Environmental Health — MCQs

Environmental Health Indian Medical PG Practice Questions and MCQs

Question 371: What does Biological Oxygen Demand (BOD) indicate?

A. Amount of organic matter in water (Correct Answer)
B. Amount of bacterial content in water
C. Presence of anaerobic bacteria
D. Amount of chemical pollutants in water

Explanation: **Explanation:** **Biological Oxygen Demand (BOD)** is defined as the amount of oxygen consumed by aerobic microorganisms to decompose the organic matter present in a water sample over a specific period (usually 5 days) at a specific temperature (20°C). 1. **Why Option A is correct:** BOD is a direct measure of **organic pollution**. When water contains high amounts of organic waste (sewage), bacteria consume large amounts of dissolved oxygen to break it down. Therefore, a high BOD value indicates a high concentration of organic matter and, consequently, a high level of water pollution. 2. **Why other options are incorrect:** * **Option B:** While bacteria are involved in the process, BOD measures the *oxygen consumed*, not the actual bacterial count. Bacterial content is measured by tests like the Multiple Tube Method (MPN) or Membrane Filtration. * **Option C:** BOD specifically measures **aerobic** decomposition. Anaerobic bacteria function in the absence of oxygen and are not measured by BOD. * **Option D:** Chemical pollutants (including inorganic matter) are measured by **Chemical Oxygen Demand (COD)**, which uses strong chemical oxidants rather than biological organisms. **High-Yield Clinical Pearls for NEET-PG:** * **BOD Values:** * **Clean water:** < 1 mg/L * **Moderately polluted:** 2–8 mg/L * **Municipal sewage:** 100–400 mg/L * **Indicator of Pollution:** BOD is the most important indicator used by environmental engineers to determine the efficiency of sewage treatment plants. * **COD vs. BOD:** COD is always higher than BOD because it measures both biodegradable and non-biodegradable organic matter.

Question 372: Diethyltoluamide is an effective agent against which of the following?

A. Larvicidal
B. Agent against pupae of Anopheles
C. Repellent (Correct Answer)
D. Space spray

Explanation: **Explanation:** **Diethyltoluamide (DEET)** is the most widely used chemical **insect repellent** worldwide. It works by interfering with the chemoreceptors on the antennae of biting insects (such as mosquitoes, ticks, and fleas), effectively "masking" the host's scent or acting as an irritant that prevents the insect from landing or biting. * **Why Option C is Correct:** DEET is the gold standard for personal protection against vector-borne diseases. It is applied topically to skin or clothing. It does not kill the insect but prevents contact between the vector and the human host. * **Why Options A & B are Incorrect:** Larvicides (e.g., Temephos, Abate) and agents targeting pupae (e.g., Paris Green or mineral oils) are used for **source reduction** in water bodies. DEET has no efficacy in killing the immature stages of the mosquito life cycle. * **Why Option D is Incorrect:** Space sprays (e.g., Pyrethrum extract) are used for "knock-down" effects in indoor or outdoor environments to kill adult mosquitoes instantly. DEET is a personal protective measure, not an environmental spray. **High-Yield Facts for NEET-PG:** * **Duration of Action:** A 30% concentration of DEET typically provides protection for about 6 hours. * **Safety:** It is generally safe for adults and children over 2 months of age, but high concentrations should be avoided in infants due to the risk of neurotoxicity (encephalopathy). * **Other Repellents:** Dimethyl phthalate (DMP), Dibutyl phthalate, and Picaridin are other examples. * **Chemoprophylaxis vs. Repellent:** While DEET prevents the bite (mechanical), drugs like Doxycycline or Mefloquine provide pharmacological prophylaxis against the pathogen itself.

Question 373: The total volume of sewage flowing in a system over a 24-hour period is referred to as:

A. Sewage rate
B. Dry weather flow (Correct Answer)
C. RCA index
D. Sludge

Explanation: ### Explanation **Correct Answer: B. Dry weather flow** In environmental engineering and public health, **Dry Weather Flow (DWF)** is defined as the total quantity of sewage flowing through a sewerage system in a 24-hour period during dry weather. It primarily consists of domestic sewage and industrial waste, excluding any contribution from rainwater or surface runoff. This measurement is critical for designing sewage treatment plants (STPs) and determining the capacity of sewer pipes to ensure they can handle the daily load without overflow. **Analysis of Incorrect Options:** * **A. Sewage rate:** This is a generic term and not a standardized technical definition in environmental health. Flow is typically measured as a "rate" (e.g., liters per second), but the 24-hour cumulative volume is specifically DWF. * **C. RCA index:** The Research cum Action (RCA) latrine is a specific type of sanitary latrine designed for rural India. The "RCA index" is not a standard term for sewage volume; rather, RCA refers to the design standards for rural sanitation. * **D. Sludge:** Sludge is the solid matter that settles at the bottom of a sedimentation tank during sewage treatment. It is a byproduct of the process, not a measure of the liquid flow volume. **High-Yield Clinical Pearls for NEET-PG:** * **Strength of Sewage:** Determined by **Biochemical Oxygen Demand (BOD)**. Normal BOD of domestic sewage is approx. **300 mg/L**. * **Sewerage vs. Sewage:** *Sewage* is the waste water; *Sewerage* is the infrastructure (pipes/pumps) that carries it. * **Self-Purification:** Rivers purify themselves through dilution, sedimentation, and oxidation. * **Eutrophication:** Excessive nutrients (Nitrates/Phosphates) in water leading to algal blooms and oxygen depletion.

