UPSC CSE Prelims
Heavy Metal Pollution Previous Year Questions (PYQs)

Detailed Explanation:

Correct Answer: ✅ Option 3 (All the three)

Many common items contain plastic materials, even when they do not appear to be made of plastic. Cigarette filters, modern eyeglass lenses, and car tyres all contain synthetic polymer-based materials that qualify as plastics or plastic-derived products.

✅ I. Cigarette Butts – Correct: Cigarette filters are primarily made of cellulose acetate, a synthetic plastic polymer.

✅ II. Eyeglass Lenses – Correct: Most modern eyeglass lenses are made from plastics such as polycarbonate or CR-39 resin, rather than glass.

✅ III. Car Tyres – Correct: Tyres contain synthetic rubber and other polymer-based materials derived from petrochemicals, which are forms of plastic.

Short Notes: Plastics in Everyday Life

• Cellulose acetate used in cigarette filters is a type of plastic.

• Most modern eyeglass lenses are made from polycarbonate due to its light weight and impact resistance.

• Car tyres contain both natural rubber and synthetic polymers.

• Synthetic rubber is produced from petroleum-based chemicals.

• Plastic waste can persist in the environment for hundreds of years.

• Cigarette butts are among the most common forms of plastic litter worldwide.

• Microplastics can be generated from the wear and tear of vehicle tyres.

Detailed Explanation:

Answer: Option 1 — Both Statement-I and Statement-II are correct and Statement-II explains Statement-I

Chewing gums are a significant source of environmental pollution, and Statement-II directly explains why this is the case.

✅ Statement-I – Correct: Many chewing gums found in the market are considered a source of environmental pollution due to their non-biodegradable nature and improper disposal, leading to persistent litter in public spaces.

✅ Statement-II – Correct: Many chewing gums contain plastic polymers (such as polyisobutylene, polyvinyl acetate, or polyethylene) as their gum base, which makes them non-biodegradable and environmentally persistent.

Explanation: Statement-II explains Statement-I because the presence of plastic-based gum base is the primary reason why chewing gums become environmental pollutants. These synthetic polymers do not decompose naturally and remain in the environment for years, creating cleanup challenges and contributing to plastic pollution.

📝 Short Notes: Chewing Gum and Environmental Pollution

• Gum Base Composition: Modern chewing gums typically use synthetic polymers (plastics) like polyisobutylene and polyvinyl acetate instead of natural chicle latex.
• Non-Biodegradable Nature: These plastic-based gum bases can take years to decades to break down in the environment, persisting as microplastic pollution.
• Urban Pollution: Discarded chewing gum is one of the most common forms of street litter, requiring expensive removal processes (often using chemical solvents or freezing techniques).
• Environmental Impact: Improperly disposed gum contributes to plastic pollution, can harm wildlife if ingested, and creates unsightly stains on pavements and public infrastructure.
• Biodegradable Alternatives: Some companies are now developing plant-based, biodegradable gum alternatives to address environmental concerns.

Detailed Explanation:

Answer: Option 2 — Only two

Two out of three statements regarding mercury pollution are correct. Gold mining activities and coal-based thermal power plants are both significant sources of mercury pollution globally. However, the claim that there is "no known safe level" is scientifically inaccurate, as regulatory bodies like WHO have established reference doses and tolerable intake levels for mercury exposure.

✅ Statement 1 – Correct: Gold mining, especially artisanal and small-scale mining, uses liquid mercury to amalgamate with gold particles, releasing significant mercury into water bodies and forests, notably in regions like the Amazon.

✅ Statement 2 – Correct: Coal-based thermal power plants (TPPs) are the largest anthropogenic source of mercury emissions, releasing mercury through fly ash and flue gases; studies show TPPs contribute over 80% of mercury emissions in countries like India.

❌ Statement 3 – Incorrect: While mercury is highly toxic, regulatory and scientific bodies establish safe exposure thresholds; WHO's Provisional Tolerable Weekly Intake for methylmercury is 1.6 µg/kg body weight/week, and drinking water limit is 1 µg/litre, demonstrating that safe levels do exist below which health risks are minimal.

📝 Short Notes: Mercury Pollution

• Sources of Mercury Pollution: Coal-fired power plants (largest source), artisanal gold mining, chlor-alkali industry, waste incinerators, cement production, and volcanic eruptions.
• Mercury in Environment: Converts to toxic methylmercury in aquatic systems through bacterial action; bioaccumulates in fish and biomagnifies up the food chain.
• Health Effects: Damages nervous system, kidneys, and developing fetuses; causes Minamata disease (severe neurological syndrome); particularly harmful to children and pregnant women.
• Minamata Convention: Global treaty (2013) to protect human health and environment from anthropogenic mercury emissions and releases; India ratified in 2018.
• Safe Exposure Levels: WHO guidelines: 1.6 µg/kg body weight/week for methylmercury; 1 µg/litre for drinking water; concept of "dose makes the poison" applies.
• Mercury from Coal Plants: Indian coal contains 0.05-0.5 ppm mercury; released during combustion; fly ash disposal in ponds creates aquatic ecosystems contaminated with mercury.

Detailed Explanation:

Answer: Option 2 — 2 and 3 Only

Copper smelting plants are a major environmental concern due to their emission of sulfur dioxide and the potential for heavy metal leaching from copper slag. The primary gaseous pollutant is SO₂, not carbon monoxide.

❌ Statement 1 – Incorrect: Copper smelting plants do not typically release lethal quantities of carbon monoxide; the primary gaseous pollutant of concern is sulfur dioxide (SO₂).

✅ Statement 2 – Correct: Copper slag, a byproduct of smelting, contains heavy metals like arsenic, lead, and cadmium, which can leach into soil and groundwater, causing environmental contamination.

✅ Statement 3 – Correct: Copper smelting releases large amounts of sulfur dioxide because most copper ores are sulfide minerals (like chalcopyrite), and sulfur is oxidized to SO₂ during roasting and smelting processes.

📝 Short Notes: Environmental Concerns of Copper Smelting

• Primary Pollutant: Sulfur dioxide (SO₂) is the main gaseous emission from copper smelting, as copper ores are predominantly sulfide minerals.
• Copper Slag: Contains heavy metals (arsenic, lead, cadmium, mercury) that can leach into environment, contaminating soil and water resources.
• Acid Rain: SO₂ emissions contribute to acid rain formation, damaging ecosystems, crops, and infrastructure.
• Health Impacts: SO₂ causes respiratory problems; heavy metals from slag can bioaccumulate and cause neurological and developmental issues.
• Mitigation Measures: Use of scrubbers to capture SO₂, proper slag management, adoption of cleaner smelting technologies, and recovery of sulfur for sulfuric acid production.

Detailed Explanation:

✅ Statement 1 – Correct: Smelting units release lead particles into air and soil during ore processing, making them a major source of environmental lead contamination.

❌ Statement 2 – Incorrect: Pencils contain graphite (carbon) and clay, not lead; the term "lead" is a historical misnomer.

✅ Statement 3 – Correct: Lead-based paints remain a significant hazard as deteriorating paint releases lead dust and chips that can be inhaled or ingested.

❌ Statement 4 – Incorrect: While some traditional cosmetics (surma/kohl) may contain lead, standard hair oils and modern cosmetics are not primary sources of lead poisoning.