Psm imp question for environment for uni mbbs exam

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PSM - Environment: Important Questions for MBBS University Exam

Based on Park's Textbook of Preventive and Social Medicine

UNIT OVERVIEW: Environment & Health

The "Environment and Health" chapter is one of the highest-weighted sections in PSM theory papers. Below are all the major exam-relevant topics with complete notes.

TOPIC 1: ENVIRONMENT - DEFINITIONS & CONCEPTS (2-5 marks)

Definition of Environment (Park's): "The aggregate of all the external conditions and influences affecting the life and development of an organism."

Types of Environment:

Physical - air, water, soil, climate, radiation
Biological - bacteria, viruses, insects, animals, plants
Psychosocial - social norms, cultural practices, economic conditions

Macro-environment vs. Micro-environment:

Macro-environment = total environment surrounding man
Micro-environment = immediate surroundings of the individual (home, workplace)

TOPIC 2: WATER SUPPLY AND PURIFICATION (High-value 10-marker)

Sources of Water (Park's, p.807)

Rain water - purest in nature; soft water; picks up impurities as it passes through atmosphere; acid rain from SO₂ + NO₂ reactions
Surface water - rivers, tanks, lakes, reservoirs; prone to contamination; needs full treatment before use
Ground water - shallow wells, deep wells, springs; relatively protected; may only need disinfection

Purification of Water on a Large Scale

The 3-step process:

I. Storage

90% of suspended impurities settle in 24 hours by gravity
Bacterial count drops by ~90% in the first 5-7 days
Optimum period of storage = 10-14 days
Overcomes algal overgrowth risk

II. Filtration

Slow Sand (Biological) Filter:

First used in 1804 in Scotland
Key feature: "Schmutzdecke" (Vital/Zoogleal layer) - slimy gelatinous layer of algae, diatoms, bacteria
This vital layer is the "heart" of the slow sand filter
Ripening = process of formation of vital layer (takes a few days); initial filtrate is run to waste
Rate of filtration: 0.1-0.4 m/hour
Removes 98-99% of bacteria
Filter cleaning: by scraping 1-2 cm off the top sand layer

Rapid Sand (Mechanical) Filter:

Rate of filtration: much faster (5-15 m/hour)
Does NOT form a vital layer
Requires coagulation + sedimentation before filtration
Cleaned by backwashing (not scraping)

Feature	Slow Sand	Rapid Sand
Rate	0.1-0.4 m/hr	5-15 m/hr
Vital layer	Yes (Schmutzdecke)	No
Cleaning	Scraping	Backwashing
Pre-treatment needed	No	Yes
Bacteria removal	98-99%	Less

III. Disinfection: Chlorination

Mechanism: Chlorine + water → HOCl + HCl (Hypochlorous acid is the active germicidal agent)

Types of Chlorination:

Simple chlorination: 0.5 ppm chlorine; contact time 30 min; residual = 0.2 ppm
Superchlorination: Large doses of Cl₂ added to heavily polluted water, followed by dechlorination
Break-point chlorination: Chlorine added until all chloramines are destroyed and free residual chlorine appears - the point where residual chlorine begins to rise = "breakpoint"
Double chlorination: Chlorine applied before and after filtration

Residual chlorine test - OT (Orthotolidine) Test:

Reagent: Orthotolidine in 10% HCl
Turns yellow in presence of chlorine; intensity = concentration
Read within 10 seconds for free chlorine
OTA (Orthotolidine-Arsenite) test distinguishes free from combined chlorine

WHO standard for drinking water: Residual chlorine ≥ 0.2 ppm; pH 6.5-8.5; Turbidity < 5 NTU

TOPIC 3: AIR POLLUTION (Common 10-marker)

Definition (Park's, p.834):

"Presence in the ambient atmosphere of substances generated by the activities of man in concentrations that interfere with human health, safety or comfort."

Types of Air Pollutants

By formation:

Primary pollutants - emitted directly from a source (factory chimney, exhaust pipe)
Secondary pollutants - formed within the atmosphere by chemical reactions of primary pollutants; e.g., ozone (formed from photochemical reactions)

By physical state:

Gaseous pollutants - gases/vapours; water-soluble ones deposit in upper respiratory tract
Particulate pollutants - solid/liquid particles; size: 1-2 μm (secondary) up to 100 μm (coarse)

Sources of Air Pollution (Park's Table 3)

Pollutant	Source	Health Effects
Oxides of Nitrogen (NOx)	Automobile exhaust, gas stoves	Respiratory tract irritation, bronchiolitis obliterans
Hydrocarbons	Automobile exhaust, cigarette smoke	Lung cancer
Ozone	Automobile exhaust, aircraft cabins	Cough, bronchoconstriction, substernal discomfort
Sulphur dioxide (SO₂)	Power plants, smelters, oil refineries	Exacerbation of asthma & COPD, death in severe exposure
Lead (Pb)	Leaded gasoline exhaust	Neuropsychological impairment in children, loss of IQ
Carbon Monoxide (CO)	Incomplete combustion	Carboxyhemoglobin formation, asphyxia

Health Effects of Air Pollution (Park's, p.839)

Immediate effects: Acute bronchitis; suffocation - e.g., London Smog Disaster, 1952

Delayed/chronic effects:

Chronic bronchitis
Lung cancer
Bronchial asthma
Emphysema
Respiratory allergies

Most vulnerable: Elderly, children, smokers, those with chronic respiratory disease

Indoor Air Pollution

Sources: biomass fuel (wood, dung, crop residue), coal, kerosene; especially affects women and children in developing countries Effects: acute respiratory infections, COPD, lung cancer

