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Caddisfly (order Trichoptera), a macroinvertebrate used as an indicator of water quality.

Bio indicators are species that can be used to monitor the health of an environment or ecosystem. They are any biological species or group of species whose function, population, or status can reveal what degree of ecosystem or environmental integrity is present. One example of a group of bio indicators are the copepods and other small water crustaceans that are present in many water bodies. Such organisms can be monitored for changes (biochemical, physiological, or behavioural) that may indicate a problem within their ecosystem. Bio indicators can tell us about the cumulative effects jjuxferent pollutants in the ecosystem and about how long a problem may have been present, which physical and chemical testing cannot.[1]

A biological monitor, or biomonitor, can be defined as an organism that provides quantitative information on the quality of the environment around it. Therefore, a good biomonitor will indicate the presence of the pollutant and also attempt to provide additional information about the amount and intensity of the exposure.


A bio indicator is an organism or biological response that reveals the presence of the pollutants by the occurrence of typical symptoms or measurable responses, and is therefore more qualitative. These organisms (or communities of organisms) deliver information on alterations in the environment or the quantity of environmental pollutants by changing in one of the following ways: physiologically, chemically or behaviourally. The information can be deduced through the study of:

  1. their content of certain elements or compounds
  2. their morphological or cellular structure
  3. metabolic-biochemical processes
  4. behaviour, or
  5. population structure(s).

The importance and relevance of biomonitors, rather than man-made equipment, is justified by the statement: "There is no better indicator of the status of a species or a system than a species or system itself."[2]:74

The use of a biomonitor is described as biological monitoring (abbr. biomonitoring) and is the use of the properties of an organism to obtain information on certain aspects of the biosphere. Biomonitoring of air pollutants can be passive or active. Passive methods observe plants growing naturally within the area of interest. Active methods detect the presence of air pollutants by placing test plants of known response and genotype into the study area.

Bioaccumulative indicators are frequently regarded as biomonitors.

Depending on the organism selected and their use, there are several types of bioindicators.[3][4]

Plant indicators[edit]

Main article: Indicator plant

The presence or absence of certain plant or other vegetative life in an ecosystem can provide important clues about the health of the environment: environmental preservation.

There are several types of plant biomonitors, including mosses, lichens, tree bark, bark pockets, tree rings, leaves, and fungi.

  • Lichens are organisms comprising both fungi and algae. They are found on rocks and tree trunks, and they respond to environmental changes in forests, including changes in forest structure – conservation biology, air quality, and climate. The disappearance of lichens in a forest may indicate environmental stresses, such as high levels of sulfur dioxide, sulfur-based pollutants, and nitrogen oxides.
  • The composition and total biomass of algal species in aquatic systems serves as an important metric for organic water pollution and nutrient loading such as nitrogen and phosphorus.

There are genetically engineered organisms, that help us indicate toxicity levels in the environment; e.g., a type of genetically engineered grass that grows a different colour if there are toxins in the soil.

Animal indicators and toxins[edit]

An increase or decrease in an animal population may indicate damage to the ecosystem caused by pollution.[5] For example, if pollution causes the depletion of important food sources, animal species dependent upon these food sources will also be reduced in number: population decline. Overpopulation can be the result of opportunistic species growth. In addition to monitoring the size and number of certain species, other mechanisms of animal indication include monitoring the concentration of toxins in animal tissues, or monitoring the rate at which deformities arise in animal populations, or their behavior either directly in the field or in a lab.[6]

Microbial indicators and chemical pollutants[edit]

Microorganisms can be used as indicators of aquatic or terrestrial ecosystem health. Found in large quantities, microorganisms are easier to sample than other organisms. Some microorganisms will produce new proteins, called stress proteins, when exposed to contaminants like cadmium and benzene. These stress proteins can be used as an early warning system to detect high levels of pollution.