Question 374: Guineaworm disease was a common public health problem which was attributed to the use of which type of water source?

A. Dug well
B. Sanitary well
C. Arsenic contaminated water source
D. Step well (Correct Answer)

Explanation: **Explanation:** **1. Why Step Wells are the Correct Answer:** Guineaworm disease (Dracunculiasis), caused by the nematode *Dracunculus medinensis*, is a water-borne parasitic infection. The transmission cycle depends on humans coming into direct physical contact with stagnant water sources. **Step wells (Baolis)** are the primary culprit because they require individuals to step into the water to collect it. When an infected person with a mature blister enters the water, the female worm releases thousands of larvae. these larvae are ingested by **Cyclops** (the intermediate host). When another person drinks this unfiltered water containing infected Cyclops, the cycle continues. **2. Analysis of Incorrect Options:** * **Dug Well:** While these are open wells, they typically involve drawing water with a bucket and rope. Unless people physically enter the water, the risk is significantly lower than step wells. * **Sanitary Well:** These are specifically designed to prevent contamination (covered top, hand pump, and parapet walls), making them the solution to, rather than the cause of, the disease. * **Arsenic Contaminated Water:** This leads to chronic arsenicosis (e.g., Blackfoot disease, hyperkeratosis), which is a chemical toxicity, not a parasitic infection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Host:** *Cyclops* (also known as water flea). * **Definitive Host:** Humans. * **Eradication Status:** India was declared **Guineaworm-free** by the WHO in **February 2000**. The last case in India was reported in July 1996 (Jodhpur, Rajasthan). * **Prevention:** The simplest method to prevent transmission is filtering water through a fine mesh cloth (to remove Cyclops) or converting step wells into sanitary wells. * **Treatment of choice for water:** Chemical treatment of water bodies using **Abate (Temephos)** to kill Cyclops.

Question 375: Mites are known to transmit which of the following diseases?

A. Scabies (Correct Answer)
B. Relapsing fever
C. Kyasanur Forest Disease (KFD)
D. Human babesiosis

Explanation: **Explanation:** **Correct Option: A. Scabies** Scabies is a contagious skin infestation caused by the itch mite, ***Sarcoptes scabiei* var. *hominis***. The female mite burrows into the stratum corneum of the skin to deposit eggs, leading to a delayed type IV hypersensitivity reaction. This results in the characteristic intense nocturnal pruritus and polymorphic lesions (vesicles, pustules, and burrows). **Analysis of Incorrect Options:** * **B. Relapsing Fever:** Louse-borne relapsing fever is transmitted by the **Body Louse** (*Pediculus humanus corporis*), while tick-borne relapsing fever is transmitted by **Soft Ticks** (*Ornithodoros*). * **C. Kyasanur Forest Disease (KFD):** This viral hemorrhagic fever is transmitted to humans via the bite of infected **Hard Ticks** (*Haemaphysalis spinigera*). * **D. Human Babesiosis:** This malaria-like parasitic disease is transmitted by the bite of **Hard Ticks** (specifically *Ixodes scapularis*). **High-Yield Clinical Pearls for NEET-PG:** * **Mite-borne diseases:** Apart from Scabies, mites are vectors for **Scrub Typhus** (transmitted by the *Leptotrombidium* chigger mite) and **Rickettsialpox** (*Liponyssoid sanguineus*). * **Scabies Treatment:** The drug of choice is **Permethrin 5% cream** (applied neck down overnight). Oral **Ivermectin** (200 µg/kg) is an alternative, especially for crusted (Norwegian) scabies. * **Vector Distinction:** Always distinguish between **Mites** (Scabies, Scrub Typhus) and **Ticks** (KFD, Babesiosis, Indian Tick Typhus) as they are frequently confused in exams.

Question 376: According to the WHO, what is the minimum bacteriological standard for drinking water?

A. All samples should not contain coliform organisms. (Correct Answer)
B. Three consecutive samples of water should not contain any coliforms.
C. Three coliforms per 100 ml of water.
D. One coliform per 100 ml of water.

