Environmental Health Practice Questions

Q: The 10-day rule is related to which of the following?

Radiation protection in pregnancy. ### Explanation **1. Why the Correct Answer is Right:** The **10-day rule** is a fundamental principle in radiation protection designed to prevent accidental fetal exposure to ionizing radiation. It states that non-emergency diagnostic X-rays of the abdomen or pelvis in women of reproductive age should be scheduled only during the **first 10 days of the menstrual cycle** (counting from the first day of the period). * **Medical Concept:** During this window, ovulation has not yet occurred, making it the safest time to ensure the woman is not pregnant. This minimizes the risk of teratogenicity or fetal death during the highly sensitive organogenesis period. **2. Why the Other Options are Wrong:** * **Sewage, Air, and Water Quality:** These fields use different standardized metrics. For example, sewage disposal is monitored by **BOD (Biological Oxygen Demand)**; air quality is measured by the **AQI (Air Quality Index)**; and water quality is assessed using **Coliform counts** or **Orthotolidine tests**. None of these environmental parameters utilize a "10-day" temporal rule for safety. **3. High-Yield Clinical Pearls for NEET-PG:** * **Evolution of the Rule:** The 10-day rule has largely been replaced by the **28-day rule** in many modern guidelines (which allows for imaging as long as the period is not overdue), but the "10-day rule" remains a classic and frequently tested concept in Community Medicine and Radiology exams. * **Most Sensitive Period:** The fetus is most sensitive to radiation-induced CNS effects between **8 to 15 weeks** of gestation. * **Dose Limit:** In pregnancy, the cumulative fetal dose of ionizing radiation should ideally not exceed **1 mSv** (or 5 mGy). * **Rule of 10 (Different Context):** Do not confuse this with the "Rule of 10" for Cleft Lip repair (10 weeks old, 10 lbs weight, 10 g hemoglobin).

Q: All of the following are methods of sewage disposal except?

Bangalore method (composting). **Explanation:** The core concept here is the distinction between **Sewage Disposal** (liquid waste) and **Refuse Disposal** (solid waste). **Why Option D is correct:** The **Bangalore Method (Anaerobic Composting)** is a method specifically designed for the disposal of **solid waste (refuse)** and night soil. Developed by Dr. Gilbert Fowler and C.N. Acharya, it involves layering refuse and night soil in trenches and allowing anaerobic decomposition over 4–6 months. Since it deals with solid waste rather than liquid sewage, it is the "except" in this list. **Why the other options are incorrect:** * **A. River Outfall:** This is a method of **primary sewage disposal** where sewage is discharged directly into a water body. It relies on the principle of "dilution" and the self-purifying capacity of river water (dissolved oxygen). * **B. Land Treatment:** Also known as sewage farming. Sewage is applied to land, where it undergoes biological oxidation. The soil acts as a filter, and the organic matter serves as fertilizer. * **C. Oxidation Ponds:** A **secondary (biological) treatment** method. It is a shallow pond where sewage is treated through the symbiotic relationship between algae (which provide oxygen) and bacteria (which decompose organic matter). **High-Yield Clinical Pearls for NEET-PG:** * **Composting:** Bangalore method is **anaerobic** (no turning required); Indore method is **aerobic** (requires frequent turning). * **Sewage Strength:** Measured by **BOD (Biochemical Oxygen Demand)**. Normal BOD of domestic sewage is approx. 300 mg/L. * **Eutrophication:** A potential complication of river outfall where excess nutrients (Nitrates/Phosphates) lead to algal blooms and oxygen depletion. * **Modern Sewage Treatment:** Follows the sequence: Primary (Physical) → Secondary (Biological/Oxidation) → Tertiary (Chemical/Disinfection).

Q: Which of the following organisms, due to its easy culture methods, is widely used as an indicator of water pollution?

