Plastic Waste Covers Bottom of Japanese Waters; Items Found Dating Back to Twentieth Century

The Yomiuri Shimbun

20:00 JST, August 7, 2025

A huge amount of plastic waste from Japan and elsewhere has been found on the deep seabed around Japan, according to a probe by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).

Talks by the Intergovernmental Negotiating Committee (INC) to draft a convention to prevent environmental pollution due to plastic waste resumed in Switzerland on Tuesday.

The JAMSTEC team that carried out the research stressed the necessity of using fewer plastic products across the globe.

The agency conducted the probe from 2019 through spring this year, to ascertain the state of plastic waste pollution on the deep ocean floor.

Using the Shinkai 6500, a manned research submarine installed with cameras, researchers probed the ocean floors of the Japan Trench, waters off the Boso Peninsula, Sagami Bay, Suruga Bay, waters off Shikoku and waters off Noto Peninsula. Depths ranged from 800 meters to 7,000 meters.

Vast quantities of plastic were found in all these locations. The most polluted areas contained 10,000 to 40,000 plastic items per square kilometer.

“It’s deeply shocking that so much plastic waste was confirmed in ocean waters tens of kilometers from the coast,” said Ryota Nakajima, a researcher on the team who specializes in biological oceanography.

Of the waste, 70% to 80% was polyethylene bags and plastic shopping bags, and the rest was primarily plastic bottles and food containers. Such waste does not deteriorate quickly in the deep sea due to the lack of light, so some of the waste was identified as products from the Showa era (1926-89).

Some product labels showed that the items had drifted on an oceanic current not only from Japan but also from China, South Korea and Southeast Asian countries and regions.

The research team also confirmed that a massive amount of microplastics — tiny fragments of plastic products — was dispersed in the seawater. Some plastic products contain chemical substances that are harmful to the human body, and it has been said that people’s health may be damaged if they eat fish that have ingested microplastics.

The regulation of plastic production has been on the agenda at the INC meeting, which seeks to draft a convention regarding plastic waste, but opinions are divided on the subject.

“The world is connected by the ocean, in which a massive amount of plastic waste is coming and going. To keep the ocean unpolluted, countries and regions must cooperate with each other. It’s hopeless otherwise,” Nakajima said. He is paying close attention to the outcome of discussions at the meeting.