Environmental Health Practice Questions

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: Which of the following is a marker of fecal contamination?

E. coli. **Explanation:** The presence of **Escherichia coli (E. coli)** in water is the most reliable indicator of recent fecal contamination. In public health and environmental engineering, E. coli is classified as a **"fecal indicator organism."** It is a normal inhabitant of the intestinal tract of humans and warm-blooded animals. Since it does not typically multiply in the environment and has a survival time similar to many waterborne bacterial pathogens (like *Vibrio cholerae* or *Salmonella typhi*), its detection in a water sample serves as a definitive marker that the water has been contaminated with feces and is unsafe for consumption. **Analysis of Options:** * **Ascaris lumbricoides:** While its eggs are transmitted via the fecal-oral route, it is a helminthic parasite and not used as a standard microbiological indicator for routine water quality testing. * **Guinea worm (Dracunculus medinensis):** This is transmitted by drinking water containing infected **cyclops** (crustaceans). It indicates the presence of an intermediate host, not general fecal contamination. * **Balantidium coli:** This is a ciliated protozoan primarily associated with pigs. While it can cause human infection via fecal-oral spread, it is not a standard index organism for monitoring water safety. **High-Yield NEET-PG Pearls:** * **Coliform Count:** The most common method to assess water quality. E. coli is the "gold standard" indicator because it is specific to fecal matter. * **Virological Indicator:** Coliphages (viruses that infect E. coli) are often used as indicators of viral contamination in water. * **Clostridium perfringens:** Used as an indicator of **remote (past) fecal contamination** because its spores are highly resistant and survive longer than E. coli. * **Fecal Streptococci:** Their presence indicates fecal pollution in the absence of E. coli or can help differentiate between human and animal fecal sources.

Q: What is the recommended per capita allowance of water per day?

150-200 liters. **Explanation:** In Community Medicine, the per capita allowance of water is a critical indicator of environmental sanitation and quality of life. According to standard public health guidelines (including the Park’s Textbook of Preventive and Social Medicine), a daily supply of **150-200 liters per head** is considered an adequate standard for an average Indian town to meet all domestic needs, including drinking, cooking, bathing, washing, and flushing toilets. **Why Option D is Correct:** This range (150-200 L) is the benchmark for urban planning. It ensures not only personal hygiene but also the efficient operation of a water-carriage sewerage system, which requires a minimum flow to prevent clogging. **Analysis of Incorrect Options:** * **Options A & B (70-120 liters):** These amounts are considered insufficient for urban areas with modern sanitation. While 70-100 liters might suffice for basic survival or rural settings without piped sewerage, it does not meet the "recommended" standard for comprehensive domestic health. * **Option C (120-150 liters):** While closer to the target, it falls on the lower end of the spectrum and may not account for the peak demands or the technical requirements of urban waste disposal systems. **High-Yield NEET-PG Pearls:** * **Minimum Requirement:** The absolute minimum water required for physiological survival is approximately **2 liters per day**, but for overall health, the WHO recommends at least **15-20 liters** for basic hygiene. * **Water Hardness:** Hardness is expressed in mEq/L or mg/L of $CaCO_3$. "Soft" water is < 1 mEq/L (50 mg/L). * **Chlorination:** The "Free Residual Chlorine" should be **0.5 mg/L** after a contact time of 60 minutes. * **Horrocks' Apparatus:** Used to estimate the dose of bleaching powder required to disinfect a given quantity of water.

Q: Which of the following is not a greenhouse gas?

