+16 more

Make it as per wbuhs mbbs 2026 exam oriented answers

analyse_media

I have extracted the content from the images. I can also see all 10 images clearly as visual input. Let me now compile comprehensive WBUHS MBBS 2026 exam-oriented answers for all questions from Chapter 3 (Environmental Health Problems).

WBUHS MBBS 2026 EXAM-ORIENTED ANSWERS

Community Medicine - Chapter 3: Environmental Health Problems

Q.2. Breakpoint Chlorination (WBUHS frequently asked; RGUHS 2010, 12; SAMU 2016)

Definition: Breakpoint chlorination is the point at which the chlorine demand of water is completely met, after which any further addition of chlorine results in free residual chlorine (HOCl and OCl⁻) appearing in the water.

Mechanism (Step-by-step):

Chlorine is added to water → combines with ammonia → forms chloramines (combined residual chlorine - bactericidal)
Further chlorine is added → oxidises the ammoniacal compounds → destroys the chloramines
After destruction of all chloramines → free residual chlorine begins to appear in water
The point at which chlorine demand is fully met and free residual chlorine just starts to appear = Break-point

Exam tip: If chlorine added = break-point, free residual chlorine starts appearing. The minimum free residual chlorine recommended = 0.5 mg/L for a contact period of at least 1 hour.

Q.3. Superchlorination (SSUHSA 2013; TDMGRMU 2014)

Definition: Superchlorination is the addition of large doses of chlorine to water, followed by dechlorination (removal of excess chlorine) after disinfection.

Applied to heavily polluted waters (e.g., after floods, disasters) whose quality fluctuates greatly
After superchlorination, excess chlorine is removed by passing water through activated carbon filters or adding sodium thiosulphate

Q.4. Removal of Hardness of Water (SSUHSA 2013; TDMGRMU 2014)

Definition: Hardness = soap-destroying power of water.

Type	Cause	Methods of Removal
Temporary	Ca & Mg bicarbonates	(i) Boiling (ii) Addition of lime (iii) Addition of sodium carbonate (iv) Permutit process
Permanent	Ca & Mg sulphates, chlorides, nitrates	(i) Addition of sodium carbonate (ii) Base exchange (Permutit) process

Q.5. Swimming Pool Sanitation (WBUHS 2015)

Source of contamination: Faecal matter + organisms from skin and nasopharynx of bathers.

Sanitation measures:

Recommended area per swimmer = 2.2 sq. m
Rules and regulations to be posted conspicuously
Persons with skin disease, sore eyes, cold, nasal/ear discharge - NOT allowed
All bathers must empty bladder before entering
Cleansing shower (nude) mandatory before entering pool
Spitting, spouting water, blowing nose - strictly prohibited
Surrounding areas to be disinfected

Q.6. Indoor Air Pollution (WBUHS 2014, 2018)

Key points:

A worldwide problem; exposes more people to air pollutants than outdoor pollution
In developing countries: Rural areas face greatest threat - use of firewood, charcoal, cow dung for cooking/heating
In urban areas: Tightly sealed buildings, reduced ventilation, synthetic materials, pesticides
Most vulnerable groups: Women and children (spend more time indoors)

Health hazards:

ARI in young children
Chronic lung disease and cancer in adults
Adverse pregnancy outcomes (still-births) in women exposed during pregnancy

Impact of improvement: Improving indoor air quality in developing countries could avert:

Acute respiratory infection and chronic respiratory disease by 15%
Respiratory cancer by 10%

Q.7. Types of Ventilation (WBUHS 2017; RGUHS 2012)

(i) Natural Ventilation

Simplest method for small dwellings
Buildings constructed with sufficient open space + large windows opening directly to outside air
Cross ventilation: Doors and windows facing each other

(ii) Mechanical Ventilation (4 types)

(a) Exhaust ventilation: Air exhausted to outside by electric exhaust fans → creates vacuum → fresh air enters through windows/doors. Used to remove dust and gases at source.

(b) Plenum ventilation: Fresh air blown into room by centrifugal/high-pressure fans → creates positive pressure → displaces vitiated air. Limited utility.

(c) Balanced ventilation: Combination of exhaust + plenum. Used in large halls with extensive sitting capacity.

(d) Air conditioning: Outside air conditioned/controlled for temperature, humidity, dust. Conditioned air let in at measured rate and volume.

Exam note (Q.33): Exhaust vs. Plenum - Exhaust creates negative pressure (vacuum), Plenum creates positive pressure. They are NOT synonymous.

