With Every Breath You Take: How Microplastics Invade Your Lungs

Tiny plastic particles, categorized by their size as microplastics, <5mm or nanoplastics, 1-100nm are everywhere. Some are manufactured, coming from cosmetics or synthetic fabrics, and others, termed secondary nano or microplastics (NMPs) fragment from larger plastic objects. Laboratory studies have demonstrated that NMPs can disrupt the cells lining our respiratory tract.

• Disrupting surfactant, the fluid that helps maintain lung elasticity needed for exhalation.
• Cell motility and adhesion – cytoskeletal “rearrangement”
• These two cellular responses “can amplify the risk of developing” asthma, scarring of the lung (pulmonary fibrosis), and chronic obstructive pulmonary disease (COPD).

Researchers are using a model of particle flow, computational fluid-particle dynamics (CFPD), to model the paths and deposition of particles as they flow down pathways. Think of modeling the pathway of a leaf you toss in a stream; in this instance, NMPs are the leaves, our breath is the water, and our lungs' architecture is the stream's map. We have seen this technique used to explore the movement of COVID viral particles from our nose to the upper airway or deep into the lungs.

The model employed “includes the nasal cavity, mouth, larynx, and airways down to generation 13,” which is quite deep into the lungs. Its mathematics involves flow, turbulence, and interactions with particles of varying sizes and shapes. Like all models, it is a simplification but seems to provide results in the same ballpark as experimental data.

Results

• The lungs are asymmetric, the right side having three lobes, the left two (one “displaced” by the presence of the heart). The main stem bronchi, the first division of the lungs to left and right, differ with the right main stem bronchus, which is shorter, straighter, and wider. Larger particles settle to the left, smaller to the right.
• Size matters, with larger particles settling in the upper airways along the front of the nasal cavity and throat (larynx). Smaller particles distribute more evenly and deeply.
• The respiratory rate also influences distribution. Faster rates favor inertia and gravity, depositing more of those larger particles in the upper airways. Slower rates favor diffusion, depositing smaller particles evenly enhancing asymmetries.
• Slower breathing facilitates longer and deeper transportation.
• The throat and mid-level bronchi are the deposition hotspots.
• Particulate shape also plays a role. Cylindrical particles align with airflow and avoid mucus and other filtration methods but tend to deposit in the upper respiratory tract. Tetrahedral shapes tumble about with the edges catching on division points in the bronchial tree (bifurcations), enhancing their deposition in these areas. Additionally, their smaller size increases a more dispersed distribution.
• The escape fraction (EF) is the proportion of inhaled particles that escape upon exhalation. Smaller particles have a greater EF, as does increasing respiratory rates. Particles deposited in the upper airways have a greater EF, as do spherical particles over other shapes.
• The deposition fraction (DF) is those inhaled particles staying put. Slow breathing, with increased deposition in the nose and throat, increases DF. Faster breathing moves deposits deeper but in smaller amounts, a lower DF.

What might we conclude?

First and foremost, we must acknowledge how little we know about microplastics and how they actually impact our health. We have laboratory data demonstrating the impact of these particles on respiratory cells and function, but the study clearly shows that not all breathing is the same. Our current measures of exposure, despite being quantified and supported by statistical measurements, are crude. Without detailed information on the particulate composition and the nature of the respirations by the exposed individuals, we have no clear-cut measure of the particulate dosage within the respiratory tree. As the researcher write,

“These simplifications, while facilitating a foundational understanding, should be recognized as limitations that may impact the comprehensive representation of real-world respiratory dynamics.”

As scientific inquiry uncovers the choreographed particulate flow within our respiratory system, we confront the stark reality of our limited understanding. Computational models offer glimpses into the interplay between particle size, shape, and respiratory dynamics. Our current measures of exposure lack the nuance of the threat posed. In the face of this uncertainty, the power to mitigate our exposure lies not in the halls of regulation but in our everyday choices. By eschewing many cosmetics and embracing natural over synthetic fibers, we can significantly reduce the microplastic penumbra surrounding us.

Source: Transport and deposition of microplastics and nanoplastics in the human respiratory tract Environmental Resources DOI: 10.1016/j.envadv.2024.100525