received application of contaminated sewage sludge, can absorb toxicants
through the roots. In the contaminated sites, high levels of heavy metals, such
as lead (Pb) and cadmium (Cd), often occur. Metallic ions are more readily
released, and thus more readily absorbed, when the soil is acidified by acid
deposition (Figure 4.1).
4.2.3 TRANSPORT
Following uptake, a toxicant may undergo mixing with the surrounding
medium of the plant, and then be transported to various organs and tissues.
Mixing involves the microscopic movement of molecules and is accompanied
by compensation of concentration differences. Generally, transport of
chemicals in plants occurs passively by diffusion and flux. Diffusion refers to
movement across phase boundaries, from a high-concentration compartment
to a low-concentration compartment. Flux, on the other hand, is due to the
horizontal movement of the medium.
4.2.4 PLANT INJURY
Besides destroying and killing plants, air pollutants can induce adverse effects
on plants in various ways. As noted previously, pollution injury is commonly
divided into acute and chronic injury. In plants, an acute injury occurs
following absorption of sufficient amounts of toxic gas or other forms of
toxicants to cause destruction of tissues. The destruction is often manifested
by collapsed leaf margins or other areas, exhibiting an initial water-soaked
appearance. Subsequently, the leaf becomes dry and bleaches to an ivory
Toxic Action of Pollutants
47
[16:54 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-004.3d]
Ref: 4365 MING-HO YU Chap-004 Page: 47 45-64
FIGURE 4.2 Cross section of a leaf, showing the air spaces which serve as passages for
pollutants.
through the roots. In the contaminated sites, high levels of heavy metals, such
as lead (Pb) and cadmium (Cd), often occur. Metallic ions are more readily
released, and thus more readily absorbed, when the soil is acidified by acid
deposition (Figure 4.1).
4.2.3 TRANSPORT
Following uptake, a toxicant may undergo mixing with the surrounding
medium of the plant, and then be transported to various organs and tissues.
Mixing involves the microscopic movement of molecules and is accompanied
by compensation of concentration differences. Generally, transport of
chemicals in plants occurs passively by diffusion and flux. Diffusion refers to
movement across phase boundaries, from a high-concentration compartment
to a low-concentration compartment. Flux, on the other hand, is due to the
horizontal movement of the medium.
4.2.4 PLANT INJURY
Besides destroying and killing plants, air pollutants can induce adverse effects
on plants in various ways. As noted previously, pollution injury is commonly
divided into acute and chronic injury. In plants, an acute injury occurs
following absorption of sufficient amounts of toxic gas or other forms of
toxicants to cause destruction of tissues. The destruction is often manifested
by collapsed leaf margins or other areas, exhibiting an initial water-soaked
appearance. Subsequently, the leaf becomes dry and bleaches to an ivory
Toxic Action of Pollutants
47
[16:54 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-004.3d]
Ref: 4365 MING-HO YU Chap-004 Page: 47 45-64
FIGURE 4.2 Cross section of a leaf, showing the air spaces which serve as passages for
pollutants.