- 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’.
- Water pollution is caused by a variety of human activities such as industrial, agricultural and domestic.
- Natural sources of pollution of water are soil erosion, leaching of minerals from rocks and decaying of organic matter.
Point and non-point sources of pollution
- Rivers, lakes, seas, oceans, estuaries and groundwater sources may be polluted by a point or non-point sources.
- 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, roads, and streets.
Causes of Water Pollution
- Sewage water includes discharges from houses, commercial and industrial establishments connected to the public sewerage system.
- The sewage contains human and animal excreta, food residues, cleaning agents, detergents and other wastes.
- Domestic and hospital sewage contain many undesirable pathogenic microorganisms, and its disposal into the water without proper treatment.
- Putrescibility is the process of decomposition of organic matter present in water by microorganisms using oxygen.
Dissolved Oxygen (DO) – Biological Oxygen Demand (BOD) – Chemical oxygen demand (COD)
- Presence of organic and inorganic wastes in water decreases the dissolved Oxygen (DO) 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.
- The demand for O2 is directly related to increasing input of organic wastes and is expressed as biological oxygen demand (BOD) 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 wastes present in water. It is expressed in milligrams of oxygen per liter of water.
- The higher value of BOD indicates low DO content of water. Since BOD is limited to biodegradable materials only. Therefore, it is not a reliable method of measuring the pollution load in the water.
- 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 oxidize organic (biodegradable and non-biodegradable)and oxidizable inorganic compounds in the water sample.
- The industries discharge several inorganic and organic pollutants, which may prove highly toxic to living beings.
- 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, etc.) and a variety of organic compounds.
- 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 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 (CHCs. E.g. DDT, Endosulfan, etc.), organophosphates, metallic salts,
carbonates, thiocarbonates, derivatives of acetic acid, etc. Many of the pesticides are non-degradable and their residues have a long life.
- The animal excreta such as dung, waste from poultry farms, piggeries, and slaughterhouses, etc. reach the water through runoff and surface leaching during the rainy season.
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 which adversely affects aquatic life.
- Unlike terrestrial organisms, aquatic organisms are adapted to a uniform steady temperature of the environment. The sudden rise in temperature kills fishes and other aquatic animals.
- Discharge of hot water in the water body affects feeding in fishes, increases their metabolism and affects their growth. Their swimming efficiency declines. Running away from predators or chasing prey becomes difficult. Their resistance to diseases and parasites decreases.
- 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.
- Oil spills are the most glaring of all oceanic pollution.
- The most common cause of oil spill is leakage during marine transport and leakage from underground storage tanks. The 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 the 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. Death of these organisms severely damages marine ecosystems.
Impact of oil spills on terrestrial life
- Bays, estuaries, shores, reefs, beaches particularly near large coastal cities or at the mouth of rivers are relatively more susceptible to the hazards of oil spills.
- A number of coastal activities, especially recreational such as bathing, boating, angling, diving, rafting is affected. As a result, tourism and hotel business in the coastal are as suffers seriously.
- Plants of water hyacinth are the world’s most problematic aquatic weed, also called ‘Terror of Bengal’.
- They grow abundantly in eutrophic water bodies and lead to an imbalance in the ecosystem dynamics of the water body.
- 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.
- Oceans are the ultimate sink of all-natural and manmade pollutants.
- Rivers discharge their pollutants into the sea.
- The sewerage and garbage of coastal cities are also dumped into the sea.
- The other sources of oceanic pollution are a navigational discharge of oil, grease, detergents, sewage, garbage, and radioactive wastes, offshore oil mining, oil spills.
Effects of Water Pollution
Effects of Water Pollution on Human Health
- Domestic and hospital sewage contain many undesirable pathogenic microorganisms, and its disposal into the water without proper treatment may cause an outbreak of serious diseases, such as amoebiasis dysentery, typhoid, jaundice, cholera, etc.
- Metals like lead, zinc, arsenic, copper, mercury, and cadmium in industrial wastewaters adversely affect humans and other animals.
- Arsenic pollution of groundwater has been reported from West Bengal, Orissa, Bihar, Western U.P. 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 and dropsy in fishes.
- 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 anemia, headache, loss of muscle power and bluish line around the gum.
- Cadmium poisoning causes cancer of lungs and liver and Itai – Itai disease (a painful disease of bones and joints, causes softening of the bones and kidney failure), etc.
- 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 (free-floating) algae [Harmful Algal Blooms and eutrophication are explained in the previous post]. This leads to aging 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.
- Thermal wastewater eliminates or reduces the number of organisms sensitive to high temperature, and may enhance the growth of plants and fish in extremely cold areas but, only after causing damage to the indigenous flora and fauna.
- Aquatic organisms take up pesticides from water which get into the food chain and move up the food chain. At the higher trophic level, they get concentrated and may reach the upper end of the food chain [Biomagnification explained in ‘Trophic Levels’].
Effects of Water Pollution on Aquatic Ecosystem
- Polluted water reduces Dissolved Oxygen (DO) content, thereby, eliminates sensitive organisms like plankton, mollusks, 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.
Water Pollution Control Measures
- Realizing the importance of maintaining the cleanliness of the water bodies, the Government of India has passed the water (Prevention and Control of Pollution) Act, 1974to safeguard our water resources.
- An ambitious plan to save the river called the Ganga Action Plan was launched in 1985. It aimed to reduce the pollution levels in the river. However, the increasing population and industrialization have already damaged this mighty river beyond repair.
- In India, the Central Pollution Control Board (CPCB), an apex body in the field of water quality management, has developed a concept of “designated best use”.
- Accordingly, the water body is designated as A, B, C, D, E on the basis of
- o pH,
o dissolved oxygen, mg/1
o BOD, (200C) mg/l
o total coliform (MPN/100ml)
o free ammonia mg/l,
o electrical conductivity, etc.
- The CPCB, in collaboration with the concerned State Pollution Control Boards, has classified all the water bodies including coastal waters in the country according to their “designated best uses”.
- This classification helps the water quality managers and planners to set water quality targets and identify needs and priority for water quality restoration programs for various water bodies in the country.
- The famous Ganga Action Plan and subsequently the National River Action Plan are results of such exercise.
- Riparian buffers: A riparian buffer is a vegetated area (a “buffer strip”) near a stream, usually forested, which helps shade and partially protect a stream from the impact of adjacent land uses. It plays a key role in increasing water quality in associated streams,
rivers, and lakes, thus providing environmental benefits.
- Treatment of sewage water and the industrial effluents before releasing it into water bodies. Hot water should be cooled before release from the power plants.
- Excessive use of fertilizers and pesticides should be avoided. Organic farming and efficient use of animal residues as fertilizers can replace chemical fertilizers.
- Water hyacinth (an aquatic weed, invasive species) 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 sawdust, oil zapper, microorganisms.
- It has been suggested that we should plant eucalyptus trees all along sewage ponds. These trees absorb all surplus wastewater rapidly and release pure water vapor into the atmosphere.