “shore” remained in a better state”. This approach allowed them to analyse how the degradation process varies according to marine conditions and how each type of waste responds in different environments.
We then “simulated how these materials would be managed in an urban solid waste treatment plant” by comparing them with the same bottles that had not undergone degradation to see if the automatic separation equipment in these plants would be able to identify and separate the plastic bottles of marine origin. “To find out, we conducted tests using an optical separation system, a type of technology that automatically classifies materials according to their composition,” and they saw that the effectiveness of separating the bottles of marine origin –both those exposed to the open air and those submerged in the sea– “was very high, comparable to that of bottles from urban waste”, said Amaia Mendoza. “These results indicate that the treatment of marine bottles in these plants is feasible and could be successfully implemented. The state of degradation is crucial when determining the feasibility of subsequently recycling them,” stressed the UPV/EHU researchers.
The authors of the work say that “the study has achieved an important breakthrough by demonstrating that PET plastic bottles of marine and urban origin can be separated in a joint process, thus establishing a first step in an area with huge potential for development”. It also “opens up the way to exploring the automatic separation of other plastics present in marine litter, such as polypropylene or polyethylene, in urban waste treatment plants”, added Amaia Mendoza.
The UPV/EHU team stresses that this work set out to evaluate the possibility of upgrading marine litter by making it attractive as a usable raw material. “If we manage to find practical applications and encourage the industrial development of these materials, collecting them will also become attractive. The more efficient and viable the management of this litter is, the greater the incentive to use it and, consequently, the greater the interest in collecting it from the sea,” said Cristina Peña.
Journal
Waste Management Bulletin
Article Title
A first step towards integrating marine plastics into urban recycling
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