Environmental Health — MCQs

Environmental Health Indian Medical PG Practice Questions and MCQs

Question 431: What is the upper limit of noise exposure, in decibels (dB), up to which there is no damage to hearing?

A. 160 dB
B. 70 dB
C. 85 dB (Correct Answer)
D. 100 dB

Explanation: **Explanation:** The correct answer is **85 dB**. This value represents the critical threshold for occupational noise exposure. According to the World Health Organization (WHO) and standard occupational health guidelines, exposure to noise levels below 85 dB for an 8-hour workday is generally considered safe and does not cause permanent hearing loss. **Why 85 dB is correct:** Prolonged exposure to noise above 85 dB leads to the destruction of the hair cells in the Organ of Corti (specifically the outer hair cells). This results in **Noise-Induced Hearing Loss (NIHL)**, which is typically bilateral and sensorineural. The "rule of thumb" in environmental health is that for every 3 dB increase above 85 dB, the safe exposure time is reduced by half (e.g., 88 dB is safe for only 4 hours). **Why other options are incorrect:** * **160 dB:** This is an extremely high intensity, equivalent to a jet engine at close range. Exposure at this level causes immediate, permanent physical damage (acoustic trauma) and potential rupture of the tympanic membrane. * **70 dB:** This is the level of normal conversation or a vacuum cleaner. While audible, it is well below the threshold of physiological damage. * **100 dB:** This level (similar to a chainsaw or jackhammer) is hazardous. Permanent damage can occur in as little as 15 minutes of unprotected exposure. **High-Yield Facts for NEET-PG:** * **Audiometric Notch:** NIHL characteristically shows a "dip" or notch at **4000 Hz** on an audiogram. * **Acceptable Indoor Noise:** For residential areas at night, the limit is **35 dB**; for hospitals, it is **25–35 dB**. * **Presbycusis:** Age-related hearing loss, which must be differentiated from NIHL (Presbycusis typically affects high frequencies progressively). * **Statutory Limit:** In India, the Factories Act prescribes 90 dB as the maximum permissible limit for 8 hours, but 85 dB is the globally accepted medical safety standard.

Question 432: Which of the following is seen in heat stroke?

A. Subnormal temperature
B. Normal mental function
C. Failure of heat regulation (Correct Answer)
D. Normal body temperature

Explanation: **Explanation:** Heat stroke is a life-threatening medical emergency characterized by a failure of the body’s thermoregulatory mechanisms. It occurs when the core body temperature rises above **40°C (104°F)**, leading to multi-organ dysfunction. 1. **Why Option C is correct:** The hallmark of heat stroke is the **failure of the hypothalamic heat-regulating mechanism**. This leads to a cessation of sweating (anhidrosis) in many cases, causing the body to lose its primary method of heat dissipation. This results in an uncontrolled rise in core temperature. 2. **Why Options A, B, and D are incorrect:** * **Subnormal/Normal Temperature (A & D):** In heat stroke, the temperature is profoundly elevated (Hyperpyrexia), typically >40°C. Subnormal or normal temperatures are seen in heat exhaustion or heat syncope, but never in heat stroke. * **Normal Mental Function (B):** Central Nervous System (CNS) dysfunction is a mandatory diagnostic criterion for heat stroke. Patients present with altered mental status, confusion, delirium, seizures, or coma. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Hyperpyrexia (>40°C), CNS dysfunction, and Anhidrosis (dry, hot skin). * **Types:** * *Exertional:* Common in young athletes/military recruits. * *Non-exertional (Classic):* Common in elderly or sedentary individuals during heatwaves. * **Management:** Immediate **rapid cooling** is the priority (e.g., ice-water immersion or evaporative cooling). * **Differential:** Unlike **Heat Exhaustion**, where the sensorium is intact and the thermoregulatory mechanism is still functioning (profuse sweating), Heat Stroke represents a total systemic breakdown.