Escherichia coli. **Explanation:** **Escherichia coli (E. coli)** is considered the best indicator of recent faecal pollution of water. It is a member of the coliform group that resides exclusively in the intestines of humans and warm-blooded animals. It is the preferred indicator because: 1. It is present in large numbers in human faeces. 2. It cannot multiply in water but survives long enough to be detected. 3. **Crucially for this question:** It is easily detectable and can be cultured using simple, rapid, and inexpensive methods (e.g., MacConkey agar or membrane filtration). **Analysis of Incorrect Options:** * **A. Faecal streptococci:** These are also indicators of faecal pollution and survive longer in water than *E. coli*. However, they are used primarily to differentiate between human and animal pollution (via the Streptococcus/Coliform ratio) and are not as easily or routinely cultured as *E. coli*. * **C. Clostridium perfringens:** These are spore-formers and survive for very long periods, even resisting chlorination. They indicate **remote (past) pollution** rather than recent contamination. * **D. Salmonella Typhi:** This is a pathogen, not an indicator organism. Pathogens are usually present in low numbers and are difficult to isolate directly from water; hence, we look for "indicators" like *E. coli* instead. **High-Yield Pearls for NEET-PG:** * **Ideal Indicator:** Must be present when pathogens are present and absent when they are absent. * **Coliform Count:** The standard measure of water bacteriology. * **Presumptive Coliform Test:** Uses Multiple Tube Fermentation method to estimate the **MPN (Most Probable Number)**. * **Eijkman Test:** A rapid test for *E. coli* performed at 44°C to confirm faecal origin.

Q: Which technique is used for the defluoridation of water?

Nalgonda technique. **Explanation:** The **Nalgonda technique** is the most widely used method for defluoridation of water at the community and household levels in India. Developed by the National Environmental Engineering Research Institute (NEERI), Nagpur, it involves the sequential addition of **Alum (Aluminium salts)**, **Lime (Calcium carbonate)**, and **Bleaching powder** to water, followed by rapid mixing, flocculation, sedimentation, and filtration. * **Mechanism:** Alum acts as the coagulant that removes fluoride ions through adsorption and precipitation. Lime is added to maintain the pH and facilitate settling, while bleaching powder ensures disinfection. It is preferred because it is cost-effective and easy to operate. **Analysis of Incorrect Options:** * **B. Soaking:** This is a step used in food preparation (e.g., legumes) to reduce anti-nutrients or in the parboiling process, but it has no role in removing chemical ions like fluoride from water. * **C. Sand filter:** Slow or rapid sand filters are used for removing physical turbidity and biological pathogens (bacteria/parasites) from water. They are ineffective at removing dissolved chemical solutes like fluoride. * **D. Parboiling:** This is a hydrothermal process used in rice milling to improve nutritional value (retaining Vitamin B12) and storage quality. It does not affect the fluoride content of water. **High-Yield Clinical Pearls for NEET-PG:** * **Safe Fluoride Levels:** The WHO recommended level is **0.5–1.0 mg/L**. * **Dental Fluorosis:** Occurs when levels exceed **1.5 mg/L** (mottling of enamel). * **Skeletal Fluorosis:** Occurs with chronic intake of **3–6 mg/L** (crippling deformity). * **Alternative Method:** **Krutti technique** (using activated alumina) is another method for defluoridation. * **Reverse Osmosis (RO):** The most effective modern household method for fluoride removal.

Q: Hardness of water is expressed as milli-equivalent per litre (mEq/L). One unit of mEq/L is equivalent to which one of the following?

50 mg CaCO3 (50 ppm). ### Explanation **1. Why Option D is Correct:** The hardness of water is primarily caused by calcium and magnesium ions. In public health and environmental chemistry, hardness is conventionally expressed in terms of **Calcium Carbonate (CaCO₃) equivalents**. To convert milli-equivalents per litre (mEq/L) to mg/L (ppm), we use the formula: * **Weight (mg) = mEq × Equivalent Weight** * The molecular weight of CaCO₃ is 100. Since Calcium is divalent ($Ca^{2+}$), its valency is 2. * **Equivalent Weight of CaCO₃** = Molecular Weight / Valency = 100 / 2 = **50**. * Therefore, 1 mEq/L of hardness = 1 × 50 mg/L = **50 mg/L (or 50 ppm)** of CaCO₃. **2. Why Other Options are Incorrect:** * **Options A, B, and C (20, 30, 40 mg/L):** These values do not correspond to the equivalent weight of Calcium Carbonate. Selecting these would imply an incorrect calculation of the chemical equivalent or molecular weight of the reference salt used to measure hardness. **3. High-Yield Clinical Pearls for NEET-PG:** * **Classification of Hardness (WHO/Park):** * **Soft:** 0–60 mg/L * **Moderately hard:** 60–120 mg/L * **Hard:** 120–180 mg/L * **Very hard:** >180 mg/L * **Health Impact:** Hard water is not proven to cause adverse health effects; however, very hard water is associated with increased soap consumption and scale formation in pipes. Some studies suggest a weak inverse correlation between water hardness and cardiovascular disease (protective effect). * **Removal:** Temporary hardness (carbonates) is removed by **boiling** or adding **lime**. Permanent hardness (sulfates/chlorides) requires methods like the **Permutit (ion-exchange) process**.

