Environmental Health — MCQs

Environmental Health Indian Medical PG Practice Questions and MCQs

Question 41: Which of the following is NOT true for Rapid sand filters?

A. No preliminary storage of raw water is required.
B. Operation requires highly skilled persons.
C. Frequent washing is not required. (Correct Answer)
D. Can be gravity type or pressure type.

Explanation: **Explanation:** The core principle of **Rapid Sand Filters (RSF)**, also known as Mechanical Filters, is their high rate of filtration (5–15 m³/m²/hr), which is about 40–50 times faster than Slow Sand Filters. Because of this high velocity, the filter bed becomes clogged with impurities much faster. **1. Why Option C is the correct answer (The False Statement):** In RSF, the sand bed gets "choked" quickly due to the rapid accumulation of suspended matter. Therefore, **frequent washing is mandatory**—usually every 24 to 48 hours. This is done via **backwashing** (reversing the flow of water and compressed air), which cleans the sand grains. Stating that frequent washing is *not* required is incorrect. **2. Analysis of Incorrect Options:** * **Option A:** Unlike Slow Sand Filters, which require long periods of storage for sedimentation, RSF uses **chemical coagulation and flocculation** (using Alum) as pretreatment. This allows the process to bypass lengthy storage. * **Option B:** RSF involves complex mechanical parts, chemical dosing, and the backwashing process, all of which necessitate **highly skilled personnel** for operation and maintenance. * **Option D:** RSF can be designed as **Gravity type** (e.g., Paterson’s Filter) or **Pressure type** (e.g., Candy’s Filter), depending on whether the water flows by its own weight or is forced through under pressure. **High-Yield Facts for NEET-PG:** * **Vital Layer:** RSF does *not* have a "Schmutzdecke" (Vital Layer) initially; it forms during the process but is less critical than in Slow Sand Filters. * **Efficiency:** RSF is highly effective at removing **turbidity** but less effective than Slow Sand Filters at removing bacteria (98-99% vs 99.9%). * **Pre-treatment:** Coagulation (Alum) is the most crucial step before filtration in RSF. * **Space:** RSF occupies very little land area compared to Slow Sand Filters.

Question 42: Strength of sewage is expressed in terms of all EXCEPT:

A. Biological Oxygen Demand
B. Chemical Oxygen Demand
C. Suspended solids
D. Coliform count (Correct Answer)

Explanation: The strength of sewage refers to the amount of organic and inorganic matter present in it, which determines its potential to pollute water bodies. **Why Coliform Count is the Correct Answer:** Coliform count (e.g., E. coli) is a measure of **bacterial contamination** and the sanitary quality of water, not the "strength" of sewage. It indicates the presence of fecal contamination and the potential risk of waterborne pathogens. While sewage contains high levels of coliforms, this metric is primarily used to assess the safety of drinking water or the efficiency of disinfection in treated effluent, rather than the concentration of organic pollutants (strength). **Explanation of Incorrect Options:** * **Biological Oxygen Demand (BOD):** This is the most important indicator of sewage strength. It measures the amount of oxygen required by microorganisms to decompose organic matter. High BOD indicates "strong" sewage. * **Chemical Oxygen Demand (COD):** This measures the oxygen required to chemically oxidize both organic and inorganic matter. It is faster to determine than BOD and is a vital indicator of sewage strength, especially when toxic substances are present. * **Suspended Solids:** These are the physical particles (organic and inorganic) that do not dissolve. High suspended solids contribute to the turbidity and sludge-forming potential of sewage, directly reflecting its strength. **High-Yield Facts for NEET-PG:** * **BOD Values:** Pure water (< 1 mg/L), Treated sewage (< 20 mg/L), Weak sewage (150 mg/L), Strong sewage (300+ mg/L). * **BOD vs. COD:** COD is always higher than BOD because it includes chemically oxidizable matter that is not biologically degradable. * **Standard BOD Test:** Conducted at **20°C for 5 days**. * **Sullage:** Wastewater from kitchens and bathrooms that does not contain human excreta.

