Zinc Phosphide Poisoning

Overview

• The Essentials of Forensic Medicine and Toxicology, 36th ed., p. 500
• Park's Textbook of Preventive and Social Medicine, p. 889

Mechanism of Toxicity

Zn₃P₂ + 6 HCl → 3 ZnCl₂ + 2 PH₃

• Inhibition of Cytochrome C Oxidase (Complex IV) of the mitochondrial electron transport chain - the same mechanism as hydrogen cyanide and aluminum phosphide poisoning
• Cellular hypoxia via mitochondrial toxicity
• Free radical-mediated oxidative damage
• Multiple organ dysfunction - cardiac, hepatic, pulmonary, renal, and neurological

• Parikh's Textbook of Medical Jurisprudence, p. 607
• Juárez-Martínez et al., Toxics 2023 [PMID: 37505522]
• Faress et al., JNMA 2025 [PMID: 41768810]

Fatal Dose and Fatal Period

• Parikh's Textbook of Medical Jurisprudence, p. 607
• The Essentials of Forensic Medicine and Toxicology, 36th ed., p. 500

Clinical Features

Early / GI Phase

• Metallic taste in the mouth
• Burning sensation in the throat, esophagus, and stomach
• Nausea, vomiting, diarrhea, abdominal pain
• Garlic/fishy odor on the breath (characteristic)
• There may be a symptom-free interval before systemic toxicity develops

Systemic / Multi-Organ Phase

• Parikh's Textbook of Medical Jurisprudence, p. 606-607

Postmortem / Pathological Findings

• Petechial hemorrhages in the skin
• Garlic odor on opening the stomach (pathognomonic clue)
• Grayish-black residues of zinc phosphide adhering to the gastric mucosa
• Congestion of liver, spleen, kidney, brain, and lungs
• Necrobiosis (coagulative necrosis) of liver cells - similar to phosphorus poisoning
• Parikh's Textbook of Medical Jurisprudence, p. 607

Treatment

1. Decontamination (Most Critical Step)

• Remove and bag contaminated clothing; wash skin with soap and water
• Gastric lavage with 3-5% sodium bicarbonate solution - the alkaline environment minimizes conversion of zinc phosphide to phosphine gas
• Caution: Zinc phosphide adheres firmly to the gastric mucosal crypts - even a small residual amount can cause death by slow absorption, so thorough lavage and prolonged observation are essential

2. Supportive Care

• Respiratory support: supplemental O₂, ventilatory support for pulmonary edema
• Cardiovascular support: vasopressors for shock; ECMO has been used in severe cases
• N-acetylcysteine (NAC) - addresses oxidative stress and free radical injury (evidence from systematic review, PMID: 34455951)
• Vitamin E - antioxidant
• Glucose-Insulin-Potassium (GIK) infusion - for myocardial support
• Vitamin K - for hemorrhagic tendency
• Corticosteroids and sedatives as needed
• Monitor and treat liver failure (targeted hepatic therapy given risk of acute liver failure)
• Correct metabolic acidosis, manage oliguria/AKI
• Keep patient under observation for delayed symptom recurrence after initial recovery

3. Monitoring

• ECG for arrhythmias
• Liver function tests, renal function tests, ABG
• Watch for delayed multi-organ failure
• Parikh's Textbook of Medical Jurisprudence, p. 607
• [Sobh et al., Crit Rev Toxicol 2023 - Systematic Review, PMID: 37387512]
• [Faress et al., JNMA 2025, PMID: 41768810]

Medicolegal Aspects

• Used commonly in suicidal poisoning, especially in rural India, South Asia, Africa, and Latin America
• Also occurs as accidental poisoning in agricultural workers
• Homicidal use is recorded but less common
• Healthcare providers handling suspected cases should wear gloves to avoid phosphine exposure
• At autopsy, the garlic odor and grayish-black gastric deposits are strong indicators

Key Differentiating Points: Zinc Phosphide vs. Aluminum Phosphide

Recent Evidence (2023-2025)

• A 2023 systematic review (Sobh et al., PMID: 37387512) covering 350 studies confirmed that no evidence-based standardized protocol exists for phosphide poisoning, and highlighted ECMO, NAC, vitamin E, GIK, and GI decontamination with oils as therapies that significantly reduced mortality in clinical trials.
• A 2025 review (Faress et al., PMID: 41768810) proposed a specific treatment protocol for zinc phosphide, emphasizing aggressive GI decontamination before absorption, targeted hepatic injury management, and adapting aluminum phosphide protocols to zinc phosphide management.
• A 2025 meta-analysis (Altaye et al., BMC Emerg Med, PMID: 40702417) flagged metallophosphide poisoning as a rising public health problem in developing countries.