Zinc Phosphide is an inorganic chemical that is used to control rats, mice, voles, ground squirrels, prairie dogs, nutria, muskrats, feral rabbits and gophers. It is also uses as a tracking powder for the control of house mice. It is used on crop areas and on non-crop areas including lawns, golf courses, highway medians, and areas adjacent to wetlands. It may be formulated as a grain based bait, as scrap bait or as a paste. Rodenticide baits usually contain 2.0 percent of zinc phosphide. Upon ingestion, zinc phosphide reacts with dilute acids in the gastrointestinal tract and produces phosphine, which enters the blood stream. Chronic exposure to phosphine may cause nausea, vomiting, diarrhea, tightness of chest, coughing, headaches, and dizzinessChemical Name: Zinc Phosphide
Chemical Formula: Zn3P2
LD50/LC50: The LD50 for the technical product (80-90% pure) is 45.7 mg/kg while the LD50 values for lower concentration formulations are slightly higher (i.e. less toxic). In sheep the LD50 ranges from 60 to 70 mg/kg. The inhalation of zinc phosphide or its breakdown product phosphine gas may result in acute toxicity. No specific doses were mentioned in the reference. The compound is non-irritating to the skin and eyes. Suffice to say that the clearance when using Phosphine gas as a fumigant is 5 ppm (parts per million). Rats fed zinc phosphide over a wide range of doses experienced toxic effects at the lowest dose tested. Increased liver, brain and kidney weights were noted in rats exposed to around 10 mg/kg. Body hair loss, reduction in body weight, and reduction of food intake were all noted at 3.5 mg/kg. Damage to the kidneys, to the liver and the stomach have been noted in humans but only at high acute doses of the rodenticide. Zinc phosphide reacts with water and stomach juices to release phosphine gas which can enter the blood stream and adversely affect the lungs, liver, kidneys, heart and central nervous system (TOXNET. 1992. Hazardous Substance Database. Zinc Phosphide. National Library of Medicine. Hazardous Substance Data Base).
Environmental Aspects:
Zinc Phosphide is highly toxic to wild birds and freshwater fish. It is also toxic to non-target mammals. Nearly sixty studies have been conducted on the toxicity of this rodenticide to wild animals. The most sensitive bird species which have been evaluated are geese (LD50 of 7.5 mg/kg for the White- fronted Goose). Pheasants, quail, mallard and ducks are also very susceptible to this compound. Blackbirds are less sensitive. The fish species which have been evaluated include bluegill sunfish (LC50 = 0.8 mg/l) and rainbow trout (0.5 mg/l). Carp were also found to be susceptible to zinc phosphide, especially in weakly acidic water. Secondary toxicity to mammalian predators from zinc phosphide is rather low primarily because the compound does not significantly accumulate in the muscles of target species. Some of the toxic effects to predators have been due to the ingestion of zinc phosphide that was in the digestive tract of the target organism (the prey). However, most predators will not eat the digestive tract. Studies on secondary organisms have focused on coyotes, fox, mink, weasels and birds of prey. Under field conditions most of the toxic effects to non-target wildlife are due to misuse or misapplication of this rodenticide
Zinc phosphide may be applied as an active ingredient in either bait or a dust. Soil acidity tends to break the compound down liberating phosphine a highly toxic gas. There is a potential for movement of this compound into adjacent, slightly acidic waters, where it can endanger fish populations.