Environmental Health — MCQs

Environmental Health Indian Medical PG Practice Questions and MCQs

Question 551: Which of the following is resistant to DDT, except?

A. Phlebotomus (Correct Answer)
B. Culex fatigans
C. Anopheles stephensi
D. Musca domestica

Explanation: **Explanation:** The question tests your knowledge of insecticide resistance patterns in medically important vectors. Resistance to DDT (Dichlorodiphenyltrichloroethane) is a significant challenge in global public health, but it is not universal across all insect species. **Why Phlebotomus is the Correct Answer:** *Phlebotomus argentipes* (the sandfly), the primary vector for Kala-azar (Visceral Leishmaniasis), remains **highly susceptible** to DDT in most regions, particularly in the Indian subcontinent. While there have been sporadic reports of emerging tolerance, DDT remains the insecticide of choice for Indoor Residual Spraying (IRS) in the National Vector Borne Disease Control Programme (NVBDCP) for Kala-azar elimination. Therefore, it is the exception to the widespread DDT resistance seen in other vectors. **Analysis of Incorrect Options:** * **Culex fatigans (C. quinquefasciatus):** This is the "classic" example of an insect that developed rapid and widespread resistance to DDT. It is the vector for Bancroftian Filariasis and is notorious for its high level of resistance to organochlorines. * **Anopheles stephensi:** A major urban malaria vector in India. It has developed extensive resistance to DDT, HCH, and malathion in many urban areas, necessitating a shift to synthetic pyrethroids. * **Musca domestica (Housefly):** Houseflies were among the first insects to demonstrate high-grade resistance to DDT shortly after its introduction in the 1940s. They possess efficient metabolic detoxification mechanisms. **High-Yield Facts for NEET-PG:** 1. **DDT Mechanism:** It is a neurotoxin that opens sodium channels in nerve cells, leading to repetitive firing and death ("DDT jitters"). 2. **Kala-azar Control:** IRS with DDT (75% WP) at a dosage of 1 $g/m^2$ is the standard protocol for sandfly control in India. 3. **Resistance Mechanism:** The most common mechanism for DDT resistance in mosquitoes is **kdr (knock-down resistance)** mutations and increased activity of **GST (Glutathione S-transferases)** enzymes.

Question 552: Recommended reflection factors include each of the following, except?

A. Ceilings 80%
B. Roofs 40% (Correct Answer)
C. Walls 50 to 60%
D. Furniture 30 to 40%

Explanation: ### Explanation In environmental health and housing standards, **Reflection Factor** (or reflectance) refers to the percentage of light that is reflected by a surface. Proper reflectance is essential to ensure adequate indoor illumination, reduce glare, and minimize the need for artificial lighting. **Why "Roofs 40%" is the correct answer (the exception):** Standard guidelines for indoor lighting and housing (often cited in Park’s Textbook of Preventive and Social Medicine) focus on **internal surfaces** to optimize the distribution of light. **Roofs** are external structures and are not typically included in the standard "Reflection Factor" recommendations for indoor illumination. Furthermore, if the question refers to floors (a common distractor), the recommended reflection factor for **floors is 15–20%**, not 40%. **Analysis of Incorrect Options:** * **A. Ceilings (80%):** This is a standard recommendation. Ceilings should have the highest reflectance (white or off-white) to reflect light downward and provide uniform illumination. * **C. Walls (50–60%):** Walls require a moderate reflection factor. This range ensures the room stays bright without causing excessive glare for the occupants. * **D. Furniture (30–40%):** Furniture and office equipment should have a lower reflectance to provide visual comfort and contrast against walls and ceilings. **NEET-PG High-Yield Pearls:** * **Daylight Factor:** The ratio of indoor light at a specific point to the outdoor light available simultaneously. For dwellings, a daylight factor of **1%** is recommended; for kitchens, it is **2%**. * **Luminance/Illumination:** Measured in **Lux**. * **Standard for Housing:** The window area should be at least **1/10th to 1/5th** of the floor area to ensure adequate light and ventilation. * **Color Impact:** Light colors increase the reflection factor, while dark colors absorb light, necessitating higher wattage for artificial lighting.

Question 553: What is the average lifespan of a housefly?