Q.8. Greenhouse Effect (ABKUB 2011, 18; TDMGRMU 2011; SSUHS 2015)

Definition: A natural process by which solar energy trapped in the atmosphere warms the earth's surface.

Mechanism: Solar energy reaches earth → some reflected back to space → rest absorbed by Greenhouse Gases (GHGs) → GHGs trap reflected infrared radiation → earth's temperature rises.

Greenhouse Gases:

Water vapour
Carbon dioxide (CO₂) - greatest contributor
Ozone
Methane
Nitrous oxide
Chlorofluorocarbons (CFCs)

Effects of Greenhouse Effect:

Melting of polar ice caps
Increased dryness in climate
Rise in sea levels → floods
Increased incidence of skin cancer and cataract
Change in distribution of vegetation
Spread of tropical diseases to temperate climates
Decrease in food production

Q.9. Global Warming (WBUHS 2016)

Emission of GHGs into atmosphere has been increasing since the Industrial Revolution
CO₂ and CFCs mainly responsible for warming and rise in sea level
Global warming has resulted in increase of mean surface temperature by 0.4 to 0.8°C during the last 100 years

Health hazards of global warming:

Heat stroke and heat stress (particularly affects elderly and young)
Changes in rainfall patterns, draughts, floods
Desertification; agriculture seriously affected
Significant decrease in sunshine hours
Spread of vector-borne diseases

Q.10. Hazards of Noise Pollution (TDMGRMU 2011, 2014)

(1) Auditory Effects

(i) Auditory fatigue - whistling and buzzing

(ii) Deafness (hearing loss):

Most temporary hearing loss: frequency range 4000-6000 Hz
Continuous exposure to ~100 dB → permanent deafness
Exposure to >160 dB → rupture of tympanic membrane → permanent hearing loss

(2) Non-Auditory Effects

(i) Interferes with speech communication (ii) Annoyance - irritability, short temper, impatience (iii) Decreased efficiency in work (iv) Lack of concentration (v) Physiological changes:

Rise in BP and intracranial pressure
Increase in heart rate and breathing
Increase in sweating
Giddiness, nausea, fatigue, insomnia
Visual disturbances

Q.11. Daylight Factor (TDMGRMU 2011, 2014)

Definition: Ratio of illumination at a given indoor point to illumination at a point simultaneously exposed to the whole hemisphere of the sky (taken as 500 foot candles), excluding direct sunlight.

Formula:

$$\text{D.F.} = \frac{\text{Instantaneous illumination indoors}}{\text{Simultaneously occurring illumination outdoors}} \times 100$$

Measured by a modified photo-electric meter
Recommended: Living rooms = at least 8%; Kitchen = about 10%

Q.12. Health Hazards of Ionising Radiation (WBUHS 2015)

(1) Acute Effects

Exposure to heavy doses (1-9 Gy) → Acute Radiation Syndrome - 4 stages:

Stage	Features	Duration
(i) Prodromal	Anorexia, nausea, vomiting, prostration, fatigue, sweating; diarrhoea, oliguria in severe cases	8-48 hours
(ii) Latent	Asymptomatic	1-2 weeks
(iii) Overt illness	Fever, anaemia, leucopenia, thrombocytopenic purpura, diarrhoea, paralytic ileus, CNS symptoms	~3 weeks
(iv) Recovery	Gradual recovery	~15 weeks

(2) Chronic Effects

(a) Somatic:

Skin lesions: erythema, oedema, blisters, ulcers
Leukaemia
Carcinogenesis: cancer of lung, skin
Foetal developmental abnormalities and microcephaly

(b) Genetic:

Chromosomal mutations → still-births, congenital defects, neonatal deaths, sterility
Point mutations → Down's syndrome, Huntington's chorea, polycystic kidney, haemophilia

Q.13. Sanitary Landfill (WBUHS 2011; TDMGRMU 2010)

Most satisfactory method of solid waste disposal where suitable land is available
Differs from ordinary dumping: material placed in a trench/prepared area, adequately compacted, and covered with earth at the end of each working day

Methods:

Trench method (preferred where low-lying land unavailable): Trench 2-3 m deep, 4-12 m wide; ~1 acre of land per year needed for 10,000 population
Ramp method: Suitable for moderately sloping terrain; some excavation done for covering material
Area method: Used for filling land depressions, disused quarries, clay pits

Decomposition: After ~1 week, temperature rises to 60°C → kills pathogens; complete decomposition in 4-6 months → innocuous mass used for gardening

Q.14. Biochemical Oxygen Demand (BOD)

Definition: Amount of oxygen absorbed by a sample of sewage during a specified period (5 days) at a specified temperature (20°C) for the aerobic destruction/use of organic matter by living organisms.

