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Carbolic Acid (Phenol) in Forensic Medicine and Toxicology

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1. Physical Characters

Note: Though called an acid, carbolic acid has no acid reaction on litmus. It is classified among organic acids in FMT.

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2. Common Preparations/Derivatives

• Lysol - 50% solution of cresol in saponified vegetable oil. Phenol is ~8 times more toxic than Lysol.
• Dettol - Chlorinated phenol with terpineol
• Other derivatives: Cresol, Creosote (coal tar), Thymol, Menthol, Tannic acid

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3. Absorption and Excretion

• Absorption: Rapidly absorbed from the alimentary tract, respiratory tract, rectum, vagina, serous cavities, wounds, and even through intact skin.
• Metabolism: Phenol is converted to hydroquinone and pyrocatechol in the body. A trace is excreted by the lungs, salivary glands, skin and stomach.
• Excretion: Excreted in urine (partly free, partly combined with sulfuric and glucuronic acids). About 36 hours required for complete excretion.
• Detoxification: Partly detoxicated by the liver.

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4. Fatal Dose and Fatal Period

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5. Mechanism of Action

1. Local action - Corrosive (coagulates protein, but does not enter into firm combination with it). This gives it remarkable penetrating power.
2. Systemic/Remote action - CNS depressant, especially the respiratory center. Acts as narcotic, inducing sleep and drowsiness.

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6. Signs and Symptoms (Carbolism)

Local Effects

• Burning and numbness (damages nerve endings)
• Precipitates and coagulates cell contents → hard, cracked, whitish surfaces
• White opaque eschar, painless, falls off in a few days leaving a brown stain
• Deep burns appear black
• Necrosis and gangrene: tissue becomes green-white or brown-white; dead tissue sloughs readily
• Lysol specifically discolors tissues brownish-purple

• Hot burning pain from mouth to stomach → tingling → anesthesia
• Swallowing and speech become painful and difficult
• Vomiting may NOT occur (due to anesthetic action on the stomach)
• Lips, mouth, tongue corroded; white, bleached, hardened burns that later turn brown with rapid sloughing
• Chin and cheeks may be burned

• Pulmonary and laryngeal edema due to irritation
• Slow, labored breathing → respiratory failure
• Aspiration of vomitus can cause bronchitis and bronchopneumonia

Systemic Effects

• Headache, giddiness, unconsciousness, coma
• Pupils contracted/pinpoint (classic sign)
• Temperature subnormal
• Skin cold and clammy, face covered with cold sweat
• Pulse rapid, feeble and irregular
• Breathing stertorous
• Dusky cyanosis
• Respiratory alkalosis and metabolic acidosis
• Liver damage
• Hemolysis and methemoglobinemia (in severe cases)
• Strong odor of phenol in breath
• Convulsions and lockjaw (sometimes)

Urine (Carboluria - Classic Finding)

• Scanty, contains albumin and free hemoglobin
• Suppression (oliguria/anuria) may follow
• Colorless or slightly green at first, turns green or even BLACK on exposure to air - this is the classic forensic finding called carboluria
• Mechanism: Hydroquinone and pyrocatechol are oxidized in urine causing green/dark coloration

Test: Add a few drops of 10% ferric chloride solution to 1 mL urine → bluish color (positive). Note: Salicylates also give a positive result.

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7. Cause of Death

1. Syncope
2. Asphyxia due to:
   • Failure of respiration (CNS depression)
   • Edema of glottis
   • Complications (bronchopneumonia)

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8. Treatment

1. Emesis often fails (anesthetic effect on stomach)
2. Gastric lavage - repeated, with plenty of lukewarm water containing activated charcoal, olive oil, castor oil, sodium sulphate, or saccharated lime (these combine with phenol to form harmless products). Soap solution or 10% glycerin may also be used. Continue until washings are clear and odorless.
3. After lavage, leave 30 g magnesium sulphate or medicinal liquid paraffin in the stomach
4. Demulcents
5. IV saline with sodium bicarbonate (7 g/L) - combats circulatory depression, dilutes carbolic acid in blood, promotes diuresis
6. Hemodialysis if renal failure develops
7. Methylene blue IV for severe methemoglobinemia
8. If phenol falls on skin: remove contaminated clothing immediately; wash skin with undiluted polyethylene glycol; if unavailable, wash with soap and water for at least 15 minutes. Olive oil, methylated spirit, or 10% ethyl alcohol act as solvents.

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9. Chronic Poisoning (Phenol Marasmus)

• Anorexia, weight loss, headache, vertigo
• Dark urine
• Pigmentation of skin and sclera
• Ochronosis - pigmentation in cornea and various cartilages caused by hydroquinone and pyrocatechol deposits

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10. Postmortem Appearances

External

• Grayish-white or brownish stains at angles of mouth and on chin
• Characteristic phenol odor
• Tongue white and swollen
• Mucous membranes of lips, mouth, throat: corrugated, sodden, whitened or ash-gray, partially detached with numerous small submucous hemorrhages

Internal

Important: Viscera must be preserved in saturated solution of sodium chloride (NOT rectified spirit). Rectified spirit is used to preserve viscera in other corrosive poisonings, but NOT carbolic acid.

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11. Medicolegal Aspects

1. Suicide - was the most common mode in the past; now largely displaced by soporifics
2. Accidental poisoning - from indiscriminate medicinal use (antiseptic use, etc.)
3. Homicide - rare, because of the distinctive smell and taste that makes it difficult to disguise
4. Criminal abortion - sometimes injected into the vagina and uterus to procure abortion
5. Carbolic acid and its derivatives (Lysol, Dettol) are widely available as disinfectants/antiseptics, increasing accidental exposure risk

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Summary of Key Forensic Points

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