Environmental Health Practice Questions

Q: What is the amount of bleaching powder required to disinfect 455 litres of water if 4, 5, and 6 cups show distinct colouration in Horrock's apparatus?

8 g. ### Explanation **1. Understanding the Calculation (Why B is Correct):** Horrock’s apparatus is used to estimate the chlorine demand of water. The test uses 6 cups, each containing a specific amount of bleaching powder solution. The **first cup** that shows a distinct blue color (indicating the presence of free residual chlorine) determines the amount of bleaching powder needed for **455 liters** of water. * **Rule of Horrock’s Apparatus:** The number of the first cup showing color indicates the number of **level teaspoons** (each teaspoon ≈ 2 grams) of bleaching powder required to disinfect **455 liters** (100 gallons) of water. * In this question, the 4th, 5th, and 6th cups show coloration. The **first** cup to show color is the **4th cup**. * Calculation: $4 \text{ (cup number)} \times 2 \text{ grams} = \mathbf{8 \text{ grams}}$. **2. Analysis of Incorrect Options:** * **Option A (2 g):** This would be the requirement if only the 1st cup showed color. * **Option D (4 g):** This would be the requirement if the 2nd cup was the first to show color. * **Option C (6 g):** This would be the requirement if the 3rd cup was the first to show color. **3. High-Yield Clinical Pearls for NEET-PG:** * **Contact Time:** After adding bleaching powder, a contact time of **30 minutes** is mandatory before the water is considered safe for consumption. * **Free Residual Chlorine:** The goal of chlorination is to leave a residual chlorine level of **0.5 mg/L** after 30 minutes. * **OT Test (Orthotolidine):** Used to measure both free and combined chlorine. The **OTA (Orthotolidine Arsenite)** test is preferred as it distinguishes free chlorine from chloramines and false positives (like nitrites/iron). * **Bleaching Powder Composition:** Fresh bleaching powder contains approximately **33% available chlorine**. It is unstable and loses chlorine content on exposure to light and air.

Q: What is the residual chlorine level required for a normal potable water supply system?

0.5 mg/L. ### Explanation **Core Concept: Chlorination of Water** Chlorination is the most common method of water disinfection. For effective disinfection, the "Chlorine Demand" of the water must first be met. The **Residual Chlorine** is the amount of chlorine remaining in the water after the demand is satisfied. According to standard public health guidelines (WHO and CPHEEO), a free residual chlorine level of **0.5 mg/L** is required for a contact period of at least **one hour**. This ensures the destruction of pathogenic bacteria and viruses while providing a "safety margin" to protect the water against subsequent post-treatment contamination during distribution. **Analysis of Options:** * **A (0.5 mg/L):** Correct. This is the standard recommended level for routine potable water supply to ensure biological safety. * **B (1 mg/L):** This level is typically maintained during emergencies or outbreaks (e.g., Cholera epidemics) to provide extra disinfection power. * **C (0.1 mg/L):** This is the minimum acceptable level at the consumer's tap (tail-end of the distribution system), but it is not the target level for the supply system. * **D (2.5 mg/L):** This is excessively high for routine supply and would result in an unpleasant taste and odor, leading to consumer dissatisfaction. **High-Yield NEET-PG Pearls:** * **Contact Time:** Minimum 30–60 minutes is essential for chlorine to act. * **OT Test (Orthotolidine Test):** Used to detect both free and combined chlorine (reads color within 10 seconds). * **OTA Test (Orthotolidine Arsenite Test):** Specifically used to differentiate between **Free Residual Chlorine** and Chloramines. * **Horrocks' Apparatus:** Used to estimate the "Chlorine Demand" of water, especially in camp settings. * **Cyclops:** Chlorine is effective against most pathogens but **not** effective against *Cyclops* (requires physical filtration or boiling) or highly resistant cysts like *Cryptosporidium*.

Q: Malathion is used once every?

3 months. **Explanation:** Malathion is an organophosphorus insecticide used in public health programs for **Residual Insecticide Spraying (RIS)** to control vectors, primarily the *Anopheles* mosquito (Malaria) and *Phlebotomus* (Kala-azar). **1. Why 3 Months is Correct:** The effectiveness of a residual spray depends on its **residual action**—the duration it remains lethal to insects on treated surfaces. Malathion (applied at a dosage of 2g/m²) has a residual life of approximately **10 to 12 weeks**. Therefore, to maintain an effective barrier against vectors, it must be reapplied every **3 months**. This frequency ensures that the concentration of the insecticide does not fall below the threshold required to kill mosquitoes resting on walls. **2. Why Incorrect Options are Wrong:** * **6 months:** This is the standard interval for **DDT** (Dichloro-diphenyl-trichloroethane), which has a much longer residual effect (6 months) compared to Malathion. * **9 and 12 months:** These intervals are too long for any currently used residual insecticide in public health. By this time, the chemical would have degraded or been covered by dust/soot, leading to a total loss of vector control and potential outbreaks. **High-Yield Clinical Pearls for NEET-PG:** * **Dosage:** Malathion is used at **2 g/m²** for residual spraying. * **Mechanism:** It is an acetylcholinesterase inhibitor. * **Safety:** It is preferred over DDT in areas with DDT resistance because it is less persistent in the environment and has low mammalian toxicity (due to rapid detoxification by plasma esterases in humans). * **Space Spray:** For ultra-low volume (ULV) fogging during epidemics, Malathion is also the drug of choice. * **Antidote:** In case of poisoning, the specific antidote is **Pralidoxime (PAM)** along with Atropine.

