Magnesium phosphide, toxicity

The magnesium phosphide that is subsequently formed can react with atmospheric moisture to form phosphine, PH3 which is toxic ... 

DOT CLASSIFICATION 4.3 Label Dangerous When Wet, Poison SAFETY PROFILE A poison. Flammable when exposed to heat, flame, or oxidizing materials. Ignites when heated in chlorine, bromine, or iodine vapors. Incandescent reaction with nitric acid. Reacts with water to evolve flammable phosphine gas. When heated to decomposition it emits toxic fumes of POx and phosphine. See also MAGNESIUM and PHOSPHIDES. 

However, these side reactions are problematic for two reasons. First, they reduce the available phosphorus content and thus lower the actual yield factor. Secondly, the phosphides of both magnesium and aluminium react with atmospheric moisture to give toxic and self-inflammable phosphanes [24]. To avoid the formation of phosphane, zirconium may be applied as fuel, which yields very stable ZrP that does not react with moisture or dilute acids. 

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