Forensic Toxicology Practice Questions

Q: Lead toxicity principally affects which type of neuron?

Motor. **Explanation:** Lead toxicity (Plumbism) is a multisystem disorder, but its neurotoxic effects are particularly characteristic. In adults, chronic lead exposure primarily manifests as **peripheral neuropathy**, which characteristically involves **motor neurons** while sparing sensory neurons. **1. Why Motor is Correct:** Lead causes segmental demyelination and axonal degeneration that selectively targets motor nerves. This leads to the classic clinical presentation of **"Wrist drop"** (paralysis of the extensor muscles of the wrist due to radial nerve involvement) and **"Foot drop"** (peroneal nerve involvement). The weakness typically starts in the most frequently used muscles. **2. Why Other Options are Incorrect:** * **Sensory:** Unlike other heavy metals (like Arsenic or Mercury), lead toxicity rarely presents with significant sensory loss or paresthesia. The absence of sensory symptoms is a key diagnostic feature that differentiates lead-induced neuropathy from other metabolic or toxic neuropathies. * **Both/None:** Since the pathology is highly specific to motor fibers, these options are incorrect. **Clinical Pearls for NEET-PG:** * **Burtonian Line:** A characteristic bluish-black line on the gums (lead sulfide deposits). * **Basophilic Stippling:** Seen on peripheral blood smears (inhibition of 5'-nucleotidase). * **Encephalopathy:** While adults get peripheral neuropathy (motor), **children** are more prone to **Encephalopathy** (CNS involvement) due to a more permeable blood-brain barrier. * **Radiology:** "Lead lines" (increased radiodensity) at the metaphyses of long bones in children. * **Treatment:** Calcium disodium EDTA, Penicillamine, or Dimercaprol (BAL). Succimer is the preferred oral chelator in children.

Q: What is the best site for blood collection for toxicology sampling?

Femoral vein. **Explanation:** The **femoral vein** is the gold standard site for post-mortem blood collection in toxicology because it minimizes the risk of **Post-mortem Redistribution (PMR)**. PMR refers to the movement of drugs from solid organs (like the liver, lungs, or stomach) into the surrounding blood vessels after death, which can falsely elevate drug concentrations. Peripheral sites like the femoral vein are distant from these central organs, providing a more accurate reflection of the drug concentration at the time of death. **Analysis of Options:** * **Femoral Vein (Correct):** It is a peripheral site. Collecting blood here (ideally by ligating the vein proximally before sampling) prevents contamination from central viscera, ensuring the most reliable toxicological results. * **Abdominal Aorta:** Being a central large vessel located near the gut and liver, it is highly susceptible to PMR and diffusion of drugs from the gastrointestinal tract. * **Carotid Artery:** While peripheral to the abdomen, it is close to the brain and lungs. Furthermore, arteries are often collapsed or empty post-mortem, making sampling difficult compared to veins. * **Hepatic Vein:** This is the worst site for toxicology. The liver is a major drug reservoir; blood here will have massive concentrations of drugs and metabolites released post-mortem, leading to "false poisoning" results. **High-Yield Pearls for NEET-PG:** * **Ideal Volume:** At least 20–30 ml of blood should be collected. * **Preservative of Choice:** **Sodium Fluoride (NaF)** at a concentration of 2mg/ml. It inhibits glycolysis and prevents microbial alcohol production. * **Vitreous Humor:** If blood is unavailable (e.g., putrefaction), vitreous humor is the next best sample for alcohol and glucose levels as it is sequestered and resistant to putrefactive changes.

Q: Chocolate brown hypostasis is seen in all poisoning except:

Hydrogen sulphide. ### Explanation The color of post-mortem hypostasis (lividity) is a high-yield topic in forensic toxicology, as it reflects the chemical state of hemoglobin at the time of death. **Why Hydrogen Sulphide is the Correct Answer:** In **Hydrogen sulphide (H₂S)** poisoning, the hypostasis is typically **bluish-green** or dark purple. This occurs because H₂S reacts with hemoglobin to form **sulfhemoglobin**, which imparts a characteristic greenish tint, especially visible in the abdominal wall and areas of lividity. It does not produce a chocolate brown color. **Analysis of Incorrect Options (Causes of Chocolate Brown Hypostasis):** Options B, C, and D are all **Methemoglobin-forming agents**. When hemoglobin is oxidized to methemoglobin (where iron is in the ferric $Fe^{3+}$ state instead of the ferrous $Fe^{2+}$ state), the blood and resulting hypostasis turn a distinct **chocolate brown** or muddy brown color. * **Aniline:** An organic compound used in dyes; a potent methemoglobin inducer. * **Nitrites:** Found in certain medications and contaminated well water. * **Potassium chlorate:** A strong oxidizing agent often found in matchsticks and explosives. **High-Yield Clinical Pearls for NEET-PG:** * **Cherry Red Hypostasis:** Carbon monoxide (CO) poisoning (due to Carboxyhemoglobin). * **Bright Red/Pink Hypostasis:** Cyanide poisoning (due to Cytochrome oxidase inhibition, leaving blood oxygenated) or cold exposure. * **Dark Blue/Violet:** Normal death (asphyxia), Opioids. * **Ash Grey:** Phosphorus poisoning. * **Sulfhemoglobinemia vs. Methemoglobinemia:** Remember that H₂S = Green; Nitrites/Aniline/Chlorates = Brown.

