Class 12 Biology

Environmental Issues

Pollution: Any undesirable change in physical, chemical or biological characteristics of air, land, water or soil is called pollution.

Air Pollution

Electrostatic Precipitator: It is the most widely used means to remove particulate matter from exhaust systems. It can remove over 99% of particulate matter in the exhaust from a thermal power plant. Electrode wires are present in electrostatic precipitator. These wires are maintained at several thousand volts. The high voltage produces a corona that releases electrons. These electrons attach to dust particles. Thus, the dust particles get net negative charge. The collecting plates in electrostatic precipitator are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust particles to fall.

Scrubber: In a scrubber, the exhaust is passed through a spray of water or lime. This helps in removing gases; like sulphur dioxide.

Fine Particles: According to Central Pollution Control Board (CPCB), particulate size 2.5 microns or less in diameter (PM 2.5) are highly dangerous for human health. These particles can enter the lungs and can cause many respiratory problems. It may even result in premature death.

Catalytic Converter: It is a device which is fitted in exhaust system of automobiles. It has expensive metals (platinum, palladium and rhodium) as catalysts. When the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively. Lead in petrol inactivates the catalyst. Hence, unleaded petrol should be used in vehicles fitted with catalytic converters.

Controlling Vehicular Air Pollution: A Case Study of Delhi

Delhi has more cars than the states of Gujarat and West Bengal put together. In the 1990s, the Supreme Court of India directed the government to take suitable measures to tackle air pollution in Delhi. As a result of this directive, all public transport buses were fitted with CNG kits. CNG is a cleaner fuel than petrol or diesel. This helped a lot in controlling air pollution in cities.

The Government of India laid out a roadmap to cut down vehicular pollution in cities. More stringent norms for fuel mean gradual reduction of sulphur and aromatic components in petrol and diesel fuels. For example; Euro II norms say that sulphur should be 350 ppm in diesel and 150 ppm in petrol. Bharat Stage II is equivalent to Euro II norms. At present, Bharat IV norms are in practice, and Bharat VI norms are being planned to be enforced from 2020 onwards.

Noise Pollution: The Air (Prevention and Control of Pollution) Act 1981 was amended in 1987 to include noise as an air pollutant. Noise pollution can result in loss of hearing, other physical problems and many psychological problems. Many laws have been made to control noise pollution. However, strict enforcement of these laws is the need of the day.

Water Pollution

The Government had passed the Water (Prevention and Control of Pollution) Act, 1974 to safeguard our water resources.

Domestic Sewage and Industrial Effluents

Domestic sewage mainly contains biodegradable organic matter. Some bacteria and other microbes decompose this organic matter. While decomposing organic matter, these microbes consume of a lot of oxygen. This results in a sharp decline in dissolved oxygen downstream; from the point of sewage discharge. Reduced level of oxygen causes mortality of fish and other aquatic creatures.

Algal Bloom: Presence of large amounts of nutrients in water also causes excessive growth of planktonic algae. This phenomenon is called algal bloom. Algal bloom imparts distinct colour to the water bodies. It causes deterioration of water quality and results in fish mortality. Some bloom-forming algae are extremely toxic to human beings and animals.

Wastewater from industries often contain toxic substances; notably; heavy metals. Some of the toxic substances can undergo biological magnification in the aquatic food chain. The increase in concentration of a toxicant at successive trophic levels is called biomagnification. This often proves harmful for animals which are at the top of the food pyramid.

Eutrophication: The natural aging of a lake by biological enrichment of its water is called eutrophication. In due course of time, a lake changes into land through natural aging. But pollutants can radically accelerate this aging process. This phenomenon is called Cultural or Accelerated Eutrophication.