Pollution — Notes

Pollution is the addition of harmful substances (pollutants) or energy to air, water or soil, making it harmful to living things.

Sources: vehicles, industries and power plants, burning of garbage, brick kilns, burning of crop stubble.

Water pollution

• Domestic sewage: organic matter decomposed by bacteria that use up dissolved oxygen; germs cause cholera, typhoid, jaundice.
• Detergents (phosphates) and fertilisers (nitrates): cause eutrophication (algal bloom); dead algae decay and use up oxygen; fish die.
• Industrial waste: poisonous chemicals and heavy metals such as mercury and lead build up in fish and people.
• Oil spills: an oil film coats birds' feathers and cuts off gas exchange between air and water.

Thermal pollution: hot water from power plants and industries raises water temperature; warm water holds less dissolved oxygen (about 9.1 mg per litre at 20 °C but about 7.6 at 30 °C), so fish and other aquatic life suffer.

Soil pollution: excess chemical fertilisers and pesticides, urban waste (plastics, metals, e-waste), industrial waste and acid rain; soil loses fertility and its organisms.

Biomedical waste: used syringes, needles, dressings, body tissues and expired medicines from hospitals and clinics. It can spread infections (such as hepatitis) and injure waste handlers, so it must be segregated at source into colour-coded containers (for example, sharps in puncture-proof containers, as under India's Bio-Medical Waste Management Rules, 2016) and treated by autoclaving, incineration or other approved methods.

Radiation pollution: sources include X-rays, radioactive waste from nuclear power plants, nuclear accidents and nuclear tests. Effects: damage to genes (mutations), cancer, burns, harm to unborn babies. Protection: lead shielding, safe storage of radioactive waste.

Noise pollution: unwanted, loud sound measured in decibels (dB). Sources: vehicle horns and traffic, loudspeakers, firecrackers, aircraft, factories and construction. Long exposure above about 80 dB can damage hearing. Effects: hearing loss, stress, irritability, sleeplessness, high blood pressure.

DDT is a non-biodegradable (persistent) pesticide. It is not broken down or excreted and is stored in body fat. As each animal eats many from the level below, DDT becomes more concentrated at each step of the food chain: biological magnification. Top consumers such as fish-eating birds are harmed most (for example, thin eggshells that break). Many countries, including India, have banned or restricted its use in farming.

Greenhouse effect: carbon dioxide, methane, nitrous oxide, CFCs and water vapour let sunlight through but trap heat given off by the Earth. More of these gases (from burning fuels, deforestation, paddy fields and cattle) cause global warming: melting glaciers and polar ice, rising sea levels, extreme weather, harm to crops and wildlife.

Acid rain: sulphur dioxide and nitrogen oxides dissolve in rain water to form sulphuric and nitric acids (rain more acidic than its normal pH of about 5.6). Effects: acidic lakes (fish die), damaged forests and soils, corroded marble and metal.

Ozone depletion: the ozone layer in the stratosphere absorbs most harmful UV rays. CFCs from old refrigerators, air conditioners and sprays release chlorine, which destroys ozone (an "ozone hole" was found over Antarctica in the 1980s). More UV-B causes skin cancer, cataract, weaker immunity and harm to crops and plankton. Under the Montreal Protocol (1987) countries agreed to phase out CFCs.

• CNG (compressed natural gas) for buses and autos: burns cleanly.
• Bharat Stage (BS) emission norms: Government of India standards limiting vehicle pollutants; BS-VI has applied across India since April 2020 (as of 2026).
• Switching off engines at long red lights; using public transport.
• Social forestry: planting trees on community land to absorb carbon dioxide and trap dust.
• Sewage treatment plants before discharge into rivers; cooling of hot water before release.
• Bans on plastics: India banned a list of single-use plastic items from 1 July 2022; many states have their own bans.
• Organic farming: compost and biological pest control instead of chemical fertilisers and pesticides.

Swachh Bharat Abhiyan (Clean India Mission), launched on 2 October 2014. Aims: a clean India; an end to open defecation through toilets; scientific solid-waste management (segregation, composting, recycling); a change in people's habits about cleanliness.