Board exam focus — Environmental Issues (CBSE & HBSE)

CBSE focuses on air pollution (pollutants, CNG, catalytic converters), water pollution (BOD, eutrophication, Ganga Action Plan), solid waste management, ozone depletion (CFCs, Montreal Protocol), global warming (greenhouse gases, Kyoto Protocol), and radioactive waste. HBSE emphasises definitions, pollutants, effects, ozone depletion, greenhouse effect, and remediation measures.

Air and Water Pollution

Air Pollution

Definition: The presence of harmful substances (physical, chemical, or biological) in the atmosphere at concentrations sufficient to adversely affect human health, other living organisms, or the environment.

Sources of Air Pollution:

Natural sources: volcanic eruptions (SO2, ash, CO2), forest fires (CO, particulates), dust storms, biological decay

Anthropogenic (human-caused) sources:

• Industry: power plants (SO2, NOx, CO2, particulates), cement industry (dust), chemical factories, oil refineries
• Transport: petrol and diesel vehicles emit CO, NOx, hydrocarbons, particulate matter, lead (older engines)
• Agriculture: ammonia from fertilisers, methane from livestock and rice paddies, pesticide drift
• Burning: biomass burning, crop residue burning (stubble burning — major issue in Punjab-Haryana-Delhi NCR), coal-based cooking

Major Air Pollutants:

1. Sulphur Dioxide (SO2):

• From: burning sulphur-containing coal, oil; volcanic eruptions; smelters
• Effects: respiratory irritant (bronchitis, asthma); oxidised to SO3 → H2SO4 (sulfuric acid) → acid rain (damages forests, acidifies lakes, corrodes buildings and metals, mobilises heavy metals in soil → water contamination)
• Acid rain: pH < 5.6 (normal rain pH = 5.6 due to CO2/carbonic acid); affected regions: Eastern North America, Europe, southern China

2. Nitrogen Oxides (NOx — NO, NO2):

• From: high-temperature combustion in vehicles and power plants (N2 + O2 → NO at >1500°C); lightning
• NO2 — brown gas; contributes to photochemical smog; reacts with unburnt hydrocarbons in sunlight → ground-level ozone + PAN (Peroxyacetyl nitrate) → photochemical smog (Los Angeles smog, Delhi smog)
• NOx also contributes to acid rain (HNO3)

3. Carbon Monoxide (CO):

• From: incomplete combustion of fossil fuels; major source: petrol/diesel vehicles
• Colourless, odourless, toxic gas
• Binds haemoglobin (Hb) ~200x stronger than O2 → forms carboxyhaemoglobin (COHb) → impairs O2 transport → dizziness, headache, death at high concentrations (>10,000 ppm)

4. Particulate Matter (PM):

• Fine particles (PM10: <10 μm; PM2.5: <2.5 μm; ultra-fine: <0.1 μm)
• PM2.5 is most dangerous — small enough to penetrate deep into alveoli → systemic inflammation, cardiovascular and respiratory disease, lung cancer
• Sources: diesel vehicles, coal combustion, industrial processes, road dust, construction
• PM2.5 responsible for ~7 million premature deaths/year globally

5. Ozone (Ground-level / Tropospheric):

• NOT protective like stratospheric ozone; ground-level ozone is a pollutant
• Formed by reaction of NOx + VOC (volatile organic compounds) in sunlight → photochemical smog
• Damages lungs; causes crop losses (reduces photosynthesis in plants)

6. Lead (Pb):

• Historically: tetraethyllead in petrol → reduced by phasing out leaded petrol; India: leaded petrol banned 2000
• Lead is a neurotoxin; impairs brain development in children (reduces IQ)

Control of Air Pollution:

A. Catalytic Converters (in vehicle exhaust systems):

• Fitted to exhaust pipes of petrol and diesel vehicles
• Contain platinum-palladium-rhodium catalysts on honeycomb structure
• Convert harmful gases to less harmful:
• CO + O2 → CO2 (oxidation)
• Hydrocarbons + O2 → CO2 + H2O (oxidation)
• NOx → N2 + O2 (reduction)
• Effective only when engine is warm; does not filter PM2.5 effectively
• Also require low-sulphur fuel (sulphur poisons catalysts)

