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NotificationsNotify me of updates to DEPOSITION OF MAN-MADE FIBERS IN THE HUMAN RESPIRATORY AIRWAY, pp. 1 - 36
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Authors:  Wei-Chung Su and Yung Sung Cheng
The U.S. Environmental Protection Agency banned the use of asbestos in 1989, since
that time man-made fibers have been manufactured and used in many applications to
replace asbestos. Studies conducted in laboratory animals have shown that certain manmade
fibers may have biological effects similar to those of asbestos, implying that
potential fiber-related lung injury might be induced in humans due to inhalation of manmade
fiber aerosols. Therefore, it is essential to investigate the exposure dosimetry of
man-made fibers in the human respiratory airway, which would particularly benefit
workers in the man-made fiber industry.
A series of intensive fiber deposition experiments using realistic human nasal and
oral-lung airway casts were conducted in our laboratory in order to fully understand the
fiber deposition in the human respiratory airway. Man-made carbon, titanium dioxide
(TiO2), and glass fibers having various fiber dimensions were employed as the test
materials, and these fiber aerosols were delivered into the casts using several inspiratory
flow rates representing different human inhalation rates. These experiments provided a
large amount of invaluable data, including the dominant deposition mechanism, airway
deposition patterns, and regional deposition efficiencies. The deposition results showed
that fiber deposition in the nasal and oral airways increases proportionally as the fiber
length and fiber inertia increases. The sites of the enhanced deposition were found around
the vestibule (nasal airway) and the oropharynx (oral airway). In the tracheobronchial
airways, the carina region in each lung generation/bifurcation was the preferred
deposition site, and the deposition efficiency increased as the fiber length and inertia
increased as well. These results imply that the inhaled small and short fibers have a high
penetration rate in the human upper airway and cause relatively more fiber deposition in
the lower respiratory tract, which could result in potential lung injures. In contrast, the
inhaled large and long fibers tend to deposit in the nasal and oral airways and are
therefore less harmful for the tracheobronchial airways. It was also interesting to note that the deposition efficiency of fiber was shown to be significantly lower than that of general
compact particles, indicating that fibers have a greater chance of entering the human deep
lung compared with the compact particles. Based on these results, empirical models were
developed for predicting the fiber deposition in the human airway. It is believed that
these proposed models can be very useful for occupational health researchers to
accurately estimate the fiber deposition in the human respiratory tract for any given fiber
exposure scenario. 

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