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CHAPTER 3 - ENVIRONMENTAL HEALTH PROBLEMS

WBUHS MBBS 2026 Exam-Oriented Question & Answer Guide

Community Medicine

GROUP A - LONG ANSWER QUESTIONS (LAQ)

Q1. Define 'Safe and Wholesome Water'. Discuss the different tests for the bacteriological surveillance of drinking water. (WBUHS 2013)

WBUHS Exam Tip: This is a frequently repeated question. Write definition, then enumerate tests in numbered format with subheadings.

DEFINITION - Safe and Wholesome Water

A safe and wholesome water is one which is:

Free from pathogenic agents
Free from harmful chemical substances
Pleasant to taste (free from colour and odour)
Usable for domestic purposes

TESTS FOR BACTERIOLOGICAL SURVEILLANCE OF DRINKING WATER

1. Presumptive Coliform Test (Two Methods)

(i) Multiple Tube Method (MPN Method)

Based on estimating the Most Probable Number (MPN) of coliform organisms in 100 ml of water
Measured quantities of sample water (0.1, 1.0, 10, 50 ml) are inoculated into tubes of McConkey's Lactose Bile Salt Broth with bromocresol purple as indicator
Incubated at 37°C for 48 hours
Tubes showing acid and gas = positive
MPN is estimated from statistical table = "Presumptive Coliform Count"

Confirmatory Test:

Each presumptive positive tube is sub-cultured in Brilliant Green Bile Broth at 44°C
Tested for gas production from lactose
Tested for indole production at 44°C

(ii) Membrane Filtration Technique

Measured volume of sample is filtered through a cellulose ester membrane
Bacteria retained on membrane surface
Inoculated on suitable media at appropriate temperature
Results within 20 hours

2. Tests for Detection of Faecal Streptococci

Faecal streptococci occur in faeces in smaller numbers than E. coli
In doubtful cases, presence of faecal streptococci = important evidence of recent faecal pollution

3. Tests for Detection of Faecal Cl. Perfringens

Water is heated at 75°C for 10 minutes (to destroy non-spore bearing organisms)
Then inoculated into Differential Reinforced Clostridium (DRC) medium in a screw-capped bottle
Incubated at 37°C for 2 days
Absence of coliform group + presence of Cl. perfringens spores = faecal contamination at some remote time

4. Colony Count (Plate Count)

Estimates general purity of water
Done at frequent intervals

Water at Point of Consumption	Plate Count after 2 days at 37°C	Plate Count after 3 days at 22°C
(i) Disinfected	0	20
(ii) Not disinfected	10	100

A sudden increase in colony count = earliest indication of contamination

Q2. Name important chemicals of health significance present in ground water of West Bengal. Describe in brief the health effects and control measures of any one. (WBUHS 2017)

WBUHS Exam Tip: The most common chemical asked is Arsenic - write its health effects in acute + long-term subheadings.

The commonest chemical of health significance in ground water of West Bengal is ARSENIC. Others include fluoride, lead, cadmium, chromium.

ARSENIC

Health Effects

Arsenic occurs in inorganic and organic forms. Inorganic arsenic (found in water) is highly toxic; organic arsenic (seafood) is less harmful.

a) Acute Effects:

Vomiting, abdominal pain, diarrhoea
Numbness and tingling of extremities
Muscle cramping
Death in extreme cases

b) Long-term Effects:

Skin: Pigmentation changes, skin lesions, hard patches on palms and soles (hyperkeratosis) - after minimum 5 years' exposure; may be precursor to skin cancer
Cancers: Bladder, lung, skin cancer with prolonged exposure
Other effects: Developmental effects, neurotoxicity, diabetes, pulmonary disease, cardiovascular disease (myocardial infarction), portal hypertension with hepatomegaly and splenomegaly
Reproductive: Adverse pregnancy outcomes, infant mortality, negative impacts on cognitive development in children