B. CNG (Compressed Natural Gas):

• Promoted by Supreme Court of India (1998); ordered Delhi's public transport (buses) to convert to CNG by 2001
• Benefits: burns cleaner than diesel/petrol (less PM, less NOx, less CO, no lead); produces CO2 (greenhouse gas) but less than coal
• Limitations: CNG vehicles more expensive initially; need separate infrastructure; CNG is still a fossil fuel

C. Electrostatic Precipitators:

• Used in thermal power plants; removes >99% of fly ash (PM) from exhaust
• Flue gas passes between charged plates → particles charged → attracted to plates → collected

D. Industrial Controls:

• Scrubbers: wash flue gases with water or chemical solutions to remove SO2 and other soluble gases
• Tall smokestacks: disperse pollutants over wider area (reduces local concentration but doesn't eliminate pollution)
• Switching to cleaner fuels, renewable energy

Water Pollution

Definition: Introduction of substances into water bodies at concentrations that impair its normal uses or the well-being of aquatic organisms.

Sources of Water Pollution:

1. Sewage and Domestic Wastewater:

• Contains organic matter (BOD), pathogens (bacteria, viruses, protozoa, helminths), nutrients (N, P), detergents
• Untreated sewage in rivers: Ganga, Yamuna, Cauvery → major cause of waterborne diseases in India

2. Industrial Effluents:

• Heavy metals (mercury, lead, cadmium, arsenic, chromium) from mining, electroplating, tanneries
• Acid mine drainage: oxidation of iron sulphide (pyrite) → sulphuric acid → toxic to aquatic life
• Thermal pollution: hot water from power plant cooling → reduces dissolved O2 → fish death

3. Agricultural Runoff:

• Pesticides: DDT, endosulphan, organophosphates → contaminate surface and groundwater
• Fertiliser runoff: excess nitrates and phosphates → eutrophication
• Bioaccumulation and Biomagnification (biological magnification):
• Persistent, lipophilic (fat-soluble) pollutants like DDT accumulate in fatty tissues
• Concentration increases at each trophic level (10-100x per level)
• Producer (algae): DDT at 0.003 ppm → zooplankton: 0.04 ppm → small fish: 0.5 ppm → large fish: 2 ppm → birds (top predators): 25 ppm
• DDT in raptors and pelicans → thin eggshells → eggs break → population collapse (bald eagle, peregrine falcon, osprey)

Eutrophication:

• Excess nutrients (especially phosphorus and nitrogen from sewage, detergents, agricultural runoff) → explosive growth of algae and cyanobacteria (algal bloom)
• Algal bloom → shades aquatic plants → they die → decomposers proliferate → oxygen consumed → BOD increases dramatically → fish kill (anoxia — hypoxic dead zone)
• Eutrophication occurs in: Baltic Sea, Gulf of Mexico (from Mississippi River agricultural runoff), Chilika Lake, Dal Lake

Minamata Disease (Japan, 1950s-60s):

• Mercury (from Chisso chemical factory) discharged into Minamata Bay
• Mercury accumulated in sediment → methylated by bacteria → methylmercury (more toxic, lipophilic, bioaccumulates)
• Biomagnification through food chain → fish/shellfish → humans
• Neurological symptoms: tremors, loss of coordination, sensory impairment, mental disturbance, congenital defects (mother to foetus)
• ~2,000+ documented cases; ~1,800 deaths; thousands more affected

Ganga Action Plan (GAP):

• Launched in 1985 (Prime Minister Rajiv Gandhi); revised as Namami Gange (2014-onwards)
• Aims: reduce pollution in Ganga River (heavily polluted by sewage and industrial effluents from cities like Kanpur, Varanasi, Patna)
• Activities: sewage treatment plants, industrial effluent treatment, solid waste management, public awareness
• Challenges: untreated sewage continues to flow; poor implementation; insufficient sewage treatment capacity

Solid Waste, Ozone Depletion and Global Warming

Solid Waste Management

Municipal Solid Waste (MSW): All solid/semi-solid materials discarded by urban households, commercial establishments, and public places.

