Water pollution is a serious health hazards in India, especially in villages. It is estimated that `50-60%` of Indian population suffers from diseases caused by it. `30-40%` of all deaths are believed to be due to it.
The principal sources of water pollution and effects of water pollutants are as follows :
`text(Domestic wastes and sewage)` :
(i) Sewage containing human faeces, urine, kitchen and cloth washings, organic waste, industrial waste etc. is usually poured into water bodies which cause water pollution.
(ii) The villagers often wash their animals, cloths and take bath in the same pond. Such water get contaminated with infectious agents for cholera, typhoid, dysentery, Jaundice and skin diseases.
(iii) Sewage provide food for decomposers, so the population of decomposers increases.
(iv) Decomposers/microorganisms causing decomposition of sewage take up most of the oxygen present dissolved in water. So in this water `text(BOD)` (Biological oxygen demand or Biochemical oxygen demand) increased very much.
(v) `text(BOD)` is the amount of oxygen in milligrams required by microorganisms for five days to metabolise waste present in one litre of water at `20^0C`.
`text(Industrial effluents (or industrial discharges))` :
Industries usually discharge waste water into ponds, lakes and rivers. Industrial waste water contains heavy metals (mercury, lead, copper, arsenic and cadmium), inorganic pollutants (acids, alkalies and bleaching liquors), organic pollutants (phenol, naphtha, proteins, aromatic compounds, cellulose fibres etc.) Industrial effluents are the most hazardous pollutants on land and water.
(a) `text(Mercury) (Hg)`-
(i) It is released during combustion of coal, smelting of metallic ores, paper and paint industries.
(ii) Mercury is highly persistent. In water it gets changed into water soluble dimethyl form [`(CH_3)_2 Hg`] and enters the food chain (undergoes biomagnification).
(iii) It kills fish and poisons the remaining fauna. Human beings feeding on such poisoned animals develop a crippling deformity called minamata disease which is characterised by impairment of various senses, diarrhoea, haemolysis, meningitis and death.
(iv) The minimata disease was first detected in Japan.
(v) Mercury inhibits chromosomal disjunction during gamete formation. So it brings about genetic changes also.
(b) `text(Lead) (Pb)`-
(i) The sources of lead pollution are smelters, battery industry, paint, chemical and pesticide industry, automobiles exhausts etc.
(ii) Lead is pollutant of air, soil and water.
(iii) It is used as anti-knock reagent in petrol and released by automobile exhausts.
(iv) Lead is a persistant pollutant and may show biological amplification or biomagnification.
(v) It is a mutagenic and causes anemia, headache, vomitting, colic, loss of muscle power, bluish lines around the gums, loss of appetite and damage of liver, kidney and brain.
(c) `text(Cadmium) (Cd)`-
(i) It is added to the environment by metal industries, welding and electroplating, pesticides and phosphate industries.
(ii) `Cd` shows biological amplification and accumulates inside kidneys, liver, pancreas and spleen.
(iii) It causes hypertension, anemia, diarrhoea and damages liver and kidneys.
`text(Oil)`-
(i) During extraction and transportation of oil from the sea to different parts, some of the oil spreads over the surface of water. Refineries also discharge a lot of oil present in their eftluents into rivers.
(ii) Oil spreading on the surface of water prevents its oxygenation and inhibits photosynthetic activity of aquatic plants. Animal life is destroyed due to reduced availability of oxygen, food and toxic effects of oil.
(iii) Oil spilled over the surface of water may catch fire and hence kill all organic life.
`text(Thermal pollution)`-
(i) Hot water is produced by many industries, power generation plants and thermal power plants.
(ii) Thermal pollution is caused by addition of hot water effluents in water bodies, it bring about rise in water temperature.
(iii) Warmer water contains less oxygen. Therefore, there is decrease in the rate of decomposition of organic matter.
(iv) In hot water green algae are replaced by less desirable blue green algae.
(v) Many organisms fail to reproduce in hot water e.g. Salmon, Trout.
