Factors Modifying Particle Deposition

During development from infancy to adulthood, the respiratory system undergoes substantial changes in airway structure and lung volume, accompanied by considerable differences in spontaneous-breathing conditions (198-206). Even in adults, distinct sex-related and racial differences are established for structural and conventional Imig function parameters (207-211). However, only limited 

Marcel Dekker, Inc. 270 Madison Avenue, New York, New York 10016 

We are unaware of deposition studies in healthy neonates or infants, probably owing to concerns over the use of radiotracers in this popnlation (33). There are some deposition studies, related to therapeutic drug dehveiy, in spontaneously breathing or ventilated infants with lung diseases (216-218). Also, filter and animal lung models have been used to assess deposition in infants (219-222). One of the limitations of these studies is that deposition is often related to the amount of radioactivity delivered into the nebulizer unit and not to what is actually inhaled. Hence, there is a clear necessity for improved deposition studies to better imderstand health risks from environmental air pollutions or to improve inhalation therapy in neonates and infants. 

Children. For particle sizes between 1 and 3 pm, deposition under ventilatory conditions of rest and light exercise was measured in 41 children by Bec-quemin et al. (212,213). Exercise caused per-breath deposition of 1-pm particles to decrease from about 20 to 15%, whereas the deposition of 2- and 3-pm particles was almost unaffected. Because the higher ventilatory demand under light exercise was accomplished mainly by an increase in breathing Irequency, respiratory flows were increased, but the residence time of particles in the respiratory system was shortened. This caused 1-pm particle deposition, which is mainly governed by sedimentation, to decrease. It appears that, for 2- and 3-pm particles, the decreased deposition probability by sedimentation was balanced by an increased effect of impaction, so that total deposition remained imaffected. Therefore, it may be speculated that regional deposition was affected with a partial shift in 

---

The permeation coefficient, K, has been modified slightly to include some other terms such as the density of the slip and a factor for converting the volume of water removed to the volume of clay particles deposited. The important point, however, is that Eq. (7.20) can now be integrated to give a relationship between the compact layer thickness and time ... 

Many chemical component-s present in such aerosols are relatively stable they can be measured long after (days, week.s, or more) the aero.sol has been collected on a filter or impactor plate, for example. Short-lived reactive and/or volatile species such as peroxides and aldehydes are not usually determined. This may make it difficult to evaluate the health and ecological effects of aerosols because chemically reactive chemical species tend to be the most active biochemically. The chemical components present in the particles collected on a filter or impactor plate may react with each other when they are in close proximity. Particle deposits in filters or on surfaces may also react with molecular components of the gases flowing over them. Chemical reactions between the gas and aerosol may not affect mea.surement.s of metallic elements but may modify chemical speciation (compound form) on the collector surface. All of these factors must be taken into account in selecting sampling and measurement methods for aerosol chemical properties. 

In spite of a great number of investigations aimed at the preparation of photocatalysts and photoelectrodes based on the semiconductors surface-modified with metal nanoparticles, many factors influencing the photoelectrochemical processes under consideration are not yet clearly understood. Among them are the role of electronic surface (interfacial) states and Schottky barriers at semiconductor / metal nanoparticle interface, the relationship between the efficiency of photoinduced processes and the size of metal particles, the mechanism of the modifying action of such nanoparticles, the influence of the concentration of electronic and other defects in a semiconductor matrix on the peculiarities of metal nanophase formation under different conditions of deposition process (in particular, under different shifts of the electrochemical surface potential from its equilibrium value), etc. 

ZnO displays similar redox and alloying chemistry to the tin oxides on Li insertion [353]. Therefore, it may be an interesting network modifier for tin oxides. Also, ZnSnOs was proposed as a new anode material for lithium-ion batteries [354]. It was prepared as the amorphous product by pyrolysis of ZnSn(OH)6. The reversible capacity of the ZnSnOs electrode was found to be more than 0.8 Ah/g. Zhao and Cao [356] studied antimony-zinc alloy as a potential material for such batteries. Also, zinc-graphite composite was investigated [357] as a candidate for an electrode in lithium-ion batteries. Zinc particles were deposited mainly onto graphite surfaces. Also, zinc-polyaniline batteries were developed [358]. The authors examined the parameters that affect the life cycle of such batteries. They found that Zn passivation is the main factor of the life cycle of zinc-polyaniline batteries. In recent times [359], zinc-polyfaniUne-co-o-aminophenol) rechargeable battery was also studied. Other types of batteries based on zinc were of some interest [360]. 

Respiratory Tract Clearance. This portion of the model identifies the principal clearance pathways within the respiratory tract. The model was developed to predict the retention of various radioactive materials. Figure 3-7 presents the compartmental model and is linked to the deposition model (Figure 3-6) and to reference values presented in Table 3-9. Table 3-9 provides clearance rates and deposition fractions for each compartment for insoluble particles. The table provides rates of insoluble particle transport for each of the compartments, expressed as a fraction per day and also as half-time. ICRP (1994a) also developed modifying factors for some of the parameters, such as age, smoking, and disease status. Parameters of the clearance model are based on human evidence for the most part, although particle retention in airway walls is based on experimental data from animal experiments. 

Particulate matter may physically become a factor in leaf physiological function if deposition is heavy enough to block light (critical to the photosynthetic machinery of the leaf) or if stomata become occluded by the particles. In the latter case both uptake of carbon dioxide for photosynthesis and water loss by the plant could be reduced. Particulate matter also has a potential to chemically alter the micro-environment of the leaf surface. Trace concentrations of heavy metals associated with deposited particles, as well as strong acid anions, may significantly modify the chemical nature of water drops or films of water in contact with plant surfaces. 

---