Composition: organic matter (50%), paper (18%), glass (5%), metals (3%), plastics (3-5%), other materials

Methods of disposal:

1. Open dumping (landfill): unscientific; most common in India; causes leachate (toxic liquid) contamination of groundwater, methane (greenhouse gas), fires, vermin, odours
2. Sanitary landfill: engineered; lined bottom; gas collection; leachate treatment; cover with soil daily — more hygienic but still a landfill
3. Incineration: burning at high temperatures; reduces volume dramatically; energy recovery possible (waste-to-energy); generates ash and air pollutants (dioxins if not properly controlled)
4. Composting: decomposing organic MSW with microbes → nutrient-rich compost; vermicomposting (using earthworms, mainly Eisenia foetida) is popular in India
5. Biogas generation: anaerobic digestion of organic fraction → biogas + digestate (fertiliser)
6. Recycling and reuse: paper, glass, metals, plastics

3R Principle: Reduce → Reuse → Recycle (hierarchy of waste management)

• Reduce: produce less waste in the first place (sustainable consumption, eco-design)
• Reuse: use products multiple times before discarding
• Recycle: process waste to recover materials

Electronic Waste (E-waste):

• Discarded electronic equipment: computers, mobile phones, TVs, refrigerators
• Contains valuable metals (gold, silver, copper, palladium) AND hazardous materials (lead, cadmium, mercury, beryllium, arsenic, flame retardants — PBBs, PBDEs)
• Informal recycling (manual disassembly, acid leaching) exposes workers to toxic chemicals
• India: one of the world's largest e-waste producers (~3.2 million tonnes/year)
• E-waste (Management) Rules 2016, 2018 (amended): producers responsible for collection and recycling (Extended Producer Responsibility — EPR)

Biomedical Waste:

• From hospitals, labs, clinics: infectious waste (sharps, blood-contaminated material), pathological waste (body parts), pharmaceutical waste, radioactive waste
• Must be segregated (colour-coded bins — yellow, red, blue/white, black), treated (autoclaving, incineration), and disposed according to Bio-Medical Waste Management Rules 2016

Agricultural Waste:

• Crop residue burning (stubble burning): Punjab, Haryana — rice straw burned after harvest → major contribution to winter smog in Delhi-NCR
• Pesticide containers, plastic mulch films, animal slurry

Ozone Depletion

The Ozone Layer:

• Ozone (O3) in the stratosphere (15-35 km altitude) absorbs harmful UV-B (280-320 nm) and UV-C radiation
• Without ozone layer, UV reaching Earth's surface would cause: skin cancer (melanoma, squamous cell carcinoma), cataracts, immunosuppression, damage to DNA, crop damage, phytoplankton reduction

Ozone Formation (Natural):

• O2 + UV → 2O (atomic oxygen)
• O + O2 → O3 (ozone)
• O3 + UV → O2 + O (ozone absorbs UV-B)
• Dynamic equilibrium maintains ozone layer thickness

Ozone Destruction by CFCs (Chlorofluorocarbons):

• CFCs (Freon — CFC-11 = CCl3F; CFC-12 = CCl2F2): used as refrigerants, aerosol propellants, foam-blowing agents, cleaning solvents
• Very stable in troposphere; rise to stratosphere slowly
• UV radiation in stratosphere cleaves CFC → Cl radical (atomic chlorine)
• Cl acts as catalyst: Cl + O3 → ClO + O2; ClO + O → Cl + O2 (net: O3 + O → 2O2)
• Each Cl atom destroys ~100,000 ozone molecules before being removed
• Ozone hole: first discovered over Antarctica (1985, Farman et al.); seasonal (spring, Sept-Oct); caused by polar stratospheric clouds (PSCs) forming in Antarctic winter → surface reactions accelerate Cl-catalysed ozone destruction
• Each year, ozone hole has been measured — at its worst (~25 million km² in 2000); gradually recovering due to CFC controls

Other ozone-depleting substances (ODS): Halons (fire extinguishers), carbon tetrachloride (CCl4), methyl chloroform, HCFCs, methyl bromide

Montreal Protocol (1987):

• International treaty to phase out production and use of ozone-depleting substances (ODS)
• Binding targets; based on science (Nobel Prize for Rowland, Molina, Crutzen — chemistry — 1995 for ozone work)
• Most successful international environmental treaty
• Production of CFC-11 and CFC-12: phase-out in developed countries by 1995; developing countries by 2010
• Result: ODS concentrations in atmosphere peaking and slowly declining; ozone layer expected to recover to pre-1980 levels by ~2060-2070
• Kigali Amendment (2016): added HFCs (potent greenhouse gases, ozone-safe CFC replacements) to phase-down schedule

Global Warming and Climate Change

The Greenhouse Effect: The natural greenhouse effect: Short-wave solar radiation passes through the atmosphere → warms Earth's surface → Earth emits long-wave infrared radiation → greenhouse gases (GHGs) in atmosphere absorb outgoing IR radiation → re-emit in all directions (including downward) → warms lower atmosphere. Without natural greenhouse effect, Earth's average temperature would be -18°C (instead of +15°C).

