(CN) — Microplastics are a toxic pollutant found in the ocean, soil, air, and in human lungs. While scientists first discovered plastic particles in human airways last year, a new study reveals where and how microplastics accumulate in the respiratory system.
The study published in Physics of Fluids Tuesday comes from a group of researchers at six universities in Australia and Iran, who integrated concepts of fluid dynamics to simulate the trajectories of inhaled microplastic particles in the upper respiratory system — a troublesome consequence of plastic pollution around the world.
Often resembling dust or sand, microplastics are defined as any tiny plastic particle of less than 5 millimeters in length. The world’s increase in plastic production is cause for global concern due to the material's affects on the environment and public health, researchers wrote, noting that millions of metric tons of plastic particles are now found in the oceans, soil and air.
The scientists said that, depending on a person's breathing rate, specific shapes and sizes of microplastic particles can accumulate in so-called “hot spots” within the nasal cavity and back of the throat.
They discovered that that spherical, tetrahedral and cylindrical particles at three varying microns — ranging from small to large — had a more even distribution throughout the nasal cavity during a slower breathing rate than a fast one. When breathing picks up, they say, most particles accumulate in the oropharynx, just above the trachea.
“The complicated and highly asymmetric anatomical shape of the airway and complex flow behavior in the nasal cavity and oropharynx causes the microplastics to deviate from the flow pathline and deposit in those areas,” said study author Mohammad S. Islam, from the School of Mechanical and Mechatronic Engineering at the University of Technology Sydney in a statement. “The flow speed, particle inertia and asymmetric anatomy influence the overall deposition and increase the deposition concentration in nasal cavities and the oropharynx area.”
The trachea is another region where the accumulation of particles is remarkable, the researchers said.
“In this region, with the presence of curvature in the trachea, the particles get trapped for not being able to follow the flow path properly,” the authors wrote.
As for particle accumulation in the lung area, it turns out that a faster breathing rate can allow most particles to become trapped, especially larger, non-spherical ones. However, researchers also found that the higher the breathing rate, the lower the overall accumulation is for all particle shapes — which is, perhaps, good news considering that humans inhale 16.2 bits of plastic every hour, the equivalent of a credit card per week.
“This study emphasizes the need for greater awareness of the presence and potential health impacts of microplastics in the air we breathe,” said study author YuanTong Gu, a professor at Queensland University of Technology, in a statement.
Moving forward, researchers plan to study the effects of microplastics on the respiratory system and the complex design of the lungs for healthy and diseased airways under certain environmental conditions like humidity and temperature.
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