Aluminium phosphide:Structure,Properties,Toxicity

Aluminium phosphide, the most common fumigant rodenticide, is available in both tablet and pellet forms, however, only the pellet formulation is recommended for rodent burrow fumigation.

Crystal structure

Aluminum phosphide crystals are dark grey to dark yellow and have a Cubic, sphalerite structure.

Properties

Aluminium phosphide crystals are dark grey to dark yellow in color and have a zincblende crystal structure with a lattice constant of 5.4510 Å at 300 K.They are thermodynamically stable up to 1,000°C (1,830 °F).

Aluminium phosphide reacts with water or acids to release phosphine:

AlP + 3 H2O → Al(OH)3 + PH3

AlP + 3 H+ → Al3+ + PH3

This reaction is the basis of its toxicity.

Toxicity

Human toxicity occurs either due to the ingestion of AlP (commonest mode) after exposure and injury from phosphine inhalation (uncommon) or even after absorption through the skin (rare). After ingestion, AlP releases phosphine gas in the presence of HCl in the stomach, which is rapidly absorbed throughout the gastrointestinal tract, leading to systemic toxic effects involving the heart, lung, kidney, and liver with the manifestation of serious cardiac arrhythmias, intractable shock, acidosis, and pulmonary edema. After absorption, phosphine is oxidized to oxyacids. Phosphine is excreted in the urine as hypophosphite and also through the lung in the unchanged form.