Greenhouse Gases (GHGs):

GWP = Global Warming Potential; measures heat-trapping relative to CO2 over 100 years.

Enhanced Greenhouse Effect (Global Warming): Human activities (fossil fuel burning, deforestation, agriculture, industry) have increased atmospheric CO2 from ~280 ppm (pre-industrial) to ~420 ppm (2023). This enhanced greenhouse effect is trapping more heat → global warming.

Observed effects:

• Global average temperature increased by ~1.1°C since pre-industrial era (as of 2020s)
• Rising sea levels: thermal expansion of water + melting of ice caps/glaciers (~20 cm rise since 1900; accelerating)
• More frequent/intense extreme weather events (heatwaves, droughts, heavy rainfall, hurricanes)
• Shifting climate zones and phenology (timing of flowering, migration, breeding earlier)
• Coral bleaching and reef damage (thermal stress)
• Arctic sea ice decline (~13%/decade); Greenland ice sheet and West Antarctic ice sheet melting
• Ocean acidification (CO2 + H2O → H2CO3 → carbonate ions reduced → harm to calcifying organisms — corals, shellfish)

IPCC (Intergovernmental Panel on Climate Change):

• Established 1988 by WMO and UNEP
• Reviews scientific literature; publishes Assessment Reports (AR6 in 2021-2022)
• Provides scientific basis for climate policy

Kyoto Protocol (1997):

• First legally binding climate agreement
• Required developed countries (Annex I) to reduce GHG emissions by ~5% below 1990 levels by 2008-2012
• USA did not ratify; developing countries (India, China) had no binding targets
• Relatively modest impact — replaced by Paris Agreement (2015)

Paris Agreement (2015, COP 21):

• Agreed to limit global warming to well below 2°C (ideally 1.5°C) above pre-industrial levels
• All countries submit nationally determined contributions (NDCs) — voluntary; no binding enforcement
• Net-zero emissions target for second half of 21st century

Radioactive Waste

Sources:

• Nuclear power plants: spent nuclear fuel (uranium, plutonium), fission products
• Nuclear weapons production and testing
• Medical uses (diagnostic radioactive isotopes: Tc-99m; therapeutic: I-131)
• Industrial uses (smoke detectors with Am-241; level gauges with Cs-137)
• Research reactors

Classification:

• High-level waste (HLW): spent nuclear fuel; most radioactive; generates heat; requires deep geological disposal
• Intermediate-level waste (ILW): cladding, resins, sludges — requires shielding; near-surface disposal insufficient
• Low-level waste (LLW): gloves, clothing, equipment — can be disposed near surface after decay

Hazards:

• Ionising radiation (alpha, beta, gamma, neutron) damages DNA → mutations → cancer → leukaemia
• Long-lived radioisotopes: Cs-137 (half-life 30 years), Sr-90 (29 years), Pu-239 (24,110 years)
• Radiation sickness at high doses (bone marrow suppression)

Management:

• HLW: stored in deep geological repositories (>300 m underground in stable rock); many countries planning (Finland's Onkalo is first in construction)
• LLW: stored in near-surface facilities with cement/concrete encapsulation
• Nuclear accidents: Chernobyl (1986, Ukraine) and Fukushima (2011, Japan) — major contamination events; exclusion zones

Soil Pollution and Remediation

Soil Pollution

Definition: Contamination of soil with chemical, biological, or physical substances that degrade its quality and harm living organisms.

Sources and Types of Soil Pollutants:

1. Pesticides:

• Organochlorine pesticides (DDT, BHC, endosulfan): persistent in soil; bioaccumulate; harmful to non-target organisms; endocrine disruptors
• Organophosphate pesticides (malathion, chlorpyrifos): less persistent; toxic to insects and vertebrates; some carcinogenic
• Effect on soil organisms: kills earthworms, beetles, beneficial insects; disrupts soil microbiome; reduces decomposition