Explanation: ### Explanation **Underlying Medical Concept** The WHO guidelines for drinking water quality are based on the principle that water intended for human consumption must be free from any pathogenic microorganisms. The primary indicator used globally to assess fecal contamination is the **Coliform group** (specifically *E. coli* or thermotolerant coliforms). According to WHO standards, for treated water entering the distribution system, **coliform organisms should be absent (0 per 100 ml)** in any sample. This "zero tolerance" policy ensures the prevention of waterborne diseases like Cholera, Typhoid, and Hepatitis A. **Analysis of Options** * **Option A (Correct):** This aligns with the WHO "Gold Standard." Ideally, all samples must show a count of zero coliforms per 100 ml to be considered safe. * **Option B (Incorrect):** Safety is not determined by a "streak" of three samples; every individual sample must meet the criteria. A single positive sample indicates a breach in the treatment or distribution system. * **Option C & D (Incorrect):** While older standards or specific guidelines for *untreated/piped water supplies* (in large populations) allowed for very occasional, minor contamination (e.g., <3 per 100ml in 5% of samples), the **minimum bacteriological standard** for safe drinking water remains **zero**. **High-Yield Facts for NEET-PG** * **Indicator Organism:** *E. coli* is the best indicator of recent fecal contamination because it is found in large numbers in human/animal feces and cannot multiply in pure water. * **Virological Standard:** Drinking water must be free from any viruses (0 per 100 ml). * **Chlorination:** The most common method of disinfection. For effective disinfection, the **Free Residual Chlorine** should be **≥ 0.5 mg/L** after a contact time of 30 minutes. * **OT Test (Orthotolidine Test):** Used to detect both free and combined chlorine; however, the **OTA (Orthotolidine-Arsenite) Test** is preferred as it distinguishes between the two.

Question 377: Autoclaving is not useful for disposal of which of the following items?

A. Surgical dressings
B. Metallic instruments
C. Petri dishes
D. Liquid paraffin (Correct Answer)

Explanation: **Explanation:** The core concept behind autoclaving is **moist heat sterilization**, which utilizes saturated steam under pressure. For autoclaving to be effective, the steam must come into direct contact with all surfaces of the material being sterilized. **Why Liquid Paraffin is the Correct Answer:** Liquid paraffin is an anhydrous (oily) substance. Oils, fats, and powders are **impermeable to steam**. Because steam cannot penetrate these substances, the latent heat of vaporization cannot be released internally to kill microorganisms. Therefore, liquid paraffin and other oily substances must be sterilized using **Dry Heat (Hot Air Oven)**, which relies on conduction rather than steam penetration. **Analysis of Incorrect Options:** * **A. Surgical Dressings:** These are porous materials. Steam easily penetrates the fibers of gauze and cotton, making autoclaving the gold standard for their sterilization. * **B. Metallic Instruments:** Stainless steel instruments are heat-stable and allow steam to condense on their surfaces, effectively destroying spores and vegetative cells. * **C. Petri Dishes:** If made of heat-resistant glass or specific plastics, these are routinely autoclaved in laboratory settings to ensure sterility before or after use. **High-Yield NEET-PG Pearls:** * **Standard Autoclave Conditions:** 121°C at 15 psi for 15–20 minutes. * **Sterilization Indicator:** *Geobacillus stearothermophilus* (formerly *Bacillus stearothermophilus*) spores are used as the biological indicator for autoclaving. * **Dry Heat (Hot Air Oven):** Used for "Glass, Oil, and Powder" (GOP). Standard cycle: 160°C for 2 hours. * **Biomedical Waste (BMW) Link:** Autoclaving is the preferred method for treating **Yellow (h) category** waste (microbiology waste) and **Red category** waste (contaminated plastics) before final disposal.

Question 378: Which of the following is NOT true about Minamata disease?

A. It is caused by methyl mercury toxicity.
B. It first occurred in Japan.
C. It is found in babies born to mothers without symptoms of mercury poisoning. (Correct Answer)
D. Affected babies are characterized by microcephaly, cerebral palsy, and severe mental retardation.

