UPSC CSE Prelims
Water Pollution Previous Year Questions (PYQs)

Detailed Explanation:

Correct Answer: ✅ Option 1

Activated carbon is one of the most widely used adsorbents in water and wastewater treatment. Its effectiveness comes from its highly porous structure and enormous surface area, while its low-cost production from carbon-rich wastes makes it an attractive and sustainable pollution-control material.

✅ Statement I is Correct: Activated carbon is extensively used to remove pollutants from industrial effluents and contaminated water through adsorption.

✅ Statement II is Correct: Activated carbon has a very large surface area and strong adsorption capacity, enabling it to capture heavy metals and other pollutants efficiently.

✅ Statement III is Correct: Activated carbon can be produced from agricultural and environmental wastes such as coconut shells, rice husks, sawdust, and other carbon-rich materials.

✅ Statement II explains Statement I: Its large surface area and adsorption capacity make it effective in pollutant removal.

✅ Statement III explains Statement I: Easy and low-cost production from waste materials makes it an attractive and sustainable remediation tool.

Short Notes: Activated Carbon

• Activated carbon is a highly porous carbon material used as an adsorbent.

• It has a surface area that can exceed 1,000 m²/g.

• Used in water purification, air filtration, and wastewater treatment.

• Effective in removing heavy metals, dyes, pesticides, and organic pollutants.

• Common raw materials include coconut shells, wood, coal, and agricultural residues.

• Works mainly through the process of adsorption, not absorption.

• It is widely used in environmental remediation and pollution control.

Detailed Explanation:

Answer: Option 4 — Wastewater treatment technologies

Membrane Bioreactors (MBRs) are advanced wastewater treatment systems that combine conventional biological treatment processes with membrane filtration (microfiltration or ultrafiltration). They are highly efficient in removing contaminants, producing high-quality effluent, and require less space compared to traditional treatment methods. MBRs are widely used in municipal and industrial wastewater treatment applications due to their superior performance in removing suspended solids, pathogens, and organic pollutants.

📝 Short Notes: Membrane Bioreactors (MBRs)

• Technology: Combines biological degradation with membrane filtration in a single unit
• Membrane Types: Uses microfiltration (MF) or ultrafiltration (UF) membranes with pore sizes of 0.1-0.4 microns
• Advantages: High effluent quality, smaller footprint, complete retention of biomass, and better pathogen removal
• Applications: Municipal wastewater treatment, industrial effluent treatment, water reuse and recycling
• Limitations: Higher capital and operational costs, membrane fouling issues, energy-intensive operation
• Environmental Significance: Enables water reuse, reduces pollution load, and supports circular economy in water management

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three statements about PFAS (perfluoroalkyl and polyfluoroalkyl substances) are correct. These synthetic chemicals, often called 'forever chemicals', are widely used in consumer products and are characterized by their environmental persistence and bioaccumulation potential.

✅ Statement 1 – Correct: PFAS are widely detected in drinking water, food items, and food packaging materials due to their extensive use in consumer products and their ability to leach into the environment.
✅ Statement 2 – Correct: PFAS are called 'forever chemicals' because the strong carbon-fluorine bond makes them extremely resistant to environmental degradation processes.
✅ Statement 3 – Correct: Due to their persistence, PFAS accumulate in the tissues of animals and humans over time, leading to bioaccumulation and potential health risks.

📝 Short Notes: PFAS (Forever Chemicals)

• Full Form: Perfluoroalkyl and Polyfluoroalkyl Substances
• Nickname: 'Forever Chemicals' due to their extremely persistent nature
• Chemical Structure: Contain strong carbon-fluorine bonds that resist breakdown
• Common Uses: Non-stick cookware, water-repellent fabrics, firefighting foams, food packaging, cosmetics
• Environmental Persistence: Do not degrade naturally; accumulate in soil, water, and air
• Health Concerns: Bioaccumulation leads to potential cancer risk, liver damage, immune system effects, and developmental issues
• Global Concern: Found in blood samples of humans and wildlife worldwide; subject to increasing regulatory scrutiny

Detailed Explanation:

Answer: Option 4 — Toiletries

Triclosan (TCS) is an antibacterial and antifungal agent commonly found in various personal care and consumer products. It is most prevalently present in toiletries such as toothpaste, soaps, hand sanitizers, body washes, and deodorants. Long-term exposure to high levels of triclosan has raised health and environmental concerns, leading to restrictions and bans in several countries.

