Japanese researchers alarmed as microplastic density off Honshu island exceeds highs in Mediterranean Sea
- The concentrations of plastic on the seabed are, in some places, 260 times higher than in the Mediterranean Sea that had the highest accumulations
- Larger pieces of plastic accumulate on the seabed as a result of currents and eddies. Many of the microplastics were also traced back to Tokyo Bay
The discovery of vast amounts of microplastics accumulated on the ocean floor off the east coast of the main Japanese island of Honshu has sparked alarm among researchers, with deposits in some areas amounting to more than 600 shards of plastic per gram of dry sediment.
The concentrations of plastic on the seabed were in places 260 times higher than in the Mediterranean Sea, which was previously considered to have the highest accumulations of microplastics in seabed sediment, and 5,500 times higher than in the North Atlantic.
The research was conducted by the Japan Agency for Marine-Earth Science and Technology (Jamstec), universities and private companies, with the findings published in the academic journal Marine Pollution Bulletin in October.
Dr Masashi Tsuchiya, deputy leader of the research team at Jamstec, said he was taken aback at the scale of the build-up.
“The microplastics in the sediment were difficult to see with the naked eye, so I did not know immediately after the sampling – but we had no idea that they had accumulated to such an extent,” he told This Week in Asia.
The scientists took samples from seven locations off the east coast of Japan. The first samples were at relatively shallow depths of around 855 metres (2,800 feet) below the surface in Sagami Bay, followed by a sample from the nearly 6,000-metre deep abyssal plain some 500km offshore.
The final tests were carried out in the depths of the Japan Trench, which runs parallel to the coast about 250km offshore and where the deepest sample was recovered from a depth of 9,232 metres.
The greatest concentrations were recovered from the abyssal plain, where the microplastics were typically 10 times denser than anywhere else.