Bio-indicators: Crucial for maintaining environment


Dr Rakesh Kumar Gupta

In developed as well as developing countries like India, U.S.A, China, etc, there is a remarkable progress at rapid pace that can be seen in every aspect of life; however, simultaneously it also cost degradation in the quality of environment. The cost of factories has been paid by air, water as well as soil that directly or indirectly are affecting all living organisms including human beings. Therefore, there is an intense need to monitor the quality of environment and raise the prevention of polluted environment. Now a day different scientific methods are available to detect any change in the quality of surroundings, however, most of these are either not commercially available and if so then are too expensive to be used by common people. Apart from scientific equipment, nature has tendency to call for its protection by bestowing us a unique way to access not only the changes (if any) in the environment but sometime helps to identify those environmental factor that has undergone marked change. This natural call is called as ‘Biological indicators’ or ‘Bio-indicator’. Bio-indicators are organisms (such as lichens, birds and bacteria etc,) that are used to monitor the health of the environment. Some organisms are very sensitive to pollution in their environment, so if pollutants are present, they may either change its morphology, physiology, behaviour, or could even die. The organisms or organism associations therefore are monitored for changes within their ecosystem. There is difference between Bio-monitoring and Bio-indicators. Bio-indicators qualitatively assesses biotic responses to environmental stress (e.g., presence of the lichen, Lecanora conizaeoides, indicates poor air quality) while biomonitors quantitatively determine a response (e.g., reductions in lichen chlorophyll content or diversity indicates the presence and severity of air pollution). There are three main functions of bio-indicators: 1. to monitor the environment (i.e., physical and/or chemical changes), 2. to monitor ecological processes, or 3 to monitor biodiversity.

