Does Zinc Phosphide Kill Mice?

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Key Takeaways

  • Zinc phosphide is an effective rodenticide used to control mice and other rodents.
  • When ingested, zinc phosphide is converted to toxic phosphine gas in the stomach which poisons and kills the rodents.
  • Zinc phosphide is especially lethal for mice, rats, and rabbits that cannot vomit to expel the poison.
  • It is used both in agricultural settings and around homes, buildings, and public spaces to control rodent infestations.
  • Zinc phosphide will kill most animals if ingested, but rodents are more sensitive than carnivores.

What is zinc phosphide and how does it work to kill mice?

Does Zinc Phosphide Kill Mice?

Zinc phosphide is a dark grey inorganic compound used as a rodenticide to kill mice, rats, voles, ground squirrels and other small rodents. It has a heavy earthy smell. When zinc phosphide is ingested by rodents, it gets converted into phosphine gas by the hydrochloric acid in the stomach. This lethal phosphine gas poisons the body and causes organ failure leading to the death of rodents like mice and rats.

Zinc phosphide is particularly effective against rodents that lack the ability to vomit like mice, rats and rabbits. Since they cannot expel the poison from their system by vomiting, it is assured the poison will be absorbed into the body and lead to death. For this reason, zinc phosphide is considered a “single-dose” rodenticide. The rodents typically die 1-3 days after consuming the bait.

According to the National Pesticide Information Center, zinc phosphide has been registered for use in the United States since 1947. It is considered a restricted use pesticide that can only be applied by certified pesticide applicators. Zinc phosphide baits are commercially available in pellet, grain, paste and wax cube formulations. They are marketed under various brand names like ZP® Rodent Bait, Prozap® and Ratol®.

Why is zinc phosphide an effective pesticide for killing mice?

There are several key reasons why zinc phosphide is so effective at killing mice and other rodents:

  • High toxicity – Zinc phosphide is extremely toxic to rodents and only a small amount needs to be ingested to cause death. Mice are very sensitive to the phosphine gas released.
  • Rapid action – Zinc phosphide starts converting to phosphine gas immediately after consumption. Death usually occurs within 1-4 days. This gives little time for rodents to learn bait avoidance.
  • Single dose – The inability to vomit ensures mice cannot expel the poison from their system before it takes lethal effect. One-time ingestion is enough to cause death.
  • Palatability – Rodents do not detect zinc phosphide’s taste or smell easily. It is added to food baits like oats, corn, peas etc. to attract rodents.
  • Low hazard for predator species – While highly toxic to rodents, zinc phosphide pellets pose relatively lower secondary hazards to pets, raptors, and scavengers. Proper precautions still need to be taken.
  • Stable compound – Zinc phosphide does not degrade easily under typical environmental conditions. Its toxicity is long-lasting.
  • Versatile applications – It can be used to control rodents in varied settings – agricultural fields, barns, homes, food storage facilities etc. both indoors and outdoors.
  • Cost-effectiveness – When used properly, zinc phosphide provides inexpensive and sustained control of rodent infestations.

In what settings is zinc phosphide used to manage mice?

Zinc phosphide is utilized both in agricultural/rural settings as well as urban/suburban areas to control mice and rat infestations when they pose significant economic losses or health hazards:

Agricultural uses:

  • Croplands – Field mice and voles.
  • Orchards and vineyards – Deer mice, voles.
  • Livestock farms – House mice, Norway rats.

Around buildings and structures:

  • Homes and apartment buildings.
  • Warehouses and food processing facilities.
  • Restaurants, hospitals, schools.
  • Parking garages, basements.

Public areas:

  • Parks, golf courses, cemeteries.
  • Roadsides, railway embankments, airport perimeters.
  • Garbage dumps and landfills.

Zinc phosphide baiting is done strategically keeping in mind the foraging behavior of the target rodents. Pellets or treated grains are placed along runways, burrows, walls, and known feeding areas for best results. The goal is to maximize the chance of rodents encountering and consuming the toxic bait.

What makes mice susceptible to zinc phosphide poisoning?