Prevention and Control of Air Pollution

Legislation (Clean Air Act, National Ambient Air Quality Standards - NAAQS)
Technical measures - cleaner fuels, catalytic converters, electrostatic precipitators
Environmental planning - green belts, industrial zoning
Monitoring - Central Pollution Control Board (CPCB) in India

TOPIC 4: WATER POLLUTION (5-10 marks)

Definition: "Alteration in quality of water rendering it unfit for intended use"

Sources of Water Pollution

Domestic sewage (most common)
Industrial effluents
Agricultural run-off (pesticides, fertilizers - nitrate pollution)
Thermal pollution (hot water from power plants)

Indicators of Faecal Pollution

Coliform organisms (E. coli) are used as indicators because:
1. Present in large numbers in faeces
2. Survive longer in water than pathogens
3. Easy to detect by simple laboratory tests
4. Do not multiply significantly in water

Diseases Transmitted Through Water

Waterborne diseases (ingested): cholera, typhoid, hepatitis A, dysentery, polio
Water-washed diseases (lack of water for hygiene): trachoma, scabies, lice
Water-based diseases (aquatic host): schistosomiasis, guinea worm
Water-related insect vector diseases (breed in water): malaria, filariasis, dengue

TOPIC 5: EXCRETA DISPOSAL (5 marks)

Sanitary Methods of Excreta Disposal:

Conservancy system - night soil collected manually (unsanitary)
Water carriage system - flush toilets connected to sewers (most sanitary)
Septic tank - anaerobic digestion; sludge settles, effluent drains to soak pit
Aquaprivy - similar to septic tank but connected directly to latrine

Latrines:

Bore-hole latrine - should be located 15 m (50 ft) away from water source to prevent water pollution
Pit latrine - simplest and most common in rural India
VIP (Ventilated Improved Pit) latrine

TOPIC 6: HOUSING & HEALTH (5 marks)

Overcrowding - defined as >1.5 persons per room (Indian standard)

Diseases associated with poor housing:

Airborne: TB, measles, meningitis, influenza
Contact: scabies, ringworm
Feco-oral: diarrhea, typhoid

Components of healthy housing: Ventilation (cross-ventilation), lighting, sanitation, safe water supply, space standards, drainage

TOPIC 7: NOISE POLLUTION (Short note - 5 marks)

Unit: Decibel (dB); 0 dB = threshold of hearing; 120-140 dB = pain threshold

WHO standards:

Residential areas: < 45 dB (day), < 35 dB (night)
Industrial areas: < 75 dB

Health effects of noise:

Auditory: Noise-Induced Hearing Loss (NIHL), Temporary Threshold Shift (TTS), Permanent Threshold Shift (PTS)
Non-auditory: hypertension, sleep disturbance, stress, decreased productivity, interference with communication

Occupational exposure limit (India): 90 dB for 8 hours/day

Control of Noise Pollution:

Source control (quieter machinery, mufflers)
Path control (barriers, distance, enclosures)
Receiver protection (ear plugs, ear muffs)

TOPIC 8: RADIATION (Short note - 5 marks)

Types:

Ionizing radiation: X-rays, gamma rays, alpha, beta, neutron particles
Non-ionizing radiation: UV, infrared, microwave, radiofrequency

Health effects of ionizing radiation:

Acute: nausea, vomiting, hair loss, bone marrow suppression (radiation sickness)
Chronic/delayed: leukemia, thyroid cancer, cataracts, genetic mutations

Safe dose: Occupational limit = 20 mSv/year (ICRP); general public = 1 mSv/year

UV radiation effects: Skin cancer (squamous cell > basal cell), photokeratitis, cataracts, immune suppression; also beneficial - vitamin D synthesis

TOPIC 9: HOSPITAL WASTE MANAGEMENT (Short note - 5 marks)

Categories of biomedical waste (BMW Rules 2016):

Category	Example	Disposal
Yellow	Anatomical waste, soiled items, expired medicines	Incineration / deep burial
Red	Plastics, tubing, IV sets	Autoclave + shredding
White (Sharps)	Needles, syringes, blades	Needle destroyer / encapsulation
Blue	Glassware	Autoclave + crushing

Key principle: Segregation at source is the most important step

TOPIC 10: SOLID WASTE MANAGEMENT (Short note - 5 marks)

Methods of disposal:

Sanitary landfill - controlled burial with daily earth cover; most preferred for municipalities
Incineration - burning at high temperature (870°C); reduces volume by 90%; best for hospital waste
Composting - biological decomposition; produces manure; ideal for organic waste
Recycling
Open dumping - most common but least sanitary; not recommended

LIKELY EXAM QUESTION PATTERNS (University MBBS)

Marks	Likely Questions
10 marks	Purification of water on a large scale / Write an essay on air pollution / Water sources, treatment and testing
5 marks	Chlorination of water / Schmutzdecke / Break-point chlorination / Slow sand vs. rapid sand filter / Health effects of air pollution / Sanitary methods of excreta disposal
2-3 marks	OT test / Coliform indicator / Noise pollution / Biomedical waste categories / Acid rain / Define air pollution / Superchlorination
MCQ/IBQ	Vital layer in slow sand filter, breakpoint chlorination, WHO standards, London smog year (1952), residual chlorine levels

Key facts to memorize:

Slow sand filter: vital layer = Schmutzdecke; removes 98-99% bacteria; cleaning = scraping
Break-point chlorination: point where all chloramines destroyed and free residual Cl₂ appears
Bore-hole latrine: minimum 15 m from water source
Water storage: bacterial count drops 90% in first 5-7 days; optimum 10-14 days
London smog disaster: 1952
Coliform organisms as faecal pollution indicators (not the pathogens directly)
NIHL: occupational noise > 85-90 dB causes hearing damage

- Park's Textbook of Preventive and Social Medicine, Chapter on Environment and Health

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