Microbial indicators in oil and gas exploration[edit]

Microbial Prospecting for Oil and Gas (MPOG) is often used in frontier basins to identify prospective areas for oil and gas occurrences. In many cases oil and gas is known to seep toward the surface as a hydrocarbon reservoir will usually leak or have leaked towards the surface through buoyancy forces overcoming sealing pressures. These hydrocarbons can alter the chemical and microbial occurrences found in the near surface soils or can be picked up directly. Techniques used for MPOG include DNA analysis, simple bug counts after culturing a soil sample in a hydrocarbon based medium or by looking at the consumption of hydrocarbon gases in a culture cell.[7]

Microalgae as bioindicators for water quality[edit]

Within the different organisms that can be used as models for bioassays, microalgae have gained a lot of attention in the last years due to several reasons:

  • Abundantly occurring organisms
  • Play a vital role in the food web of aquatic systems
  • Higher sensitivity than invertebrates and fish
  • Easy to perform: not difficult to perform cultures, do not demand a lot of area for algae growth, easy to handle when comparing ecotoxicological assays with invertebrates or fish
  • Ethical reasons: it avoid the use of experimental animals like rats and rabbits.

Euglena gracilis is a freshwater photosynthetic flagellate of the phylum Euglenozoa, with 35-55 μm long and 6-25 μm wide. It moves thanks to its single flagellum, inserted at the front end of the cell. Although Euglena is rather tolerant to acidity, it responds rapidly and sensitively to environmental stressors like heavy metals or inorganic and organic compounds. Typical responses are the inhibition of movement and the change of orientation parameters. Moreover, this organism is very easy to handle and grows, making it a very useful tool for ecotoxicological assessments. One very useful particularity of this organism is the gravitactic orientation, which is very sensitive to pollutants.

Gravitactic mechanism of the microalgae Euglena gracilis (A) in the absence and (B) in the presence of pollutants.

Euglena gracilis orients itself in the water column thanks to phototaxis and gravitaxis. In the dark, the cells move mostly against the gravity vector, in other words upward, through an active mechanism. Since the cell body has a higher density than the surrounding medium the cell content accumulates downward (1) and leads to the stretching of the plasma membrane (2). This provokes the activation of mecanosensitive ion channels, also called gravireceptors (3), which will modify the membrane potential, causing a short hyperpolarization followed by a depolarization (4). This process leads to the reorientation of the cell by the mean of the altered flagellum’s movement (5). (See Gravitactic mechanism figure) The gravireceptors are impaired by pollutants like heavy metals and organic or inorganic compounds. Therefore the presence of such substances is associated with random movement of the cells in the water column. For short term tests, gravitactic orientation of E. gracilis is very sensitive.[8][9] Other species like Paramecium biaurelia (see Paramecium aurelia) also use gravitactic orientation.[10]

ECOTOX is an automatic bioassay device used to test the quality of water samples, by the detection of toxic chemicals.[11] It is composed of a compact size hardware containing a miniaturized microscope linked to a camera, the observation cuvette, pumps to mix the water samples with the microalgae; everything being connected to a computer equipped with software. One of the biggest advantages of this device is the automated measurements and analysis, which reduces the risks of personal error. Moreover, it is easy to use, quite cheap and fast: only 10 min are necessary to test a watersample and the corresponding control. Examples of use are the test of seepage water or the determination of the efficiency of purification systems by testing treated waste water before and after purification.[11] The determination of the samples quality is realized using several parameters related to the movement of the microalgae. All measurements are made automatically with real time image analysis. First the orientation behavior of the cells is determined using two parameters: the percentage of cells moving upwards giving the direction of the movement and the r-value indicating the precision of the gravitactic orientation which varies from a random movement (r-value=0) to a single direction (r-value=1). Other important parameters are the velocity, the cell motility which represents the percentage of cells moving faster than the minimum velocity and the cell compactness giving information about the shape of the cell. All parameters are compared with a control sample of unpolluted tap water and the percentage of inhibition is calculated. An inhibition indicates the presence of a pollutant. Depending on the aim of the study, the EC50 (the concentration of sample which affects 50% of organisms) and the G-value (lowest dilution factor at which no-significant toxic affect can be measured), are calculated. From all those parameters, the gravitactic orientation represented with upward swimming and r-value is the most sensitive.[12]

