Environmental Health — MCQs

Environmental Health Indian Medical PG Practice Questions and MCQs

Question 381: What is the minimum illumination accepted for satisfactory vision?

A. 15 to 20 foot candles (Correct Answer)
B. 30 to 40 candles
C. 40 to 50 candles
D. 70 to 90 candles

Explanation: ### Explanation **1. Understanding the Correct Answer (Option A)** In Community Medicine and Environmental Health, illumination is measured in **foot-candles (fc)** or **Lux** (1 fc ≈ 10.76 lux). According to standard public health guidelines (often cited from Park’s Textbook of Preventive and Social Medicine), the **minimum illumination** required for satisfactory vision and to prevent eye strain during ordinary tasks is **15 to 20 foot-candles**. This level provides sufficient contrast and brightness for the retina to process visual information comfortably without causing "asthenopia" (eye fatigue). **2. Analysis of Incorrect Options** * **Options B, C, and D:** These values (30 to 90 candles) represent significantly higher intensities. While higher illumination (e.g., 30–50 fc) may be required for **fine precision work** (like watch repairing or surgery), they exceed the "minimum" threshold for general satisfactory vision. Furthermore, excessively high levels without proper shielding can lead to **glare**, which is as detrimental to vision as poor lighting. **3. High-Yield Facts for NEET-PG** * **Measurement Units:** * **Luminous Intensity:** Measured in **Candela**. * **Luminous Flux:** Measured in **Lumens**. * **Illumination (Illuminance):** Measured in **Lux** or **Foot-candles**. * **Standards of Lighting:** * **Minimum for casual reading:** 15–20 foot-candles. * **Fine work/Sewing:** 50–100 foot-candles. * **Factors affecting "Good Lighting":** It depends on five factors: Intensity, Distribution (uniformity), Absence of Glare, Absence of Sharp Shadows, and Color of Light. * **The Inverse Square Law:** Illumination of a surface decreases in proportion to the square of the distance from the source.

Question 382: The majority of the waste produced by health-care providers is:

A. Chemical waste
B. Infectious waste
C. General waste (Correct Answer)
D. General waste

Explanation: In the context of Biomedical Waste (BMW) Management, it is crucial to distinguish between hazardous and non-hazardous waste generated in healthcare settings. **Explanation of the Correct Answer:** According to the World Health Organization (WHO) and the Biomedical Waste Management Rules, approximately **75% to 90%** of the total waste generated by healthcare facilities is **General (Non-hazardous) waste**. This waste is comparable to domestic or municipal waste and includes items like paper, packaging, food scraps, and office supplies. Because it does not pose a biological, chemical, or radiological risk, it is managed through the municipal waste stream rather than specialized treatment. **Analysis of Incorrect Options:** * **Infectious Waste:** This constitutes only about **15% to 25%** of the total healthcare waste. While it is the most concerning category due to the risk of disease transmission (e.g., sharps, blood-soaked materials), it is not the "majority." * **Chemical Waste:** This represents a very small fraction (usually **<3%**) of the total waste. It includes laboratory reagents, disinfectants, and heavy metals (like mercury from broken thermometers). **High-Yield Clinical Pearls for NEET-PG:** * **The 85/15 Rule:** Remember that 85% of hospital waste is non-infectious (General), and 15% is infectious/hazardous. * **Color Coding:** General waste is collected in **Black bags/bins** (as per standard protocols, though municipal rules may vary by location to Green/Blue for wet/dry). * **Segregation at Source:** This is the most important step in BMW management to prevent the 85% general waste from becoming contaminated by the 15% infectious waste. * **Cytotoxic Waste:** Must be disposed of in **Yellow bags** marked with a cytotoxic symbol and incinerated at >1200°C.

Question 383: What is the heart of the activated sludge process?