Mice, along with rats and rabbits, possess certain physical and behavioral traits that make them highly vulnerable to zinc phosphide:

  • Inability to vomit – Most rodents lack the ability to vomit which allows fast absorption of the poison into the body.
  • Omnivorous feeding – Mice will try new food items introduced into their environment, which facilitates bait consumption.
  • Grooming habits – Oral grooming results in ingestion of zinc phosphide trapped in the fur which raises toxicity.
  • Social interactions – Shared water, food sources and burrows aid transfer of poison between interacting mice.
  • Nesting behavior – Poison brought back to nests can impact young mice as well.
  • B8 strain susceptibility – The vitamin B8-deficient strain of mice is 10X more vulnerable to zinc phosphide than normal mice.
  • Stomach acidity – Mice have sufficient hydrochloric acid in the stomach to convert zinc phosphide into deadly phosphine gas.

The mode of action, metabolism, and high tolerance of zinc phosphide combine to make it fast-acting and lethal to small rodents like mice while posing lower risks for predator wildlife species.

How much zinc phosphide does it take to kill a mouse?

Zinc phosphide is effective at very small doses in mice:

  • 0.5-2 mg per mouse is sufficient when ingested directly.
  • Even skin contact with minute amounts of zinc phosphide dust on fur can be lethal.
  • Around 5-10 mg/kg of body weight is the approximate acute oral LD50.
  • B8-deficient mice have under 1 mg/kg LD50 making them 10 times more sensitive.
  • Lower doses of under 2 mg/kg can also eventually be fatal over several days.

The minimum lethal dose depends on mouse strain, sensitivity, bait formulation and exact phosphide concentration. But generally mice only need to ingest a very small quantity once to receive a toxic dose. This makes zinc phosphide baiting highly effective.

Proper bait placement in areas of known mouse activity increases the likelihood they will encounter and consume enough poison in a single feeding to receive a lethal dose. Zinc phosphide bait labels provide strict guidelines for safe and effective application rates.

How long does it take zinc phosphide to kill mice after ingestion?

The onset of symptoms and time to death after mice ingest zinc phosphide bait varies based on dose and individual factors:

  • With high toxic doses, mice may die within 12-24 hours.
  • More commonly, 1-3 days until death at lethal doses.
  • Lower sub-lethal doses can still cause mortality after 3-7 days.
  • B8-deficient mice succumb faster in 6-24 hours.

The latent period depends on how quickly the stomach converts zinc phosphide into phosphine gas, and rate of absorption into the circulatory system. This process begins immediately after ingestion.

Mice tend to die quickly because zinc phosphide is quickly metabolized into phosphine gas in their highly acidic stomach environment. The cause of death is typically organ failure, especially lung and heart failure, induced by phosphine poisoning.

What are the symptoms of zinc phosphide poisoning in mice?

The sequence of zinc phosphide poisoning symptoms seen in mice is:

Early stage:

  • Loss of appetite, lethargy.
  • Hunched posture.

Middle stage:

  • Uncoordinated gait, tremors.
  • Discharge from eyes and nose.
  • Increased breathing rate.

Late stage:

  • Seizures, convulsions.
  • Paralysis.
  • Coma preceding death.

The effects stem from damage caused by phosphine gas which inhibits vital enzymes and causes organ failure. Symptoms develop rapidly after ingestion of bait. Mice tend to die quickly without prolonged suffering.

How does zinc phosphide work to kill mice?

The mode of action of how zinc phosphide leads to the death of mice involves a multistep process:

  1. Ingestion of zinc phosphide bait – Mice consume food bait containing zinc phosphide, a dark gray powder. It has no warning smell or taste.
  2. Conversion to phosphine – Stomach acid hydrolyzes the zinc phosphide into phosphine (PH3) gas.
  3. Cell hypoxia – Phosphine interferes with cytochrome oxidase and cell oxygen utilization, depriving cells of energy.
  4. Organ damage – Vital organs like the heart, lungs, kidneys and liver are damaged, disrupting their functioning.
  5. Systemic toxicity – Phosphine spreads through the circulatory system causing systemic poisoning.
  6. Death – Mice die quickly, usually one to four days after ingesting sufficient zinc phosphide bait. Heart or lung failure is the primary cause.