  1. Based on IUCBS Bio-indicators are of following types:
    1.Microbial indicators: Micro-organisms play an important role for the assessment of surrounding environment. They can be used as indicators of aquatic as well as terrestrial ecosystem health. The bacterial species that have been used as indicators in monitoring environmental quality are Coliform, E.coli, Streptococcus sp., Pseudomonas sp., Vibrio sp., Clostridia sp., Bifidobacterium pseudolongum, Arcobacter sp., Thiobacillus sp., etc. These bacteria can act as indicators of household waste (human and animal feces, household waste and other), heavy metal pollution or crude oils and other types of pollution:
    i. Heavy metal pollution indicators: There are many strains of bacteria whose mere presence indicates heavy metal pollution. E.g. (a) Thiobacillus sp bacteria is a pollution indicator of mercury in marine environment. (b) Pseudomonas sp also acts as indicator of mercury pollution. (c) Serrata marcoscens indicates presence of cadmium and lead.
    ii. Faecal contamination indicator: Presence of (a) Coliform bacteria such as Streptococcus sp., Vibrio sp, E. coli, Clostridia sp., Bifidobacterium sp., Arcobacter burzleri, A. Skirrowii etc. indicates the human faecal contamination in water bodies. E.g. (a) Streptococcus sp. act as an indicator of faecal pollution in water bodies such as lakes, rivers, estuarine etc. (b) Vibrio sp is an indicator of faecal pollution in water bodies.
    iii. Waste water pollution: Presence of some bacterial strains such as Streptococcus sp, Pseudomonas aeruginosa and Salmonella sp clearly indicates the household waste water pollution.
    iv. Oil pollution indicators: Chromatium sp act as bio-indicator of environment pollution cause by crude oil.
  2. Plants as Bio-indicators: Due to industrialization and urbanization, the problem of contamination of water and water pollution has intensified. Plants are immobile and rapidly obtain equilibrium with their natural surroundings therefore provide valuable information to predict the status of aquatic environment. Some of the plants that indicate specific environmental pollution are:
    (a) Plants such as Petunia, Pinto Bean, Green Bean, Tobacco, White pine, Watermelon etc indicate ozone pollution in environment.
    (b) Annual weeds and short lived perennials like Amaranthus, Chenopodium and Polygonum etc. grow better in overgrazed areas. They are the indicators of overgrazing.
    (c) Abundance of Eichhornia indicates sewage and heavy metal pollution of water.
    (d) Decrease in the populations of mosses (Sphagnum, Bryum) and lichens (Parmelia) generally indicates air pollution by SO2, NO2, fluorides and HCl.
    (e) Equisetum sp. indicates presence of gold in soil.
    (d) Absence of some of bryophytes such as Sphagnum and Bryum indicates atmospheric SO2 pollution.
    (e) Lichens (symbiotic association of an algae and a fungus) grow together, are indicators of pollution cause by sulphur dioxide. Usually Leafy lichens tolerate some air pollution and crusty lichens can survive with higher levels of pollutants, however, if no lichens are present, it usually indicates heavy air pollution.
    (f) Scenedesmus obliguos: Colonies of Scenedesmus obliguos were used for determining cadmium and lead pollution in river basin in Thailand and Federal Republic of Germany.
  3. Planktons: Planktons react rapidly to ecological changes and are viewed as excellent indicators of water quality and trophic conditions due to their short time and rapid rate of reproduction. The rate of reproduction in plankton increase many fold in water body having contaminated with phosphorous and Nitrogen, thereby indicates water pollution of these pollutants. Some planktons act as indicator of heavy metal pollution for example
    (a) Chlamydomonas reinhardtii was sensitive to cadmium, methyl mercury, and lead. (b) Trichotria indicates heavy metal as well as phosphorous pollution in lakes. (c) Cladocerans (Bosmina, Moina, and Daphnia) and copepods (Phyllodiaptomus and cylops) presence indicate polluted water body.
  4. Invertebrates: Invertebrates fauna inhabit soil as well as water bodies and play an important role in food chain by converting soil into fertile cast, feeding on dead decay organisms, on protozoans, and eaten by higher trophic level organisms. Due to dumping of waste in soil as well as water bodies, both terrestrial and aquatic life has been threaten to marked level. These organisms survive in optimal environmental conditions and any remarkable changes in surrounding threaten their life and thereby clearly indicate the level of damage done to terrestrial or aquatic habitat. For example (a) Earthworm: The density and biomass of earthworm is influence by heavy metals therefore acted as indicator of heavy metal pollution.
    (b) Orders Ephemoptera: This include Mayflies, stoneflies and Caddisflies etc and are all pollution sensitive taxa. They are well known worldwide for their sensitivity to decreasing depletion of dissolved oxygen and therefore indicate water pollution.
    (c) Chirnomid larvae: Presence of Chironomid larvae indicates the aquatic pollution and water unfit for use.
    (d) Honey bee: Decrease in honey bee population depicts presence of toxic molecules in environment.
    (e) Collembolan: Their population exhibits dramatic reduction in population in soil acidified by chemical fertilizers or pesticides, thereby indicates soil pollution.
  5. Fishes: Fishes are on the most dominant vertebrates in water bodies. Some fishes are pollution tolerant while other confine to very narrow range of environmental conditions. Some of the important fishes that act as biological indicators are as:
    (a) Acipenser: A highly migratory species, the decline of the Lake Sturgeon has been attributed to the widespread damming of rivers, pollution, siltation, and overfishing.
    (b) Garra sp and Labeo sp: Besides many species that indicates heavy metal pollution Garra and Labeo hold its important value. Presence of heavy metal leads to degeneration of their gills, remarkable change in morphology as well as number of formed elements.
  6. Amphibians: Frogs are also Bio-indicators of quality of environment and changes in environment. Amphibians’ thin skins help them drink and breathe, but also make them susceptible to environmental contaminants, particularly agricultural, industrial, and pharmaceutical chemicals. For example Southern Leopard frog deformed limbs are formed in presence of methoprene pesticide in surrounding environment.
  7. Reptiles: Snakes and Snapping Turtle indicate Organichlorine pollution. They accumulate heavy metals in their body and die soon.
  8. Birds: Some of the important species of birds that indicate heavy metal pollution are: Pica pica, Columba livia, Passer domesticus, Turdus merula and Accipitter gentilis that indicate pollution cause by heavy metals such as Pb, Cd, As, Sb, Ge, Ti and Hg.
    Unlike mammals that can widely distributed and mostly adapt to different types of environment, some of organisms i.e. Bio-indicators are confine to optimal conditions and therefore represent the type of environment they inhabit. Their sudden appearance or disappearance clearly indicates the change in environmental factors and therefore the quality of air, water or soil thus act as natural call for revival of environment that otherwise might be prove harmful in future.
    (The author is Lecturer in Zoology at GHSS Ramgarh, 181141).