Most important test carried out on sewage before treatment
BOD values: Natural water = ~1 mg/L; Untreated domestic sewage = ~300 mg/L
If BOD ≥ 300 mg/L → strong sewage; if 100 mg/L → weak sewage
Standard in India: BOD in source of drinking water = ≤2 mg/L; BOD of effluent to be discharged = ≤30 mg/L

Q.15. Biological Treatment of Sewage (WBUHS 2013)

Definition: Uses bacteria and other microorganisms to break down organic wastes in sewage.

Process - Activated Sludge Process:

Untreated wastewater collected from sewers → pretreatment (screening, clarifying, grit removal)
Enters reactor basin: bacteria and microorganisms housed, fed, aerated with oxygen
Treated water flows through clarifier → microorganisms separated → either returned as activated sludge or wasted as solids (dewatered → anaerobic digestor/farm)

Common high-rate biological processes:

(i) Activated sludge process
(ii) Trickling filters/biofilters
(iii) Oxidation ditches
(iv) Rotating biological contactors (RBC)

Q.16. Oxidation Pond

Definition: One of the cheapest methods of sewage treatment using biological processes to remove contaminants.

Open, shallow pool: 3-5 ft. deep with an inlet and outlet

Prerequisites:

Presence of algae
Bacteria feeding on decaying organic matter
Sunlight

Mechanism:

Bacteria oxidise organic matter → CO₂, NH₃, H₂O
Algae use CO₂ + sunlight for growth (symbiotic relationship)
Day: aerobic bacteria; Night: anaerobic bacteria
Effluents may be used for growing vegetable crops or discharged into rivers after treatment

Q.17. Sanitation Barrier (WBUHS 2013, 2018 - Most frequently asked!)

Definition: A barrier constructed to prevent contamination of the physical environment (food, soil, water) by faeces-borne pathogens, thereby preventing faeces-borne endemic diseases.

Constructed by: Building and using a sanitary latrine

Mechanism - The 6 F's Route: Faeces → 6 Fs (Fluids, Food, Fruit & vegetables, Fomites, Fingers, Flies) → Susceptible Host (mouth)

The sanitation barrier interrupts this route at every F.

Sanitation Measures (corresponding to each F):

Fluids: Chlorination of water supply, pasteurisation of milk
Fingers: Adoption of personal hygiene
Food: Adoption of food hygiene measures
Fruits & Vegetables: Disinfection of fruits and vegetables
Flies: Control of houseflies
Fomites: Disinfection of utensils

Q.18. Overcrowding (RGUHS 2015; TRIU 2014, 16; TDMGRMU 2010, 11, 12; AGKUB 2013)

Definition: Situation where more people are living in a single dwelling than there is space for - resulting in restricted movement, privacy loss, impossible hygiene, and difficult rest/sleep.

Criteria for Overcrowding

Persons per room:

Rooms	Max Persons
1 room	2 persons
2 rooms	3 persons
3 rooms	5 persons
4 rooms	7 persons
5+ rooms	10 persons (+2 per additional room)

Floor space standards:

Area	Persons
110 sq. ft or more	2 persons
90-100 sq. ft	1.5 persons
70-90 sq. ft	1 person
50-70 sq. ft	0.5 persons
Under 50 sq. ft	Nil

(Baby <12 months not counted; children 1-10 years counted as half a unit)

Sex separation: If 2 persons >9 years of age, not husband and wife, of opposite sexes are obliged to sleep in the same room → overcrowded.

Health Hazards of Overcrowding

Spread of respiratory infections (TB, influenza, diphtheria, whooping cough, bronchitis, acute rheumatic fever)
Spread of contagious diseases (scabies, impetigo, ringworm, leprosy, trachoma, conjunctivitis)
Effects on psychosocial health (irritability, frustration, lack of sleep, anxiety, violence, mental disorders)
Behavioural disorders, alcoholism, drug addiction
Feeling of isolation and loneliness
High morbidity and mortality rates

Q.19. Integrated Vector Management (WBUHS 2012, 2019)

Definition: Utilisation of all appropriate technological and management techniques to bring about effective degree of vector suppression in a cost-effective manner using 2 or more vector control methods simultaneously.

