Health Effects of Aerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 573

TABLE 23.3
Factors That Affect Particle Deposition Exclusive of Particle Characteristics
Respiratory tract geometry
Airway caliber
Airway branching pattern
Airway path length to terminal airways and alveoli
Ventilation
Pattern of breathing: oral, nasal, oronasal
Ventilation rate [272]
Duration of pauses between breaths
Tidal volume (volume of each breathing during quiet breathing)
Ventilation distribution
Other factors
Respiratory tract disease [273]
Altered airway geometry, branching patterns, and path lengths
Altered ventilation patterns
Altered distribution of ventilation
Changing patterns of pattern of breathing with age
Infants are preferential nasal breathers [274]
Sex
Females with greater deposition of nanoparticles [272]
Source: Adapted from Schlesinger, R.B., Deposition and clearance of inhaled particles, in McClellan,
R.O. and Henderson, R.F., Eds., Concepts in Inhalation Toxicology , Taylor & Francis,
Washington, DC, pp. 191-224, 1995.
Retention of PM in human lungs has been studied by a number of investigators. The number of
particles retained is related to the ambient concentrations (Figure 23.8; [24]). Particle retention is
also a function of the level of the airways in which the particle is deposited, the type of particle, and
the functional integrity clearance mechanisms (for an extensive discussion of speciic mechanisms,
see Ref. [25]). In 42 left lungs obtained from the Coroner's Ofice in Fresno, CA (19 from cigarette
smokers; all Hispanic males), carbonaceous and birefringent silica particles were rarely found in
the walls of larger airways [26]. In contrast, at the level of respiratory bronchioles (beyond the 12th
generation of airways), such particles were frequently found in the airway walls [26]. Similar obser-
vations were made by Churg and Vidal [23] in the lungs of nonsmokers from Vancouver, Canada
(Figure 23.9). These investigators also noted that ultraine PM constituted <15% of the retained
PM (expressed as millions of particles/gram of tissue), virtually all of which were crustal minerals.
This was in contrast to their indings in lungs from Mexico City, where lungs contained an average
of 25% of chained aggregates of carbonaceous particles [24]. As noted previously, airway branch
points are also sites of increased deposition [23]. For example, in the fourth generation of airways,
Churg and Vidal [23] observed that the geometric mean particle number concentrations (mean of
ten lungs) were two logs greater (per 10 −6 /g dry weight) at bifurcation points (4.0 ± 1.2) compared to
tubular segments (6.1 ± 1.4) both in the upper and lower lobes.
Deposition of particles is inluenced by sex (greater deposition in females in the extrathoracic
and tracheobronchial tree), age (increased deposition in the tracheobronchial region in children and
young adults based on modeling), and underlying respiratory tract disease [27,28]. Figure 23.10
presents simulated deposition data presented by the U.S. EPA [28] and illustrates the variability in
mass deposition (μg/day) as a function of age and sex. The largest predicted mass depositions for the