Environmental Health Practice Questions

Q: The 'NALGONDA technique' is used in which condition?

Endemic fluorosis. **Explanation:** The **Nalgonda technique** is a method for the **defluoridation** of water, specifically designed for use at both the community and household levels in areas where **Endemic Fluorosis** is prevalent. Developed by the National Environmental Engineering Research Institute (NEERI) in Nagpur, it involves the sequential addition of **Alum (Aluminium sulphate)**, **Lime (Calcium oxide)**, and **Bleaching powder** to water, followed by rapid mixing, flocculation, sedimentation, and filtration. Alum acts as the coagulant to remove fluoride ions, while lime ensures the correct pH and bleaching powder provides disinfection. **Analysis of Incorrect Options:** * **B. Epidemic dropsy:** Caused by the ingestion of mustard oil adulterated with **Argemone mexicana** (Sanguinarine toxin). Management focuses on removing the adulterated oil and symptomatic treatment, not water purification. * **C. Endemic ascites:** Associated with the consumption of **Pyrrolizidine alkaloids** (found in *Crotalaria* seeds) contaminating staple grains like millet. * **D. Neurolathyrism:** A neurological condition caused by the excessive consumption of *Lathyrus sativus* (Khesari dal) containing the neurotoxin **BOAA**. Prevention involves parboiling or steeping the pulse, not the Nalgonda technique. **High-Yield Clinical Pearls for NEET-PG:** * **Fluoride levels:** Ideal in water is **0.5–0.8 mg/L**. Dental fluorosis occurs at >1.5 mg/L; Skeletal fluorosis at >3–6 mg/L. * **Other Defluoridation methods:** Activated Alumina (Prashanti technique), Ion exchange resins, and Reverse Osmosis. * **Nalgonda Technique sequence:** Alum (Removal) → Lime (pH adjustment) → Bleaching powder (Disinfection). * **Target:** It reduces fluoride to the permissible limit of <1.0 mg/L.

Q: Which of the following is NOT a feature of a septic tank?

Ideal retention period is 48 hours. ### Explanation A septic tank is a watertight masonry tank used for the primary treatment of domestic sewage. It operates on the principle of anaerobic digestion and sedimentation. **Why Option A is the Correct Answer (The False Statement):** The ideal retention period for a septic tank is **24 hours**, not 48 hours. While the retention period can range from 12 to 36 hours depending on the design and population load, 24 hours is the standard benchmark used in public health engineering. A period of 48 hours is unnecessarily long and would require a much larger tank capacity without significant added benefit. **Analysis of Other Options:** * **Option B (Minimum capacity is 500 gallons):** This is a standard technical requirement. A septic tank must be large enough to allow for the settling of solids and the formation of scum; 500 gallons is the recommended minimum capacity for a small household. * **Option C (Aerobic oxidation takes place outside):** This is a true statement. Inside the septic tank, only **anaerobic** digestion occurs. The effluent (liquid) that leaves the tank is still highly contaminated and must undergo **aerobic oxidation** in a subsoil dispersion trench or soak pit. * **Option D (Sludge is solids settling down):** This is the definition of sludge. In the tank, organic solids settle to the bottom (sludge) where they are decomposed by anaerobic bacteria, while lighter materials like fat and grease float to the top (scum). **High-Yield NEET-PG Pearls:** * **Biological Action:** The primary process inside the tank is **Anaerobic Digestion**. * **Cleaning Frequency:** Sludge should be removed at least once a year (or every 2–3 years depending on usage). * **Inlet/Outlet:** The outlet is usually 5 cm lower than the inlet to prevent backflow. * **Efficiency:** A septic tank removes about 60% of Suspended Solids and 30% of BOD (Biochemical Oxygen Demand).

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

Vital layer. ### 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.

Q: Which of the following chemicals is not included in the WHO's list of 10 chemicals of major public health concern?

