Basic knowledge of marine plastic pollution

Plastic, a cheap, lightweight, and durable material, is processed into a wide variety of packaging materials and containers, making our lives comfortable and convenient. However, if we broaden our horizons from our daily lives and look at it from the perspective of the global environment, these advantages of plastics generally become major disadvantages. Light and strong plastics do not corrode and decompose, breaking into small pieces and flowing out of rivers into the sea. Such plastic waste weighs heavily on our world as a major marine environmental problem. In this six-part series, we will explain the basics of marine plastic pollution.

Content

Part 1: What is Marine Plastic Pollution?

1. Where did marine plastic waste come from? Plastic that is consumed and easily discarded. Currently, about 30 million tons are discarded annually worldwide without proper treatment (reference: Jambeck, J. R. et al., Science, 347, 768–771, 2015), of which about 2 million tons flow into the sea. (Reference: Lebreton, L. et al., Nature Communications, 8:15611, 2017). About 20% (by number) of all marine litter (floating litter and drifting litter) is plastic litter such as fisheries litter that is dumped directly into the sea. It flows into the sea via rivers (reference: Morales-Caselles, C. et al. Nature Sustainability, 2021). Once light plastic is released into the ocean, it will easily be carried around the world by currents and winds. In addition, tough plastics that do not corrode or decompose will never disappear from the earth even if they shatter into small pieces.

Looking at the current state of waste plastic in Japan, 99% of it is properly disposed of without leaking into the environment. just,……

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2. Discovery of marine microplastics dating back to the 1970s

Plastic waste that hardly decomposes and decomposes is washed ashore and spoils the landscape (Fig. 1). Not only that, but there have also been many reports of the effects of marine life, such as entanglement and accidental ingestion (explained next), from around the 1970s to the present.

Fig. 1: Plastic waste washed ashore on the coast (photographed at Ishigaki Island)

Recently, you may have heard more and more about microplastics (Fig. 2), which are created by crushing plastic waste.

Figure 2: Microplastics collected in the Sea of ​​Japan

If plastic waste washed ashore on the coast is left unattended for about half a year, it will continue to deteriorate due to factors such as ultraviolet rays. Deteriorated plastic waste is crushed by waves, and it is gradually broken into fine pieces by being stimulated by friction with sand. Shattering and deterioration will progress even with broken pieces of plastic, and will change into even smaller pieces. in this way,……

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3. Where will the microplastics go?

By the way, what will happen to these microplastics in the end? In fact, the whereabouts of this plastic is of great interest to researchers involved in marine plastic pollution. Through repeated degradation and crushing, microplastics continue to become finer and still drift in the sea. This is the worst possible scenario. This is because the smaller they are, the more likely they are to be eaten by a wide variety of organisms, and they may pass through internal tissues and cause damage (explained next time).

On the other hand, algae and bacteria gradually adhere to the pieces of plastic floating in the ocean. They can also get caught in plankton masses. In this way, pieces of plastic, which are originally lighter than seawater, become heavier and eventually sink to the seafloor. this is,……

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Part 2: What is the Problem of Marine Plastic Pollution?

In the previous article, I explained what marine plastic pollution is, its sources, and microplastics, which have become a new problem. . This time, I will explain the impact of marine plastic litter on the environment, marine organisms, and the human body.

1. What is the problem of marine plastic litter?

As mentioned in the previous article, plastic litter that hardly decomposes by corrosion marshes the landscape by washing ashore. Currently, about 100,000 tons of drifted litter is scattered along the coasts of Japan, and about 3 billion yen is spent every year on coastal cleaning projects to maintain the tourist value of scenic spots and beaches. (Reference: Atsuhiko Isobe, The Truth About Marine Plastic Issues – The Reality and Future Predictions of Microplastics, DOJIN Selected Books 86 Kagaku Doujin, 2020). However, the impact of marine plastic litter is not limited to spoiling the landscape. First, the effects on marine life include entanglement and accidental ingestion. Once plastic waste that does not decompose corrodes becomes entangled with marine organisms, it does not leave the body until it degrades and crumbles. If you do an image search for "marine plastic waste" on the Internet, you will find photos of sea turtles entangled in ropes and plastic bags. Alternatively, there have been many reports of ghost fishing, in which marine organisms are killed by fishing nets made of chemical fibers that have been dumped into the sea and sunk to the seabed (Fig. 1).

Figure 1: Abandoned fishing net entangled in coral

Also, some seabirds seem to like to eat pieces of plastic. The reason remains unclear whether it's color or smell. Today, 59% of the world's seabird species are...

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2. What is the problem of microplastics?

Small microplastics are hard to notice because they are mixed with sand, and even if they are scattered on the coast, they will not impair tourism value (Fig. 2). However, its small size creates another problem. Only a limited number of organisms can accidentally eat large pieces of plastic waste. However, if it is a small microplastic, it can be collected from plankton (reference: Frias, J.P.G.L. et al. Marine Environmental Research, 95, 89–95, 2014) to whales (reference: Lusher, A. L., G. et al., Environmental Pollution, 199). , 185–191, 2015) will be eaten by various marine organisms. In fact, cases of accidental ingestion of microplastics from the world's oceans have been reported one after another. In short, not only plastics, but also microplastics are already deeply ingrained in marine ecosystems.

