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Chapter 15: Environment and Health — Complete Answers

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LONG ESSAYS

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1. Define safe water. Enumerate the sources of water. What are the various methods of purification of water on a small scale? [D13(RS3)]

• Free from pathogenic agents
• Free from harmful chemical substances
• Pleasant to taste, i.e., free from colour and odour
• Usable for domestic purposes

1. Rainwater - Collected directly; relatively pure but may pick up atmospheric pollutants. Used in rainwater harvesting systems.
2. Surface water
   • Rivers and streams
   • Lakes and ponds
   • Tanks and reservoirs
3. Ground water
   • Shallow wells (unconfined aquifer)
   • Deep/artesian wells (confined aquifer)
   • Springs (natural emergence of ground water)
4. Sea water - requires desalination; not normally used as a drinking source

• Most reliable household method
• Water is brought to a rolling boil for at least 1 minute (at high altitudes, 3 minutes)
• Kills all pathogenic organisms including cysts and oocysts
• Drawback: does not remove chemical pollutants; fuel cost; water may be recontaminated

• Chlorine-based agents are most widely used
  • Bleaching powder (chlorinated lime): 0.5 mg/L free residual chlorine; contact time 30 minutes
  • Chlorine tablets (Halogen tablets): Convenient, portable
  • Potassium permanganate (Lal dawa): Pinkish colour; weak disinfectant; mainly used as first aid in the field
  • Iodine tablets (Globaline, Potable Aqua): Effective against Giardia
  • Lugol's iodine solution: 3-4 drops per litre

• Household candle filters (Pasteur-Chamberland filter): Ceramic/Berkfeld candles; remove bacteria but not viruses; must be cleaned regularly
• Domestic sand filter (pot filter): Simple bio-sand filter using layers of sand and gravel
• Activated carbon filters: Remove taste, odour, and some chemicals
• UV water purifiers: Ultraviolet light inactivates microorganisms; does not alter taste or add chemicals

• Developed at NEERI, Nagpur
• Alum + bleaching powder added to water; allowed to flocculate and sediment
• Removes excess fluoride from water

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2. Classify water-borne diseases. Describe the various methods of purification of water on a large scale. [J22(RS3)]

• Raw water stored in natural or artificial reservoirs
• Physical: ~90% suspended particles settle in 24 hours by gravity
• Chemical: aerobic bacteria oxidize organic matter; free ammonia levels fall; nitrates rise
• Biological: bacterial count drops by 90% in 5-7 days; pathogens die out
• Optimum storage period: 10-14 days
• Drawback: algal growth if stored too long

• First used in Scotland (1804)
• Components: supernatant water layer, fine sand bed (0.2-0.3 mm), coarse sand, gravel, drainage system
• The vital layer = Schmutzdecke (biological film of algae, bacteria, diatoms on top of sand)
• Rate of filtration: 0.1-0.4 m/hour (100-400 litres/m²/hour)
• Removes 98-99% bacteria
• Cleaned by scraping the top layer; not backwashed
• Advantages: simple to operate, effective, no chemicals needed
• Disadvantages: requires large land area, slow, affected by turbid water

• Coarser sand (0.4-1.2 mm), filtration rate 40-50× faster than slow sand
• Rate: 4-8 m/hour (4000-8000 litres/m²/hour)
• Preceded by coagulation and sedimentation (alum added as coagulant)
• Cleaned by backwashing (reversing water flow) - takes ~15 minutes
• Advantages: handles turbid water directly, less land needed, flexible operation
• Disadvantages: needs pretreatment, requires skilled operation, more equipment

• Chlorine is the standard disinfectant
• Cl₂ + H₂O → HCl + HOCl (hypochlorous acid - the active germicidal agent)
• HOCl ⇌ H⁺ + OCl⁻ (hypochlorite ion - less active)
• Germicidal efficiency ↑ at lower pH and higher temperature
• Contact time: minimum 30 minutes (MCQ answer: A - 30 minutes)
• Residual chlorine maintained: 0.2-0.5 mg/L free residual chlorine
• Methods: chlorine gas, bleaching powder, sodium hypochlorite, chloramines

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3. What are the causes of water pollution? Write in detail about rapid sand filtration. [J19(RS3)]

1. Sewage and domestic wastewater: Most significant - introduces pathogens, organic matter, nutrients
2. Industrial effluents: Heavy metals (Pb, Hg, Cd, As), organic chemicals, acids
3. Agricultural runoff: Pesticides, fertilizers (nitrates, phosphates) → eutrophication
4. Mining activities: Acid mine drainage, heavy metals
5. Radioactive waste: Nuclear power plants, medical/research facilities
6. Oil spills: Petroleum products
7. Atmospheric pollution: Acid rain depositing into water bodies
8. Garbage and solid waste dumping in or near water bodies
9. Animal waste: Farm/feedlot runoff
10. Natural causes: Geological leaching of minerals (fluoride, arsenic in ground water)

1. Coagulation: Alum (aluminium sulphate) added at ~5-40 mg/L. Alum hydrolyses to form Al(OH)₃ - a gelatinous floc that captures suspended particles and colloidal matter
2. Flocculation: Gentle stirring to encourage floc particle collisions and formation of larger aggregates
3. Sedimentation: Flocs settle out in sedimentation tanks (retention time 2-6 hours), removing up to 70-80% of turbidity and bacteria

