UGC NET Forensic Science Notes: Metallic Poisons
Comprehensive notes on metallic poisons for the NTA-UGC NET Forensic Science exam, covering key metals, tests, antidotes, and forensic applications.
1. Introduction to Metallic Poisons
Metallic poisons are toxic heavy metals or their compounds that cause acute or chronic poisoning via ingestion, inhalation, or absorption. In forensic toxicology, they are analyzed to determine poisoning in accidental, occupational, suicidal, or homicidal cases.
Key Points
- Compounds: Heavy metals (arsenic, mercury, lead), metalloids, organometallics.
- Forensic Role: Identify metals in blood, urine, hair, or environmental samples for medicolegal cases.
- Exam Focus: Metal identification, symptoms, tests, antidotes.
2. Common Metallic Poisons
Memorize these high-yield metals, their sources, symptoms, and forensic significance for factual and case-based questions:
| Metal | Sources | Symptoms | Forensic Notes |
|---|---|---|---|
| Arsenic | Pesticides, groundwater, smelting | Nausea, diarrhea, Mees’ lines, neuropathy | Chronic arsenicosis; homicidal use. |
| Mercury | Fish, dental amalgams, thermometers | Tremors, memory loss, kidney damage | Minamata disease; occupational exposure. |
| Lead | Paint, pipes, batteries | Anemia, colic, encephalopathy, wrist drop | Chronic exposure in children; industrial risk. |
| Thallium | Rodenticides, electronics | Alopecia, peripheral neuropathy, coma | “Poisoner’s poison”; difficult to detect. |
| Cadmium | Batteries, pigments, cigarette smoke | Kidney damage, bone pain (Itai-Itai disease) | Environmental contamination. |
| Antimony | Flame retardants, alloys | Vomiting, cardiotoxicity, respiratory failure | Rare; mimics arsenic poisoning. |
| Chromium | Industrial processes, leather tanning | Skin ulcers, lung cancer (hexavalent) | Occupational exposure; carcinogenic. |
Exam Tip
Focus on arsenic, mercury, lead, and thallium for questions like “Which metal causes alopecia?” or “What is detected by the Reinsch test?”
3. Classification and Toxicological Effects
Understand the types and effects for analytical questions:
Classification
- Heavy Metals: Arsenic, mercury, lead, cadmium, thallium.
- Metalloids: Arsenic (sometimes classified).
- Organometallics: Methylmercury, tetraethyl lead.
- Forms: Inorganic (salts) or organic.
Effects
- Acute: Immediate symptoms (e.g., arsenic gastroenteritis).
- Chronic: Cumulative effects (e.g., lead encephalopathy).
- Mechanisms: Enzyme inhibition, oxidative stress, ion disruption.
Exam Tip
Questions may ask to differentiate acute (e.g., arsenic) vs. chronic (e.g., lead) poisoning.
4. Extraction Methods
Extraction isolates metals from biological or environmental samples. Key methods include:
Methods
- Wet Digestion: Uses nitric/sulfuric acid for tissues, hair.
- Dry Ashing: Incinerates samples, dissolves ash in acid.
- Solvent Extraction: Chelating agents (e.g., dithizone).
- Solid-Phase Extraction (SPE): Selective isolation.
- Instrumentation:
- AAS: Trace metals (e.g., lead).
- ICP-MS: Multi-metal analysis.
- XRF: Non-destructive for solids.
Exam Tip
Memorize AAS for lead and ICP-MS for thallium. Questions like “How to detect mercury in hair?” are common.
5. Presumptive Tests
Initial tests for metal identification, frequently tested:
Tests
- Reinsch: Arsenic, mercury, antimony (metallic deposit on copper).
- Gutzeit: Arsenic (arsine gas, silver nitrate detection).
- Marsh: Arsenic, antimony (mirror deposit).
- Spot Tests:
- Lead: Sodium rhodizonate (red).
- Mercury: Dithizone (orange-red).
- Thallium: Rhodamine B (fluorescent).
Exam Tip
Focus on Reinsch, Gutzeit, and Marsh for questions like “Which test detects arsenic?”
6. Confirmatory Tests
Validate presumptive results for analytical questions:
Tests
- AAS: Lead, cadmium, mercury.
- ICP-MS: Multi-metal (thallium, arsenic).
- ICP-OES: Broad metal detection.
- Electrothermal AAS: Ultra-trace (thallium).
Exam Tip
Prioritize AAS and ICP-MS for questions like “Which technique confirms lead?”
7. Antidotes
Treatment for metallic poisoning, often tested:
Antidotes
- Dimercaprol (BAL): Arsenic, mercury, lead.
- DMSA (Succimer): Lead, mercury.
- EDTA: Lead, cadmium.
- Prussian Blue: Thallium.
Exam Tip
Memorize BAL for arsenic and Prussian Blue for thallium for questions like “What treats lead poisoning?”
8. Forensic Significance
Metallic poisons are vital in:
Applications
- Cause of Death: Links symptoms (e.g., Mees’ lines for arsenic).
- Criminal Investigations: Detects poisoning (e.g., thallium homicides).
- Environmental Forensics: Analyzes contamination (e.g., cadmium).
- Medicolegal Reports: Supports court testimony.
- Chain of Custody: Ensures sample integrity.
Exam Tip
Case-based questions may ask, “Alopecia indicates which metal?” (Answer: Thallium).
9. Sample Collection and Preservation
Procedures
- Samples: Blood, urine, hair, nails, liver.
- Preservation: Metal-free containers, store at 4°C or -20°C.
- Packaging: Airtight, tamper-proof.
- Forwarding: Send with documentation.
Exam Tip
Know metal-free containers for questions like “How to preserve blood for lead analysis?”
10. Sample Questions
Question 1: Which test detects arsenic in a biological sample?
Explanation: Reinsch test detects arsenic, mercury, and antimony via metallic deposit on a copper strip.
Question 2: A victim shows alopecia and peripheral neuropathy. Which metal?
Explanation: Thallium causes characteristic alopecia and neuropathy, often used in homicides.
Question 3: Which technique is best for detecting trace lead in blood?
Explanation: Atomic Absorption Spectroscopy is highly sensitive for detecting lead in blood.
11. Preparation Tips
Tips to Crack Metallic Poison Questions
- Study Time: 3–5 hours for metallic poisons within toxicology.
- Memorize: Arsenic, mercury, lead, thallium; Reinsch, Gutzeit, AAS, ICP-MS.
- Practice: Solve 20–30 MCQs from 2019–2025 papers.
- Focus: Symptoms (Mees’ lines, alopecia), antidotes (BAL, Prussian Blue).
