Article Abstract

Deposition of carbon nanotubes in the human respiratory tract: a theoretical approach

Authors: Robert Sturm


Background: The study aims to describe the behavior of single-wall and multi-wall carbon nanotubes (SWCNT, MWCNT) in the human respiratory tract (HRT). Based on a theoretical deposition model, possible accumulation of these particles in different lung regions is subject to a detailed investigation. Predictions made by the theoretical approach should help to develop appropriate risk assessments for highly anisometric ultrafine particles.
Methods: Particle geometry expressed by the aspect ratio was approximated by using the aerodynamic diameter concept. Transport and deposition of SWCNT and MWCNT in the HRT was simulated with the help of a random-walk model based on the Monte-Carlo method. Random particle paths were computed for a stochastic lung architecture. For the simulation of particle deposition, empirical and analytical equations describing the physical processes exerting on the particles (i.e., Brownian motion, impaction, interception, and gravitational settling) were used. Simulations were conducted for adult lungs and two different breathing conditions.
Results: For sitting breathing (low tidal volume and breathing frequency), SWCNT exhibit a total deposition of 77.7%, with 34.3% being accumulated in the extrathoracic airways, 35.1% being deposited in the thoracic airways (lung generation 1–27), and 8.3% being targeted to the alveoli. MWCNT show a total deposition of 23.1%, whereby extrathoracic deposition amounts to 10.2%, bronchial deposition to 10.1, and alveolar deposition to 2.8%. For heavy-work breathing (high tidal volume and breathing frequency), total deposition of SWCNT is decreased (67.2%) and regional deposition is significantly modified (extrathoracic: 4.5%, bronchial: 43.5%, alveolar: 19.2%). Total deposition of MWCNT is reduced (15.4%), resulting in a remarkable change of extrathoracic (1.1%), bronchial (8.1%), and alveolar deposition (6.2%).
Conclusions: Inhalation of SWCNT and MWCNT may bear considerable health risks, as high numbers of inspired particles are deposited in lung regions (distal bronchioles, alveoli) being predisposed to various pulmonary diseases.