NCERT Solution Environmental Class 12 Chapter 16

Environmental class 12 Introduction

Human population size has grown enormously over the last hundred years. This means an increase in demand for food water homes, electricity roads automobiles, and numerous other commodities. These demands are exerting tremendous pressure on our natural resources, and are also contributing to the pollution of air water, and soil.

Environmental class 12

The need of the hour is to check the degradation and depletion of our precious natural resources and pollution without halting the process of development. Pollution is any undesirable change in physical, chemical, or biological characteristics of air, land, water, or soil. Agents that bring about such an undesirable change are called pollutants.

In order to control environmental pollution, the Government of India has passed the Environment (Protection) Act, of 1986 to protect and improve the quality of our environment (air, water, and soil).

Environmental class 12 Definition

In ecology, the term environment” generally refers to the study and understanding of the interactions between living organisms and their environment. It covers many issues like the environment, biodiversity, natural resources, pollution, climate change, sustainable development, and human impact on the environment.

The study of environmental science aims to examine the relationship between people and their environment, including the effects of human activities on the natural world and beyond. It also seeks to develop solutions and strategies to solve environmental problems and promote the conservation and use of natural resources for present and future generations.

Environmental class 12 NCERT Important Notes

  1. Ecosystems: Understand the structure and function of ecosystems, including the roles of producers, consumers, and decomposers, energy flows, and cycling.
  2. Biodiversity: Explore the importance of biodiversity, the factors that cause biodiversity loss, and conservation measures to protect species and habitats.
  3. Natural Resources: Explore the concept of natural resources, including renewable and non-renewable resources, their sustainable management, and the consequences of resource scarcity.
  4. Pollution: Study of various types of pollution such as air pollution, water pollution, soil pollution, air pollution and its sources, environmental and human health impacts, and mitigation strategies.
  5. Climate Change: Understand the causes and effects of climate change, including global warming, rising sea levels, extreme weather events, and the role of human activities such as deforestation and the burning of fossil fuels
  6. Sustainable Development: Exploration of the principles of sustainable development, aiming to meet the needs of the current generation without compromising the resources of the next generation.

Environmental class 12 Explanation

16.1 AIR POLLUTION AND ITS CONTROL We are dependent on air for our respiratory needs. Air pollutants cause injury to all living organisms. They reduce growth and yield of crops and cause premature death of plants. Air pollutants also deleteriously affect the respiratory system of humans and of animals. Harmful

Effects depend on the concentration of pollutants, duration of exposure, and the organism. Smokestacks of thermal power plants, smelters, and other industries release particulate and gaseous air pollutants together with harmless gases, such as nitrogen, oxygen, etc.

These pollutants must be separated/filtered out before releasing the harmless gases into the atmosphere.

There are several ways of removing particulate matter; the most widely used of which is the electrostatic precipitator (Figure 16.1), which can remove over 99 percent of particulate matter present in the exhaust from a thermal power plant.

Environmental class 12

It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded and attract the charged dust particles.

The velocity of air between the plates must be low enough to allow the dust to fall. A scrubber (Figure 16.1) can remove gases like sulfur dioxide. In a scrubber, the exhaust is passed through a spray of water or lime.

Recently we have realized the dangers of particulate matter that are very very small and are not removed by these precipitators. According to the Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) is responsible for causing the greatest harm to human health.

These fine particulates can be inhaled deep into the lungs and can cause breathing and respiratory symptoms, irritation, inflammation damage to the lungs, and premature death.

Automobiles are a major cause of atmospheric pollution, especially in metro cities, and as the number of vehicles increases on the streets, this problem is now shifting to other cities as well.

Proper maintenance of automobiles, along with the use of lead-free petrol or diesel, can reduce the pollutants they emit. Catalytic converters, fitted with expensive metals like platinum-palladium and rhodium as catalysts, are installed in automobiles to reduce the emission of poisonous gases.

As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, while carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively. Motor vehicles equipped with catalytic converters should use unleaded petrol because lead in the petrol inactivates the catalyst.

