Pollution Class 8 Science Notes Maharashtra Board

Pollution Class 8 Science Notes Maharashtra State Board

Many problems have arisen on the earth due to human interference in nature. Industrialization, increasing population, mining, transportation, and indiscriminate use of pesticides and fertilizers are causing pollution on the earth. It is affecting human beings.

Pollution:

Contamination of the natural environment that will be harmful to ecosystems is called as pollution.

Pollutants:

Factors affecting the natural functions of the ecosystem and causing harmful effects on abiotic and biotic factors are called as pollutants. Pollutants make the environment poisonous and unhealthy. Pollutants may be natural or manmade. Natural pollutants are destroyed in due course of time by nature’s rule; however, manmade pollutants are not.

A. Air Pollution:

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

Reasons of Air Pollution

Natural Reasons:

1. Volcanic eruption: Solid, gaseous, and liquid materials emerge through the eruption.
   Ex. Hydrogen sulphide, sulphur dioxide, carbon dioxide, ammonium chloride, hydrogen, vapors, dust, etc.
2. Earthquake: Poisonous gases and water vapors from the inside of the earth are released into the air.
3. Cyclones and dust storms: Dust, soil, garbage, pollens, and microbes are mixed with air.
4. Forest fires: Forest fires release carbon dioxide, sulphur dioxide, hydrogen sulfide, and smoke into the air.
5. Microbes in the air: spores of bacteria, and fungi are mixed with the air.

Manmade Reasons

1. Fuel:
   • Burning of fuel like coal, timber, LPG, kerosene, diesel, and petrol releases carbon dioxide, carbon monoxide, nitrogen oxide, sulphur dioxide, lead compounds, etc. are released into the air.
   • Burning of solid waste, agricultural waste, etc. in open space causes air pollution.
2. Industrialization: Smoke is released in large quantities from various factories. sulphur powder, nitrogen oxide, and Cotten seed powder in the air.
3. Atomic energy plants and blasts: The use of elements like uranium, thorium, graphite, and plutonium releases radiation in the air, and thus pollution occurs.

Air Pollutants: Sources and Effects

Air Pollutants	Source	Effects
1. Sulphur Dioxide (SO2)	Factories (where coal and mineral oil are used as fuel)	Irritation of eyes, respiratory tract, excess mucus, cough, breath.
2. Carbon Monoxide (CO)	Vehicular and industrial smoke.	Lowered O2 carrying capacity of blood.
3. Oxides of Nitrogen	Vehicular smoke	Irritation of the respiratory tract and lungs
4. Particulate Matter	Vehicular and industrial smoke	Respiratory diseases
5. Dust	Vehicular and industrial smoke	Silicosis
6. Pesticides	Production and use of Pesticides	Mental weakness, death due to prolonged exposure
7. Methane (CH4)	Industrial leakage	Poisoning, skin cancer, asthma, respiratory diseases.

The worst ever industrial accident had occurred in Bhopal on the night of 2nd Dec.1984. Eight thousand people had been died due to accidental gas leakage. Collect more information about the Bhopal gas accident and discuss the nature of the accident, reasons, aftereffects, and preventive measures.

Effect of Air Pollution on Plants and Animals

Depletion in the Ozone layer:
Earlier, we have studied that the ozone layer is present below the stratosphere, at a height of 48 kilometers from the earth’s surface. It protects the living world of the earth from ultraviolet rays (UV-B) radiating from the Sun. However, nowadays, the ozone layer is getting depleted due to the following reasons.

Green House Effect and Global Warming:
Though CO₂ is present in very small quantities in the atmosphere, it plays a very important role in the absorption of solar heat. Over the last 100 years, the proportion of CO₂ has been increased due to industrialization. The effect of this CO₂ on the earth’s temperature is nothing but the greenhouse effect. Similar to CO₂, nitrous oxide, methane, and CFC also trap the heat. Collectively, these are called greenhouse gases.

Global temperature is gradually increasing due to the greenhouse effect. Due to this, the atmosphere is changing, causing disturbances in agricultural yield, and the distribution of wild animals. Icebergs and glaciers are melting causing an increase in sea level.

Acid Rain:
Oxides of sulphur and nitrogen are released into the atmosphere through the burning of coal, timber, and fuel oils. Those oxides mix with rainwater and form acids like sulphuric acid, nitric acid, nitrous acid, etc. These acids mix with raindrops and snowflakes and come down as rain, called acid rain.

Effects of Acid Rain:

• The acidity of soil and water bodies increases due to acid rain. It harms the aquatic organisms, plants, and entire forest life. Total ecosystems are adversely affected.
• Erosion of buildings, busts, historical monuments, bridges, metal idols, wire fences, etc. occurs due to acid rain.
• Heavy metals like mercury and cadmium are absorbed by plants and thereby enter the food chain indirectly due to acid rain.
• Due to the acidification of water in water bodies and pipes, leaching of metal and plastic material occurs in water, and thereby serious health problems arise.

Preventive Measures of Air Pollution:

• Smoke emerging from factories contains harmful particles. Hence, pollution-controlling machinery should be used. Ex. Arresters, filters.
• Proper disposal of stinking waste generated in cities.
• Control of atomic tests, chemical weapons, etc.
• Control/ban over CFC production.

