• ‘Addition of certain substances to the water such as organic, inorganic, biological, radiological, heat, which degrades the quality of water so that it becomes unfit for use’.
  • Water pollution is not only confined to surface water, but it has also spread to ground water, sea and ocean.



  • Presence of organic and inorganic wastes in water decreases the dissolved oxygen content of the water.
  • Water having DO content below 8.0 mg/L may be considered as contaminated.
  • Water having DO content below. 4.0 mg/L is considered to be highly polluted.
  • DO content of water is important for the survival of aquatic organisms.
  • A number of factors like surface turbulence, photosynthetic activity, O2consumption by organisms and decomposition of organic matter are the factors which determine the amount of DO present in water.
  • The higher amounts of waste increase the rates of decomposition and O2consumption thereby decreases the DO content of water.



  • Water pollution by organic wastes is measured in terms of Biochemical Oxygen Demand (BOD).
  • BOD is the amount of dissolved oxygen needed by bacteria in decomposing the organic wastespresent in water. It is expressed in milligrams of oxygen per litre of water.
  • The higher value of BOD indicates low DO content of water.
  • Since BOD is limited to biodegradable materials, it is not a reliable method of measuring water pollution.



  • Chemical oxygen demand (COD) is a slightly better mode used to measure pollution load in the water.
  • COD measures the amount of oxygen in parts per million required to oxidise organic (biodegradable and non-biodegradable) and oxidizable inorganic compoundsin the water sample.





  • When pollutants are discharged from a specific location such as a drain pipe carrying industrial effluents discharged directly into a water body it represents point source pollution.
  • In contrast, non-point sources include discharge of pollutants from diffused sources or from a larger area such as runoff from agricultural fields, grazing lands, construction sites, abandoned mines and pits, etc.



  1. Sewage water
  • Sewage water includes discharges from houses and other establishments.
  • The sewage contains human and animal excreta, food residues, cleaning agents, detergents, etc.
  • Domestic and hospital sewage contain many undesirable pathogenic microorganisms.
  1. Industrial Wastes
  • Discharge of wastewater from industries like petroleum, paper manufacturing, metal extraction and processing, chemical manufacturing, etc., that often contain toxic substances, notably, heavy metals (defined as elements with density > 5 g/cm3such as mercury, cadmium, copper, lead, arsenic) and a variety of organic compounds.
  1. Agricultural Sources
  • Fertilizers contain major plant nutrients such as nitrogen,phosphorus and potassium.
  • Excess fertilizers may reach the ground water by leaching or may be mixed with surface water of rivers, lakes and ponds by runoff and drainage.
  • Pesticides include insecticides, fungicides, herbicides, nematicides, rodenticides and soil fumigants.
  • They contain a wide range of chemicals such as chlorinated hydrocarbons, organophosphates, metallic salts, carbonates, thiocarbonates, derivatives of acetic acid etc. Many of the pesticides are non-degradable and their residues have long life.
  • The animal excreta such as dung, wastes from poultry farms, piggeries and slaughter houses etc. reach the water though run off and surface leaching during rainy season.
  1. Thermal and Radiation Pollution
  • Power plants – thermal and nuclear, chemical and other industries use a lot of water for cooling purposes, and the used hot water is discharged into rivers, streams or oceans.
  • Discharge of hot water may increase the temperature of the receiving water by 10 to 15 °C above the ambient water temperature. This is thermal pollution.
  • Increase in water temperature decreases dissolved oxygenin the water.
  • Unlike terrestrial organisms, aquatic organisms are adapted to a uniform steady temperature of the environment. A sudden rise in temperature kills fishes and other aquatic animals.
  • One of the best methods of reducing thermal pollution is to store the hot water in cooling ponds, allow the water to cool before releasing into any receiving water body
  • Nuclear accidents near water bodies or during natural calamities like tsunami and earthquakes pose the risk of radiation leakage (radiation exposure) into water bodies. E.g. Fukushima Daiichi nuclear disaster.
  • Radiation exposure causes mutations in the DNA of marine organisms. If those mutations are not repaired, the cell may turn cancerous.
  • Radioactive iodinetends to be absorbed by the thyroid gland and can cause thyroid cancer.
  1. Marine Pollution
  • Oceans are the ultimate sink of all natural and manmadepollutants.
  • Rivers discharge their pollutants intothe sea.
  • The sewerage and garbage of coastal cities arealso dumped into the sea.
  • The other sources of oceanicpollution are navigational discharge of oil, grease, detergents,sewage, garbage and radioactive wastes, offshore oil mining, oil spills.