• Filter bed: coarse sand (effective size 0.4-1.2 mm, uniformity coefficient <1.7), depth 60-90 cm
• Underlayer: graded gravel 30-45 cm deep
• Underdrain system: collects filtered water
• Supernatant water: maintained at 1-1.5 m above sand
• Filter box: reinforced concrete

• Water percolates downward through sand by gravity (or pressure in pressure filters)
• Suspended matter deposited in upper layers of sand
• As impurities accumulate, "loss of head" increases
• When loss of head reaches 7-8 feet, filter is taken offline for backwashing

1. Inlet valve closed; drain outlet opened
2. Wash water pumped upward through the filter (reverse flow) at high velocity (~0.9 m/min)
3. Sand bed expands ("fluidises") - dirt particles dislodged and washed away
4. In some filters, compressed air agitation precedes the water wash
5. Wash water and dirt drain away
6. Process takes ~15 minutes
7. Filter returned to service; first filtrate discarded

• Removes 99%+ of bacteria after chlorination
• Does not remove dissolved substances

1. Can handle turbid raw water directly (after pre-treatment)
2. Filter beds occupy less space
3. Filtration 40-50× faster
4. Easy washing by backwashing
5. More operational flexibility
6. Can be automated

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4. Air pollution - sources, effects and prevention and control. [J18(RS3), J02]

• Volcanic eruptions (SO₂, H₂S, particulates)
• Dust storms, forest fires
• Pollen, fungal spores
• Natural radioactivity

1. Combustion - motor vehicles (CO, NOₓ, hydrocarbons, lead), industrial furnaces, power plants (SO₂, particulates, CO₂)
2. Industry - chemical plants (HF, Cl₂, H₂SO₄ mists), cement works (dust), oil refineries
3. Domestic - burning of coal, wood, dung cakes for cooking/heating (significant in India)
4. Agricultural - burning of crop residues, pesticide spraying
5. Radioactive sources - nuclear reactors, weapons testing

• London/Reducing smog: Coal combustion + fog + SO₂ + smoke; cold, humid conditions; London 1952 killed ~4000
• Photochemical/Los Angeles smog: Sunlight + NOₓ + hydrocarbons → ozone, peroxyacetylnitrate (PAN); causes eye irritation, crop damage

• Air Quality Index (AQI) / Air Pollution Index (API)
• Soiling index (stain on filter paper)
• Suspended particulate concentration
• COH (Coefficient of Haze)

1. Switch to cleaner fuels (CNG, LPG, natural gas)
2. Catalytic converters in vehicles
3. Electrostatic precipitators, cyclone separators, bag filters in industries
4. Tall smokestacks (dispersion; not elimination)
5. Scrubbers to remove SO₂ and acidic gases

• Air (Prevention and Control of Pollution) Act, 1981 (India)
• Environment Protection Act, 1986
• Euro emission standards for vehicles

• Green belts around industrial areas
• Locating industries away from residential zones (taking wind direction into account)

• Avoid outdoor activity during high pollution
• Use face masks
• Promote public transport, cycling

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5. Health effects of global warming and measures to prevent it. [N20(RS3)]

• Carbon dioxide (CO₂) - fossil fuel combustion (55%)
• Methane (CH₄) - cattle, rice paddies, landfills (15%)
• Nitrous oxide (N₂O) - fertilizers, combustion (6%)
• Chlorofluorocarbons (CFCs) - refrigerants, aerosols (24%)
• Water vapour

1. Direct heat effects: Increased heat waves → heat exhaustion, heat stroke, cardiovascular deaths; particularly dangerous for elderly, outdoor workers, miners
2. Vector-borne diseases: Warmer temperatures expand geographic range of mosquitoes (malaria, dengue, chikungunya moving to higher altitudes/latitudes); extended transmission seasons
3. Waterborne diseases: Flooding contaminates water supplies → cholera, typhoid outbreaks; drought → water scarcity and poor hygiene
4. Air quality: Higher temperatures increase ground-level ozone; worsens asthma, COPD
5. Food security: Crop failures due to droughts/floods → malnutrition
6. Sea level rise: Coastal flooding; displacement of populations; saltwater intrusion into freshwater sources
7. Extreme weather events: Cyclones, floods, droughts → injury, deaths, mental health impacts
8. UV radiation: Ozone layer depletion → increased skin cancer, cataracts, immunosuppression
9. Emerging infections: New zoonotic disease emergence as ecosystems disrupted

1. Reduce GHG emissions
   • Shift from fossil fuels to renewable energy (solar, wind, hydro)
   • Improve energy efficiency
   • Reduce deforestation; afforestation/reforestation
2. Kyoto Protocol (1997): Binding GHG reduction targets for developed nations
3. Paris Agreement (2015): Limit warming to <2°C; aim for 1.5°C
4. Refrigerant replacement: Phase out CFCs (Montreal Protocol 1987) with HFCs
5. Carbon capture and storage (CCS)
6. Individual actions: Reduce meat consumption, use energy-efficient appliances, reduce air travel
7. Adaptation measures: Develop heat action plans, flood-resistant housing, drought-resistant crops

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6. Enumerate vector-borne diseases and add a note on prevention and control. [J14(RS3)]

1. Source reduction - eliminate/reduce breeding sites
   • Drain stagnant water, fill pits
   • Proper disposal of containers, tyres (Aedes)
   • Irrigation management
2. Environmental antilarval measures - seepage control, weeding of water bodies, alternate wetting and drying of paddy fields