In India, the Air (Prevention and Control of Pollution) Act came into force in 1981 but was amended in 1987 to include noise as an air pollutant. Noise, characterized by undesired high levels of sound, causes psychological and physiological disorders in humans.

Loud sounds, often associated with pleasure and entertainment, can damage eardrums and permanently impair hearing ability. Chronic exposure to lower noise levels in cities can also damage hearing abilities and cause sleeplessness, increased heart rate, and altered breathing patterns, leading to considerable stress.

Reduction of noise pollution in industries can be achieved by using sound-absorbent materials or muffling noise.

Stringent enforcement of laws related to noise pollution, such as the delimitation of horn-free zones around hospitals and schools, permissible sound levels of crackers and loudspeakers, and regulations on loudspeaker usage timings, is necessary to protect against noise pollution.

16.1.1 Controlling Vehicular Air Pollution: A Case Study of Delhi

With its large population of vehicular traffic, Delhi leads the country in levels of air pollution. In the 1990s, Delhi ranked fourth among the 41 most polluted cities globally. Air pollution problems prompted a public interest litigation (PIL) filed in the Supreme Court of India.

Under Supreme Court directives, the government was asked to take appropriate measures, including switching the entire fleet of public transport from diesel to compressed natural gas (CNG).

By the end of 2002, all Delhi buses were converted to run on CNG. CNG is preferred over diesel due to its lower emissions and environmental benefits.

CNG burns most efficiently in automobiles, leaving very little unburnt residue compared to petrol or diesel. Additionally, CNG is cheaper and less prone to theft and adulteration. However, the main challenge with transitioning to CNG is the establishment of pipelines for distribution and ensuring uninterrupted supply.

In Delhi, efforts to reduce vehicular pollution include phasing out old vehicles, promoting the use of unleaded petrol and low-sulphur fuels, installing catalytic converters, and enforcing stringent pollution norms for vehicles.

The Government of India has implemented a new auto fuel policy to reduce vehicular pollution across Indian cities. The policy includes stricter norms for fuel quality, gradually reducing sulphur and aromatic content in petrol and diesel.

For example, Euro III norms mandate controlling sulphur levels at 350 ppm in diesel and 150 ppm in petrol, with aromatic hydrocarbons limited to 42% of the fuel. The ultimate goal is to reduce sulphur levels to 50 ppm and aromatic content to 35%. Vehicle engines will also need upgrades to meet these standards.

Mass Emission Standards (Bharat Stage II, equivalent to Euro-II norms) are no longer applicable in any Indian city. The latest Mass Emission Standards in India are outlined in

Thanks to the efforts made, the air quality of Delhi has significantly improved. According to estimates, there has been a substantial decrease in CO2 and SO2 levels in Delhi between 1997 and 2005.


Human beings have been abusing water bodies around the world by disposing of all kinds of waste into them. We often believe that water can wash away everything, ignoring the fact that water bodies are not only our lifeline but also essential for all other living organisms.

Can you list what we try to wash away through our rivers and drains? Due to such human activities, ponds, lakes, streams, rivers, and oceans have become polluted and unfit for many forms of life.

Environmental class 12
Environmental class 12

Water pollution occurs due to the discharge of domestic sewage, industrial effluents, and agricultural runoff containing fertilizers and pesticides into water bodies. These pollutants degrade water quality, harm aquatic life, and pose serious health risks to humans.

Environmental class 12
Environmental class 12

To control water pollution, various measures need to be implemented, including the treatment of domestic and industrial wastewater before discharge, proper disposal of solid waste, regulation of agricultural practices to minimize runoff, and protection of water bodies from further contamination.

Government regulations and public awareness campaigns play a crucial role in preventing water pollution and ensuring the sustainable management of water resources for present and future generations.

