Zinc Phosphide

Lead Editor

Overview


Zinc phosphide is a highly potent rodenticide that was first registered in 1947. It has a wide range of uses commercially and residentially, including the protection of food crops and grasses. It may also be used as an insecticide (#NPIC).

Zinc phosphide may be sold under trade names including Arrex, Commando, Denkarin Grains, Gopha-Rid, Phosvin, Pollux, Ridall, Ratol, Rodenticide AG, Zinc-Tox and ZP (#EXTOXNET).

Chemical Description


Zinc phosphide is a gray black powder. It has an odor similar to that of garlic. It is practically insoluble in water (#NPIC).
Zinc phosphide is commercially available as bait pellets, granules, dust, and tracking powder (#NPIC).

Uses


Zinc phosphide is used for rodent control on crops including grapes, sugarcane, artichoke, sugar beet, alfalfa, barley, berries, oats, sugar maple, wheat, corn, and hay. It is also used on grasses such as home lawns, rangeland, and golf courses (#EPA).

Zinc phosphide targets household rodent pests, such as mice and rats, in addition to field rodents including voles, ground squirrels, pocket gophers, prairie dogs, and jack rabbits (#NPIC).

Human Health Effects


Zinc phosphide highly toxic in acute exposures. It is converted to phosphine gas by the moisture and acidity of the stomach. The acute oral LD50 is 21 mg/kg for rats and 60-70 mg/kg for sheep. Zinc phosphide is converted into phosphine via ingestion, which is the compound which causes its high toxicity (#NPIC). However the EPA placed both the inhalation and oral routes of exposure in Toxicity Category I, the possible highest toxicity rating (#EPA).

People chronically exposed to small amounts of zinc phosphide have reported weakness, anemia, toothache, necrosis of the jaw bones, weight loss, and spontaneous fractures. Blood samples taken from fumigation workers handling zinc phosphide revealed a higher rate of chromosomal abnormalities (#NPIC).

Zinc phosphide is listed as a developmental toxin in the Toxics Release Inventory (#PANNA).

Zinc phosphide is known to cause a number of symptoms such as coughing, diarrhea, headache, fatigue, nausea, vomiting, burning sensations. Exposing the eyes may cause photophobia. Specific to ingestion are abdominal pain, dizziness, unconsciousness, and ataxia (#PANNA). Failure to treat zinc phosphide poisoning may result in catastrophic outcomes.

Environmental Health Effects


The toxicity of zinc phosphide comes from phosphine after it is chemically converted in the stomach. Thus, zinc phosphide must be ingested to become toxic. After phosphine is absorbed in the gastrointestinal tract, it inhibits cytochrome C oxidase, which is vital to mitochondrial respiration. It is suspected that there are other modes of action in its toxicity (#NPIC).

Zinc phosphide has a high avian toxicity. The acute oral LD50 for northern bobwhite quail is 12.9 mg/kg. If in solution, it can also be highly toxic to fish. The 96-hour LC50 for rainbow trout is .0097 ppm (#NPIC).

Zinc phosphide is expected to persist for approximately two weeks in soil. The degeneration of zinc phosphide may be accelerated by soil acidity and moisture, but this may also cause the release of toxic phosphine gas (#EXTOXNET).

Zinc phosphide is expected to have a low mobility in soil (#EPA).

Regulation


Zinc phosphide is a Restricted Use Pesticide, meaning that it can only be purchased and used by certified applicators. However, formulations in lower concentrations are available for the general public to purchase.

Precautionary Notes


Zinc phosphide is highly toxic to humans. A single swallow of zinc phosphide rodent bait could be fatal to a young child (#EPA). Treated areas may release toxic phosphine gas.

Integrated Pest Management


Integrated pest management (IPM) is an approach to pest management that can significantly reduce pesticide use. Widely used in agriculture, landscape maintenance, and structural pest control, it emphasizes prevention and monitoring of pest problems and considers pesticide applications only when nonchemical controls are ineffective or impractical.

To learn more about IPM, see Toxipedia's sister site IPMopedia, which includes information on control of vertebrates.

 



References



Environmental Protection Agency. RED Facts: Zinc Phosphide. (July 1998). http://www.epa.gov/oppsrrd1/REDs/factsheets/0026fact.pdf [Accessed 9-20-10].


Extension Toxicology Network. Zinc Phosphide. (June 1996). http://extoxnet.orst.edu/pips/zincphos.htm [Accessed 9-20-10].


National Institute for Occupational Safety and Health. Zinc Phosphide. http://www.cdc.gov/niosh/ipcsneng/neng0602.html [Accessed 9-20-10].


National Pesticide Information Center. Technical Fact Sheet: Zinc Phosphide. (September 2010). http://npic.orst.edu/factsheets/znptech.pdf [Accessed 9-20-10].


Pesticide Action Network North America. Zinc Phosphide. http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_Id=PC34737 [Accessed 9-20-10].

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