Revision: Environmental Issues Zoology HSC Science Class 12 Tamil Nadu Board of Secondary Education

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.

Noise is defined as any unpleasant, loud, undesired sound that interferes with one’s hearing and concentration, and the pollution caused by noise is termed noise pollution.

Noise is defined as any unpleasant/loud undesired sound interfering with one's hearing and concentration and the pollution caused due to noise is termed as noise pollution.

The natural process of aging of a lake due to gradual enrichment of its water with nutrients, leading to increased biological productivity, is called eutrophication.

A sustainable system of human waste management that safely recycles human excreta without using water is called ecological sanitation (Ecosan).

• 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.

• 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.

• Noise pollution is an undesirable high level of sound. Included as an air pollutant under Air (Prevention and Control of Pollution) Act, 1981, amended in 1987.
• Sources - machines, transportation, construction sites, industries, festivals and public functions.
• Exposure to 150 dB or more causes permanent hearing loss. Other effects - sleeplessness, increased heartbeat, altered breathing, psychological stress and negative impact on the child's learning.
• Control measures - sound absorbent materials, muffling noise, and horn-free zones near schools and hospitals.
• Supreme Court banned loudspeakers at public gatherings after 10 pm. The government has rules against firecrackers and loudspeakers.

1. Soil degradation: Excessive use of chemical fertilisers reduces soil microbes, causes mineral imbalance, erosion, and lowers plant disease resistance.
2. Water pollution: Nitrates and phosphates reach water bodies, causing eutrophication, oxygen depletion, algal blooms, and death of aquatic life.
3. Human health hazards: Nitrate-contaminated water causes methaemoglobinaemia, blue baby syndrome, respiratory disorders and cancer risks.
4. Pesticide toxicity: Persistent pesticides (DDT, BHC, aldrin, PCBs) bioaccumulate, damaging kidneys, brain, nervous system and threatening ecological security.

• Organic farming is an eco-friendly agricultural system that avoids chemical fertilizers and pesticides and maintains natural balance in farming.
• It uses organic wastes, biofertilizers, animal manure, and microbes to supply nutrients and maintain soil fertility.
• Crop rotation, biological pest control, and resistant local varieties are used to manage weeds and diseases naturally.
• Organic farming promotes sustainable agriculture, soil health, biodiversity, and long-term productivity, ensuring safe food for humans and environment.