Phosphide salts (commonly zinc and aluminum) release phosphine gas in the presence of acids and have been extensively used as vertebrate pesticides. Veterinarians are most commonly exposed to phosphine via inhalation when attempting to decontaminate and treat animals that have been poisoned with zinc or aluminum phosphide rodenticides or during necropsy/sample collection procedures on animals that died from these poisonings. Phosphine gas is also used as a fumigant for grain and other agricultural products.
Phosphine is a colorless, flammable, and explosive gas. Technical grade phosphine (the type most commonly encountered by veterinarians) has an unpleasant, garlic-like, rotting fish-like smell, due to the presence of substituted phosphine and diphosphane. The human odor threshold for phosphine is below relevant exposure limits; the implication is that persons who can smell phosphine are being exposed to a hazardous level.
Phosphine is described as a “general protoplasmic poison,” and it is extremely and acutely toxic after inhalation. Acute inhalation exposure to phosphine can result in respiratory, neurologic, and GI effects. Signs and symptoms may include headaches, dizziness, fatigue, drowsiness, burning substernal pain, nausea, vomiting, GI distress, cough with fluorescent green sputum, labored breathing, chest tightness, pulmonary irritation, pulmonary edema, tremors, and convulsions (which may occur after apparent recovery). Skin contact with phosphides may result in numbness and paresthesia. Chronic occupational exposure effects include upper respiratory tract inflammation, weakness, dizziness, nausea, jaundice, liver effects, increased bone density, and symptoms referable to the GI, cardiorespiratory, and central nervous systems.
Veterinarians are very strongly encouraged to use respiratory and eye protection when dealing with patients poisoned by zinc or aluminum phosphide; emergency room staff casualties have occurred during treatment of human patients poisoned with these agents.
There is no antidote for phosphine poisoning, and emergency treatment requires specialist care.