Permethrin

Template:Chembox new Permethrin is a common synthetic chemical, widely used as an insecticide and acaricide and as an insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to harm most mammals or birds. It generally has a low mammalian toxicity and is poorly absorbed by skin.

Uses

In agriculture, permethrin is mainly used on cotton, wheat, maize, and alfalfa crops, and is also used to kill parasites on chickens and other poultry. It is also extensively used in Europe as a timber treatment against wood boring beetle (woodworm). Its use is controversial since, as a broad-spectrum chemical, it kills indiscriminately; as well as the intended pests, it can harm beneficial insects including honey bees, aquatic life, and small mammals such as mice. Permethrin is toxic to cats, which can become ill or die after being given flea treatments intended for dogs, or after contact with dogs who have recently been treated with permethrin.

However, permethrin can be used in a targeted manner as well. This is the basis for a method of reducing populations of the deer tick Ixodes scapularis (I. dammini). Biodegradable cardboard tubes stuffed with permethrin-treated cotton, are sold under the brand name Damminix, Mice collect the cotton for lining their nests, and the pesticide on the cotton kills any immature ticks that are feeding on the mice.

Permethrin is also used in healthcare, to eradicate parasites such as head lice and mites responsible for scabies, and in industrial and domestic settings to control pests such as ants and termites.

Permethrin kills ticks on contact with treated clothing. According to the Connecticut Department of Public Health, it "has low mammalian toxicity, is poorly absorbed through the skin and is rapidly inactivated by the body. Skin reactions have been uncommon."

Permethrin is used in tropical areas to prevent mosquito-borne disease such as dengue fever and malaria. Mosquito nets used to cover beds may be treated with a solution of permethrin. This increases the effectiveness of the bed net by killing parasitic insects before they are able to find gaps or holes in the net. Malaria kills 1-3 million people per year, and permethrin is believed to have low toxicity in humans. Military personnel training in malaria-endemic areas may be instructed to treat their uniforms with permethrin as well. An application should last several washes.

Recently, in South Africa, residues of permethrin were found in breast milk, together with DDT, in an area that experienced DDT treatment for malaria control, as well as the use of pyrethroids in small-scale agriculture. DDT is only used because of the desperate need of a cost-effective means to control the widespread malaria epidemic, and given the lack of funding, and lack of cost-effective solutions that are environmentally benign. DDT is very inexpensive and highly effective insecticide. Given the well known risks, its use is very limited and restricted only to spraying the walls of dwellings in areas endemic with malaria.

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The insecticide permethrin (in the synthetic pyrethroid family) is widely used on cotton, wheat, corn, alfalfa, and other crops. In addition, over 100 million applications are made annually in and around U.S. homes.

Permethrin, like all synthetic pyrethroids, is a neurotoxin. Symptoms include tremors, incoordination, elevated body temperature, increased aggressive behavior, and disruption of learning. Laboratory tests suggest that permethrin is more acutely toxic to children than to adults.

The U.S. Environmental Protection Agency has classified permethrin as a carcinogen because it causes lung tumors in female mice and liver tumors in mice of both sexes. Permethrin inhibits the activity of the immune system in laboratory tests, and also binds to the receptors for a male sex hormone. It causes chromosome aberrations in human and hamster cells.

Permethrin is toxic to honey bees and other beneficial insects, fish, aquatic insects, crayfish, and shrimp. For many species, concentrations of less than one part per billion are lethal. Permethrin causes deformities and other developmental problems in tadpoles, and reduces the number of oxygen-carrying cells in the blood of birds.

Permethrin has been found in streams and rivers throughout the United States. It is also routinely found on produce, particularly spinach, tomatoes, celery, lettuce, and peaches.

A wide variety of insects have developed resistance to permethrin. High levels of resistance have been documented in cockroaches, head lice, and tobacco budworm.

Products containing permethrin

Products containing 0.5% permethrin:

• Repel Permanone
• Permethrin Tick Repellent

• Bonide Ant Dust (0.25%)

• Nix 1% shampoo for head lice.

• Rentokil woodworm Killer 1.8% w/w

• Elimite 5% skin cream or generic equivalent for scabies, lice, head lice, bird mites, tropical rat mites, bed bugs, and other mites.

• Lyclear 5% skin cream or generic equivalent for scabies and crab lice.

• Most flea and tick repellant for dogs (Adams, Bio-Spot, K9-Advantix, Cutter)

• Dragnet, a pesticide for home use, also contains permethrin.

• Raid Ant and Roach killer, another home insecticide contains 0.2% permethrin.

• Cutter Bug Free Backyard contains 2.5% permethrin

• Flit

Products containing 12.6% permethrin:

• Raid fumigator

Products containing 0.05% permethrin:

• Sergeant's Flea and Tick Spray for Cats

Stereochemistry

Permethrin has four stereoisomers (two enantiomeric pairs), arising from the two stereocentres in the cyclopropane ring. The trans enantiomeric pair is known as transpermethrin.

• 
  (1R)-trans-acid moiety, known as biopermethrin
• 
  (1S)-trans-acid moiety
• 
  one cis enantiomer
• 
  the other cis enantiomer

Toxicity

Permethrin is extremely toxic to fish. Extreme care must be taken when using products containing permethrin near water sources. Permethrin is also highly toxic to cats. Flea and tick repellent formulas intended (and labeled) for dogs may contain permethrin and cause feline permethrin toxicosis in cats: specific flea and tick control formulas intended for feline use, such as those containing fipronil, should therefore be used for cats instead.

Currently, permethrin is not considered a carcinogen by any recognized authoritative body, but a few studies have lead the US EPA to classify the substance as a Category C carcinogen: Possible human carcinogen (the data show limited evidence of carcinogenicity in the absence of human data). Carcinogenic action in nasal mucosal cells for inhalation exposure is suspected due to observed genotoxicity in human tissue samples, and in rat livers the evidence of increased preneoplastic lesions lends concern over oral exposure. However, these results are seen as preliminary and marginal, at best.

See also

• Methoprene

External links

• Pesticide link to Parkinson Disease
• Permethrin Fact Sheet - National Pesticide Information Center
• Permethrin-treated Clothing Hot Topic - National Pesticide Information Center
• Permethrin Pesticide Information Profile - Extension Toxicology Network
• Permethrin chemical data
• Example of permethrin river poisoning