Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and 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 rapidly harm most mammals or birds, but is highly toxic to fish and cats^[1][2]. It generally has a low mammalian toxicity and is poorly absorbed by skin. Permethrin has recently been linked to poisoning dogs as a flea/tick repellent.

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,^[3] and small mammals such as mice.

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.^[4]

Permethrin is toxic to cats and many cats die after being given flea treatments intended for dogs, or by contact with dogs who have recently been treated with permethrin.^[5]

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. However, the British National Formulary states that permethrin has low efficiency in eradicating head lice.

Permethrin kills ticks on contact with treated clothing. A method of reducing deer tick populations in terms of rodent vectors involves utilizing biodegradable cardboard tubes stuffed with permethrin treated cotton. Damminix Tick Tubes [1], a commercially available anti-tick device works in the following way. Mice collect the cotton for lining their nests. Permethrin on the cotton instantly kills any immature ticks that are feeding on the mice. It is important to put the tubes where mice will find them, such as in dense, dark brush, or at the base of a log; mice are unlikely to gather cotton from an open lawn. Tick Tubes [2] are most effective in preventing Lyme disease with regular applications early in the spring and again in late summer. According to the Connecticut Department of Public Health, permethrin "has low mammalian toxicity, is poorly absorbed through the skin and is rapidly inactivated by the body. Skin reactions have been uncommon."^[6] Permethrin is also used on humans for lice or scabies, the common prescription is Permethrin with 5% concentration for scabies, and OTC (over the counter) treatment for head lice/crabs is usually permethrin with 1% concentration.

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 very low if any 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.

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.

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.^[1] Flea and tick repellent formulas intended (and labeled) for dogs may contain permethrin and cause feline permethrin toxicosis in cats.

Permethrin is classified by the US EPA a likely human carcinogen, based on reproducible studies in which mice fed permethrin developed liver and lung tumors.^[2] 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.^[3][4]

References

1. ↑ BBC NEWS | UK | Cats 'killed by flea treatment'
2. ↑ Permethrin Facts, US EPA, June 2006.
3. ↑ M. Tisch, P. Schmezer, M. Faulde, A. Groh and H. Maier (2002). "Genotoxicity studies on permethrin, DEET and diazinon in primary human nasal mucosal cells". European Archives of Oto-Rhino-Laryngology 259 (3): 150–153. doi:10.1007/s004050100406. 
4. ↑ K. Hakoi, R. Cabral, T. Hoshiya, R. Hasegawa, T. Shirai and N. Ito (1992). "Analysis of carcinogenic activity of some pesticides in a medium-term liver bioassay in the rat". Teratogenesis, Carcinogenesis, and Mutagenesis 12 (6): 269–276. doi:10.1002/tcm.1770120605. 

See also

• Insect repellents from natural sources such as plants
• 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 (broken link)