Rivers, estuaries, and oceans are becoming polluted in several parts of the world. Realizing the importance of maintaining the cleanliness of water bodies, the Government of India passed the Water (Prevention and Control of Pollution) Act, 1974, to safeguard our water resources

Environmental class 12

16.2.1 Domestic Sewage and Industrial Effluents

As we use water in our homes in cities and towns, we wash everything into drains. Have you ever wondered where the sewage from our houses goes? What happens in villages? Is the sewage treated before being discharged into the nearest river and mixed with it? Even a mere 0.1 percent impurities make domestic sewage unfit for human use (Figure 16.2).

You have read about sewage treatment plants in Chapter 10. Solids are relatively easy to remove, but what is most difficult to remove are the organic and inorganic impurities and pathogens.

Sewage treatment plants help remove these impurities and pathogens before the treated water is discharged back into water bodies or reused for various purposes. However, in many places, especially in rural areas and developing countries, sewage treatment facilities are inadequate or absent, leading to widespread contamination of water bodies by untreated sewage and industrial effluents.

This poses serious health risks to both humans and aquatic life and contributes to waterborne diseases and ecosystem degradation. Therefore, proper treatment of domestic sewage and industrial effluents is essential to prevent water pollution and protect human health and the environment.

Dissolved salts such as nitrates, phosphates, and other nutrients, as well as toxic metal ions and organic compounds, are common components of domestic sewage and industrial effluents.

Domestic sewage primarily contains biodegradable organic matter, which readily decomposes with the help of bacteria and other microorganisms present in the water. The amount of biodegradable organic matter in sewage water can be estimated by measuring Biochemical Oxygen Demand (BOD).

BOD indicates the amount of dissolved oxygen needed by microorganisms to decompose the organic matter present in the water. This relationship between BOD, microorganisms, and biodegradable matter was discussed in the chapter on microorganisms.

When sewage is discharged into a river, microorganisms involved in the biodegradation process consume a significant amount of oxygen, leading to a sharp decline in dissolved oxygen levels downstream from the discharge point. This oxygen depletion can result in fish kills and other aquatic life disturbances.

The presence of excessive nutrients in water bodies, such as those found in sewage and industrial effluents, can lead to the overgrowth of planktonic algae, causing algal blooms. These blooms can discolor the water and degrade its quality, leading to fish mortality and other ecological imbalances.

Some types of algae involved in these blooms can produce toxins harmful to humans and animals.

Water hyacinth (Eichhornia crassipes) is an example of an invasive aquatic weed that proliferates rapidly in water bodies, causing blockages and ecological disruptions.

Despite its attractive appearance, water hyacinth has become a significant problem worldwide due to its ability to outgrow native vegetation and impede water flow, posing challenges for water management and ecosystem health.

Environmental class 12
Environmental class 12

‘Terror of Bengal’. They proliferate in eutrophic water bodies, disrupting the ecosystem dynamics. Sewage, including that from hospitals, often contains pathogenic microorganisms, posing serious health risks if discharged into water bodies without proper treatment. Diseases like dysentery, typhoid, jaundice, and cholera can result from untreated sewage.

Industrial wastewater, from sectors like petroleum, paper manufacturing, and chemical processing, contains toxic substances such as heavy metals (e.g., mercury, cadmium, lead) and various organic compounds.

Some of these substances can undergo biological magnification in aquatic food chains, where their concentration increases with each trophic level. Mercury and DDT are well-known examples.

For instance, DDT concentrations can rise from 0.003 ppb in water to 25 ppm in fish-eating birds due to biomagnification. High DDT levels disrupt calcium metabolism in birds, leading to eggshell thinning and population decline.

Eutrophication is the natural aging of a lake due to nutrient enrichment, primarily nitrogen and phosphorus, which stimulate the growth of aquatic organisms. Initially cold and clear, the lake becomes more fertile over time, supporting increased plant and animal life.

As organic matter accumulates, the lake grows shallower and warmer, transitioning from a cold-water to a warm-water ecosystem. Marsh plants colonize the shallows, eventually converting the lake into land. The process varies based on factors like climate and lake size.

waste without the need for water. It involves the use of dry toilets or urine-diverting toilets, which separate urine and feces to prevent odor and facilitate decomposition. The collected waste can then be composted and used as fertilizer, closing the nutrient loop and reducing water consumption.