Q: Indoor air pollution does not lead to which of the following?

Impaired neurological development. **Explanation:** Indoor air pollution (IAP), primarily caused by the combustion of solid fuels (biomass, coal, dung) in poorly ventilated kitchens, is a major public health challenge. The primary pollutants involved are particulate matter (PM2.5), carbon monoxide (CO), and polycyclic aromatic hydrocarbons. **Why "Impaired Neurological Development" is the correct answer:** While chronic exposure to air pollution is being researched for potential cognitive links, it is **not** currently established as a direct, primary consequence of indoor air pollution in standard medical textbooks (like Park’s PSM). The classic morbidity profile of IAP focuses on respiratory and reproductive systems rather than neurodevelopmental disorders. **Analysis of Incorrect Options:** * **Chronic Lung Disease:** Long-term exposure to smoke leads to Chronic Obstructive Pulmonary Disease (COPD) and chronic bronchitis, especially in women who spend significant time cooking. * **Adverse Pregnancy Outcomes:** CO and particulate matter cross the placental barrier, leading to systemic inflammation and reduced oxygen delivery. This is a proven cause of Low Birth Weight (LBW) and stillbirths. * **Pneumonia in Children:** IAP is a leading risk factor for Acute Lower Respiratory Infections (ALRI) in children under five, as their developing lungs are highly susceptible to irritants. **High-Yield Clinical Pearls for NEET-PG:** * **The "Chulha" Effect:** Biomass fuel use is the strongest risk factor for IAP in rural India. * **Kerosene:** Often mistaken as "clean," it is a significant source of IAP (PM and CO). * **Cancer Link:** IAP is a known risk factor for nasopharyngeal and lung cancers. * **Indicator:** The most common indicator used to measure IAP is **Particulate Matter (PM2.5)**.

Q: What color does the indicator used in Horrock's apparatus produce in the presence of residual chlorine?

Blue. **Explanation:** **Horrock’s Apparatus** is a field-level tool used to estimate the dose of bleaching powder required to disinfect a given quantity of water. It is a cornerstone of rural environmental health and a high-yield topic for NEET-PG. **1. Why Blue is Correct:** The indicator used in Horrock’s apparatus is **Starch-Iodide**. When bleaching powder is added to water, it releases free chlorine. If the chlorine demand of the water is met and residual chlorine remains, it reacts with the potassium iodide in the indicator to release free iodine. This free iodine then reacts with starch to form a characteristic **blue-colored complex**. The first cup in the series that shows a distinct blue color indicates the amount of bleaching powder needed for disinfection. **2. Why Other Options are Incorrect:** * **Yellow:** This color is associated with the **Orthotolidine (OT) test**, where residual chlorine produces a yellow color. While the OT test measures the *presence* of chlorine, Horrock’s apparatus uses starch-iodide to *calculate the dose*. * **Green/Red:** These colors are not associated with standard chlorine estimation tests in community medicine. **High-Yield Clinical Pearls for NEET-PG:** * **Contents:** The apparatus contains 6 white cups (each 200ml), 1 black cup, 2 metal spoons (2g each), and the starch-iodide indicator. * **Calculation:** If the $n^{th}$ cup shows the blue color, then $n \times 2$ grams of bleaching powder are required to disinfect 455 liters (100 gallons) of water. * **Contact Time:** The blue color should be observed after a contact time of **30 minutes**. * **Bleaching Powder:** Ideally contains **33% available chlorine**. It is unstable and loses chlorine on exposure to air, light, or moisture.

Q: A confirmed case of fluorosis is defined by the presence of fluoride in urine more than which of the following values?