Q: Which element is often referred to as a "double-edged sword" in public health due to its benefits in preventing dental caries but potential for harm at higher concentrations?

Fluorine. ### Explanation **Correct Answer: B. Fluorine** Fluorine is famously known as a **"double-edged sword"** in public health because of its narrow therapeutic index. Its effects are strictly dose-dependent: 1. **The Benefit:** At optimal levels (0.5–0.8 mg/L in drinking water), it prevents dental caries by reducing the solubility of enamel in acids and promoting remineralization. 2. **The Harm:** At higher concentrations (>1.5 mg/L), it leads to **Dental Fluorosis** (mottling of enamel). At levels >3–10 mg/L, prolonged exposure causes **Skeletal Fluorosis**, characterized by increased bone density, calcification of ligaments, and "knock-knees" (Genu valgum). --- ### Why the other options are incorrect: * **A. Chlorine:** Used primarily for water disinfection. While excessive chlorine can cause taste issues or form trihalomethanes, it is not characterized by the specific "double-edged" benefit-to-toxicity ratio regarding dental health. * **C. Lead:** A pure environmental toxin with no known physiological benefit to humans. It causes plumbism, anemia, and neurotoxicity. * **D. Selenium:** While also a trace element with a narrow safety range (essential for glutathione peroxidase but toxic in excess), it is not the classic answer associated with dental caries prevention in public health terminology. --- ### NEET-PG High-Yield Pearls: * **Safe Limit:** The WHO guideline for fluoride in drinking water is **1.5 mg/L**. * **Defluoridation:** The **Nalgonda Technique** (using alum and lime) is the most common method used in India for removing excess fluoride. * **Clinical Sign:** **Mottling of teeth** is the earliest sign of dental fluorosis; it is permanent and occurs during the period of tooth formation. * **Skeletal Fluorosis:** Primarily affects the spine and small joints; "Crippling fluorosis" occurs with long-term intake of >10 mg/day.

Question 1

Hardness of water has a beneficial effect on which one of the following?

Accepted Answer

Cardiovascular diseases

Answer

Renal diseases

Answer

Metabolic diseases

Answer

Cerebrovascular diseases

Question 2

The 10-day rule is related to which of the following?

Accepted Answer

Radiation protection in pregnancy

Answer

Sewage disposal

Answer

Air quality

Answer

Water quality

Question 3

All of the following are methods of sewage disposal except?

Accepted Answer

Bangalore method (composting)

Answer

River outfall

Answer

Land treatment

Answer

Oxidation ponds

Question 4

Which of the following organisms, due to its easy culture methods, is widely used as an indicator of water pollution?

Accepted Answer

Escherichia coli

Answer

Faecal streptococci

Answer

Clostridium perfringens

Answer

Salmonella Typhi

Question 5

Which of the following should not be incinerated as it contains cadmium?

Accepted Answer

Red

Answer

Blue

Answer

Black

Answer

Yellow

Question 6

Which technique is used for the defluoridation of water?

Accepted Answer

Nalgonda technique

Answer

Soaking

Answer

Sand filter

Answer

Parboiling

Question 7

Hardness of water is expressed as milli-equivalent per litre (mEq/L). One unit of mEq/L is equivalent to which one of the following?

Accepted Answer

50 mg CaCO3 (50 ppm)

Answer

20 mg CaCO3 (20 ppm)

Answer

30 mg CaCO3 (30 ppm)

Answer

40 mg CaCO3 (40 ppm)

Question 8

Which element is often referred to as a "double-edged sword" in public health due to its benefits in preventing dental caries but potential for harm at higher concentrations?

Accepted Answer

Fluorine

Answer

Chlorine

Answer

Lead

Answer

Selenium

Question 9

A known HIV-positive patient is 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 10

What is the recommended daily per capita water consumption?

Accepted Answer

150-200 litres

Answer

50-100 litres

Answer

100-150 litres

Answer

200-250 litres

Environmental Health — MCQs

Environmental Health — MCQs

On this page

Practice by Chapter

Want unlimited practice?