Class 12 Biology – Environmental Issues

Air pollution is the presence of harmful substances in the atmosphere at concentrations that affect life or materials. Primary pollutants: particulate matter (PM), SO₂, NO_x, CO, VOCs.

PM₁₀ ≤ 10 µm affects upper respiratory tract; PM_2.5 ≤ 2.5 µm penetrates deep into lungs and bloodstream, causing greater health risks.

SO₂: burning sulfur-rich fossil fuels (coal, oil), smelters. NO_x: vehicle exhausts, power plants, industrial combustion.

Photochemical smog forms when sunlight acts on NO_x and VOCs producing secondary pollutants like ozone (O₃) and peroxyacetyl nitrate (PAN); causes eye irritation and plant damage.

Catalytic converters convert CO to CO₂, unburnt hydrocarbons to CO₂ and H₂O, and NO_x to N₂, reducing vehicular emissions.

Electrostatic precipitators and bag filters for particulates; flue-gas desulfurization and low-NO_x burners for gases; fuel switching to cleaner fuels.

Warming of Earth’s surface due to trapping of outgoing infrared radiation by greenhouse gases (CO₂, CH₄, N₂O, water vapor, ozone).

Asthma and bronchitis; increased cardiovascular risks and premature mortality.

Air Quality Index summarizes air quality based on key pollutants into categories (e.g., Good to Hazardous) to communicate health risks.

Precipitation with low pH due to atmospheric conversion of SO₂ and NO_x to sulfuric and nitric acids; damages ecosystems and structures.

Biochemical Oxygen Demand is the amount of oxygen required by microbes to decompose organic matter; high BOD indicates severe organic pollution.

Point sources have identifiable discharge points (sewage outfall); non-point sources are diffuse (agricultural runoff, urban stormwater).

Nutrient enrichment (N, P) of water bodies causing algal blooms, decreased DO, fish kills, and loss of biodiversity.

Primary (screening, sedimentation) → Secondary (biological treatment via activated sludge/trickling filters) → Tertiary (nutrient removal, disinfection).

Coliform bacteria (e.g., E. coli) and high BOD/low DO.

Metals like mercury, lead, cadmium; bioaccumulate and cause neurotoxicity, kidney damage, and developmental issues.

Increase in concentration up food chains; e.g., methylmercury increases from plankton to large fish and humans.

Wastewater treatment before discharge; buffer strips/wetlands to intercept runoff; strict effluent standards.

Reduce → Reuse → Recycle; focus first on waste prevention (Reduce).

Sanitary landfills isolate waste with liners and leachate collection; open dumps are uncontrolled and polluting.

Discarded electronic products; hazards include toxic metals (Pb, Hg) and brominated flame retardants causing health and environmental risks.

Formal collection, authorized recyclers, data wiping, material recovery, Extended Producer Responsibility (EPR) policies.

Biological decomposition of organic waste to humus-rich compost; vermicomposting uses earthworms to accelerate the process.

High-temperature combustion reduces waste volume; advantage: energy recovery; disadvantage: air pollution and ash disposal.

Undesirable sound levels causing hearing loss, stress, sleep disturbance, and reduced work performance.

Source control (maintenance, silencers), barriers and green belts, zoning, and personal protection in workplaces.

Increase in water temperature (e.g., power plant cooling water) reducing DO and harming aquatic life.

Contamination by radioactive substances; safety: shielding, time minimization, proper storage and disposal of radioactive waste.

Weather is short-term atmospheric conditions; climate is long-term patterns over decades or more.

CO₂ (fossil fuel combustion, deforestation); CH₄ (rice paddies, ruminants, landfills).

Total GHG emissions caused by activities; reduce via energy efficiency, renewable energy, public transport, and plant-based diets.

Capturing and storing atmospheric CO₂ in forests, soils, oceans, or geological formations.

Stratospheric ozone is destroyed by chlorine and bromine radicals from CFCs and halons, thinning the protective layer.

An international treaty (1987) to phase out ozone-depleting substances, leading to gradual ozone layer recovery.

Stratospheric ozone (good) shields UV; tropospheric ozone (bad) is a pollutant causing smog and respiratory issues.

Skin cancer, cataracts, immune suppression in humans; reduced phytoplankton productivity and plant damage.

Afforestation: establishing forests on non-forested land; reforestation: replanting in deforested areas.

Coastal protection (mangroves, embankments), drought-resistant crops, water harvesting, heat action plans.

Agricultural expansion, logging, mining, infrastructure development, and forest fires.

Loss of biodiversity and ecosystem services; soil erosion, altered rainfall, increased CO₂.

A participatory approach where local communities and forest departments jointly manage forests and share benefits.

Chipko movement (forest protection) and Bishnoi conservation ethos; both emphasize non-violent protection of trees and wildlife.

Development that meets present needs without compromising the ability of future generations to meet their own needs.

Vegetated zones around urban/industrial areas that absorb pollutants, reduce heat islands, and provide recreation.

When an activity raises threats of harm to the environment or health, precautionary measures should be taken even if cause–effect relationships are not fully established.

Prevention, recovery (reuse/recycling/composting, energy recovery), and disposal (as last resort).

A policy approach where producers are responsible for post-consumer collection and recycling of their products (e.g., e-waste, plastics).

To prevent and control pollution, maintain water and air quality, and establish boards to enforce standards and permits.

Segregate waste at source and compost organics; conserve energy/water, use public transport, avoid single-use plastics.

Adopt Integrated Urban Environmental Management: compact city design, public transit, green infrastructure, circular waste systems, and strict emissions control.