Ecological sanitation promotes water conservation, reduces pollution of water bodies, and improves soil fertility. It is particularly beneficial in areas with water scarcity or inadequate sanitation infrastructure.

By minimizing water usage for waste disposal, ecological sanitation contributes to sustainable resource management and environmental protection.

In addition to conserving water and reducing pollution, ecological sanitation offers health benefits by preventing the contamination of water sources with fecal pathogens. It also supports agricultural productivity by providing nutrient-rich compost for soil enrichment.

Overall, ecological sanitation represents a holistic approach to waste management that aligns with principles of sustainability, resource efficiency, and environmental stewardship.

As communities worldwide grapple with the challenges of water scarcity, pollution, and sanitation, ecological sanitation emerges as a promising solution for promoting human health and environmental well-being.

excreta, using dry composting toilets. This is a practical, hygienic, efficient, and cost-effective solution to human waste disposal. The key point to note here is that with this composting method, human excreta can be recycled into a resource (as natural fertilizer), which reduces the need for chemical fertilizers.

There are working ‘EcoSan’ toilets in many areas of Kerala and Sri Lanka. 16.3 SOLID WASTES refer to everything that goes out in the trash. Municipal solid wastes are wastes from homes, offices, stores, schools, hospitals, etc., that are collected and disposed of by the municipality.

The Municipal solid wastes generally comprise paper, food wastes, plastics, glass, metals, rubber, leather, textiles, etc. Burning reduces the volume of the waste, although it is generally not burnt to completion and open dumps often serve as the breeding ground for rats and flies. Sanitary landfills were adopted as the substitute for open-burning dumps.

In a sanitary landfill, wastes are dumped in a depression or trench after compaction, and covered with dirt every day. If you live in a town or city, do you know where the nearest landfill site is? Landfills are also not really much of a solution since the amount of garbage generation especially in the metros has increased so much that these sites are getting filled too.

Also there is danger of seepage of chemicals, etc., from these landfills polluting the underground water resources. A solution to all this can only be in human beings becoming more sensitive to these environment issues.

All waste that we generate can be categorized into three types – (a) bio-degradable, (b) recyclable, and (c) non-biodegradable. It is important that all garbage generated is sorted. What can be reused or recycled should be separated out; our kabadiwallahs and rag-pickers do a great job of separating of materials for recycling.

The biodegradable materials can be put into deep pits in the ground and be left for natural breakdown. That leaves only the nonbiodegradable to be disposed off. The need to reduce our garbage generation should be a prime goal, instead, we are increasing the use of non-biodegradable products.

Just pick any readymade packet of any ‘good quality’ eatable, say a biscuit packet, and study the packaging – do you see the number of protective layers used? Note that at least one layer is of plastic.

We have started packaging even our daily use products like milk and water in polybags!! In cities, fruits and vegetables can be bought packed in beautiful polystyrene and plastic packaging – we pay so much and what do we do? Contribute heavily to environmental pollution.

State Governments across the country are trying to push for a reduction in the use of plastics and use of eco-friendly packaging. We can do our bit by carrying a cloth or other natural fiber carry-bags when we go shopping and by refusing polythene bags.

Hospitals generate hazardous wastes that contain disinfectants and other harmful chemicals, as well as pathogenic micro-organisms. Such wastes also require careful treatment and disposal.

The use of incinerators is crucial to the disposal of hospital waste. Irreparable computers and other electronic goods are known as electronic wastes (e-waste). E-waste is buried in landfills or incinerated.

Over half of the e-waste generated in the developed world are exported to developing countries, mainly to China, India and Pakistan, where metals like copper, iron, silicon, nickel and gold are recovered during the recycling process.

Unlike developed countries, which have specifically built facilities for recycling of e-waste, recycling in developing countries often involves manual participation thus exposing workers to toxic substances present in e-waste. Recycling is the only solution for the treatment of e-waste, provided it is carried out in an environmentally friendly manner.