6. Underground Water Pollution

  • In India at many places, the groundwater is threatened with contamination due to seepage from industrial and municipal wastes and effluents, sewage channels and agricultural runoff.
  • Pollutants like fluorides, uranium, heavy metals and nutrients like nitrates and phosphatesare common in many parts of India.
  • Nitrates
  • Dissolved nitrates commonly contaminate groundwater.
  • Excess nitrate in drinking water reacts with haemoglobinto form non functional methaemoglobin and impairs oxygen transport. This condition is called methemoglobinemia or blue baby syndrome.
  • High level of nitrates may form carcinogens and can accelerate eutrophication in surface waters.

7. Oil Spills

  • The most common cause of oil spill is leakage during marine transport and leakage from underground storage tanks.
  • An oil spill could occur during offshore oil production as well.

Impact of oil spill on marine life

  • Oil being lighterthan water covers the water surface as a thin film cutting off oxygen to floating plants and other producers.
  • Within hours of an oil spill, the fishes, shellfish, plankton die due to suffocation and metabolic disorders.
  • Birds and sea mammals that consume dead fishes and plankton die due to poisoning.

8. Arsenic

  • Seepage of industrial and mine discharges, fly ash ponds of thermal power plants can lead to arsenic in groundwater.
  • In India and Bangladesh (Ganges Delta), millions of people are exposed to groundwater contaminated with high levels of arsenic, a highly toxic and dangerous pollutant.
  • Chronic exposure to arsenic causes black foot disease. It also causes diarrhoea and also lung and skin cancer.

9. Fluoride

  • Excess fluoride in drinking water causes neuromuscular disorders, gastrointestinal problems, teeth deformity, hardening of bones and stiff and painful joints (skeletal fluorosis).
  • Pain in bones and joint and outward bending of legs from the knees is called Knock-Knee syndrome.
  • Fluorosis is a common problem in several states of the country due to the intake of high fluoride content water.





A) Effects of Water Pollution on Human Health

  • Polluted water usually contains pathogens like virus, bacteria, parasitic protozoa and worms, therefore, it is a source of water borne diseases like jaundice, cholera, typhoid, amoebiasis etc
  • Mercury compounds in waste water are converted by bacterial action into extremely toxic methyl mercury, which can cause numbness of limbs, lips and tongue, deafness, blurring of vision and mental derangement.
  • Water contaminated with cadmium can cause itai itai disease also called ouch-ouch disease (a painful disease of bones and joints) and cancer of lungs and liver.
  • The compounds of lead cause anaemia, headache, loss of muscle power and bluish line around the gum.

B) Effects of Water Pollution on Aquatic Ecosystem

  • Polluted water reduces Dissolved Oxygen (DO) content, thereby, eliminates sensitive organisms like plankton, molluscs and fish etc.
  • However, a few tolerant species like Tubifex (annelid worm)and some insect larvae may survive in highly polluted water with low DO content. Such species are recognized as indicator species for polluted water.
  • Biocides, polychlorinated biphenyls (PCBs)and heavy metals directly eliminate sensitive aquatic organisms.
  • Hot waters discharged from industries, when added to water bodies, lowers its DO content.