1. Larvivorous fish - Gambusia affinis, Lebistes reticulatus in water bodies, wells, tanks
2. Bacillus thuringiensis israelensis (Bti) - bioinsecticide for larvae
3. Predatory insects, copepods

1. Larvicides: Temephos (Abate) - organophosphate; malathion; pyriproxyfen (IGR)
2. Adulticides: DDT (residual spraying), malathion (space spraying), pyrethrin, synthetic pyrethroids (deltamethrin, lambda-cyhalothrin)
3. Insect growth regulators (IGRs): Methoprene, pyriproxyfen - disrupt larval development

1. Bed nets (insecticide-treated nets/LLINs)
2. Repellents (DEET, picaridin)
3. Protective clothing

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7. Explain chemical control of arthropods of public health importance. [D07(RS2)]

• Examples: DDT, BHC (lindane), dieldrin, aldrin
• Mechanism: Disrupt Na⁺ channel closing in nerve axons → prolonged depolarisation → hyperexcitability → paralysis
• DDT: Highly effective, cheap, long residual action; however, banned/restricted due to persistence in environment, bioaccumulation, resistance
• Use: DDT still used for indoor residual spraying (IRS) for malaria in India

• Examples: Malathion, parathion, temephos (Abate), DDVP (dichlorvos), fenitrothion
• Mechanism: Irreversible inhibition of acetylcholinesterase → accumulation of ACh → overstimulation of cholinergic synapses → SLUDGE syndrome (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis)
• Less persistent in environment, biodegradable
• Temephos used as a safe larvicide; malathion for space spraying
• Antidote: Atropine + pralidoxime (if used early)

• Examples: Carbaryl (Sevin), propoxur
• Mechanism: Reversible inhibition of acetylcholinesterase
• Less toxic than OPs

• Natural pyrethrins from Chrysanthemum cinerariaefolium
• Synthetic: Permethrin, deltamethrin, lambda-cyhalothrin, cypermethrin
• Mechanism: Disrupt Na⁺ channels (similar to DDT but more potent, less persistent)
• Low mammalian toxicity; widely used for IRS, bed net impregnation, space spraying
• Deltamethrin: Used for IRS by National Vector Borne Disease Control Programme

• Juvenile hormone analogues: Methoprene, pyriproxyfen - prevent metamorphosis; larvae cannot develop to adults
• Moulting hormone analogues: Tebufenozide, methoxyfenozide
• Chitin synthesis inhibitors: Diflubenzuron - prevent cuticle formation
• Advantage: Highly specific to insects; minimal effect on mammals

• Methyl bromide, phosphine, formaldehyde
• Used for stored grain pests and rodents

• DEET (N,N-diethyl-meta-toluamide) - most effective; protects for 2-12 hours
• Picaridin, IR3535
• Applied to skin or clothing; keep mosquitoes from biting

• Applied to walls and indoor surfaces as residual spraying
• DDT, Malathion, Synthetic pyrethroids
• Contact-kill action: arthropods resting on treated surfaces absorb lethal dose
• Duration of action: DDT 6-12 months; synthetic pyrethroids 2-3 months; malathion 2-3 months

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SHORT ESSAYS

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1. Thickness of plastic bags - why should they be regulated? [J11(RS2)]

• Thin plastic (<50 microns) is too light to be collected and recycled efficiently
• Thin bags fragment into microplastics easily
• Animals ingest thin plastic bags → intestinal obstruction, deaths
• Clog drains → waterlogging, mosquito breeding → disease transmission
• Persist in environment for 400-1000 years
• Thicker bags (≥50 microns) are more durable, reusable, and more likely to be returned for recycling

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2. Greenhouse Effect [D19(RS3), J05]

1. CO₂ (55%) - fossil fuel combustion, deforestation
2. CFCs (24%) - refrigerants, aerosols
3. CH₄ (15%) - agriculture, landfills, natural gas leaks
4. N₂O (6%) - fertilizers, combustion

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3. Safe disposal of sullage in villages [D08(RS2), D02]

1. Soak pits (soakage pits): Most common method in rural areas. A pit of suitable size (1.5-2 m deep, 1-2 m diameter) lined with dry brick/rubble walls with gaps to allow seepage. Sullage percolates into soil; microorganisms purify it. Must be ≥15 m from wells to prevent contamination.
2. Surface drains: Lined drainage channels that carry sullage to a common disposal site. Must be covered to prevent mosquito breeding.
3. Wastewater irrigation: Used directly for vegetable gardens and fields (not for vegetables eaten raw).
4. Simple soak trench: Shallow trench filled with gravel; allows rapid dispersal.
5. Constructed wetlands / reed beds: Plants absorb nutrients and filter water.

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4. Steps of water purification [J16(RS3), D13]

1. Intake/Screening: Raw water drawn from source; coarse screens remove large debris
2. Aeration: Water sprayed into air to remove dissolved gases (H₂S, CO₂) and oxidize iron and manganese
3. Coagulation: Alum added (5-40 mg/L); forms Al(OH)₃ floc
4. Flocculation: Gentle stirring; small flocs aggregate into larger ones
5. Sedimentation: Flocs settle out in settling tanks (retention time 2-6 hours)
6. Filtration: Slow sand or rapid sand filtration; removes 99% bacteria
7. Disinfection (Chlorination): Chlorine added; contact time minimum 30 minutes; free residual chlorine 0.2-0.5 mg/L
8. pH correction: If needed; sodium carbonate added to correct acidity
9. Fluoridation: In areas with low natural fluoride (<0.5 ppm), fluoride added to 1 ppm
10. Distribution: Pumped to reservoir and distributed under pressure