16.3.1 Case Study of Remedy for Plastic Waste A plastic sack manufacturer in Bangalore has managed to find the ideal solution to the ever-increasing problem of accumulating plastic waste. Ahmed Khan, aged 57 years old, has been producing plastic sacks for 20 years. About 8 years ago, he realized that plastic waste was a real problem.

Polyblend, a fine powder of recycled modified plastic, was developed then by his company. This mixture is mixed with the bitumen that is used to lay roads. In collaboration with R.V.College of Engineering and the Bangalore City Corporation, Ahmed Khan proved that blends of Polyblend and bitumen, when used to lay roads, enhanced the bitumen’s water-repellant properties, and helped to increase road life by a factor of three.

The raw material for creating Polyblend is any plastic film waste. So, against the price of Rs. 0.40 per kg that rag pickers had been getting for plastic waste, Khan now offers Rs.6. Using Khan’s technique, by the year 2002, more than 40 km of road in Bangalore has already been laid. At this rate, Khan will soon be running short of plastic waste in Bangalore, to produce Polyblend.

Thanks to innovations like Polyblend, we might still avoid being smothered by plastic waste. 16.4 AGRO-CHEMICALS AND THEIR EFFECTS In the wake of green revolution, use of inorganic fertilizers and pesticides has increased manifold for enhancing crop production. Pesticides, herbicides, fungicides, etc., are being increasingly used.

These incidentally, are also toxic to non-target organisms, which are important components of the soil ecosystem. Do you think these can be biomagnified in terrestrial ecosystems? We know what the addition of increasing amounts of chemical fertilisers can do to aquatic ecosystems vis-à-vis eutrophication. The current problems in agriculture are, therefore, extremely grave

16.4.1 Case Study of Organic Farming Integrated organic farming is a cyclical, zero-waste procedure, where waste products from one process are cycled in as nutrients for other processes.

This allows the maximum utilization of resources and increases the efficiency of production. Ramesh Chandra Dagar, a farmer in Sonipat, Haryana, is doing just this. He includes bee-keeping, dairy management, water harvesting, composting, and agriculture in a chain of processes, which support each other and allow an extremely economical and sustainable venture.

There is no need to use chemical fertilizers for crops, as cattle excreta (dung) are used as manure. Crop waste is used to create compost, which can be used as a natural fertilizer or can be used to generate natural gas to satisfy the energy needs of the farm.

Enthusiastic about spreading information and helping on the practice of integrated organic farming, Dagar has created the Haryana Kisan Welfare Club, with a current membership of 5000 farmers.

16.5 RADIOACTIVE WASTES Initially, nuclear energy was hailed as a non-polluting way of generating electricity. Later on, it was realized that the use of nuclear energy has two very serious inherent problems.

The first is accidental leakage, as occurred in the Three Mile Island and Chernobyl incidents and the second is safe disposal of radioactive wastes. Radiation, that is given off by nuclear waste is extremely damaging to organisms because it causes mutations at a very high rate.

At high doses, nuclear radiation is lethal but at lower doses, it creates various disorders, the most frequent of all being cancer. Therefore, nuclear waste is an extremely potent pollutant and has to be dealt with utmost caution.

It has been recommended that storage of nuclear waste, after sufficient pre-treatment, should be done in suitably shielded containers buried within the rocks, about 500 m deep below the earth’s surface.

However, this method of disposal is meeting stiff opposition from the public. Why do you think this method of disposal is not agreeable to many people? 16.6 GREENHOUSE EFFECT AND GLOBAL WARMING The term ‘Greenhouse effect’ has been derived from a phenomenon that occurs in a greenhouse.

Have you ever seen a greenhouse? It looks like a small glass house and is used for growing plants, especially during winter. In a greenhouse, the glass panel lets the light in but does not allow heat to escape.

Therefore, the greenhouse warms up, very much like inside a car that has been parked in the sun for a few hours. The greenhouse effect is a naturally occurring phenomenon that is responsible for the heating of the Earth’s surface and atmosphere. You would be

Environmental class 12 summary

Major issues relating to environmental pollution and depletion of valuable natural resources vary in dimension from local, regional to global levels. Air pollution primarily results from burning of fossil fuel, e.g., coal and petroleum, in industries and in automobiles.