A. 5 days
B. 10 days
C. 1 month (Correct Answer)
D. 1 year

Explanation: **Explanation:** The housefly (*Musca domestica*) is a significant mechanical vector in community medicine. The correct answer is **1 month**, as the average lifespan of an adult housefly under optimal environmental conditions (warmth and food availability) typically ranges from **15 to 30 days**. **Why Option C is Correct:** In tropical climates like India, the life cycle from egg to adult is rapid (8–12 days). Once the adult emerges, its survival depends on temperature and humidity. While some may die sooner, the biological average cited in standard public health textbooks (like Park’s PSM) for the adult stage is approximately 30 days. **Why Other Options are Incorrect:** * **A & B (5–10 days):** These durations are too short for the average lifespan. While high predatory pressure or extreme heat may kill flies early, they are biologically capable of living much longer. * **D (1 year):** This is far beyond the physiological limit of a housefly. Only certain insects with diapause or hibernation stages live this long; houseflies have high metabolic rates and short reproductive cycles. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Houseflies act as **mechanical vectors** (carrying pathogens on their feet, body hairs, or through vomitus/faeces). They do not support the biological development of the pathogen. * **Diseases Spread:** Typhoid, paratyphoid, cholera, bacillary dysentery, amoebiasis, and helminthic infestations. * **Breeding Sites:** They prefer decaying organic matter, especially horse manure and human excreta. * **Control Measure of Choice:** Environmental sanitation (proper disposal of refuse and excreta) is more effective than chemical insecticides due to rapidly developing resistance.

Question 554: At what level of fluoride in drinking water does crippling fluorosis occur?

A. 0.5-0.8 mg/litre
B. 1.5 mg/litre
C. 3-6 mg/litre
D. > 10 mg/litre (Correct Answer)

Explanation: **Explanation:** The correct answer is **D (> 10 mg/litre)**. Fluoride is often called a "two-edged sword" because while it prevents dental caries at low concentrations, excessive intake leads to progressive toxic effects known as fluorosis. The severity of fluorosis is strictly dose-dependent: * **Dental Fluorosis:** Occurs at levels of **1.5–3 mg/L**. It manifests as "mottling" of enamel (chalky white patches or brownish discoloration). * **Skeletal Fluorosis:** Occurs with prolonged exposure to **3–10 mg/L**. It involves increased bone density (osteosclerosis) and calcification of ligaments. * **Crippling Fluorosis:** Occurs when levels exceed **10 mg/L**. This is the most severe form, characterized by permanent deformities, "poker back" (rigid spine), and severe neurological complications due to spinal cord compression. **Analysis of Incorrect Options:** * **A (0.5–0.8 mg/L):** This is the **optimal level** recommended for drinking water to prevent dental caries. * **B (1.5 mg/L):** This is the WHO upper limit for fluoride in drinking water. Beyond this, dental fluorosis begins. * **C (3–6 mg/L):** This range is associated with skeletal fluorosis but is not yet considered "crippling." **High-Yield Clinical Pearls for NEET-PG:** * **Safe Limit:** 0.5–0.8 mg/L (India) or up to 1.0 mg/L (WHO). * **Genu Valgum (Knock-knees):** A manifestation of endemic fluorosis seen in the "Nalgonda technique" context (though the technique itself is for defluoridation). * **Defluoridation:** The **Nalgonda Technique** uses alum and lime to remove fluoride. * **Biomarker:** Urinary fluoride levels are the most reliable indicator of recent fluoride exposure.

Question 555: The Coliform test is used to detect which type of contamination?

A. Air pollution
B. Water contamination (Correct Answer)
C. Sound pollution
D. None of the above

Explanation: **Explanation:** The **Coliform test** is the standard microbiological procedure used to detect **water contamination**, specifically fecal pollution. Coliform bacteria (such as *E. coli*, *Klebsiella*, and *Enterobacter*) are normal inhabitants of the intestinal tract of humans and warm-blooded animals. Their presence in a water sample serves as a "surrogate marker" or **indicator organism**, signaling that the water has been contaminated with fecal matter and may contain dangerous enteric pathogens like *Salmonella typhi*, *Vibrio cholerae*, or Hepatitis A. **Why other options are incorrect:** * **Air pollution:** Monitored using parameters like PM2.5, PM10, Sulfur dioxide, and Nitrogen dioxide levels. Biological indicators for air are rarely used in standard testing. * **Sound pollution:** Measured in Decibels (dB) using a Sound Level Meter. It is a physical hazard, not a biological one. **High-Yield Clinical Pearls for NEET-PG:** * **Indicator Organisms:** *E. coli* is the best indicator of **recent** fecal contamination because it does not survive long outside the gut. *Streptococcus faecalis* and *Clostridium perfringens* indicate remote/past contamination. * **Presumptive Coliform Count:** Usually performed using the Multiple Tube Fermentation method to derive the **Most Probable Number (MPN)**. * **WHO Standard:** For drinking water, coliforms must be **zero per 100 ml** of water. * **OT Test (Orthotolidine):** Do not confuse this with the Coliform test; OT is used to detect **free and combined chlorine** in water.

Question 556: In a slow sand filter, what element is responsible for yielding bacteria-free water?

