Environmental Health — MCQs

Environmental Health Indian Medical PG Practice Questions and MCQs

Question 391: In the chlorination of water, what is the primary disinfecting agent?

A. Hydrogen ions
B. Hydrochloric acid
C. Hypochlorous acid (Correct Answer)
D. Chloride ions

Explanation: ### Explanation **1. Why Hypochlorous Acid (HOCl) is the Correct Answer:** When chlorine is added to water, it reacts to form two main compounds: **Hypochlorous acid (HOCl)** and Hypochlorite ions (OCl⁻). Among these, **Hypochlorous acid (HOCl)** is the primary disinfecting agent. It is a neutral molecule that can easily penetrate the negatively charged cell walls of bacteria and microorganisms, destroying their vital enzymes and proteins. It is approximately **70–80 times more effective** as a germicide than the hypochlorite ion. **2. Analysis of Incorrect Options:** * **Hydrogen ions (H⁺):** These determine the pH of the water but do not possess antimicrobial properties. However, a lower pH (acidic) is preferred because it shifts the equilibrium to favor the formation of HOCl over OCl⁻. * **Hydrochloric acid (HCl):** While formed during the reaction of chlorine with water, HCl dissociates into H⁺ and Cl⁻ ions and does not contribute to the disinfection process. * **Chloride ions (Cl⁻):** These are stable, inactive ions (like those found in common salt) and have no disinfecting power. **3. NEET-PG High-Yield Clinical Pearls:** * **Free Residual Chlorine:** This refers to the sum of HOCl and OCl⁻. For effective disinfection, a contact time of **one hour** is required, and the free residual chlorine should be at least **0.5 mg/L**. * **Chlorine Demand:** The amount of chlorine needed to react with organic matter and impurities before a free residual can be established. * **Break-point Chlorination:** The point where the chlorine demand has been fully met, and any further addition of chlorine appears as "free" residual chlorine. * **Horrocks' Apparatus:** Used to estimate the dose of bleaching powder required to disinfect a given quantity of water. * **OT Test (Orthotolidine):** Used to detect both free and combined chlorine; however, the **OTA (Orthotolidine-Arsenite) test** is superior as it distinguishes between the two.

Question 392: What is the required daily intake of fluorine in ppm for the development of skeletal fluorosis?

A. 1.0 - 2.0 ppm
B. 2.0 - 3.0 ppm
C. 3.0 - 6.0 ppm (Correct Answer)
D. 6-9 ppm

Explanation: **Explanation:** Fluorine is often called a "two-edged sword" because while trace amounts are essential for dental health, excessive intake leads to toxicity. The clinical manifestations of fluorosis are strictly dose-dependent based on the concentration of fluoride in drinking water. **Why Option C is Correct:** Skeletal fluorosis occurs with a prolonged daily intake of fluorine in the range of **3.0 to 6.0 ppm**. At this concentration, fluoride accumulates in the bones, leading to increased bone density (osteosclerosis), calcification of ligaments (especially the broad ligament), and crippling deformities. It typically manifests after 10–20 years of exposure. **Analysis of Incorrect Options:** * **Option A (1.0 - 2.0 ppm):** This range is associated with the prevention of dental caries (optimum level is ~0.5–0.8 mg/L). However, levels above 1.5 ppm start causing **Dental Fluorosis** (mottling of enamel). * **Option B (2.0 - 3.0 ppm):** This range causes significant dental fluorosis but is generally insufficient to cause systemic skeletal changes in the majority of the population. * **Option D (6-9 ppm):** While these levels will certainly cause skeletal fluorosis, the *threshold* for the development of the disease starts at the 3.0–6.0 ppm range. Levels above 10 ppm are associated with severe "crippling fluorosis." **High-Yield Clinical Pearls for NEET-PG:** * **Dental Fluorosis:** Occurs when intake is >1.5 mg/L. It is an irreversible cosmetic defect (mottling) occurring during the period of tooth formation. * **Genu Valgum:** Also known as "Knock-knees," this is a characteristic manifestation of endemic fluorosis seen in parts of India (e.g., Nalgonda district). * **Safe Limit:** The WHO guideline for fluoride in drinking water is **1.5 mg/L**. * **Nalgonda Technique:** A common community-based method for defluoridation using alum and lime.

