Pollution
ICSE Class 9 · Geography · Chapter 16
What this chapter covers
- Meaning of pollution
- Types of pollution
- Air pollution
- Water pollution
- Freshwater pollution
- Marine pollution
- Soil pollution
- Radiation pollution
- Noise pollution
- Comparing the types of pollution
Key points
- Pollution is the addition of substances or energy to the environment faster than it can disperse, break down or store them, so that its quality is harmed.
- A pollutant may be a material, such as smoke or plastic, or a form of energy, such as sound, heat or radiation.
- Pollution may be natural or human-made, and pollutants may be biodegradable or non-biodegradable.
- The five types in the syllabus are air, water (freshwater and marine), soil, radiation and noise pollution.
- Air pollution involves gases such as carbon monoxide, sulphur dioxide, oxides of nitrogen and ozone, and particulate matter such as PM10 and PM2.5; air quality is shown by the AQI from 0 to 500.
- Smog is a mixture of smoke, fog and pollutants trapped near the ground, severe in the northern plains of India in winter.
- Water pollution makes water unfit for use; dissolved oxygen and BOD are key measures of its health.
- Freshwater pollution affects rivers, lakes and groundwater; marine pollution affects the seas, mainly through oil, plastics and waste carried by rivers.
- Soil pollution comes from excess fertilisers, pesticides, bio-medical and industrial waste and plastics, and reduces fertility.
- Radiation pollution is the release of ionising radiation or radioactive substances above the natural level; doses are measured in sieverts, and radioactive fallout can travel great distances.
- Noise pollution is loud or unwanted sound measured in decibels; every 10 dB rise means ten times the sound energy, and silence zones have the lowest limits.
- The types of pollution are linked, because pollutants move between air, water and soil through rain, seepage, wind and food.
Questions answered
Define pollution and pollutant. Why is sound counted as a pollutant even though it is not a material substance?
Pollution is the addition of any substance or form of energy to the air, water or soil faster than the environment can disperse, break down or store it, so that its quality is harmed. A pollutant is any substance or form of energy that, in more than a certain amount, causes such harm. Sound is energy, and loud or prolonged sound harms hearing, sleep and health, so in excess it is a pollutant.
Distinguish between biodegradable and non-biodegradable pollutants, with two examples of each.
Biodegradable pollutants are broken down by decomposers into harmless substances within a short time, for example sewage and kitchen waste. Non-biodegradable pollutants cannot be broken down, or only over hundreds of years, so they build up; examples are plastic bags and mercury.
Name the five types of pollution in the syllabus and state which of them are named after a medium and which after a form of energy.
Air, water, soil, radiation and noise pollution. Air, water and soil pollution are named after the medium polluted; radiation and noise pollution are named after the form of energy that causes harm.
What is particulate matter? Why is PM2.5 considered more harmful than PM10?
Particulate matter is the mixture of tiny solid particles and liquid droplets, such as dust, soot and smoke, suspended in the air. PM2.5 particles are 2.5 micrometres or less across, so they reach deep into the lungs and can pass into the blood, while the larger PM10 particles are mostly stopped in the nose, throat and windpipe.
Why do the cities of the northern plains of India suffer severe smog in winter, while Mumbai's air is usually cleaner?
In winter the northern plains have calm, cold nights when cold air near the ground is trapped below warmer air, so smoke, dust and gases cannot rise and collect near the surface; the enclosed plain and light winds add to this. Mumbai is on the coast, where regular sea breezes carry pollutants away.
The AQI of a city is 180 on one day and 420 on another. Name the category of each day.
An AQI of 180 is "Moderately polluted" (101–200), and an AQI of 420 is "Severe" (401–500).
Ground-level ozone is a pollutant, but the ozone layer is useful. Explain.
In the stratosphere the ozone layer absorbs harmful ultraviolet rays from the Sun and protects life. Near the ground, ozone formed from vehicle exhaust gases in sunlight is breathed in and irritates the eyes and lungs, so there it is a pollutant.
Define dissolved oxygen. Why does the discharge of sewage into a river lower it?
Dissolved oxygen is the amount of oxygen gas dissolved in water, usually given in milligrams per litre. Sewage is organic waste, and the bacteria that break it down use up the oxygen in the water, so the level falls and fish may die.
Past board exam questions
ICSE 2019 sample paper · 2 marks
(i) Name any two sources of soil pollution. (ii) State the impact of soil pollution on agricultural production.
Show answer
(i) Any two: excessive use of chemical fertilisers and pesticides; industrial waste (effluents, heavy metals); urban/domestic solid waste such as plastics; mining waste; acid rain.
(ii) Soil pollution reduces soil fertility and kills useful soil organisms, so crop yields fall; toxic chemicals are absorbed by crops and enter the food chain, making the produce harmful.
ICSE 2019 sample paper · 2 marks
(i) What is the cause of ozone depletion? (ii) State the impact of ozone depletion on human life.
Show answer
(i) Ozone depletion is caused mainly by chlorofluorocarbons (CFCs) released from refrigerators, air conditioners, aerosol sprays and foam, and by halons and nitrogen oxides; chlorine from them breaks down ozone molecules in the stratosphere.
(ii) More ultraviolet rays reach the Earth, causing skin cancer, cataract (eye damage) and weakening of the immune system in human beings.
ICSE 2019 sample paper · 2 marks
Explain how industrial waste and vehicular emission act as the source of air pollution.
Show answer
Industries burn coal and oil and release smoke containing sulphur dioxide, nitrogen oxides, carbon monoxide, dust/particulate matter and toxic gases into the air. Vehicles burn petrol and diesel and emit carbon monoxide, nitrogen oxides, hydrocarbons, lead and fine particles through their exhaust. These pollutants mix with the air and pollute it.
ICSE 2019 sample paper · 2 marks
Which health hazards are associated with radioactive waste?
Show answer
Radiation from radioactive waste can cause cancer (e.g. leukaemia, skin cancer), genetic mutations and birth defects in children, damage to body tissues and organs, burns, sterility, and even death on heavy exposure.