It is well known that plastic waste that accumulates on land eventually ends up in the ocean as microplastics. It is now speculated that microplastics are also present in the atmosphere, held in clouds.
Microplastics are plastic particles less than 5mm in size. They are often found in industrial effluent or form from the degradation of bulkier plastic waste. Research shows that large amounts of microplastics are ingested or inhaled by humans and animals and have been detected in the lungs, heart, blood, placenta and feces.
Microplastics end up in the ocean and are then released by the ocean spray and find their way into the atmosphere. They may have become an essential component of clouds, contaminating nearly everything we eat and drink via ‘plastic rainfall’. While most studies on microplastics have focused on aquatic ecosystems, few have looked into their impact on cloud formation and climate change as airborne particles.
In a new study led by Professor Hiroshi Okochi at Waseda University, a group of researchers has explored the path of airborne microplastics (AMPs) as they circulate in the biosphere, adversely affecting human health and the climate. Their study was recently published in the journal Environmental Chemistry Letters with contributions from co-authors Yize Wang from Waseda University and Yasuhiro Niida from PerkinElmer Japan Co. Ltd.
“Microplastics in the free troposphere are transported and contribute to global pollution,” explained Okochi. “If the issue of ‘plastic air pollution’ is not addressed proactively, climate change and ecological risks may become a reality, causing irreversible and serious environmental damage in the future.”
To investigate the role of these tiny plastic particles in the troposphere and the atmospheric boundary layer, the team collected cloud water from the summit and foothills of Mount Fuji, and the summit of Mount Oyama – regions at altitudes ranging from 1,300-3,776m. Using advanced imaging techniques including attenuated total reflection imaging and micro-Fourier transform infrared spectroscopy (µFTIR ATR imaging), the researchers determined the presence of microplastics in the cloud water and examined their physical and chemical properties.
They identified nine types of polymers and one type of rubber in the AMPs detected. Notably, most of the polypropylene that was detected in the samples was degraded and had carbonyl (C=O) and/or hydroxyl (OH) groups. The Feret diameters of these AMPs ranged from 7.1-94.6µm, the smallest seen in the free troposphere. Moreover, the presence of hydrophilic polymers in the cloud water was abundant, suggesting that they were removed as cloud condensation nuclei. These findings confirm that AMPs play a key role in rapid cloud formation, which may eventually affect the overall climate.
Accumulation of AMPs in the atmosphere, especially in the polar regions, could cause major changes in the ecological balance of the planet, leading to severe loss of biodiversity. Okochi concluded by saying, “AMPs are degraded much faster in the upper atmosphere than on the ground due to strong ultraviolet radiation, and this degradation releases greenhouse gases and contributes to global warming. As a result, the findings of this study can be used to account for the effects of AMPs in future global warming projections.”