Figure 2: Microplastics washed ashore

As mentioned earlier, the surface of microplastics drifting in the ocean adsorbs contaminants spread in the surrounding seawater. Contaminants are carried into the bodies of marine organisms along with ingested microplastics, and are said to be a factor in various disorders, including increased mortality (Reference: de Sá, L. C. et al., Science of the Total Environment). , 645, 1029–1039, 2018). Additives that melt into the body from accidental ingested plastic pieces...

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3. Effects on the human body

What is the amount of microplastics that humans take into our bodies from the food and drink we consume on a daily basis, and from the air we breathe? In 2021, two papers tackling this problem were published one after another. I don't think there was any quantitative discussion before these announcements. One, published by researchers in Australia and Singapore, suggests that people take in between 0.1 and 5g of microplastics per week (see Senathirajah, K. et al., Journal of Hazardous Materials, 404, 124004, 2021). According to another paper by a team of researchers from the Netherlands...

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Part 3: Current Status of Marine Plastic Pollution 1

In the previous article, I explained the impact of marine plastic litter on the environment, marine organisms, and the human body. In this issue, we will introduce research on marine plastic litter currently being conducted in the world's oceans and rivers, as well as the state of the forefront.

1. Survey of marine plastic litter

Marine plastic litter includes those dumped into the ocean by factors such as fishing. However, as I said in Part 1, it's only about 20% of the total. Some aggregations indicate even lower percentages (Reference: Morales-Caselles, C. et al. Nature Sustainability, 2021, ). Some of this could be plastic waste carelessly dumped on the beach by anglers and vacationers. However, it is irrational to explain the diversity of coastal litter surveyed in Japan over the past five years by coastal use alone (Fig. 1).

Figure 1: Number of litter ashore by item (reference: Atsuhiko Isobe, The Truth About the Marine Plastic Problem – Actual State and Future Prediction of Microplastics, DOJIN Selection 86, Kagaku Dojin, 2020)

Diversity of marine plastic litter , suggesting that the source of these is our everyday life. In particular, single-use (disposable) plastics, which are used on the premise of being thrown away, are difficult to manage because their disposal is entrusted to individuals. Therefore, it seems that it is difficult to avoid leakage of about 1 to 2% from the collection route (Reference: Atsuhiko Isobe, The Truth of the Marine Plastic Problem – The Reality and Future Prediction of Microplastics, DOJIN Selection 86, Kagaku Dojin, 2020). In fact, as you can see in Figure 1, most beach litter turns out to be single-use plastic (or its fragments).

Recently, the results of a survey of 12 million pieces of marine debris (including non-plastic) found in the world's rivers, coasts, and from the surface of the ocean to the deep sea have been announced (Reference: Morales). -Caselles, C. et al. Nature Sustainability, 2021). According to the paper, the most common marine debris found to date is...

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2. The Forefront of Marine Plastic Litter Investigation

The aforementioned marine plastic litter investigations have basically been conducted visually, both on the coast and in the ocean. In coastal surveys, we measure the number and weight of plastic waste scattered in an area of ​​about 100m in length along the shoreline. Visual observation from the ship during the day will actually record the number of plastic waste floating on the surface of the sea. Since physical quantities are not measured by sensors, it is unlikely that high accuracy can be expected for the amount of litter that was surveyed (the amount of litter and the amount of drift). There is a limit to the accuracy of visual observation. Alternatively, it may take a number of years to collect data, such as measuring biomass on a particular coast or sea area. Nonetheless, the above-mentioned survey, which collected data from 12 million cases, has a high degree of reliability due to the power of numbers.

Unsatisfied with this result, the authors and other researchers have been working hard to obtain more accurate observation data. Then, we decided to conduct long-term observations using web cameras (live cameras) (Fig. 3). First, web cameras are installed on the coast to take continuous pictures and measure the amount of marine plastic litter (Reference: Kako, S. et al., Marine Pollution Bulletin, 60, 775–779, 2010). While adjusting the angle of the camera, we will continue to automatically take pictures every hour for a year and a half so that we can see a lot of washed-up debris. Image data will be transferred to the laboratory via the Internet, and the power required for automatic photography and transfer will be secured by installing a solar panel. Then, by image processing, brightly colored plastic litter is extracted, the area covered on the coast is calculated, and the area every hour is recorded as an indicator of the amount of litter present.

Figure 3: Web camera installed on the coast of Ishigaki Island for observing litter

Hourly measurement of beach litter using a web camera...

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Part 4: Current State of Marine Plastic Pollution 2

In the previous issue, I explained the research on marine plastic litter being conducted in the world's oceans and rivers, and the state of the front line. bottom. This time, we will continue to discuss the current state of marine plastic litter, especially microplastics, and the forecast for the next 50 years.

