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




May 26, 2008


Filed under: Environment — gargpk @ 1:32 pm
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Most of the algae are aquatic and are found in fresh water or marine habitat. Therefore, they are related with different aspects of fresh-water or marine pollution.

Algae as water pollutants

During the favourable season of algal growth, water bodies like lakes, ponds and rivers show so much growth of various species of blue-green algae, green algae and golden brown algae that the water becomes turbid, cloudy and yellowish/greenish in colour. Filamentous planktonic algae form thick floating mats on the water surface. Such excessive algal growth is called water bloom. This bloom cuts off the light to deeper layers of water body and thus inhibits decomposition of organic matter in that water body. The algae further add a large amount of organic matter after death and decay to the water body which is not decomposed quickly due to prevailing conditions in that water body. This causes serious water pollution.

Many algae like Microcystis, Aphanizomenon produce toxic substances that are harmful to fishes and aquatic animals. These toxins also harm the land animals drinking this polluted water.

In general, water blooms make water oily, unpleasant in smell, fishy in taste and unfit for drinking.

Many species of blue-green and green algae that form excessive growths also choke the water tanks, pipe lines and other associated installations causing undesirable problems.

Algae as pollution indicators

Analysis of the composition and growth pattern of the algal flora in a water body can be used to identify the type and level of water pollution. Such studies of algal flora have been used in identification of following types of water pollution problems:

  1. Water acidity: Increase in the acidity of water initially causes general increase in filamentous algae. However, high levels of water acidity due to pollution by acid forming chemicals or acid rains results in decrease in planktonic algae in the water body. Most algae and diatoms disappear completely in water below the pH 5.8.
  2. Diatoms are highly sensitive to pH and different species of diatoms are found at different pH values of water body. Thus changes in the species composition of diatoms very accurately indicates the pH level of the water body.
  3. Sewage, organic matter and chemical fertilizers: Increase in the organic matter or chemical fertilizers that are washed off into the water body results in increased nutrient supply for algal growth. Such a condition of increased nutrient supply is termed eutrophication and results in water blooms of various types of algae. The water blooms of planktonic algae like Microcystis, Scendensmus, Hydrodictyon and Chlorella indicate pollution of water body due to excessive addition of organic matter, nitrates or phosphates.
  4. Heavy metals: Some algae like Cladophora and Stigeoclonium absorb and accumulate many heavy metals from the water. Thus the excessive growth of these algae in the water indicates pollution due to heavy metals.
  5. Oil pollution: Excessive growth of algae like Duniella tertiolacta, Skeletonema costatum, Cricosphaera carterae, Amphidium carterae, Cyclotella cryptica and Pavlova lutheri indicate oil pollution of water bodies.

Algae in pollution control

Algae like Chlorella, Chlamydomonas, Scendensmus and Spirullina are grown in sewage treatment plants along with suitable bacteria (algal-bacterial systems). Organic sewage degraded by bacteria is used up by algae in their photosynthesis and growth. The abundant algal growth the treatment plant is periodically removed and used as animal feed or source of protein. The polluted water is thus cleaned by the combined action of bacteria and algae.

For the treatment of water containing metals as pollutants, alage like Chlorella are cultured in the polluted water. These algae absorb the metals from the water. The algal growth is periodically removed and destroyed.