Question 393: Which of the following is a chemical stomach poison for mosquitoes?

A. DDT
B. Malathion
C. Paris green (Correct Answer)
D. Pyrethrum

Explanation: ### Explanation **Correct Answer: C. Paris Green** **Why Paris Green is the correct answer:** Paris Green (Copper acetoarsenite) is a classic **stomach poison** used primarily as a larvicide. It is an emerald-green micro-crystalline powder that is insoluble in water but floats on the surface. When applied to water bodies, it is ingested by surface-feeding mosquito larvae (specifically **Anopheles**). Once inside the digestive tract, the arsenic acts as a potent toxin, leading to the death of the larvae. It is highly effective because it does not harm fish or other aquatic life when used in recommended concentrations, as it must be ingested to be toxic. **Why the other options are incorrect:** * **A. DDT (Dichlorodiphenyltrichloroethane):** This is a **contact poison** belonging to the Organochlorine group. It acts by opening sodium channels in the insect's neurons, leading to spasms and death upon physical contact. * **B. Malathion:** This is an Organophosphorus compound that acts as a **contact and respiratory poison**. It works by inhibiting the enzyme acetylcholinesterase, causing neuromuscular paralysis. * **C. Pyrethrum:** Derived from Chrysanthemum flowers, this is a **natural contact poison**. It is known for its rapid "knock-down" effect on adult mosquitoes and is frequently used in space sprays. **High-Yield Clinical Pearls for NEET-PG:** * **Paris Green** is specifically used for **Anopheles** larvae (surface feeders). It is ineffective against *Culex* larvae because they are bottom feeders. * **Abate (Temephos)** is the preferred chemical larvicide for potable (drinking) water because of its low mammalian toxicity. * **Residual Sprays:** DDT, Malathion, and Lindane are used for Indoor Residual Spraying (IRS). * **Biological Control:** *Gambusia affinis* and *Poecilia reticulata* (Guppy) are the "larvivorous fish" of choice for biological larval control.

Question 394: Which disease is caused by a mite?

A. Scrub typhus (Correct Answer)
B. Fever
C. Trench fever
D. Endemic typhus

Explanation: **Explanation:** **Scrub Typhus (Correct Answer):** Scrub typhus is caused by the bacterium *Orientia tsutsugamushi*. It is transmitted to humans through the bite of the infected **larval stage of trombiculid mites** (commonly known as **chiggers** or harvest mites). These mites serve as both the vector and the reservoir (via transovarial transmission). A characteristic clinical feature is the **eschar**—a painless, black crusty lesion at the site of the mite bite. **Analysis of Incorrect Options:** * **B. Q Fever:** Caused by *Coxiella burnetii*. It is primarily an airborne zoonosis transmitted via inhalation of contaminated dust or aerosols from infected livestock (cattle, sheep, goats). It is not mite-borne. * **C. Trench Fever:** Caused by *Bartonella quintana*. It is transmitted by the **human body louse** (*Pediculus humanus corporis*). * **D. Endemic Typhus:** Also known as Murine typhus, it is caused by *Rickettsia typhi*. The primary vector is the **rat flea** (*Xenopsylla cheopis*). **High-Yield NEET-PG Pearls:** * **Vector Mnemonic:** Remember **"Mite-y Scrub"** to link Mites with Scrub Typhus. * **Drug of Choice:** Doxycycline is the gold standard treatment for all rickettsial diseases, including scrub typhus. * **Diagnostic Test:** The **Weil-Felix test** shows heterophile agglutination with **OX-K** antigens for Scrub Typhus (unlike Epidemic/Endemic typhus which react with OX-19 and OX-2). * **Habitat:** It is prevalent in areas with secondary scrub vegetation, often referred to as "tsutsugamushi triangles."

