Revision: Pollution General Science SSC (English Medium) 8th Standard Maharashtra State Board

Pollutant is any such constituent which causes pollution.

Pollution is the addition of any such constituent to air, water or land which deteriorates the natural quality of the environment.

Air pollution means degradation of the air quality which harmfully affects the living organisms as well as certain objects.

or

Contamination of air by harmful substances like poisonous gases, smoke, particulate matter, microbes, etc., is called air pollution.

Oil spills are the accidental discharges of petroleum into oceans or estuaries. The sources of spills are overturned oil tankers, offshore oil mining, and oil refineries.

Water pollution means any change in the water quality which makes it unsuitable for use by humans and by other living organisms.

The amount of heat that is needed to raise the temperature of a unit mass of a substance by 1°C is called specific heat capacity.

Pesticides such as DDT (dichloro-diphenyl-trichloroethane) are used in agriculture to destroy pests, alter the basic structure of the soil, kill microorganisms in it, and may even reach the human body through food grown in such soils.

The contamination of soil by natural or synthetic substances that adversely affect its physical, chemical, and biological properties and reduce its productivity is called soil pollution.

Sanitary landfills are places where waste is dumped in a ground depression and covered with dirt every day.

• Air pollutants are of two types - particulate (smoke, smog, dust, heavy metals) and gaseous (CO₂, CO, SO₂, NO, NO₂). PM2.5 particles cause the greatest harm, penetrating deep into the lungs, causing irritation and breathing disorders.
• NO₂ + water vapour = nitric acid, causing irritation to eyes, lungs, liver and kidneys. CO is a poisonous gas produced by the incomplete combustion of fuel.
• Three control mechanisms - Electrostatic Precipitator (removes 99% soot/dust from industrial exhaust), Exhaust Gas Scrubber (removes SO₂ using lime/water spray), Catalytic Converter (removes poisonous gases from automobile exhaust; requires unleaded petrol).
• Delhi was 4th most polluted city in 1990. Following Supreme Court orders, all city buses were converted to CNG by 2002 — economic, efficient and adulteration-proof.
• India adopted BS-VI emission standards in 2018, skipping BS-V, reducing CO₂ and SO₂ levels in Delhi.

1. Control at Source: Air pollution can be reduced by proper planning and siting of industries, improved design of equipment, correct fuel–air mixture, use of fuel additives, and efficient engine design in vehicles.
2. Vehicular Pollution Control: Installation of catalytic converters, use of unleaded petrol, adoption of CNG/LPG, and enforcement of Bharat Stage (Euro) emission norms significantly reduce harmful exhaust emissions.
3. Industrial Pollution Control Devices: Emissions from industries and power plants are controlled using cyclone collectors, scrubbers, and electrostatic precipitators, which remove particulate matter and harmful gases before release into the atmosphere.
4. Legislative and Policy Measures: Laws such as the Air (Prevention and Control of Pollution) Act, 1981 and Environment (Protection) Act, 1986, along with emission standards and fuel regulations, play a crucial role in controlling air pollution.
5. Afforestation and Public Awareness: Planting pollution-tolerant trees around urban and industrial areas, along with environmental education and public awareness programmes, helps improve air quality and reduce pollution impacts.

• The Water (Prevention and Control of Pollution) Act, 1974, was passed to safeguard water resources. Main sources — domestic sewage, industrial effluents and agricultural run-off.
• BOD (Biochemical Oxygen Demand) is the dissolved oxygen required by microorganisms to decompose organic matter in water. High BOD = high pollution = low oxygen = death of aquatic organisms.
• Algal bloom — excessive growth of planktonic algae due to excess nitrogen and phosphorus. Releases toxins and causes fish mortality. Water hyacinth (Eichhornia crassipes) — "Terror of Bengal" — is an invasive plant that chokes water bodies.
• Eutrophication — natural ageing of a lake by nutrient enrichment. When accelerated by human activities, it is called Cultural/Accelerated Eutrophication, depleting oxygen and killing aquatic life.
• Biomagnification — increase in concentration of toxic pollutants (DDT, mercury) at successive trophic levels. Non-degradable, accumulate in tissues and pass to the next trophic level.
• Thermal pollution — caused by thermal and nuclear power plants releasing hot coolant water, raising water temperature and killing aquatic flora and fauna.

• Proper maintenance of water bodies and avoiding the disposal of waste into them helps reduce sewage pollution.
• Use of pesticides and chemical fertilisers should be minimised to prevent water contamination.
• Sewage should be properly treated before being released into rivers and other water bodies.
• Ecological sanitation (Ecosan) uses dry composting toilets to recycle human waste into organic manure, reducing the need for fertilisers.
• Ecosan toilets save water, prevent groundwater contamination, and are useful in water-scarce areas.
• Recycling of sewage water using reverse osmosis (RO) helps solve water scarcity and waste disposal problems.
• Rainwater harvesting and sewage recycling in cities help conserve water and reduce sewage generation.