Environmental Health Practice Questions

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.

Q: Radon exposure is known to cause which of the following?

Carcinoma lung. **Explanation:** **Radon (Rn-222)** is a colorless, odorless, radioactive noble gas produced by the natural decay of Uranium-238 found in soil and rocks. It is the **second leading cause of lung cancer** globally, trailing only tobacco smoking. 1. **Why Carcinoma Lung is Correct:** Radon decays into short-lived alpha-emitting particles (Radon progeny). When inhaled, these particles deposit in the respiratory epithelium. The high-energy **alpha particles** cause direct DNA damage and double-strand breaks in the bronchial epithelial cells, leading to carcinogenesis. In the context of NEET-PG, remember that radon is the most significant source of natural background radiation exposure for the general public. 2. **Why Other Options are Incorrect:** * **Leukemia:** While high-dose ionizing radiation (like X-rays or gamma rays) is a known risk factor for leukemia, the alpha particles from Radon have low penetrative power and primarily affect the site of contact (the lungs). * **Carcinoma Colon & Brain Tumors:** There is no established epidemiological evidence linking radon inhalation to these malignancies. Radon is an inhalation hazard; its systemic absorption is negligible compared to its localized effect on the pulmonary system. **High-Yield Clinical Pearls for NEET-PG:** * **Synergistic Effect:** The risk of lung cancer from radon is significantly higher (multiplicative) in **smokers** compared to non-smokers. * **Indoor Air Pollution:** Radon levels are highest in poorly ventilated basements and underground mines (e.g., uranium miners). * **Measurement:** Radon levels are measured in **Becquerels per cubic meter (Bq/m³)** or PicoCuries per liter (pCi/L). * **Type of Radiation:** Radon is an **Alpha emitter**.

Q: The total volume of sewage flowing in a system over a 24-hour period is referred to as:

Dry weather flow. ### Explanation **Correct Answer: B. Dry weather flow** In environmental engineering and public health, **Dry Weather Flow (DWF)** is defined as the total quantity of sewage flowing through a sewerage system in a 24-hour period during dry weather. It primarily consists of domestic sewage and industrial waste, excluding any contribution from rainwater or surface runoff. This measurement is critical for designing sewage treatment plants (STPs) and determining the capacity of sewer pipes to ensure they can handle the daily load without overflow. **Analysis of Incorrect Options:** * **A. Sewage rate:** This is a generic term and not a standardized technical definition in environmental health. Flow is typically measured as a "rate" (e.g., liters per second), but the 24-hour cumulative volume is specifically DWF. * **C. RCA index:** The Research cum Action (RCA) latrine is a specific type of sanitary latrine designed for rural India. The "RCA index" is not a standard term for sewage volume; rather, RCA refers to the design standards for rural sanitation. * **D. Sludge:** Sludge is the solid matter that settles at the bottom of a sedimentation tank during sewage treatment. It is a byproduct of the process, not a measure of the liquid flow volume. **High-Yield Clinical Pearls for NEET-PG:** * **Strength of Sewage:** Determined by **Biochemical Oxygen Demand (BOD)**. Normal BOD of domestic sewage is approx. **300 mg/L**. * **Sewerage vs. Sewage:** *Sewage* is the waste water; *Sewerage* is the infrastructure (pipes/pumps) that carries it. * **Self-Purification:** Rivers purify themselves through dilution, sedimentation, and oxidation. * **Eutrophication:** Excessive nutrients (Nitrates/Phosphates) in water leading to algal blooms and oxygen depletion.

Question 1

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 2

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

Accepted Answer

Red

Answer

Blue

Answer

Black

Answer

Yellow

Question 3

Which technique is used for the defluoridation of water?

Accepted Answer

Nalgonda technique

Answer

Soaking

Answer

Sand filter

Answer

Parboiling

Question 4

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 5

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 6

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 7

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

Question 8

Which of the following wastes should NOT be incinerated?

Accepted Answer

Wastes with a moisture content above 30%

Answer

Wastes with a low heating volume

Answer

Wastes whose content of combustible matter is above 60%

Answer

Wastes whose content of non-combustible material is high

Question 9

Radon exposure is known to cause which of the following?

Accepted Answer

Carcinoma lung

Answer

Leukemia

Answer

Carcinoma colon

Answer

Brain tumors

Question 10

The total volume of sewage flowing in a system over a 24-hour period is referred to as:

Accepted Answer

Dry weather flow

Answer

Sewage rate

Answer

RCA index

Answer

Sludge

Environmental Health — MCQs

Environmental Health — MCQs

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