Question 395: Which of the following are criteria for drinking water quality recommended by WHO?

A. Colour < 15 TCU
B. pH 6.5-8.5
C. Chloride 200-600 mg/L
D. All of the above (Correct Answer)

Explanation: The World Health Organization (WHO) and the Bureau of Indian Standards (BIS: 10500) establish specific physical and chemical parameters to ensure that drinking water is safe, palatable, and non-corrosive. **Explanation of the Correct Answer:** The correct answer is **D (All of the above)** because each parameter listed falls within the internationally accepted guidelines for potable water: * **Colour (Option A):** The guideline value is **< 15 True Colour Units (TCU)**. Beyond this limit, water becomes aesthetically unacceptable to consumers and may indicate the presence of organic matter or metals like iron. * **pH (Option B):** The acceptable range is **6.5 to 8.5**. This range is critical because extremes in pH can lead to pipe corrosion (if acidic) or scale formation and reduced germicidal efficiency of chlorine (if alkaline). * **Chloride (Option C):** The desirable limit is **250 mg/L**, but it is acceptable up to **1000 mg/L** (per BIS) if no other source is available. The range of **200-600 mg/L** mentioned in the option is a standard benchmark where concentrations above 250 mg/L start imparting a detectable salty taste. **High-Yield Facts for NEET-PG:** * **Turbidity:** Should ideally be **< 1 NTU** (Nephelometric Turbidity Unit), though up to 5 NTU is acceptable. * **Hardness:** Expressed as $CaCO_3$. The desirable limit is **200 mg/L**; the permissible limit is **600 mg/L**. * **Fluoride:** The most "asked" parameter. The ideal level is **0.5–0.8 mg/L**. Levels **> 1.5 mg/L** lead to dental fluorosis, and **> 3-10 mg/L** lead to skeletal fluorosis. * **Nitrates:** Limit is **45 mg/L**. Excess causes Infantile Methemoglobinemia (Blue Baby Syndrome). * **Free Residual Chlorine:** Minimum **0.5 mg/L** for 1 hour of contact time is essential for disinfection.

Question 396: All of the following statements about Hardness of Water are true, except?

A. Hardness is the soap-destroying power of water.
B. Bicarbonates cause permanent hardness. (Correct Answer)
C. Carbonate hardness can be removed by boiling.
D. Hardness is mainly caused by calcium and magnesium salts.

Explanation: ### Explanation **1. Why Option B is the Correct Answer (The Exception):** Hardness of water is classified into two types: **Temporary** and **Permanent**. Bicarbonates of calcium and magnesium cause **Temporary Hardness** (also known as carbonate hardness), not permanent hardness. Permanent hardness is caused by the presence of chlorides, sulfates, and nitrates of calcium and magnesium. Therefore, the statement "Bicarbonates cause permanent hardness" is factually incorrect. **2. Analysis of Other Options:** * **Option A:** Hardness is defined as the "soap-destroying power" of water. This occurs because calcium and magnesium ions react with soap to form an insoluble curd (scum), preventing the formation of lather until the hardness is neutralized. * **Option C:** Temporary (Carbonate) hardness is easily removed by **boiling**. Boiling decomposes the soluble bicarbonates into insoluble carbonates, which precipitate out (forming scale). * **Option D:** While other polyvalent metallic ions (like iron or aluminum) can contribute, hardness is **mainly** caused by the salts of Calcium and Magnesium. **3. High-Yield Clinical Pearls for NEET-PG:** * **Removal Methods:** Temporary hardness is removed by boiling or addition of lime (Clark’s process). Permanent hardness requires chemical methods like the **Permutit process** (ion exchange) or addition of sodium carbonate. * **Health Impact:** Hard water is associated with increased risk of **urolithiasis** (urinary stones) and may lead to higher soap consumption and scaling of boilers. * **Hardness Scale:** * Soft: 0–50 mg/L * Moderately hard: 50–150 mg/L * Hard: 150–300 mg/L * Very hard: >300 mg/L * **WHO Guideline:** There is no firm health-based guideline value, but water above 200 mg/L is generally considered poor for domestic use.

