English translation:

Simulation on plastic particles in the air

Microplastics settle in the nose and throat through breathing
People come into contact with microplastics all the time - they even breathe in the tiny particles. A model now shows how the particles can spread in the organism and where they are deposited.

The consequences of microplastics for the human body and health have not yet been conclusively investigated. What is certain, however, is that microplastics surround us all - they are in the soil, in the water and in the air we breathe. Researchers have now simulated how the potentially harmful plastic particles accumulate in the nose and at the back of the throat. They have published their results in the journal Physics of Fluids.

In 2022, studies found microplastics deep in the human respiratory tract for the first time. This is worrying, says Mohammad Islam, co-author of the current study. Every hour, humans inhale about 16.2 pieces of microplastic - adding up to the amount of a credit card in a week, the researchers conclude from previous research. Islam and the team wanted to find out how microplastic particles move in the human body.

To do this, the group simulated the process in the body in a model and fed it with different data - such as whether the microplastic is spherical, tetrahedral or cylindrical. They also varied the size of the particles and whether someone breathes quickly or slowly.

Nasal cavity and pharynx particularly affected

The result of the computer simulation: the tiny plastic particles accumulated in the model particularly in the nasal cavity and pharynx (oropharynx). “The complicated and highly asymmetric anatomical shape of the airways and the complex flow behavior in the nasal cavity and oropharynx cause the microplastic to deviate from the flow line and deposit in these areas,” says Islam.

Respiratory conditions and the size of the microplastic also reportedly influenced how much microplastic could be deposited in the respiratory tract overall. According to the study, increased flow velocity resulted in less deposition, and the largest microplastics were deposited in the respiratory tract more frequently than their smaller counterparts.

Many parameters that could help determine how microplastics spread through the body were not considered in the current model. The researchers therefore want to adjust and, for example, analyze the transport of microplastics in a large-scale, patient-specific model of the entire lung that also takes into account environmental parameters such as humidity and temperature.