Question 433: Dental caries is prevented by -

A. Iron
B. Fluoride (Correct Answer)
C. Iodide
D. Iron

Explanation: **Explanation:** **Fluoride** is the correct answer because it is the most effective mineral for preventing dental caries. It works through three primary mechanisms: 1. **Remineralization:** It promotes the deposition of calcium and phosphate into demineralized enamel. 2. **Structural Integrity:** It replaces the hydroxyl ion in hydroxyapatite to form **Fluorapatite**, which is significantly more resistant to acid dissolution. 3. **Antibacterial Action:** It inhibits the enzyme *enolase* in bacteria (like *S. mutans*), reducing their ability to produce acid from dietary sugars. **Analysis of Incorrect Options:** * **Iron (Options A & D):** Iron is essential for hemoglobin synthesis. Deficiency leads to anemia, but it has no direct role in preventing dental decay. Excessive oral iron supplements can actually cause extrinsic staining of the teeth. * **Iodide (Option C):** Iodine is critical for thyroid hormone synthesis. Deficiency leads to Goiter and Cretinism, but it does not influence dental enamel resistance. **High-Yield Clinical Pearls for NEET-PG:** * **Optimal Fluoride Level:** The recommended level in drinking water to prevent caries is **0.5 to 0.8 mg/L (ppm)**. * **Dental Fluorosis:** Occurs when fluoride levels exceed **1.5 mg/L**. It presents as "mottling" of enamel. * **Skeletal Fluorosis:** Occurs with prolonged exposure to levels > **3–10 mg/L**. * **Defluoridation:** The **Nalgonda Technique** (using alum and lime) is the standard method for removing excess fluoride from water. * **Topical vs. Systemic:** While water fluoridation is systemic, fluoride toothpaste provides a high-concentration topical benefit.

Question 434: What is sullage?

A. Liquid excreta
B. Byproduct of the chemical industry
C. Wastewater from the kitchen (Correct Answer)
D. Wastewater from an industry

Explanation: **Explanation:** In Environmental Health and Sanitation, wastewater is categorized based on its source and content. **Sullage** refers specifically to wastewater that does not contain human excreta. **1. Why the correct answer is right:** Sullage is the wastewater derived from household activities such as **kitchens, bathrooms, and laundries**. It contains organic matter, soap, and grease but lacks the high pathogenic load associated with human feces. In the context of the options provided, "Wastewater from the kitchen" is the most accurate description. **2. Analysis of incorrect options:** * **Option A (Liquid excreta):** This is referred to as **Sewage**. Sewage is a mixture of sullage and excreta (feces and urine), making it significantly more hazardous and prone to spreading water-borne diseases. * **Option B & D (Industrial byproducts/wastewater):** These are classified as **Industrial Effluents**. They often contain toxic chemicals, heavy metals, and specific pollutants that require specialized treatment processes different from domestic waste. **3. High-Yield Facts for NEET-PG:** * **Sullage vs. Sewage:** The presence of human excreta is the defining difference. If excreta is present, it is *Sewage*; if absent, it is *Sullage*. * **BOD (Biochemical Oxygen Demand):** Sewage has a much higher BOD than sullage due to the high organic load from feces. * **Sewerage:** This refers to the entire infrastructure (pipes, pumps, and disposal works) used to transport sewage. * **Refuse:** This is the term for solid waste (garbage and rubbish), whereas sullage and sewage are liquid wastes. * **Public Health Importance:** While less dangerous than sewage, sullage still requires proper disposal (e.g., soakage pits) to prevent mosquito breeding and dampness around dwellings.

Question 435: All of the following are incinerated except?

