Environment of Earth

August 4, 2008


Filed under: Environment — gargpk @ 1:03 pm
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Plants can effectively be used as cheap and naturally available monitoring systems or bioassays of the level and type of air, soil and water pollution in an area. The type and concentration of a pollutant can be reliably found out by various characteristics damage symptoms produced in the plants because such damage symptoms are pollutant specific as well as concentration specific. For example, in young needles of Pinus, chlorois indicates SO2 pollution, necrosis indicates HF pollution, beaching indicates NO2 pollution while chlorotic mottle indicates Cl2 pollution in the atmosphere. These characteristic symptoms of damage in young pine needles appear only when concentration is 0.3 ppm for SO2, 0.07 ppm for HF and 1.0 ppm for Cl2. Similarly, browning in moss leaves due to fluoride accumulation is 5% in 65 ppm dry weight accumulation but rises to 90% in 4500 ppm dry weight accumulation. However, certain precautions have to be taken while using plants as pollution indicators.

Precautions in use of plants as pollution indicators

  1. The damage symptoms in plants should preferably be studied in the local native species. Cultivated and introduced species should be avoided.

  2. The species sensitive to pollutants should be first identified in the local flora and then used for pollution monitoring. Tolerant species should be identified and avoided in such work.

  3. Damage symptoms for a particular pollutant should be studied in different species sensitive to that pollutant so that presence of the pollutant in the area may be cross-checked. For example, grey necrosis in Geranium, ivory necrosis in Zinnia, brown necrosis in Chrysanthemum and reddish necrosis in Azalea indicates absolutely certain presence of SO2 pollution in the area.

  4. Many types of damage symptoms viz. morphological, anatomical, ultra-structural physiological, biochemical etc. should be studied in one or more sensitive plant species to ascertain the presence of a particular pollutant in the area.

  5. Samples should be taken from as many different sites in the area as possible. From such data the extent of pollution can be determined and the possibility of symptoms being due to some pathogen is also excluded because the intensity of damage symptoms due to pollution varies in different sites according to the distance from the source of pollution while it is same in all sites in case of a pathogenic disease.

  6. The possibility of damage symptoms in plants occurring due to some cause other than pollution e.g. due to pathogen, environmental condition or nutritional deficiency/excess should be thoroughly checked and ruled out.

Important characteristics of plant species used in pollution monitoring

The plant species used to monitor pollution in an area should have certain important features for the success of such programme. Most important such features are:

  1. Species should be easy to identify in the field and easy to handle for damage analysis.

  2. Species should have a wide range of distribution so that it can be used in different areas.

  3. Species should be sensitive to many types of pollutants so that it can be used to monitor different types of pollutants in the area.

  4. Species should produce highly specific damage symptoms in response to particular types and concentrations of pollutants.

Plants commonly used as pollution indicators

Though all types of sensitive species can be used in monitoring pollution, most useful and commonly used plants include sensitive species of lichens, mosses, plankton algae, aquatic ferns and angiosperms, other ferns, conifers oaks and many crop plants. Mosses, lichens, ferns algae and aquatic plants are generally more useful in pollution monitoring because their range of pollutant specificity is usually much higher than that of higher vascular plants. Examples of some common types of plants useful as pollution monitors are given below.

Plant type