C) Effects of Water Pollution on Environment

  • Micro-organisms involved in biodegradation of organic matter in sewage waste consume a lot of oxygen and make water oxygen deficient killing fish and other aquatic creatures.
  • Presence of large amounts of nutrients in water results in algal bloom(excessive growth of planktonic algae. This leads to ageing of lakes.
  • A few toxic substances, often present in industrial wastewaters, can undergo biological magnification (Biomagnification) in the aquatic food chain. This phenomenon is well-known for mercury and DDT.
  • High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing a decline in bird populations.



  • Lakes receive their water from surface runoff and along with its various chemical substances and minerals.
  • Over periods spanning millennia, ageing occurs as the lakes accumulate mineral and organic matter and gradually, get filled up.
  • The nutrient-enrichment of the lakes promotes the growth of algae, aquatic plants and various fauna. This process is known as natural eutrophication.
  • Similar nutrient enrichment of lakes at an accelerated rate is caused by human activities and the consequent ageing phenomenon is known as cultural eutrophication.
  • On the basis of their nutrient content, lakes are categorized as Oligotrophic (very low nutrients), Mesotrophic (moderate nutrients)and Eutrophic (highly nutrient rich).
  • A vast majority of lakes in India are either eutrophic or mesotrophicbecause of the nutrients derived from their surroundings or organic wastes entering them.

A) Eutrophication and Algal Bloom

  • Eutrophic water body: it is a body of water rich in nutrients and so supporting a dense plant population, the decomposition of which kills animal life by depriving it of oxygen.
  • Eutrophication is the response to the addition of nutrients such as nitratesand phosphates naturally or artificially, fertilising the aquatic ecosystem.
  • Phytoplankton (algae and blue-green bacteria) thrive on the excess nutrients and their population explosion covers almost entire surface layer. This condition is known as algal bloom.
  • Water temperature has also been related to the occurrence of algal blooms, with unusually warm water being conducive to blooms.
  • Algal blooms can be any colours, but the most common ones are red or brown. These blooms are commonly referred to as red or brown tides.

B) Mechanism

  • Phytoplankton are photosynthetic during day timeadding oxygen to the aquatic ecosystem.
  • But during nights, they consume far more oxygenas they respire aggressively i.e. Algal blooms accentuate the rate of oxygen depletion as the population of phytoplankton is very high.
  • The primary consumers like small fish are killed due to oxygen deprivation caused by algal blooms.
  • Death of primary consumers adversely affects the food chain.
  • Further, more oxygen is taken up by microorganisms during the decomposition processof dead algae, plants and fishes.
  • The new anaerobic conditions (absence of oxygen) created to promote the growth of bacteria such as Clostridium botulinumwhich produces toxins deadly to aquatic organisms, birds and mammals.

C) Effects of Eutrophication

  1. Change in ecosystem:
  • Eutrophication eventually create detritus layer in the ponds & lakes and produces successively shallower depth of surface water.
  1. Decreased biodiversity
  • Algal blooms restrict the sunlight to penetrate & affects the photosynthesizing plants. It causes death of plants.
  • Bacteria consumes all the oxygen on decomposition & results in devoid of oxygen. Eventually it leads to death of all living organism in aquatic ecosystem.
  1. New species invasion
  • Eutrophication may cause the ecosystem competitive by transforming the normal limiting nutrient to abundant level. This cause shifting in species composition of ecosystem
  1. Toxicity
  • Some algal blooms when die or eaten, release neuro & hepatotoxins which can kill aquatic organism & pose threat to humans. (e.g) Shellfish poisoning.
  • Depletion of dissolved oxygen level.
  • Increased incidences of fish kills & loss of desirable fish species & reduction in harvesting
  • Loss of coral reefs.
  • Decrease in water transparency and increased turbidity.
  • Increased biomass of inedible toxic phytoplankton.