A. Valve
B. Vital layer (Correct Answer)
C. Supernatant water
D. Under-drainage system

Explanation: ### Explanation The **Slow Sand Filter** (or biological filter) is a cornerstone of large-scale water purification. The correct answer is the **Vital Layer**, also known as the **Schmutzdecke**, biological layer, or zoogleal layer. **Why the Vital Layer is Correct:** The vital layer is a slimy, gelatinous membrane that forms on the surface of the sand bed over a period of a few days. It consists of algae, plankton, diatoms, and bacteria. This layer is the "heart" of the filter because it performs the actual purification through: 1. **Biological Action:** Organic matter is oxidized by the bacteria in the layer. 2. **Mechanical Strainer:** It traps very fine particles. 3. **Bacteriological Action:** It is responsible for removing **98% to 99% of bacteria** and reducing the organic content of the water. **Why Other Options are Incorrect:** * **Valve:** These are mechanical components used to regulate the flow of water and maintain a constant rate of filtration; they have no biological purification properties. * **Supernatant Water:** This is the 1–1.5 meter column of raw water above the sand. Its primary role is to provide a constant head of pressure and allow time (3–12 hours) for sedimentation; it does not filter bacteria. * **Under-drainage System:** Located at the bottom of the filter, this consists of porous pipes that collect the filtered water and provide support for the filter medium. It does not contribute to the removal of pathogens. **High-Yield Facts for NEET-PG:** * **Rate of Filtration:** 0.1 to 0.4 $m^3/m^2/hour$ (Slow sand filters are roughly 20–50 times slower than Rapid Sand Filters). * **Effective Size of Sand:** 0.2 to 0.35 mm. * **Cleaning:** Done by **scraping** the top layer of sand (unlike Rapid Sand Filters, which use backwashing). * **Efficiency:** Highly efficient at removing bacteria but less effective at removing high turbidity compared to rapid sand filters.

Question 557: The soiling index is a measure for what type of pollution?

A. Air pollution (Correct Answer)
B. Water pollution
C. Faecal contamination
D. Milk contamination

Explanation: **Explanation:** The **Soiling Index**, also known as the **Coefficient of Haze (COH)**, is a traditional method used to measure **Air Pollution**, specifically the concentration of suspended particulate matter (smoke) in the atmosphere. 1. **Why Air Pollution is Correct:** The index is determined by drawing a known volume of air through a filter paper (usually for 24 hours). The resulting dark spot or "soiling" on the paper is measured using a reflectometer or densitometer. The degree of darkness (optical density) correlates directly with the amount of smoke and particulate matter present in the air. It is a key indicator of the aesthetic and physical "dirtiness" of urban air. 2. **Why Other Options are Incorrect:** * **Water Pollution:** Measured using parameters like BOD (Biochemical Oxygen Demand), COD, and dissolved oxygen, not by filter paper staining. * **Faecal Contamination:** Assessed via bacteriological indicators, primarily the **Coliform count** (E. coli) or the Multiple Tube Method (MPN). * **Milk Contamination:** Evaluated using the **Methylene Blue Reduction Test (MBRT)** for bacterial load or Phosphatase tests for pasteurization efficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Indicator of Air Pollution:** While the Soiling Index measures smoke, **Sulphur Dioxide ($SO_2$)** is considered the best single indicator for air pollution levels in general. * **Air Quality Index (AQI):** Modern monitoring uses AQI, which tracks five major pollutants: Ground-level ozone, particulate matter (PM2.5/PM10), CO, $SO_2$, and $NO_2$. * **Lichens:** These are biological indicators of air pollution (sensitive to $SO_2$).

Question 558: When was the International Drinking Water Supply and Sanitation Decade Programme launched?

A. 1975
B. 1978
C. 1984
D. 1981 (Correct Answer)

Explanation: **Explanation:** The **International Drinking Water Supply and Sanitation Decade (IDWSSD)** was a global initiative launched by the United Nations to provide universal access to safe drinking water and adequate sanitation. **1. Why 1981 is Correct:** The decade was officially launched in **1981** and spanned from **1981 to 1990**. It was a direct outcome of the 1977 UN Water Conference in Mar del Plata, Argentina. The primary goal was to reduce the burden of water-borne diseases (like cholera and typhoid) and improve hygiene in developing nations. In India, this led to the accelerated implementation of the National Water Supply and Sanitation Programme. **2. Why Other Options are Incorrect:** * **1975:** This year is associated with the launch of the **Integrated Child Development Services (ICDS)** scheme in India, not water sanitation. * **1978:** This is a landmark year in public health for the **Alma-Ata Declaration**, which established the concept of "Primary Health Care" (PHC). While PHC includes "safe water and basic sanitation" as one of its eight essential components, the specific Decade Programme was not launched until 1981. * **1984:** This year is significant in environmental health for the **Bhopal Gas Tragedy**, but it does not mark the start of any major international water decade. **3. High-Yield Clinical Pearls for NEET-PG:** * **Target:** The decade aimed for 100% coverage of safe water and 50-80% coverage of sanitation. * **Current Context:** The IDWSSD was a precursor to the **Millennium Development Goals (MDGs)** and the current **Sustainable Development Goal (SDG) 6**, which aims for "Clean Water and Sanitation for all" by 2030. * **India Specific:** The **Jal Jeevan Mission (2019)** is the current flagship program in India aiming to provide Functional Household Tap Connections (FHTC) to every rural household by 2024.