Air Quality Index:
Citizens need to know the extent of air pollution in their city. To define the air quality index, the proportion of SO₂, CO, NO₂, ozone, particulate matter, etc. is measured every day. Boards indicating the air quality index are displayed in busy squares in metro cities. Air pollutants with sulphur cause colour changes in paints, oil paintings, nylon, cotton fabrics, leather articles, papers, etc.

B. Water Pollution:

Water is said to be polluted when it becomes unclean and poisonous due to the mixing of natural or artificial unwanted material when it becomes harmful to living organisms due to decreased oxygen content, and when epidemic diseases are spread through the water. Freshwater or marine water pollution includes physical, chemical, and biological changes. A large number of tanning centers are present in Tamilnadu. Waste water from those centers is released into the Palar River. Hence that river is referred to as Puzzar (Gutter River).

Water Pollutants:

• Biological Pollutants: Water does not remain potable due to algae, bacteria, viruses, parasites, etc. Diseases are spread due to biological pollution.
• Inorganic Pollutants: Suspended particles like fine sand, dust, soil, precipitates of salt, compounds of arsenic, cadmium, lead, mercury, and traces of radioactive material.
• Organic Pollutants: Weedicides, insecticides, fertilizers, sewage, industrial effluents, etc.

Reasons of Water Pollution

1. Natural Reasons

• Aquatic weeds: Depletion in O2 level, Changes in natural qualities of water.
• Decomposing matter: Decomposing bodies of plants, and animals.
• Mud/Sludge: River current and its diversion
• Soil Erosion: Many biotic and abiotic factors are added to water due to soil erosion.
• Microbes Like Fungi and Bacteria: grow on organic matter decaying in water.
• Algae: Excessive algal growth pollutes water.
• Nematodes: Soil nematodes flow in with rainwater.

2. Manmade Reasons

• Domestic Sewage: Domestic sewage from villages and cities is disposed of in river water.
• Industrial effluent: Various pigments, bleaching chemicals, leather pieces, fibers, mercury, lead, etc. are released into the water.
• Oil spillage: While transporting, and cleaning tankers oil spills into water.
• Use of fertilizers and pesticides: N, P, K containing chemical fertilizers. Pesticides like endrin, chlorine, and carbonate-containing pesticides, flow, and mix with water.
• Other reasons: Disposal of human wastes, washing of clothes, decomposing hemp and flax in water, disposal of ashes, floral offerings to god, water from thermal power plants, etc.

Effects of Water Pollution

1. Effects on Human beings
   • Diseases like hepatitis, typhoid, and diseases of the skin and alimentary canal.
   • Ailments of liver, kidneys, brain, deformities in bones, hypertension.
2. Effects on Ecosystem
   • Retarded plant growth
   • Loss of plant species
   • Increase in salt content of water
   • Decreased dissolved oxygen level
   • Disturbance in aquatic ecosystem
   • Death of aquatic animals
   • Adverse effects on sea birds
3. Other Effects
   • Changes in physical and chemical properties of water.
   • Changes in natural color and taste.
   • Useful aquatic fauna is destroyed.
   • Soil fertility is affected.
   • Toxic materials are added to crops.

C. Soil Pollution:

Out of the total land area of the soil, some is covered by ice; some is desert, whereas some is occupied by mountains and hills. Very little area of land is available for human use. Soil is said to be polluted when there are changes in its physical biological and chemical properties and its fertility decreases due to either natural or manmade reasons.

Effects of Soil Pollution:

• Soil fertility decreases due to the mixing of salty, acidic water from the industry.
• Radioactive and other pollutants enter and pass through the food chain like the soil, crop, water, and human body.
• The problem of water pollution increases due to soil pollution. Toxic substances leach into the water. Similarly, diseases spread through various pathogens.

Relationship of Soil Pollution with Air and Water Pollution
If wet waste is dumped in the wrong places instead of composting, pathogens grow upon it, which are then mixed with water causing water pollution. Insecticides, chemical fertilizers, and weedicides are used in agriculture, which causes soil pollution. Excessively sprayed insecticides and weedicides are mixed with air causing air pollution. Similarly, excessive use of chemical fertilizers causes water pollution. Soil pollution occurs due to the mixing of human wastes, birds, and animal waste. This releases various stinking gases causing air pollution. The same waste may cause water pollution if mixed with water.

Pollution – Prevention and Control:
The government of India has enacted some laws for the control, regulation, and prevention of pollution. Following are laws regarding pollution control.

• Water pollution and prevention act, 1974.
• Air pollution and prevention act, 1981.
• Environmental Protection Act, 1986.

Various laws and rules exist about biomedical waste, harmful effluents, solid waste, and sound pollution. Government statutory bodies like the Maharashtra Pollution Control Board and Central Pollution Control Board supervise whether the industries, industrial areas and local governing bodies like municipalities, district councils, panchayat samiti, gram panchayat, etc. follow the laws about pollution control.

Well-structured Maharashtra State Board Class 8 Science Notes Pollution can reduce exam anxiety.