In Pakistan, rivers receive directly wastewater from industries and domestic facilities, often without treatment. In 2011, Azizullah et al. investigated the effect of industrial and domestical wastewaters discharges in the Indus river (Pakistan).[13] The ecotoxicological effects of wastewater samples from 5 different sources were determined: two industrial water samples, one sample from the municipal effluent poured into the river, and also upstream and downstream samples from the discharge site in the Indus river. The aim of the study was to determine, with the help of ECOTOX, whether the discharge of wastewater in the river influences its quality. The most sensitive response was given by the r-value which was lower when regarding the downstream sample, than the upstream sample, showing the contamination of the Indus river by domestic and industrial wastewater. The impairment of the gravitactic orientation can be due to the presence of heavy metals found in the industrial wastewaters.

Macroinvertebrate bioindicators[edit]

Macroinvertebrates are useful and convenient indicators of the ecological health of a waterbody or river.[14] They are almost always present, and are easy to sample and identify. The sensitivity of the range of macroinvertebrates found will enable an objective judgement of the ecological condition to be made. Tolerance values are commonly used to assess water pollution.[15]

In Australia, the SIGNAL method has been developed and is used by researchers and community "Waterwatch" groups to monitor water health.[4]

In Europe, a new generation of remote online biomonitoring system was designed in 2006. It is based on bivalve molluscs and the exchange of real time data between a remote intelligent device in the field (able to work for more than 1 year without in-situ human intervention) and a data centre designed to capture, process and distribute on the web information derived from the data. The technique relates bivalve behavior, specifically shell gaping activity, to water quality changes. This technology has been successfully used for the assessment of coastal water quality in various countries (France, Spain, Norway, Russia, Svalbard (Ny Alesund) and New Caledonia).[6]

In the United States, the Environmental Protection Agency (EPA) has published Rapid Bioassessment Protocols, based on macroinvertebrates, as well as periphyton and fish. These protocols are used by many federal, state and local government agencies to design biosurveys for assessment of water quality.[16] Volunteer stream monitoring organizations around the U.S., working in cooperation with government agencies, typically use macroinvertebrate methods.[17] The species identification procedures are conducted in the field without the use of specialized equipment, and the techniques can be easily taught in volunteer training sessions.[18]

In South Africa, the Southern African Scoring System (SASS) method was developed as a rapid bioassessment technique, based on benthic macroinvertebrates, and is used for the assessment of water quality in Southern African rivers. The SASS aquatic biomonitoring tool has been refined over the past 30 years and is now on the fifth version (SASS5) which has been specifically modified in accordance with international standards, namely the ISO/IEC 17025 protocol.[19] The SASS5 method is used by the South African Department of Water Affairs as a standard method for River Health Assessment, which feeds the national River Health Programme and the national Rivers Database.

The imposex phenomenon in the dog conch species of sea snail leads to the abnormal development of a penis in females, but does not cause sterility. Because of this, the species has been suggested as a good indicator of pollution with organic man-made tin compounds in Malaysian ports.[20]

See also[edit]


