CM3.1-8 | Environmental Health — Practice Quiz

Correct. IS 10500 specifies a minimum residual free chlorine of 0.2 mg/L at the consumer end to ensure microbiological safety throughout the distribution network.

Chlorination is the final barrier against waterborne pathogens. The desirable limit at the tap is 0.2 mg/L and the maximum permissible limit is 1.0 mg/L. At the treatment plant the dosing is adjusted so that this residual persists after contact time (CT value).

Incorrect. The IS 10500 standard mandates at least 0.2 mg/L residual free chlorine at the consumer's tap — enough to kill pathogens without imparting objectionable taste.

Correct. IS 10500:2012 sets the maximum permissible limit for arsenic at 0.05 mg/L when no alternative source is available (desirable limit: 0.01 mg/L as per WHO 2011 guideline).

Arsenic contamination in groundwater is a major problem in the Indo-Gangetic plain (West Bengal, Bihar, Assam). Chronic exposure causes arsenicosis — keratosis, Mees' lines, Bowen's disease, and internal cancers (skin, bladder, lung). The BIS desirable limit is 0.01 mg/L; permissible is 0.05 mg/L.

Incorrect. IS 10500:2012 sets the maximum permissible limit for arsenic at 0.05 mg/L. The WHO guideline value is 0.01 mg/L but India's permissible limit when no other source is available is 0.05 mg/L.

Correct. Dental fluorosis becomes apparent in endemic communities when fluoride exceeds 1.5 mg/L — the IS 10500 maximum permissible limit. Skeletal fluorosis and crippling fluorosis occur at higher concentrations (>3 mg/L and >10 mg/L respectively).

Fluoride is a double-edged ion: at 0.5–1.0 mg/L it prevents dental caries; above 1.5 mg/L it causes dental fluorosis; above 3 mg/L it causes skeletal fluorosis; above 10 mg/L it causes crippling fluorosis. High-fluoride groundwater is endemic in Rajasthan, Andhra Pradesh, Tamil Nadu, and Gujarat.

Incorrect. Dental fluorosis appears when fluoride exceeds 1.5 mg/L, which is the IS 10500 permissible upper limit. The desirable range for caries prevention is 0.5–0.8 mg/L.

Correct. India's NAAQS 2009 sets the 24-hour PM2.5 standard at 60 µg/m³ (annual mean: 40 µg/m³). For comparison, the WHO 2021 guideline value is 15 µg/m³ for 24-hour average.

PM2.5 (particles ≤2.5 µm aerodynamic diameter) penetrate to the alveoli and are the most health-damaging fraction. India's NAAQS 2009: PM2.5 annual mean = 40 µg/m³, 24-hour = 60 µg/m³; PM10 annual = 60 µg/m³, 24-hour = 100 µg/m³. The WHO 2021 guidelines are far more stringent (5 µg/m³ annual, 15 µg/m³ 24-hour).

Incorrect. India's NAAQS 2009 specifies a 24-hour PM2.5 standard of 60 µg/m³. This is much higher than the WHO guideline (15 µg/m³) reflecting feasibility constraints in a rapidly industrialising nation.

Correct. BMW Rules 2016 classifies human anatomical waste (body parts, organs, tissues) under Category 1, which must be incinerated or deep-buried in a common bio-medical waste treatment facility (CBWTF).

BMW Rules 2016 replaced the 1998 Rules. There are now 4 colour-coded bags: Yellow (Categories 1,2,3,6 — incinerated/deep-buried), Red (Category 3 — autoclaved), Blue (Category 4 sharps — needle destroyers/autoclaved), White translucent (Category 5 — returned to manufacturer).

Incorrect. Category 1 covers human anatomical waste. Category 2 is animal waste; Category 3 is microbiology and biotechnology waste; Category 4 is sharps waste; Category 5 is discarded medicines.

Correct. Cholera is a classic waterborne disease transmitted via the faecal-oral route. Floodwater contaminating the dug well introduced V. cholerae O1 from sewage, causing the point-source outbreak.