A. Primary sedimentation tank
B. Sludge digestor
C. Aeration tank (Correct Answer)
D. Final settling tank

Explanation: ### Explanation The **Activated Sludge Process** is a biological method of secondary sewage treatment. The **Aeration Tank** is considered the "heart" of this process because it is where the core biological action occurs. **1. Why Aeration Tank is the Correct Answer:** In this tank, primary effluent is mixed with "activated sludge" (a mixture of aerobic bacteria and protozoa). Compressed air is continuously pumped in, providing oxygen for aerobic oxidation. The microorganisms break down organic matter into carbon dioxide, water, and new microbial biomass. This conversion of dissolved organic pollutants into settleable biological solids is the fundamental mechanism of the entire process. **2. Why Other Options are Incorrect:** * **Primary Sedimentation Tank:** This is part of *primary treatment* (physical process) where large suspended solids settle by gravity. It occurs before the activated sludge process begins. * **Sludge Digestor:** This is used for the anaerobic decomposition of the sludge collected from the tanks. It is a separate stage focused on waste disposal and biogas production, not the purification of the sewage itself. * **Final Settling Tank (Secondary Clarifier):** While essential for separating the purified water from the microbial mass (sludge), it is a passive physical process. The actual "work" of purification has already been completed in the aeration tank. **High-Yield Facts for NEET-PG:** * **Activated Sludge:** It is called "activated" because it is teeming with live, metabolically active microorganisms. * **BOD Reduction:** The primary goal of the activated sludge process is to significantly reduce the **Biological Oxygen Demand (BOD)** of the sewage (usually by 80-95%). * **Recycling:** A portion of the sludge from the final settling tank is pumped back into the aeration tank to maintain the microbial population; this is known as **Return Activated Sludge (RAS)**.

Question 384: Aerobic digestion of sludge takes place in which of the following?

A. Trickling filter (Correct Answer)
B. Broad irrigation
C. Activated sludge
D. Septic tank

Explanation: ### Explanation The core concept here is the distinction between **aerobic** and **anaerobic** processes in sewage treatment. **1. Why Trickling Filter is correct:** A trickling filter (also known as a percolating filter) is a secondary treatment method where sewage is sprayed over a bed of crushed stones or slag. As the sewage trickles down, it comes into contact with a biological film (zoogleal layer) consisting of aerobic bacteria, algae, and fungi. Because the bed is ventilated, there is a constant supply of oxygen, ensuring that the **digestion of organic matter (sludge) occurs aerobically**. **2. Why the other options are incorrect:** * **Activated Sludge Process:** While this is an aerobic process, it involves the oxidation of *sewage* in an aeration tank. The resulting "activated sludge" is then sent to a separate **Sludge Digestion Tank**, where it typically undergoes **anaerobic digestion** to produce methane. * **Broad Irrigation:** This is a primary disposal method where raw or settled sewage is applied to land. It relies on surface filtration and natural soil bacteria, but it is not a specialized "digestion" process for sludge. * **Septic Tank:** This is a classic example of **anaerobic digestion**. The solids settle at the bottom and are decomposed by anaerobic bacteria over a period of months. ### High-Yield Pearls for NEET-PG: * **Trickling Filter:** Key features include the "Zoogleal layer" and the fact that it is a biological oxidation process. * **Activated Sludge Process:** The most efficient method for large-scale urban sewage treatment; it reduces BOD (Biochemical Oxygen Demand) by 90-95%. * **BOD (Biochemical Oxygen Demand):** The most important indicator of organic pollution. A high BOD indicates high pollution. * **Sludge Digestion:** In most modern plants, sludge is digested **anaerobically** in closed tanks to produce "sludge gas" (methane), which can be used for power.

Question 385: Which of the following is NOT true regarding malathion?

A. Used as a spray
B. Can be used as an alternative to DDT
C. Most toxic of all members of the group (Correct Answer)
D. Belongs to organophosphorous insecticides

Explanation: ### Explanation **Malathion** is a widely used organophosphorous insecticide in public health programs. The question asks for the statement that is **NOT** true. **1. Why Option C is the Correct Answer (The False Statement):** Malathion is actually considered one of the **least toxic** organophosphorous compounds for mammals. Its selective toxicity is due to the fact that mammals possess enzymes (carboxylesterases) that rapidly detoxify malathion, whereas insects convert it into the highly toxic metabolite **malaoxon**. In contrast, other members of the organophosphate group, such as Parathion or Nerve Gases (Sarin, VX), are significantly more lethal. **2. Analysis of Incorrect Options:** * **Option A (Used as a spray):** This is true. Malathion is used as a residual spray (at a dosage of 2g/m²) for indoor residual spraying (IRS) and as an ultra-low volume (ULV) fog for space spraying during epidemics. * **Option B (Alternative to DDT):** This is true. In areas where vectors (like *Anopheles* mosquitoes) have developed resistance to DDT and HCH, Malathion is the recommended alternative for malaria control. * **Option D (Belongs to organophosphorous insecticides):** This is true. It is a non-systemic organophosphate that acts by inhibiting acetylcholinesterase. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Antidote:** Atropine is the specific physiological antidote for malathion poisoning; Pralidoxime (2-PAM) is used as a cholinesterase reactivator. * **Dosage:** For IRS, it is applied at **2g/m²** every 3 months. * **Odor:** Malathion has a characteristic strong, pungent "garlic" or "rotten egg" odor due to its sulfur content. * **Safety:** Because of its low mammalian toxicity, it is the insecticide of choice for **delousing** (treating head and body lice).

