Since 2007, our project has been approved and supported by the Ministry of the Environment’s Environment Research and Technology Development Fund. Our project focuses on plastic waste which account for a large percentage of marine debris. From an oceanographic point of view, we have been working to clarify how plastic waste are transported to the ocean, as well as predicting the abundance of plastic waste in the future. Achievements from our studies are presented as follows.
Recently, the main interest of our research lies in “microplastics”, which are plastic waste in the ocean that have been fragmented through the natural weathering process and are smaller than a few centimeters. These can be as small as zooplanktons and absorb toxic chemicals such as PCBs, which raises concerns for the marine ecosystem as microplastics can easily enter the system by mistakenly eating them as food. Although microplastics themselves are non-toxic, they do not do any good to marine organisms and may become a cause of stress by ingesting them.
Since 2018, Professor Isobe has been working as a project leader of a strategic project supported by the Ministry of the Environment’s Environment Research and Technology Development Fund. This is the largest comprehensive research project focusing on microplastics in Japan, and our challenge is to predict the world’s marine plastic pollution level of the next fifty years.
We are also conducting a collaborative study with researchers from Thailand and other Southeast Asian countries. We are working toward the realization of a society with reduced plastic use based on scientific evidence that will lead to the reduction of marine plastic pollution in the neighboring countries (details will be updated soon).
Isobe. A., S. Iwasaki, K. Uchida, and T. Tokai "Abundance of non-conservative microplastics in the upper ocean from 1957 to 2066", Nature Communications, 10, 417, 2019. DOI: 10.1038/s41467-019-08316-9
Plastic waste on shores and in the ocean deteriorates and breaks down into pieces over time, gradually becoming very small fragments called “Microplastics” (MP). It is known that marine organisms consume MP by accidentally ingesting them as food. Our study group reproduced the abundance of MP in the past and present through a simulation method using previous observation data, and furthermore predicted MP abundance of the next fifty years. The MP simulation model shows the emission and transport of MP, and how MP become missing (it seems that MP disappears somewhere from the ocean surface after about 3 years). It shows that the abundance of MP increases especially around Japan and in the Central North Pacific during the summer, and if marine plastic debris continue to increase, weight concentrations of MP in the area would become about two times higher by 2030 and about 4 times higher by 2060. This suggests the possibility of damage to marine organisms in the future. However, previous experimental studies which point out the impact of MP on marine organisms have been using particle sizes that are one to four orders of magnitude smaller than those used in the present simulation and observation study (>300μm). Therefore, predicting the future abundance of MP by actually monitoring the amount of particle sizes used in the experimental studies would be important when considering the impact on marine organisms.
We are currently expanding our studies to create a simulation model of MP in the world’s oceans.
Together with Tokyo University of Marine Science and Technology, we have been conducting a survey of microplastics around Japan and from areas along the Pacific Ocean stretching from Antarctica to Tokyo. According to the results of the study in 2014 which took place in the waters around Japan, we found that the concentration of microplastics were significantly higher in the Sea of Japan and in the East Asian region compared to other oceans in the world. Concentration of microplastics in the waters around Japan (evaluated by vertical integration values to reduce the effects of wave height and wind speed) was 27 times higher than the world’s average (Isobe et al., 2015). This research paper put together the analysis results and described the East Asian region as a “hot spot” of microplastics. Today, many researchers are working on assessing the impact of the predicted increase of the concentration of microplastics on the marine ecosystem. The impact of microplastics to the ecosystem may be first noticed in the East Asian region than in any other part of the world. We are also the first to find microplastics in the Antarctic Ocean, and presented this in an academic article (Isobe et al., 2017). The fact of microplastics detected in the Antarctic Ocean which is the least populated area in the world may suggest that marine plastic pollution has spread across the world’s oceans.
Concentration of microplastics collected in the East Asian region (left: To eliminate the effects of vertical mixing, concentration value is converted into the vertical integration of microplastics in the entire water column). Collecting plastic particles from the ocean on the Shinyomaru (right). The East Asian region is a “hot spot” of microplastics.
The collection and analysis of microplastics along the route from the Antarctic Ocean and Tokyo took place between January and March 2016 (Isobe et al., 2017). The left picture shows the observation points. The middle shows pictures of microplastics collected from the Antarctic Ocean and concentration (particle count per unit seawater volume. Concentration of each microplastic in the picture are shown in black). The right picture is an observation scene in the Antarctic Ocean on the Umitakamaru (picture offered by Tokyo University of Marine Science and Technology).
Most of the microplastics shown in the above photos are plastic waste along the coast that have deteriorated and broken down into pieces by exposure to UV rays and heat. However, when examining microplastics collected from the sea, we sometimes find round pieces that are smaller than 1mm in size (below photos). The possibility of plastic fragments to become naturally round through the deterioration process is extremely rare. These are thought to be artificial plastic particles (microbeads) that are used as plastic scrubbers found in a variety of products such as deodorants, shampoos and conditioners, body soaps and lipsticks. There is also a possibility that microbeads may be used as industrial abrasives, but is unknown. Analysis of data from an observation study conducted in 2015 by the Ministry of the Environment showed that out of 26 observation stations, microbeads (size range is above 0.3mm and below 0.8mm) were found in 9 observation stations. When comparing with the concentration of microplastics of similar size in the 9 stations, spherically shaped microbeads accounted for about 10% of all microplastics and is a matter that can no longer be ignored.
Microbeads collected from Japan’s coastal waters (left pictures: the square frame is 5mm x 5mm). A microbead taken out from a product sold in a supermarket near the university (right).
Our study of microplastics started 10 years ago. Being first surprised by the abundance of microplastics collected in a surface net in the beautiful waters of the Goto Islands (a personal experience and thus not written in research papers), we began collecting microplastics from several stations in the Seto Inland Sea. Looking at the distributions of microplastics by size, we noticed that the closer it was to the shore, the bigger the plastic fragments were, regardless of the existence of river mouths. By conducting a transport simulation of microplastics, we presented the idea of “selective transport process” in the ocean.
Taking samples from the Seto Inland Sea (pictures a, b) and microplastics collected from the samples (pictures c, d)
Concentration of microplastics (by size) from collection points far from the shore (a, c) and collection points near the shore (b, d)
Plastic particles which are lighter than seawater float on the ocean surface. They are transported by ocean currents and Stokes drift generated by wind waves. Relatively large plastic particles tend to be transported onshore because they float near the ocean surface due to their buoyancy, and particles closer to the ocean surface are more easily transported to the shore by Stoke drift which is stronger on the ocean surface. These particles are washed ashore on beaches, degraded by UV rays and temperature differences, and become more smaller particles called microplastics. Microplastics get swept away by sea waves and return to the ocean. These can float deeper below the ocean surface, where there is less effect of Stoke drift, thus spreading its distribution area offshore. We could say that coastal waters have a function that could effectively fragment plastic particles into microplastics.
Illustration of the selective transport model of microplastics