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5. Chlorination of water - principles [J16(RS3), D13]

Cl₂ + H₂O → HCl + HOCl

• HCl is neutralized by the alkalinity of water
• HOCl (hypochlorous acid) ionizes:

HOCl ⇌ H⁺ + OCl⁻

• HOCl (undissociated hypochlorous acid) is the primary germicidal agent - ~80× more effective than OCl⁻
• At pH 7-8 (optimal): HOCl predominates → greater germicidal activity
• At higher pH: more OCl⁻ → less activity

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6. Break-point chlorination [D16(RS3), J10]

• Stage 1 (0 to point A): Added chlorine reacts with reducing substances; no chlorine residual appears
• Stage 2 (Point A to B): Chloramines form → combined residual rises
• Stage 3 (Point B to breakpoint C): Chloramines oxidized and destroyed → residual falls
• Breakpoint (C): All chloramines destroyed; minimum residual
• After breakpoint: Any additional chlorine appears as free residual chlorine

• Eliminates taste and odour from chloramines
• Destroys ammonia and nitrogenous compounds
• Provides free residual chlorine (more germicidal)
• Removes colour
• Disadvantage: higher chlorine doses needed; may form trihalomethanes (THMs) - potential carcinogens

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7. Residual chlorine and free residual chlorine [J11(RS2), J02, J04, D04]

1. Free residual chlorine (FRC): Cl₂, HOCl, and OCl⁻ in solution. Most effective germicidal form.
2. Combined residual chlorine: Chloramines (monochloramine NH₂Cl, dichloramine NHCl₂, trichloramine NCl₃). Less active but more persistent.

• Free residual chlorine: 0.2 mg/L minimum at consumer's tap
• At treatment plant: 0.5 mg/L
• In emergencies/epidemic situations: up to 1 mg/L

1. Acts as a safety factor against recontamination in the distribution system
2. Serves as an index of the adequacy of disinfection
3. Can detect break in distribution system (sudden drop in residual)
4. Provides continued protection to consumers

• Orthotolidine reagent (yellow liquid) added to water sample
• In presence of chlorine → yellow-orange colour (free chlorine) immediately
• Deeper yellow/orange = higher chlorine concentration
• Compared to standard Lovibond comparator disc
• The test distinguishes free residual chlorine (immediate yellow) from combined residual chlorine (slow developing colour after acidification)

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8. Small scale/domestic water purification methods [J10(RS2), D12(RS3), D18(RS3), D01, D07]

1. Boiling - most reliable; 1 minute rolling boil
2. Chemical disinfection - chlorine, potassium permanganate, iodine
3. Filtration - candle filters, bio-sand filters, UV purifiers
4. Nalgonda technique for fluoride removal

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9. Methods of household disinfection of water [D11(RS2)]

1. Bleaching powder: 2.5 g per 100 litres (or 1 teaspoon per 200 L), stir and wait 30 minutes
2. Chlorine tablets (Aquatabs, Halazone): 1 tablet per litre; contact 30 minutes
3. Potassium permanganate (KMnO₄): 30 mg/L; turns water pink; weak disinfectant
4. Iodine: Tincture 2% - 5 drops/L; wait 30 minutes; effective against Giardia
5. Sodium hypochlorite solution: Household bleach (5% NaOCl) - 2 drops per litre
6. SODIS (Solar Disinfection): Fill clear PET bottles; expose to sunlight for 6 hours (or 2 days if cloudy); UV + IR inactivates pathogens; WHO-recommended for resource-poor settings
7. UV lamps: Germicidal UV (254 nm); no taste/chemical change; cannot penetrate turbid water

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10. Well chlorination (steps in disinfection of a well during epidemic) [J13(RS3), D05]

1. Calculate the volume of water in the well: V = π r² × depth of water column (in litres, multiply by 1000)
2. Determine chlorine dose: Calculate amount of bleaching powder (containing ~33% available chlorine) needed to give 2 mg/L (epidemic) or 0.5 mg/L (normal)
3. Prepare bleaching powder solution: Dissolve required amount of bleaching powder in a bucket of water; allow to settle; decant the supernatant (do NOT use the sediment)
4. Add to well: Pour bleaching solution into well while drawing water continuously to distribute chlorine
5. Allow contact time: Minimum 30 minutes
6. Test for residual chlorine: Using orthotolidine test - should show free residual chlorine
7. Clear the well: If taste is unpleasant (excess chlorine), allow to dissipate or aerate by drawing and discarding water
8. Repeat daily during epidemic

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11. Surveillance of drinking water quality [J16(RS3)]

1. Sanitary surveys: Inspection of water sources, treatment facilities, distribution systems for potential hazards
2. Water quality monitoring: Regular bacteriological and chemical testing at source, treatment plant, and distribution points
3. Bacteriological standards (India/WHO):
   • Coliforms: 0/100 mL in treated piped supply
   • E. coli: 0/100 mL
4. Chemical standards: pH 6.5-8.5; TDS <500 mg/L; fluoride 0.5-1.5 mg/L; nitrates <45 mg/L; arsenic <0.01 mg/L
5. Residual chlorine monitoring: At consumer tap ≥0.2 mg/L
6. Epidemiological surveillance: Alert for clustering of gastrointestinal illness indicating water-borne outbreak

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12. Bacteriological quality of water / faecal contamination [D09(RS2), J04, D04]