Incorrect. Cholera spreads via the faecal-oral route — ingestion of water (or food) contaminated with V. cholerae. Floodwater mixing with sewage created the contaminated well.

Correct. For a contaminated open well during an outbreak, hyperchlorination (adding sufficient bleaching powder to achieve ≥0.5 mg/L residual free chlorine after 1 hour contact) followed by sealing is the standard response.

Incorrect. Boiling is a household measure but does not decontaminate the well itself. The well must be hyperchlorinated (bleaching powder dose: 50–100 mg/L achievable concentration) and sealed until bacteriological safety is confirmed.

Correct. The standard minimum air space recommended is 14.2 cubic metres (approximately 500 cubic feet) per person to prevent overcrowding and reduce airborne disease transmission.

Housing standards include: minimum air space 14.2 m³/person, minimum floor area 9.3 m² (100 sq ft)/person for a sleeping room, window/floor area ratio ≥1:10, natural lighting ≥0.2 lux at floor level. Overcrowding index = persons per room >2.

Incorrect. The recommended minimum air space is 14.2 cubic metres (500 cubic feet) per person. Overcrowding below this threshold accelerates droplet-spread diseases like TB, measles, and meningococcal disease.

Correct. Aedes aegypti is the primary vector of dengue, chikungunya, and Zika virus in India. It breeds in clean, stagnant water in artificial containers (tyres, coolers, flower vases) and is a day-biting mosquito.

Vector-disease associations in India: Anopheles stephensi/culicifacies → malaria; Aedes aegypti → dengue/chikungunya/Zika; Culex quinquefasciatus → lymphatic filariasis (Wuchereria bancrofti) and Japanese encephalitis; Phlebotomus argentipes → Kala-azar (visceral leishmaniasis); Aedes albopictus is a secondary dengue vector in rural areas.

Incorrect. Aedes aegypti is the primary dengue vector. It is identifiable by white lyre-shaped markings on the thorax and breeds in clean peridomestic water containers.

Correct. Both the assertion and reason are true, and the reason correctly explains the mechanism. Organophosphates (malathion, dichlorvos, temephos) irreversibly inhibit acetylcholinesterase, causing accumulation of acetylcholine, continuous neuronal firing, and eventual insect paralysis and death. The same mechanism causes human toxicity — treat with atropine + pralidoxime.

Insecticide classes and mechanisms: Organophosphates (malathion, dichlorvos) → AChE inhibition. Pyrethroids (permethrin, deltamethrin) → Na+ channel prolonged opening. Organochlorines (DDT) → Na+ channel disruption. Carbamates (propoxur) → reversible AChE inhibition. Neonicotinoids → nAChR agonism. OP toxicity antidote: atropine (for muscarinic excess) + pralidoxime (reactivates AChE if given early).

Incorrect. Both statements are true AND the reason correctly explains the assertion. Organophosphates work by inhibiting acetylcholinesterase, which is directly responsible for their insecticidal (and toxic) effect.

Correct. IS 10500:2012 sets the maximum permissible nitrate limit at 45 mg/L (desirable: ≤45 mg/L as NO3−). High nitrate causes methaemoglobinaemia in infants ('blue baby syndrome') because infants have lower gastric acidity allowing nitrate reduction to nitrite and their foetal haemoglobin is more susceptible to oxidation.

Nitrate contamination of groundwater occurs primarily from agricultural fertilisers and sewage. The WHO guideline value is 50 mg/L as NO3−. India's IS 10500 desirable limit and maximum permissible limit are both set at 45 mg/L — meaning no relaxation is recommended. Infants under 6 months and pregnant women are the most vulnerable populations.

Incorrect. The IS 10500:2012 maximum permissible nitrate limit is 45 mg/L as NO3−. Nitrate above this level is associated with methaemoglobinaemia in bottle-fed infants under 6 months.