Question 397: What is the primary indicator of the strength of sewage?

A. Escherichia coli (E. coli) count
B. Suspended solids (Correct Answer)
C. Nitrate concentration
D. Coliform count

Explanation: **Explanation:** The strength of sewage is primarily determined by its organic matter content and physical debris. **Suspended solids** (Option B) are the most direct indicator of sewage strength because they represent the insoluble organic and inorganic fraction that requires treatment. Along with **Biochemical Oxygen Demand (BOD)**, suspended solids dictate the complexity and duration of the sewage treatment process. Higher concentrations of suspended solids indicate "strong" sewage, whereas lower concentrations indicate "weak" or diluted sewage. **Analysis of Incorrect Options:** * **Options A & D (E. coli and Coliform count):** These are indicators of **bacterial contamination** and the sanitary quality of water, particularly for drinking purposes. While present in sewage, they measure the potential for pathogen transmission rather than the physical "strength" or organic load of the waste. * **Option C (Nitrate concentration):** Nitrates are an indicator of **remote (past) pollution**. Their presence suggests that organic nitrogen has already undergone oxidative decomposition. **High-Yield NEET-PG Pearls:** * **BOD (Biochemical Oxygen Demand):** Defined as the amount of oxygen consumed by aerobic bacteria to decompose organic matter in 5 days at 20°C. It is the most important chemical indicator of sewage strength. * **COD (Chemical Oxygen Demand):** Measures both biodegradable and non-biodegradable organic matter; it is always higher than BOD. * **Strength Classification:** * *Strong Sewage:* BOD > 300 mg/l * *Weak Sewage:* BOD < 100 mg/l * **Sludge:** The solid portion that settles out during sewage treatment; **Sullage** refers to wastewater from kitchens and bathrooms that does not contain human excreta.

Question 398: All of the following are true about safe and wholesome water, except?

A. It is free from color and odor
B. It is free from pathogenic agents
C. It is unusable for domestic purposes (Correct Answer)
D. It is free from harmful chemical contaminants

Explanation: ### Explanation **Concept of Safe and Wholesome Water** In Community Medicine, water is classified as "safe and wholesome" when it meets specific criteria that ensure it does not pose a health risk to the consumer and is aesthetically acceptable. By definition, safe and wholesome water must be **usable for domestic purposes** (such as drinking, cooking, and bathing). Therefore, Option C is the correct answer because it incorrectly states that such water is "unusable." **Analysis of Options:** * **Option A (Free from color and odor):** This is a true characteristic. Safe water must be aesthetically pleasing. It should be clear, colorless, and odorless to be acceptable for human consumption. * **Option B (Free from pathogenic agents):** This is a fundamental requirement. The water must not contain bacteria, viruses, protozoa, or helminths that cause water-borne diseases (e.g., Cholera, Typhoid, Hepatitis A). * **Option D (Free from harmful chemical contaminants):** This is also true. Safe water must not contain toxic substances like arsenic, fluorides, nitrates, or heavy metals in concentrations that exceed permissible limits. **High-Yield NEET-PG Pearls:** * **Definition:** Safe and wholesome water is defined as water that is: (1) Free from pathogenic agents, (2) Free from harmful chemical substances, (3) Pleasant to taste (free from color/odor), and (4) **Usable for domestic purposes.** * **Polluted vs. Contaminated Water:** *Polluted* water contains physical or chemical impurities (e.g., turbidity), while *Contaminated* water specifically contains infectious agents or poisonous substances. * **Standard:** The WHO Guidelines for Drinking-water Quality are the international benchmark used to define these parameters. * **Domestic Consumption:** In India, for an average urban community, the recommended supply is **150–200 liters per capita per day (lpcd)**.

Question 399: What is a Venturi meter used for?