Prevention and Control Measures

Substitute high-arsenic groundwater sources with low-arsenic, microbiologically safe sources (rainwater, treated surface water)
Discriminate between high-arsenic and low-arsenic sources - test water and paint tube wells/hand pumps different colours
Blend low-arsenic water with higher-arsenic water to achieve acceptable concentration level
Install arsenic removal systems - centralized or domestic:
- Technologies: oxidation, coagulation-precipitation, absorption, ion exchange, membrane techniques
Long-term actions: Reduce occupational exposure from industrial processes
Education and community engagement for successful interventions
Monitor high-risk populations for early signs (usually skin problems)
Treatment of arsenicosis is unsatisfactory and mostly symptomatic

Q3. Enumerate the water-borne diseases. Discuss in brief about purification of water at household level. What is a Problem Village? (WBUHS 2010, 2023)

WBUHS Exam Tip: Enumerate clearly, then write household methods under Physical/Chemical/Mechanical/UV headings.

WATER-BORNE DISEASES

(1) Those caused by infectious organisms:

Type	Examples
Viral	Hepatitis A, Hepatitis E, Poliomyelitis, Rotavirus diarrhoea in infants
Bacterial	Typhoid, Paratyphoid fever, Bacillary dysentery, E. coli diarrhoea, Cholera
Protozoal	Amoebiasis, Giardiasis
Helminthic	Ascariasis, Enterobiasis, Hydatid disease
Leptospiral	Weil's disease

(2) Those caused by aquatic hosts:

Snail: Schistosomiasis
Cyclops: Dracunculosis (Guinea worm disease), Fish tapeworm

PURIFICATION OF WATER AT HOUSEHOLD LEVEL

(1) Physical Methods

(i) Boiling

Water must be brought to rolling boil for 10-20 minutes
Kills all bacteria, spores, cysts, ova and viruses - yields sterile water
Also removes temporary hardness (drives out CO₂, precipitates CaCO₃)
Disadvantages: Taste of water is altered; no residual protection
Water should be boiled and stored in the same container

(2) Chemical Methods

Agent	Details
Bleaching Powder	Contains 33% available chlorine; free residual chlorine of 0.5 mg/litre at end of 1 hour
Chlorine Solution	5% solution prepared when 4 kg of 25% bleaching powder is mixed with 20 litres water
HTH (High Test Hypochlorite)	Contains 60-70% available chlorine; more stable than bleaching powder
Chlorine tablets (Halazone)	0.5 mg tablet sufficient to disinfect 20 litres of water; removes turbidity
Iodine	2 drops of 2% ethanol solution for 1 litre clear water; for emergency use only
Potassium Permanganate	May kill cholera vibrios; little use against other organisms

(3) Mechanical (Filtration)

Ceramic filters: Pasteur-Chamberland filter, Berkefeld filter, Katadyn filter
Candle inside each filter arrests microorganisms except viruses
Needs cleaning at regular intervals

(4) UV Irradiation (Acquaguard Domestic Filter)

UV rays have germicidal properties against bacteria, yeast, viruses, fungi, algae, protozoa

(5) Multistage Reverse Osmosis

Makes water both chemically and microbiologically potable
Reduces total dissolved solids, hardness, heavy metals, disease-causing bacteria, viruses, protozoa and cysts

PROBLEM VILLAGE

A problem village is one where:

No source of safe water is available within 1.6 km / 15 m deep, OR
Where water source has excess salinity, iron, fluorides and other toxic elements, OR
Where water is exposed to the risk of cholera

Q4. Classify the water-related diseases. Describe the surveillance of drinking water quality. (WBUHS 2013, 2023)

WBUHS Exam Tip: Use Bradley's classification with a table, then write surveillance elements under 4 numbered headings.

CLASSIFICATION OF WATER-RELATED DISEASES (Bradley, 1977)

Sl.No.	Type	Cause	Example
1	Water-borne	Consumption of contaminated water	Diarrhoea, Hepatitis A, Cholera, Typhoid, Guinea worm
2	Water-washed	Poor personal hygiene due to non-availability of adequate water	Diarrhoea, Typhoid, Trachoma, skin and eye infections
3	Water-based	Intermediate host dwelling in water	Guinea worm, Schistosomiasis
4	Water-related	Vectors breeding in water	Malaria, Filarial, Dengue, Chikungunya

SURVEILLANCE OF DRINKING WATER QUALITY

According to WHO (1976): "Drinking water supply surveillance is the continuous and vigilant public health assessment and review of the safety and acceptability of drinking water supplies."