• Escherichia coli - best indicator of recent faecal contamination
• Coliform group (thermotolerant/faecal coliforms)
• Enterococci (useful in marine water)

1. Presumptive test (Multiple Tube Method / MPN method):
   • Water samples inoculated into MacConkey's broth tubes
   • Incubated 37°C for 48 hours
   • Acid + gas production = positive (presumptive coliform)
   • Calculate Most Probable Number (MPN) per 100 mL
2. Confirmatory test:
   • Positive tubes sub-cultured on EMB/Eosin Methylene Blue agar
   • Metallic sheen colonies = E. coli
3. Membrane filtration technique:
   • 100 mL water passed through 0.45 μm membrane filter
   • Filter placed on selective medium (m-Endo agar for coliforms)
   • Count colonies after 24-hour incubation at 37°C
   • More sensitive; gives results in 18-24 hours
4. H₂S test (Hydrogen Sulphide test):
   • Field test; water sample + H₂S paper strip in a bottle
   • Blackening = positive; indicates faecal contamination
   • Simple, cheap; no lab needed
5. Presence-absence test: Simplified version for field use.

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13. Removal of hardness of water [J15(RS3)]

• Temporary hardness: Due to bicarbonates (Ca(HCO₃)₂, Mg(HCO₃)₂) - removed by boiling
• Permanent hardness: Due to sulphates and chlorides (CaSO₄, MgSO₄, CaCl₂) - cannot be removed by boiling

1. Boiling: Removes temporary hardness only Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂
2. Lime-soda process (Clark's process):
   • Add slaked lime (Ca(OH)₂) and soda ash (Na₂CO₃)
   • For temporary: Ca(OH)₂ precipitates bicarbonates as CaCO₃
   • For permanent: Na₂CO₃ precipitates CaSO₄ as CaCO₃
   • Used for large-scale softening
3. Base exchange / Ion exchange (Zeolite process):
   • Water passed through zeolite (sodium aluminosilicate) or synthetic ion exchange resins
   • Ca²⁺ and Mg²⁺ exchanged for Na⁺
   • Regenerated with NaCl brine
   • Used in households and industries
4. Reverse osmosis: Removes almost all dissolved salts including hardness
5. Distillation: Produces pure water but expensive

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14. Indices of thermal comfort [D07(RS2), D16]

1. Effective Temperature (ET): Combines dry-bulb temperature, wet-bulb temperature, and air velocity into a single index indicating the sensation of warmth. Developed by Houghton and Yaglou.
2. Corrected Effective Temperature (CET): Uses globe thermometer temperature (instead of dry-bulb) to account for radiant heat. More accurate than ET.
3. Kata thermometer cooling power: Measures rate of heat loss from a body-like surface. Expressed in milliCalories per cm² per second (mCal/cm²/sec). A measure of the cooling effect of environment (both temperature and air movement).
4. WBGT (Wet Bulb Globe Temperature) Index: Used for hot environments, especially outdoor/occupational settings.
   • WBGT = 0.7 × NWB + 0.2 × GT + 0.1 × DB (outdoor, with solar load)
   • NWB = natural wet bulb temperature; GT = globe temperature; DB = dry bulb temperature
5. Heat Stress Index: By Belding and Hatch; based on ratio of required evaporation to maximum evaporative capacity.
6. Predicted Mean Vote (PMV) / Fanger's Index: Used in building design.

• Winter: 17-21°C CET
• Summer: 19-23°C CET

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15. Air pollutants, sources, health effects [J10(RS2), D14(RS3)]

1. RSPM (Respirable Suspended Particulate Matter): PM₁₀ and PM₂.₅ measured by gravimetric samplers
2. SO₂, NOₓ: By chemical analysers (pararosaniline method for SO₂)
3. CO: By infrared analyser
4. Air Quality Index (AQI): Composite index; colour-coded 0-500; monitored by CPCB/SPCB in India
5. COH (Coefficient of Haze): Tape sampler; optical density of dust on filter paper
6. Soiling Index: Similar to COH; measures deposition on filter

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16. Prevention of indoor air pollution in India [D17(RS3)]

1. Improved cookstoves (chulhas): Well-designed stoves with better combustion efficiency and chimneys (e.g., Pradhana Mantri Ujjwala Yojana)
2. Switch to clean fuels: LPG/PNG (Piped Natural Gas) distribution to rural households - PMUY scheme
3. Proper ventilation: Ensure kitchens are well-ventilated; kitchen outdoors or in separate room
4. Smokeless chulhas: National Programme on Improved Chulha
5. Solar cookers: In areas with abundant sunlight
6. Ban on tobacco smoking indoors - COTPA 2003
7. Biogas plants: Utilise agricultural waste to produce clean biogas
8. Education: Behaviour change communication

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17. Ventilation - standards and types [J12(RS2), J10, D10, J13]

• Minimum: 1000 cubic feet (28 m³) of air space per person
• Fresh air supply: 30 cubic feet (0.85 m³) per minute per person
• Air change rate: At least 3-6 air changes per hour in living rooms; more in hospitals

1. Natural ventilation:
   • Inlet ventilation: Windows, doors, ventilators, louvers
   • Uses wind pressure differences and thermal (stack) effect (warm air rises, draws in cool air from below)
   • Depends on: wind speed, direction, building orientation, window size and placement
2. Artificial/Mechanical ventilation:
   • Supply system: Fresh air pumped in by fans/blowers; positive pressure
   • Exhaust system: Stale air removed by exhaust fans; negative pressure (used in kitchens, labs, industrial areas)
   • Combined supply and exhaust: Both inlet and outlet mechanical; full control of air quality
   • Air conditioning: Full control of temperature, humidity, purity, and air movement
3. Special purpose ventilation:
   • Local exhaust ventilation (LEV): In industries to remove dust/fumes at source
   • Operating theatre ventilation: Laminar flow; positive pressure; HEPA filters; ultra-clean air

