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

Published: Tuesday 31 December 1996

The neem: one of our reliable< (Credit: Amit Shanker / CSE)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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