Water pollution is a serious health hazards in India, especially in villages. It is estimated that `50-60%` of Indian population suffers from diseases caused by it. `30-40%` of all deaths are believed to be due to it.
The principal sources of water pollution and effects of water pollutants are as follows :
`text(Domestic wastes and sewage)` :
(i) Sewage containing human faeces, urine, kitchen and cloth washings, organic waste, industrial waste etc. is usually poured into water bodies which cause water pollution.
(ii) The villagers often wash their animals, cloths and take bath in the same pond. Such water get contaminated with infectious agents for cholera, typhoid, dysentery, Jaundice and skin diseases.
(iii) Sewage provide food for decomposers, so the population of decomposers increases.
(iv) Decomposers/microorganisms causing decomposition of sewage take up most of the oxygen present dissolved in water. So in this water `text(BOD)` (Biological oxygen demand or Biochemical oxygen demand) increased very much.
(v) `text(BOD)` is the amount of oxygen in milligrams required by microorganisms for five days to metabolise waste present in one litre of water at `20^0C`.
`text(Industrial effluents (or industrial discharges))` :
Industries usually discharge waste water into ponds, lakes and rivers. Industrial waste water contains heavy metals (mercury, lead, copper, arsenic and cadmium), inorganic pollutants (acids, alkalies and bleaching liquors), organic pollutants (phenol, naphtha, proteins, aromatic compounds, cellulose fibres etc.) Industrial effluents are the most hazardous pollutants on land and water.
(a) `text(Mercury) (Hg)`-
(i) It is released during combustion of coal, smelting of metallic ores, paper and paint industries.
(ii) Mercury is highly persistent. In water it gets changed into water soluble dimethyl form [`(CH_3)_2 Hg`] and enters the food chain (undergoes biomagnification).
(iii) It kills fish and poisons the remaining fauna. Human beings feeding on such poisoned animals develop a crippling deformity called minamata disease which is characterised by impairment of various senses, diarrhoea, haemolysis, meningitis and death.
(iv) The minimata disease was first detected in Japan.
(v) Mercury inhibits chromosomal disjunction during gamete formation. So it brings about genetic changes also.
(b) `text(Lead) (Pb)`-
(i) The sources of lead pollution are smelters, battery industry, paint, chemical and pesticide industry, automobiles exhausts etc.
(ii) Lead is pollutant of air, soil and water.
(iii) It is used as anti-knock reagent in petrol and released by automobile exhausts.
(iv) Lead is a persistant pollutant and may show biological amplification or biomagnification.
(v) It is a mutagenic and causes anemia, headache, vomitting, colic, loss of muscle power, bluish lines around the gums, loss of appetite and damage of liver, kidney and brain.
(c) `text(Cadmium) (Cd)`-
(i) It is added to the environment by metal industries, welding and electroplating, pesticides and phosphate industries.
(ii) `Cd` shows biological amplification and accumulates inside kidneys, liver, pancreas and spleen.
(iii) It causes hypertension, anemia, diarrhoea and damages liver and kidneys.
`text(Oil)`-
(i) During extraction and transportation of oil from the sea to different parts, some of the oil spreads over the surface of water. Refineries also discharge a lot of oil present in their eftluents into rivers.
(ii) Oil spreading on the surface of water prevents its oxygenation and inhibits photosynthetic activity of aquatic plants. Animal life is destroyed due to reduced availability of oxygen, food and toxic effects of oil.
(iii) Oil spilled over the surface of water may catch fire and hence kill all organic life.
`text(Thermal pollution)`-
(i) Hot water is produced by many industries, power generation plants and thermal power plants.
(ii) Thermal pollution is caused by addition of hot water effluents in water bodies, it bring about rise in water temperature.
(iii) Warmer water contains less oxygen. Therefore, there is decrease in the rate of decomposition of organic matter.
(iv) In hot water green algae are replaced by less desirable blue green algae.
(v) Many organisms fail to reproduce in hot water e.g. Salmon, Trout.