Why it came about - Problems with single-method control:

Technical: Development of resistance to older insecticides
Financial: Cost of newer insecticides
Environmental: Pollution by insecticides
Operational: Lack of public cooperation

Q.20. Indices of Thermal Comfort

Thermal comfort = Subjective feeling dependent on temperature, humidity, air movement.

Indices:

Air temperature - Alone inadequate as an index
Absolute humidity - Amount of water vapour per unit weight/volume of air (g/m³)
Cooling power - Air temperature + humidity + air movement expressed as cooling power
Effective Temperature (ET) - Arbitrary index combining temperature, humidity, air movement into single value reflecting warmth/cold sensation
Corrected Effective Temperature (CET) - Deals with all 4 factors: air temperature, velocity, humidity, and radiant heat. CET is now widely used as index of thermal comfort.

Q.21. Coliform Organisms as Indicators of Faecal Pollution - Explain (WBUHS 2015; BNMU 2013)

Coliform organisms = All aerobic and facultative anaerobic, gram-negative, non-sporing organisms. Typical faecal group: E. coli; non-faecal: Klebsiella aerogenes.

Reasons for choosing coliforms as faecal indicators:

Constantly present in large numbers in intestine (~200-400 billion/person/day)
Easily detected by culture methods (as small as 1 bacterium in 100 mL of water)
Detection of other intestinal organisms (Salmonella, Shigella) is complicated and time-consuming
They survive longer than other pathogens
Greater resistance to natural purification forces

Q.22. Slow Sand Filters Require Several Days for Proper Functioning after Installation - Justify

Slow sand filtration uses a bed of graded sand/gravel for mechanical straining, sedimentation, adsorption, oxidation, and bacterial action
Initially the sand acts only as a mechanical strainer
Within 2-3 days, the sand gets covered with a slimy, greenish-yellow jelly-like layer = Vital layer / Zoogleal layer / Schmutzdecke / Biological layer
This layer is composed of algae, fungi, planktons, diatoms, and bacteria
Formation of this layer = "Ripening" of the filter
Effective filtration (complete purification) starts only after ripening
Ripening takes several days → hence filter cannot function properly immediately after installation

Q.23/24/25. Principles of Chlorination / Chlorination is an Effective Method of Water Disinfection (WBUHS 2013, 2018, 2019, 2022 - Highly repeated!)

Principles of Chlorination:

Water to be chlorinated should be clear and free from turbidity
Chlorine demand must be estimated (= difference between chlorine added and residual chlorine after 60 min contact at given temperature and pH)
Breakpoint chlorination must be reached (chlorine demand must be fully met)
Contact period: Free residual chlorine must be present for at least 1 hour to kill bacteria and viruses
Minimum free residual chlorine = 0.5 mg/L for 1 hour
Correct dose = Chlorine demand + 0.5 mg/L free residual chlorine

Why chlorination is effective: It kills bacteria, viruses, and spores; oxidises organic matter; eliminates taste and odour; its effect can be measured and monitored using simple tests (OT/OTA test).

Q.26. OTA Test is Better than OT Test - Explain (WBUHS 2013)

Feature	OT Test	OTA Test
Reagent	Orthotoluidine	Orthotoluidine-arsenite
Detects	Both free + combined chlorine together (turns yellow)	Free and combined chlorine separately
Interference	False yellow with iron, manganese, nitrates	Overcomes this error
Accuracy	Less accurate	More accurate

Conclusion: OTA test is superior because it can estimate free and combined chlorine in water separately, and overcomes false positives from iron, manganese, and nitrates.

Q.27. Criteria for a Sanitary Latrine / Best Latrine for Rural Area (WBUHS 2010, 2013, 2022; TRIU 2016; RGUHS 2014)

Criteria for a sanitary latrine:

Excreta should NOT contaminate ground or surface water
Excreta should NOT pollute the soil
Excreta should NOT be accessible to flies, rodents, animals, and other vehicles of transmission
Excreta should NOT create nuisance due to odour or unsightly appearance

Examples of sanitary latrines:

Dug well latrine
Water seal latrine (RCA latrine, Sulabh Shauchalaya)
Septic tank
Aqua privy

Recommended Latrine for Rural Area: "Two Pit Pour Flush Latrine"

Has two pits; designed for family use (not community)
One pit used until full → second pit opened
First (filled) pit undergoes anaerobic digestion of night soil for observation period
After putrefaction complete, the soil becomes fertiliser for cultivation of land
Flushing system uses water poured into pan after defaecation
Alternate pit use continues for family indefinitely

Q.28. Overcrowding Can Influence Health - Justify (WBUHS 2010, 2013, 2022; TRIU 2016; RGUHS 2014)

Overcrowding = more people in dwelling than there is space for.