  1. ^ Karr, James R. (1981). "Assessment of biotic integrity using fish communities". Fisheries 6: 21–27. doi:10.1577/1548-8446(1981)006<0021:AOBIUF>2.0.CO;2. ISSN 1548-8446. 
  2. ^ Tingey, David T. (1989). "Bio indicators in Air Pollution Research -- Applications and Constraints". Biologic Markers of Air-Pollution Stress and Damage in Forests. (Washington, DC: National Academies Press): 73–80. ISBN 978-0-309-07833-7. 
  3. ^ Government of Canada. "Biobasics: Bioindicators".  2008-07-08.[dead link]
  4. ^ a b Chessman, Bruce (2003). SIGNAL 2 – A Scoring System for Macro-invertebrate (‘Water Bugs’) in Australian Rivers (PDF). Monitoring River Heath Initiative Technical Report no. 31. Canberra: Commonwealth of Australia, Department of the Environment and Heritage. ISBN 0642548978. 
  5. ^ Grabarkiewicz, Jeffrey D.; Davis, Wayne S. (November 2008). "An Introduction to Freshwater Fishes As Biological Indicators" (Report). Washington, D.C.: U.S. Environmental Protection Agency. p. 1. Document No. EPA-260-R-08-016. 
  6. ^ a b Université Bordeaux et al. MolluSCAN eye project
  7. ^ "Discussion on Microbial Prospecting"[self-published source]
  8. ^ Azizullah, Azizullah; Murad, Waheed; Muhammad, Adnan; Waheed, Ullah; Häder, Donat-Peter (2013). "Gravitactic orientation of Euglena gracilis - a sensitive endpoint for ecotoxicological assessment of water pollutants". Frontiers in Environmental Science 1 (4): 1–4. doi:10.3389/fenvs.2013.00004. 
  9. ^ Tahedl, Harald; Donat-Peter, Haeder. "Automated Biomonitoring Using Real Time Movement Analysis of Euglena gracilis". Ecotoxicology and Environmental Safety 48: 161–169. doi:10.1006/eesa.2000.2004. 
  10. ^ Hemmersbach, Ruth; Simon, Anja; Waßer, Kai; Hauslage, Jens; Christianen, Peter C.M.; Albers, Peter W.; Lebert, Michael; Richter, Peter; Alt, Wolfgang; Anken, Ralf (2014). "Impact of a High Magnetic Field on the Orientation of Gravitactic Unicellular Organisms—A Critical Consideration about the Application of Magnetic Fields to Mimic Functional Weightlessness". Astrobiology 14 (3). doi:10.1089/ast.2013.1085. 
  11. ^ a b Tahedl, Harald; Hader, Donat-Peter (1999). "Fast examination of water quality using the automatic biotest ECOTOX based on the movement behavior of a freshwater flagellate". Water Research 33 (2): 426–432. doi:10.1016/s0043-1354(98)00224-3. 
  12. ^ Ahmed, Hoda; Häder, Donat-Peter (2011). "Monitoring of Waste Water Samples Using the ECOTOX Biosystem and the Flagellate Alga Euglena gracilis". Water Air Soil Pollution 216: 547–560. doi:10.1007/s11270-010-0552-4. 
  13. ^ Azizullah, Azizullah; Jamil, Muhammad; Richter, Peter; Häder, Donat-Peter (2014). "Fast bioassessment of wastewater and surface water quality using freshwater flagellate Euglena gracilis - a case study from Pakistan". Journal of Applied Phycology 26: 421–431. doi:10.1007/s10811-013-0100-x. 
  14. ^ Gooderham, John; Tsyrlin, Edward (2002). The Waterbug Book: A Guide to the Freshwater Macroinvertebrates of Temperate Australia. Collingswood, Victoria: CSIRO Publishing. ISBN 0 643 06668 3. 
  15. ^ Chang, F.C., J.E. Lawrence, B. Rios-Touma, and V.H. Resh (2014). "Tolerance Values of Benthic Macroinvertebrates for Stream Biomonitoring: Assessment of Assumptions Underlying Scoring Systems Worldwide". Environmental Monitoring and Assessment 186: 2135–2149. doi:10.1007/s10661-013-3523-6. 
  16. ^ Barbour, M.T., J. Gerritsen, B.D. Snyder, and J.B. Stribling (1999). "Rapid Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates and Fish, Second Edition." EPA 841-B-99-002. U.S. Environmental Protection Agency; Office of Water; Washington, D.C.
  17. ^ Izaak Walton League of America. Gaithersburg, MD."Biological Stream Monitoring." Accessed 2010-08-14.
  18. ^ U.S. EPA. Washington, DC. "Volunteer Stream Monitoring: A Methods Manual." November 1997. Document No. EPA 841-B-97-003.
  19. ^ Dickens CWS and Graham PM. 2002. "The Southern Africa Scoring System (SASS) version 5 rapid bioassessment for rivers." African Journal of Aquatic Science, 27:1-10.
  20. ^ Cob, Z. C.; Arshad, A.; Bujang, J. S.; Ghaffar, M. A. (2011). "Description and evaluation of imposex in Strombus canarium Linnaeus, 1758 (Gastropoda, Strombidae): a potential bio-indicator of tributyltin pollution". Environmental Monitoring and Assessment 178 (1-4): 393–400. doi:10.1007/s10661-010-1698-7. 

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