A. Measuring the amount required for chlorination
B. Measuring air velocity
C. Measuring bed strength in a slow sand filter (Correct Answer)
D. Measuring the dissolving capacity of a gas

Explanation: **Explanation:** In the context of Environmental Health and Water Purification, a **Venturi meter** is a device used to measure the **bed strength (or resistance)** of a slow sand filter. As water passes through the sand bed, the "Schmutzdecke" (vital layer) and the sand itself offer resistance to the flow. Over time, as the filter becomes clogged with impurities, this resistance increases, leading to a "loss of head." The Venturi meter measures this pressure differential. When the resistance (loss of head) exceeds the critical limit (usually 0.7 to 1.2 meters), it indicates that the filter bed needs cleaning (scraping). **Analysis of Incorrect Options:** * **Option A:** The amount of chlorine required for chlorination is measured using the **Horrocks’ Apparatus**. * **Option B:** Air velocity is measured using an **Anemometer** (specifically a Kata Thermometer for low velocities in indoor environments). * **Option D:** The dissolving capacity of a gas is a physical property (solubility) and is not measured by a Venturi meter, which is a fluid flow measurement device. **High-Yield Facts for NEET-PG:** * **Slow Sand Filter (Biological Filter):** Best suited for rural areas; the most important component is the **Schmutzdecke** (Zoogleal layer), which takes 2-3 days to form. * **Rapid Sand Filter (Mechanical Filter):** Uses alum as a coagulant; cleaning is done by **backwashing**. * **Loss of Head:** This is the primary indicator for cleaning a slow sand filter, monitored via the Venturi meter. * **Free Residual Chlorine:** The standard requirement is **0.5 mg/L** for a contact period of one hour.

Question 400: Auditory fatigue occurs most readily at which frequency range?

A. 2000 Hz
B. 3000 Hz
C. 4000 Hz (Correct Answer)
D. 8000 Hz

Explanation: **Explanation:** The correct answer is **4000 Hz**. This is a classic high-yield concept in Occupational Health and Environmental Medicine. **1. Why 4000 Hz is correct:** Auditory fatigue (Temporary Threshold Shift) and permanent noise-induced hearing loss (NIHL) occur most readily at **4000 Hz**. This phenomenon is known as the **"4000 Hz Notch"** or **Carhart's Notch** (though the latter is more specific to otosclerosis, the term "notch" is universally used for noise damage). The anatomical reason is the resonance of the external auditory canal, which peaks between 2000–5000 Hz. This amplifies sound pressure levels reaching the cochlea in this range. Specifically, the basal turn of the cochlea, which is responsible for sensing high-frequency sounds, is most susceptible to mechanical and metabolic exhaustion from loud noise. **2. Why other options are incorrect:** * **2000 Hz & 3000 Hz:** While these frequencies are within the range of human speech and can be affected by prolonged noise exposure, they are not the *initial* or *most sensitive* points of fatigue. * **8000 Hz:** This is at the higher end of the clinical audiogram. While noise can affect this frequency, the maximum dip typically occurs at 4000 Hz and then shows a slight recovery at 8000 Hz (the "V-shaped" notch). **3. NEET-PG High-Yield Pearls:** * **Definition of Noise:** Sound that is unwanted. * **Safe Limit:** 85 dB is generally considered the limit for an 8-hour workday. * **Audiometry:** The first sign of noise-induced hearing loss is a notch at 4000 Hz. * **Presbycusis:** Age-related hearing loss, which typically affects high frequencies but lacks the specific 4000 Hz notch seen in noise trauma. * **Unit of Sound:** Frequency is measured in **Hertz (Hz)**, while intensity is measured in **Decibels (dB)**.

Practice by Chapter

Water Quality and Health

Practice Questions

Air Pollution and Health Effects

Practice Questions

Solid Waste Management

Practice Questions

Hazardous Waste Management

Practice Questions

Housing and Health

Practice Questions

Noise Pollution

Practice Questions

Radiation Health Effects

Practice Questions

Climate Change and Health

Practice Questions

Environmental Impact Assessment

Practice Questions

Disaster Management and Preparedness

Practice Questions

Vector Control

Practice Questions

Environmental Legislation

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free