A. Mercury
B. Radiological waste
C. Halogen containing plastics
D. All (Correct Answer)

Explanation: ### Explanation The core principle behind this question is the **Bio-Medical Waste (BMW) Management Rules**, which strictly prohibit the incineration of certain materials due to the risk of toxic emissions and environmental hazards. **Why "All" is the Correct Answer:** Incineration is a high-temperature dry oxidation process. However, it is contraindicated for the following materials: * **Mercury (Option A):** Mercury is a heavy metal that volatilizes at high temperatures. Incinerating mercury-containing devices (like broken thermometers or BP apparatus) leads to the release of toxic mercury vapors into the atmosphere, causing severe neurotoxicity and environmental "minamata-like" contamination. * **Radiological Waste (Option B):** Incineration does not destroy radioactivity; instead, it can disperse radioactive isotopes into the air via fly ash and flue gases. These must be disposed of as per Atomic Energy Regulatory Board (AERB) guidelines (e.g., decay-in-storage). * **Halogen-containing Plastics (Option C):** Plastics like PVC (Polyvinyl Chloride) release highly carcinogenic **dioxins and furans** when burnt. BMW rules mandate that these be recycled or autoclaved/microwaved rather than incinerated. **High-Yield NEET-PG Pearls:** 1. **Incineration Temperature:** Primary chamber (800° ± 50°C); Secondary chamber (1050° ± 50°C). 2. **Retention Time:** Gas residence time in the secondary chamber must be at least **2 seconds**. 3. **Color Coding:** Incinerable waste (Anatomical waste, soiled waste, expired medicines) goes into **Yellow Bags**. 4. **Cytotoxic Drugs:** Must be incinerated at temperatures >1200°C. 5. **Prohibited for Incineration:** Reactive chemical waste, pressurized containers, and heavy metals (Lead, Cadmium, Mercury).

Question 436: What is true regarding DDT?

A. Synthetic insecticide (Correct Answer)
B. Natural insecticide
C. Organophosphate insecticide
D. No incidence of resistance

Explanation: **Explanation:** **1. Why Option A is Correct:** DDT (Dichloro-diphenyl-trichloroethane) is a **synthetic crystalline organochlorine** compound. It was first synthesized in 1874, but its insecticidal properties were discovered by Paul Müller in 1939 (for which he received a Nobel Prize). It is a man-made chemical and does not occur naturally in the environment. **2. Why the other options are Incorrect:** * **Option B (Natural insecticide):** Natural insecticides (botanicals) are derived from plants, such as **Pyrethrum** (from Chrysanthemum flowers), Rotenone, and Nicotine. DDT is entirely laboratory-synthesized. * **Option C (Organophosphate insecticide):** DDT belongs to the **Organochlorine** group. Organophosphates (e.g., Malathion, Parathion) have a different chemical structure and mechanism (acetylcholinesterase inhibition). * **Option D (No incidence of resistance):** This is false. Extensive use of DDT in malaria control programs led to widespread **physiological resistance** in *Anopheles* mosquitoes. This resistance was a primary reason for the shift from the Global Malaria Eradication Programme to Malaria Control strategies. **3. High-Yield NEET-PG Pearls:** * **Mechanism:** DDT is a contact poison that affects the sodium channels in the insect's nervous system, leading to paralysis and death. * **Residual Action:** It is highly persistent in the environment (half-life of 2-15 years). In India, it is used for **Indoor Residual Spray (IRS)** at a dosage of 1-2 $g/m^2$. * **Biomagnification:** Being lipid-soluble, DDT undergoes "biomagnification," increasing in concentration up the food chain, which led to its ban for agricultural use in many countries. * **Storage:** In the human body, DDT is primarily stored in **adipose (fatty) tissue**.

Question 437: Biological fixation of nitrogen most commonly occurs in which of the following crops?