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18. Lighting standards [D16(RS3)]

• Lux: SI unit of illuminance (lumens/m²)
• Foot-candle: Older unit; 1 foot-candle = 10.76 lux

1. Adequate intensity
2. Even distribution (no glare or deep shadows)
3. Correct colour rendering
4. Natural light preferred over artificial
5. Light should come from the left side for right-handed work

• Eye strain, headache, visual fatigue
• Accidents and injuries
• Myopia in children

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19. Noise pollution - effects, control and prevention [F24(RS4), D08(RS2), D15(RS3)]

1. Noise-Induced Hearing Loss (NIHL): Most significant effect
   • Temporary threshold shift (TTS): reversible; after acute exposure
   • Permanent threshold shift (PTS): irreversible; from chronic exposure
   • NIHL starts at 4 kHz (4000 Hz notch on audiogram) and spreads to other frequencies
   • Risk: >85 dB(A) for 8 hours/day over years
   • Occupational limit: 90 dB(A) for 8 hours (OSHA); India: 90 dB(A) daytime

• Residential: Day 55 dB(A), Night 45 dB(A)
• Commercial: Day 65 dB(A), Night 55 dB(A)
• Industrial: Day 75 dB(A), Night 70 dB(A)
• Silence zones (hospitals, schools): Day 50 dB(A), Night 40 dB(A)

1. Engineering controls - use quieter machinery, vibration dampening, mufflers
2. Proper maintenance of equipment
3. Substitute noisy processes

1. Acoustic barriers/walls
2. Sound-absorbing materials in buildings
3. Green belts around industrial areas
4. Locating industries away from residential areas

1. Personal protective equipment: earplugs (25-30 dB reduction), earmuffs (30-40 dB reduction)
2. Job rotation to reduce exposure time
3. Audiometric surveillance

• Noise Pollution (Regulation and Control) Rules, 2000 (India)
• Environment Protection Act, 1986

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20. Radiation - hazards and prevention [D10(RS2), J18(RS3), J19(RS3)]

• Alpha (α): Low penetration (stopped by paper); dangerous if inhaled/ingested
• Beta (β): Moderate penetration (stopped by aluminum)
• Gamma (γ): High penetration (requires lead/concrete shielding)
• X-rays: Similar to gamma
• Neutrons: Highly penetrating; cause secondary radioactivity

1. Acute radiation syndrome (ARS): High dose exposure
   • Haematopoietic syndrome (<6 Gy): bone marrow suppression, pancytopenia, infection, haemorrhage
   • Gastrointestinal syndrome (6-10 Gy): nausea, vomiting, diarrhoea, death
   • Central nervous system syndrome (>10 Gy): rapid death within hours-days
2. Chronic effects: Leukaemia (especially CML), thyroid cancer, lung cancer
3. Cataracts: From chronic exposure to lens of eye
4. Skin changes: Erythema, desquamation, radiation burns

• Gray (Gy): Absorbed dose (J/kg)
• Sievert (Sv): Effective dose (accounts for type of radiation)
• Permissible dose: 20 mSv/year for radiation workers; 1 mSv/year for general public

1. Time: Minimize exposure time
2. Distance: Inverse square law - doubling distance reduces dose by 4×
3. Shielding: Lead aprons, lead glass, lead-lined rooms for X-rays; concrete for reactors
4. Containment: Proper storage and handling of radioactive materials
5. Monitoring: Film badges, TLDs (thermoluminescent dosimeters), pocket dosimeters
6. ALARA principle: As Low As Reasonably Achievable
7. Regulatory controls: Atomic Energy Act (India); AERB (Atomic Energy Regulatory Board) sets standards
8. Non-ionizing radiation (UV): Sunscreens, protective clothing, UV-blocking glasses; limit sun exposure

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21. Criteria for healthful housing [D07(RS2)]

1. Protection against diseases: Safe water supply, sanitary disposal of excreta and waste, adequate food storage, protection against vectors (insects, rodents)
2. Protection against accidents: Structural safety, fire protection, electrical safety, safe stairways
3. Protection against atmospheric hazards: Adequate ventilation, natural lighting, adequate temperatures, noise control
4. Promotion of mental health: Privacy, adequate space, aesthetically pleasing, promotes social relationships
5. Social aspects: Adequate space, separate sleeping areas, access to social facilities

• Minimum floor area: 9.2 m² (100 sq ft) per person
• Cubic capacity: ≥14.2 m³ (500 cubic feet) per person
• Windows: ≥10% of floor area (natural light); ≥5% openable (ventilation)
• Height: ≥2.4 m (8 ft)

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22. Housing standards for rural areas [D08(RS2), J11]

1. Site: Well-drained land; away from industry; free from flooding; ≥15 m from latrines/soak pits
2. Floor area: Minimum 9.2 m² per person; separate rooms for sleeping
3. Room height: ≥2.4 m (8 ft) minimum
4. Ventilation: Cross-ventilation; windows on both sides of rooms; ≥10% floor area for windows
5. Lighting: Adequate natural light; windows/doors ≥10% floor area
6. Kitchen: Separate; well-ventilated; improved chulha with chimney
7. Water supply: Safe and adequate water within premises or close proximity
8. Sanitation: Sanitary latrine (VIP latrines or pour-flush latrines) and soak pit
9. Sullage disposal: Soakage pit or drain
10. Solid waste: Covered bins; proper disposal
11. Vermin/vector control: Rat-proof construction, insect screening