Elements of a surveillance programme:

1. Sanitary Survey

First step in water quality surveillance
Purpose: to detect and correct faults and deficiencies in the entire water supply system
Essential for adequate interpretation of laboratory results

2. Collection of Water Sample

Tap/Pump: Remove anything attached to tap, clean outlet with dry cloth, sterilise with flame, allow initial water to flow for 1 minute, then collect in sterile bottle
Well/Storage tank: Sterile bottle attached to string is lowered into the well, allowed to fill, then raised and stopper replaced

3. Transport and Storage of Sample

Bacteriological analysis should begin as soon as possible after collection
If not feasible: keep in ice; must be analysed within 48 hours of collection

4. Bacteriological Surveillance

Tests as described in Q1 (Presumptive coliform test, Faecal streptococci test, Colony count, etc.)

Q5. Describe water conservation and rainwater harvesting in urban areas. (RGUHS 2010, 2012; SAMU 2011; ABKUB 2018; BNMU 2014)

WATER CONSERVATION

All living things need water for cellular activities. Due to:

Declining rainfall
Rapid urbanisation and industrialisation
Deforestation
Population explosion

...surface waters (rivers, ponds, lakes) are shrinking and sub-soil water level is falling alarmingly, worsened by dependence on tube wells.

Conservation has two components:

(a) Prevention of wastage: Widespread awareness about economical use of water
(b) Water harvesting: Preserving and building up underground water reserves

RAINWATER HARVESTING

Rainwater harvesting is the simple process of conserving rainwater by collecting, storing, conveying and purifying rainwater that runs off from rooftops, parks, roads, open grounds, etc., for later use.

Components of Rainwater Harvesting System:

Catchment - Used to collect and store captured rainwater
Conveyance system - Transports harvested water from catchment to recharge zone
Flush - Flushes out first spell of rain
Filter - Filters collected rainwater; removes pollutants
Tanks and recharge structures - Stores filtered water ready for use

The process involves collection and storage of rainwater using artificially designed systems that run off naturally or man-made catchment areas (rooftop, compounds, rock surface, hill slopes, artificially repaired impervious or semi-pervious land surface).

Q6. What is Air Pollution? Mention the sources of air pollution. Describe the hazards of air pollution. (WBUHS 2019; SSUHSA 2010, 11, 17; DU 2013, 15; SMU 2011, 12)

WBUHS Exam Tip: This is a high-yield question - appeared in WBUHS 2019. Define, then write sources and hazards under separate numbered headings.

DEFINITION

Air pollution is defined as the presence of toxic chemicals or compounds (including those of biological origin) in the air, at levels that pose a health risk. In a broader sense, it means the presence of chemicals or compounds in the air which lower air quality or cause detrimental changes (e.g. damage to ozone layer, global warming).

SOURCES OF AIR POLLUTION

Domestic: Combustion of coal, wood or oil (The London disaster of 1952 was due to domestic coal burning)
Automobiles: Motor vehicles are the major source in urban areas; emit hydrocarbons, CO, lead, nitrogen oxides and particulate matter
Industries: Iron and steel, paper, cement, fertilisers, thermal power plants, petroleum refineries
Miscellaneous: Tobacco smoking, burning refuse, incinerators, nuclear explosions, forest fire

HAZARDS OF AIR POLLUTION

1. Immediate and Acute Effects

Mostly due to photochemical oxidants in air
Common effects: Conjunctivitis, allergic rhinitis, acute pharyngitis, acute bronchitis, bronchial asthma (acute attacks)
May result in suffocation and death
Examples: London disaster, England (1952); Bhopal gas tragedy, India (1984)

2. Delayed and Chronic Effects

Chronic bronchitis, bronchiectasis, emphysema, COPD, bronchial asthma, lung cancer