Explanation: **Explanation** Minamata disease is a classic example of environmental toxicology caused by the consumption of fish contaminated with **methyl mercury** (organic mercury). **Why Option C is the correct answer (The "Not True" statement):** In cases of congenital Minamata disease, the mother **does** typically exhibit symptoms of mercury poisoning, although they may be milder than those seen in the infant. Methyl mercury is highly lipophilic and crosses the placental barrier easily. It acts as a potent neurotoxin to the developing fetus. The concept that the mother must be asymptomatic is incorrect; both mother and child are affected, but the fetal brain is significantly more vulnerable to permanent damage. **Analysis of other options:** * **Option A:** Methyl mercury is the specific organic form of mercury responsible for the outbreak. It bioaccumulates in the food chain (biomagnification), reaching high concentrations in predatory fish. * **Option B:** The disease was first identified in 1956 in **Minamata City, Japan**, caused by the release of industrial wastewater from a chemical factory. * **Option C:** This is the false statement. * **Option D:** Congenital Minamata disease presents with severe neurological deficits including **microcephaly**, ataxia, **cerebral palsy-like symptoms**, and profound **mental retardation** due to the disruption of neuronal migration in the fetal brain. **High-Yield Clinical Pearls for NEET-PG:** * **Target Organ:** The Central Nervous System (CNS) is the primary target. * **Hunter-Russell Syndrome:** The clinical triad in adults includes paresthesia, constriction of visual fields (tunnel vision), and ataxia. * **Pink Disease (Acrodynia):** Associated with exposure to inorganic mercury in children (presents with pinkish discoloration of hands/feet). * **Antidote:** Chelating agents like Dimercaprol (BAL) or Penicillamine are used for inorganic mercury, but they are less effective for methyl mercury.

Question 379: Which of the following mosquitoes is involved in the spread of Japanese encephalitis?

A. Aedes
B. Anopheles
C. Culex (Correct Answer)
D. Mansonoides

Explanation: **Explanation:** **Japanese Encephalitis (JE)** is a viral zoonosis caused by a Group B Arbovirus (Flavivirus). The correct answer is **Culex** because the primary vectors for JE are mosquitoes of the *Culex vishnui* group, specifically ***Culex tritaeniorhynchus***. These mosquitoes are "exophilic" (outdoor resters) and "exophagic" (outdoor biters), typically breeding in irrigated rice fields and shallow ditches. **Why other options are incorrect:** * **Aedes:** Primarily responsible for transmitting Dengue, Chikungunya, Zika, and Yellow Fever. They are "day-biters" and breed in artificial containers. * **Anopheles:** The principal vector for Malaria. They typically breed in clean, stagnant water (like ponds or overhead tanks). * **Mansonoides:** The primary vector for Brugian (Malayan) Filariasis. They are unique because their larvae attach to the roots of aquatic plants like *Pistia*. **High-Yield NEET-PG Pearls:** 1. **Reservoir/Host:** The **Pig** is the "amplifier host" (the virus multiplies rapidly in pigs without making them sick). **Ardeid birds** (herons, egrets) are the "natural reservoir." 2. **Dead-end Host:** Humans are dead-end hosts because the viremia is insufficient to infect a biting mosquito. 3. **Seasonality:** In India, JE shows a distinct seasonal pattern, usually peaking during the monsoon and post-monsoon periods. 4. **Vaccination:** The most commonly used vaccine in the National Immunization Schedule is the live attenuated **SA-14-14-2** strain (given at 9 months and 16–24 months).

Question 380: Which form of chlorine disinfection is most effective?

A. Hypochlorous acid (Correct Answer)
B. Hypochlorous ion
C. Hypochlorite ion
D. None of the above

Explanation: **Explanation:** The germicidal efficacy of chlorine in water disinfection depends on the chemical form it takes when added to water. When chlorine gas or hypochlorite is added to water, it undergoes hydrolysis to form **Hypochlorous Acid (HOCl)** and **Hypochlorite Ion (OCl⁻)**. **1. Why Hypochlorous Acid (HOCl) is the Correct Answer:** Hypochlorous acid is the most potent germicidal form of chlorine. It is electrically neutral and has a low molecular weight, allowing it to easily penetrate the negatively charged cell walls of microorganisms. Once inside, it destroys vital enzymes and proteins. It is estimated to be **70 to 80 times more effective** at killing bacteria than the hypochlorite ion. **2. Why the Incorrect Options are Wrong:** * **Hypochlorite Ion (OCl⁻):** While it possesses disinfecting properties, it carries a negative electrical charge. Since bacterial cell surfaces are also negatively charged, the ion is electrostatically repelled, making it much slower and less efficient at penetrating the cell. * **Hypochlorous Ion:** This is a chemically incorrect term in the context of water disinfection; the active species are the acid (HOCl) and the ion (OCl⁻). **High-Yield NEET-PG Clinical Pearls:** * **pH Dependency:** The dissociation of HOCl into OCl⁻ is pH-dependent. At a **pH of 7**, about 75% is HOCl. As pH increases (becomes more alkaline), more HOCl dissociates into the less effective OCl⁻. Therefore, disinfection is most efficient at a lower pH. * **Free Residual Chlorine:** This refers to the sum of HOCl and OCl⁻. For effective disinfection, a contact time of at least **30 to 60 minutes** is required. * **Chlorine Demand:** This is the amount of chlorine used up in reacting with organic matter and impurities before a free residual is formed.

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