Minuscule airborne plastic particles are spreading to all corners of the planet, penetrating deep into human bodies and sparking alarm among researchers of the relatively new subject matter.

Studies are shedding light on the origins, transport mechanisms and impact of these pollutant microplastics, which are too small to be seen with the naked eye.

They have been found in skies above Mount Fuji, in European rain, Arctic snow and within human bodies. These byproducts of human activity could also be fueling extreme weather conditions.

“Marine microplastic pollution has drawn so much attention that the ocean has been assumed as the final destination for microplastics, but recent studies indicate that airborne plastic pollution is spreading at an alarming rate,” said Hiroshi Okochi, a Waseda University professor of environmental chemistry.

Okochi leads a research team that has been studying airborne microplastics since 2017 and was the first to show that the pollutants had made their way into cloud water.

According to studies conducted on how plastic waste is damaging marine creatures and the ocean environment, plastic litter that flows into seas degrades into “marine microplastics,” which measure 5 millimeters or less in particle size.

By contrast, few studies are available on “airborne microplastics,” most of which measure less than 2.5 micrometers (0.0025 millimeter) across.

One study published in 2016 found plastics in fiber form in rainwater in Paris, showing that plastic particles were wafting in the air. 

Okochi’s team in 2023 published a study that showed water in clouds covering the top of Mount Fuji contained 6.7 pieces of microplastics per liter.

Airborne microplastics travel in different manners at different altitudes.

In the free troposphere, an atmospheric layer extending above an altitude of 2,000 to 2,500 meters, substances are transported intercontinentally over long distances by prevailing westerly winds and other air currents. They are rarely affected by things on the ground.

The microplastic particles found above 3,776-meter-tall Mount Fuji where clouds can form were carried far from their sources, Okochi’s team said.

POSSIBLE CAUSE OF TORRENTIAL DOWNPOURS

According to one theory, when a large-scale atmospheric depression forms and generates ascending air currents, ground-based and seaborne microplastics are swirled up by the wind and sea spray and carried high up into the skies.

Once in the free troposphere, strong winds push the microplastics to higher levels and at enormous speeds, polluting the layer.

A team of scientists from Germany and Switzerland reported that they had found more than 10,000 pieces of microplastics per liter of snow in the Arctic. They said such microplastics are likely traveling over long distances in the air and being deposited with snow.

Microplastics may even be inducing cloud formation.

Clouds naturally form when dust serves as nuclei for water vapor to condense on. Typical ingredients of plastic products, such as polyethylene and polypropylene, naturally repel water.

Microplastics, however, change in chemical structure and obtain hydrophilicity, or affinity for water, when they are degraded by ultraviolet rays.

That likely facilitates cloud formation through vapor condensation, Okochi said.

Some experts say microplastics could be causing sudden torrential downpours and other extreme weather phenomena.

Studies have also found that microplastics, when degraded by ultraviolet rays, emit greenhouse gases, such as methane and carbon dioxide.

PLASTICS ENTERING LUNGS

Although plastics have been found in various regions of the human body, it is not yet known what impact the airborne substances have on health.

Airborne microplastic particles measuring 1 micrometer (0.001 millimeter) or less in size are believed capable of reaching the alveoli of the lung.

A study conducted in Britain said microplastics were detected in 11 of 13 lung tissue samples from patients who underwent lung surgeries. The highest levels were found in the lowermost region of the lung.

A human breathes more than 20,000 times a day, which adds up to 600 million to 700 million times throughout a lifetime.

There is no standard method for measuring airborne microplastics, so estimated amounts being inhaled by humans vary wildly from one research article to another.

Okochi said he hopes to develop a unified method for measuring the shapes, types, sizes and concentrations of airborne plastics so researchers across the globe can use it in their observations.

“We inevitably end up inhaling airborne microplastics without knowing it because the pollution they are causing is invisible,” Okochi said. “So little is clearly known about their possible impact on health and the environment, which is only beginning to be discussed. There should be more fact-finding studies on the matter.”

HOPES ON FOREST ADSORPTION

Airborne microplastics come from various sources, including road dust, tire abrasions, artificial turf and clothing.

Effective measures to reduce exposure include avoiding the use of synthetic fiber clothes and washing clothes in mesh laundry bags to prevent the garments from rubbing together.

In the larger picture, society could reflect on whether certain plastic products in close surroundings are really necessary or could be replaced with non-plastic materials.

For airborne plastics that are too small to be visible, absorption by forests is drawing attention as a hopeful measure.

A group of researchers, including Okochi and scientists from Japan Women’s University, found that “konara” oak leaves adsorb airborne plastics through “epicuticular wax,” a coating layer on the leaf surface that defends the tissue from ultraviolet rays and external enemies.

Konara forests in Japan can absorb an estimated 420 trillion pieces of airborne microplastics a year, Okochi said,

His team is now studying the use of fast-growing paulownia trees to fight the airborne microplastics.

There are hopes this tree variety can address other environmental problems. The trees absorb large volumes of carbon dioxide and can be used to absorb radioactive substances in the soil in Fukushima Prefecture, the site of the 2011 nuclear disaster.

“Planting the trees on the roadside could help reduce inhalation by humans,” Okochi said. “We hope to pursue the potential of this new emissions reduction measure using fast-growing paulownia trees to lower the risk of human exposure.”