D) Mitigation of Eutrophication

  • Treating Industrial effluents domestic sewage to remove nutrient-rich sludge through wastewater processing.
  • Riparian buffer:Interfaces between a flowing body of water and land created near the waterways, farms, roads, etc. in an attempt to filter pollution.
  • Sediments and nutrients are deposited in the buffer zones instead of deposition in water (Wetlands, estuaries are natural riparian buffers).
  • Increase in efficiency of nitrogen & phosphorous fertilisers and using them inadequate levels.
  • Nitrogen testing & modelling: N-Testing is a technique to find the optimum amount of fertiliser required for crop plants. It will reduce the amount of nitrogen lost to the surrounding area.
  • Encouraging organic farming.
  • Reduction in nitrogen emission from vehicles and power plants.





  • Algae or phytoplankton are microscopic organisms that can be found naturally in coastal waters. They are major producers of oxygen and food for many of the animals that live in these waters.
  • When environmental conditions are favorable for their development, these cells may multiply rapidly and form high numbers of cells and this is called an algal bloom.
  • Most algal blooms are not harmful but some produce toxins and do affect fish, birds, marine mammals and humans. The toxins may also make the surrounding air difficult to breathe. These are known as Harmful Algal Blooms (HABs).

A) Causes of these blooms

  • Blooms occur when several colonies start combining rapidly when conditions such as nutrient concentrations, salinity and temperature are optimal.
  • Blooms can be due to a number of reasons. Two common causes are nutrient enrichment and warm waters.
  • Nutrient enrichment of water, especially phosphates and nitrogen, is often the result of pollution and can cause algal blooms.
  • Water temperature has also been related to the occurrence of algal blooms, with unusually warm water being conducive to blooms.



  • Marine pollution refers to the emptying of chemicals into the ocean and its harmful effects.
  • The potentially toxic chemicals stick to tiny particles and these are taken up by plankton and benthos animals which are deposit or filter feeders concentrating upward within food chains.
  • As animal feeds usually have a high fish meal or fish oil content, toxins can be found in consumed food items obtained from livestock and animal husbandry.
  • To curb marine pollution and regulate the use of the world’s oceans by individual States, the nations of the world have come together to form two major conventions:
    • Convention on the Dumping of Wastes at Sea, to be replaced by the 1996 Protocol)and
    • United Nations Convention on Law of the Sea or UNCLOS.

A) Convention on Dumping of Wastes at Sea

  • An inter-governmental conference on the Convention on the Dumping of Wastes at Sea met in London in November 1972 to adopt this instrument, the London Convention.
  • The Convention has a global character and is aimed at international control and putting an end to marine pollution.
  • The definition of dumping under the Convention relates to deliberate disposal at sea of wastes or other materials from vessels, aircraft, platforms and other man-made structures.
  • ‘Dumping’ here does not cover wastes derived from the exploration and exploitation of sea-bed mineral resources.
  • The 1978 amendment dealt with the incineration of wastes at sea.
  • Another set of amendments adopted at the same time related to introduction of new procedures for dispute settlement.
  • The 1993 amendments banned dumping of low-level radioactive wastes into the seas.
  • They phased out the dumping of industrial wastes by 1995 and called for an end to incineration of industrial wastes at sea.
  • It is to be noted that dumping of low-level radioactive wastes and industrial wastes as well as incineration of wastes were earlier permitted by the Convention.
  • The changing approach, keeping in view the need of the times, led to the adoption of the 1996 Protocol on November 7, 1996.

B) 1996 Protocol

  • The Protocol, which became effective in 2006, replaces the 1972 Convention.
  • The 1996 Protocol is much more restrictive as compared to the 1972 Convention that allowed dumping provided certain conditions were satisfied.
  • 1996 Protocol calls for appropriate preventive measures to be taken when wastes thrown into the sea are likely to cause harm “even when there is no conclusive evidence to prove a cause relation between inputs and their effects.”
  • The Protocol states that “the polluter should, in principle, bear the cost of pollution”.
  • The Contracting Parties must ensure that the Protocol does not simply result in pollution being transferred from one part of the environment to another.
  • The Protocol prohibits the Contracting Parties from dumping “wastes or any other matter with the exception of those listed in Annex 1”.
  • Annex 1 includes dredged material; sewage sludge; fish waste from industrial fish processing operations etc. for which the concern is mainly physical impact.
  • The Protocol prohibits incineration of wastes at sea (permitted by the 1972 convention but prohibited under the 1993 amendments).
  • The Protocol states that “Contracting Parties shall not allow the export of wastes or other matter to other countries for dumping or incineration at sea”.
  • The International Maritime Organization (IMO)is responsible for Secretariat duties with respect to the Protocol.