Nitrogen (N2). **Explanation:** The greenhouse effect is a natural process where certain atmospheric gases trap heat, maintaining the Earth's temperature. To be a **greenhouse gas (GHG)**, a molecule must be able to absorb and emit infrared radiation, which typically requires a complex molecular structure (triatomic or larger) or asymmetry. **Why Nitrogen (N2) is the correct answer:** Nitrogen (N2) makes up about 78% of the Earth's atmosphere. However, it is a **homonuclear diatomic molecule** (two identical atoms bonded together). Because it is symmetrical and has no dipole moment, it cannot absorb infrared radiation. Therefore, it does not contribute to the greenhouse effect. **Analysis of Incorrect Options:** * **Carbon dioxide (CO2):** The most abundant anthropogenic GHG. It is the primary contributor to global warming due to fossil fuel combustion. * **Methane (CH4):** A potent GHG with a much higher "Global Warming Potential" (GWP) than CO2. Major sources include livestock (enteric fermentation), rice paddies, and landfills. * **Sulfur dioxide (SO2):** While not a direct greenhouse gas (it actually has a cooling effect by reflecting sunlight), it is often discussed in environmental health. However, in the context of this question, **Nitrogen** is the definitive "non-greenhouse" gas among the choices. **High-Yield Facts for NEET-PG:** * **Major GHGs:** Water vapor (most abundant naturally), CO2, Methane (CH4), Nitrous Oxide (N2O), Chlorofluorocarbons (CFCs), and Ozone (O3). * **Kyoto Protocol:** An international treaty aimed at reducing the emission of six specific GHGs to combat global warming. * **Health Impact:** Global warming leads to the expansion of vector habitats (e.g., Malaria, Dengue), heat-related illnesses, and respiratory issues due to increased ground-level ozone. * **Note:** Do not confuse **Nitrogen (N2)** with **Nitrous Oxide (N2O)**; the latter is a very potent greenhouse gas.

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 is the maximum flight distance of a sandfly?

50 yards. **Explanation:** The sandfly (*Phlebotomus argentipes*), the primary vector for Kala-azar (Visceral Leishmaniasis), is a small, delicate insect characterized by its weak flying ability. Unlike mosquitoes, sandflies do not fly in long, continuous stretches; instead, they exhibit a characteristic **"hopping" or "jerking" flight pattern**. **Why 50 yards is correct:** Due to their small size and fragile wings, sandflies are highly susceptible to wind currents and lack the stamina for long-distance travel. Their effective flight range is extremely limited, typically not exceeding **50 yards (approx. 45 meters)** from their breeding sites (usually damp soil, cattle sheds, or cracks in mud walls). This limited range is a critical epidemiological factor, as it means the risk of infection is localized to the immediate vicinity of the vector's breeding habitat. **Analysis of Incorrect Options:** * **Options B, C, and D (100, 200, 300 yards):** These distances significantly overestimate the sandfly's physiological capability. While wind may occasionally drift a sandfly further, their active, self-propelled flight is restricted to the 50-yard limit. **High-Yield Clinical Pearls for NEET-PG:** * **Size:** Sandflies are about 1/4th the size of a mosquito (approx. 2.5 mm). * **Feeding Habit:** Only the **female** sandfly bites (hematophagous). They are nocturnal feeders. * **Life Cycle:** The duration from egg to adult is approximately **1 to 2 months**. * **Control Measure:** Because they are weak fliers, they cannot hop higher than the first floor of a building; therefore, sleeping on upper floors or using fine-mesh insecticide-treated nets (ITNs) is an effective preventive strategy. * **Drug of Choice for Kala-azar:** Liposomal Amphotericin B (single dose).

Question 1

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 2

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 3

Malathion is used once every?

Accepted Answer

3 months

Answer

6 months

Answer

9 months

Answer

12 months

Question 4

Which of the following is a marker of fecal contamination?

Accepted Answer

E. coli

Answer

Ascaris

Answer

Presence of Guinea worm

Answer

Balantidium coli

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

What is the recommended per capita allowance of water per day?

Accepted Answer

150-200 liters

Answer

70-80 liters

Answer

80-120 liters

Answer

120-150 liters

Question 7

Which of the following is not a greenhouse gas?

Accepted Answer

Nitrogen (N2)

Answer

Carbon dioxide (CO2)

Answer

Sulfur dioxide (SO2)

Answer

Methane

Question 8

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 9

What is the maximum flight distance of a sandfly?

Accepted Answer

50 yards

Answer

100 yards

Answer

200 yards

Answer

300 yards

Question 10

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

Environmental Health — MCQs

Environmental Health — MCQs

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