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Aiming for a sustainable society: tackling the challenges of plastic waste and microplastics

In recent years, marine plastics have become a great social concern.
We interviewed Associate Professor Haruhiko Nakata,
who has been proactively addressing the issues of plastic waste and microplastics.
His research interest covers not only marine but also terrestrial waters such as lakes.


If we do not take action, the rising microplastics level will threaten aquatic life 50 years from now

Interviewer (◆ hereafter): Please tell us about your research on plastic waste.

Prof. Nakata: In recent years, a great deal of social attention has been paid to pollution of marine environments with plastic waste. The world’s first scientific study on marine plastic pollution was conducted in 1972, approximately 50 years ago. This study used a survey ship with nets to catch marine plastic debris from seawater in the North Atlantic Ocean. They found 12,000 pieces of plastic waste per square kilometer in the survey area with the highest density of plastic.
 Among different types of plastic waste, particular attention has been paid to microplastics. The best-known examples of microplastics are microbeads contained in face wash and cosmetic products. However, plastic products used by people also cause serious microplastic pollution by being degraded, primarily by ultraviolet radiation, and fragmented into tiny pieces. We can easily find discarded plastics, the source of microplastics, everywhere on the planet, even on the deep seabed.
 Microplastics cannot be recovered if they spread out into the vast ocean. The problem is exacerbated by the fact that as microplastics spread out and accumulate across aquatic ecosystems, they can be taken up by marine organisms.
 The toxicity of original plastic polymers like polyethylene and polypropylene is low. However, commonly used commercial plastic products contain a variety of additives, which have hazardous properties. For example, flame retardants are added to plastic materials used in electrical systems, whereas plasticizers are used to soften hard plastics. Most of these additives are persistent and less degradable in the environment, raising the risk of harming wildlife.
 Another problem is that microplastics absorb hazardous substances in the seawater. Plastics are hydrophobic, and their surfaces easily absorb hazardous chemicals including PCB and dioxin. When fish and marine animals take up microplastics with hazardous chemicals on their surfaces, the hazardous chemicals are absorbed in their stomach and intestines, resulting in bioaccumulation.
 To date, the volume of plastic waste, including microplastics, has continued to increase. If we do not take any corrective action to improve the situation, the total weight of marine plastic waste (including microplastics) is expected to exceed that of all fish. Fifty years from now, the level of plastics in the seawater will reach a level that threatens aquatic life.

To decrease plastic waste, we strive to understand and organize the issues


◆: Please tell us about what surveys and studies you are performing.

Prof. Nakata: Our research aims to precisely understand how microplastics are dispersed into the aquatic environment, resulting in continuous accumulation of hazardous chemicals, as well as how to resolve the issue.
Our research activities have two primary pillars. The first is to clarify the current situation with microplastic pollution. To this end, we visit lakes and seas and collect microplastics in sediments to understand the distribution of microplastics.We are also striving to identify the final destination of microplastics. The second pillar is investigating the sources of microplastics. Because microplastics are minute particles, we cannot see where they come from or what they were originally. Understanding the sources of microplastics helps us to develop and take countermeasures against the problem. To identify their origins, we are developing chemical analysis methods for the microplastics we collect and characterize their composition.

  Our research covers terrestrial waters such as lakes and rivers, and the deep ocean, for which fewer surveys have been conducted than other parts of the ocean.
For example, we investigate lake sediments collected from Ezuko, a lake located in Kumamoto City, and the stomach contents of non-native fish species. One of our investigations at Ezuko found that the mean level of microplastics in sediments was 1000 particles per kilogram of dry sediment weight, with a higher level at Kami-Ezuko and lower level at Shimo-Ezuko. We also found that a certain area of Ezuko had a particularly high microplastics level, and that the compositions of the microplastics differed from those found in other areas. We closely inspected the samples to identify their sources and found that they came from paint applied to leisure boats. In addition, in collaboration with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), we are performing a survey on deep-sea plastic debris.

Examining pieces of plastic taken from the stomach of black bass caught at Ezuko

◆: Do you think we have to reduce use of plastics?

Prof. Nakata: As I mentioned earlier, our survey at Ezuko showed that boat paints could be a cause of microplastic pollution. However, that does not mean that leisure boats should be banned. During the COVID-19 pandemic, the hygiene advantages of plastic products have been emphasized. In addition, modern life is impossible without the use of diverse chemical substances.
Balance is critical. It is important for us to enjoy the benefits of plastics while avoiding, to the greatest extent possible, the discharge of plastic waste into the environment. We need to properly understand the challenges that we face and decrease plastic waste. In order to take effective measures to address these challenges, we must identify the sources of microplastics. Another issue that we have to consider is disaster debris, which is generated in large quantities by typhoons and floods. No one on Earth would want a future, 50 years from now, in which many forms of wildlife are severely suffering from plastics.

Ezuko in Kumamoto City is home to our research activities.
We also regularly investigate Ohorikoen Pond in Fukuoka city.

International Collaboration is critical for tackling plastic pollution.
I would like to foster the professional development of individuals who can tackle challenges toghther with global partners.

◆: Please send a message to those who are thinking of majoring in science or pursuing a career as a researcher.

Prof. Nakata: My field of expertise is environmental chemistry. This is an interdisciplinary field because to perform studies on this topic, diverse perspectives and approaches are needed. For example, analyzing soil and sediments requires a geological perspective, measuring bioaccumulation of chemical substances requires a biological perspective, and using various reagents and microanalyzers requires knowledge and experience in chemistry. Environmental chemistry and other related research fields are not well known, and the number of researchers involved is quite small, particularly in emerging countries, which are experiencing remarkable economic development. This is one reason why environmental pollution is becoming more serious in these countries.
 In this context, we should not turn a blind eye to those issues by thinking of them as other countries’ challenges. Plastic debris and microplastics are brought to Japan by the movements of ocean water and the atmosphere, without regard to borders. We must collaborate and harmonize with other countries in order to decrease waste.
 Currently, international students from Myanmar and Indonesia are studying in my laboratory. I hope that they will learn and study plastic waste from the perspective of the environment here, and then in the future go back to their home countries with the knowledge and skills they have learned to implement environmental studies in their home countries. Fostering such talents is also an important goal of my research activities.


Nakata Haruhiko, Associate Professor, Faculty of Advanced Science and Technology