A. Pulses (Correct Answer)
B. Cereals
C. All tuber crops
D. Sugarcane and beetroot

Explanation: ### Explanation **1. Why Pulses is the Correct Answer:** Biological Nitrogen Fixation (BNF) is the process by which atmospheric nitrogen ($N_2$) is converted into ammonia ($NH_3$) by specific microorganisms. This occurs most efficiently in **Pulses** (leguminous plants like peas, beans, and lentils). These plants have a symbiotic relationship with **Rhizobium bacteria**, which reside in specialized **root nodules**. The bacteria possess the enzyme *nitrogenase*, which breaks the triple bond of atmospheric nitrogen, enriching the soil and the plant with essential nutrients. **2. Analysis of Incorrect Options:** * **Cereals (B):** Crops like wheat, rice, and maize are non-leguminous. They lack root nodules and cannot fix atmospheric nitrogen naturally; they rely heavily on synthetic nitrogenous fertilizers. * **All Tuber Crops (C):** While some tubers (like sweet potatoes) may have minor associative nitrogen fixation via endophytes, they do not possess the robust symbiotic nodulation mechanism found in pulses. * **Sugarcane and Beetroot (D):** These are high-biomass crops that deplete soil nitrogen rather than fixing it. While some research shows *Acetobacter* can fix nitrogen in sugarcane, it is not the "most common" or primary mechanism compared to pulses. **3. High-Yield Facts for NEET-PG:** * **The Nitrogen Cycle:** Nitrogen is a critical component of amino acids and proteins. In environmental health, excessive use of nitrogenous fertilizers can lead to **Methemoglobinemia (Blue Baby Syndrome)** due to nitrate leaching into groundwater. * **Key Organisms:** * *Symbiotic:* Rhizobium (Pulses). * *Free-living:* Azotobacter, Clostridium. * *Cyanobacteria:* Anabaena (found in Azolla used in rice paddies). * **Leghemoglobin:** A pink pigment found in root nodules that regulates oxygen levels to protect the oxygen-sensitive *nitrogenase* enzyme.

Question 438: What is the safe limit of Fluorine in drinking water?

A. 0.2–0.5 mg/L
B. 0.5–0.8 mg/L (Correct Answer)
C. 0.8–1.2 mg/L
D. 1.2–2.0 mg/L

Explanation: **Explanation:** The concentration of fluoride in drinking water is a classic "double-edged sword" in public health. The correct answer is **0.5–0.8 mg/L** because this range is considered the "optimal" or safe limit that provides maximum protection against dental caries without causing systemic toxicity. 1. **Why 0.5–0.8 mg/L is correct:** At this concentration, fluoride promotes remineralization of tooth enamel by forming fluorapatite, which is more resistant to acid attacks. According to the WHO and Indian standards (CPHEEO), this range is ideal for tropical climates like India, where water consumption is higher. 2. **Why other options are incorrect:** * **0.2–0.5 mg/L:** This level is too low to provide significant protection against dental caries (deficiency zone). * **0.8–1.2 mg/L:** While used as a standard in colder Western countries, in India, this level increases the risk of dental fluorosis due to higher daily water intake. * **1.2–2.0 mg/L:** Concentrations above 1.5 mg/L are associated with **Dental Fluorosis** (mottling of enamel), and levels above 3–10 mg/L lead to **Skeletal Fluorosis**. **High-Yield Clinical Pearls for NEET-PG:** * **Dental Fluorosis:** Occurs when fluoride >1.5 mg/L. Characterized by "Mottled Enamel." * **Skeletal Fluorosis:** Occurs with chronic intake of >3–10 mg/L. Key signs include "poker back" (permanent stiffness) and "knock-knees" (Genu Valgum). * **Nalgonda Technique:** The method of choice for **defluoridation** at the domestic/community level using alum, lime, and bleaching powder. * **Biomarker:** Urinary fluoride levels are the best indicator of recent fluoride exposure.

Question 439: Which of the following is used as an indicator for recent fecal contamination of water?

