In chronic arsenic poisoning, the pathognomonic skin sign is Mees' lines on nails. However, which of the following MOST reliably confirms chronic arsenic exposure over the prior 3–6 months?
- A 24-hour urinary arsenic levels
- B Hair arsenic analysis by neutron activation ✓
- C Blood arsenic levels
- D Liver arsenic concentration at autopsy
Correct answer: B. Hair arsenic analysis by neutron activation
Explanation
Hair grows approximately 1 cm per month, and arsenic deposited in hair keratin remains fixed. Neutron activation analysis of segmental hair samples can map arsenic exposure month by month over the preceding 3–6 months, making it the gold standard for proving chronic exposure timeline. Urine arsenic reflects only recent (24–72 hour) exposure and is affected by dietary seafood. Blood arsenic has a short half-life. Liver concentration indicates total body burden but cannot time-stamp exposure.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
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