Radium. The World Health Organization (WHO) has identified **10 chemicals or groups of chemicals** that constitute a major public health concern due to their widespread use, environmental persistence, and significant toxicity. **Explanation of the Correct Answer:** **D. Radium** is the correct answer because it is **not** included in the WHO’s top 10 list. While radium is a known radioactive hazard (linked to bone cancers and osteosarcoma), it is not considered a global "major public health concern" in the same category as the others, which have more pervasive environmental and industrial exposure routes affecting larger populations. **Explanation of Incorrect Options:** * **A. Arsenic:** Included. It is a major contaminant of groundwater in regions like West Bengal and Bangladesh, leading to chronic arsenicosis and skin/lung cancers. * **B. Asbestos:** Included. All forms of asbestos are carcinogenic, causing mesothelioma, lung cancer, and asbestosis. * **C. Dioxins:** Included. These are persistent organic pollutants (POPs) produced as by-products of industrial processes and waste incineration, known for their immunotoxic and reproductive effects. **High-Yield NEET-PG Facts:** To master this topic, memorize the complete **WHO List of 10 Chemicals of Major Public Health Concern**: 1. **Arsenic** 2. **Asbestos** 3. **Benzene** 4. **Cadmium** 5. **Dioxins and dioxin-like substances** 6. **Inadequate or excess Fluoride** 7. **Lead** (Most common cause of chronic metal poisoning) 8. **Mercury** (Associated with Minamata disease) 9. **Highly hazardous pesticides** 10. **Air pollution** (Specifically particulate matter and gases) **Clinical Pearl:** Note that **Lead** is often cited as the most important environmental toxin for children (neurotoxicity), while **Fluoride** is unique on this list because it is a concern in both deficiency (dental caries) and excess (fluorosis).

Q: All of the following are water-borne diseases except?

Scabies. **Explanation:** The classification of water-related diseases is a high-yield topic for NEET-PG. To answer this correctly, one must distinguish between **water-borne** and **water-washed** diseases. **1. Why Scabies is the correct answer:** Scabies is classified as a **water-washed disease**, not a water-borne disease. Water-washed diseases occur due to a lack of adequate water for personal hygiene and washing. When water is scarce, skin and eye infections spread easily through direct contact. Other examples include trachoma and pediculosis. **2. Why the other options are incorrect:** * **Salmonella (Typhoid/Paratyphoid):** These are classic **water-borne diseases**. They are transmitted via the feco-oral route when pathogenic microorganisms are ingested through contaminated drinking water. * **Cholera:** Caused by *Vibrio cholerae*, this is the prototype of water-borne diseases, often leading to explosive outbreaks when a common water source is contaminated. * **Hepatitis A:** This is a viral infection transmitted through the feco-oral route, primarily via contaminated water or food. **Clinical Pearls for NEET-PG:** * **Water-borne:** Ingesting contaminated water (e.g., Cholera, Typhoid, Amoebiasis, Giardiasis, Hepatitis A & E). * **Water-washed:** Lack of water for hygiene (e.g., Scabies, Trachoma, Conjunctivitis). * **Water-based:** Aquatic intermediate host involved (e.g., Schistosomiasis, Guinea worm). * **Water-related (Insect Vector):** Insects breeding in/near water (e.g., Malaria, Filariasis, Dengue). * **Note:** Hepatitis E is the most common cause of epidemic viral hepatitis in India, transmitted via the water-borne route.

Q: All are components of sewer gas except?

