weight gains, loss of hair, nephrosis in kidneys, myocardial degeneration, and
accelerated aging.
Many studies have demonstrated the health effects of acidic aerosols on
laboratory animals. Changes in pulmonary function, particularly increases in
pulmonary flow resistance, occur after acute exposure. H 2 SO 4 is shown to be
more irritating than any of the sulfate salts in this regard. The irritant effect of
H 2 SO 4 depends in part on droplet size, smaller droplets being more effective.
13
For instance, animals exposed to 0.3 to 0.6 mm H 2 SO 4 droplets at various
concentrations showed either slowed or accelerated bronchial mucociliary
clearance function, depending on the concentration of the aerosol. Studies on
the comparative effects of exposure to H 2 SO 4 and ammonium bisulfate
(NH 4 HSO 4 ) showed alteration of phagocytic activity, with more pronounced
effect exhibited by H 2 SO 4 . Repeated exposures to H 2 SO 4 caused the
production of hyper-responsive airways in previously healthy animals. Such
exposure also resulted in histological changes, such as increased numbers of
secretory cells in distal airways and thickened epithelium in airways of
midsized bronchi and terminal bronchioles.
14
8.2.5 HEALTH EFFECTS
Epidemiological evidence from studies during the London smog episodes
suggests that effects of SO 2 may occur at or above 0.19 ppm (24-hour average),
in combination with elevated particulates levels. Short-term, reversible declines
in lung function may occur at SO 2 levels above 0.10 to 0.18 ppm. These effects
may be caused by SO 2 alone, or by formation of H 2 SO 4 or other irritant
aerosols. It appears more likely that the role of SO 2 involves transformation
products, such as acidic fine particles. H 2 SO 4 and sulfates have been shown to
influence both sensory and respiratory function, such as increased respiratory
rates and tidal volumes, and slowing of mucus clearance in humans.
15
The effect of SO 2 on human health varies markedly with the health status
and physical activity of individuals. For example, in asthmatics and others with
hyper-reactive airways exposed to SO 2 at 0.25 to 0.50 ppm and higher while
exercising, rapid bronchoconstriction (airway narrowing) was shown as the
most striking acute response. This is usually demonstrated by elevated airway
resistance, lowered expiratory flow rates, and the manifestation of symptoms
such as wheezing and shortness of breath. The time required for SO 2 exposure
to induce significant bronchoconstriction in exercising asthmatics is brief.
Exposure durations as short as 2 minutes at 1.0 ppm have produced significant
responses.
16 The combined effect of SO 2 and cold, dry air exacerbates the
asthmatic response.
17 The bronchoconstrictive effects of SO 2 are reduced under
warm, humid conditions.
18
Exposure to submicrometer-sized H 2 SO 4 aerosols increases tracheobronchial and alveolar rates of clearance in humans, the effects increasing with in
line with SO 2 concentration and duration. Although the altered clearance rates
may be an adaptive response of the mucociliary system to acid exposures, they
may also be early stages in the progression toward more serious dysfunctions,
116
Environmental Toxicology
[16:53 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-008.3d]
Ref: 4365 MING-HO YU Chap-008 Page: 116 111-134
accelerated aging.
Many studies have demonstrated the health effects of acidic aerosols on
laboratory animals. Changes in pulmonary function, particularly increases in
pulmonary flow resistance, occur after acute exposure. H 2 SO 4 is shown to be
more irritating than any of the sulfate salts in this regard. The irritant effect of
H 2 SO 4 depends in part on droplet size, smaller droplets being more effective.
13
For instance, animals exposed to 0.3 to 0.6 mm H 2 SO 4 droplets at various
concentrations showed either slowed or accelerated bronchial mucociliary
clearance function, depending on the concentration of the aerosol. Studies on
the comparative effects of exposure to H 2 SO 4 and ammonium bisulfate
(NH 4 HSO 4 ) showed alteration of phagocytic activity, with more pronounced
effect exhibited by H 2 SO 4 . Repeated exposures to H 2 SO 4 caused the
production of hyper-responsive airways in previously healthy animals. Such
exposure also resulted in histological changes, such as increased numbers of
secretory cells in distal airways and thickened epithelium in airways of
midsized bronchi and terminal bronchioles.
14
8.2.5 HEALTH EFFECTS
Epidemiological evidence from studies during the London smog episodes
suggests that effects of SO 2 may occur at or above 0.19 ppm (24-hour average),
in combination with elevated particulates levels. Short-term, reversible declines
in lung function may occur at SO 2 levels above 0.10 to 0.18 ppm. These effects
may be caused by SO 2 alone, or by formation of H 2 SO 4 or other irritant
aerosols. It appears more likely that the role of SO 2 involves transformation
products, such as acidic fine particles. H 2 SO 4 and sulfates have been shown to
influence both sensory and respiratory function, such as increased respiratory
rates and tidal volumes, and slowing of mucus clearance in humans.
15
The effect of SO 2 on human health varies markedly with the health status
and physical activity of individuals. For example, in asthmatics and others with
hyper-reactive airways exposed to SO 2 at 0.25 to 0.50 ppm and higher while
exercising, rapid bronchoconstriction (airway narrowing) was shown as the
most striking acute response. This is usually demonstrated by elevated airway
resistance, lowered expiratory flow rates, and the manifestation of symptoms
such as wheezing and shortness of breath. The time required for SO 2 exposure
to induce significant bronchoconstriction in exercising asthmatics is brief.
Exposure durations as short as 2 minutes at 1.0 ppm have produced significant
responses.
16 The combined effect of SO 2 and cold, dry air exacerbates the
asthmatic response.
17 The bronchoconstrictive effects of SO 2 are reduced under
warm, humid conditions.
18
Exposure to submicrometer-sized H 2 SO 4 aerosols increases tracheobronchial and alveolar rates of clearance in humans, the effects increasing with in
line with SO 2 concentration and duration. Although the altered clearance rates
may be an adaptive response of the mucociliary system to acid exposures, they
may also be early stages in the progression toward more serious dysfunctions,
116
Environmental Toxicology
[16:53 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-008.3d]
Ref: 4365 MING-HO YU Chap-008 Page: 116 111-134