Question 43: Paris green is a type of:

A. Stomach poison (Correct Answer)
B. Contact poison
C. Repellent
D. Rodenticide

Explanation: **Explanation:** **Paris Green (Copper acetoarsenite)** is a highly toxic inorganic compound historically used as a pigment and insecticide. In public health and community medicine, it is classified as a **stomach poison**. 1. **Why it is a Stomach Poison:** Paris green acts through ingestion. When used in anti-larval operations, it is applied as a 2% dust over stagnant water bodies. The surface-feeding larvae of *Anopheles* mosquitoes ingest the floating particles. Once inside the digestive tract, the arsenic component acts as a potent metabolic toxin, leading to the death of the larvae. It does not penetrate the cuticle, hence it is not a contact poison. 2. **Analysis of Incorrect Options:** * **Contact Poison:** These (e.g., DDT, Malathion) kill insects upon physical contact by penetrating the exoskeleton and targeting the nervous system. Paris green is ineffective unless swallowed. * **Repellent:** These (e.g., DEET, Dimethyl phthalate) merely deter insects from biting or landing; they do not aim to kill the larvae or adults. * **Rodenticide:** While arsenic compounds are toxic to mammals, Paris green is specifically categorized under "Larvicides" in environmental sanitation for malaria control. Common rodenticides include Zinc phosphide or Warfarin. **High-Yield Facts for NEET-PG:** * **Target Organism:** Specifically used for **Anopheline larvae** (surface feeders). It is ineffective against *Culex* larvae as they are bottom feeders. * **Composition:** It is chemically **Copper acetoarsenite**. * **Application:** It is used as a **2% dust** (mixed with diluents like lime or soapstone). * **Limitation:** It does not kill mosquito eggs or pupae (as pupae do not feed).

Question 44: Greenhouse gases are called as such because they:

A. Are used in warming plant growth chambers.
B. Help in maintaining atmospheric O2 and CO2 balance.
C. Are produced by green photosynthesizing plants and are trapped in the earth's atmosphere.
D. Prevent the escape of heat waves reradiated from the earth's surface. (Correct Answer)

Explanation: ### Explanation **Concept:** The Greenhouse Effect is a natural phenomenon essential for maintaining the Earth's temperature. The term is derived from glass greenhouses used in cold climates. Just as glass allows short-wave solar radiation to enter but traps long-wave heat radiation inside, greenhouse gases (GHGs) act as a thermal blanket for the planet. **Why Option D is Correct:** The Earth absorbs short-wave UV and visible radiation from the sun and re-emits it as **long-wave infrared radiation (heat waves)**. Greenhouse gases (like $CO_2$, Methane, and Nitrous Oxide) are transparent to incoming solar radiation but opaque to outgoing long-wave radiation. They absorb and redirect this heat back toward the Earth's surface, preventing it from escaping into space. This leads to the warming of the troposphere. **Analysis of Incorrect Options:** * **Option A:** While greenhouses are used for plant growth, the gases themselves are not "used" as a fuel or tool in chambers; the name is an analogy for their physical property of trapping heat. * **Option B:** Maintaining $O_2$ and $CO_2$ balance is a function of photosynthesis and respiration, not the defining characteristic of why these gases are termed "greenhouse gases." * **Option C:** GHGs are not primarily produced by photosynthesis; in fact, photosynthesis *removes* $CO_2$. Most GHGs result from fossil fuel combustion, decomposition, and industrial processes. **High-Yield NEET-PG Pearls:** * **Major GHGs:** Carbon dioxide ($CO_2$) is the most abundant, but **Methane ($CH_4$)** has a much higher global warming potential per molecule. * **Kyoto Protocol (1997):** An international treaty aimed at reducing GHG emissions. * **Health Impact:** Global warming leads to the expansion of vector habitats (e.g., Malaria and Dengue moving to higher altitudes/latitudes) and increases the frequency of heat-related illnesses and respiratory issues due to increased ground-level ozone.

Question 45: What does the soiling index determine?