Q7. Discuss in brief about the Indicators of air pollution. How can air pollution be prevented and controlled? (BNMU 2013; WBUHS 2019; DU 2015; MU 2019)

INDICATORS OF AIR POLLUTION

Sulphur-dioxide index - Concentration of SO₂ estimated in all air pollution surveys
Smoke (Soiling) index - Known volume of air filtered through white filter paper under specified condition; stain measured by photoelectric meter; expressed as Coh units/1000 linear feet of air
Suspended particles (Grit and dust concentration) - Measured using instrument 'Midget Impinger'; expressed in mgm per cubic meter of air
Coefficient of Haze - Amount of smoke or other aerosol per cubic metre of air
Air Pollution Index - Arbitrary index taking into account one or more pollutants as measure of severity
- Example (USA): 10 × SO₂ concentration + 2 × CO concentration + 2 × coefficient of haze; alarm when value > 50

PREVENTION AND CONTROL OF AIR POLLUTION

1. Engineering Measures

(a) Location of industries - Far from human habitation

(b) Containment measures - Prevention of escape of toxic substances into ambient air:

Controlling dust production by wet method
Prevention of dust escape using enclosures, hood, exhaust pipes
Development of arresters for removal of contaminants

(c) Replacement measures - Replace polluting technology:

Use of electricity/natural gas instead of coal
Use of unleaded petrol for smoke reduction

2. Legislations

(a) Indian Factories Act, 1948
(b) The Air (Prevention and Control of Pollution) Act, 1981
(c) Smoke Nuisance Act

3. General Measures

Traffic control by construction of bypass roads
Dilution measures - Green belts between industrial and residential areas
Health education about hazards and prevention
Population stabilisation

4. International Action

WHO established international network of laboratories for monitoring air pollution worldwide
Two international centres: London and Washington
20 laboratories in various parts of the world; issue warnings of air pollution when necessary

Q8. Mention the impact of climate change on human health. (WBUHS)

Sl.No.	Change of Climate	Effect on Environment	Health Hazards
1	More extreme weather	Air pollution	Asthma, cardiovascular disease
		Changes in vector ecology	Malaria, Dengue, Encephalitis, Rift valley fever, Lyme disease, Chikungunya, West Nile virus
2	Rising sea levels	Increasing allergens	Respiratory allergies, asthma
		Water quality impacts	Cholera, cryptosporidiosis, campylobacter, leptospirosis, harmful algal blooms
3	Increasing CO₂ levels	Water and food supply impacts	Malnutrition, diarrhoeal disease
		Environmental degradation	Forced migration, civil conflict, mental health impacts
4	Rising temperature	Extreme heat	Heat-related illnesses and death, cardiovascular failure
		Severe weather	Injuries, fatalities, mental health impacts

Q9. Enumerate soil-borne diseases. What are the criteria for a Sanitary Latrine? What is the importance of water seal type of latrine? What is a Sanitary Barrier? (WBUHS 2023)

WBUHS Exam Tip: This was directly asked in WBUHS 2023 - very important for 2026.**

SOIL-BORNE DISEASES (Common in India)

Intestinal roundworms (Ascariasis)
Hookworms - Necator americanus and Ancylostoma duodenale
Whipworm (Trichuris trichiura)

CRITERIA OF A SANITARY LATRINE

A sanitary latrine is one which fulfils the following criteria:

Excreta should not contaminate ground or surface water
Excreta should not pollute the soil
Excreta should not be accessible to flies, rodents, animals (pigs, dogs, cattle) and other vehicles of transmission
Excreta should not create a nuisance due to odour or unsightly appearance

IMPORTANCE OF WATER SEAL TYPE OF LATRINE

This type of latrine is fitted with a water seal. The water seal performs two important functions:

(a) Prevents access by flies - the night soil is sealed off from flies by a small depth of water contained in a bent pipe called the trap

(b) Prevents escape of odours and foul gases - thereby eliminates nuisance from smell

(c) Once flushed, the night soil is no longer visible

SANITARY BARRIER

(Discussed in Group B Short Notes)

Q10. Criteria and health effects of poor ventilation. (WBUHS)

