A survey by Assistant Professor Mamoru Tanaka of the Tokyo University of Science's Faculty of Science and Technology has revealed that the amount of plastic waste collected from rivers and other streams nationwide amounts to approximately 1,000 tons per year. The survey collated data on waste collection during river cleanup activities by the government and citizens, and was the first to quantitatively evaluate the amount of plastic waste collected in Japan.
According to Tokyo University of Science, the research group received and analyzed data provided by the Ministry of Land, Infrastructure, Transport and Tourism on the amount of waste collected from 109 first-class river systems nationwide from fiscal 1 to fiscal 2016. Because the MLIT data included the amount of collected plastic waste together with paper waste, the group devised a conversion formula to calculate the amount of plastic waste from waste collected by participating in cleanup activities on the Ohori River, which flows through Chiba Prefecture, and applied the formula to national data to make an estimate.
As a result, it was found that the amount of plastic waste collected nationwide during the five-year period under review fluctuated between 5 and 763 tons, for an annual average of 1,177 tons. Of this, about 938% was accounted for by seven river systems, including the Yodo River system in Kansai, the Yoshino River system in Shikoku, and the Tone River system in Kanto.
A moderate correlation was observed between the plastic collection rate and population and cleanup participants, and it was shown that in particular, in the Yodo River basin and the Tone River basin, many citizens were involved in collection and the amount of plastic collected was large. This is thought to be because the populations of the respective river systems are very large, at approximately 1,100 million and 1,300 million, and therefore both the amount of plastic waste generated and the number of citizens involved in collection were large.
The results also suggest that the amount of plastic waste collected in each river system is affected by extreme weather phenomena such as typhoons and heavy rains. For example, the Ota River and Kiso River systems, which flow through areas that were particularly hard hit by the 2018 Western Japan heavy rains, saw a significantly higher amount of plastic waste collected in fiscal year 2018. The Abukuma River system also saw a higher amount of plastic waste collected in fiscal year 2019, which is presumed to be due to the flood damage caused by Typhoon Hagibis.
Plastic waste released into the natural environment breaks down into microplastics through weathering. Microplastics are virtually impossible to recover and take a very long time to decompose, making them a global environmental problem. Therefore, in addition to reducing plastic waste, it is important to recover plastic waste before it breaks down into microplastics, but there have been no cases to date in which the amount of plastic waste recovered at a domestic level has been evaluated.
This study found that the annual amount of plastic collected nationwide in Japan is much less than the annual land-based plastic emissions previously estimated. The research group states that the results reaffirm the importance of reducing plastic waste emissions themselves and continuing to collect waste in order to solve the microplastic problem.
Paper information:[Marine Pollution Bulletin]Country-wide assessment of plastic removal rates on riverbanks and water surfaces
