Results of a Fact-finding Study of Floating and Sea Floor Marine Debris Conducted in Offshore Waters in FY2014
Release date: 2015.04.23
Research Results Physical Sciences
Between July and November 2014, a Kyushu University professor conducted a study of floating and sea floor marine debris in offshore waters around the Japanese archipelago. This survey included an investigation of microplastics (*), which have recently become the focus of concerns over their impact on marine ecosystems. The results have now been compiled and can be disclosed.
Plastic debris accounts for around 70% of floating and washed up debris. Exposure to ultraviolet rays and substantial temperature differences causes this plastic debris to degrade, and physical stimuli such as abrasion by coastal sand turn it into smaller and smaller particles. Plastic particles that are 5mm or less in size are called microplastics; to date, extremely fine particles measuring anywhere between a few hundred micrometers and 1mm have been found suspended in waters across the globe. With a size similar to that of zooplankton, microplastics can easily enter the ecosystem when mistakenly ingested by fish, so it has been pointed out that they could be a medium for the entry of pollutants adhering to the surface of those particles into the bodies of living organisms.
■Results of the Study
(1) Visual Inspection of Floating Debris
A visual inspection of floating debris was carried out in offshore waters around Japan. As a result, it emerged that approximately 56% of the debris floating on the sea’s surface was man made, such as petrochemicals (e.g. expanded polystyrene, PET plastic bottles, plastic grocery bags, and fragments of plastic).
This man-made material was found in greater quantities in the Sea of Japan – particularly in the area stretching from the East China Sea to the northeastern Tsushima Strait – than in Pacific waters or the Seto Inland Sea. Although expanded polystyrene is also found in the East China Sea, it was found in particularly large concentrations (up to 60 pieces/km2) near the Tsushima Strait. Moreover, large numbers of PET plastic bottles, glass bottles, and beverage cans were seen in the East China Sea. (Tokyo University of Marine Science and Technology)
(2) Study of Microplastics Suspended on the Sea’s Surface
In conjunction with the visual inspection of floating debris described in (1) above, a Neuston net (a net with a mesh size of 0.35mm, which is usually used for collecting plankton, fish eggs and fry suspended on the surface) was used to collect plastic fragments 2-3 times per day. The plastic fragments collected were analyzed at Kyushu University’s Research Institute for Applied Mechanics, classified by size, and the number of each calculated.
Looking at the density (number of fragments per 1m3 of seawater filtered using the Neuston net) of plastic fragments measuring 5mm or less in the waters surveyed, around half of all sites (22 out of 45 in total) had a density in excess of that of the western Seto Inland Sea (0.4 fragments/m3) in a previous survey (Isobe et al., 2014, Marine Pollution Bull.) (Kyushu University)
(3) Study of Debris on the Sea Floor
In a study conducted primarily in the East China Sea, a trawl net was used to gather debris from the sea floor. As well as beverage cans, fishing equipment and other plastic items were among the debris collected, even from the sea floor more than 200km offshore. Of the 40 man-made items of debris collected, fishing equipment was the most numerous, accounting for half (20) of the items, followed by plastic products, which made up 25% (10 items). The average distribution density of man-made items estimated on the basis of these figures was 39 items/km2 (number of items) and 10.16kg/km2 (weight of debris). (Tokyo University of Marine Science and Technology)
This joint study by Kyushu University and Tokyo University of Marine Science and Technology was carried out with the assistance of two of the latter’s training ships (the Umitaka-maru and the Shinyo-maru ).
Map of concentration of microplastics
This press release was a prompt report of the microplastics surveys in 2014. The latest report was published as Isobe et al (2015, MPB; open access).