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23. Overcrowding and its effects [D13(RS3), D16]

• More than 1.5 persons per room (WHO) indicates overcrowding
• More than 2 persons per sleeping room = overcrowding (India, National Buildings Code)

1. Respiratory infections: Tuberculosis (TB), influenza, pneumonia, common cold, measles, meningococcal meningitis, diphtheria, pertussis - all spread by droplets/aerosols; overcrowding facilitates transmission
2. Skin diseases: Scabies, tinea, impetigo - spread by direct contact
3. Louse-borne diseases: Typhus, relapsing fever - lice spread easily in crowded conditions

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24. Solid waste disposal methods [J18(RS3), M22(RS3), D07, D15]

1. Open dump: Simply depositing waste on land; primitive; causes disease vector breeding, pollution; NOT recommended.
2. Sanitary landfill: Controlled disposal on land in engineered cells; waste compacted and covered daily with 15 cm soil; lining to prevent leachate; gas collection. Acceptable method.
3. Composting: Biological decomposition of organic waste → stable humus-like material (compost) used as soil conditioner/fertilizer
   • Windrow composting: Waste piled in long rows; turned regularly
   • Mechanical composting (Indore process modified): Shredded waste + night soil, turned periodically; 4-6 weeks; used in India
   • Bangalore method: waste trenched, covered with soil; anaerobic decomposition; 4-6 months
4. Incineration: High-temperature burning (850-1100°C); reduces volume by 90%, weight by 75%; ash requires landfill; air pollution if uncontrolled; used for hospital/biomedical waste; expensive.
5. Recycling: Material recovery of paper, glass, metal, plastic - reduces waste volume; economically valuable.
6. Biogas production (Anaerobic digestion): Organic waste → biogas (methane) + digestate; clean fuel produced.
7. Vermicomposting: Using earthworms to decompose organic waste.
8. Pyrolysis/Gasification: Thermal decomposition without oxygen; produces syngas.

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25. Composting [S21(RS3)]

1. Organic waste (refuse + night soil or cattle dung in 3:1 ratio) placed in pits 1.5 m × 1 m × 0.7 m
2. Layers alternate refuse:nightsoil
3. Moisture maintained; turned every 7 days
4. Temperature rises to 60-70°C (destroys pathogens)
5. Completed in 4-6 weeks

1. Waste placed in trenches (1.8 m × 0.9 m × 0.6 m)
2. Alternate layers of refuse and earth
3. Not turned; anaerobic decomposition
4. Completed in 4-6 months

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26. Why human faecal matter needs treatment before disposal? [J11(RS2)]

1. Pathogenic bacteria - Salmonella typhi, Vibrio cholerae, Shigella, Campylobacter
2. Helminths - Ascaris, Hookworm, Trichuris, Taenia eggs/cysts
3. Protozoa - E. histolytica cysts, Giardia cysts, Cryptosporidium oocysts
4. Viruses - Poliovirus, Hepatitis A, Rotavirus, Norovirus
5. Organic matter that depletes oxygen in water

• Contaminates water sources and soil → water-borne and soil-borne disease transmission
• Attracts flies → fly-borne (faeco-oral) disease transmission
• Provides breeding grounds for mosquitoes in latrines
• Degrades environment; depletes dissolved oxygen in water bodies (eutrophication)

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27. Sanitation barrier [D19(RS2), J11, J17]

1. Safe excreta disposal: Latrines, sewers - contain faeces and prevent environmental contamination
2. Safe water supply: Piped treated water prevents waterborne transmission
3. Food hygiene: Proper cooking, covering food, refrigeration
4. Personal hygiene: Handwashing with soap (most effective single intervention)
5. Vector control: Controlling flies that transmit faecal-oral pathogens
6. Environmental sanitation: Solid waste management, drainage

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28. Oxidation pond [D11(RS2), J08]

• Sewage enters the pond
• Bacteria decompose organic matter; release CO₂, H₂O, nitrates, phosphates
• Algae use CO₂, sunlight, and nutrients for photosynthesis → produce O₂
• Symbiotic cycle: Bacteria consume O₂ and organic matter; algae produce O₂ and consume CO₂ and nutrients
• Sunlight kills pathogens (UV effect; pH rise due to algal photosynthesis)

1. Aerobic pond: Shallow (<1.5 m); complete aerobic decomposition; for polishing treated effluent
2. Anaerobic pond: Deep (2-5 m); BOD reduction 50-70%; for heavily loaded sewage
3. Facultative pond: Most common; aerobic upper zone + anaerobic lower zone; intermediate depth (1-2 m)

• Retention time: 5-30 days
• BOD removal: 70-90%
• Pathogen removal: Good (Salmonella, poliovirus, helminth eggs)

• Low cost; minimal maintenance; no energy input
• Effective in tropical climates (India)
• Pathogen removal good

• Large land area required
• Odour nuisance
• Seasonal variation in efficiency

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29. Methods of control of arthropods [J13(RS3)]