A. Contraception failure
B. Air pollution (Correct Answer)
C. Number of hookworm eggs
D. Ratio of mucus secreting glands to thickness of the wall of airways

Explanation: ### Explanation **Correct Answer: B. Air Pollution** The **Soiling Index** (also known as the Coefficient of Haze or COH) is a measurement used to determine the level of **suspended particulate matter (SPM)** in the air. It is calculated by drawing a known volume of air through a filter paper and measuring the resulting "darkness" or discoloration of the filter using a reflectometer or densitometer. A higher index indicates a greater concentration of smoke and soot, reflecting significant atmospheric pollution. **Analysis of Incorrect Options:** * **A. Contraception failure:** This is measured by the **Pearl Index**, which calculates the number of unintended pregnancies per 100 woman-years of exposure. * **C. Number of hookworm eggs:** This is typically assessed via the **Stoll’s Egg Count** or Kato-Katz technique to determine the intensity of helminthic infection. * **D. Ratio of mucus-secreting glands to airway wall thickness:** This describes the **Reid Index**, which is a pathological hallmark used to diagnose and assess the severity of **Chronic Bronchitis**. **High-Yield Clinical Pearls for NEET-PG:** * **Air Quality Index (AQI):** A composite index used to communicate how polluted the air currently is. It typically monitors five major pollutants: Ground-level ozone, Particle pollution (PM2.5/PM10), Carbon monoxide, Sulfur dioxide, and Nitrogen dioxide. * **Indicator of Air Pollution:** While the Soiling Index measures smoke/soot, **Sulfur Dioxide ($SO_2$)** is considered the best biological indicator of air pollution caused by fossil fuel combustion. * **Lichens:** These are sensitive **biological indicators**; their disappearance from an area often signals high levels of $SO_2$ pollution.

Question 46: All of the following are true about breakpoint chlorination, except –

A. Free chlorine is released in water after breakpoint chlorination.
B. Chlorine demand is the amount needed to kill bacteria, oxidize organic matter, and neutralize ammonia.
C. 1 ppm free chlorine should be present in water after breakpoint has been reached. (Correct Answer)
D. A contact period of 1 hour is necessary.

Explanation: ### Explanation **Breakpoint chlorination** is the point at which the chlorine demand of water has been fully satisfied. Beyond this point, any further addition of chlorine results in the appearance of **free residual chlorine** (HOCl and OCl-). **1. Why Option C is the Correct Answer (The False Statement):** After reaching the breakpoint, the standard requirement for drinking water is a free residual chlorine level of **0.5 mg/L (0.5 ppm)** for a contact period of **one hour**, not 1 ppm. This level is sufficient to provide a safety margin against subsequent post-treatment contamination. **2. Analysis of Other Options:** * **Option A:** This is true. Once the "breakpoint" is crossed, all ammonia and organic matter have been oxidized. Any additional chlorine added exists as "free" chlorine, which is the most potent disinfectant form. * **Option B:** This is true. **Chlorine Demand** is defined as the difference between the amount of chlorine added to the water and the amount of residual chlorine (free and combined) remaining at the end of a specific contact period. It accounts for the neutralization of impurities. * **Option C:** This is true. For effective disinfection, the chlorine must remain in contact with the water for at least **60 minutes** before the water is distributed to consumers. **High-Yield NEET-PG Pearls:** * **Horrocks’s Apparatus:** Used to estimate the chlorine demand of water (specifically for bleaching powder). * **OT Test (Orthotolidine):** Measures both free and combined chlorine but is less accurate than the **OTA (Orthotolidine-Arsenite) Test**, which distinguishes between the two. * **Chlorine Demand Formula:** Chlorine Added – Residual Chlorine = Chlorine Demand. * **Cyclical Nature:** If ammonia is present, adding chlorine initially forms chloramines (combined chlorine). The "breakpoint" is the dip in the curve where these chloramines are destroyed.

Question 47: What is the recommended method for the disposal of placenta at a Primary Health Centre (PHC)?