Question 386: The release of which one of the following into ponds and wells helps in controlling mosquitoes?

A. Crab
B. Dogfish
C. Gambusia fish (Correct Answer)
D. Snail

Explanation: **Explanation:** The correct answer is **Gambusia fish** (*Gambusia affinis*), commonly known as the mosquitofish. This is a classic example of **biological control** of vectors, a key strategy in Integrated Vector Management (IVM). **Why Gambusia fish is correct:** * **Larvivorous Nature:** Gambusia is a surface-feeding fish that specifically preys on mosquito larvae and pupae. * **Efficiency:** A single full-grown Gambusia fish can consume about 100 to 300 larvae per day. * **Hardiness:** These fish are preferred because they are hardy, can survive in varying water temperatures, and multiply quickly. They are primarily used to control *Anopheles* (malaria vector) and *Culex* (filariasis vector) breeding in permanent water bodies like ponds and wells. **Why other options are incorrect:** * **Crab:** Crabs are crustaceans and do not feed on mosquito larvae as a primary food source; they have no role in vector control. * **Dogfish:** This is a type of small shark found in saltwater. It is not suitable for freshwater ponds/wells and does not predate on mosquito larvae. * **Snail:** Snails are actually detrimental to public health as they serve as intermediate hosts for parasites like *Schistosoma* (causing Schistosomiasis). **High-Yield Facts for NEET-PG:** * **Other Larvivorous Fish:** *Lebistes reticulatus* (Guppy) is another common example used in India. * **Biolarvicides:** *Bacillus thuringiensis israelensis* (Bti) and *Bacillus sphaericus* are microbial agents used for the same purpose. * **Environmental Modification:** This falls under "Source Reduction," which is the most effective long-term method of mosquito control. * **Target:** Biological control specifically targets the **aquatic stages** (larvae/pupae) of the mosquito life cycle, not the adult stage.

Question 387: Soil acts as a source as well as reservoir for which of the following diseases?

A. Rabies
B. Tetanus (Correct Answer)
C. Typhoid
D. Measles

Explanation: **Explanation:** The correct answer is **Tetanus**. In epidemiology, a **reservoir** is the natural habitat where an infectious agent lives, grows, and multiplies, while a **source** is the person, animal, or object from which the host acquires the infection. **Why Tetanus?** Tetanus is caused by *Clostridium tetani*, an anaerobic, spore-forming bacterium. The soil acts as a **reservoir** because the spores can survive in the environment for years, maintaining a constant presence. It acts as a **source** because infection is typically acquired when soil contaminated with these spores enters the body through a wound or injury. **Analysis of Incorrect Options:** * **Rabies:** The reservoir and source are infected animals (primarily dogs in India). The virus is transmitted via saliva through bites; it cannot survive in soil. * **Typhoid:** Humans are the only reservoir for *Salmonella typhi*. The source is usually contaminated food or water (fecal-oral route), not the soil itself. * **Measles:** This is a highly contagious viral infection where humans are the only reservoir. Transmission occurs via respiratory droplets. **High-Yield Clinical Pearls for NEET-PG:** * **Other Soil-transmitted diseases:** Anthrax, Gas gangrene, and Soil-Transmitted Helminths (STH) like Hookworm, *Ascaris*, and *Trichuris*. * **Tetanus Toxin:** *Tetanospasmin* blocks the release of inhibitory neurotransmitters (GABA and Glycine), leading to spastic paralysis. * **Epidemiological Fact:** Tetanus is one of the few infectious diseases that is **non-communicable** (cannot be spread from person to person). * **Elimination:** India has achieved "Maternal and Neonatal Tetanus Elimination" (MNTE), defined as <1 case per 1,000 live births in every district.

Question 388: The mean radiant temperature is measured by:

A. Dry bulb thermometer
B. Wet bulb thermometer
C. Six's maximum and minimum thermometer
D. Globe thermometer (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Globe thermometer** The **Globe thermometer** (specifically the Vernon’s Globe Thermometer) is the standard instrument used to measure **Mean Radiant Temperature (MRT)**. It consists of a mercury-in-glass thermometer placed inside a 6-inch hollow copper sphere painted matte black. The black surface absorbs infrared radiation from surrounding objects, and the equilibrium temperature reached inside the globe reflects the combined effect of air temperature and radiant heat. **Analysis of Incorrect Options:** * **A. Dry bulb thermometer:** Measures the actual air temperature (ambient temperature). It is not influenced by radiation or humidity. * **B. Wet bulb thermometer:** Measures the lowest temperature reachable by evaporative cooling. It is used primarily to assess humidity and the cooling power of the air. * **C. Six’s maximum and minimum thermometer:** Used to record the highest and lowest temperatures reached during a specific period (usually 24 hours). It does not measure radiant heat. **High-Yield Clinical Pearls for NEET-PG:** * **Kata Thermometer:** Measures "cooling power" of air and air velocity (especially low velocities). * **Anemometer:** Measures high-velocity air/wind speed. * **Psychrometer (Sling Psychrometer):** Used to measure relative humidity (contains both dry and wet bulb thermometers). * **Corrected Effective Temperature (CET):** An index that adjusts the Effective Temperature to include the effect of radiant heat (measured by the Globe thermometer). * **Comfort Zone:** In India, the ideal indoor temperature is considered **25°C to 27°C**.