Q: Which of the following is a polychlorinated hydrocarbon?

Dieldrin/Endrin. **Explanation** In forensic toxicology, insecticides are broadly classified into four major chemical groups: Organophosphates, Organochlorines, Carbamates, and Pyrethroids. **Why Dieldrin/Endrin is Correct:** **Dieldrin and Endrin** belong to the **Organochlorine** group, specifically the **Polychlorinated Hydrocarbons** (specifically, the cyclodiene subgroup). These compounds are highly lipid-soluble, stable in the environment, and act as CNS stimulants by inhibiting the GABA-A receptors (antagonizing the inhibitory neurotransmitter GABA), which leads to seizures. Endrin is notoriously known as "20-perrin" in some regions and is considered one of the most toxic organochlorines. **Why the Other Options are Incorrect:** * **A, B, and C (Parathion, Malathion, Diazinon):** These are all **Organophosphorus (OP) compounds**. They function by irreversibly inhibiting the enzyme Acetylcholinesterase, leading to an accumulation of acetylcholine and resulting in a "cholinergic crisis" (SLUDGE syndrome). * *Parathion* is a highly toxic "Agricultural" OP compound. * *Malathion* is a less toxic "Household" OP compound. **High-Yield Clinical Pearls for NEET-PG:** * **Organochlorines (Dieldrin/Endrin):** Treatment is symptomatic (Diazepam for seizures). There is **no specific antidote**. Avoid adrenaline as it may induce ventricular fibrillation due to myocardial sensitization. * **Organophosphates:** Characterized by miosis and garlic-like odor. Antidotes include **Atropine** (muscarinic antagonist) and **Pralidoxime/2-PAM** (oximes to reactivate cholinesterase). * **Endrin Poisoning:** Often presents with sudden onset of status epilepticus without prior warning symptoms.

Q: The FeCl3 test is used in the diagnosis of which of the following substances?

Phenol. **Explanation:** The **Ferric Chloride (FeCl3) test** is a classic chemical test used to detect compounds containing a **phenolic hydroxyl group**. When neutral ferric chloride is added to **Phenol**, it reacts to form a complex salt (ferric phenoxide), resulting in a characteristic **violet or purple coloration**. This is a high-yield diagnostic test in forensic toxicology for identifying carbolic acid poisoning. **Analysis of Options:** * **Phenol (Correct):** As a cyclic aromatic compound with an -OH group, it reacts specifically with FeCl3 to produce a deep violet color. * **Hydrochloric acid (HCl):** This is a strong inorganic (mineral) acid. It does not contain a phenolic group and would not produce the characteristic color change; instead, it is typically identified using the silver nitrate test (forming a white precipitate). * **Acetic acid:** While it can react with FeCl3 to produce a deep red color (forming ferric acetate), the test is most classically associated with Phenol in the context of forensic toxicology and the NEET-PG syllabus. * **Alcohol:** Aliphatic alcohols (like Ethanol) do not react with ferric chloride to produce a color change because their -OH group is not attached to an aromatic ring. **Clinical Pearls for NEET-PG:** * **Phenol (Carbolic Acid):** Known for its "mousy" or "phenolic" odor. * **Ochronosis:** Chronic phenol poisoning can lead to the deposition of pigment in cartilages. * **Urine Findings:** In phenol poisoning, urine turns **dark green or black** on standing (due to oxidation products like hydroquinone and pyrocatechol), a condition known as **carboluria**. * **Antidote:** Gastric lavage with olive oil or castor oil (to dissolve phenol) is preferred; avoid water as it increases absorption.

