Deposition of naphthalene and tetradecane vapors in models of the human respiratory system

Abstract

Jet-propulsion fuel (particularly JP-8) is currently being used worldwide, exposing especially Air Force personnel and people living near airfields to JP-8 vapors and aerosols during aircraft fueling, maintenance operations, and/or cold starts. JP-8 is a complex mixture containing >200, mostly toxic, aliphatic and aromatic hydrocarbon compounds of which tetradecane and naphthalene were chosen as two representative chemical markers for computer simulations. Thus, transport and deposition of naphthalene and tetradecane vapors have been simulated in models of the human respiratory system. The inspiratory deposition data were analyzed in terms of regional deposition fractions (DFs) and deposition enhancement factors (DEF). The vapor depositions are affected by vapor properties (e.g. diffusivity), airway geometric features, breathing patterns, inspiratory flow rates, as well as airway-wall absorption parameter. Specifically, the respiratory uptake of vapors is greatly influenced by the degree of airway-wall absorption. For example, being an almost insoluble species in the mucus layer, the deposition of tetradecane vapor is nearly zero in the extrathoracic and tracheobronchial (TB) airways, that is, the DF is <1%. The remaining vapors may penetrate further and deposit in the alveolar airways. The DF of tetradecane vapors during inhalation in the alveolar region can range from 7% to 24%, depending on breathing waveform, inhalation rate, and thickness of the mucus layer. In contrast, naphthalene vapor almost completely deposits in the extrathoracic and TB airways and hardly moves downstream and deposits in the respiratory zone. The DFs of naphthalene vapor in the extrathoracic airways from nasal/oral to trachea under normal breathing conditions (Q = 15–60 L/min) are about 12–34%, although they are about 66–87% in the TB airways. In addition, the variation of breathing routes (say, from nasal breathing to oral breathing) may influence the vapor deposition in the regions of nasal and oral cavities, nasopharynx and oropharynx, but hardly affects the deposition at and beyond the larynx. The different deposition patterns of naphthalene and tetradecane vapors in the human respiratory system may indicate different toxic and hence health effects of these toxic jet-fuel components.

Keywords::

• Computational analysis
• toxic vapor deposition
• lung airway model

Acknowledgements

This effort was sponsored by the Air Force Office of Scientific Research, Air Force Material Command, USAF, under grant number FA9550-07-1-0461 (Dr. Walt Kozumbo, Program Manager), and the NSF Grant CBET-0834054 (Dr. Marc S. Ingber, Program Director). The U.S. Government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation thereon. The use of both CFX software from ANSYS Inc. and IBM Linux Cluster at the High Performance Computing Center at North Carolina State University (Raleigh, NC) are gratefully acknowledged as well. The authors also thank Professor Andrew Pollard and Mr. Christopher Ball of Queen’s University at Kingston for supplying their geometry of the oral airway model (see Figure 1).

Declaration of interest

The authors declare no conflict of interest.