PMF IAS Current Affairs
PMF IAS Current Affairs

Water Pollution: Causes & Effects, Eutrophication, Algal Blooms

Water Pollution

  • Water pollution is the addition/presence of undesirable substances to/in water such as organic, inorganic, biological, radiological, heat, which degrades the quality of water so that it becomes unfit for use’.
  • Natural sources of pollution of water are soil erosion, leaching of minerals from rocks (due to natural solubility and solubility triggered by acid rain) and decaying of organic matter.
Point and non-point sources of pollution
  • 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.

Causes of Water Pollution

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.
Dissolved Oxygen (DO)
  • 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, O2 consumption 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 O2 consumption thereby decreases the DO content of water.
Biological Oxygen Demand (BOD)
  • 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 wastes present 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.
Q. Biological Oxygen Demand (BOD) is a standard criterion for (2017)
  1. Measuring oxygen levels in blood
  2. Computing oxygen levels in forest ecosystems
  3. Pollution assay in aquatic ecosystems
  4. Assessing oxygen levels in high altitude regions
Chemical oxygen demand (COD)
  • 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 compounds in the water sample.

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/cm3 such as mercury, cadmium, copper, lead, arsenic) and a variety of organic compounds.

Agricultural sources

  • Agricultural runoff contains dissolved salts such as nitrates, phosphates, ammonia and other nutrients, and toxic metal ions and organic compounds.
  • Fertilizers contain major plant nutrients such as nitrogen, phosphorus and potassium.
  • Excess fertilisers may reach the groundwater by leaching or may be mixed with surface water.
  • Pesticides include insecticides, fungicides, herbicides, etc. They contain a wide range of chemicals such as chlorinated hydrocarbons (CHCs. E.g. DDT, Endosulfan etc.), organophosphates, metallic salts, carbonates, etc.
  • Many of the pesticides are non-degradable, and their residues have a long life.
  • Wastes from poultry farms, piggeries and slaughterhouses etc. reach the water though runoff.

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 oxygen in 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 iodine tends to be absorbed by the thyroid gland and can cause thyroid cancer.

Marine pollution

  • Oceans are the ultimate sink of all natural and manmade pollutants.
  • The sewerage and garbage of coastal cities are also dumped into the sea.
  • The other sources of oceanic pollution are navigational discharge of oil, grease, detergents, sewage, garbage and radioactive wastes, offshore oil mining, oil spills.
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 lighter than 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.

Invasive species

  • Plants of water hyacinth are the world’s most problematic aquatic weed, also called ‘Terror of Bengal’.

Water Hyacinth - Terror of Bengal

  • They grow abundantly in eutrophic water bodies and lead to an imbalance in the ecosystem.
  • They cause havoc by their excessive growth leading to stagnation of polluted water.

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 phosphates are common in many parts of India.
  • Dissolved nitrates commonly contaminate groundwater.
  • Excess nitrate in drinking water reacts with haemoglobin to form non-functional methaemoglobin and impairs oxygen transport. This condition is called methemoglobinemia or blue baby syndrome.

Methaemoglobin is a form of the oxygen-carrying metalloprotein haemoglobin. Methaemoglobin cannot bind oxygen, unlike oxyhaemoglobin.

  • High level of nitrates may form carcinogens and can accelerate eutrophication in surface waters.
Trace metals
  • Include lead, mercury, cadmium, copper, chromium and nickel.
  • These metals can be toxic and carcinogenic.
  • 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.
  • 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.
Q. Which of the following can be found as pollutants in the drinking water in some parts of India?
  1. Arsenic
  2. Sorbitol
  3. Fluoride
  4. Formaldehyde
  5. Uranium

Select the correct answer using the codes given below.

  1. 1 and 3 only
  2. 2, 4 and 5 only
  3. 1, 3 and 5 only
  4. 1, 2, 3, 4 and 5


  • The easiest option is 3) Fluoride. So, (b) can be eliminated.
  • The next easiest option is Arsenic (Heavy metal). Damn!
  • Nest easiest option is Uranium. Many columns are written on uranium mining and its ill-effects. So, (a) also can be elevated. (a) and (b) eliminated. (c) and (d) remains.
  • The knowledge of either “Sorbitol” or “Formaldehyde” will tell us the answer.
  • Formaldehyde is more known than sorbitol. Googling didn’t give me any authentic source that called formaldehyde a water pollutant. It is used as a preservative to preserve human organs. It finds some application in textile, resigns and wood industry.
  • Sorbitol (glucitol) is a sugar alcohol with a sweet taste which the human body metabolises slowly.