CRITERIA OF POOR VENTILATION (Ventilation Standards)

Floor space: Optimum floor space requirements per person = 50 to 100 ft²
Cubic space: 1000-1200 ft³ fresh air supply per person per hour is considered sufficient for comfort
Air change: Recommended number of air changes in a living room = 2-3 per hour; in workrooms and assemblies = 4-6 per hour
Windows:
- At least 2 windows per living room; at least one opening directly to open space
- Windows at height of not more than 3 ft from ground
- Window area = one-fifth of floor area
- Doors and windows combined = two-fifth of floor area

EFFECTS OF POOR VENTILATION ON HEALTH

Higher chances of spread of air-borne diseases
Poor indoor air quality leading to fatigue, hypersensitivity, headache and sinus congestion
Sick Building Syndrome - symptoms: irritation of eyes, nose, headache, fatigue, susceptibility to colds and flu
Dampness in rooms leading to rats and insect infestations
Excessive workplace odours causing discomfort and poor concentration
High levels of CO₂ and low oxygen levels causing fatigue (especially in large gatherings in ill-ventilated spaces)

Q11. What is smog? What is AQI? The AQI of your city is falling within 200-300 during last 7 days in March. What are the health effects? What measures can be adopted? (WBUHS 2024)

WBUHS Exam Tip: WBUHS 2024 direct question - write definition of smog, AQI table with all 6 categories, then clinical scenario-based answer.**

SMOG

Smog is air pollution that reduces visibility. The term was first used in the early 1900s to describe a mix of smoke and fog. Most smog seen today is photochemical smog.

AQI (Air Quality Index)

AQI is a tool for effective communication of air quality status to people. It:

Transforms complex air quality data into a single number (index value), nomenclature and colour
Air quality subindex and health breakpoints are evolved for 8 pollutants: PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃, and Pb
Short-term (up to 24 hours) national ambient quality standards are prescribed

AQI	Air Quality	Possible Health Impacts
0-50	Good	Minimal impact
51-100	Satisfactory	Minor breathing discomfort to sensitive people
101-200	Moderate	Breathing discomfort to people with lung, heart disease, children and older adults
201-300	Poor	Breathing discomfort to people on prolonged exposure
301-400	Very Poor	Respiratory illness to people on prolonged exposure
>400	Severe	Respiratory effects even on healthy people

CLINICAL SCENARIO (AQI 200-300 for 7 days):

Health Effects:

Breathing discomfort to the general population on prolonged exposure
Worsening of asthma, COPD, chronic bronchitis
Increased risk of cardiovascular events
Eye and throat irritation

Measures to Adopt:

Avoid outdoor activity, especially prolonged exertion
Wear N95 masks outdoors
Keep windows closed; use air purifiers indoors
Avoid burning biomass, garbage, or fireworks
Engineering and legislative measures (as per Q7)
Alert vulnerable groups (children, elderly, those with lung/heart disease)

Q12. What are the different methods of solid waste management? Describe composting and biogas generation in detail. (WBUHS 2024)

WBUHS Exam Tip: WBUHS 2024 direct question. Enumerate all 7 methods first, then describe composting and biogas in detail.**

METHODS OF SOLID WASTE DISPOSAL

Recycling - Materials recovered from products after use, subjected to recycling
Dumping - Refuse dumped in low lying areas; method of reclamation and easy disposal
Controlled Tipping / Solitary Landfill - Most satisfactory method; material placed in trench/prepared area, compacted, covered with earth at end of working day
Composting - Biodegradable organic matter subjected to aerobic digestion
Incineration - Combustion of waste to reduce volume; sent for disposal
Manure pits - In rural areas; garbage, cattle dung, straw and leaves dumped into manure pits and covered with earth after each day
Sewage treatment - Treatment of raw sewage water; effluent discharged into seawater/river; sludge incinerated or disposed in landfill

COMPOSTING (in detail)

Definition: Composting is a method of combined disposal of refuse and nightsoil or sludge. It is a process of nature whereby organic matter breaks down under bacterial action resulting in the formation of relatively stable humus-like material called the compost, which has considerable manurial value for the soil.