Effects on health:

Poor ventilation → rise in temperature + excessive humidity + air stagnation → lowers vitality → susceptibility to disease
Rapid spread of respiratory diseases by droplet infection: TB, influenza, diphtheria, acute rheumatic fever, whooping cough, bronchitis
Spread of contagious diseases: scabies, impetigo, ringworm, leprosy, trachoma, conjunctivitis
Psychosocial effects: irritability, frustration, lack of sleep, anxiety, violence, mental disorders

Q.29. Poor Housing Can Have Adverse Effects on Health - Explain

Housing is a part of total environment; strong relationship established between poor housing and:

Respiratory infections: Common cold, TB, influenza, measles
Skin infections: Scabies, ring-worm, impetigo, leprosy
Rat infection: Plague
Arthropods: Housefly, mosquitoes, fleas, bugs
Accidents: Common in defective houses
High morbidity and mortality
Psychosocial effects: Loneliness (upper floors of high buildings), isolation → neurosis, behaviour disorders

Q.30. Partially Blocked Flea is More Dangerous than Completely Blocked Flea - Explain

Feature	Completely Blocked Flea	Partially Blocked Flea
Proventriculus	Completely blocked by plague bacilli	Only partially blocked
Feeding ability	Cannot feed → starvation	Partially fed
Survival	Dies soon (starved)	Survives longer
Number of persons bitten	Few	More persons
Force of regurgitation	High	Less
Number of bacilli	Large	Less per bite

Epidemiologically, partially blocked flea is more dangerous because:

It survives longer → bites more persons
It is partially fed, so it keeps trying to feed → transmits to more hosts
Blood is regurgitated with greater force and more bacilli enter the wound

Q.31. Environmental Control - Best Approach to Control Arthropods - Justify

Environmental control offers the best approach because results are likely to be permanent.

Examples of environmental manipulation:

Elimination of breeding places (source reduction):
- Filling and drainage operations
- Carefully planned water management
- Provision of piped water supply
- Proper disposal of refuse and other wastes
- Cleanliness in and around houses
Intensive health education of public
Political support as essential prerequisite

Q.32. Resistance to Synthetic Insecticide is a Global Problem - Explain

Resistance (as per IRAC): A heritable change in sensitivity of a pest population, reflected in repeated failure of a product to achieve expected level of control when used according to label recommendations.

Resistance due to biochemical factors: toxicant converted to non-toxic form by enzymes
Resistance due to genetic factors: transmitted through genes

DDT resistance is commonest; then HCH (both are organochlorine compounds). Only effective action = change to organo-phosphorous and carbamate insecticides. However:

Cross resistance exists between most organo-phosphorous and most carbamate compounds
Insecticide resistance is growing → steadily diminishing choice of effective insecticides → global problem

Q.33. Exhaust and Plenum Ventilation are NOT Synonymous

Both are mechanical/artificial types of ventilation but differ:

Feature	Exhaust Ventilation	Plenum Ventilation
Mechanism	Air extracted out by exhaust fans	Fresh air blown in by centrifugal fans
Pressure created	Negative (vacuum) → fresh air enters through doors/windows	Positive → displaces vitiated air
Fan type	Exhaust fans	Centrifugal/high-pressure fans
Use	Removes dust/gases at source	General ventilation
Utility	Widely used	Limited utility

MCQs (Group C) - Answers

All criteria of safe and wholesome water EXCEPT: (d) Usable for domestic purposes - this is not a criterion of safety; the criteria are freedom from pathogens, harmful chemicals, palatability, and being usable for domestic purposes (actually all are criteria - the odd one is the phrasing; look at options carefully in exam)
All are viral water-borne diseases EXCEPT: (b) Hepatitis C - Hepatitis C is spread by blood/parenteral route, not water. (Hepatitis A, E, Rotavirus are water-borne)

WBUHS 2026 Exam Strategy:

Most frequently asked from WBUHS: Sanitation barrier (Q.17), Principles of chlorination (Q.23-25), Overcrowding (Q.18, 28), Sanitary latrine (Q.27), Indoor air pollution (Q.6), Ventilation (Q.7)

Write answers in structured bullet/table format for maximum marks

Always include definitions first, then mechanisms, then examples

For Q.17 (Sanitation barrier), always draw the diagram of the 6 F's

This is a shared conversation. Sign in to Orris to start your own chat.