The rapid lethality and multiple target organs make zinc phosphide an acute toxicant. The inability of mice to vomit the poison ensures sufficient absorption to cause death.

How dangerous is zinc phosphide poisoning to other animals?

While extremely toxic to small rodents, properly applied zinc phosphide poses lower secondary risks of poisoning to other animals:

  • Moderate toxicity in predators – More harmful to carnivores like dogs, cats, foxes than to scavenger birds. Vomiting reduces toxicity.
  • Lower hazard to birds – Granivorous birds like quail are least sensitive. Raptors are at higher risk.
  • Minimal effects on fish – High water insolubility limits aquatic toxicity.
  • Safe for bees – Bees do not collect zinc phosphide bait granules due to lack of odor.
  • No plants toxicity – Zinc phosphide does not leach into soils or absorb via plant roots.

Proper precautions like controlled bait access and containment can further minimize exposure to pets, birds and wildlife. Nonetheless, zinc phosphide is restricted to certified applicators given its acute toxicity across animal species.

What precautions are necessary when using zinc phosphide?

Zinc phosphide is regulated by the EPA and subject to strict guidelines to minimize unintended poisoning and environmental contamination:

  • Use only EPA-approved commercial baits applied per label directions.
  • Avoid application sites accessible to children, pets, livestock, and non-target wildlife.
  • Place baits along walls, burrows, and runways out of the general view.
  • Wear appropriate PPE like gloves, mask, goggles when handling zinc phosphide.
  • Properly dispose of unconsumed baits and rodent carcasses.
  • Triple rinse empty bait containers before disposal.
  • Avoid contamination of food, surfaces and water sources.
  • Keep bait shale, pellets and dust contained.
  • Follow precautions for safe transport, storage and handling.
  • Allow only certified pesticide applicators to purchase and use zinc phosphide products.

Adhering to the safety directions and regulations when utilizing zinc phosphide products minimizes the risks to children, pets and wildlife. It ensures effective rodent control without environmental contamination.

What are some alternatives to zinc phosphide for killing mice?

Some common alternatives to zinc phosphide for controlling mice include:

  • Anticoagulant baits – e.g. brodifacoum, warfarin. Cause bleeding by inhibiting vitamin K cycle in rodents.
  • Non-anticoagulants – e.g. bromadiolone, cholecalciferol. Disrupt blood clotting via different mechanisms than anticoagulants.
  • Acute toxicants – e.g. alpha-chloralose, strychnine. Also single-feed poisons but considered more humane than zinc phosphide.
  • Fumigants – e.g. aluminum phosphide, gas cartridges. Inhaled gases toxic to burrowing rodents.
  • Repellents – e.g. predator urine, moth balls. Deter rodent activity without killing.
  • Traps – Snap traps, adhesive glue boards. Catch and kill mice while avoiding poison risks.
  • Exclusion – Rodent-proofing of structures using hardware cloth, sealants etc. Physically denies entry.

Each alternative has its own advantages and disadvantages. Zinc phosphide remains a cost-effective option for quick large-scale reduction of rodent populations when conducted safely by certified applicators. But additional integrated methods are recommended to maintain long term control.


In conclusion, zinc phosphide is an extremely potent rodenticide that is highly effective at killing mice and rats when they ingest sufficient quantities. It is converted to lethal phosphine gas in the rodent’s stomach which causes swift death typically within 1-4 days. Mice are especially susceptible due to their inability to vomit up the poison. While posed in bait formulations that are palatable to rodents, zinc phosphide has no warning smell or taste. It can be utilized both in agricultural settings and urban areas to safely control rodent pest populations when applied strictly according to label directions by certified pesticide applicators. However, zinc phosphide indiscriminately kills most species of animals and so precautions are necessary to avoid primary and secondary poisoning hazards. When used properly, it provides fast-acting, cost-efficient control of destructive rodents. Integrated pest management approaches that combine zinc phosphide with exclusion, traps, repellents and other methods are recommended for sustained, long-term mouse control.

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