Phosphine is a colorless gas that is heavier than air. It is odorless in its pure form, but impurities give it a characteristic fishy or garlic-like odor. It has been used for fumigation, and it is a serious potential hazard in operations producing metal phosphides, in which phosphine can be released in the chemical reaction of water and metal alloys. Workers at risk include metal refiners, acetylene workers, firefighters, pest control operators, and those in the semiconductor industry. Magnesium phosphide and aluminum phosphide are available in pellets or tablets and are used as fumigants and rodenticides.
Zinc phosphide is a crystalline, dark gray powder mixed into food as rodent bait. Phosphides are a leading cause of fatal suicides and accidental ingestions in India and many developing countries.
Mechanism of toxicity. Phosphine is a highly toxic gas, especially to the lungs, brain, kidneys, heart, and liver. The pathophysiologic action of phosphine is not clearly understood but may be related to inhibition of electron transport in mitochondria. Phosphides liberate phosphine gas upon contact with moisture, and this reaction is enhanced in the acidity of the stomach. Phosphine is then absorbed through the GI and respiratory tracts.
Phosphine gas. The ACGIH-recommended workplace exposure limit (TLV-TWA) is 0.3 ppm (0.42 mg/m3), which is much lower than the minimal detectable (fishy odor) concentration of 1–3 ppm. Hence, the odor threshold does not provide sufficient warning of dangerous concentrations. An air level of 50 ppm is considered immediately dangerous to life or health (IDLH). Chronic exposure to sublethal concentrations for extended periods may produce toxic symptoms.
Phosphides. Ingestion of as little as 500 mg of aluminum phosphide has caused death in an adult. In a reported case series, survivors had ingested about 1.5 g (range, 1.5–18 g), whereas fatal cases had ingested an average of 2.3 g (range, 1.5–36 g). The 50% lethal dose (LD50) for
zinc phosphide in rats is 40 mg/kg; the lowest reported lethal dose in humans is 4 g. A 36-year-old man who ingested 6 mg/kg of zinc phosphide and was treated with ipecac and activated charcoal remained asymptomatic.
Clinical presentation. Inhalation of phosphine gas is associated with cough, dyspnea, headache, dizziness, and vomiting. Phosphide ingestion may cause nausea, vomiting, diarrhea, hypotension unresponsive to pressors, and a rotten fish or garlicky odor sensed by caregivers. Adult respiratory distress syndrome (ARDS), acute renal failure, hepatitis, seizures, and coma may occur. Myocardial injury manifested by elevated cardiac enzymes, ST-T–wave changes, global hypokinesia, and various atrial and ventricular arrhythmias have been reported, as well as pericardial and pleural effusions, adrenal necrosis, and pancreatitis. Methemoglobinemia has also been reported. The onset of symptoms is usually rapid, although delayed onset of pulmonary edema has been described. Survivors of acute poisoning have been reported to develop esophageal complications including esophageal strictures and tracheo-esophageal fistula.
Diagnosis is based on a history of exposure to the agent. Caution: Pulmonary edema may have a delayed onset, and initial respiratory ...