C) 2006 Amendments to the Protocol

  • Adopted in 2006, the amendments were enforced in 2007.
  • The amendments have created a basis in international environment law to regulate carbon capture and storage in subsealed geological formation.
  • It is part of the measures being considered to address climate change and ocean acidification like developing low carbon energy forms especially for sources of enormous CO2
  • The amendments allow storage of carbon dioxide (CO2)under the seabed but regulate the sequestration of CO2 streams from CO2 capture processes in sub-seabed geological formations.

D) The United Nations Convention on Law of the Sea

  • UNCLOS establishes general obligations for safeguarding the marine environment and protecting freedom of scientific research on the high seas.
  • It also creates an innovative legal regime for controlling mineral resource exploitation in deep seabed areas beyond national jurisdiction, through an International Seabed Authority.
  • UNCLOS can hold states liable for damage caused by violation of their international obligations to combat pollution of the seas.



  • Treatment of sewage water and the industrial effluents should be done before releasing it into water bodies.
  • Hot water should be cooled before release from the power plants
  • Domestic cleaning in tanks, streams and rivers, which supply drinking water, should be prohibited.
  • Excessive use of fertilizers and pesticides should be avoided.
  • Organic farming and efficient use of animal residues as fertilizers.
  • Water hyacinth (an aquatic weed) can purify water by taking some toxic materials and a number of heavy metals from water.
  • Oil spills in water can be cleaned with the help of bregoli – a by-product of paper industry resembling saw dust, oil zapper, micro-organisms.
  • The steps taken by the Government to address the issues of water pollution include the following:-
  • Preparation of action plan for sewage management and restoration of water quality in aquatic resources byState Governments;
  • Installation of Online Effluent Monitoring System to check the discharge of effluent directly into the rivers and water bodies.
  • Setting up of monitoring network for assessment of water quality;
  • Action to comply with effluent standards is taken by SPCBs / PCCs to improve the water quality of the rivers.
  • Financial assistance for installation of Common Effluent
  • Treatment Plants for cluster of Small Scale Industrial units;
  • Issuance of directions for implementation of Zero Liquid Discharge.
  • Issuance of directions under Section 5 of Environment (Protection) Act, 1986 to industries and under Section 18(1)(b) of Water (Prevention and Control of Pollution) Act, 1974.
  • Implementation of National Lake Conservation Plan (NLCP) and National Wetland Conservation Programme (NWCP) for conservation and management of identified lakes and wetlands in the country which have been merged in February, 2013 into an integrated scheme of National Plan for Conservation of Aquatic Eco-systems (NPCA) to undertake various conservation activities including interception, diversion and treatment of waste water, pollution abatement, lake beautification, biodiversity conservation, education and awareness creation, community participation etc.

A) Phytoremediation

  • Phytoremediation is the use of plantsto remove contaminants from soil and water.
  • Natural phytoremediation is carried out by mangroves, estuarine vegetation and other wetland vegetation.
  • Phytoextraction/phytoaccumulation: plants accumulate contaminants into the roots and aboveground shoots or leaves.

B) Sewage Water Treatment for Domestic Use

  • Substances that are removed during the process of drinking water treatment include suspended solids, bacteria, algae, viruses, fungi, and minerals such as iron and manganese.
  • The processes involved in removing the contaminants include physical processes such as settling and filtration, chemical processes such as disinfection and coagulation and biological processes such as slow sand filtration.




