stimulate the oxidation of SO 2 . In the presence of SO 3
2À and HSO 3
À , more
O 2
Á À is formed by free-radical chain oxidation. Other free radicals may also be
formed. These oxidizing radicals can have detrimental effects on leaf cells.
Alternatively, SO 3
2À and SO 4
2À formed may be reduced and assimilated with a
carbon skeleton to cysteine.
6
Plant metabolism has been shown to be affected by SO 2 in a variety of
ways: stimulation of phosphorus (P) metabolism and reduction in foliar
chlorophyll concentration,
7 increase or decrease in carbohydrate concentrations in red kidney bean plants exposed to low or high levels of SO 2 ,
8 and
inhibition of lipid biosynthesis in pine needles treated with SO 2 .
9
Malhotra and Khan
9 found that pine-needle tissues, particularly the
developing tissues, actively incorporate acetate [114 C] into phosphogalactoand neutral lipids. The major incorporation of the label among these lipids was
always in the phosphatidyl choline fraction. Treatment of needle tissues with
gaseous or aqueous SO 2 markedly inhibited lipid biosynthesis. A partial or
complete recovery in lipid biosynthesis capacity occurred when plants were
removed from the SO 2 environment.
SO 2 has been shown to affect a number of enzyme systems in different plant
species. Enzymes studied include alanine and aspartate aminotransferases,
glutamate dehydrogenase, malate dehydrogenase, glycolate oxidase, glyceraldehyde-3-phosphate dehydrogenase, glucose-6-phosphate dehydrogenase,
fructose-1,6-bisphosphatase, ribulose-5-phosphate kinase, peroxidase, and
superoxide dismutase (SOD). Enzyme activity may be enhanced or depressed
by exposure to SO 2 at different concentrations. With Chinese guger-tree
seedlings exposed to 325 ppb of SO 2 , for example, peroxidase activity increased
significantly, while SOD activity was unaffected.
4
It is widely known that differences in tolerance of plant species to SO 2 occur
under similar biophysical conditions. This suggests that delicate biochemical
and physiological differences in plants could affect the sensitivity of a particular
plant species to SO 2 .
8.2.4 EFFECTS ON ANIMALS
Although SO 2 is an irritating gas for the eyes and upper respiratory tract, no
major injury from exposure to any reasonable concentrations of this gas has
been demonstrated in animal experiments. Even exposure to pure gaseous SO 2
at concentrations 50 or more times ambient values produced little distress.
10,11
Concentrations of 100 or more times ambient are required to kill small
animals. Mortality is associated with lung congestion and hemorrhage,
pulmonary edema, thickening of the interalveolar septa, and other relatively
nonspecific changes of the lungs, such as pulmonary hemorrhage and
hyperinflation. These changes were associated with salivation, lacrimation,
and rapid, shallow ventilation. Mice exposed to 10 ppm SO 2 for 72 hours
showed necrosis and sloughing of the nasal epithelium.
12 The lesions were more
severe in animals with preexisting infection. Other symptoms include decreased
Air Pollution – Inorganic Gases
115
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Ref: 4365 MING-HO YU Chap-008 Page: 115 111-134
2À and HSO 3
À , more
O 2
Á À is formed by free-radical chain oxidation. Other free radicals may also be
formed. These oxidizing radicals can have detrimental effects on leaf cells.
Alternatively, SO 3
2À and SO 4
2À formed may be reduced and assimilated with a
carbon skeleton to cysteine.
6
Plant metabolism has been shown to be affected by SO 2 in a variety of
ways: stimulation of phosphorus (P) metabolism and reduction in foliar
chlorophyll concentration,
7 increase or decrease in carbohydrate concentrations in red kidney bean plants exposed to low or high levels of SO 2 ,
8 and
inhibition of lipid biosynthesis in pine needles treated with SO 2 .
9
Malhotra and Khan
9 found that pine-needle tissues, particularly the
developing tissues, actively incorporate acetate [114 C] into phosphogalactoand neutral lipids. The major incorporation of the label among these lipids was
always in the phosphatidyl choline fraction. Treatment of needle tissues with
gaseous or aqueous SO 2 markedly inhibited lipid biosynthesis. A partial or
complete recovery in lipid biosynthesis capacity occurred when plants were
removed from the SO 2 environment.
SO 2 has been shown to affect a number of enzyme systems in different plant
species. Enzymes studied include alanine and aspartate aminotransferases,
glutamate dehydrogenase, malate dehydrogenase, glycolate oxidase, glyceraldehyde-3-phosphate dehydrogenase, glucose-6-phosphate dehydrogenase,
fructose-1,6-bisphosphatase, ribulose-5-phosphate kinase, peroxidase, and
superoxide dismutase (SOD). Enzyme activity may be enhanced or depressed
by exposure to SO 2 at different concentrations. With Chinese guger-tree
seedlings exposed to 325 ppb of SO 2 , for example, peroxidase activity increased
significantly, while SOD activity was unaffected.
4
It is widely known that differences in tolerance of plant species to SO 2 occur
under similar biophysical conditions. This suggests that delicate biochemical
and physiological differences in plants could affect the sensitivity of a particular
plant species to SO 2 .
8.2.4 EFFECTS ON ANIMALS
Although SO 2 is an irritating gas for the eyes and upper respiratory tract, no
major injury from exposure to any reasonable concentrations of this gas has
been demonstrated in animal experiments. Even exposure to pure gaseous SO 2
at concentrations 50 or more times ambient values produced little distress.
10,11
Concentrations of 100 or more times ambient are required to kill small
animals. Mortality is associated with lung congestion and hemorrhage,
pulmonary edema, thickening of the interalveolar septa, and other relatively
nonspecific changes of the lungs, such as pulmonary hemorrhage and
hyperinflation. These changes were associated with salivation, lacrimation,
and rapid, shallow ventilation. Mice exposed to 10 ppm SO 2 for 72 hours
showed necrosis and sloughing of the nasal epithelium.
12 The lesions were more
severe in animals with preexisting infection. Other symptoms include decreased
Air Pollution – Inorganic Gases
115
[16:53 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-008.3d]
Ref: 4365 MING-HO YU Chap-008 Page: 115 111-134