1. Investigation of Marine Microplastics

Since 2014, we have been subsidized by the Ministry of the Environment to conduct research on two vessels, Umitaka Maru and Shinyo Maru (both training ships of Tokyo University of Marine Science and Technology). We have been conducting surveys on the floating amount of microplastics off the coast of Japan. Since 2017, Hokkaido University, Nagasaki University, and Kagoshima University have also participated in this offshore survey, expanding the system to five survey vessels. There is no other example in the world of systematic and continuous observations of this scale, and Japan is undoubtedly at the forefront of research on marine plastic pollution. These survey results are published on the website of the Ministry of the Environment and used as basic materials for academic papers (Reference: Isobe, A. K. Uchida, T. Tokai, and S. Iwasaki, Marine Pollution Bulletin, 101, 618- 623, 2015).

Furthermore, we succeeded in the world's first survey of floating microplastics in the Antarctic Ocean (Reference: Isobe, A. K. Uchiyama-Matsumoto, K. Uchida, and T. Tokai: Marine Pollution Bulletin, 114, 623 -626, 2017). We are also conducting a survey along the Pacific Ocean from the Antarctic Ocean to Tokyo (reference: Isobe. A. et al., Nature Communications, 10, 417, 2019).

・Collection of microplastics

The method of collecting microplastics follows the traditional net collection of zooplankton and juvenile fish in oceanography. In this collection method, a net with a mesh size of about 0.3 mm is submerged near the surface of the sea and pulled laterally by a boat to filter out suspended matter contained in the seawater that has passed through the net (Fig. 1). Floating microplastics are mostly polyethylene and polypropylene, which are lighter than seawater, so they are thought to float near the surface of the sea. Of course, if the mesh size is finer than 0.3mm, even smaller microplastics can be collected. However, there are limits to the subsequent analysis process, and this size is the lower limit of microplastics that can be collected and measured.

Figure 1: Tow net survey of microplastics by ship (Tokyo University of Marine Science and Technology, survey scene in the South Pacific by the Umitaka Maru) Published on the ministry website (Reference: Michida, Y. et al., Ministry of the Environment, Guidelines for Harmonizing Ocean Surface Microplastic Monitoring Methods, 2020).

The concentration of microplastics in the world's oceans collected according to these guidelines is...

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2. Current Status of Marine Microplastics

From the results of the survey so far, it has become clear that the East Asian waters near Japan are a "hot spot" with particularly large amounts of floating microplastics. rice field. The number of suspended particles per 1m³ of seawater near the sea surface is 3.7, which is an order of magnitude higher than in other sea areas. Even when converted to the floating number per 1 km² of the sea surface, it is 27 times the average value in the world's oceans (Reference: Isobe, A. K. Uchida, T. Tokai, and S. Iwasaki, Marine Pollution Bulletin, 101, 618-623, 2015).

In addition, even in the Antarctic Ocean, which is the furthest from the living area, floating microplastics have been confirmed (Reference: Isobe, A. K. Uchiyama-Matsumoto, K. Uchida, and T. Tokai: Marine Pollution Bulletin, 114, 623 -626, 2017). Already, there seems to be no sea in the world that does not contain floating pieces of plastic. Looking at the concentration distribution of microplastics floating in the world's oceans in August, which was created from the database mentioned above, not only around East Asia, but also in the Pacific and central Atlantic oceans, as well as in the Indian and Arctic oceans, A high concentration of floating microplastics can be seen (Fig. 2).

Figure 2: Floating weight of microplastics per unit seawater volume in the world's oceans in August (outlined areas are unobserved sea areas) (cited by Isobe, A. et al., Microplastics & Nanoplastics, 1, 16, 2021) p>From the time plastics were widely distributed around the world to the present...

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3. Marine Microplastics in 50 Years

We used computer simulations to predict the amount of floating microplastics in the Pacific Ocean over the next 50 years (reference: Isobe, A. et al., Nature Communications, 10, 417, 2019). In another simulation, the values ​​of ocean currents and waves are determined from the Pacific Ocean, and virtual particles that are likened to microplastics are flowed into it for verification. As a result, if the outflow of waste plastics into the ocean continues at this rate, the weight concentration of airborne microplastics in seawater in the waters near Japan and the central North Pacific will drop to 1g/m³ by 2060. (Fig. 3). In fact, according to many laboratory experiments that have been published recently, organisms are more likely to accidentally ingest microplastics in sea areas where this amount of microplastics float, leading to various effects such as reduced body length. (Reference: Isobe, A. et al., Nature Communications, 10, 417, 2019).

Figure 3: Suspended weight of microplastics per unit seawater volume in August in the Pacific Ocean, simulated predictions for 2066 (cited by Isobe, A. et al., Nature Communications, 10, 417, 2019)

However, observations And while the plastic pieces targeted for simulation are 0.3 mm or more, ...

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