Q: Viscera should be preserved if the cause of death is suspected. All of the following does not require preservatives, EXCEPT:

Brain. **Explanation:** In medicolegal autopsies, the preservation of viscera is crucial for toxicological analysis. The choice of preservative depends on whether the tissue is organic/soft or inorganic/hard. **Why the Correct Answer is Right:** **Option D (Brain)** is a soft, organic tissue. In cases of suspected poisoning (especially involving volatile substances or alkaloids), the brain must be preserved to prevent putrefaction and enzymatic degradation. The standard preservative used for soft viscera (except in cases of alcohol or acid poisoning) is **Saturated Solution of Common Salt**. Without a preservative, the organic matter would decompose, making toxicological detection impossible. **Why the Incorrect Options are Wrong:** * **Options A, B, and C (Nail, Hair, and Bone):** These are considered "dry" or "hard" samples. They are composed of keratin or mineralized matrices that do not undergo rapid bacterial putrefaction. Therefore, they are collected in dry, clean glass bottles or plastic packets and **do not require any chemical preservative** for transport to the Forensic Science Laboratory (FSL). **High-Yield Clinical Pearls for NEET-PG:** * **Standard Preservative:** Saturated Saline is the most common preservative for viscera. * **Exception (Alcohol Poisoning):** If alcohol poisoning is suspected, **Rectified Spirit** is used as a preservative (except for the brain/liver, where saline is still preferred). * **Formalin Warning:** Never use Formalin for preserving viscera intended for toxicology, as it hardens tissues and interferes with the extraction of many poisons (especially cyanides and alkaloids). * **Quantity:** Ideally, 500g of the most affected organ (usually liver) and half of each kidney should be preserved.

Q: Calcium gluconate is indicated in the management of poisoning by which acid?

Hydrofluoric acid. **Explanation:** **Why Hydrofluoric Acid (HF) is the correct answer:** Hydrofluoric acid poisoning is unique among corrosive acids because of its systemic toxicity. When HF comes into contact with the body, it dissociates into hydrogen and fluoride ions. The **fluoride ions** have a high affinity for divalent cations, specifically **calcium and magnesium**. They bind to these ions to form insoluble salts (calcium fluoride), leading to profound **hypocalcemia** and hypomagnesemia. **Calcium gluconate** is the specific antidote because it serves two purposes: 1. **Neutralization:** It provides exogenous calcium to bind with free fluoride ions, preventing further tissue penetration and deep "liquefactive-like" necrosis. 2. **Replacement:** It corrects the life-threatening systemic hypocalcemia that can lead to fatal cardiac arrhythmias (QT prolongation). It can be administered topically (as a gel), intra-arterially, or intravenously. **Why other options are incorrect:** * **Sulphuric Acid & Nitric Acid:** These are strong mineral acids that cause coagulative necrosis. Management is primarily supportive (airway, IV fluids, and dilution). There is no specific role for calcium gluconate as they do not cause systemic electrolyte depletion. * **Carbolic Acid (Phenol):** This is a coal tar derivative. Management involves gastric lavage with olive oil or castor oil and skin decontamination with Polyethylene Glycol (PEG). **High-Yield Clinical Pearls for NEET-PG:** * **The "Pain out of Proportion" Sign:** HF burns often show minimal initial skin changes but cause excruciating deep pain. * **ECG Finding:** Look for **QT interval prolongation** in HF poisoning due to hypocalcemia. * **Magnesium:** Magnesium sulfate is also used as an adjunct to treat associated hypomagnesemia. * **Antidote for Carbolic Acid:** Swabbing with **Glycerine** or PEG is the preferred decontamination method.

Q: About 20 gms of hairs are required to be preserved in cases of suspected heavy metal poisoning. Which of the following is most indicative of heavy metal poisoning based on hair sample analysis?

Heavy metal poisoning. **Explanation:** **1. Why the Correct Answer is Right:** In forensic toxicology, hair is considered a "calendar of exposure" for **heavy metal poisoning** (e.g., Arsenic, Antimony, Thallium, Lead, and Mercury). Unlike blood or urine, where toxins are cleared rapidly, heavy metals bind to the **sulfhydryl groups of keratin** in hair follicles. As hair grows (approximately 1 cm/month), the metals are incorporated into the hair shaft, providing a chronological record of exposure. A sample of **20 grams** (or a pencil-thick lock) is typically required to ensure sufficient concentration for detection via techniques like Atomic Absorption Spectroscopy (AAS) or Neutron Activation Analysis (NAA). **2. Why the Incorrect Options are Wrong:** * **Aconite Poisoning:** Aconite contains alkaloids (aconitine) that are rapidly metabolized and primarily detected in gastric contents, blood, or liver. They do not accumulate in hair in a manner that indicates chronic poisoning. * **Iodine Poisoning:** Iodine is a volatile element/halogen. Acute poisoning is diagnosed via gastric lavage (blue-black color with starch) and clinical signs like "iodism," not hair analysis. * **Codeine Poisoning:** While some opioids can be detected in hair, codeine is an organic alkaloid. Hair analysis is primarily the gold standard for **heavy metals** due to their unique affinity for keratin disulfide bonds. **3. High-Yield Clinical Pearls for NEET-PG:** * **Arsenic:** Hair and nail analysis is most specific for Arsenic. Look for **Mees' Lines** (white transverse bands on nails). * **Thallium:** Characterized by **alopecia** (hair loss) and "Mee’s-like" lines. * **Growth Rate:** Forensic experts calculate the time of poisoning by measuring the distance of the metal deposit from the hair root (1 cm = 1 month). * **Sample Collection:** Hair should be plucked with roots intact or cut close to the scalp, tied together, and labeled "proximal" and "distal" ends.

