Microplastics polluting Japanese rivers, nearby seas: researcher

TOKYO -- Microplastics polluting Japanese rivers are flowing into nearby seas, according to a study by a Tokyo University of Science researcher.

Waters around Japan have a higher density of microplastics than the global average, and are known as "hotspots" of the pollutants. Some of the microplastics drift into waters surrounding Japan from Asian countries such as China and South Korea. But Professor Yasuo Nihei, a river engineering specialist who conducted the study, says efforts must be made to curb plastic waste in daily life in Japan. "It's not something Japanese people can ignore as someone else's problem."

The study examined the density of microplastics in 29 rivers nationwide, except for the Chubu region in central Japan and the Kinki region in western Japan, from 2015 through 2018.

Every river contained the pollutant, and the average density was 2.53 particles per one cubic meter of water. The figure for waters around Japan was close to an average of 3.74. Onetime use plastic bags and cups are considered to have contributed to the pollution.

The highest density was recorded in the Ohori River in Chiba Prefecture east of Tokyo at 13.6 particles per one cubic meter. The Tone River, a major waterway running through the Kanto plain including the capital, had 8.7. The figure for the Arakawa River in Saitama Prefecture north of Tokyo was 4.6. Microplastic densities were higher in highly populated or urban areas, indicating serious pollution in cities.

Microplastic particle sizes are almost the same in rivers as in oceans -- a finding suggesting that most of the particles were pulverized before they reached the sea. Some rivers in the southern Japanese city of Kumamoto had higher densities likely because of the 2016 earthquake, which destroyed many buildings and left a large amount of debris, according to Nihei.

"People have focused on countermeasures for marine (plastic) pollution so far, but steps are needed to control pollution sources on land," said the professor. Nihei explained that plastic products such as buckets and clothespins can turn into microplastics from degradation when left outside for long periods of time. "The particles can become airborne and pollute rivers," he warned.

A similar survey was conducted between May and September 2018 by the environmental protection venture firm Pirika Inc. in Tokyo's Shibuya Ward. The probe found microplastics in 25 out of 26 locations along a total of 11 rivers in the Kanto region in eastern Japan and the Kansai region in western Japan. The highest density of 19.8 particles per one cubic meter was recorded along the Okawa River in the city of Osaka in western Japan.

(Japanese original by Kayo Mukuda, Lifestyle News Department)