A. Treat with bleaching powder and burial (Correct Answer)
B. Deep burial
C. Boiling
D. Dry burning

Explanation: **Explanation:** The disposal of anatomical waste, such as the placenta, is governed by the **Bio-Medical Waste (BMW) Management Rules**. According to these guidelines, the placenta is categorized under **Human Anatomical Waste**. **Why Option A is Correct:** At the Primary Health Centre (PHC) level, especially in rural or remote areas where common biomedical waste treatment facilities (CBMWTF) are often unavailable, the standard protocol for anatomical waste is **local deep burial**. However, before burial, the waste must be pre-treated with a disinfectant like **bleaching powder (calcium hypochlorite)** to ensure the destruction of pathogens and prevent the spread of infection into the soil or groundwater. **Why Other Options are Incorrect:** * **B. Deep Burial:** While deep burial is the ultimate disposal method, it is incomplete without the chemical disinfection (bleaching powder) step required for infection control. * **C. Boiling:** Boiling is a method of sterilization/disinfection for instruments, not a recognized final disposal method for anatomical waste. * **D. Dry Burning:** Open burning of biomedical waste is strictly prohibited under BMW rules as it releases toxic dioxins and furans into the atmosphere. **High-Yield NEET-PG Pearls:** * **BMW Color Coding:** In urban settings with facilities, the placenta should be disposed of in a **Yellow Bag** for incineration or plasma pyrolysis. * **Deep Burial Standards:** The burial pit should be 2 meters deep, located away from water bodies, and covered with a layer of lime and soil. * **Chlorinated Plastics:** Never incinerate chlorinated plastics (like IV sets/tubing); they must be autoclaved/microwaved and recycled. * **Anatomical Waste:** Includes human tissues, organs, and body parts; it is always disposed of in **Yellow Bags**.

Question 48: Hard tick causes which of the following diseases?

A. Relapsing fever (Correct Answer)
B. Kyasanur Forest Disease (KFD)
C. Indian tick typhus
D. Tularemia

Explanation: **Explanation:** The question asks for the disease caused by the **Hard Tick** (*Ixodidae*). While the provided answer key indicates Relapsing fever, it is crucial to clarify a distinction often tested in NEET-PG: **Relapsing fever** is typically categorized into two types: 1. **Louse-borne:** Caused by *Borrelia recurrentis* (transmitted by body lice). 2. **Tick-borne:** Caused by various *Borrelia* species transmitted by **Soft Ticks** (*Ornithodoros*). However, in the context of standard medical entrance exams, Hard Ticks are the primary vectors for a specific set of diseases. Let’s evaluate the options: * **Kyasanur Forest Disease (KFD):** This is the classic "textbook" answer for Hard Ticks (*Haemaphysalis spinigera*). * **Indian Tick Typhus:** Caused by *Rickettsia conorii*, transmitted by Hard Ticks (*Rhipicephalus sanguineus*). * **Tularemia:** Can be transmitted by Hard Ticks (*Dermacentor*), though it has multiple modes of transmission. **Why the discrepancy?** In some older question banks, "Relapsing Fever" is used broadly, but scientifically, Hard Ticks are most famously associated with **KFD, Tick Typhus, and Viral Hemorrhagic Fevers.** **Analysis of Incorrect Options:** * **Relapsing Fever:** Primarily transmitted by **Soft Ticks** (Endemic) or **Lice** (Epidemic). If this is the marked correct answer, it may be a specific reference to rare *Borrelia* strains, but it is less common than Soft Tick transmission. * **KFD & Indian Tick Typhus:** These are definitive Hard Tick-borne diseases. **High-Yield Clinical Pearls for NEET-PG:** * **Hard Tick (Ixodidae):** Morphologically has a dorsal shield (*Scutum*). Diseases: KFD, Tick Typhus, Tularemia, Babesiosis, Lyme disease, Tick paralysis. * **Soft Tick (Argasidae):** No scutum. Diseases: **Q** fever (rarely), **E**ndemic Relapsing Fever. (Mnemonic: **S**oft **S**hell for **S**urvival/Relapsing). * **KFD Vector:** *Haemaphysalis spinigera* (Hard tick). * **Lyme Disease Vector:** *Ixodes* (Hard tick).