Question 389: In the composition of normal dry air of the atmosphere at ground level in an unpolluted area, which one among the following is found in the highest concentration?

A. Carbon dioxide (Correct Answer)
B. Hydrogen
C. Methane
D. Nitrous oxide

Explanation: **Explanation:** The composition of normal dry air at ground level is dominated by Nitrogen (~78%) and Oxygen (~21%), followed by Argon (~0.93%). The remaining fraction consists of "trace gases." Among the options provided, **Carbon dioxide (CO₂)** is the correct answer as it is the most abundant trace gas in an unpolluted atmosphere. 1. **Why Carbon Dioxide is Correct:** In a standard unpolluted environment, the concentration of CO₂ is approximately **0.03% to 0.04% (300–400 parts per million)**. While this seems small, it is significantly higher than the concentrations of the other gases listed in the options. 2. **Analysis of Incorrect Options:** * **Hydrogen (B):** Found in minute traces, approximately 0.00005% (0.5 ppm). * **Methane (C):** A potent greenhouse gas, but present at only about 0.00017% (1.7–1.8 ppm). * **Nitrous oxide (D):** Present in extremely low concentrations, approximately 0.00003% (0.3 ppm). **High-Yield Clinical Pearls for NEET-PG:** * **Standard Air Composition:** Nitrogen (78.08%), Oxygen (20.94%), Argon (0.93%), and CO₂ (0.03%). * **Expired Air:** Contains approximately 16.3% Oxygen and **4.0% CO₂**. The significant rise in CO₂ in expired air is a common physiological fact tested in exams. * **Indicator of Ventilation:** In indoor settings, CO₂ levels are used as an indicator of air freshness. Levels should ideally remain below **0.1% (1000 ppm)**; levels exceeding this indicate poor ventilation (the "Guildford limit"). * **Vitiated Air:** Air rendered impure by breathing and perspiration is termed "vitiated air," characterized by increased humidity, temperature, and CO₂.

Question 390: Which of the following is a bacteriological indicator of water quality?

A. Staphylococcus aureus
B. Clostridium tetani
C. E.coli (Correct Answer)
D. Yersinia pestis

Explanation: ### Explanation **Correct Answer: C. E.coli** **Why E.coli is the correct answer:** In public health and environmental engineering, **Coliform organisms** (specifically *Escherichia coli*) are used as the primary indicators of fecal contamination of water. *E. coli* is an ideal bacteriological indicator because: 1. It is a normal inhabitant of the intestinal tract of humans and warm-blooded animals and is excreted in large numbers in feces. 2. It cannot multiply in water but survives long enough to be detected. 3. It is easy to detect and enumerate using simple laboratory tests (e.g., Multiple Tube Fermentation or Membrane Filtration). 4. Its presence indicates recent fecal pollution, suggesting that enteric pathogens (like *Vibrio cholerae* or *Salmonella*) might also be present. **Analysis of Incorrect Options:** * **A. Staphylococcus aureus:** While it can cause skin infections in swimming pools, it is not used as a standard indicator for drinking water quality as it is not primarily an enteric organism. * **B. Clostridium tetani:** This is a soil-borne anaerobe. It is not used to monitor water safety because it does not signify fecal contamination. * **D. Yersinia pestis:** This is the causative agent of Plague, transmitted primarily by flea bites or respiratory droplets, not through contaminated drinking water. **High-Yield NEET-PG Pearls:** * **Best Indicator of Fecal Pollution:** *E. coli* (Fecal coliforms). * **Indicator of Remote (Past) Pollution:** *Clostridium perfringens* (due to its resistant spores). * **Indicator of Human Fecal Contamination (Specific):** *Streptococcus faecalis* (Enterococci). * **Virological Quality:** Coliphages (viruses that infect *E. coli*) are often used as indicators for the presence of human enteric viruses. * **Standard for Drinking Water:** For a 100 ml sample of drinking water, *E. coli* or thermotolerant coliform bacteria must **not be detectable**.

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