Pollutant Particle Size Affects Deposition in the Lung, Study Finds

Researchers found that inhaled pollutant particles with a large diameter, density, and flow rate can deposit in the upper human lung, while particles with a small diameter, density, and flow rate can enter the deep lung.

These findings were published in Powder Technology, where the study authors used computational fluid dynamics (CFD) to measure the transportation and deposition (TD) of nano- and micro-sized pollutant particles in the mouth-throat and tracheobronchial lung airways.

The 3 types of pollutant particles included were traffic, smoke, and dust particles.

“Because of its huge hazard to human health, pollutant-related particle emission has been a significant source of worry in recent years,” the authors said, noting that particle size can affect the risk, with finer particles being more hazardous than larger particles. “Fine particles may pose a significant threat to people because of their potential to penetrate deep into the lungs and lung cell membranes, and affect the entire organ system, including the brain.”

The numerical simulations in the study included 3 particle densities, 3 flow rates, and 5 particle sizes in nanoscales and microscales. Size categories were defined differently between the 3 types of particles.

In the CFD model, most of the large particles—defined as 10 micrometers—deposited in the upper lung, with a very small number of large particles entering the deep lung.

However, large dust particles with low density (400 kg/m3) could also enter the deep lung, with an estimated 64.28% of large diameter, low density particles entering the deep lung.

Additionally, nanoparticles were more evenly distributed in the airways compared with microparticles.

“This is because the airway geometry affects the impaction mechanism, but the diffusion mechanism does not,” the authors noted, adding that “impaction induced deposition only happens wherever the airway bends, bifurcates or change diameter, while diffusion occurs everywhere if it is strong.”

The model also showed that if the particle diameter was extremely small (5 nanometers), its density did not have a significant influence on particle deposition.

When measuring escape rate of the particles, the authors also found that more particles entered from the left side of the lung—regardless of size, density, or flow rate—compared with the right side. According to the authors, this is likely credited to the general asymmetry of the human lung.

Overall, the study found that different mechanisms such as diameter, density, and flow rate have an effect on the depth of deposition of pollution particles in lungs.

“This conclusion helps design strategies of protecting human lungs from different kinds of pollutant,” the authors concluded. “If particles are electrically charged, an improved model needs to be developed in the future to consider the interparticle interaction, which enhances with the increase of electrical charge.”

Reference

Rahman M, Zhao M, Islam MS, Dong K, Saha SC. Numerical study of nano and micro pollutant particle transport and deposition in realistic human lung airways. Published online April 7, 2022. Powder Technol. doi:10.1016/j.powtec.2022.117364