Revision: Ecology and Environment >> Environmental Issues Biology (Theory) ISC (Science) ISC Class 12 CISCE

Environmental chemistry is the study of chemical and biochemical processes occurring in nature. It deals with the study of origin, transport, reaction, effects, and fates of various chemical species in the environment.

Any undesirable change or imbalance in the physical, chemical, or biological components of the environment that harms life is called environmental pollution.

Any substance which causes pollution is called a pollutant.

Air pollution means degradation of the air quality which harmfully affects the living organisms as well as certain objects.

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

The natural phenomenon by which certain atmospheric gases trap heat and warm the Earth’s surface is called the greenhouse effect.

The gradual increase in the average surface temperature of the Earth due to rising concentrations of greenhouse gases in the atmosphere is called global warming.

The gradual increase in Earth’s average surface temperature due to rising concentrations of greenhouse gases in the atmosphere is called global warming.

The warming up of the atmosphere due to trapping of the solar radiation reflected by the earth by gases like carbon dioxide is called Greenhouse effect.

The global impact on climate and weather caused by the eastward movement of warm Pacific waters and changes in atmospheric pressure is called the El Nino effect.

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.

The amount of heat that is needed to raise the temperature of a unit mass of a substance by 1°C is called specific heat capacity.

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.

The amount of dissolved oxygen required by bacteria and other microorganisms to decompose and stabilise organic matter present in wastewater is called Biochemical Oxygen Demand (BOD).

The progressive increase in the concentration of toxic substances at successive higher trophic levels of a food chain is called biomagnification.

The accumulation of pesticides or other toxic substances within the body of living organisms over time is called bioaccumulation.

The process by which substances present in very low or insignificant amounts in the environment enter and concentrate within organisms through food chains is called bioconcentration.

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

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.

Noise pollution, also known as sound pollution, is defined as the presence of excessive, unwanted, or harmful sounds in the environment that disrupt normal activities and adversely affect the health and well-being of humans and other living organisms.

The basic unit used to measure the loudness or intensity of sound is called decibel (dB).

The increase in natural background radiation due to human activities involving the use of naturally occurring or artificially produced radioactive materials is called radioactive pollution.

Pesticides such as DDT (dichloro-diphenyl-trichloroethane) are used in agriculture to destroy pests, alter the basic structure of the soil, kill microorganisms in it, and may even reach the human body through food grown in such soils.

The contamination of soil by natural or synthetic substances that adversely affect its physical, chemical, and biological properties and reduce its productivity is called soil pollution.

Sanitary landfills are places where waste is dumped in a ground depression and covered with dirt every day.

The loss of soil or disturbance of the soil structure is called soil erosion.

Irreparable computers and other electronic goods are known as electronic wastes (e-wastes).

Deforestation is the conversion of forested areas into non-forested areas for agricultural, industrial, urban or other human uses.

• Air pollutants are broadly classified into gaseous pollutants (CO, SO₂, NOₓ, hydrocarbons, ozone) and particulate pollutants (dust, smoke, metals, radioactive particles).
• Gaseous pollutants may be primary (emitted directly) or secondary (formed in the atmosphere, e.g., ozone and photochemical smog).
• Carbon monoxide, mainly from automobile exhausts, is one of the most abundant and dangerous air pollutants.
• Oxides of sulphur and nitrogen, released from fossil fuel combustion and industries, cause respiratory problems and contribute to smog and acid rain.
• Particulate pollutants include solid and liquid particles such as smoke, heavy metals, pesticides and radioactive substances that damage lungs and the environment.

1. Control at Source
   Air pollution can be reduced by proper planning and siting of industries, improved design of equipment, correct fuel–air mixture, use of fuel additives, and efficient engine design in vehicles.
2. Vehicular Pollution Control
   Installation of catalytic converters, use of unleaded petrol, adoption of CNG/LPG, and enforcement of Bharat Stage (Euro) emission norms significantly reduce harmful exhaust emissions.
3. Industrial Pollution Control Devices
   Emissions from industries and power plants are controlled using cyclone collectors, scrubbers, and electrostatic precipitators, which remove particulate matter and harmful gases before release into the atmosphere.
4. Legislative and Policy Measures
   Laws such as the Air (Prevention and Control of Pollution) Act, 1981 and Environment (Protection) Act, 1986, along with emission standards and fuel regulations, play a crucial role in controlling air pollution.
5. Afforestation and Public Awareness
   Planting pollution-tolerant trees around urban and industrial areas, along with environmental education and public awareness programmes, helps improve air quality and reduce pollution impacts.

1. Acid rain forms when rainwater absorbs industrial gases like CO₂, SO₂, and nitrogen oxides, making it more acidic.
2. It harms soil and vegetation, corrodes buildings, damages monuments by reacting with calcium, and reduces visibility.
3. It also acidifies water bodies, endangering fish and aquatic life.
4. Soil pollution reduces soil fertility and nutrients.
5. Waste control is essential to protect soil health.

• Climate change refers to long-term changes in temperature, rainfall, wind and other climatic patterns due to natural and human causes.
• Human activities like burning fossil fuels and deforestation increase greenhouse gases, strengthening the greenhouse effect.
• Natural factors such as volcanic activity, ocean circulation and changes in Earth’s orbit also influence climate change.
• Major signs include rising global temperatures, melting glaciers and polar ice, sea-level rise and changing rainfall patterns.
• Future impacts may include frequent heat waves, stronger storms, flooding, ecosystem disruption and socio-economic damage.