Answer: c) 1, 3 and 5 only

Effects of Water Pollution

Effects of Water Pollution on Human Health

  • Domestic and hospital sewage contain many undesirable pathogenic microorganisms, and its disposal into water without proper treatment may cause an outbreak of serious diseases, such as typhoid, cholera, etc.
  • Metals like lead, zinc, arsenic, copper, mercury and cadmium in industrial wastewaters adversely affect humans and other animals.
  • Consumption of such arsenic polluted water leads to accumulation of arsenic in the body parts like blood, nails and hairs causing skin lesions, rough skin, dry and thickening of the skin and ultimately skin cancer.
  • Mercury compounds in wastewater 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.
  • Pollution of water bodies by mercury causes Minamata (neurological syndrome) disease in humans.
  • Lead causes lead poisoning (Lead interferes with a variety of body processes and is toxic to many organs and tissues).
  • The compounds of lead cause anaemia, headache, loss of muscle power and bluish line around the gum.
  • 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.

Effects of Water Pollution on the 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.

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.


  • 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 mesotrophic because of the nutrients derived from their surroundings or organic wastes entering them.

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 nitrates and 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.
  • Phytoplankton are photosynthetic during day time adding oxygen to the aquatic ecosystem.
  • But during nights, they consume far more oxygen as 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 process of dead algae, plants and fishes.
  • The new anaerobic conditions (absence of oxygen) created to promote the growth of bacteria such as Clostridium botulinum which produces toxins deadly to aquatic organisms, birds and mammals.

Eutrophication and 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.

Effects of Eutrophication

  • Loss of freshwater lakes: Eutrophication eventually creates detritus layer in lakes and produces successively shallower depth of surface water.
  • Eventually, the water body is reduced into marsh whose plant community is transformed from an aquatic environment to a recognizable terrestrial environment.
  • Algal Blooms restrict the penetration of sunlight resulting in the death of aquatic plants and hence restricts the replenishment of oxygen.
  • 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 the ecosystem.
  • Loss of coral reefs: Occurs due to decrease in water transparency (increased turbidity).
  • Affects navigation due to increased turbidity; creates colour (yellow, green, red), smell and water treatment problems; increases biomass of inedible toxic phytoplankton, benthic and epiphytic algae and bloom of gelatinous zooplankton.
Harmful Algal Blooms
  • Most algal blooms are not harmful, but some produce toxins. These are known as Harmful Algal Blooms (HABs).
  • Toxicity: Some algal blooms when died or eaten, release neuro & hepatotoxins which can kill aquatic organism & pose a threat to humans. E.g. Shellfish poisoning.
  • HAB events adversely affect commercial and recreational fishing, tourism, and valued habitats, creating a significant impact on local economies and the livelihood of coastal residents.

Dead zones

  • Dead zones (biological deserts) are increasing in the coastal delta and estuarine regions.
  • Hypoxic zones (zones deprived of oxygen) can occur naturally (due to upwelling of nutrients).
  • They can be created or enhanced by human activity to form dead zones.
  • Dead zones are areas in the ocean with very low oxygen concentration (hypoxic conditions).
  • Dead zones emerge when influx of chemical nutrients spur algae growth.
  • These zones usually occur 200-800 meters (in the saltwater layer) below the surface.
  • Dead zones are detrimental to animal life. Most of the animal life either dies or migrates from the zone.
  • One of the largest dead zones forms in the Gulf of Mexico every spring (farmers fertilize their crops and rain washes fertilizer off the land and into streams and rivers).
  • There’s a dead zone in Gulf of Oman and it’s growing.

Dead zones

Red circles show the size and location of dead zones in 2010. Black dots indicate dead zones of unknown size. Dark blue regions indicate overly fertile water that may give rise to dead zones. (NASA Earth Observatory)

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.

Harmful Algal Blooms

  • 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 favourable for their development, these cells may multiply rapidly and form high numbers of cells, and this is called an algal bloom.

Marine Pollution

  • 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:
  1. Convention on the Dumping of Wastes at Sea, to be replaced by the 1996 Protocol) and
  2. United Nations Convention on Law of the Sea or UNCLOS.

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.

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.

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.

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.
Sharing is Caring !!

Newsletter Updates

Subscribe to our newsletter and never miss an important update!

Assured Discounts on our New Products!

One comment

  1. Can You Please Afford The Aquatic Biology Notes For Elective Zoology Of Second Semester Of Bsc First Year?

Leave a Reply

Your email address will not be published. Required fields are marked *


Never miss an important update!