1. Environmental/Physical control (source reduction):
   • Remove/drain breeding sites
   • Proper sewage and waste disposal
   • Screening of windows/doors
2. Biological control:
   • Larvivorous fish (Gambusia, Lebistes)
   • Bacillus thuringiensis israelensis (Bti)
   • Predatory insects, copepods
3. Chemical control:
   • Larvicides: Temephos, malathion, Bti, IGRs
   • Adulticides: DDT (IRS), malathion (fogging), pyrethroids
   • Repellents: DEET, picaridin
4. Genetic/Biological methods:
   • Sterile insect technique (SIT): Release sterile male insects to reduce population
   • Genetically modified mosquitoes (GM Aedes): OX513A male Aedes aegypti; offspring die before maturity
5. Integrated Vector Management (IVM): Combination of above methods

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30. Integrated vector control (Culex mosquito) [J10(RS2), D11(RS2), D13(RS3), D14(RS3), J16(RS3)]

1. Environmental control:
   • Drainage of stagnant water, cesspools, drains
   • Proper solid waste management (prevent waterlogging)
   • Eliminate polluted/stagnant water - Culex breeds in dirty, polluted water
   • Removal of overhead water tanks that are not covered
2. Biological control:
   • Larvivorous fish in water bodies and drains
   • Bti application in drains/water collections
   • Copepods in water containers
3. Chemical control:
   • Larviciding: Temephos (Abate) 1 mg/L in water bodies; malathion
   • Indoor Residual Spraying (IRS): Synthetic pyrethroids on indoor walls
   • Space spraying: Malathion thermal fogging
   • Anti-larval oil: Light oil on water surface - suffocates larvae
4. Personal protection:
   • Bed nets (LLINs)
   • Mosquito repellents (DEET)
   • Protective clothing (long sleeves at night)
5. Community participation: Involving communities in keeping surroundings clean, eliminating breeding sites
6. Health education: Awareness about disease, prevention, symptoms

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SHORT ANSWERS

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• Advantages: Rapid action, effective, relatively cheap, large-scale application possible
• Limitations: Development of resistance (DDT resistance in Anopheles), environmental persistence/bioaccumulation, non-target toxicity, health hazards to applicators, costly infrastructure

1. Suspended particulate matter (SPM/RSPM) concentration
2. SO₂, NOₓ levels
3. CO levels
4. AQI (Air Quality Index) - composite index
5. COH (Coefficient of Haze)
6. Soiling index
7. Visibility reduction

• High altitude (low pressure): Mountain sickness, HAPE (high altitude pulmonary oedema), HACE (cerebral oedema), hypoxia
• Increased pressure (hyperbaric): Nitrogen narcosis (Rapture of the deep), decompression sickness (Caisson disease/"the bends" - nitrogen bubble formation in tissues), barotrauma

1. Collection: Door-to-door collection, community bins
2. Segregation: Wet (organic) vs dry (recyclable) vs hazardous
3. Transportation: Compactor trucks
4. Treatment: Composting, incineration, biogas plants
5. Disposal: Sanitary landfills Governed by: Municipal Solid Wastes (Management and Handling) Rules, 2000; SWM Rules 2016.

1. Land disposal: Irrigation, sewage farms (pathogens removed by soil filtration)
2. Dilution: Into rivers/sea (with adequate dilution factor ≥8:1)
3. Sewage treatment plants: Primary (screening, sedimentation) → secondary (biological: activated sludge, trickling filters) → tertiary (advanced)
4. Oxidation ponds/Waste stabilization ponds
5. Septic tanks + soak pits: For individual houses

• Stegomyia (House) Index: Number of houses positive for larvae/pupae ÷ total houses inspected × 100. Level >1% indicates dengue risk.
• Container index: Positive containers ÷ total containers inspected × 100
• Breteau index (BI): Number of positive containers per 100 houses inspected. BI >5 = risk; BI >20 = high risk.

1. Source reduction (drain stagnant water)
2. Larviciding (temephos, Bti)
3. Larvivorous fish (Gambusia)
4. IRS with insecticides
5. Space spraying/fogging
6. Bed nets (LLINs)
7. Repellents (DEET)
8. Screening of windows/doors

• Hard ticks (Ixodes): Lyme disease (Borrelia burgdorferi), TBE, RMSF
• Soft ticks (Ornithodoros): Q fever (Coxiella burnetii), tick-borne relapsing fever (Borrelia)
• CCHF (Crimean-Congo Haemorrhagic Fever): Hyalomma tick
• Kyasanur Forest Disease (KFD): Haemaphysalis tick + KFD virus

• Acute/fast-acting: Zinc phosphide (most commonly used in India), sodium fluoroacetate, thallium sulphate (now banned)
• Chronic (anticoagulants): Warfarin, brodifacoum, bromadiolone - cause internal bleeding over several days; less risk of bait shyness; antidote: Vitamin K₁

• Rabies (dog, bat → humans)
• Plague (rat → flea → humans)
• Brucellosis (cattle, goat → humans via unpasteurised milk)
• Leptospirosis (rat urine → humans via contaminated water)
• Anthrax (cattle, sheep → humans)
• Tuberculosis (bovine TB; M. bovis)
• Toxoplasmosis (cats → humans)
• Hydatid disease (dog → humans; Echinococcus granulosus)
• Q fever (cattle/sheep → humans)
• Psittacosis (birds → humans; Chlamydia psittaci)
• Japanese Encephalitis (pigs, birds → mosquito → humans)
• Nipah virus (bats → humans)
• Avian influenza H5N1 (birds → humans)

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MCQ

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