Rat poison

For the UNIX window manager, see ratpoison.

Rat poisons are a category of pest control chemicals intended to kill rats.

Single feed baits are chemicals sufficiently dangerous that the first dose is sufficient to kill.

Rats and certain other vermin are difficult to kill with poisons because their feeding habits reflect their place as scavengers. They will eat a small bit of something and wait, and if they don't get sick, they continue. A good rat poison must be tasteless and odorless in lethal concentrations, and have a delayed effect.

Poisonous chemicals

Fatal internal bleeding is caused by overdose of anticoagulants such as Coumatetralyl or Warfarin.

Coagulant drugs or Vitamin K1 have been suggested as possible antidotes for pets accidentially exposed to anticoagulant poisons. In addition, since some of these poisons act by inhibiting liver enzymes, a blood transfusion (with the products of the correct enzymes present) can save a person who inadvertently takes them, an advantage over some older poisons.

Metal phosphides

Metal phosphides have been used as a means of killing rodents. A mixture of food and a phosphide is left where the rodents can eat it. The acid in the digestive system of the rodent reacts with the phosphide to generate the toxic phosphine gas. This method of vermin control has possible use in places where rodents immune to many of the common poisons have appeared.

Zinc phosphide is typically added to rodent baits in amount of around 0.75-2%. The baits have strong, pungent garlic-like odor characteristic for phosphine liberated by hydrolysis. The odor attracts rodents, but has repulsive effect on other animals; birds, notably wild turkeys, are not sensitive to the smell, feed on the bait, and become collateral damage.

The tablets or pellets may also contain other chemicals which evolve ammonia which helps to reduce the potential for spontaneous ignition or explosion of the phosphine gas.

Phosphides do not accumulate in the tissues of poisoned animals, therefore the risk of secondary poisoning is low.

Before the advent of anticoagulants, phosphides were the favored kind of rat poison. During the World War II, they came in use in United States because of shortage of strychnine due to its high-volume use in Europe. Phosphides are the slowest acting rat poisons with exception of the coagulants, resulting in the rats dying in open areas instead of in the affected buildings.

Phosphides used as rodenticides are:

Hypercalcemia

Cholecalciferol (vitamin D3) is used as a rat poison, which is toxic to rodents for the same reason that it is beneficial to humans: it helps in calcium absorption in the body. In rodents it causes hypercalcemia, raising the calcium level sufficiently that blood vessels, kidneys, the stomach wall and lungs are mineralised (form crystals), leading to heart problems and bleeding and possibly kidney failure. In family pets, accidental ingestion is generally considered safe for cats but dangerous for dogs.

Other

Other chemical poisons include:

Arsenic
Barium (a toxic heavy metal) compounds
- Barium carbonate
Bromethalin (which affects the nervous system, no antidote)
Curare
1,3-difluoro-2-propanol
Fluoroacetamide
Paris Green
Sodium fluoroacetate ("1080")
Strychnine
Tetramethylenedisulfotetramine ("tetramine")
Thallium (a toxic metal) compounds
Zyklon B (hydrogen cyanide solution absorbed in an inert carrier)

Alternatives

Mechanical rat traps are one possible alternative to poisons; another alternative is to buy a cat, although cats capable of dealing with rats are relatively rare; in many cultures, hunting dogs have been used instead. Both of these methods have a disadvantage of being comparatively messy, a particular problem when the building with a rat problem is to be uninhabited for some months. Anticoagulants have the advantage that their first effect is dehydration from blood loss, causing the unfortunate rodent to leave the building in search of water.

Newer rodenticides have been developed to work with by reducing the sperm count in males to deprive them of the ability to procreate rather than to kill rodents outright. They are usually administered in the breeding seasons of most rodents.

References

Rodenticides