📝 Short Notes: Triclosan

• Chemical Nature: Triclosan is a synthetic antimicrobial compound used to reduce or prevent bacterial contamination.
• Common Products: Found in antibacterial soaps, toothpaste, hand sanitizers, body washes, detergents, cosmetics, and some medical equipment.
• Health Concerns: Prolonged exposure may disrupt hormone regulation (endocrine disruption), contribute to antibiotic resistance, and cause skin irritation.
• Environmental Impact: Triclosan can persist in the environment, contaminate water bodies, and harm aquatic ecosystems.
• Regulatory Actions: The US FDA banned triclosan from over-the-counter antiseptic wash products in 2016; the EU restricted its use in cosmetics in 2014.
• Alternatives: Manufacturers are increasingly using safer alternatives like alcohol-based sanitizers and natural antimicrobial agents.

Detailed Explanation:

Answer: Option 3 — Pollution assay in aquatic ecosystems

Biological Oxygen Demand (BOD) is a standard criterion for measuring the amount of dissolved oxygen consumed by microorganisms while decomposing organic matter in water bodies. It serves as a key indicator of water pollution—higher BOD values indicate greater organic pollution and potential harm to aquatic life due to oxygen depletion. BOD testing is widely used in environmental monitoring to assess the health and quality of aquatic ecosystems.

Detailed Explanation:

Answer: Option 1 — 1 and 2 only

✅ Statement 1 – Correct: NGRBA adopts the river basin as the unit of planning and management, moving away from fragmented state-wise approaches to a holistic basin-level conservation strategy.

✅ Statement 2 – Correct: NGRBA was established to spearhead river conservation efforts at the national level for the Ganga. It functions as the apex planning, financing, monitoring, and coordinating authority for Ganga rejuvenation.

❌ Statement 3 – Incorrect: The Prime Minister of India serves as the Chairman of NGRBA, not Chief Ministers on rotation. Chief Ministers of Ganga basin states are members of the Authority along with relevant Union Cabinet Ministers.

Detailed Explanation:

✅ Statement 1 – Correct: Brominated flame retardants (BFRs) are persistent organic pollutants (POPs) that are highly resistant to environmental degradation, remaining in ecosystems for extended periods.

✅ Statement 2 – Correct: BFRs are lipophilic (fat-soluble) and undergo bioaccumulation in fatty tissues of humans and animals, leading to potential endocrine disruption and neurotoxicity.

Detailed Explanation:

✅ Arsenic (1) – Correct: Found in groundwater of West Bengal, Bihar, Uttar Pradesh, Assam, Jharkhand due to natural leaching from arsenic-bearing rocks; causes arsenicosis and skin lesions.
❌ Sorbitol (2) – Incorrect: A sugar alcohol used as artificial sweetener and humectant; not a naturally occurring groundwater pollutant in India.
✅ Fluoride (3) – Correct: Endemic in Rajasthan, Andhra Pradesh, Tamil Nadu, Gujarat, Haryana and other states; causes dental and skeletal fluorosis from geological sources.
❌ Formaldehyde (4) – Incorrect: An industrial chemical and disinfectant; not a common groundwater contaminant in Indian drinking water systems.
✅ Uranium (5) – Correct: Detected in groundwater of Punjab, Rajasthan, Haryana and parts of southern India; leaches from uranium-bearing granitic rocks.

Detailed Explanation:

✅ Statement 1 – Correct: Calcareous phytoplankton (like coccolithophores) need carbonate ions to build calcium carbonate shells; ocean acidification reduces these ions, impairing their calcification, growth, and survival.

✅ Statement 2 – Correct: Coral reefs are made of calcium carbonate; increased acidity lowers the saturation state, making it harder for corals to build skeletons and can cause reef dissolution.

✅ Statement 3 – Correct: Many marine invertebrates (mollusks, echinoderms) have phytoplanktonic larvae sensitive to seawater chemistry changes; acidification impairs their development and shell formation, increasing mortality.

❌ Statement 4 – Incorrect: While acidification may reduce dimethyl sulfide (DMS) production affecting cloud condensation nuclei, this is an indirect climatic feedback, not a primary direct concern for ocean ecosystems.