2. Heavy Metals:

• Cadmium (Cd): from phosphate fertilisers, industrial effluents, batteries; accumulates in kidney, causes itai-itai disease (Japan — cadmium in rice paddy)
• Lead (Pb): from leaded petrol, paint, batteries, smelters; neurotoxin
• Arsenic (As): naturally occurring + industrial sources; causes skin lesions, cancer; major groundwater problem in Bangladesh, West Bengal
• Chromium: from tanneries (hexavalent Cr is carcinogenic)

3. Fertiliser Excess:

• Excess nitrogen fertilisers: leaching of nitrates into groundwater → nitrate contamination (>10 mg/L NO3-N causes methemoglobinaemia — 'blue baby syndrome' in infants)
• Phosphorus accumulation in soil

4. Industrial Effluents and Mining:

• Acid mine drainage: oxidation of iron sulphide → H2SO4 → pH <3 → kills soil organisms; leaches heavy metals
• Industrial solvents, chlorinated compounds, polycyclic aromatic hydrocarbons (PAHs)

5. Solid Waste:

• Municipal solid waste in open dumps leaches organic matter and heavy metals
• Plastic waste: microplastics accumulate in soil; physical harm to soil organisms

Soil Remediation Technologies

1. Phytoremediation:

• Use of plants to absorb, accumulate, or detoxify soil contaminants
• Hyperaccumulators: plants that accumulate very high concentrations of heavy metals in shoots; Thlaspi caerulescens (alpine penny-cress — Zn, Cd); Pteris vittata (arsenic hyperaccumulator); Noccaea caerulescens; Sedum alfredii (Zn, Cd)
• Brassica juncea (Indian mustard): efficiently phytoextracts lead and other metals from contaminated soil
• Sunflowers used around Chernobyl site to extract Cs and Sr from contaminated ponds
• Phytodegradation: plants metabolise organic contaminants using root enzymes
• Rhizofiltration: plant roots filter water/soil for heavy metals

2. Bioremediation:

• Use of microorganisms to degrade pollutants
• Pseudomonas putida: degrades hydrocarbons (aromatic compounds, toluene, naphthalene)
• Rhodococcus, Mycobacterium: degrade polycyclic aromatic hydrocarbons (PAHs)
• White rot fungus (Phanerochaete chrysosporium): ligninase enzyme degrades diverse organic pollutants including chlorinated compounds (PCBs, DDT, dioxins)
• Deinococcus radiodurans: highly radiation-resistant bacterium; modified to also metabolise mercury and toluene → potential for radioactive waste bioremediation

3. Soil Washing:

• Ex situ technique: contaminated soil excavated; washed with water or chemical solutions (acid, chelating agents like EDTA) → removes metals → water treated to recover metals; clean soil returned

4. Thermal Remediation:

• High-temperature treatment (>300°C) destroys organic contaminants; soil vitrification (melting)
• Expensive; destroys soil structure and microbiome

Integrated Approach to Environmental Issues

Sustainable Development: Development that meets the needs of the present without compromising the ability of future generations to meet their own needs (Brundtland Commission, 1987). Balances: economic development + social equity + environmental protection.

Agenda 21 (Rio Earth Summit, 1992): Action plan for sustainable development. SDGs (Sustainable Development Goals, 2015): 17 goals including clean water, affordable and clean energy, climate action, life below water, life on land.

Clean Development Mechanism (CDM) and Carbon Markets:

• Developed countries invest in emissions reduction projects in developing countries; receive carbon credits
• Part of Kyoto Protocol architecture

Key Legislation in India:

• Environment Protection Act 1986: umbrella legislation; Central Government empowered to set standards, regulate industry
• Air (Prevention and Control of Pollution) Act 1981: regulates air quality; establishes PCBs (Pollution Control Boards)
• Water (Prevention and Control of Pollution) Act 1974: regulates water quality; PCBs
• National Green Tribunal (NGT) Act 2010: fast-track environmental cases; established NGT
• Coastal Regulation Zone (CRZ) Notifications: protect coastal ecosystems

Frequently asked questions

Are these Environmental Issues notes free?

Yes — the Environmental Issues notes for Biology (Class 12) on Siksha Sarovar are completely free to read, with no account required.

Do these notes follow CBSE and HBSE?

Yes. The Environmental Issues notes are NCERT-aligned and include guidance for both CBSE and Haryana Board (HBSE), with important questions and MCQs for revision.

What does the Environmental Issues chapter cover?

Concept explanations, key formulas and definitions, fully solved examples and board-pattern practice questions for Environmental Issues.