SO2. **Explanation:** The composition of **sewer gas** is a high-yield topic in Environmental Health, specifically concerning the anaerobic decomposition of organic matter in sewage systems. **Why SO2 is the correct answer:** Sewer gas is primarily a mixture of gases produced by the action of anaerobic bacteria on waste. **Sulfur Dioxide (SO2)** is typically a byproduct of industrial combustion (like burning fossil fuels) and is not a natural product of organic decomposition in sewers. Therefore, it is not a component of sewer gas. **Analysis of other options:** * **Methane (CH4):** This is a major component of sewer gas. It is highly flammable, odorless, and can lead to explosive hazards in confined spaces. * **Hydrogen Sulfide (H2S):** This is the most characteristic and dangerous component. It gives sewer gas its "rotten egg" odor. It is highly toxic and can cause "olfactory fatigue," where a person loses the ability to smell the gas before reaching lethal concentrations. * **Carbon Dioxide (CO2):** A common byproduct of the microbial breakdown of organic compounds, CO2 displaces oxygen in sewers, contributing to the risk of asphyxiation for sanitation workers. **NEET-PG High-Yield Pearls:** 1. **Primary Hazard:** The most immediate life-threatening gas in sewers is **Hydrogen Sulfide (H2S)**, which acts as a chemical asphyxiant similar to cyanide. 2. **Composition:** Sewer gas consists of Methane (approx. 25%), CO2 (approx. 5%), Nitrogen, and trace amounts of H2S and Ammonia. 3. **Occupational Health:** Workers entering manholes must follow the "Rule of Ventilation" and use gas detectors to check for oxygen deficiency and toxic gas buildup. 4. **Clinical Sign:** H2S poisoning can be identified by the smell of rotten eggs on the breath or clothing of the victim (though this disappears at high concentrations).

Question 1

The 'NALGONDA technique' is used in which condition?

Accepted Answer

Endemic fluorosis

Answer

Epidemic dropsy

Answer

Endemic ascites

Answer

Neurolathyrism

Question 2

An epidemiologic study evaluates the rate of dental caries and tooth abscesses among children living in communities within a metropolitan area. Investigators discover that the rate is high among children living in an upper-middle-class community but low in children living in a community below the poverty level. The levels of trace elements in the water supplies for those communities are measured. A higher level of which of the following minerals in the water is most likely to be associated with a lower rate of dental decay among the children living in the poor community?

Accepted Answer

Fluoride

Answer

Copper

Answer

Iodine

Answer

Selenium

Question 3

A known HIV-positive patient admitted in an isolation ward after abdominal surgery following an accident. The resident doctor who changed his dressing the next day found it to be soaked in blood. Which of the following would be the right method of choice for discarding the dressing?

Accepted Answer

Put the dressing material directly in an appropriate bag and send for incineration.

Answer

Pour 1% hypochlorite on the dressing material and send it for incineration in an appropriate bag.

Answer

Pour 5% hypochlorite on the dressing material and send it for incineration in an appropriate bag.

Answer

Pour 2% Lysol on the dressing material and send it for incineration in an appropriate bag.

Question 4

Which of the following is NOT a feature of a septic tank?

Accepted Answer

Ideal retention period is 48 hours

Answer

Minimum capacity is 500 gallons

Answer

Aerobic oxidation takes place outside

Answer

Sludge is solids settling down

Question 5

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

Accepted Answer

Vital layer

Answer

Valve

Answer

Supernatant water

Answer

Under-drainage system

Question 6

All of the following are indicators of air pollution except?

Accepted Answer

Smoking index

Answer

CO

Answer

SO2

Answer

Soiling index

Question 7

Which of the following chemicals is not included in the WHO's list of 10 chemicals of major public health concern?

Accepted Answer

Radium

Answer

Arsenic

Answer

Asbestos

Answer

Dioxin

Question 8

What are the proposed guideline values for Radioactivity in drinking water?

Accepted Answer

Gross alpha activity 0.1 Bq/L and Gross beta activity 1.0 Bq/L

Answer

Gross alpha activity 1.0 Bq/L and Gross beta activity 10.0 Bq/L

Answer

Gross alpha activity 1.0 Bq/L and Gross beta activity 0.1 Bq/L

Answer

Gross alpha activity 10 Bq/L and Gross beta activity 1.0 Bq/L

Question 9

All of the following are water-borne diseases except?

Accepted Answer

Scabies

Answer

Salmonella

Answer

Cholera

Answer

Hepatitis - A

Question 10

All are components of sewer gas except?

Accepted Answer

SO2

Answer

H2S

Answer

CO2

Answer

Methane

Environmental Health — MCQs

Environmental Health — MCQs

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