5.7 BIOLOGICAL FACTORS
5.7.1 PLANTS
Plants exhibit marked differences in their susceptibility to different pollutants.
Genetic variation is probably the most important factor affecting plant
response to environmental pollutants. Response varies between species of a
given genus and between varieties within a given species. Such variation is a
function of the influence genetic variability has on morphological, physiological, and biochemical characteristics of plants. For instance, gladiolus is
known to be extremely sensitive to fluoride, and different gladiolus varieties
show different responses to fluoride. The susceptibility of different species of
plants to different pollutants varies markedly. For example, DDT applied to
soil at a rate of 50 mg/g inhibited germination, seedling height, and fresh and
dry weight in oil seed plants, but had no effect on rice, barley, and mung bean
plants. In the oil seed plants, the DDT exposure caused a reduction in cell
number and length and inhibited ion uptake, especially potassium ions (K
þ )
and calcium ions (Ca
2þ ).
12
It has been shown that the sensitivity of two onion cultivars to O 3 is
controlled by a single gene pair. After exposure to O 3 the stomata of an O 3 -
resistant cultivar were found to be closed, with no appreciable injury, whereas
the stomata of O 3 -sensitive cultivar remained open, with obvious injury.
13 The
sensitivity of plants to air pollutants is also affected by leaf maturity. Generally,
young tissues are more sensitive to peroxyacyl nitrate (PAN) and hydrogen
sulfide (H 2 S), and maturing leaves are most sensitive to the other airborne
pollutants. According to Linzon,
7 in white pine the greatest chronic injury
occurred in second-year needles exposed to SO 2 .
5.7.2 ANIMALS AND HUMANS
Genetics, development, health status, gender, and behavior are among the
most important factors that affect the response of animals and humans to
pollutant toxicity.
5
5.7.2.1 Genetic Factors
Not all organisms, including humans, react in the same way to a given dose of
an environmental pollutant. In animal experiments, variation between species,
as well as variation between strains within the same species, occurs. As shown
in Table 5.2, the toxicity of the insecticides DDT and dieldrin differs markedly
for different species. Substantial epidemiological data exist to illustrate that the
interplay between environmental and genetic factors in the development of
congenital malformations is significant. In animals, for example, it has often
been shown that the rates of congenital anomalies differ between different
strains of mice in response to the same dose of a teratogen.
14
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Environmental Toxicology
[16:54 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-005.3d]
Ref: 4365 MING-HO YU Chap-005 Page: 70 65-84
5.7.1 PLANTS
Plants exhibit marked differences in their susceptibility to different pollutants.
Genetic variation is probably the most important factor affecting plant
response to environmental pollutants. Response varies between species of a
given genus and between varieties within a given species. Such variation is a
function of the influence genetic variability has on morphological, physiological, and biochemical characteristics of plants. For instance, gladiolus is
known to be extremely sensitive to fluoride, and different gladiolus varieties
show different responses to fluoride. The susceptibility of different species of
plants to different pollutants varies markedly. For example, DDT applied to
soil at a rate of 50 mg/g inhibited germination, seedling height, and fresh and
dry weight in oil seed plants, but had no effect on rice, barley, and mung bean
plants. In the oil seed plants, the DDT exposure caused a reduction in cell
number and length and inhibited ion uptake, especially potassium ions (K
þ )
and calcium ions (Ca
2þ ).
12
It has been shown that the sensitivity of two onion cultivars to O 3 is
controlled by a single gene pair. After exposure to O 3 the stomata of an O 3 -
resistant cultivar were found to be closed, with no appreciable injury, whereas
the stomata of O 3 -sensitive cultivar remained open, with obvious injury.
13 The
sensitivity of plants to air pollutants is also affected by leaf maturity. Generally,
young tissues are more sensitive to peroxyacyl nitrate (PAN) and hydrogen
sulfide (H 2 S), and maturing leaves are most sensitive to the other airborne
pollutants. According to Linzon,
7 in white pine the greatest chronic injury
occurred in second-year needles exposed to SO 2 .
5.7.2 ANIMALS AND HUMANS
Genetics, development, health status, gender, and behavior are among the
most important factors that affect the response of animals and humans to
pollutant toxicity.
5
5.7.2.1 Genetic Factors
Not all organisms, including humans, react in the same way to a given dose of
an environmental pollutant. In animal experiments, variation between species,
as well as variation between strains within the same species, occurs. As shown
in Table 5.2, the toxicity of the insecticides DDT and dieldrin differs markedly
for different species. Substantial epidemiological data exist to illustrate that the
interplay between environmental and genetic factors in the development of
congenital malformations is significant. In animals, for example, it has often
been shown that the rates of congenital anomalies differ between different
strains of mice in response to the same dose of a teratogen.
14
70
Environmental Toxicology
[16:54 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-005.3d]
Ref: 4365 MING-HO YU Chap-005 Page: 70 65-84