Advantages:

Reduction of waste for landfill and incineration
Recovery of useful organic matter for use as soil amendment

Disadvantages:

Bioaerosols - organic dust containing bacteria or fungal spores
Emits volatile organic compounds
Potential pathway from use on land for contaminants to enter food chain

BIOGAS GENERATION (in detail)

Definition: Biogas is a renewable fuel produced when organic matter (food or animal waste) is broken down by microorganisms in the absence of oxygen (anaerobic digestion).

Biogas Plant Components:

(1) Reception Area:

Where raw materials arrive and are prepared for anaerobic digestion
Popular biomass: crop residues, municipal/industrial sewage, agricultural material, live-stock manures, seaweed, food processing and paper wastes

(2) The Digester:

Air-tight, water-proof container
Raw materials are transformed into energy
Agitators shift biomass periodically to free gases and prevent layer formation

(3) The Gas Holder:

Air-proof container (preferably steel)
Collects gas generated during fermentation
Has gas outlet that allows biogas to come out and produce energy and heat

Biogas plants follow an automatic, straight-forward process to replicate natural anaerobic digestion in an artificial environment - making biogas production simple and carbon neutral.

GROUP B - SHORT ANSWER QUESTIONS / SHORT NOTES

Q1. Biological Filter (WBUHS 2019)

Slow sand filtration is also known as biological filtration.

Water is subjected to various putrefying influences as it percolates through the sand bed
Impurities removed by a combination of straining, sedimentation, biochemical and biological processes
Shortly after start of filtration, a slow sand filter acts primarily biologically by forming a slimy "Zoogleal" layer on the sand bed, also known as:
- "Vital layer"
- "Schmutzdecke"
This layer consists of algae, biological organisms such as plankton, diatoms, and other minute plants and protozoa
They feed on organic matter and convert it into small harmless substances
This vital layer (heart of the filter):
- Removes organic matter
- Holds back bacteria
- Oxidizes ammoniacal nitrogen into nitrates
- Helps in yielding bacteria-free water

(Additional Short Notes based on WBUHS pattern:)

Q2. Sanitation Barrier

The sanitation barrier refers to any obstacle that interrupts the faecal-oral route of disease transmission.

The key barriers are:

Safe excreta disposal (sanitary latrines)
Safe water supply
Personal hygiene (handwashing)
Food hygiene
Protection of stored water

A well-maintained sanitary latrine with water seal type represents one of the most effective sanitation barriers, as it prevents flies, odour, and direct contamination of soil and water.

Q3. AQI (Air Quality Index) - Short Note

AQI transforms complex air quality data of 8 pollutants into a single index value
Pollutants: PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃, Pb
Categories from 0 (Good) to >400 (Severe)
Helps alert public and policymakers about air quality status
(Full AQI table - see Q11 in LAQ)

Q4. Problem Village - Short Note

A problem village is defined as one where:

No source of safe water is available within a distance of 1.6 km / 15 m deep, OR
Source has excess salinity, iron, fluorides and other toxic elements, OR
Water is exposed to the risk of cholera

Q5. Smog - Short Note

Smog = air pollution reducing visibility
Term coined in early 1900s for smoke + fog
Two types:
1. Classical smog (London type) - from burning coal; SO₂ + fog
2. Photochemical smog (modern type) - from automobile exhaust; nitrogen oxides + UV light → ozone, PANs, aldehydes
Health effects: Bronchitis, asthma, eye irritation, lung damage
London smog disaster 1952 - 4000+ deaths

Note: All answers above are aligned to the WBUHS MBBS pattern with reference to WBUHS-specific past papers (2010, 2013, 2017, 2019, 2023, 2024). For 2026 exams, focus especially on Q11 (AQI + Smog - WBUHS 2024) and Q12 (Solid waste + Biogas - WBUHS 2024) as these are fresh additions to the pattern. Q3 (water-borne diseases + problem village), Q4 (water-related diseases + surveillance), and Q9 (sanitary latrine - WBUHS 2023) are also high-yield repeat questions.

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