A. Escherichia coli
B. Corynebacterium diphtheriae
C. Pseudomonas
D. Streptococci (Correct Answer)

Explanation: **Explanation** In water microbiology, indicators of fecal pollution are used to assess the safety of drinking water. While several organisms inhabit the intestines, their survival rates in water vary, determining whether they indicate recent or remote contamination. **Why Streptococci is the Correct Answer:** **Fecal Streptococci (Enterococci)** are highly reliable indicators of **recent fecal contamination**. Unlike *E. coli*, which can sometimes persist or even multiply in certain environmental conditions, Streptococci do not multiply in water. Their presence indicates that the contamination occurred very recently, as they die off relatively quickly once outside the host. Furthermore, they are more resistant to drying and high salinity than coliforms. **Analysis of Incorrect Options:** * **A. Escherichia coli:** While *E. coli* is the most commonly used "index of fecal pollution" and indicates *potential* presence of pathogens, it is not as specific for "recent" contamination as Streptococci because it can survive slightly longer in water. * **B. Corynebacterium diphtheriae:** This is the causative agent of Diphtheria (an upper respiratory infection). It is transmitted via droplets and is not an indicator of fecal contamination. * **C. Pseudomonas:** These are ubiquitous environmental bacteria. While they can be opportunistic pathogens in water systems, they are not used as indicators of fecal pollution. **High-Yield NEET-PG Pearls:** * **Best Indicator of Fecal Pollution:** *E. coli* (specifically Thermotolerant/Fecal coliforms). * **Indicator of Recent Contamination:** Fecal Streptococci. * **Indicator of Remote/Past Contamination:** *Clostridium perfringens* (due to its highly resistant spores). * **Coliform Count:** The standard measure for water bacteriology. For chlorinated piped water, *E. coli* should be **0 per 100 ml**.

Question 440: Which of the following is the least likely cause of indoor air pollution?

A. Carbon monoxide
B. Nitrogen dioxide
C. Radon
D. Mercury vapour (Correct Answer)

Explanation: **Explanation:** The correct answer is **Mercury vapour**. Indoor air pollution is primarily driven by products of combustion, building materials, and soil-derived gases. **1. Why Mercury Vapour is the least likely cause:** Mercury is a heavy metal that typically exists in liquid form at room temperature. While it can vaporize, it is not a common or widespread indoor air pollutant in residential settings. Exposure is usually limited to specific accidental spills (e.g., broken thermometers or sphygmomanometers) or specific industrial/occupational settings. It does not represent a routine component of the "indoor air pollution" profile compared to combustion by-products. **2. Analysis of Incorrect Options:** * **Carbon monoxide (CO):** A major indoor pollutant resulting from the incomplete combustion of biomass fuels (chulhas), coal, or gas heaters. It is a leading cause of indoor air toxicity. * **Nitrogen dioxide (NO₂):** Commonly released from gas stoves, space heaters, and tobacco smoke. It is a significant respiratory irritant found in most urban households. * **Radon:** A naturally occurring radioactive gas that seeps into buildings from the soil and rocks beneath foundations. It is the second leading cause of lung cancer globally and a major indoor environmental concern. **3. High-Yield Clinical Pearls for NEET-PG:** * **Biomass Fuel:** The most common source of indoor air pollution in rural India, linked to **COPD** and **cataracts** in women. * **Radon:** Associated with **Lung Cancer** (non-smokers). * **Sick Building Syndrome:** A condition where occupants experience acute health effects (headache, fatigue) linked to time spent in a building with poor ventilation and chemical contaminants (like Formaldehyde). * **Mosquito Coils:** Burning one coil is equivalent to smoking roughly 100 cigarettes in terms of particulate matter (PM 2.5) exposure.

Practice by Chapter

Water Quality and Health

Practice Questions

Air Pollution and Health Effects

Practice Questions

Solid Waste Management

Practice Questions

Hazardous Waste Management

Practice Questions

Housing and Health

Practice Questions

Noise Pollution

Practice Questions

Radiation Health Effects

Practice Questions

Climate Change and Health

Practice Questions

Environmental Impact Assessment

Practice Questions

Disaster Management and Preparedness

Practice Questions

Vector Control

Practice Questions

Environmental Legislation

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free