Combustion of leaded gasoline results in the formation of, among other
substances, several kinds of lead halides. Tetraethyl lead (Pb(C 2 H 5 ) 4 in leaded
gasoline reacts with molecular oxygen (O 2 ) and halogenated scavengers, such
as dichloroethane and dibromoethane, producing various forms of lead halide
particles that are emitted into the atmosphere:
PbðC 2 H 5 Þ 4 þ O 2 þ ðhalogenated scavengersÞ ! CO 2 þ H 2 O
þ PbCl 2 þ PbBrCl þ PbBr 2
ð9:5Þ
Additionally, whole gasoline vapor alone has been shown to contribute
significantly to atmospheric aerosol formation.
5
9.4 HEALTH EFFECTS
Fly-ash particles are generally composed of stable elements or compounds that
are usually not considered directly toxic in concentrations found in ambient
air. However, subtle toxicity has been recognized under some conditions. In
particular, many trace elements have important biological activity and are,
therefore, potential health hazards.
The toxicity of PM generally arises from any of the following factors. The
particles may themselves be toxic, e.g., particles containing toxic metals and
nonmetals, such as Pb, Cd, Ni, mercury (Hg), arsenic (As), and radionuclides
6, 7
Alternatively, the particles may adsorb toxic chemicals, such as carcinogens,
7,8
and enhance their effect by either increasing their penetration into the lungs, or
prolonging their residence time in the respiratory tract. Particles may also serve
as condensation nuclei for water and other vapors, producing droplets and
enhancing biological effects. Finally, if there are large quantities present in the
respired air, particles may overtax the mucociliary apparatus, thus decreasing
the rate of removal of toxic chemicals from the lung.
Many occupational activities cause the formation of dust. Mining, metal
grinding, and sand blasting have been shown to cause pneumonoconiosis, a
disease of the lung caused by habitual inhalation of irritant mineral or metallic
particles. The disease is characterized by fibrous degeneration known as
fibrosis. Several factors contribute to the development of pneumonoconiosis,
and those related to workers and to dust are particularly important. The
factors pertaining to workers include duration of exposure to dust and the
susceptibility of individual workers. The size of particles, their chemical
composition, and their concentrations are also important. Researchers have
identified various specific diseases, based on the chemical elements involved in
fibrosis formation. For example, silicosis results from inhalation of silicon
oxide (SiO 2 ); silicatosis, from silicate; siderosis, from hematite (Fe 2 O 3 ); talcosis,
from talc (Mg 3 Si 4 O 10 (OH) 2 ); and bariosis, from barium (Ba).
The size of particles is very important in the pathogenesis of pneumonoconiosis. This is because the size affects the concentration of particles that may
Air Pollution – Particulate Matter
137
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-009.3d]
Ref: 4365 MING-HO YU Chap-009 Page: 137 135-148
substances, several kinds of lead halides. Tetraethyl lead (Pb(C 2 H 5 ) 4 in leaded
gasoline reacts with molecular oxygen (O 2 ) and halogenated scavengers, such
as dichloroethane and dibromoethane, producing various forms of lead halide
particles that are emitted into the atmosphere:
PbðC 2 H 5 Þ 4 þ O 2 þ ðhalogenated scavengersÞ ! CO 2 þ H 2 O
þ PbCl 2 þ PbBrCl þ PbBr 2
ð9:5Þ
Additionally, whole gasoline vapor alone has been shown to contribute
significantly to atmospheric aerosol formation.
5
9.4 HEALTH EFFECTS
Fly-ash particles are generally composed of stable elements or compounds that
are usually not considered directly toxic in concentrations found in ambient
air. However, subtle toxicity has been recognized under some conditions. In
particular, many trace elements have important biological activity and are,
therefore, potential health hazards.
The toxicity of PM generally arises from any of the following factors. The
particles may themselves be toxic, e.g., particles containing toxic metals and
nonmetals, such as Pb, Cd, Ni, mercury (Hg), arsenic (As), and radionuclides
6, 7
Alternatively, the particles may adsorb toxic chemicals, such as carcinogens,
7,8
and enhance their effect by either increasing their penetration into the lungs, or
prolonging their residence time in the respiratory tract. Particles may also serve
as condensation nuclei for water and other vapors, producing droplets and
enhancing biological effects. Finally, if there are large quantities present in the
respired air, particles may overtax the mucociliary apparatus, thus decreasing
the rate of removal of toxic chemicals from the lung.
Many occupational activities cause the formation of dust. Mining, metal
grinding, and sand blasting have been shown to cause pneumonoconiosis, a
disease of the lung caused by habitual inhalation of irritant mineral or metallic
particles. The disease is characterized by fibrous degeneration known as
fibrosis. Several factors contribute to the development of pneumonoconiosis,
and those related to workers and to dust are particularly important. The
factors pertaining to workers include duration of exposure to dust and the
susceptibility of individual workers. The size of particles, their chemical
composition, and their concentrations are also important. Researchers have
identified various specific diseases, based on the chemical elements involved in
fibrosis formation. For example, silicosis results from inhalation of silicon
oxide (SiO 2 ); silicatosis, from silicate; siderosis, from hematite (Fe 2 O 3 ); talcosis,
from talc (Mg 3 Si 4 O 10 (OH) 2 ); and bariosis, from barium (Ba).
The size of particles is very important in the pathogenesis of pneumonoconiosis. This is because the size affects the concentration of particles that may
Air Pollution – Particulate Matter
137
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-009.3d]
Ref: 4365 MING-HO YU Chap-009 Page: 137 135-148