  • Bioremediation is the use of microorganisms (bacteria and fungi) to degrade the environmental contaminants into less toxic forms.
  • Microorganisms can be specifically designed for bioremediation using genetic engineering techniques.

A) In situ bioremediation

  • In situ — It involves treatment of the contaminated material at the site.
  • Bioventing:supply of air and nutrients through wells to contaminated soil to stimulate the growth of indigenous bacteria.
  • Biosparging:Injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by naturally occurring bacteria.
  • Bioaugmentation:Microorganisms are imported to a contaminated site to enhance the degradation process.
  • Using bioremediation techniques, TERI has developed a mixture of bacteria called ‘Oilzapper and Oilivorous-S’ which degrades the pollutants of oil-contaminated sites, leaving behind no harmful residues.

B) Ex situ bioremediation

  • Ex situ — involves the removal of the contaminated material to be treated elsewhere.
  • Landfarming:contaminated soil is excavated and spread over a prepared bed and periodically tilled until pollutants are degraded. The goal is to stimulate indigenous biodegradative microorganisms and facilitate their aerobic degradation of contaminants.
  • Bioreactors:it involves the processing of contaminated solid material (soil, sediment, sludge) or water through an engineered containment system.
  • Composting:Composting is nature’s process of recycling decomposed organic materials into a rich soil known as compost.

C) Advantages of bioremediation

  • Useful for the destruction of a wide variety of contaminants.
  • Less expensive.
  • The destruction of target pollutants is possible.
  • Environment-friendly.

D) Disadvantages of bioremediation

  • Bioremediation is limited to biodegradable compounds. Not all compounds are susceptible to rapid and complete degradation.
  • Bioremediation often takes a longer time than other treatment processes.



  • Designed by Railwaysalong with DRDO.
  • Why Bio Toilets in Rail?
  • Direct discharge of human waste from the existing toilet system in trains causes corrosion of the tracks, costing crores to replace the rail tracks.
  • The bio-toilets are fitted underneath the lavatories and the human waste discharged into them is acted upon by a particular kind of bacteria that converts it into non-corrosive neutral water.



A) Terms associated with Bio-Toilets

  • Bio tank:The term bio tank is used for the tanks made up of concrete for the anaerobic digestion of human waste.
  • Bio-digesters:The term biodigester is used for the shells made up of steel for the anaerobic digestion of human waste.
  • Aerobic Bacteria:Aerobic bacteria are those which flourish in the presence of free dissolved oxygen in the wastewater and consume organic matter for their food, and thereby oxidising it to stable end products.
  • Anaerobic Bacteria:Anaerobic bacteria flourish in the absence of free dissolved oxygen, and survive by utilizing the bounded molecular oxygen in compounds like nitrates (NO3) and sulphates (SO4) thereby reducing them to stable end products along with evolution of foul-smelling gases like H2S (hydrogen sulphide), CH4 (methane).
  • Anaerobic Microbial inoculums:a mixture of different types of bacteria responsible for the breakdown of complex polymers into simple sugars which are further broken down into low chain fatty acids and finally into biogas.
  • Facultative Bacteria:Facultative bacteria can operate either as aerobically or as anaerobically.

B) Anaerobic biodegradation system

  • Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen.
  • The final waste is Methaneand Carbon Dioxide.

C) Aerobic biodegradation

  • In this forced aeration is essential which is energy intensive.
  • Incomplete aeration (partial aerobic condition) leads to a foul smell.
  • Cannot tolerate detergents
  • Generates a large amount of sludge.
  • Repeated addition of bacteria/enzyme is required for the process.
  • Maintenance & recurring cost is high.

D) Anaerobic biodegradation

  • In this no aeration is required.
  • Complete anaerobic conditions.
  • More than 99% pathogen inactivation.
  • Anaerobes can even degrade detergents/phenyl.
  • Sludge generation is very less.
  • One time bacterial inoculation is enough.
  • Minimal maintenance and no recurring cost.



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