They are harmful to humans, animals and plants, and therefore must be removed to keep our air clean. Domestic sewage, the most common source of pollution of water bodies, reduces dissolved oxygen but increases the biochemical oxygen demand of receiving water

Domestic sewage is rich in nutrients, especially, nitrogen and phosphorus, which cause eutrophication and nuisance creating algal blooms. Industrial wastewaters are often rich in toxic chemicals, especially heavy metals and organic compounds.

Industrial waste water harms living organisms. Municipal solid wastes also create problems and must be disposed of in landfills. Disposal of hazardous wastes like defunct ships, radioactive wastes, and e-waste requires additional efforts.

Soil pollution primarily results from agricultural chemicals (e.g., pesticides) and leachates from solid wastes deposited over it. Two major environmental issues of global nature are the increasing greenhouse effect, which is warming Earth, and the depletion of ozone in the stratosphere.

The enhanced greenhouse effect is mainly due to increased emission of carbon dioxide, methane, nitrous oxide, and CFCs., and also due to deforestation. It may drastically change rainfall patterns, and global temperatures, besides deleteriously affecting living organisms.

Ozone in the stratosphere, which protects us from the harmful effects of ultraviolet radiation, is depleting fast due to the emission of CFCs thus increasing the risks of skin cancer, mutation, and other disorders.

Environmental class 12 Question and Answer

Question:1 What are the environmental concerns of Class 12?


  1. Water Pollution: Learn about the sources and effects of water pollution, such as industrial runoff, agricultural runoff, and sewage pollution, and their effects on aquatic ecosystems and human health.
  2. Soil Degradation: Examine the causes and consequences of soil pollution, including the use of pesticides, chemical fertilizers, industrial waste disposal, and its impact on soil fertility and environmental health.
  3. Solid Waste Management: Understand the challenges associated with solid waste disposal, landfill management, waste recycling and promoting sustainable waste management practices.
  4. Hazardous Waste Management: Learn about the use, treatment, and disposal of hazardous waste generated in industries, healthcare facilities, and other locations to prevent environmental pollution and health hazards.
  5. Global Warming and Climate Change: Exploring the causes and consequences of global warming, greenhouse gas emissions, ecosystems, weather patterns, sea levels and the impact of climate change on society.

Question:2 What are the three types of environment class 12?

Answer : Three types of Environmental

  1. Internal environment.
  2. External macro environment.
  3. External microenvironment

Question:3 What are the three factors of economic environment class 12?


  1. Economic Policy: It is the strategies, rules, and measures adopted by the government to manage and control the economic activities within the country. Economic policy includes fiscal policy (concerned with government spending and taxation),(concerned with foreign countries, exports, the budget, and trade relations),
  2. Economic Systems: Economic systems refer to the structure and organization of the economy, the allocation of resources, the production and distribution of goods and services, and the distribution of income among individuals and groups (resource commons and central planning or collective ownership),
  3. Economic conditions: Economic conditions include various indicators of health and economic performance. These indicators include gross domestic product (GDP), inflation rate, unemployment rate, exchange rate, balance of payments, consumer spending, business investment, and government spending. Economic factors influence business decisions, consumer behavior, investment patterns

Question:4 What is the scope of the environment?

Answer: The environment is large and diverse and includes many dimensions that are connected and influence each other. The core is the ecological dimension, which refers to the relationship between living organisms and their environment, including ecosystems, biodiversity and natural processes.

Environmental quality is another important aspect that examines the cleanliness, health and safety of important things like air, water, soil and air. I

n addition, environmental protection and conservation initiatives seek to conserve natural resources, protect ecosystems, and ensure the health of present and future generations.

Read also

  1. Reproduction in Organisms class 12
  2. Sexual Reproduction in Flowering Plants Class 12
  3. Human Reproduction Class 12
  4. Reproductive Health class 12
  5. Principles of Inheritance and Variation Class 12

Leave a Comment