Q: All are features of organophosphorus poisoning except?

Dilated pupil. **Explanation:** Organophosphorus (OP) compounds act by irreversibly inhibiting the enzyme **Acetylcholinesterase (AChE)**. This leads to an accumulation of Acetylcholine (ACh) at the neuromuscular junctions and cholinergic synapses, resulting in overstimulation of the parasympathetic nervous system. **Why "Dilated pupil" is the correct answer:** In OP poisoning, the hallmark ocular finding is **Pinpoint Pupils (Miosis)** due to intense stimulation of the pupillary constrictor muscles (muscarinic effect). **Dilated pupils (Mydriasis)** are generally not seen in OP poisoning; instead, they are characteristic of Belladonna/Atropine poisoning or the early "sympathetic" phase of certain other toxins. **Analysis of other options (Features of OP Poisoning):** The clinical features are best remembered by the mnemonic **DUMBELS**: * **B. Bradycardia:** Excess ACh slows the heart rate via the vagus nerve (Muscarinic M2 effect). * **C. Lacrimation:** Stimulation of exocrine glands leads to excessive tearing. * **D. Sweating:** ACh is the neurotransmitter for sympathetic postganglionic fibers to sweat glands; hence, profuse sweating (diaphoresis) is a classic sign. **High-Yield Clinical Pearls for NEET-PG:** * **Management:** The specific antidote is **Pralidoxime (PAM)**, which reactivates the enzyme if given before "aging" occurs. The physiological antagonist is **Atropine** (titrated until secretions dry and tachycardia occurs). * **Diagnosis:** Best initial test is measuring **Serum Pseudocholinesterase** levels (more sensitive but less specific than RBC cholinesterase). * **Odor:** OP poisoning typically presents with a characteristic **Garlic-like odor** of the breath/vomitus. * **Intermediate Syndrome:** Occurs 24–96 hours after exposure, characterized by proximal muscle weakness and respiratory paralysis.

Question 1

Lead toxicity principally affects which type of neuron?

Accepted Answer

Motor

Answer

Sensory

Answer

Both of the above

Answer

None of the above

Question 2

What is the best site for blood collection for toxicology sampling?

Accepted Answer

Femoral vein

Answer

Abdominal aorta

Answer

Carotid artery

Answer

Hepatic vein

Question 3

Chocolate brown hypostasis is seen in all poisoning except:

Accepted Answer

Hydrogen sulphide

Answer

Aniline

Answer

Nitrites

Answer

Potassium chlorate

Question 4

Which of the following is a polychlorinated hydrocarbon?

Accepted Answer

Dieldrin/Endrin

Answer

Parathion

Answer

Malathion

Answer

Diazinon

Question 5

Which of the following statements regarding naphthalene poisoning is false?

Accepted Answer

It causes hypothermia due to the formation of naphthylamines.

Answer

It causes haemolysis in G-6-PD deficient patients.

Answer

Oily and fatty preparations should be avoided during treatment.

Answer

The fatal dose is approximately 2 grams.

Question 6

The FeCl3 test is used in the diagnosis of which of the following substances?

Accepted Answer

Phenol

Answer

Hydrochloric acid (HCl)

Answer

Acetic acid

Answer

Alcohol

Question 7

Viscera should be preserved if the cause of death is suspected. All of the following does not require preservatives, EXCEPT:

Accepted Answer

Brain

Answer

Nail

Answer

Hair

Answer

Bone

Question 8

Calcium gluconate is indicated in the management of poisoning by which acid?

Accepted Answer

Hydrofluoric acid

Answer

Sulphuric acid

Answer

Nitric acid

Answer

Carbolic acid

Question 9

About 20 gms of hairs are required to be preserved in cases of suspected heavy metal poisoning. Which of the following is most indicative of heavy metal poisoning based on hair sample analysis?

Accepted Answer

Heavy metal poisoning

Answer

Aconite poisoning

Answer

Iodine poisoning

Answer

Codeine poisoning

Question 10

All are features of organophosphorus poisoning except?

Accepted Answer

Dilated pupil

Answer

Bradycardia

Answer

Lacrimation

Answer

Sweating

Forensic Toxicology — MCQs

Forensic Toxicology — MCQs

On this page

Practice by Chapter

Want unlimited practice?