Question 49: Which one of the following methods is used for the estimation of the chlorine demand of water?

A. Chlorometer
B. Horrock's apparatus (Correct Answer)
C. Berkfeld filter
D. Double pot method

Explanation: ### Explanation **Correct Answer: B. Horrock’s apparatus** **Why it is correct:** Horrock’s apparatus is the standard field test used to estimate the **chlorine demand** of water. Chlorine demand is the difference between the amount of chlorine added to water and the amount of residual chlorine remaining after a specific contact period (usually 30 minutes). * **Mechanism:** It utilizes a series of white cups, a standardized bleaching powder solution, and a starch-iodide indicator. The first cup in the series that shows a distinct blue color indicates the amount of bleaching powder required to disinfect 455 liters (100 gallons) of that specific water source. **Analysis of Incorrect Options:** * **A. Chlorometer:** This is a general term for devices used to measure residual chlorine (like a colorimeter), but it is not the specific apparatus used to calculate the initial "demand" or dosage required for large-scale disinfection. * **C. Berkfeld filter:** This is a ceramic candle filter used for the **physical removal** of bacteria and suspended particles from water. It does not involve chemical estimation or chlorination. * **D. Double pot method:** This is a method of **water purification** (not estimation) used specifically during emergencies or floods to provide chlorinated water for small communities or households for about 2-3 weeks. **High-Yield Pearls for NEET-PG:** * **OT Test (Orthotolidine Test):** Used to determine both free and combined **residual chlorine** in water. * **OTA Test (Orthotolidine-Arsenite Test):** Used to differentiate between **free** and **combined** residual chlorine. * **Contact Time:** For effective chlorination, a minimum contact time of **30 to 60 minutes** is essential. * **Free Residual Chlorine:** The recommended level for drinking water is **0.5 mg/L** after 1 hour of contact. * **Bleaching Powder:** Contains approximately **33%** available chlorine.

Question 50: What are the criteria for a slaughterhouse?

A. The glass area should be 25% of the floor area. (Correct Answer)
B. Window panes should be sloped at 25 degrees.
C. Doorways should be 1 meter high.
D. None of the above.

Explanation: In Community Medicine, the hygiene and structural standards of a slaughterhouse are critical to prevent the transmission of zoonotic diseases (like Anthrax or Brucellosis) and ensure meat safety. ### **Explanation of Options** * **Option A (Correct):** Adequate lighting and ventilation are mandatory to ensure proper inspection of carcasses and maintain hygiene. According to standard public health guidelines, the **glass area (windows/skylights) should be at least 25% of the floor area** to allow sufficient natural light. * **Option B (Incorrect):** While window sills should be sloped to prevent the accumulation of dust and debris, the standard requirement is an angle of **45 degrees**, not 25 degrees. This steep slope ensures that items cannot be placed on the sills, maintaining a sterile environment. * **Option C (Incorrect):** Doorways must be large enough to allow the easy passage of carcasses and equipment. The standard requirement is a width of at least **1.5 meters**, and the height must be significantly more than 1 meter (usually enough to accommodate overhead rails) to prevent contact with the floor or walls. ### **High-Yield Facts for NEET-PG** * **Location:** Slaughterhouses should be located away from residential areas, preferably downwind. * **Floors:** Must be impervious (e.g., cement/concrete), non-slippery, and have a gradient of **1 in 60** toward a surface drain for easy cleaning. * **Water Supply:** Must be abundant and potable; "Lairage" (resting area) is essential for animals to rest for **24 hours** before slaughter. * **Antemortem Inspection:** Crucial to identify diseases like Tetanus or Febrile conditions where slaughter is contraindicated.

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Water Quality and Health

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Air Pollution and Health Effects

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Noise Pollution

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Radiation Health Effects

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Climate Change and Health

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Environmental Impact Assessment

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Disaster Management and Preparedness

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Vector Control

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Environmental Legislation

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