In every sphere of human endeavour, the use of biological indicators provides an elegant device, as they do not disrupt the stability of natural ecosystems
CAN one think of a pollutant indicator
growing for years in his backyard? Not
really. Today, hi-tech equipments and
systems are much in demand. But plants
like tulsi, neern and peepal have been in
use for ages. Have we ever tried to analyse
the rationale behind their contined use?
The reason probably is their ability to
withstand pollution. For instance, the ber
plant which is known for its juicy fruits,
is much more than a mere thorny shrub.
Biological methods can be successfully
applied in predicting the impact of
human activities, particularly of pollutants, well in advance since they present
an effective and reliable method of
evaluating the effect of anthropogenic
substances on living organisms.
Bioindicators provide a practical
way of assessing the health of environment. A bioindicator actually indicates
the general toxicity of the environment,
without pointing out the exact physical
or chemical factors responsible for this
toxicity. There are a variety of biological
systems used as indicators of harmful
anthropogenic subs4nces. Plants can be
successfully employed to indicate different levels of sensitivity and assess and
predict environmental changes in a
timely manner. Such plants are called
'plant indicators'. Each response of
these indicators is the effect of some factors or factor complex acting as a cause
and is, therefore, the indication of this
factor. It is thus evident that every plant
is a product of the conditions under
which it grows and is therefore, a measurement of environment. Dominant
species in an area are most important
indicators, as they receive the full
impact of the habitat over long periods.
Various groups of higher plants serve
as bioindicators. Sensitive species are
employed to detect and monitor specific
air pollutants. Tolerant (indicator) species are used to determine
the incidence of particular
soil conditions. Others
can be used to detect and
monitor gaseous (sulphur
dioxide, ozone, nitrogen
oxides) as well as heavy
metal pollutants like zinc,
calcium and cadmium.
The zinc tolerance by
the Anthoxanthum species, copper tolerance by
Agrostis sp, lead tolerance
by Festuca sp and cadmium tolerance by Impatiens SP deserve mention.
Some common plants
like neem, peepal, dalbergia, bouganvillae and
ber are all pollution
tolerant. These plants
thrive well even in highly
polluted surroundings.
The plants are not
only indicators but also
act as scavengers. A wide
spectrum of phenotypic,
metabolic and anatomical changes in the plant system reflect
the nature of the pollutants to which the
plants are exposed. Silvery white spots
along with chlorosis and cupping of
leaves are damages caused by nitrogen
oxides; discoJouration, early senescence
and reduced yield are a result of sulphur
dioxide pollution; weathered flakes of
tobacco or chlorotic flakes of pine needles are examples of ozone damage; the
collapse, glazing and bronzing of leaf
cells are products of damage by peroxyacetyl nitrate.
Taking physiological and anatomical parameters into account inhibition of photosynthesis, malfunctioning of respiratory enzymes and encircled
necrotic regions on leaves are associated
with fluorine damage. Bleaching of
petals and stamen injury are indicators
of mercury poisoning. The nature of
stomata pigmentation, chlorosis and
bleaching are generalised effects.
Activities of several metabolites and
enzymes can be excellent indicators of
environmental effects.
Realising the importance of biological monitoring, the International
'Union of Biological Sciences has
decided to initiate a worldwide
Programme for identifying and applying biological indicators in environmental monitoring.
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