• Kyoto Protocol is a legally binding international agreement adopted in 1997 (Kyoto, Japan) under the UNFCCC to reduce greenhouse gas emissions.
• It came into force in 2005 and required industrialized countries to reduce emissions by about 5.2% below 1990 levels during 2008–2012.
• It targeted six greenhouse gases including CO₂, CH₄, N₂O, HFCs, PFCs and SF₆.
• The protocol introduced mechanisms like national emission targets, adaptation fund, accounting, reporting and compliance systems.
• Its main aim was to prevent dangerous human interference with the climate system by stabilizing greenhouse gas concentrations.

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.

1. Health hazards
   Radioactive pollution causes severe health problems such as radiation sickness, cancer, anemia, hair loss, skin ulceration and even death at high exposure levels.
2. Cellular and tissue damage
   Ionizing radiations (α, β, γ, X-rays, UV) damage living tissues by causing ionization, leading to destruction of cells, organs and vital systems.
3. Genetic effects
   Radiation induces mutations in genes and chromosomes, resulting in abnormal births, inherited defects and long-term effects on future generations.
4. Effects through food chain
   Radioactive substances enter the food chain and accumulate in organisms, causing indirect contamination and widespread biological damage.
5. Acute and chronic effects
   Low doses cause delayed effects like leukemia, cataract and sterility, while high doses cause radiation sickness and rapid mortality, as seen in Hiroshima and Nagasaki.

1. Land degradation
   Land degradation is the general wearing away and loss of productivity of land due to factors such as salinization, erosion, deforestation, flooding, water-logging and unplanned urbanization.
2. Importance of top soil
   The fertile top soil (15–20 cm thick) contains essential plant nutrients, and its degradation directly reduces agricultural productivity.
3. Soil salinization
   Soil salinization is caused by the accumulation of soluble salts (mainly sodium, calcium and magnesium salts) which adversely affect soil structure and crop yield.
4. Causes of salinization
   Salinization occurs due to inadequate leaching in semi-arid regions, rising and fluctuating groundwater table, rapid evaporation, saline irrigation water, canal seepage and seawater intrusion in coastal areas.
5. Extent and impact in India
   About 7 million hectares of land in India are salt-affected, especially in coastal, arid, semi-arid and Indo-Gangetic regions, posing a serious threat to sustainable agriculture.

• Soil erosion is the removal of the top fertile layer of soil by water, wind, and human activities.
• Soil erosion by water includes sheet erosion, rill erosion, gully erosion, leaching, sea erosion, and stream-bank erosion.
• Wind erosion occurs in dry and semi-arid regions where loose soil is carried away by strong winds, reducing soil fertility.
• Human activities such as deforestation, overgrazing, improper farming, and shifting cultivation greatly increase soil erosion.
• Soil erosion reduces agricultural productivity, leads to land degradation, and creates a cycle of poverty.

1. Land degradation problem
   Population growth, faulty agricultural practices, deforestation, erosion, salinisation, water-logging and urban encroachment have reduced land productivity in India.
2. Forest conservation measures
   The Forest (Conservation) Act, 1980 (amended in 1988) restricts deforestation; measures include controlling shifting cultivation, banning felling above 1000 m, afforestation of hills and protection of catchment areas.
3. Water management challenges
   Floods, siltation, misuse of Himalayan slopes and reservoir damage cause loss of cultivable land and depletion of water resources.
4. Improving irrigation efficiency
   Water-logging and salinity affect over 20% of irrigated land; solutions include lining canals, proper drainage, land levelling and efficient farm-level water management.
5. Role of groundwater
   Groundwater is economical, easily available, less prone to losses and vital in arid regions; its management is guided nationally by the Central Ground Water Board.

1. Afforestation and Reforestation
   Large-scale afforestation programmes are promoted to increase forest cover, while reforestation helps restore forests that were destroyed earlier, either naturally or through human efforts.
2. Social Forestry
   Started in 1976, social forestry encourages plantation on community and public lands to supply firewood, fodder and small timber, reducing pressure on natural forests and involving local people.
3. Agroforestry
   Agroforestry integrates agriculture, forestry and animal husbandry on the same land to increase productivity, conserve the environment and meet demands for fuel, fodder and timber.
4. Urban Forestry
   Urban forestry focuses on planting trees in towns and cities for aesthetic value, pollution control and improvement of urban environment.
5. Forest Policies and Legislation
   The National Forest Policy (1988) and the Forest (Conservation) Act, 1980 aim to protect forests, prevent diversion of forest land, promote sustainable use and encourage people’s participation in forest conservation.

1. Mercury pollution causes Minamata disease, leading to severe neurological damage and death due to bioaccumulation in fish.
2. Persistent pesticides like DDT biomagnify in food chains and cause hormonal disorders, cancers and neurological problems.
3. Exposure to pesticides and heavy metals is a major risk factor for Parkinson’s disease by damaging dopamine-producing neurons.
4. Air pollution and smoking are the leading causes of lung cancer, causing uncontrolled growth of lung tissues.
5. Bioaccumulation and biomagnification increase the toxicity of pollutants, making humans the most affected at the top of the food chain.