Water pollution can be defined as the addition of certain substances to water which can be organic, inorganic, biological, radiological, heat etc., which degrade the quality of water so that it becomes unfit for use.
Water pollution is not only confined to the surface but it has also spread to groundwater, as well as seas and oceans. Most of the major water bodies in cities are facing the brunt of the water pollution. Disposal of waste-water from industries, untreated waste from municipalities and solid waste dumping close to water sources has remained the major cause of water pollution.
Sources of pollution
They can be point sources or non-point sources. Point sources are those whose influence can be directly attributable. Here the pollutant travels directly from the source to the water body. Point sources are easy to regulate. Non-point sources are also known as diffused sources. They are difficult to attribute and can be many in number. They vary spatially as well as temporally and hence are difficult to regulate.
The following are the major sources of water pollution
Community wastewater: It includes discharge from domestic, commercial, and industrial establishments which are connected to the public sewerage system. The sewage contains human and animal excreta, food residues, cleaning agents, detergents and other wastes.
Industrial wastes: The industries discharge several inorganic and organic pollutants which may prove highly toxic to the living beings.
Agricultural sources: Fertilizers contain plant nutrients such as nitrogen, phosphorous, and potassium. Excess fertilizers may reach the groundwater by leaching or may get mixed with surface water bodies such as rivers, lakes, and ponds via drainage and runoff. Chemicals such as pesticides, insecticides, herbicides, fungicides, rodenticides, and soil fumigants contain harmful substances such as chlorinated hydrocarbons, organophosphates, metallic salts, carbonates, thiocarbonates, derivatives of acetic acid etc. Many of these chemicals are non-biodegradable and have a long residue life. Animal wastes such as excreta from cattle, poultry farms, piggeries, and slaughterhouses can also reach the local water bodies through runoff and surface leaching during the rainy season.
Thermal Pollution: Major sources of thermal pollution are the thermal and nuclear power plants which use water as a coolant. They release the hot water after using it back to the original source. A sudden rise in the water temperature reduces the dissolved oxygen levels and kills many fish and other aquatic animals.
Groundwater Pollution: Groundwater is threatened with contamination due to seepage from industrial and municipal wastes, effluents, sewage channels, and agricultural runoff.
Marine Pollution: Oceans are the ultimate sinks of all natural and man-made pollutants. Rivers discharge their pollutants into the sea. The sewage and garbage of coastal cities mostly get dumped into the sea. Other sources of oceanic pollution include navigational discharges of oil, grease, detergents, ballast waters, sewage, garbage, radioactive wastes, and offshore oil spills.
Effects of Water Pollution
- Polluted water contains lower dissolved oxygen due to higher biological and chemical oxygen demand, which is needed to degrade the organic and inorganic pollutants present in the water, and can threaten or even eliminate sensitive organisms such as plankton, molluscs, and several species of fish.
- Hot waters discharged from industries lower the dissolved oxygen content and threaten the survival of several species.
- Biocides, polychlorinated biphenyls (PCBs) and heavy metals are highly toxic to aquatic species.
Effects on human health
- Polluted waters contain disease-causing pathogens such as viruses, bacteria, parasitic protozoa, worms etc. They are a cause of water-borne diseases such as jaundice, cholera, typhoid, amoebiasis etc.
- Mercury compounds in wastewater are converted by bacterial action into extremely toxic methyl-mercury, which can cause numbness of limbs, lips, tongue, deafness, blurring of vision and mental derangement. They are known to cause the Minamata disease.
- Water contaminated with cadmium can cause itai-itai disease which is also called ouch ouch disease. It is a painful disease of bones and joints. It can also cause cancers of lungs and liver.
- The compounds of lead can cause anaemia, headache, loss of muscle power, and a bluish line around the gums.
Hazards of groundwater pollution
- Presence of excess nitrate in drinking water is dangerous for human health and may be fatal for infants. Excess nitrate in drinking water interacts with haemoglobin to form non-functional methaemoglobin which impairs oxygen transport. This condition is called methemoglobinemia or blue baby syndrome.
- Excess fluoride in drinking water causes neuro-muscular disorders, gastrointestinal problems, teeth deformity, hardening of bones and stiff and painful joints (skeletal fluorosis). High concentration of fluoride ions is present in drinking water in 13 states of India. The maximum level of fluoride, which the human body can tolerate is 1.5 parts per million. Long-term ingestion of fluoride ions causes fluorosis.
- Overexploitation of groundwater may lead to leaching of arsenic from soil and rock sources and contaminate groundwater. Chronic exposure to arsenic causes black foot disease. It also causes diarrhoea, peripheral neuritis, hyperkeratosis and also lung and skin cancer.
- Arsenic contamination is a serious problem in the tubewell dug areas of the Gangetic delta.
- Biological magnification and eutrophication.
- Treatment of sewage water and industrial effluents should be done before releasing them into water bodies.
- Hot water should be let to cool off before its release from the power plants.
- Domestic cleaning (of clothes and utensils) should be prohibited in water bodies which supply drinking water such as tanks, streams, and rivers
- Excessive use of fertilizers and pesticides should be avoided.
- Organic farming and efficient use of animal residues as fertilizers should be encouraged.
- Water hyacinth (an aquatic weed) can purify water by absorbing toxic materials and a number of heavy metals from water.
- Oil spills in water can be cleaned with the help of bigoli - a byproduct of paper industry resembling sawdust, oil zapper microorganisms.