Question 559: What is the number of holes per square inch of a standard mosquito net?

A. 100
B. 150 (Correct Answer)
C. 250
D. 175

Explanation: ### Explanation The correct answer is **150 (Option B)**. In public health and vector control, the effectiveness of a mosquito net depends on a balance between preventing insect entry and allowing adequate ventilation. According to standard guidelines (including WHO and Park’s Textbook of Preventive Medicine), a standard mosquito net must have **150 holes per square inch**. **Why 150 is the correct answer:** * **Size of the Mesh:** This density ensures that the size of each hole is small enough to prevent the entry of common disease-carrying mosquitoes (like *Anopheles*, *Culex*, and *Aedes*). * **Ventilation:** A hole count of 150 provides the optimal "bursting strength" and airflow. If the holes were larger, mosquitoes could enter; if they were significantly smaller, the net would become stuffy and uncomfortable for the user, leading to poor compliance. **Analysis of Incorrect Options:** * **Option A (100):** This mesh is too coarse. The holes would be large enough for smaller mosquitoes or those that can squeeze through wider apertures to enter, rendering the net ineffective. * **Option C (250) & D (175):** While a higher hole count (like 250) provides a better barrier against very small insects (like sandflies), it significantly restricts air circulation. In tropical climates where mosquito-borne diseases are endemic, a net with 250 holes/sq inch would be too hot for the user. **High-Yield Clinical Pearls for NEET-PG:** 1. **Sandfly Netting:** For protection against Sandflies (*Phlebotomus*), the mesh must be much finer, requiring at least **285 holes per square inch**. 2. **LLINs (Long-Lasting Insecticidal Nets):** These are the current gold standard. They are treated with pyrethroids (e.g., alpha-cypermethrin or deltamethrin) and maintain efficacy for at least **3 years or 20 washes**. 3. **The "Square Inch" Rule:** The diameter of the thread used also matters, but for exam purposes, the number **150** is the most frequently tested metric for standard mosquito control.

Question 560: All of the following are indicators of air pollution except?

A. CO
B. SO2
C. Soiling index
D. Smoking index (Correct Answer)

Explanation: **Explanation:** The correct answer is **Smoking Index**. In Community Medicine and Environmental Health, indicators of air pollution are standardized metrics used to monitor the quality of ambient (outdoor) air. 1. **Why "Smoking Index" is the correct answer:** The **Smoking Index** is a clinical tool used to quantify an individual’s cumulative exposure to tobacco smoke (calculated as: *number of cigarettes smoked per day × number of years of smoking*). It is an indicator of **personal lifestyle risk** and a predictor for chronic obstructive pulmonary disease (COPD) or lung cancer, rather than a measure of environmental air pollution. 2. **Analysis of incorrect options (Indicators of Air Pollution):** * **CO (Carbon Monoxide):** A major primary pollutant resulting from incomplete combustion of fossil fuels. It is a standard parameter in the Air Quality Index (AQI). * **SO2 (Sulphur Dioxide):** A key indicator of air pollution, primarily arising from coal combustion and industrial processes. It serves as a proxy for acid rain potential and respiratory irritants. * **Soiling Index (Coefficient of Haze):** This is a traditional physical method used to measure particulate matter (smoke) in the air. It involves drawing a known volume of air through a filter paper and measuring the resulting blackness (stain) using a reflectometer. **High-Yield NEET-PG Pearls:** * **Best Indicator of Air Pollution:** While many exist, **Sulphur Dioxide (SO2)** is traditionally considered the best indicator of air pollution caused by fuel combustion. * **Lichens:** These are biological indicators (bio-indicators) of air pollution; they disappear in areas with high SO2 concentrations. * **AQI Parameters:** In India, the National Air Quality Index monitors 8 pollutants: PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb. * **Smoke Measurement:** Apart from the Soiling Index, the **Ringelmann Chart** is used to estimate the density of smoke emitting from stacks or chimneys.

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