CM3.1-8 | Environmental Health — Graded Quiz

Correct. A sanitary risk score of 0–2 indicates low risk; 3–5 medium risk; 6–8 high risk; 9–12 very high risk.

The WHO sanitary risk scoring system uses yes/no questions about defects (cracked apron, missing cover, latrine within 10 m, etc.). Each 'yes' scores 1 point. The score guides the intensity of corrective action.

Incorrect. Score 0–2 = low risk; 3–5 = medium; 6–8 = high; 9–12 = very high. Low-risk sources still require bacteriological testing every 6 months.

Correct. The incubation period for cholera is a few hours to 5 days, typically 1–2 days. This short incubation means explosive point-source outbreaks appear rapidly after a contamination event.

Waterborne disease incubation periods: cholera 6h–5d; typhoid 10–14d; hepatitis A 14–28d; hepatitis E 15–64d. A short incubation and explosive onset suggest cholera or a toxic cause; a longer incubation suggests typhoid or viral hepatitis.

Incorrect. Cholera has a very short incubation period — a few hours to 5 days. This distinguishes it from typhoid (10–14 days) and hepatitis E (15–64 days) and explains explosive point-source outbreaks.

Correct. Noise Pollution Rules 2000 set night time limits for residential areas at 45 dB(A). Day time limit for residential is 55 dB(A).

Residential zone noise limits (Noise Pollution Rules 2000): Day (6AM–10PM) = 55 dB(A); Night (10PM–6AM) = 45 dB(A). Safe occupational limit: 90 dB(A) for 8 hours. Noise-induced hearing loss (NIHL) is the most common preventable occupational disease.

Incorrect. The night-time limit in a residential area is 45 dB(A). Day time = 55 dB(A); Commercial area: day = 65 dB(A), night = 55 dB(A); Industrial: day = 75 dB(A), night = 70 dB(A).

Correct. The pit bottom must remain at least 1.5 metres (5 feet) above the highest seasonal water table to prevent faecal contamination of groundwater.

Sanitary latrine siting rules: ≥15 m from any water source; pit bottom ≥1.5 m above highest water table; slab fully covers the pit; superstructure provides privacy. The two-pit alternating (Sulabh) design allows safe composting when one pit is resting.

Incorrect. The pit bottom must be at least 1.5 m above the highest water table. Additionally, latrines should be located at least 15 m from any drinking water source.

Correct. Anopheles breeds in clean, clear, still or slow-flowing water bodies — paddy fields, irrigation channels, ponds with aquatic vegetation. This is distinct from Aedes (artificial containers) and Culex (organically polluted water).

Vector breeding habitats determine control strategy: Anopheles → drain/fill paddy field margins, larvicide (temephos), biological control (Gambusia fish); Aedes → empty/cover containers weekly, source reduction; Culex → drain/clean drains, larvicide in drains.

Incorrect. Anopheles prefers clean, slow-flowing or stagnant natural water. Aedes breeds in clean artificial containers; Culex in polluted water. Knowing the breeding habitat guides source-reduction strategies.

Correct. Alum (aluminium sulphate) acts as a coagulant: it dissociates in water to release Al3+ ions, which neutralise the negative charge on colloidal particles, allowing them to flocculate (form flocs) that settle by sedimentation in the clarifier.

Water treatment sequence: Screening → Sedimentation → Coagulation (alum, dose 5–30 mg/L) → Flocculation → Sedimentation → Rapid sand filtration → Slow sand filtration (optional) → Disinfection (chlorination). Coagulation removes 80–90% of turbidity and colloidal matter, which also reduces chlorine demand.

Incorrect. Alum is a coagulant that neutralises the charge on colloidal particles, causing them to aggregate into flocs. Disinfection is achieved later by chlorination; hardness removal uses lime-soda process.

Correct. Anopheles larvae lack a siphon. They have a spiracular plate on the dorsal aspect of the 8th abdominal segment and must float parallel (horizontally) to the water surface to breathe. Culex and Aedes larvae have a siphon and hang at an angle.

Larval ID: Anopheles — no siphon, lies parallel to surface, palmate hairs visible. Culex — long curved siphon, hangs at angle. Aedes — short stout siphon. Adult ID: Anopheles — rests at 45°, has spotted wings, palps equal to proboscis length in both sexes. Culex — rests parallel, abdomen rounded. Aedes — white lyre-shaped thorax markings.

Incorrect. Anopheles larvae are unique in having no siphon. They float horizontally at the water surface. This horizontal resting posture and absence of siphon are the key identifying features.

Correct. In Indian cities, 40–55% of MSW by weight is organic/biodegradable matter (food waste, vegetable peels) compared to 10–15% in high-income countries. This high organic fraction makes composting and biogas extraction particularly suitable technologies.

Indian MSW composition (approximate): organic/biodegradable 40–55%, inert material (dirt, dust, ash) 30–40%, paper 4–7%, plastic 4–5%, metal 0.5–1%, glass 0.5–1%. The high biodegradable fraction justifies composting and anaerobic digestion; the high inert fraction is because many households burn waste or mix ash with garbage.

Incorrect. India's MSW is dominated by organic/biodegradable material (40–55%), unlike high-income country waste which has a higher paper and plastic fraction. This high biodegradable fraction supports decentralised composting as a primary strategy.

Correct. DDT was curtailed primarily because of (1) resistance in Anopheles culicifacies in many Indian states, and (2) its extreme persistence in the environment (t½ = 2–15 years), bioaccumulation in fat, and biomagnification through the food chain — threatening wildlife and human health.

DDT characteristics: organochlorine, very lipophilic, t½ = 2–15 years in soil, bioaccumulates in fat, biomagnifies through the food chain (raptors at the top most affected). Resistance in Anopheles species reported in many Indian states. Still permitted under the Stockholm Convention for indoor residual spraying (IRS) for malaria control where alternatives are unavailable and resistance is not established.

Incorrect. DDT was discontinued mainly due to vector resistance and its persistent environmental contamination (very long half-life, bioaccumulation, biomagnification). It was not discontinued because it was acutely highly toxic — at operational doses it is relatively safe for humans.

Correct. Overcrowded, poorly ventilated housing directly facilitates droplet- and airborne-spread diseases, most importantly pulmonary TB (droplet nuclei remain suspended for hours) and measles (airborne spread). Overcrowding is the primary social determinant of TB incidence.

Diseases directly associated with poor housing: Overcrowding → TB, measles, meningococcal meningitis, influenza, diphtheria. Damp → rheumatic fever, respiratory infections, mould-related asthma. Inadequate lighting → rickets (inadequate sunlight), eye strain. Poor sanitation → diarrhoeal diseases. Vector access → malaria, dengue.

Incorrect. Droplet-spread diseases (TB, measles, meningococcal disease) are directly facilitated by overcrowded, poorly ventilated housing. Cholera/typhoid are waterborne; malaria/filariasis are vector-borne; kala-azar is transmitted by sandflies; plague by fleas.