Microplastics Discovered in Air at Mount Fuji Summit

Microplastics found in the air at the summit of Mount Fuji.

“When we think of microplastics, we usually think of plastic waste on land being carried to the ocean through rivers, but in fact, they are also present in the atmosphere.”

This statement comes from Professor Hiroshi Okouchi of the Faculty of Science and Engineering at Waseda University.

During his air pollution research around the Angkor ruins, he witnessed plastic waste scattered on the roadside and scenes of people digging holes to bury plastic bottles for disposal.

“Southeast Asia has high temperatures, high humidity, and strong UV rays. Plastic waste deteriorates easily, and we thought microplastics would be released into the atmosphere.”

In fact, until Professor Okouchi and his team conducted their research, there had been little study of microplastics in the atmosphere.

Professor Okouchi and his team initially conducted research at Mount Fuji’s summit, the rooftop of an 18-story research building in Shinjuku, and in Cambodia.

The atmospheric boundary layer extends up to 2 km from the ground, where atmospheric pollutants accumulate under the influence of the surface. The area from 2 km to 10 km above the ground is called the free convection zone, and Mount Fuji’s summit lies within this zone.

“While the presence of microplastics had not been confirmed in the free convection zone, we found microplastics at the summit of Mount Fuji during our research.”

In Shinjuku, there is usually about one microplastic particle per cubic meter of air, but at the summit of Mount Fuji, the number ranges from 0.01 to 0.06 particles.

“However, the concentration of microplastics in the air varies with the season and weather. When a large low-pressure system like a typhoon occurs, polypropylene increases in Shinjuku, and on clear, sunny days with a strong high-pressure system, up to seven microplastic particles per cubic meter were detected.

At the summit of Mount Fuji, when the air from Southeast Asia is brought over by a typhoon, both the concentration and variety of microplastics increase. This was a significant discovery, even in the free convection zone.”

In Cambodia’s atmospheric boundary layer, when surveyed during the rainy season of 2019, 49 microplastic particles were detected per cubic meter, but in the dry season of 2023, only 4 particles were found per cubic meter.

When a large low-pressure system like a typhoon occurs, an updraft is generated, and air from the ground rises into the free convection zone. During this time, oceanic microplastics are also lifted. In a winter survey of surface seawater off Noto, Japan, between 20,000 and 330,000 microplastic particles per cubic meter were detected.

 

Additionally, due to the westerly winds in the free convection zone, microplastics from Southeast Asia and China are transported, which increases the concentration of microplastics over Japan.

The microplastics carried into the free convection zone circulate around the Earth by the wind. While it may seem that if they are just circulating in the atmosphere, they would not affect us on the ground,

“When high pressure builds up in the atmosphere, it causes a downdraft, and microplastics fall to the ground. They can also be carried down by rain or snow.”

The detection of microplastics in the free convection zone indicates that microplastic pollution is occurring on a global scale.

Microplastics have also been reportedly detected in “brains.

Generally, microplastics refer to plastic particles smaller than 5mm. Particles larger than 0.1mm, which are visible to the naked eye, tend to fall to the ground quickly once they rise into the air, so the microplastics suspended in the atmosphere are extremely small.

The most concerning impact of these tiny microplastics is their potential health risks.

Among air pollutants, there are tiny particles known as PM2.5, which are smaller than 2.5 micrometers (μm) in diameter. Research by Professor Hiroshi Okouchi and his team has revealed that microplastics are part of this group, along with nitrates, sulfates, black carbon, and organic matter.

These tiny pollutants can enter the lungs and have been linked to respiratory diseases and increased risks of circulatory diseases, such as arrhythmias.

“That’s not all. Plastics bind to harmful substances in the environment and concentrate them. Moreover, plastics degrade and continue to produce harmful substances, as our group’s research has shown.”

In other words, inhaling microplastics increases the health risks even further.

“Microplastics inhaled through the nose or mouth not only remain in the lungs, but they can break down into nanoplastics and enter the bloodstream, circulating throughout the body.

Previously, it was believed that the blood-brain barrier would prevent microplastics from reaching the brain, but reports this year indicate that micro and nanoplastics have been found in the brain as well.”

At present, the exact health risks of this are not fully understood, but there have been reports that individuals who have microplastics detected in their carotid artery plaques are more likely to experience strokes or heart attacks.

Could it also be a cause of guerrilla downpours?

Microplastics may also contribute to more than just health risks.

“It’s possible that microplastics in the atmosphere could be linked to the occurrence of guerrilla downpours in places like Tokyo,” says Professor Okouchi.

For rain to fall, certain conditions are necessary: water vapor, upward air currents, and another component—nuclei to form clouds.

Traditionally, cloud-forming nuclei have been thought to include sea salt particles, sulfate, and nitrate. Sea salt particles are created when seawater spray evaporates in the air, leaving behind salt particles. Sulfate is formed from sulfur dioxide generated by burning coal, and nitrate is produced from nitrogen oxides in vehicle emissions.

These particles easily absorb water vapor and help form cloud droplets. On the other hand, plastics typically repel water, so microplastics were not believed to serve as cloud nuclei.

“However, when we actually collected and analyzed the components of clouds, we found that plastics, including hydrophilic ones containing oxygen and degraded polyethylene and polypropylene, were present in high amounts.”

It is also known that even plastics without oxygen can become less water-repellent when they degrade. As a result, the increasing presence of microplastics in the atmosphere could make it easier for clouds to form, thus raising the likelihood of intense, localized rainfall.

“Moreover, the upper atmosphere is exposed to strong UV rays, which accelerates the degradation of plastics. When plastics break down, they release methane and CO2.”

Not only could microplastics be contributing to guerrilla downpours, but they might also be increasing greenhouse gases.

So, what should we do?

“A key step is properly disposing of plastic products used in the home. It’s also important to minimize the use of outdoor plastic products.

For example, artificial turf is made entirely of plastic, and because it’s subjected to heavy use, it sheds small pieces into the air. It also degrades easily under sunlight. Replacing artificial turf with natural grass is a better option.

Playground equipment should avoid plastic use, and plastic plant pots pose a risk as they break down into microplastics that can be inhaled. If possible, ceramic pots are preferable.”

Hiroshi Okouchi – Environmental Chemist. Professor at the Faculty of Science and Engineering, Waseda University. He is engaged in research projects that aim to contribute to the early detection and resolution of environmental issues. His recent work includes cross-border atmospheric pollution monitoring using Mount Fuji, studying the generation mechanisms of guerrilla and mountain rainfall, developing environmental-friendly decontamination techniques for radioactive materials in satoyama (traditional rural landscapes), evaluating the impact of air pollution on the Angkor ruins in Cambodia, investigating the dynamics, origins, and health risks of atmospheric microplastics, and pursuing green transformation through early-growing paulownia trees.