1 mg/L. **Explanation:** The diagnosis of Fluorosis is based on clinical presentation and biochemical markers. Fluoride is primarily excreted through the kidneys; therefore, urinary fluoride levels are the most sensitive and reliable indicator of recent fluoride exposure. **1. Why Option A is Correct:** According to the World Health Organization (WHO) and the National Programme for Prevention and Control of Fluorosis (NPPCF) in India, a **urinary fluoride level >1.0 mg/L** is considered the diagnostic threshold for a confirmed case of fluorosis. This indicates that the individual is consuming fluoride in excess of the permissible limits (usually >1.5 mg/L in drinking water), leading to systemic accumulation. **2. Why Other Options are Incorrect:** * **Options B, C, and D (3, 5, and 7 mg/L):** These values represent significantly higher concentrations. While these levels are frequently seen in patients with advanced skeletal fluorosis, they are not the *minimum* threshold for diagnosis. Using these higher values would lead to under-diagnosis of early-stage cases. **High-Yield Clinical Pearls for NEET-PG:** * **Permissible Limit in Water:** The ideal level is **0.5–0.8 mg/L**. The "Upper Permissible Limit" is **1.0 mg/L** (WHO) or up to **1.5 mg/L** (BIS, if no alternative source is available). * **Dental Fluorosis:** Occurs when fluoride levels exceed **1.5 mg/L**. It manifests as "Mottling of Enamel." * **Skeletal Fluorosis:** Occurs with prolonged exposure to levels **>3–6 mg/L**. Characteristic signs include "Poker Back" (stiff spine) and "Genu Valgum" (Knock-knees). * **Nalgonda Technique:** A common community-level method for defluoridation using **Alum and Lime**. * **Safe Limit:** Fluoride is often called a "double-edged sword" because 1.5 mg/L leads to fluorosis.

Q: Kata thermometer is used to measure which of the following?

Cooling power of air. **Explanation:** The **Kata Thermometer**, developed by Leonard Hill, is a specialized alcohol thermometer used primarily to measure the **cooling power of air**. 1. **Why Option D is correct:** The cooling power of air depends on the combined effect of air temperature, humidity, and air velocity. The Kata thermometer measures the time taken for the alcohol level to fall from 100°F to 95°F (38°C to 35°C). This duration reflects how quickly the environment can remove heat from a surface, which is a crucial indicator of thermal comfort and ventilation efficiency in occupational settings. 2. **Why other options are incorrect:** * **Options A & B (Maximum/Minimum temperature):** These are measured using a **Six’s Maximum and Minimum Thermometer**, which records the highest and lowest temperatures reached during a 24-hour period. * **Option C (Radiant heat):** Radiant heat (infrared radiation) is measured using a **Globe Thermometer**. It consists of a standard thermometer bulb encased in a 6-inch hollow copper sphere painted matte black. **High-Yield Clinical Pearls for NEET-PG:** * **Air Velocity:** While the Kata thermometer was originally designed for cooling power, it is now more frequently used as an **anemometer** to measure low air velocities (below 1 m/s). * **Dry vs. Wet Kata:** A "Dry Kata" measures cooling by radiation and convection, while a "Wet Kata" (bulb covered with a wet silk wick) also accounts for cooling by evaporation. * **Psychrometer (Hygrometer):** Used to measure **humidity** (Dry and Wet bulb temperatures). * **Anemometer:** Used specifically for **wind speed/air velocity**.

Question 1

What is the amount of bleaching powder required to disinfect 455 litres of water if 4, 5, and 6 cups show distinct colouration in Horrock's apparatus?

Accepted Answer

8 g

Answer

2 g

Answer

6 g

Answer

4 g

Question 2

In the bioaccumulation of DDT in the aquatic food chain of Plankton 
 Clams 
 Fish 
 Fish-eating birds, which group of organisms exhibits the highest concentration of DDT?

Accepted Answer

Fish-eating birds

Answer

Plankton

Answer

Clams

Answer

Fish

Question 3

What is the residual chlorine level required for a normal potable water supply system?

Accepted Answer

0.5 mg/L

Answer

1 mg/L

Answer

0.1 mg/L

Answer

2.5 mg/L

Question 4

Malathion is used once every?

Accepted Answer

3 months

Answer

6 months

Answer

9 months

Answer

12 months

Question 5

Which of the following is NOT an advantage of ground water?

Accepted Answer

It is likely to be hard.

Answer

It is likely to be free from pathogenic organisms.

Answer

It usually requires no treatment.

Answer

The supply is likely to be certain even during the dry season.

Question 6

Indoor air pollution does not lead to which of the following?

Accepted Answer

Impaired neurological development

Answer

Chronic lung disease

Answer

Adverse pregnancy outcomes

Answer

Pneumonia in children

Question 7

Sewage is defined as:

Accepted Answer

Wastewater from a community containing solid and liquid excreta

Answer

Discarded waste arising from human activities

Answer

Waste matter arising from preparation, cooking and consumption of food

Answer

Wastewater which does not contain human excreta

Question 8

What color does the indicator used in Horrock's apparatus produce in the presence of residual chlorine?

Accepted Answer

Blue

Answer

Yellow

Answer

Green

Answer

Red

Question 9

A confirmed case of fluorosis is defined by the presence of fluoride in urine more than which of the following values?

Accepted Answer

1 mg/L

Answer

3 mg/L

Answer

5 mg/L

Answer

7 mg/L

Question 10

Kata thermometer is used to measure which of the following?

Accepted Answer

Cooling power of air

Answer

Maximum temperature

Answer

Minimum temperature

Answer

Radiant heat

Environmental Health — MCQs

Environmental Health — MCQs

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